Digital Rebel Kit Lens ...

[Digital Prophet]

So I was sitting here at my desk thinking to myself. To be more specific I was thinking about something that I had read about how a 50mm lens on a 35mm SLR is a standard lens and give the same focal range as the human eye.

Ok well then I am thinking about the sensor magnification factor. And I figure that a 30mm prime lens would give me the same effect (if there is such a thing). Then my attention turns to my kit lens. It is 18-55mm. Then it dawns on me.

Does the EF-S lens focal length markings take into account the 1.6x magnification. In other words when I set the lens to 55mm does it act like a 55mm lens or a 88mm lens (55x1.6)? I mean the EF-S lens is specifically designed for the Digital Rebel. So shouldn't it take that into account?

- Digital Prophet -

[Olegis]

The 18-55mm does not take into account the x1.6 factor, you just have to multiply this lenght by 1.6 in order to get "real" focal length. The 18-55 lens is actually 29-88mm on 300D.

[cmM]

I think the crop factor is not taken into consideration when stating the focal length. So yea, I think it acts like a 88mm lens, as you said.
It's not designed only for the DRebel(it's also designed for future SLRs with the EFs mount, according to Canon), it just happens to be the first EFs lens. Now is the last one too ? :roll: Dunno.

I'm not sure though, just a thought.

[theoldmoose]

What's really dumb is that the EXIF data will also only tell you the real focal length of the lens, instead of including the 1.6x factor. So, unless you happen to know that the Digital Rebel (as identified elsewhere in the EXIF data) is a 1.6x crop factor camera, you are left guessing. To be pendatic, though, the focal length really doesn't change, which effects depth of field calculations. But, it would be nice if some portion of the EXIF would include an 'effective focal length' or some such.

Couple that with the fact that the camera also doesn't adjust for the crop factor when talking to the 'EX' flashes that have motorized zoom heads. So, when you set your EF-S 18-55mm lens to about 28mm (there is a mark on the lens scale that indicates the full-frame equivalent of 50mm, or 'normal view'), the 'EX' flash zoom head will zoom to 28mm, not 50mm. This means the flash is zoomed wider then necessary, wasting some of the flash power, and so the quide number is not as good as it might be.

Considering that stuff like that is all firmware based, either Canon's software developers (or their suppliers/contractors) are just lazy/stupid, or this is some grand scheme of theirs to 'make everything 35mm full-frame-centric'.

Frankly, I'd rather have the true crop factor displayed in my file info, and have the flash zoom head work correctly.

[CoolToolGuy]

50mm is 50mm, regardless of the crop factor. The 'normal' comes from an approximation of the angle of view of the human eye. The actual size for a 35mm film frame is about 44mm.

So, a 28mm lens is approximately normal for a Drebel or 10D (coincidence that Canon makes a 28mm f1.8 lens?).

The size of the frame (sensor in digital) must always be taken into account when considering what is normal, wide-angle, or telephoto.

Have Fun,

[Jesper]

Like CoolToolGuy said: 50mm is still 50mm, that is, the focal length of the lens is 50mm, whether you put it on a Digital Rebel, which has an 1.6x crop factor compared to 35mm film (note, it is a crop factor, not a focal length multiplier factor!) or any other camera. So it wouldn't really make sense to say that the kit lens at 18mm is "28.8mm" - the focal length is still 18mm, not 28.8mm.

Note that the image that a 50mm lens on a camera with an 1.6x crop factor is NOT the same as the image on a full frame camera with a 80mm lens - the depth-of-field will be different. The image of the 1.6x camera with the 50mm lens WILL be the same as the image of a full frame camera with the same 50mm lens, with a border cropped off - that's why it is a crop factor, not a focal length multiplier factor.

[Digital Prophet]

Well now I am just lost. All this time I have been told that it was a "focal length multiplier". Hell I was pretty sure that I had read it several times too. Now I just don't get it.

Man, noone but me asks a question and ends up knowing less than he did before he asked.

- Digital Prophet -

[cmM]

let's see.....
Normal focal length =~ the diagonal size of the frame (sensor)

Now since the DRebel (and 10D) is 1.6 X smaller than a full frame (film SLR)
Therefore, this crop factor directly reflect the focal length (looked at from a specific camera(sensor size)'s point of view. That's why you could say it's a focal length factor.

But all these lenses are build according to standards (so far the standard is 35mm frame). I guess Canon could include some calculations there in the Exif info to display focal lengths and such taking the crop factor into consideration, but I think that would make things even more confusing for some.

[Tom W]

Well, if somebody comes from a background of shooting 35 mm, then it makes a good reference point. But, if someone has been shooting medium format all their life and decides to get a 1D Mk II, they'll not have any "crop factor" reference from which to judge a lenses' length. A lens with a "35-mm equivalent of 50 mm" means nothing when normal on medium format might be 85 mm.

I think that if we are going to declare a standard (and one really hasn't been declared - they just seem to like to refer to 35 mm), then angle-of-view might serve as a good standard. Or, perhaps a "diagonal frame measurement ratio" might serve even better, noting that a lens with a focal length equal to the diagonal of the sensor/film frame is roughly a "normal" lens.

What really bothers me is that a couple of P&S cameras have their lenses marked as 28-200 mm or whatever, when the actual focal length is nowhere near that amount. Now you're going to have people running around having nary a clue what focal length really is, given that they have two or three dissimilar lenses all marked with the same value. Length is length - it is a measured value.

[EXA1a]

...I just imagine how the "old" forum members lean back and watch how the "newbies" try explain the famous "1.6 multiplication factor". They (the oldies) went through that kind of discussion many, many times...

--Jens:-)

[dbren]

All this 1.6x stuff is rather crazy, especially to digital slr owners who have never shot 35mm slr. I think this is a growing crowd. At any rate when I get my 50 mm lense out, it is a 50 mm. When I view the picture I relate it to my 50 mm lense, I could care less what a 35 mm slr pic might look like with a 50 mm lense, it just isn't relavent. When I use the kit I am using the 18 to 55 zoom and I know what to expect. I realize that aprox 30 mm is a normal view. So stop already with the 1.6 crop and all the mental gyrations and comparisons we are shooting with the 300d at whatever size lense we have on at the time.

[cmM]

...how the "newbies" try explain the famous "1.6 multiplication factor". They (the oldies) went through that kind of discussion many, many times...
Are we (the newbies) doing okay ?

[Tom W]

All this 1.6x stuff is rather crazy, especially to digital slr owners who have never shot 35mm slr. I think this is a growing crowd. At any rate when I get my 50 mm lense out, it is a 50 mm. When I view the picture I relate it to my 50 mm lense, I could care less what a 35 mm slr pic might look like with a 50 mm lense, it just isn't relavent. When I use the kit I am using the 18 to 55 zoom and I know what to expect. I realize that aprox 30 mm is a normal view. So stop already with the 1.6 crop and all the mental gyrations and comparisons we are shooting with the 300d at whatever size lense we have on at the time.

That's why I like the 'angle of view' approach. 45 degrees is the same whether its a 50 mm lens on 35 mm film, an 85 mm on medium format, a 28 on the 10D, or 12 mm or so on something the size of the S-400. The only problem with just quoting angle of view is that it doesn't convey the ability to use shallow DOF very will. Angle of view along with a focal length specification certainly will.

Unfortunately, with interchangeable lenses and not less than 3-4 different sized sensors inside 35-mm sized DSLR's, its hard to put any specification like that on a lens since it will vary with the size of the sensor. However, an angle-of-view readout in EXIF would be nice.

[ron chappel]

There are some false statements here...

Most importantly a 50mm lens on a 35mm camera gives the same MAGNIFICATION of the human eye.
Not angle of view
Not nessesarily perspective

But you can't compare the magnification directly by looking through the viewfinder with one eye and using the other eye as a reference....because all viewfinders have different magnification settings.

The only way you can test the theory is to take pictures and see which ones look the most normal

[Tom W]

There are some false statements here...

Most importantly a 50mm lens on a 35mm camera gives the same MAGNIFICATION of the human eye.
Not angle of view
Not nessesarily perspective

But you can't compare the magnification directly by looking through the viewfinder with one eye and using the other eye as a reference....because all viewfinders have different magnification settings.

The only way you can test the theory is to take pictures and see which ones look the most normal

Of course, angle of view of a lens correlates directly with magnification as well as perspective when the picture is viewed. In fact, the relationship between angle of view and magnification is mathematical, though it helps to define a base or 1:1 point. Perspective is a more subjective term, though I think we'd have no problem defining the fisheye lens as compared to the "normal" or telephoto.

You're right though, the viewfinder is a poor place to compare the eye with the lens. Large differences are obvious, but smaller ones are not. And, as you said, the viewfinder itself has its own magnification effect.

[Jesper]

I don't understand why people have such a difficult time to understand the crop factor. It's really very simple.

The crop factor comes from the fact that the sensor of your digital camera is smaller than a standard 35mm film frame. For example, the sensor of the 10D and Digital Rebel is 22.7 x 15.1 mm, while a 35mm film frame is 36 x 24 mm. So if you compare it with 35mm film, it's as if the edges of the frame are cut off. There's no magic thing that magnifies your image, other than if you print both the image from the 10D and the 35mm film image on the same format (say, 4 x 6 inches), you'll be enlarging the 10D photo 1.6x more than the 35mm image.

If you want it explained with pictures, have a look here:
Size Matters (http://www.photo.net/equipment/digital/sensorsize/) by Bob Atkins on photo.net
Understanding the DSLR Magnification Factor (http://www.luminous-landscape.com/tutorials/understanding-series/dslr-mag.shtml) by Nick Rains on Luminous Landscape

[Tom W]

I don't understand why people have such a difficult time to understand the crop factor. It's really very simple.

The crop factor comes from the fact that the sensor of your digital camera is smaller than a standard 35mm film frame. For example, the sensor of the 10D and Digital Rebel is 22.7 x 15.1 mm, while a 35mm film frame is 36 x 24 mm. So if you compare it with 35mm film, it's as if the edges of the frame are cut off. There's no magic thing that magnifies your image, other than if you print both the image from the 10D and the 35mm film image on the same format (say, 4 x 6 inches), you'll be enlarging the 10D photo 1.6x more than the 35mm image.

If you want it explained with pictures, have a look here:
Size Matters (http://www.photo.net/equipment/digital/sensorsize/) by Bob Atkins on photo.net
Understanding the DSLR Magnification Factor (http://www.luminous-landscape.com/tutorials/understanding-series/dslr-mag.shtml) by Nick Rains on Luminous Landscape

Its not the concept that bothers people - its the terminology. Some camera manufacturers are throwing focal length figures around like they're meaningless - and trying to use 35 mm as some kind of standard "equivalent" when it would be so much more functional to give actual focal length and field-of-view ranges. After all, not everyone comes from a 35 mm background.

I've seen at least one manufacturer (not Canon) that advertized a P&S camera with a 28-200 lens or some such thing, when in reality, the lens didn't even reach 50 mm of focal length at its maximum telephoto. Granted, the FOV might be the same as a 200 mm lens on a 35 mm film camera, but you'd have a much harder time getting a nice blurred background at f/4.0 with that little lens than you would with a lens that has a physically measurable focal length of 200 mm.

How did all those medium format people survive all these years without a "35 mm equivalent" rating stamped on their lens or owners' manual?

[Belmondo]

One of the reasons it's critical that we understand 'crop factor' is that as we change bodies and move closer to full-frame sensors (or away from them as the case may be), we have to understand how it impacts field of view as well as other lens characteristics.

There is something beguiling about the notion that our 400mm lenses are somehow magically transformed into the equivalents of 640mm lenses on a 10D or Rebel. If people’s understanding of crop factor stops there, they might be reluctant to give up the erroneously perceived idea of ‘extra magnification’ because of their failure to understand what’s really happening inside the camera.

At times it seems like we’re fighting a losing battle with the marketing types who keep selling this characteristic of smaller sensors as a benefit. People want to believe that their lenses really are 1.6 times more powerful because of the ‘magnification factor’, while it’s really more important that they understand the sensor (thus the image) has roughly .6X the field of view as a full-frame sensor or 35mm film image.

To me, a side benefit of the 1.3X crop factor in the Mk II is the extra FOV I’m getting with my 16-35L and Sigma 12-24. Pretty soon I will be able to take a picture of my own ears. Imagine.

[Bruce Hamilton]

The 18-55 lens is actually 29-88mm on 300D.

I think it might be 29-88 on 35mm... I have a 28-90, and the difference is substantial on both ends of the spectrum.

[PhotosGuy]

I think it all boils down to knowing your equipment. With my Nikons, I knew that 105mm coverage was the same as holding my arm out with the thumb & fingers (fingers together) spread. 50mm was 2 thumbs together & fingers spread. 35mm = 3 hands, etc.
Less ‘measurebating’ = more pic taking.
:wink:

[robertwgross]

...I just imagine how the "old" forum members lean back and watch how the "newbies" try explain the famous "1.6 multiplication factor". They (the oldies) went through that kind of discussion many, many times...


That is why I ceased to call it "1.6 magification factor" or "1.6 crop factor". To end the argument, I simply call it the "1.6 factor".

---Bob Gross---

[robertwgross]

To me, a side benefit of the 1.3X crop factor in the Mk II is the extra FOV I?m getting with my 16-35L and Sigma 12-24. Pretty soon I will be able to take a picture of my own ears. Imagine.

Better get a fisheye lens.

---Bob Gross---