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Old Jun 28, 2006, 6:30 PM   #21
TDN
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John Hill wrote:
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The lens is not longer, the picture is smaller.
Oh, I see. But does that affect the quality at all?

If I'm getting it right, this should enlarge things like purple fringing. Because you're "enlarging" a smaller picture, right?

So basicly it just "seems" like you've zoomed in further, because of the cropped image you get...

allright thanks for the explaination
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Old Jun 28, 2006, 6:46 PM   #22
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TDN wrote:
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So basicly it just "seems" like you've zoomed in further, because of the cropped image you get...
I'm as guilty as anyone in how I explain this, since the "popular" thing to do is call it a crop factor.

But, when you think about it, there is no "crop factor" involved. Remember, you've got lenses designed specifically for a DSLR with an APS-C size sensor, with smaller image circles.

Are you still looking at a cropped view then? No.

Do you still need to use a multiplier to see how the angle of view would compareto the same focal length lens on a 35mm camera? Yes.

Look at cameras like the Olympus E-1, E-300, E-500, etc.. These Olympus DSLR models have sensors that are even smaller than the one in most other DSLR models. Do they have a cropped view, just because you need to multiply the actual focal length of the lenses by 2x to see how the angle of view compares to a 35mm camera? Nope.

How about a model with an even smaller sensor. Let's look at something like my little Konica KD-510z pocket camera. It's lens is marked as 8-24mm. Is it being cropped in some manner to give me the same angle of view I'd have on a 35mm model using a 39-117mm lens? No.

The lenses are correctly marked with theactual focal length of the lens (and in the case of fixed lens consumer models, the "35mm equivalent focal range" is also given in their specifications).

What changes is the angle of view, which will depend on the sensor (or film) size, for any given actual focal length.

The mainreason that you see the 35mm equivalent focal lengths of the lenses mentioned, and crop factors/focal length multiplierspublished, is so that users of 35mm cameras have a better idea of how the angle of view compares to the same focal length lens on a 35mm model.

This is only because 35mm cameras are so popular.

Let me repeat that.

This is only because 35mm cameras are so popular.

What compounds the confusion, isthat DSLR bodies are often designed so that a lens from the same manufacturer's 35mm bodies can be used on it. In this case, the image circle is larger than the sensor. That's notwhat makes the angle of view different.

You see the same types of differences when you go to film that's larger than 35mm, too. The actual focal lengths of the lenses are still marked on them. Yet, you'll have a widerangle of view for any given actual focal length compared to a 35mm model (versus a narrower angle of view like you'd have using the same focal length lens on a model with a smaller sensor orfilm size).

For example, a 45mm (actual focal length) lens on a 645 format camera would have a 35mm equivalent focal length of approximiately 29mm. What I mean by that is the angle of view would appear to be the same as a 29mm lens would have on a 35mm camera.

So, if 645 format models were more popular than 35mm cameras, we may be seeing focal length multipliers/crop factors for 35mm cameras (so that users would understand how the angle of viewcompares, when using the same focal length lens on a 35mm camera that they were accustomed to using on a camera using a larger film size.

If 35mm models weren't so popular, there would be no reason to even mention a "35mm equivalent focal length" or "crop factor".It's done for comparison purposes, since the actual focal lengths of the lenses is are how they are marked.

Does it make any difference that the sensor happens to be smaller than 35mm film for detail purposes? Not if the sensor is capable of capturing what you need, just as if you were comparing 35mm film witha larger film format (only with digital, you're able to get more photosites into a smaller sensor, so that the sensor can resolve enough detail compared to a larger sensor with the same number of photosites).

Ditto for things like angle of view or depth of field. Sure there is a difference. That's because of the sensor or film size, and how yourangle of view changes with the film or sensor size,for any given actual focal length lens.

Should we abandon 35mm because 645 is larger, or abandon 645 because I can get an 8x10" camera? LOL

You use works best for you.

Are focal length multipliers/crop factors useful (even if these terms are relatively inaccurate)?

Sure they are.

They help users that are familiar with 35mm cameras determine how a lens at a given focal length compares when using a DSLR that has a sensor size that is smaller, from an angle of view perspective.

If you were using the samefocal length lens on a model with a larger sensor or film size, you'd have a wider angle of view.

If you were using the same focal length lens on a model with a smaller sensor or film size, you'd have a narrower angle of view.

That's what the so called "crop factors" and "focal length multipliers" are good for -- so that users familiar with using a 35mm camera have a better understanding of how the angle of view compares for agivenfocal length lens,when it's used on a DSLR with a smaller sensor.


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Old Jun 29, 2006, 1:55 PM   #23
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Ok, I see. But it will seem like you've zoomed in further when you print out the image on the same size, right?

Let me use these pictures to explain what I mean.

Say this is the picture you get with a 200mm lens on a 35mm camera:


Applying your theory, what you'll get with the same lens on a DSLR with a smaller sensor will be something like this:


Now if we extract that same picture to the same size as the original we get:



See? it seems like we've zoomed in 1,5 times further, while in reality, we just expanded a cropped image.


Does this make any sense? or am I completely wrong ?

TDN

P.S.: Sorry to go on and on about this, but it's my nature I cant help it. If there's something I dont understand and then I need to figure it out one way or another
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Old Jun 29, 2006, 2:36 PM   #24
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It's not a cropped image if the image circle of the lens is designed for a given sensor or film size. ;-)

Yet, you will still have angle of view differences based on the size of the film or sensor for a given focal length lens.

Yes, the final image you view is going to be enlarged to a given image size for viewing. But, as long as the sensor is not outresolving the lens, you're fine with digital, because you're able to increase pixel density (although we're probably getting close to a point where we'll level off in the rate of increase).

With film, you have more of a difference between smaller and larger film formats in final output quality due to increasing resolution with surface area.

So, by using 645 format film, where you'd have a wider angle of view for a given focal length lens compared to a 35mm camera, you get more benefits from the larger surface area of the film from increased resolution.

In any event, I don't look at it as a crop, since you have angle of view differences between film and sensor sizes for any given focal length, and you have lenses made with image circles designed for specific film and sensor sizes.

If you use the samefocal length lens on a model with a larger sensor or film size, you have a wider angle of view.

If you use the same focal length lens on a model with a smaller sensor or film size, you have a narrower angle of view.

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