[farfisa]

I would ask you why the term was NEVER bandied about when people shot various formats of film?

I have a friend who buys gear and whenever the guy behind the counter mentions the "focal length in 35mm," he replies, "oh, so like a 55mm on my 6x7?" He's never gotten a reply.

I think the only difference is that you can use the exact same lens on a film camera that you would on a APS-C DSLR and get a different result, so they had to explain it somehow. Or could you share lenses between various film formats? I honestly don't know.

My old point and shoot has a 7.4mm to 22.2mm lens, which means less than nothing to me except that it's a 3x zoom.

[Nick Siebers]

Well, the OP has a point, which is that a 1:1 macro lens, on a 35mm camera, will "fill the frame" with something 35mm long. On an APS camera you can "fill the frame" with something 23mm across. It is, essentially, a crop of the larger picture. So in a practical sense, you can take a picture of something smaller using a 1:1 lens on a smaller sensor body.

If you shot with film for years, the concept of a crop factor is quite helpful. If you consult old books about photography as well. But it does take a little while to understand it.

edit to add: for me it is, anyway. YMMV

[RioRico]

Well, the OP has a point, which is that a 1:1 macro lens, on a 35mm camera, will "fill the frame" with something 35mm long. On an APS camera you can "fill the frame" with something 23mm across. It is, essentially, a crop of the larger picture. So in a practical sense, you can take a picture of something smaller using a 1:1 lens on a smaller sensor body.

But filling the frame has nothing to do with the magnification at which the photo is taken. At 1:1, an object that is A x B mm in the real world, will also be A x B mm on the frame or sensor. Suppose I shoot a bug that is 3x4mm, with ANY lens setup that is 1:1. What size is that bug on a 6x9cm frame? It is 3x4mm. What size is it on a 645cm frame? It is 3x4mm. What size is it on a 36x24mm (135/FF) frame? It is 3x4mm. What size is it on a 110 frame? It is 3x4mm. That is what 1:1 means.

(Of the examples I just cited, that 3x4mm bug only comes close to filling the 110 frame. Filling the other frames would require magnification much greater than 1:1.)

If you shot with film for years, the concept of a crop factor is quite helpful. If you consult old books about photography as well. But it does take a little while to understand it.

I shot film for years. I simultaneously shot 135/HF and 135/FF and 6x6 and 6x9 and 9x12. I regularly mounted FF (full frame) glass on a HF (half frame) SLR. As now, I also shot with enlarger or MF or LF lenses on a bellows mounted on HF and FF SLRs. I never once heard or thought of "crop factor". For each format, I learned which lenses covered which angles.

I admit, when I first got my HF Oly Pen-FT and mounted a Spiratone 400mm tele on it, I thought, "Oh wow! It's like having a 600mm lens!" But I quickly learned that, no, it's NOT like having a longer lens; it's like having a 400mm lens on a FF camera, and cutting the negatives in half. A smaller frame gets less of the picture, that's all.

The BS term "crop factor" is obviously misleading and confusing, as proved by all the zillions of confused questions and comments we see in any forum. Camera and lens marketers will continue to use the misleading terms CF and 'equivalent' because it's simpler than educating customers. Well, it'll keep the forums busy.

[Derridale]

Actually, I don't find it the least bit confusing. With my Pentax, I simply multiply the stated focal length of the lens by 1.5x to get the EFFECTIVE focal length in terms of angle of view. It's a simple as that. Canon users without FF cameras use 1.6x

It's all about the angle of view - nothing more, nothing less.

[Nick Siebers]

I understand about magnification, now, but when I was first starting macro shooting with a DSLR, I did not. I did something similar to the coin experiment described above, and it was quite helpful.

Filling the frame has a large inpact in how the photo looks on the computer screen. The 3x4mm bug will be more impressive in an APS shot viewed fullscreen than on a 35mm or a MF shot, viewed full screen. Of course that matters to a beginner. And since it is all about getting the photo one wants, sometimes getting less of the picture is helpful. Which is why people buy 400mm lenses, as opposed to just shooting with a normal lens.

I suspect for every person who posts on a forum about not understanding the crop factor, there are at least 2 who find it useful, but I could be wrong. As for the term "crop factor", does anyone have a better way to succinctly describe the effect? It is a crop of a 35mm image, and variable from maker to maker, so "crop factor" seems like decent terminology to me.

It is frustrating that camera makers convince people that a APS sensor "makes" a lens into a longer focal length. But getting to the truth is part of learning photography, right? And there are lots of snapshooters out there who never need to know that they don't have a magical extending lens, they just want to shoot what they see.

<getting off soapbox now> :-) nick

[RioRico]

As for the term "crop factor", does anyone have a better way to succinctly describe the effect?

In the Wikipedia entry on CROP FACTOR [/me makes hand gestures against evil] I encountered a term I now prefer:

The term format factor is sometimes also used, and is a more neutral term that corresponds to the German word for this concept, Formatfaktor.

But it's still not right, especially if the concept still leads people to believe that a 100mm lens magically becomes a 150mm lens when placed on their Kx. It's sloppy language, like using 'theory' to mean "wild-ass guess".

[Marc Sabatella]

But filling the frame has nothing to do with the magnification at which the photo is taken.

True, but it has 8everything* to do with why anyone cares about magnification. No one cares how big the projection of an insect is on the sensor. They care how much that big will fill the frame when they actually view or print the image. So in *exactly* the same way that the crop factor is meaningful (to those few on this site with experience in film or reason to need to compare) with respect to FOV, it's also meaningful with respect to magnification.

Stated another way:

No one cares about the focal length or the magnification ratio of their lenses directly. They care about the *consequences* of those: the angle of view produced by the lens, or the maximum size of a small subject in a print of a given size. And both of those things *are* affected by sensor size.

So to those few on this site for whom focal length or magnification factors on film were useful points of reference, the "crop factor" helps them figure out what lens on APS-C would produce similar images with respect to angle of view or maximum size of small objects in a print of a given size.

But for those of us without a lot of experience with film (at least, not enough that focal lengths or magnification ratios really connote anything with respect to that format), it is just as correct o say the crop factor is equally useless whether talking about focal length or magnification. I know kind of FOV a 24mm lens has on *my* camera - an APS-C camera - and it doesn't help one bit to know that a 36mm lens would produce the same FOV on the film camera I lost track of many years. Similarly, I know how big a dandelion appears in the frame with a 1:2 macro lens on my APS-C camera, and it really doesn't do me a bit of good to know that I'd need a 1:1.33 lens to get the dandelion to look as big on that old film camera (hmm, it's late, not sure i did the math right on that).

I never once heard or thought of "crop factor". For each format, I learned which lenses covered which angles.

That's fine. I also used to balance my checkbook without a calculator. Even learned to use a slide rule. That doesn't mean I don't take advantage of tools that are helpful.

I admit, when I first got my HF Oly Pen-FT and mounted a Spiratone 400mm tele on it, I thought, "Oh wow! It's like having a 600mm lens!" But I quickly learned that, no, it's NOT like having a longer lens; it's like having a 400mm lens on a FF camera, and cutting the negatives in half.

Which is, for most people's practical purposes, the same thing.

[GregK8]

Marc's entry in the debate helped me restate my question in perhaps more practical terms, based on the consequences of the various lens/medium combinations.

If I take a picture of a clock tower from a distance with a 100mm lens on a full frame camera, what lens do I need to be able to take the exact same picture, from the same spot, with my APS-C camera? Likewise, if I take a picture of a bug with my 1:2 macro lens on a full frame camera, what lens do I need to take the exact same picture on my APS-C camera?

I think that is a much simpler way to state my original question, because it can be answered without anyone having to use the term crop factor.

[Derridale]

For the clock tower, a lens of 66mm would give you the same viewing angle (i.e. 2/3 of the 100mm). So, the nearest you could get to that. Probably a zoom set to 66mm....

For the bug, you don't state whether or not you're happy to move in or out a bit on the distance, or the focal length of the lens. But if it's 1:2, with all other factors constant, you'd need a lens that would give you 1:1.33 or thereabouts. In real life, of course, you'd simply move a bit further away if using the same lens.

I think those quick calculations are about right, but happy to be corrected if wrong.

[Blue]

True, but it has 8everything* to do with why anyone cares about magnification. No one cares how big the projection of an insect is on the sensor. They care how much that big will fill the frame when they actually view or print the image. So in *exactly* the same way that the crop factor is meaningful (to those few on this site with experience in film or reason to need to compare) with respect to FOV, it's also meaningful with respect to magnification.

Stated another way:

No one cares about the focal length or the magnification ratio of their lenses directly. They care about the *consequences* of those: the angle of view produced by the lens, or the maximum size of a small subject in a print of a given size. And both of those things *are* affected by sensor size.

So to those few on this site for whom focal length or magnification factors on film were useful points of reference, the "crop factor" helps them figure out what lens on APS-C would produce similar images with respect to angle of view or maximum size of small objects in a print of a given size.

But for those of us without a lot of experience with film (at least, not enough that focal lengths or magnification ratios really connote anything with respect to that format), it is just as correct o say the crop factor is equally useless whether talking about focal length or magnification. I know kind of FOV a 24mm lens has on *my* camera - an APS-C camera - and it doesn't help one bit to know that a 36mm lens would produce the same FOV on the film camera I lost track of many years. Similarly, I know how big a dandelion appears in the frame with a 1:2 macro lens on my APS-C camera, and it really doesn't do me a bit of good to know that I'd need a 1:1.33 lens to get the dandelion to look as big on that old film camera (hmm, it's late, not sure i did the math right on that).



That's fine. I also used to balance my checkbook without a calculator. Even learned to use a slide rule. That doesn't mean I don't take advantage of tools that are helpful.



Which is, for most people's practical purposes, the same thing.

The thing is, the ratio of the diagonal from one format to another doesn't really matter. For example, the DA 35mm ltd and Sigma 105mm are both capable of 1:1 macro shots. It does, however effect the background i.e. the DA 35 and 105mm on the K20d or the 105 on the K20d and K2.

With a 1:1 ratio, the image will be the same size on slide/negative film or image sensor as in real life. Like wise with a 1:5 ratio will be 1/5 the size on sensor/film as it is in real life. Due to the small size of 35mm negatives and digital sensors, a 1:5 ratio is almost life size when printed onto 4x6" photo paper. It doesn't matter if I take an image with the 105mm @ 1:1 on my K20d or on a 135 negative and scan it. They will be the same size when they are printed on the same size paper assuming that no cropping is done with either during the PP.

Or to put it more simply, when I go out to do macro, I don't care if its the K20d or K2, SuperProgram or my Canon EOS 10s, I am more concerned with the lenses macro ratio and not the film or sensor size.

[Blue]

Marc's entry in the debate helped me restate my question in perhaps more practical terms, based on the consequences of the various lens/medium combinations.

If I take a picture of a clock tower from a distance with a 100mm lens on a full frame camera, what lens do I need to be able to take the exact same picture, from the same spot, with my APS-C camera? Likewise, if I take a picture of a bug with my 1:2 macro lens on a full frame camera, what lens do I need to take the exact same picture on my APS-C camera?

I think that is a much simpler way to state my original question, because it can be answered without anyone having to use the term crop factor.

Derridale answered you on the clock tower. With the macro, the 1:2 part will be the same. However, the background will be different with the 2 images assuming you don't crop them in PP and print them on the same size paper. The image of the subject should be the same size. The same thing would hold true if you use a 1:1 lens like a 105mm and DA 35mm on the APS-C camera. The subject will be the same size but the background will be different. Its kind of like parking a truck in a 2 car garage vs. a 1 car garage. It will fit on both, its just that there is room for more crape around the truck in a 2 car garage.

[Marc Sabatella]

With the macro, the 1:2 part will be the same.

No, it won't, at least not in the sense I assume was meant. A 1:2 lens on FF will show a 72mm object just barely filling the frame (72 = 36*2, where 36mm is the width of the film frame). A 1:2 lens on APS-C can fill the frame with a 48mm object (48 = 24*2). Meaning the 72mm object that just barely filled the FF frame will actually be go way off the edges of the APS-C frame. You'd get the 72mm object filling the frame with a 1:3 lens (72 = 24*3).

Which is to say, the "crop factor" applies here in the same way it does to FOV. A 1:3 lens on APS-C produces basically the same image as a 1:2 lens on FF. That's assuming you've got the corresponding focal lengths and apertures worked out too so the FOV and DOF also match - it is indeed true that the backgrounds will differ otherwise.

So if you want the exact same image on APS-C that you obtain with a 50mm lens at f/11 and 1:2 magnification on FF, you'd need a 35mm lens (to match FOV) at f/8 (to match DOF). You'd shoot that 35mm lens on APS-C from the exact same position as you did the 50mm lens on FF to give the exact same composition / perspective. The resulting prints would turn out identical as far as any of this goes, but the magnification ratio would be only 1:3 - you are literally reproducing the object smaller on the smaller sensor to get the same image.

[Blue]

No, it won't,

Yes it will. The confusion in this thread arises from the notion that macro photography is about filling the frame. You may not be able to fill the frame with a mosquito's eye at 1:1 and in fact may require 2.5 or 3 to 1 which means more of the FOV from 1:1 will drop out as the eye fills the frame or less background. Even at 3:1 or 4:1, the eye won't fill the frame. It would end up being a portrait of the head, thorax, front legs, mesothoraxic legs and part of the antennae.

1:1 will get you something like this.

at least not in the sense I assume was meant. A 1:2 lens on FF will show a 72mm object just barely filling the frame (72 = 36*2, where 36mm is the width of the film frame). A 1:2 lens on APS-C can fill the frame with a 48mm object (48 = 24*2). Meaning the 72mm object that just barely filled the FF frame will actually be go way off the edges of the APS-C frame. You'd get the 72mm object filling the frame with a 1:3 lens (72 = 24*3).

You don't need macro to photograph a 72mm subject. Try this with a 5 millimeter subject at 1:1 with a 105 macro on the K20d and print it at 4 x 6 and use the same lens on film and request 4 x 6 prints. You will see that the subject will be the same in the two, but the surrounding background will not.

Which is to say, the "crop factor" applies here in the same way it does to FOV. A 1:3 lens on APS-C produces basically the same image as a 1:2 lens on FF. That's assuming you've got the corresponding focal lengths and apertures worked out too so the FOV and DOF also match - it is indeed true that the backgrounds will differ otherwise.

Not exactly. It effects the background area of the macro. But I'm not talking about the FOV. I am talking about the 1:1.

So if you want the exact same image on APS-C that you obtain with a 50mm lens at f/11 and 1:2 magnification on FF, you'd need a 35mm lens (to match FOV) at f/8 (to match DOF). You'd shoot that 35mm lens on APS-C from the exact same position as you did the 50mm lens on FF to give the exact same composition / perspective. The resulting prints would turn out identical as far as any of this goes, but the magnification ratio would be only 1:3 - you are literally reproducing the object smaller on the smaller sensor to get the same image.

"crop factor" nor focal length will effect the 1:1 or 1:2 ratio. That has to do with a specific focus distance of a given lens. The only difference in the DA 35 and Sigma 105mm in my above example is the focus distance at 1:1. They are both 1:1 capable lenses and the format won't change that.

[Lowell Goudge]

We have now wasted 2 pages with people arguing about trying to re define physical properties of lenses with all sorts of implied meanings

The fact remains focal length is a property of a lens irrespective of format

In the same way aperture is the ratio of focal length over diameter and

Magnification ratio is the ratio of imigensize to subject size

None are changed by format only the vield of view changes

Additionally the lens magnificTion ratio does not change because you look at the image on a larger screen all that changes is the print size

Let's get on with talking about photography as opposed to trying to redefine physical lens characteristics just because we are using a smaller part of the image a lens projects

[RioRico]

We have now wasted 2 pages with people arguing about trying to re define physical properties of lenses with all sorts of implied meanings
...
aperture is the ratio of focal length over diameter

Actually it's the other way around: D/FL

Other than that, you're dead-on right.

Let's declare this thread CLOSED.