Request: 50mm on crop body compared to 85mm FF

[TCOMC]

I read the sticky on perspective and now I'm curious of the difference between a focal length from a crop body and 1.6x that focal length on a FF camera (or however the math goes). I understand that the 1.6x crop is just that - a crop from the full frame but I"m interested in how the field of view changes. People always bring up the word "equivalent" and I would really like to see how much merit there is in that.

Please! If someone has the facilities to do this (ie. a full frame and a crop body camera), would you be able to take some quick pictures to compare the two? :-D

If this has already been covered, please provide me with a link. I've had no luck..

[toxic]

The point is they will look exactly the same.

A 53mm lens on APS-C and 85mm lens on 35mm both have a 24 degree horizontal AoV, so you will stand the exact same distance away for the same framing. The perspective is the same and you get the same image, DoF notwithstanding.

http://photography-on-the.net/forum/showpost.php?p=9046790&postcount=61
http://photography-on-the.net/forum/showpost.php?p=8368060&postcount=9

Notice that the only difference is the DoF, and the size of the subject relative to other objects is the same.

[Mike Bowen]

here is a quick crude demonstration

40D w/ 50mm @ f/2

http://www.mikebowenphoto.com/random/IMG_9059.jpg



5D w/ 85mm @ f/2

http://www.mikebowenphoto.com/random/IMG_8681.jpg

[DStanic]

Wow, quite a difference! In one of those links I read that the DOF difference is 1.6x, so a f2.8 on crop would look similar to f4 on FF (which is how the difference in the above pics look to me).

I have been pondering what I'd like for my next camera (upgrade the 20D) and a 5D looks to be much more appealing then a 50D or 7D at this point, despite the lack of newer features.

[Frugal]

I have been pondering what I'd like for my next camera (upgrade the 20D) and a 5D looks to be much more appealing then a 50D or 7D at this point

Not debating the 5D vs 50D, but if Mike had put the 85mm on the 40D and moved 1.6x farther away from the subject it would look the same as the second picture DOF-wise and field of view.

[DStanic]

Not debating the 5D vs 50D, but if Mike had put the 85mm on the 40D and moved 1.6x farther away from the subject it would look the same as the second picture DOF-wise and field of view.

I understand that, and think it would be great using longer lenses but not having to stand back so far. The 70-200 for example I love to be closer to the subject.

The 50mm f/1.4 would have awsome bokeh on FF compared to my 30mm f/1.4 on crop! :)

[toxic]

Not debating the 5D vs 50D, but if Mike had put the 85mm on the 40D and moved 1.6x farther away from the subject it would look the same as the second picture DOF-wise and field of view.

I don't know how you came to that conclusion, but the DoF is not the same...and the perspective changes, so the images aren't comparable anyway.

The 50mm f/1.4 would have awsome bokeh on FF compared to my 30mm f/1.4 on crop! :)

Bokeh is a lens quality. It doesn't change (or only changes minimally) when you put the same lens on two different camera formats.

The Sigma 30 has better bokeh than the Canon 50/1.4, but it won't yield as thin a DoF.

[Wilt]

Not debating the 5D vs 50D, but if Mike had put the 85mm on the 40D and moved 1.6x farther away from the subject it would look the same as the second picture DOF-wise and field of view.

Go find yourself one of many DOF calculators available on line. You'll be able to prove or disprove assumptions for yourself.

FF: 10.1' 85mm, DOF = 0.3769' at f/1.8 (FOV 2.8' x 4.2')
APS-C: 16' 85mm, DOF = 0.5973' at f/1.8 (FOV 2.8' x 4.2')

[HappySnapper90]

Wow, quite a difference! In one of those links I read that the DOF difference is 1.6x, so a f2.8 on crop would look similar to f4 on FF (which is how the difference in the above pics look to me).


No, there is 1 1/3 stops difference for effective DOF between Canon aps-c and FF. So f2.8 on aps-c would be f5 on FF/film.

[Bobster]

Go find yourself one of many DOF calculators available on line. You'll be able to prove or disprove assumptions for yourself.

FF: 10.1' 85mm, DOF = 0.3769' at f/1.8 (FOV 2.8' x 4.2')
APS-C: 16' 85mm, DOF = 0.5973' at f/1.8 (FOV 2.8' x 4.2')

Full frame is @ 10.1ft the crop is @ 16ft of course the dof is different!!! At the same distance dof will be the same... there are plenty of images that show this online..

[gkarris]

It's kinda rough on a crop body - too zoomed in. I end up using my 28/2.8 a lot because of it.

Try to get as close to a 50mm equivalent as possible.

I rented a Zeiss 25mm for my Olympus E-420 (50mm Equivalent) and it was heaven!

[Wilt]

Full frame is @ 10.1ft the crop is @ 16ft of course the dof is different!!! At the same distance dof will be the same... there are plenty of images that show this online..

APS-C: 10' 50mm f/1.8, FOV = 2.95' x 4.43', DOF = 0.676'
FF: 10' 50mm f/1.8, FOV= 4.72' x 7.08', DOF = 1.08'
FF: 10' 80mm f/1.8, FOV = 2.92' x 4.38', DOF = 0.42'

Statement in blue is disproven. As I said earlier to another post, go find yourself one of many DOF calculators available on line. You'll be able to prove or disprove assumptions for yourself.

[chauncey]

Wilt is correct for stated reasons but there is also a significant difference in bokeh.
I found this comparison to be very enlightening http://creativetechs.com/training/john-greengo-episode-011/

[Wilt]

Wilt is correct for stated reasons but there is also a significant difference in bokeh.
I found this comparison to be very enlightening http://creativetechs.com/training/john-greengo-episode-011/

Not your fault for misuse of a term like 'bokeh', which is the quality of out of focus areas, not the quantity of how much blurring exists.

[DrPablo]

No, there is 1 1/3 stops difference for effective DOF
Since when did we start measuring DOF in stops?

[toxic]

Since when did we start measuring DOF in stops?

Because it's a way of translating DoF between formats, given the same AoV.

[DrPablo]

Because it's a way of translating DoF between formats, given the same AoV.
I shoot 8 different formats (8x15mm, 15x24mm, 35mm, 6x6, 6x9, 6x12, 4x5, and 8x10), so I do have an appreciation for this issue and I take complete exception to the idea that it's quantifiable in stops. DoF is a distance that can be modified VARIABLY by aperture depending on how you deal with other integral variables like distance to subject.

The top image is from a 4x5 large format view camera at f/8 with a 210mm lens. How many "stops" different is the DoF from FF and APS-C?

The second image is f/2.8 on 6x6 medium format with an 80mm lens. How many "stops" different is the DoF from FF and APS-C? Do these questions even make any sense?

http://www.pbase.com/drpablo74/image/64659458.jpg

http://www.pbase.com/drpablo74/image/104473147.jpg

[toxic]

I shoot 8 different formats (8x15mm, 15x24mm, 35mm, 6x6, 6x9, 6x12, 4x5, and 8x10), so I do have an appreciation for this issue and I take complete exception to the idea that it's quantifiable in stops. DoF is a distance that can be modified VARIABLY by aperture depending on how you deal with other integral variables like distance to subject.

The comparison puts the camera the same distance and with the same AoV, which fixes the DoF variables. It just so happens that a 1.6x smaller sensor yields essentially the same DoF as the "control" sensor from a given f-stop when the lens attached to the control sensor is stopped down 1 1/3 stops (from the given f-stop).

So f/2 on APS-C yields about the same DoF as f/3.2 on 135, which in turn is about f/5 on 645, given the same subject distance and framing.

[Wilt]

I can understand your issue, Dr. Pablo, but a DOF calculation program would reveal that FF 50mm f/2 lens has DOF of 1.20' at focus distance of 10'. Put a 31mm lens on APS-C and at focus distance of 10', the DOF equals 1.22' when the f/stop is about f/1.24

[DrPablo]

I can understand your issue, Dr. Pablo, but a DOF calculation program would reveal that FF 50mm f/2 lens has DOF of 1.20' at focus distance of 10'. Put a 31mm lens on APS-C and at focus distance of 10', the DOF equals 1.22' when the f/stop is about f/1.24
My issue is that if you hold focal length, distance to subject, and aperture constant, then the difference in DoF needs to be expressed in units of distance and not f/stops. If I take the 50 f/1.2 and stand 10 feet from my subject, and take shots on both APS-C and FF, then the difference in DoF is a matter of distance and the difference in composition is a matter of angle.

Talking about DoF in terms of f/stop equivalents makes no sense because you can never have f/stop the only variable in DoF. You either preserve the same angle of view by changing distance to subject, or you sacrifice angle of view by preserving distance to subject. Thus, f/stop will ALWAYS be merely a component and not a measure of DoF.

Move back or forward to preserve angle of view and you have changed perspective. Crop the FF down to APS-C size and your DoF needs to be calculated based on APS-C and not FF. There is simply no scenario in which aperture becomes the measure but with everything else constant.

[krb]

My issue is that if you hold focal length, distance to subject, and aperture constant, then the difference in DoF needs to be expressed in units of distance and not f/stops. If I take the 50 f/1.2 and stand 10 feet from my subject, and take shots on both APS-C and FF, then the difference in DoF is a matter of distance and the difference in composition is a matter of angle.

Talking about DoF in terms of f/stop equivalents makes no sense because you can never have f/stop the only variable in DoF. You either preserve the same angle of view by changing distance to subject, or you sacrifice angle of view by preserving distance to subject. Thus, f/stop will ALWAYS be merely a component and not a measure of DoF.
You're misunderstanding the concept. In any comparison between the two formats, if the distance is equal and the focal length is equal after adjusting for the crop factor to match the angle of view then you will then need about 1 1/3 stops difference in aperture to get an equal DOF. The specific distance, focal length and aperture do not matter so long as they are matched between the two formats.

[Wilt]

You're misunderstanding the concept. In any comparison between the two formats, if the distance is equal and the focal length is equal after adjusting for the crop factor to match the angle of view then you will then need about 1 1/3 stops difference in aperture to get an equal DOF. The specific distance, focal length and aperture do not matter so long as they are matched between the two formats.

^ I think it is fair to quantify the difference between two format either in distance or in f/stops. The former concept makes people aware of how much less distance a large format will present as 'in focus', while the latter concept conveys the manner in which one CAN compensate with appropriate adjustment of aperture to obtain the 'same shot'.

So, if one had deep DOF at f/11 using 17mm lens with APS-C, one would use f/20 with 28mm lens with FF to obtain an equivalent shot.

Nothing wrong with conveying a method of compensation to make two formats more similar (the larger format winning the IQ battle, which is another discussion)

[DrPablo]

You're misunderstanding the concept.
No, just objecting on both conceptual and mathematical grounds to defining something in terms of one of its component variables. If distance over time equals velocity, then you cannot express velocity as a unit of distance. If length times height is area, then you cannot express area as a unit of length. If f/stop is a component variable of DoF, then you cannot express DoF as an f/stop.

If you throw in your caveats about holding things constant, then it's a different verbal expression -- you're essentially "solving for" aperture in the equation. That's different than describing DoF in stops.

In any comparison between the two formats, if the distance is equal and the focal length is equal after adjusting for the crop factor to match the angle of view then you will then need about 1 1/3 stops difference in aperture to get an equal DOF.

But you're predicating this on changing the focal length of the lens, which is a fundamental component variable in DoF calculations. So are you arguing now that you can talk about DoF in focal length equivalents?

[krb]

But you're predicating this on changing the focal length of the lens, which is a fundamental component variable in DoF calculations. So are you arguing now that you can talk about DoF in focal length equivalents?
Exactly. Changing the sensor formats means that for the same perspective you have to change the focal length to get the same angle of view. Given that change in focal length, you then would need to adjust the aperture (by about 1 1/3 stops) to get the same DOF. This is simply a tool for comparing two different sensor formats. This doesn't tell me jack about what DOF I will get with my camera at a given distance but if I have a shot taken with my 35mm film camera and want to get take a shot with the same perspective, field of view and DOF using my digital crop camera then this will get me pretty close. Or if I'm looking at a shot taken with my crop camera and wondering what it would have looked like with a full frame camera then this gives me an idea.

[landmeiner]

can anyone compare crop vs full frame with same lens such as 85mm 1.8 but not from same distance
full frame closer to the subject so subject size is the same on both crop and full frame
i wanna see the bokeh and dof difference

[SkipD]

can anyone compare crop vs full frame with same lens such as 85mm 1.8 but not from same distance
full frame closer to the subject so subject size is the same on both crop and full frame
i wanna see the bokeh and dof differenceDo you realize that the two images will be very different regarding perspective (the relative sizes of foreground and background elements)?