How to achieve normal perspective on 1.6 DSLR?

[DocFrankenstein]

I am confused by this. On a 35mm sensor the 50mm is considered "normal"... because the eye is approximately 50mm deep?

What lens would give a "normal" perspective on the Rebel sized sensor?

Would a 50 mm lens give a normal perspective, just cropped?
Or do I need a 50/1.6= 31.25 mm lens to get normal perspective?
Or something else?

Please advise.

[timmyquest]

I am confused by this. On a 35mm sensor the 50mm is considered "normal"... because the eye is approximately 50mm deep?

What lens would give a "normal" perspective on the Rebel sized sensor?

Would a 50 mm lens give a normal perspective, just cropped?
Or do I need a 50/1.6= 31.25 mm lens to get normal perspective?
Or something else?

Please advise.

i'm not sure if you'll find a 31.25mm lens, or a 30mm lens for that matter. 28mm is pretty darn close though.

[leony]

this is unfounded, but i recall hearing that a "normal" lens is a lens which has a focal length equal to the diagonal of the film frame.

as such, for 35mm full-frame, the film frame is 24x36 mm so normal lens then is:

square rt of (24^2+36^2) - hypotenuse of a right triangle with sides of 24 & 36 mm = 43.26... mm

for 4x5 camera that would be roughly 64mm lens. for 6x6 (2.25"x2.25") it would be 84mm lens.

hense you get the 50mm, 65mm and 80mm lenses.

using the same methodics i would assume that a APS sized chip on canon's cams would be as follows (calculated for 10D) 22.7 x 15.1mm size chip, hence "normal" lens would be a tiny bit over 27mm. 43/1.6=26mm - close enough.

[jaypie77]

I suppose you can set your kit lens, if you got it, to 31.25 mm, approximately.

[phili1]

The confusion is the angle of degree. If you have a 100 mm lens on a 35 mm camera and put it on adsdalr with a 1.6 factor the angle of degree would be the same as a 160mm lens on a 35mm camera.

In my opinion when n the say you have the same asw if you put a 160mm tele on it, I disagree. The lens does not give you anymore pulling power as if it were on a 35mm camera but its appearence in crop factor gives you that effect. An example is if you took a photo with a 400mm lens of a heron on a 20D it would fill the sensor up but on a 35 mm it would on fill about 2/3 thus giving the apperaence that it has greater magnification. But in fact 400mm is 400 mm, in opinion.

[edsarkiss]

But in fact 400mm is 400 mm, in opinion.

fact or opinion? ;-)

the truth is 400mm is indeed 400mm.

the "normal" lens for a 1.6x DSLR would be a 28mm or 35mm. canon makes a couple models of each of these.

[DocFrankenstein]

Yeah, relative to 35mm frame, it's a 400mm lens...

But then... 35mm frame was taken pretty much randomly. Right? It could've been "30mm" or "40 mm format" as standard.

Then, with 30 mm format, the lens would've been around 450mm...

Then... if we take an 80 mm hasselblad medium format lens and put a 35mm film behind it. What does the lens become?

[CyberDyneSystems]

Are you sure that none of these threads can answer your question?

-=CROP FACTOR=- 10,000 posts on the X-Factor (http://photography-on-the.net/forum/showthread.php?t=45388)

[DocFrankenstein]

DOH... At least it's the right forum :D

[DocFrankenstein]

Sorry CDS... nobody gives a definite answer.

I am confused... yet again.

I am not concerned about the image quality.
I don't care what you call the "crop factor"

I am concerned about:
1) Angle of view
2) Depth of field

Now. On 35mm film you get certain angle and certain DOF with 50mm f/1.4

Question: What focal length and what aperture do you need to get the same image in Drebel sensor???

Some guy quotes:

Thus, an 80mm lens on full frame 35mm at f5.6 produces the same Field of View and DoF as a 50mm lens on the 300D at f3.5.
He divides the film focal length and aperture by 1.6...

So... is this a huge limitation of the small sensors using 35mm lenses? Does it mean that equivalent picture on 1.6 sensor can be achieved with only:
31.25mm f/0.875 lens?

If so, all small sensor cameras are fundamentally flawed when using the 35mm format lens?

It would mean that even the most expensive glass, like 24L and 35L translate to mediocre equivalents of 35mm because of DOF restraints they produce:
24L = 38.4mm f/2.24
35L = 56 mm f/2.24

The aperture stays the same, but we are getting depth of field similar to slow lenses!

If we take "usual" lenses, the equivalen DOF can be too big!
28 f/2.8 which translates into a "normal" 44.8mm lens would on a 1.6 sensor produce a picture with a depth of field which is equivalent to 44.8mm f/4.5 lens on 35mm film!

Now... you're still getting the same amount of light, and it keeps your shutter speed the same. But what you're losing with 1.6 size sensor is small DOF of 35mm film.

Makes sense?

[DocFrankenstein]

The quote is from Rayz at the bottom of the page.

http://photography-on-the.net/forum/showthread.php?t=40821

CDS: I am stirring this because I did not see anybody post about the DOF issue on the smaller sensors.

Is would mean that while f stops are the same, it's impossible to get as small DOF as we would with full frame sensors.

Or am I wrong?

[ron chappel]

There is allways alot of confusion on this issue.
A 'normal' lens has nothing to do with either focal length nor angle of view.It's got everything to do with magnification
Approx 30mm is normal on a 1.6 crop DSLR.But don't expect to open your spare eye when looking though the viewfinder and see the same sized image because viewfinders have magnifications of thier own

[DocFrankenstein]

There is allways alot of confusion on this issue.
A 'normal' lens has nothing to do with either focal length nor angle of view.It's got everything to do with magnification
Approx 30mm is normal on a 1.6 crop DSLR.But don't expect to open your spare eye when looking though the viewfinder and see the same sized image because viewfinders have magnifications of thier own
ok, what about DOF? do you need aperture 1.6 times faster to get the same DOF?

[KennyG]

The longer the focal length of a lens the flatter the perspective, assuming framing the subject identically. This is irrespective of sensor size. So, a 28mm lens will show a greater perspective than a 50mm. This is not the same as FOV.

You can try it yourself with two or three objects spaced front to back on a table, using three different focal lengths frame the front one the same and see the effect on the other two.

[CoolToolGuy]

this is unfounded, but i recall hearing that a "normal" lens is a lens which has a focal length equal to the diagonal of the film frame.

as such, for 35mm full-frame, the film frame is 24x36 mm so normal lens then is:

square rt of (24^2+36^2) - hypotenuse of a right triangle with sides of 24 & 36 mm = 43.26... mm

for 4x5 camera that would be roughly 64mm lens. for 6x6 (2.25"x2.25") it would be 84mm lens.

hense you get the 50mm, 65mm and 80mm lenses.

using the same methodics i would assume that a APS sized chip on canon's cams would be as follows (calculated for 10D) 22.7 x 15.1mm size chip, hence "normal" lens would be a tiny bit over 27mm. 43/1.6=26mm - close enough.
This is precisely why Canon makes an EF 28mm f1.8 lens...

Have Fun,

[CoolToolGuy]

There is allways alot of confusion on this issue.
A 'normal' lens has nothing to do with either focal length nor angle of view.It's got everything to do with magnification
Approx 30mm is normal on a 1.6 crop DSLR.But don't expect to open your spare eye when looking though the viewfinder and see the same sized image because viewfinders have magnifications of thier own
I beg to differ - The angle of view of a 'normal' lens approximates the angle of view of the human eye - That's why its a 'normal' lens.

Have Fun,

[Andy_T]

The longer the focal length of a lens the flatter the perspective, assuming framing the subject identically. This is irrespective of sensor size. So, a 28mm lens will show a greater perspective than a 50mm. This is not the same as FOV.


That is not totally correct.

The lens is 'flattering for a portrait' if the perspective is correct.
The perspective, however, is only a function of your distance to the object.
FOV determines how much you see of an object, at a given distance.

So when you want to fill the frame, you move closer (with a short focal length) or farther (with a long focal length) from your object ... and that changes the perspective.

Best regards,
Andy

[gcogger]

If we take "usual" lenses, the equivalen DOF can be too big!
28 f/2.8 which translates into a "normal" 44.8mm lens would on a 1.6 sensor produce a picture with a depth of field which is equivalent to 44.8mm f/4.5 lens on 35mm film!

Now... you're still getting the same amount of light, and it keeps your shutter speed the same. But what you're losing with 1.6 size sensor is small DOF of 35mm film.

Makes sense?

You are correct. If you put a 50mm lens on a 1.6 factor camera, and an 80mm lens on a full frame camera, they will give you the same shot in every way except that the DOF will be greater on the 1.6 factor camera (for the same aperture).

If you're a portrait photographer you probably regard that as a bad thing. If you're a landscape photographer, you probably regard it as a good thing :)

[gcogger]

I beg to differ - The angle of view of a 'normal' lens approximates the angle of view of the human eye - That's why its a 'normal' lens.

Have Fun,

???

My eye has a field of view of nearly 180 degrees, which is way more than a 50mm lens!

50mm is a 'standard' lens by convention, and for no other reason. (It certainly has nothing to do with perspective, since that is simply defined by your distance from the subject and is not affected by focal length).

[EXA1a]

That is not totally correct.

The lens is 'flattering for a portrait' if the perspective is correct.
The perspective, however, is only a function of your distance to the object.
FOV determines how much you see of an object, at a given distance.

So when you want to fill the frame, you move closer (with a short focal length) or farther (with a long focal length) from your object ... and that changes the perspective.

Best regards,
Andy

Thanks, Andy, for getting this straight (once again)! I'm just surprised that it took 16 replies to clarify the rather simple definition of "perspective".
--Jens--

[PaulB]

The 50mm lens on a 36mmx24mm film camera comes from the original Leica.
Oskar Barnak wanted to design a compact camera using roll film.
He came up with the film first - 35mm wide movie stock was ideal, could be loaded into cassettes and developed in the same way as movie film; and it was readilly available! But the movie industry used what we would call half-frame of 24mm x 18mm, which did not give enough resolution in a still camera with the existing emulsions. So the 36mm x 24mm negative was born.
Barnak now needed a lens for his camera body and once more turned to the movie industry for the design - here a 50mm focal length was common and cheap and readilly available. As 50mm is close to what Barnak wanted - that 43-ish mm of the frame diagonal, that is what he used.
The rest simply followed on from there.
Pentax and Nikon did a 40mm lens in their ranges many years back and indeed Pentax still do offer a 43mm/1.9 (I believe it is) 'standard' in their range today for the purists amongst their users.
As to the 'crop' factor! A 50mm lens is still a 50mm lens whatever body it is mounted upon. The rest of you can argue about Depth of Field until next year and still get no majority decision...............................

[CyberDyneSystems]

Hey Doc,

No probem at all.. my posting the link was just an FYI... I was not sure your particular question was going to be answered directly.. I just did not know if you had found our "repository" of X-Factor threads yet. :)

Yes,. the "X-Factor" does effect DOF... the extreme examples are the small digicam where a "35mm equivelent" 85mm focal length at f/2.8 will yeild VASTLY larger depth of feild than a full frame sensor and the true 85mm lens.

However.. the difference in size between 1.6 and full frame results in a much smaller difference.

I am not at all sure what the math would be... to calculate the difference but.. THIS (http://www.dofmaster.com/dofjs.html) handy item will calculate it for you.

Lastly.. DOF and "perspective" are not the same.. so your initial question I think has been answered many times in the links provided.. ie, to acheive the perspective of a 50mm lens on full frame using a 1.6X sensor one should use a lens as close to 31mm as possible (ie: 35mm)

This will yeild the same "field of view" anyway. Perspective is a result of object distance.. and field of view tends to play a large factor in subject distance...

[CyberDyneSystems]

Oh yes.. I just wanted to re-iterate what I've said 10,000 times before.. :)

...if you were to take a crop from your full frame sensor that was equal to the feild of view and pixel desity of a 1.6 sensor, both using the same lens... the DOF, perspective etc... would all be indentical.

[DocFrankenstein]

Ok... I trust the DOF calculator, cause it's a mathematical tool and somebody knew what they were doing in terms of relating everything in there.

I played around with it a bit, and it seems like there are some implications with DOF and 1.6 sensors. (or any other smaller sensors):
Given the same set of lenses:
1) The DOF is smaller, (thinner) on a full frame sensor.
2) The DOF is larger on a 1.6 sensor.

basically, there is no way you can get the same subject separation with 1.6 sensor as with full frame sensor.

I'll play around with it a bit more and will make another post toward the end of the weekend.

Cheers

[CyberDyneSystems]

Although a 1.6X sensor will alter the DOF of your images vs. a full frame equivelent;

Just a thing to remember.. that kind of short DOF that produces a smooth "creamy" background... involves a relatively large amount of distance between subject and background.

Most times "The Ideal" lens allows you to have enough DOF to keep all of the subjects important features in focus.. but blurs the background.

For portraits for example.. a super narrow DOF may mean that parts of a persons face are OOF ... which may not be desired. This is why mid telephotos can be advantageous, as increasing distance gives deeper focus on the subject.. while maintaining excellent "bokeh" for the more distant background.

My point is.. the difference in DOF that a 1.6 sensor will offer may be enough to effect DOF in general.. it may even make it easier to get more of the subject in focus... but whaere the background is concerned... at many feet beyind the primary focus point (as opposed to a matter of fractions of an inch where to tip of a subjects nose is concerned) the 1.6X DOF change tends to have little effect.

Another thing that is said often in these threads that I will re-iterate now...

Unless you are working with both formats.. there is little to NO reason to worry about the apples and oranges comparison.

What your camera does relative to a 35mm film camera is of little importance in the long run. Get to know YOUR camera and how aperture, distance, focal length etc effects the images you make with YOUR equipment. Unlees you are constantly switching from one format to the other.. your refernce pont emains constant.. and you will not need to compare the other formats.

With this in mind.. (I use three formats/sensor sizes, two of them often.. ) I have long since "forgotten" to worry about comparing them... and just my viewfinder. All I consider is that I may get a wider feild of view by using the larger sensor... but even that is rarely a consideration for me.. as my widest lens is plenty wide for me on whatever camera i use it on.

Hope this helps. :)

[Longwatcher]

For some reason I had to go and read this thread...

Now I am going to have to try out DoF between my 1DsMkII and my 10D. Time for a ruler test when I go home this evening (just after noon here).

I am expecting no difference between the two cameras with my 50mm prime set on the same settings as far as DoF goes, but if the FoV is the same I will be really really surprised ;-)


Its all of your fault...:D

[DocFrankenstein]

Longwatcher:
Try comparing an X mm lens on 10D to a 1.6X mm lens on MKII at the same aperture.

The MKII should have shallower DOF.

[CoolToolGuy]

???

My eye has a field of view of nearly 180 degrees, which is way more than a 50mm lens!

50mm is a 'standard' lens by convention, and for no other reason. (It certainly has nothing to do with perspective, since that is simply defined by your distance from the subject and is not affected by focal length).The 'angle of view' is the angle that can be viewed without moving the eyeball. If you have an angle of view of 180 degrees, you have 'fisheyes'.

I stand by my original statement.

Have Fun,

[DocFrankenstein]

I have fisheyes too then :)

If all you see is your monitor and nothing else when you're silling 1.5 feet away from it, then you have a 50mm len.

I have peripheral vision which captures about 120 degrees vertically and close to 180 degrees horisontally. Try it, look straight ahead and notice the farthest angle when you see your hand. :)

[ArtierSquare]

Hold on... I was going to keep out of this as it was all incredably technical and math was never a good point (though I do understand DOF)

However. I think we are talking of just one eye at a time here and I know I don't see anywhere near 180 degrees because my nose gets in the way!

[Longwatcher]

Longwatcher:
Try comparing an X mm lens on 10D to a 1.6X mm lens on MKII at the same aperture.

The MKII should have shallower DOF.

How about I try my 50/1.4 on both at f1.4 and 2.8
then I put my 70-200 on both and take pictures at 100 and 160 on both at f2.8

and see what happens,
I expect no DOF difference between 50 and 50
I expect no DOf difference between 100 and 100 or 160 and 160,
But I expect setting 100 on 10D and 160 on 1DsMkII will result in in a smaller DoF on 1DsMkII, while the reverse will have smaller on 10D, since a longer focal length will result in smaller DoF. But I will see for myself.

I expect this because the distance between the focal/sensor plane and the lens is the same on both the 10D and the 1DsMkII (or should be) so the DoF should be the same at the same settings.

On the flip side the Field of View will be different on all but 100 on 10D and 160 on 1DsMkII.

When I get done, if I have time this weekend I will post results to my equipment test page and link from here.

[PacAce]

How about I try my 50/1.4 on both at f1.4 and 2.8
then I put my 70-200 on both and take pictures at 100 and 160 on both at f2.8

and see what happens,
I expect no DOF difference between 50 and 50
I expect no DOf difference between 100 and 100 or 160 and 160,
But I expect setting 100 on 10D and 160 on 1DsMkII will result in in a smaller DoF on 1DsMkII, while the reverse will have smaller on 10D, since a longer focal length will result in smaller DoF. But I will see for myself.

I expect this because the distance between the focal/sensor plane and the lens is the same on both the 10D and the 1DsMkII (or should be) so the DoF should be the same at the same settings.

On the flip side the Field of View will be different on all but 100 on 10D and 160 on 1DsMkII.

When I get done, if I have time this weekend I will post results to my equipment test page and link from here.

Tim, I would agree with your regarding the DOF of 50 and 50, or 100 and 100, etc. if you were viewing both images with the "target" or subject in both images being of the same size regardless of the differences in the FoV of each images (obviously the FF is going to have a wider FoV than the 10D). However, if you were to print both of the images on, say, an 8x10 paper, then I would expect DOF to be different between the two images with the 10D image having a narrower DOF.

[gcogger]

However. I think we are talking of just one eye at a time here and I know I don't see anywhere near 180 degrees because my nose gets in the way!

I hadn't thought of that :)

[CoolToolGuy]

I have fisheyes too then :)

If all you see is your monitor and nothing else when you're silling 1.5 feet away from it, then you have a 50mm len.

I have peripheral vision which captures about 120 degrees vertically and close to 180 degrees horisontally. Try it, look straight ahead and notice the farthest angle when you see your hand. :)Peripheral vision doesn't count - you can't focus on it and you can't define detail. I'm sitting in my office, and I can 'see' the cars on the road out front while looking at my monitor, and if a truck goes by I can tell what it is, but without moving my eye I couldn't tell you what the name on the side is.

I still stand by my original statement - A normal lens approximates the normal human angle of view. Trust me - been there, done that.

Have Fun,

[gcogger]

Peripheral vision doesn't count - you can't focus on it and you can't define detail. I'm sitting in my office, and I can 'see' the cars on the road out front while looking at my monitor, and if a truck goes by I can tell what it is, but without moving my eye I couldn't tell you what the name on the side is.

I still stand by my original statement - A normal lens approximates the normal human angle of view. Trust me - been there, done that.
Trust you? Please don't be patronising...

The FOV of the human eye is, IMHO, nothing like a 50mm lens whichever way you look at it.
On the one hand, if you consider the entire FOV, the eye is near 180 degrees.
Or, if you only consider the part you can actually focus on without moving the eyeball, the FOV of the eye is tiny - way, way smaller than a 50mm lens. (Try looking at a page of text - you cannot actually see more than a few letters at a time without very slight movements of the eye).

[CyberDyneSystems]

We are getting into a symantics issue... with NUMBERS! :)

Note the following.. when we discuss angle of view for "peripheral vision" etc... we have numbers ike 180* or 120*...

Lens MM is works in the opposite direction... 50mm is wider than 180mm ... and degrees has nothing to do with it.

FYI.. I think "normal" is an odd number for which we no longer have lenses made.. (I can't recall if it is 44mm or 54mm or something in between... either way.. it's not really 50mm )

50mm is supposed to offer a 40* feild of view on a 35mm film plane.

Well.. one eye still offers more than 40* of peripheral vision in my book...

BUT... the surface of the human eye is curved rather dramatically... our prepheral vision is not the same as the sweet spot that we can focus on. One must understand that the retina is "variable density".. with far more "photo receptors" towards the center than in our periphery.

Somewhere a cut off is made between "normal" vision and peripheral... based largely on actual photo receptors and nodal point ... but there is no clear line in the sand. The detail of our vision "falls off" ... it does not step down in a sudden increment. Therefro we can only say that our single eyes sweet spot is "about" 40*...

I have allways assumed that the "normal" lens covered what we see with our eyes' "sweet spot" in front of us.. and not our extreme periphery.

I could be mistaken,. that has allways been my take.

[CoolToolGuy]

Trust you? Please don't be patronising...

The FOV of the human eye is, IMHO, nothing like a 50mm lens whichever way you look at it.
On the one hand, if you consider the entire FOV, the eye is near 180 degrees.
Or, if you only consider the part you can actually focus on without moving the eyeball, the FOV of the eye is tiny - way, way smaller than a 50mm lens. (Try looking at a page of text - you cannot actually see more than a few letters at a time without very slight movements of the eye).Check this out:

http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_01.htm

I'm sure there are loads of other reference links that will say the same thing.

Sorry if you took my replies as patronizing.

Have Fun,

[KennyG]

That is not totally correct.

The lens is 'flattering for a portrait' if the perspective is correct.
The perspective, however, is only a function of your distance to the object.
FOV determines how much you see of an object, at a given distance.

So when you want to fill the frame, you move closer (with a short focal length) or farther (with a long focal length) from your object ... and that changes the perspective.

Best regards,
Andy

Andy, if you read my post you will see what I said was exactly right. I did say the shots had to be framed the same. I don't see where I mentioned flattering for a portrait, or do I post invisible words now?

[RichardtheSane]

That is not totally correct.

The lens is 'flattering for a portrait' if the perspective is correct.
The perspective, however, is only a function of your distance to the object.
FOV determines how much you see of an object, at a given distance.

So when you want to fill the frame, you move closer (with a short focal length) or farther (with a long focal length) from your object ... and that changes the perspective.

Best regards,
Andy

Are you saying that distance it the only thing that alters the persective? Do you have any information to back this up as I am unsure as to wether this concept in entirely accurate.

From the way I read your posts it seems you are suggesting that say a 50mm lens on a 1.6x DSLR will produce exactly the same images as an 80mm on a 35mm with the subject filling the same amount of the frame and at the same aperture? Is this correct or have I read too deep into your posts?

[gcogger]

Check this out:

http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_01.htm

I'm sure there are loads of other reference links that will say the same thing.

Sorry if you took my replies as patronizing.

Have Fun,
I agree that this explanation is commonly given, but that doesn't make it correct ;-)
It's also often said that a 50mm lens gives 'the same perspective' as the human eye, which I think we are all aware is incorrect. (Perspective depends on distance to subject, and nothing else).
I found this link on a page of common photography myths that I think explains the situation pretty well:
http://www.mhohner.de/essays/myths.php#50mm

[PacAce]

Are you saying that distance it the only thing that alters the persective? Do you have any information to back this up as I am unsure as to wether this concept in entirely accurate.

From the way I read your posts it seems you are suggesting that say a 50mm lens on a 1.6x DSLR will produce exactly the same images as an 80mm on a 35mm with the subject filling the same amount of the frame and at the same aperture? Is this correct or have I read too deep into your posts?

If we are just talking about perspective here, I would have to agree with Andy. For the same distance to the subject, the perspective will be the same no matter what lens (focal length) you are using. Obviously, the field of view will be different but not the perspective.

[gcogger]

Are you saying that distance it the only thing that alters the persective? Do you have any information to back this up as I am unsure as to wether this concept in entirely accurate.

From the way I read your posts it seems you are suggesting that say a 50mm lens on a 1.6x DSLR will produce exactly the same images as an 80mm on a 35mm with the subject filling the same amount of the frame and at the same aperture? Is this correct or have I read too deep into your posts?
I hope Andy doesn't mind me answering for him...

Yes, perspective is only affected by distance to subject, and not the lens focal length. Another link to the useful 'photography myths' page:
http://www.mhohner.de/essays/myths.php#focalper

And yes, an 80mm lens on a full frame camera will give an identical image to a 50mm lens on a 1.6 factor camera, with the exception of depth-of-field (which will be greater on the 1.6 factor camera).

[RichardtheSane]

gcogger, thanks for that link. Very useful info and explained very well - I am certianly much clearer about that now.

re: the second part of my post I really wanted to clarify that Andy wasn't suggesting that the image would be exactly the same, including DOF. Clearly they won't be but I was doing my best to be diplomatic :)

[gcogger]

No problem - I hope we're all learning from this thread. I know I am :)

[FlyingPete]

OK, I know I am joining this tread late, but from reading it, it seems to answer one of the questions I was going to submit separately, but I was wading through all the 'X Factor' stuff first.

Right, back in days of old, I was told that I should use an 85mm lens for portraiture, as it gives the most flattering perspective, not filed of view and not DOF, but perspective.

Now with this in mind originally I would have though that on a 1.6x sensor, this would hold true, as it is just a cropped image, but now it seems that perspective differs from full frame and 1.6x on the same lens, correct?

If this is indeed correct, and if what I was told all those years ago, then I should wander down to my local camera shop (or website!) and buy my self a 50mm, because it has roughly the same perspective on a 1.6x as an 85mm would on a full frame 35mm?

Straight answers please, no arguing :smile: (also I am assuming 85mm is the best, I have also been told that 135mm is also the best lens for portraiture, whatever it is the theory is still the same)

[gcogger]

At the risk of answering every post in this thread...

Technically, the lens focal length does not affect perspective - it is dictated solely by your distance from the subject. In this case, however, if we're talking about (say) a head-and-shoulders photo then a given lens will force you to stand at a certain distance to get the framing correct.

If you want to get the same perspective for your portraits as you do with an 85mm lens on a 35mm camera, you need a lens that will require you to stand at the same distance in order to get the same framing of the shot. In this case, that's roughly a 50mm (i.e. 85/1.6).

If you used the 85mm on the 1.6 factor camera, you'd have to stand further from the subject and the perspective would change.

[CyberDyneSystems]

It's the stuff of legends........

[FlyingPete]

It's the stuff of legends........

Perhaps Canon should have saved us all the trouble and made all the SLR's have full frame sensors!

BTW, has anyone actually asked a lens builder such as Canon on this one, they might know, after all they make the things!

[RDKirk]

???

My eye has a field of view of nearly 180 degrees, which is way more than a 50mm lens!

50mm is a 'standard' lens by convention, and for no other reason. (It certainly has nothing to do with perspective, since that is simply defined by your distance from the subject and is not affected by focal length).

Only partially correct. It's distance from the subject AND angle of view. A 40mm lens on a 6x6 camera at six feet from the subject will show expanded perspective of the subject relative to objects farther from and closer to the camera. A 50mm lens on a 20.5x15mm camera at the same distance will not show such expanded perspective--in fact, it will show compressed perspective (it also won't show all the same objects--the difference is angle of view).

[donb]

I'm not at all sure why this continues to baffle people. If you were to take a piece of 35mm film and cut out the center so that it's the same size as your 1.6 sensor, then the local photo lab would give you an 8x10 print that looks exactly like it came from your digi camera.

The only effects of a "1.6 crop" (bleahh, it's a 5/8ths crop but that's another story) is that less of the image is captured vs. full-frame.

Now, since you would naturally enlarge a cropped "negative" more to reach the same 8x10 (or whatever size) print, anything that is inherently affected by enlarging (same as it's always been in the wet-print world) will still be a factor with a digital print. Enlarging the image 60% more means any unsharpness or graininess (i.e., noise) in the digital image will be 1.6 times more noticable.

The "crop factor" is a planar phenomenon, occurring at the recording surface. All other optical factors that deal in the z-azis, perpendicular to the recording surface, are completely unaffected and relevant to the degree of cropping that occurs.

However, let's say you have a 1 meter tall stick to photograph. You want that 1 meter stick to exactly reach from top to bottom of the frame. For a 1.6 crop, that means you have to stand 60% farther away than you'd need to stand with a full-frame camera. Now, that does impact things like DOF and perspective, because you've changed the position between the stick and the recording surface.

[CyberDyneSystems]

:Nods in agreement: :)

[CoolToolGuy]

:Nods in agreement: :)Now I know why you get frustrated with this topic...

Fighting. . . . the urge. . . . to find. . . . all of the . . . . references . . . . about . . . . normal lenses . . . . and the relationship . . . . to frame size. Must resist. . . .

Have Fun,

[RDKirk]

[QUOTE=DocFrankenstein]I am confused by this. On a 35mm sensor the 50mm is considered "normal"... because the eye is approximately 50mm deep?

What lens would give a "normal" perspective on the Rebel sized sensor?

Would a 50 mm lens give a normal perspective, just cropped?
Or do I need a 50/1.6= 31.25 mm lens to get normal perspective?
Or something else? [QUOTE]

According to the photographic references of the last 50 or so years, at least, the "normal" focal length of a format has been defined as the diagonal measure of the format (see, for instance: http://www.britannica.com/ebi/print?tocId=229824&fullArticle=false). At this focal length, the image will present "normal" perspective within the area contained by the frame. That is, the viewer will not perceive either exagerated wide angle perspective or compressed telephoto perspective. Please note that the perceived perspective is a function of both distance AND framing--which is why the format is a factor.

Thus, the "normal" focal length of the APS-C format should be 28mm (a bit more than 27mm, actually, with 28mm being the closest available lens).

The normal lens for 24x36mm (full frame 35mm) is therefore actually 43mm. There are historical reasons why manufacturers settled on 50mm, with the primary reason being the limitations of lens design at the time (especially trying to accomodate the SLR mirror box). For a number of years, "normal" varied from 40mm to 58mm.

It's important to think about focal lengths for interchangeable lenses in terms of "difference from normal," not "crop factors." This "crop factors" junk was invented by marketers to get 35mm folk into DSLRs. But photographers have been using interchangeable lenses and multiple focal lengths since cameras were invented without this "crop factor" foolishness.

Think like this: Normal is 28mm. If I want to double the size of the image (as though I was half the distance), I want to use 2x the focal length. If I want to make the image half as large (as though doubling the distance), I want .5x the focal length. If I want to compare it to another format, then I do it by comparing the differences from each format's normal.

This has nothing to do with eyepiece magnification. There can be wide variance in eyepiece magnification for any given format as manufacturers balance viewfinder brightness with viewfinder magnification. Back when SLRs (particularly Nikon) were challenging rangefinder cameras, the selling point was the big viewfinder image, compared to the tiny image of the rangefinder. So 1x magnification became the SLR holy grail. One-Ex magnification means that with the "normal" lens on the camera, you can look through the camera with one eye, open the other eye, and see the same image in the same size.

But remember, that the "normal" focal length for 35mm is actually 43mm, and 50mm is really a short telephoto...so to get a 1x magnification, you need slightly less than 1x at the eyepiece. If you check the specs, that's exactly what the top-tier cameras give you: Somewhat less than 1x.

However, higher magnification also dims the image (you can't get something for nothing--TANSTAAFL rules all). So if the manufacturer has done other things that tend to dim the image (such as trim pentaprism size to save weight), they have to limit viewfinder magnification to keep the image from being too dim.

Canon pulls a shell game on us in this respect with the APS-C cameras. According to the specs, we are getting "0.9x (-1 dpt. with 50mm lens at infinity)." How BOGUS! The normal lens for the camera is 28m, but at the true normal focal length, you only get about .6x magnification because Canon is working so hard to keep up the viewfinder brightness cheaply.

It's possible to do better. If you get the chance, take a look through an old Olympus OM camera to see how a small camera really does a big, bright screen.

[HKFEVER]

I give up all the corp factor problems from 1.6 300D, 1.3 1D MKII & 1.5 D70:

- Use wide 35mm to have normal 50mm perspective, but now about the barrel effect from the wide angle?
- 1.3 to 1.6 is not very good nor effective to corp pictures, you need to get use to compose the shoot in different way (less corp after the shoot).

So I give up 2 days ago and go for 1DS MKII.

[DocFrankenstein]

Why is diagonal measure considered normal then?

[ron chappel]

A completely different subject but a good question.
I think i'll refer you to the excellent article by bob atkins on photo.net-

http://www.photo.net/learn/optics/dofdigital/


Hmmm-is the "quote' feature not up and working yet?
I was responding to a question from doc i think...

[phili1]

Did anybody touch on the original question. I have heard allot of comments in other areas but he asked what is a normal lens for a 1.6 factor Camera.

Now I hear from allot of people that my 100-400 lens on my 20D gives me a 640mm lens and I say no way, (but I am not sure) And the reason I say that is it does not pull the subject in closer.

Example if I put my 100-400 on and put it on 100mm and go to 400 mm the subject is pulled in closer. But if I put this lens on my Eos 35mm at 400 and then put it on my 20D at 400 mm the subject is still the same distance away, but it crops it, or does it work like going from 2 1/4 x 2 1/4 to 35mm. If it does and no one has been able to give a definate answer to this then.

Then the answer to his question is that if a 50mm lens is normal on a 35mm camera, then a 31.125 lens is normal on a 1.6 crop digital camera

I do not know the answer to this and I have searcherd the web for an answer and no one has had a difinative answer that shows me from a technical stand point that in fact this is the answer. If someone has it I would love to learn as I am sure allot of us would.

[RDKirk]

Did anybody touch on the original question. I have heard allot of comments in other areas but he asked what is a normal lens for a 1.6 factor Camera.
<snip>

Then the answer to his question is that if a 50mm lens is normal on a 35mm camera, then a 31.125 lens is normal on a 1.6 crop digital camera

I do not know the answer to this and I have searcherd the web for an answer and no one has had a difinative answer that shows me from a technical stand point that in fact this is the answer. If someone has it I would love to learn as I am sure allot of us would.

I gave the answer. The "normal" focal length for a format is the diagonal measure of the format. Thus, the normal focal length for 20.5x15mm (Canon 20D) is 28mm.

The normal for 24x36mm (full frame 35mm) is 43mm, not 50mm. Manufacturers have settled on 50mm for historical reasons.

If you want to find more information than I gave above on why "normal" is the diagonal of the format, Google on "normal focal length" and "diagonal."

[DocFrankenstein]

I feel like I haven't been going to my physics lectures and when I came in the professor puts me in front of the auditorium:

Well, young man. I see you've decided to come in late. Here's a question for you: My CoC is 30 micron on a macro lens. What's yours?

For some reason... the answer I gave him was not the answer he wanted. And everybody laughed...

Jokes aside... 10D sensor is a different format, but we're forced to live with lenses from a full frame format. This increases DOF in general and we won't be able to achieve the same subject isolation as with full frame sensors.

Is the difference significant? It may or may not be, depending on the focal length you are trying to use and DOF you're trying to achieve. It's easier to get the landscape photo in focus, but to get the same DOF in portraiture you'll "just" need a lens one or 2 stops faster. And we all know what that means. :D

[DocFrankenstein]

This must've been done and calculated about 100 years ago... more actually. (when did they have different formats for the 1st time, with apertures and lenses that can focus?)

It's just an issue of difference in formats...

Is there a good book describing this issue?

[HKFEVER]

10D sensor is a different format, but we're forced to live with lenses from a full frame format. This increases DOF in general and we won't be able to achieve the same subject isolation as with full frame sensors. :DPlease provide more detail about the "This increases DOF in general "

[DocFrankenstein]

Please provide more detail about the "This increases DOF in general "
I did... read through the first three pages of the thread.

[Steven M. Anthony]

Okay--I DIDN'T read all 4 pages... but the 50mm lens on a 35mm format camera is, I believe, considered "normal" because it provides a similar field of view as a human eye (which is really closer to the FOV of a 47mm lens on a 35mm format camera--but I haven't seen too many 47mm lenses out there...).

A 28mm lens on a 10D provides a field of view of a 45mm lens on a 35mm-format camera. So that's your best bet.

[Andy_T]

Okay--I DIDN'T read all 4 pages...

That was actually obvious from your post... ;)

Best regards,
Andy

[RTMiller]

Wow, I DID read all the pages and there was alot of great information in this thread
BUT, I think this sums it all up for me...

Unless you are working with both formats.. there is little to NO reason to worry about the apples and oranges comparison.

What your camera does relative to a 35mm film camera is of little importance in the long run. Get to know YOUR camera and how aperture, distance, focal length etc effects the images you make with YOUR equipment. Unlees you are constantly switching from one format to the other.. your refernce pont emains constant.. and you will not need to compare the other formats.I in few years when they stop making film and film cameras, we won't have to make this comparison anymore and things can return to NORMAL.

[Longwatcher]

I have not had time to post my examples to my web site yet, but the results were as expected.

There is no Depth of Field (DoF) difference between the same lens from the same spot aiming at the same target, whether it is on a 10D (1.6x) or a 1DsMkII (1x). But there is a huge Field of View (FoV) difference. And within the area of coverage of the 10D there is no difference in perspective or anything else that I could notice. I deliberately did not pay attention to resolution or whte balance as this is irrelevant information to this issue.

The only difference is the 1DsMkII has a wider FoV (along with all the distortion/aberrations one would expect at the edges of the lenses).

If I wasn't leaving to visit folks for holidays, I would post sometime this week, it will just have to wait until after new years.

Note: My longer FL test was actually done at 95mm and 153/155mm as I can only guess so accurately on my 70-200/2.8. But the 50mm at f1.4 and about 2 meters was pretty definate and obvious.