1.6 crop with Canon 100-400 IS

[westernminnguy]

Hello All,

First post from me. I'm new to this forum.

I've got an XT and purchased the Canon 100-400 IS last fall. I've really had fun with this lens. I'm just a hobbyist photographer...mostly a birder.

Anyway, I understand my XT has the 1.6 (FOV right?) crop.

Does that mean that my 100-400 is effectively:

100 x 1.6 = 160mm

400 x 1.6 = 640mm

So my 100 - 400 on my XT is really 160mm-640mm.

Is this correct?

thanks

westminnguy(western minnesota guy)

[LightRules]

Welcome, and yes, your numbers are accurate insofar as field of view.

[SkipD]

Hello All,

First post from me. I'm new to this forum.

I've got an XT and purchased the Canon 100-400 IS last fall. I've really had fun with this lens. I'm just a hobbyist photographer...mostly a birder.

Anyway, I understand my XT has the 1.6 (FOV right?) crop.

Does that mean that my 100-400 is effectively:

100 x 1.6 = 160mm

400 x 1.6 = 640mm

So my 100 - 400 on my XT is really 160mm-640mm.

Is this correct?The answer to the question is NO, but let me explain....

Absolutely nothing about a lens changes when you put it on different format camera bodies. Focal length does not change. Focal length range of a zoom does not change. Aperture settings do not change.

What changes has nothing to do with the lens. It's the difference between the format (size of the film frame or digital sensor) that changes, and that's all. The result of that change is a difference in field of view. What that means is that a camera with a smaller sensor (or film frame) will record less of an image projected by a given lens than a camera with a larger sensor/film frame. The effect is similar to extending the focal length (relative to using the same lens on a 35mm film camera), but in reality the focal length does NOT change.

Thus, making the statement that "my 100 - 400 on my XT is really 160mm-640mm" is totally false.

The true statement that would say roughly the same thing but using the actual facts is this: My 100mm-400mm lens, used on my XT, provides a field of view that is equivalent to using a 160mm-640mm lens on a 35mm film camera (or "full-frame" digital camera).

The reason so many folks are confused about the "crop factor" issues is the way that manufacturers handled the introduction of their DSLR's which use image sensors that are significantly different in size from the 35mm film frame. The problem is that they built the DSLR's to emulate the physical proportions of a 35mm film SLR, and used the existing lenses originally designed for 35mm film cameras rather than design, build, and market a completely different set of lenses. There was never a problem, for example, in realizing that a 6x6cm "medium format" camera such as a Hasselblad uses different focal length lenses to achieve the same field of view as a 35mm film camera. However, the manufacturers made the major mistake of publishing a "magnification factor" in the beginning, then changing the verbage to "crop factor". Their own literature - to this day - does not properly explain the actual difference so that uninformed folks can understand.

This image, made by someone else in these forums, illustrates the relative size difference between a 35mm film frame and the APS-C sized sensor in all the "1.6 crop" cameras: 87150

[cjm]

The thing I really don't get about this ever confusing crop factor story is the EF-S lens and how apparently they are crop factored effected also.

Reason I don't understang that is, I thought EF-S means "Electronic Focus - Small" and that the EF-S lens are built for small sensors. So why not make them so they are the same as putting a film lens on a 5D? Or Full Frame?

That's the most confusing thing I can think of.

[coreypolis]

The thing I really don't get about this ever confusing crop factor story is the EF-S lens and how apparently they are crop factored effected also.

Reason I don't understang that is, I thought EF-S means "Electronic Focus - Small" and that the EF-S lens are built for small sensors. So why not make them so they are the same as putting a film lens on a 5D? Or Full Frame?

That's the most confusing thing I can think of.

that in general is there purpose. they are generally wider (17, 18 or 10mm), so that they would be the same as a wide or normal lens on a cropped body. they can't change the size of a sensor, so the lens sits further into the camera and has a smaller circle if illumination produced, so replicate that on a traditional lens. thus the 10-22 is suppose to be similar to the 16-35 or 17-40.

[RichardtheSane]

The thing I really don't get about this ever confusing crop factor story is the EF-S lens and how apparently they are crop factored effected also.

Reason I don't understang that is, I thought EF-S means "Electronic Focus - Small" and that the EF-S lens are built for small sensors. So why not make them so they are the same as putting a film lens on a 5D? Or Full Frame?

That's the most confusing thing I can think of.

I think the confusing thing is that everyone still tries to equate lenses on an aps-c camera to their 35m equivalent.

The EF-S 60mm lens has the same field of view as a 100mm lens, but it is still optically a 60mm lens.
It would be incorrect to market it as anything other than a 60mm lens.

If users of aps-c camera's were to stop worrying about what the 35mm equivalent of their lens is and get to know what focal lenghts give the desied efect the crop factor debate would be much easier!
:)

[stupot]

The answer to the question is NO, but let me explain....



ive seen you write all that down so many times...:) i guess its a sticky somewhere, if not it should be!

[SkipD]

The thing I really don't get about this ever confusing crop factor story is the EF-S lens and how apparently they are crop factored effected also.

Reason I don't understang that is, I thought EF-S means "Electronic Focus - Small" and that the EF-S lens are built for small sensors. So why not make them so they are the same as putting a film lens on a 5D? Or Full Frame?

That's the most confusing thing I can think of.Let's continue the lesson from my previous post......

The APS-C cameras have a smaller sensor than a 35mm film frame. If you limit the lens selection to those lenses designed to fill a 35mm frame, you will find that there are no ultra-wide-angle lenses for the APS-C camera. The shortest zoom lens focal length in the EF lens family is 16mm. There are two primes that are a bit shorter, and one of those is a "fisheye" lens. NONE are what the average photographer would call "affordable".

To design an ultra-super-wide-angle lens such as a 10mm non-fisheye lens for a 35mm camera is a VERY expensive proposition, which is why there are none.

By making some changes to the design criteria - reducing the "film" area to be covered by the lens, and allowing the lens to project deeper into the mirror box (the rear element of the lens closer to the "film"), it becomes much more economically possible to design lenses for the task. Thus, the EF-S family of lenses was born. The mount is different so that you cannot mount the EF-S lenses on cameras that were not specifically designed for them. If you modify an EF-S to put on a 35mm camera, the mirror will crash into the lens at certain zoom settings. Also, the 35mm film frame would have a dark circle around the edges and the image inside the circle.

Now that you have some understanding of what the EF-S lenses are all about - note that there are NO long lenses with the EF-S design as they aren't needed - you need to understand that focal length is focal length is focal length. An EF 50mm prime lens designed for a 35mm camera, when used on an APS-C camera, will provide you with EXACTLY the same image size as an EF-S 18-55 lens set to 50mm. If you could cobble together a mount for a Hasselblad 50mm lens and use it on a 20D, you would again have the same size image as a result. Thus, there is no reason to print a "fake" focal length number on the EF-S lens.

Again - the "crop factor" is totally and purely a function of the size of the film frame or digital sensor and has absolutely nothing in the world to do with the focal length or design criteria of the lens itself.

[foxbat]

Somebody please compile Skip's posts into a sticky, he must be getting RSI by now. :)

[In2Photos]

Skip I sure hope you have this written somewhere else so you can cut and paste.:D

[westernminnguy]

Thanks Skip and others. I think I'm beginning to finally understand this crop factor.

I appreciate your time taken to explain.

[westernminnguy]

One other thought. When many folks talk about this crop factor they use what almost appears as a multiplication factor.

i.e.

Your 100mm lens will show the same FOV(if I understand Skip correctly) as a 160mm lens. 100 x 1.6 crop factor.

What if we reversed the process and looked at FOV(on a 1.6 crop factor sensor) as a percentage of what we would see on a full frame sensor?

Actually, it would make more sense to me to talk about the crop factor as a percentage of the view of a full frame sensor.

In other words, if I understand this correctly, a 160mm lens on a sensor with a 1.6 crop factor, would actually only show 62% of what that lens would show(FOV) on a full frame camera.

i.e.

100mm/160mm = 62%

Am I anywhere close on this?

[johnathan]

Thank you all for the lesson that I badly needed ! There is so much bad info out there !
So the zoom or magnification is just as stated it just shows a tighter Field of view over the 8meg sensor! Similar to cropping an image !

This is good news as you lose nothing as far as power of the lens except packing more info on the sensor of a full frame camera . If you crop at 62 % it is the same except it is spread over less megapixels of some of the other 8.2 mp cameras .
Johnathan

[coreypolis]

its actually a great thing for weaker lenses, as you are using the center of the glass instead of edge to edge where optics are generally best

[mrklaw]

An EF 50mm prime lens designed for a 35mm camera, when used on an APS-C camera, will provide you with EXACTLY the same image size as an EF-S 18-55 lens set to 50mm. If you could cobble together a mount for a Hasselblad 50mm lens and use it on a 20D, you would again have the same size image as a result

when you say you get EXACTLY the same image size, do you mean the light coming through the lens projects the same size image onto the sensor? its just that because the sensor is smaller it only captures the middle part of it, the rest just bleeds around the sides and is not used?

[steved110]

The crop factor thing is good for telephoto enthusiasts in that you get more reach ( or at least think you do...:confused: )
the real problem is the loss of wide angles, but there are now lenses in the range 10-24mm that redress this issue so really the problems go away.
Ultimately I'd prefer to have full frame, so am trying to avoid EF-S lenses, and I still use my film camera ( a bit...) and like my lenses to mix and match, as it were.

[SkipD]

when you say you get EXACTLY the same image size, do you mean the light coming through the lens projects the same size image onto the sensor? its just that because the sensor is smaller it only captures the middle part of it, the rest just bleeds around the sides and is not used?When using EF and EF-S lenses for comparison, the actual size of a portion of the image that fits on the sensor will be the same size for both lenses that are using the same focal length. The EF lens will project a larger image circle than the EF-S lens, though, and a portion of that image circle is lost in the APS-C cameras.

[braduardo]

its actually a great thing for weaker lenses, as you are using the center of the glass instead of edge to edge where optics are generally best

This was actually the answer to the question I had when I browsed into this one.

I had read that the optics tended to be better in the center of the lens than the edges, and was really wondering if that was how it worked.

[cjm]

I agree, Skip you should repost those replies into a post and a moderator should sticky it or that guy with the lens thread could have a link in it at the very least. Very imformative and clears up a lot of confusion.