[Marc Sabatella]

As a bit of an experiment, I pulled out my old ME Super with a 1.4 50mm lens, and compared it to my K100D and KX, with a 1.4 FA 50mm, and my DA 18-55 set at 50mm. I swapped lenses around to all cameras and the only difference was the field of view. Magnification was the same for all three cameras, irregardless of the lens used, which is what I would have expected.

Don't get confused by magnification in the viewfinder, which is as much an attribute of the viewfinder as the lens. How big something appears inthe viewfinder has nothing to do with how the picture turns out. You could put a giant magnifier on your viewfinder and see images really big, but that doesn't change the picture. Focal length is all about FOV.

[Blue]

What is this "film" thing you're referring to?

Thanks for clearing this up once and for all. I've always considered magnification a better descriptor for a zoom lens than the mm's...

Talking about magnification compared to for example 3x or 4x sometimes referred to in a zoom lens may not be what you think it is. It is the ratio between longest the shortest focal length. or example a 50-150mm zoom would be a 3x zoom but so would a 20-60mm. The same holds true for a 100-300mm but it has a far greater "reach" than any of the 3 examples.

[Marc Sabatella]

Yes, thanks for catching that. Magnification factors (as in 3X or whatever) are *useless* in evaluating zoom range on a DSLR. They get used in P&S camera because they all *start* in more or less the same place - 28-35mm in FF equiv). So it's always true that a 3X zoom means wide to short telephoto. But for a DSLR, a 3X zoom might be ultra wide to not quite as wide, or telephoto to super telephoto. Or it might mean wide to short tele. You have no way of knowing without seeing the focal lengths.

I think people have this erroneous impression that the "X" in a P&S zoom specification has to do with "how much bigger something looks through the viewfinder than with the unaided eye", because that's how binoculars and cheap telescopes are often rated. But for P&S cameras, it doens't mean that at all - it just means how much more magnification there is at the long end than the short end". how big it looks in the viewfinder doesn't enter into it. And in fact, most P&S cameras have viewfinders so small that even at "5X", they are still smaller than with the unaided eye.

[Myltlpny]

Don't get confused by magnification in the viewfinder, which is as much an attribute of the viewfinder as the lens. How big something appears inthe viewfinder has nothing to do with how the picture turns out. You could put a giant magnifier on your viewfinder and see images really big, but that doesn't change the picture. Focal length is all about FOV.

My point wasn't so much about the magnification of the viewfinder as that objects appeared the same in all three cameras with three different 50mm lenses. When I looked at a picture on the wall for instance, the picture appeared to be the same relative size in all three cameras. All that changed was the field of view, which is what I expected. If I zoomed out my 18-55mm to get the same field of view with my Kx as I did with my ME Super, the focal length was somewhere around 35mm in the Kx and that same picture appeared smaller, again as expected. It wasn't a scientific experiment by any means, but it helped to clear up the confusion over what I had read (or mis-read) vs. my experience with film cameras.
I'm still rather new to DSLR, so I'm finding I'm having to re-learn or adapt to the technology. I shot 35mm film for years and while many of the concepts are the same, I find myself trying to make parallels to my film experience to better understand the technology, and these forums have helped immensely.

[Marc Sabatella]

My point wasn't so much about the magnification of the viewfinder as that objects appeared the same in all three cameras with three different 50mm lenses.

Well, yes - because the viewfinders of those camera happened to work out that way.

When I looked at a picture on the wall for instance, the picture appeared to be the same relative size in all three cameras.

You mean if you made a print of the image each camera took? No way that could possibly true if you printed the same size. Larger FOV means objects appear smaller in a print. Couldn't possibly be any other way.

Or maybe you mean, looking at a object (that happened to be a picture on a wall) *through the different cameras' viewfinders*. If so, then yes - as I observed, you've learned something about the viewfinders of your cameras. You've learned nothing really about how FF and APS-C relate. If your FF camera happened to have a smaller viewfinder (like mine did), or your APS-C camera a larger viewfinder, you'd have seen *entirely* different results.

Again, don't be fooled by how big things look in the viewfinder when it comes to comparing compares, because chances are, you're comparing viewfinders, not format sizes. Actually, you're comparing both at once, but with no way of differentiate how much of the effect is due to one versus the other.

I'm still rather new to DSLR, so I'm finding I'm having to re-learn or adapt to the technology.

Yes, this happens. Again, I'm just saying, don't be fooled by sizes of objects in the viewfinder - consider only how they look in the pictures taken. Otherwise you're liable to get very wrong impressions of how it really works.

[Class A]

On an APS-C sensor, the normal lens is more or less 30 mm. Anything shorter is wide, and anything longer is tele.

On FF, 50mm is "normal", less than that is wide, more than that is tele.

Both are right, even though the focal lengths are different. Why? Because of the crop factor. So it is not "crap" one should forget about. One may choose to call it "format conversion" factor instead of "crop" factor, but it is real.

Perhaps it helps to realise that the format conversion factor does not affect the focal length but the AOV (angle of view) a lens produces on a certain format. Also, it does not apply to AOV only, but also to f-ratios. The equivalent of a 75/2 on FF is a 50/1.4 on APS-C.

Finally, the real normal focal lengths are ~43mm for FF and ~28mm for APS-C. The ubiquitous "50mm" was chosen because at the time it was easy to make it sharper than a 43mm. Ever wondered why the FA 43mm has this focal length?

[flyer]

"Crop factor" is still crap. When I use MF, nobody talks about crop facltor. When I use large format, nobody hears about crop factor, so why do you use it with digital APS-C cameras? Just get use to the lens focal length and forget the bloody "crap factor".

[Class A]

When I use large format, nobody hears about crop factor, so why do you use it with digital APS-C cameras?

Perhaps because APS-C cameras are "crop cameras" in the sense that they use a mount designed for the 35mm format but have smaller sensors (to reduce costs)?

I don't know how interchangeable lenses are in your MF world. If you cannot move a lens from one camera to another with a different format than obviously there is no point talking about a crop factor.

Since many lenses that are used on APS-C cameras really are FF lenses it pays off to not simply assume they will continue to have the characteristics they have and are recommended for in FF. For example, many recommend a "fast fifty" as a "normal lens" that provides you with neither wide- nor telephoto characteristics. They recommend it to improve your compositional skills because the lens won't add any effect on its own. That advice has merit when the "fast fifty" is used on a 35mm camera. It is much less applicable when it is used on an APS-C camera (where you'd have to use 32mm or better 28mm lens for the same effect).

So the crop factor is useful to convert the old FF-stories to the new APS-C land.

If you don't read about lenses than you don't need to translate stories and hence don't need a crop factor. Most people hanging out on camera forums tend to read about lenses, though.

A fun fact as an aside: Sigma sells a lot more 70-200 lenses on APS-C than 50-150. Is it because now 100-300 (~35 mm equivalent of 70-200) is much more popular than 70-200 has been in the FF world? It seems much more likely that the 70-200 range (that has its certain purpose in the 35mm world) is simply adopted by many APS-C shooters without making the crop translation.

[flyer]

The "crop factor" is absolutely useless. It just keeps people in the 35mm bubble. A 50mm lens is a 50 mm lens. It doesn't matter if it is on an APS-C, 35mm or 645 camera. The angle of view will be different, and you need to get used to that, but the focal length didn't change.

When working with an APS-C size sensor/film, you should get used to what a specific lens will do on your camera. Trying to compare to 35mm all the time is just handicapping you.

It's like speaking a second language. You must associate the word to the idea it represents, not to it's translation.

[enoeske]

The "crop factor" is absolutely useless. It just keeps people in the 35mm bubble. A 50mm lens is a 50 mm lens. It doesn't matter if it is on an APS-C, 35mm or 645 camera. The angle of view will be different, and you need to get used to that, but the focal length didn't change.

When working with an APS-C size sensor/film, you should get used to what a specific lens will do on your camera. Trying to compare to 35mm all the time is just handicapping you.

It's like speaking a second language. You must associate the word to the idea it represents, not to it's translation.

I am a mathematician. Some people, like me, like to try to explain our physical world in a simple, straight-forward fashion. For instance, when we drop an object, it seems to always fall at the same rate. Maybe we can measure this and make predictable results in the future. Ah ha! Every object falls at 9.8m/s^2 (when in a vacuum). Now I can drop things for whatever purpose I have and know or plain ahead exactly how it will act.

In lens talk, whenever a change a lens from my film camera to my Dslr, the angle of view seems to change. Maybe I can measure that and make predicable results for the future. Ah ha! Every lens has the same characteristics but appears cropped by a factor of 1.5. Now I can switch lenses in the future and predict exactly what it will look like ahead of time. Neat!

[MrApollinax]

enoeske, for you it makes a difference as you have transitioned from the Film world to the Digital world with your old lenses in tow. For many here an APS-C camera is their first DSLR (myself included) and the talk of crop factor can become confusing as those users have no prior experience in the film world to compare to.

[Class A]

The "crop factor" is absolutely useless.

Yves, it doesn't look like we will be able to convince each other. I won't prolong this but let me give me one more example:

You are interested in portraiture and read that the classic range recommended for portraiture is 85-135mm. But you own an APS-C camera and while you could mount a lot of lenses in the range of 85-135 on your camera, you should rather be mounting lenses in the range 55-87. That doesn't sound "totally useless" to me, unless you want everyone to rediscover what has been discovered in the FF world.

It just keeps people in the 35mm bubble.

I'd say it allows people to learn from 35mm experiences.

A 50mm lens is a 50 mm lens.

Of course, only beginners think that a focal length could change. However, "50mm" doesn't mean anything. The only meaning "50mm" has is its association with a certain AOV. If we used AOV to refer to lenses then we could say "I love my 46.8° AOV lens" and that sentence would make sense independently of the format.

If someone says "I love my 50mm lens" (on FF) then this has to be translated. We could translate the sentence to refer to an AOV but since most photographers talk about AOV in terms of the focal length associated with it, we use a focal length that represents that AOV. Since it is a different focal length on a different format, the "crop factor" comes into play.

The angle of view will be different, and you need to get used to that, but the focal length didn't change.

I agree that anytime one uses a focal length that was obtained by using a crop factor one should qualify it with the term "<old format>-equivalent", e.g., "50mm FF-equivalent".

When working with an APS-C size sensor/film, you should get used to what a specific lens will do on your camera. Trying to compare to 35mm all the time is just handicapping you.

I fully agree with the first statement. The second doesn't apply to me and, I feel, not to a lot of other photographers either.

You must associate the word to the idea it represents, not to it's translation.

I see your point but note that there are a lot of books that associate words to translated words (not to the ideas they represent). These books are called "foreign language dictionaries". Are they useless?

[Class A]

For many here an APS-C camera is their first DSLR (myself included) and the talk of crop factor can become confusing as those users have no prior experience in the film world to compare to.

Confusing it may be but maybe after a while it becomes helpful. Consider the blurb that comes with the description of the Pentax FA 50/1.4:

The PENTAX smc P-FA 50mm F1.4 lens provides a perspective similar to the human eye. Its natural perspective of subjects makes it ideally suited for everyday use including indoor photography, traveling, and hiking.

Now that's just rubbish for any APS-C user like you. On your K100D super the 50mm will be a short tele.

So even if you have never used film (I certainly never did) it is useful to know how the characteristics of lenses translate on different formats.

You may think that using "equivalent focal lengths" is confusing but then photographers speak in terms of focal length, not in AOV, so that's why this is the convention.

[flyer]

These books are called "foreign language dictionaries". Are they useless?

These books are used to represent an idea in words, so you can associate the word with the idea it represent.

Case closed.

[Blue]

The "crop factor" is absolutely useless. It just keeps people in the 35mm bubble. A 50mm lens is a 50 mm lens. It doesn't matter if it is on an APS-C, 35mm or 645 camera. The angle of view will be different, and you need to get used to that, but the focal length didn't change.

When working with an APS-C size sensor/film, you should get used to what a specific lens will do on your camera. Trying to compare to 35mm all the time is just handicapping you.

It's like speaking a second language. You must associate the word to the idea it represents, not to it's translation.

It may be useless for the "average consumer." However, the crop factor or conversion factor or whatever you want to call it is used to calculate the fov or angle of view for a lens on one sensor or film size relative to a different one. This includes a 6x7 lens on a 24 x36 film body or aps-c sensor. It also applies to a 6 x7 lens on a 645 film camera or 645D version. So it has it purpose and utility. You don't even have to use the lens on 2 different film/senor sizes for this to have utility. For example, If I shoot an old abandoned church with a DA 21mm ltd on the K20d and want to replicate the shoot with the 6x7 on Portra NC, I won't be using a 21mm lens. What I have as wide angle for the 6x7 is a 55mm and 75mm. Which of those do you think will get me closer to the fov of the 21mm on APS-c from the same perspective?

(This is a real example I'm doing this week.)