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02-22-2012, 07:35 AM   #1
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Crop factors

Hi

Ive tested taking shot with an M 28mm (FF lens) and a 18-55 kit lens at 28mm. They both come out with same focal length. I thought that when using a FF lens the crop factor (1.5x) will be like 42mm?

Does it mean that Ive misunderstood it all the time? That the focal length is always the one written on the lens. the crop factor thingy just shows what it is equivalently in FF?

Pentax is coming out with a new 50mm. Will it have the same focal length despite crop factor?

02-22-2012, 07:40 AM   #2
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The focal length remains the same no matter on which camera you mount the lens. On the other side a 28mm lens on a on a cropped sensor will give the same viewing angle as a 42mm lens on a FF camera.
02-22-2012, 08:37 AM   #3
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QuoteOriginally posted by striker_ Quote
Hi
.......
Does it mean that Ive misunderstood it all the time? That the focal length is always the one written on the lens. ......
...
Pentax is coming out with a new 50mm. Will it have the same focal length despite crop factor?
Yes you have - and yes, it is, But don't worry, you are not the first and you will not be the last. Focal Lenght (FL) is a physical property of your lens and totally independent of the camera body.

An object (say a bird) will always have the same size on the sensor when photographed with the same lens at the same distance. But if the sensor is larger, you will capture more of the bir'd surroundings on the sensor. The sensor - and not the lens - will give you a larger field of view.
02-22-2012, 08:40 AM   #4
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There are really 3 physical characteristics for a lens. These do not change, and two of them are completely irrelevent of the format you shoot.

Focal length is the distance from the focal plane (ie the sensor ) that parallel light rays focus to a point(ie light from a subject an infinite distance away). Aperture is the ratio of the focal length to the lens diameter , and the image circle is the diameter of the image made before the lens vignettes.

Focal length and aperture dont impact anything relative to format, but the image circle is important, DA lenses are designed to project an image circle that covers the ASP-C sensor, the internal baffles of a DA lens limit the light that is outside the image circle because this results in reduced contrast

02-22-2012, 09:15 AM   #5
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Just literally imagine only being able to see half of what your eyes could see... That's the limitations of having a crop sensor camera.
02-22-2012, 09:46 AM   #6
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QuoteQuote:
Just literally imagine only being able to see half of what your eyes could see... That's the limitations of having a crop sensor camera.
Oh please... that's a really poor analogy, and you know why... you're not going to convince me you're that stupid.
02-22-2012, 11:11 AM   #7
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If you put your kit lens at 18mm on an APSc camera and look through the viewfinder, you will see what you would see if you look through the viewfinder of an FF camera with an 28mm lens.

As other said, the focal length does not change.
02-22-2012, 11:29 AM   #8
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QuoteOriginally posted by Stone G. Quote
Yes you have - and yes, it is, But don't worry, you are not the first and you will not be the last. Focal Lenght (FL) is a physical property of your lens and totally independent of the camera body.

An object (say a bird) will always have the same size on the sensor when photographed with the same lens at the same distance. But if the sensor is larger, you will capture more of the bir'd surroundings on the sensor. The sensor - and not the lens - will give you a larger field of view.
I really like the way you explained that !

02-22-2012, 05:50 PM   #9
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Moving a lens from one camera to another does not stretch nor shrink the lens. No Procrustean beds here, thanks! The lens' focal length stays the same no matter where it is. Cameras with smaller frames see less of the projected image, that's all. The camera crops the image.

As was mentioned, a lens on a smaller-frame camera will have the same AOV (angle of view) as a longer lens on a larger-frame camera. That's the crap.factor. Unless you're an experienced 35mm film photographer who's transitioning to APS-C, forget that you ever heard of crap.factor. It is totally misleading.

I can take a 28mm T-mount lens and various adapters, and mount that lens on different cameras. On a 645 medium-format camera, it's AOV is VERY wide. On a 35mm FF camera, it's somewhat wide. On an APS-C camera, it's exactly 'normal'. On an m4/3 camera, it's a short tele. On a Q, it's a fairly long tele. But the lens doesn't change. Smaller formats just see less of what's projected.
02-22-2012, 08:21 PM   #10
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QuoteOriginally posted by Vicboy Quote
Just literally imagine only being able to see half of what your eyes could see... That's the limitations of having a crop sensor camera.
You can remove one of your eyeballs and it wouldn't halve your field of view! :ugh:
02-22-2012, 08:39 PM - 1 Like   #11
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QuoteOriginally posted by cali92rs Quote
You can remove one of your eyeballs and it wouldn't halve your field of view! :ugh:
Close one eye and tell us that again.

OK, it's not half. But we can't really equate our binocular visual system with a single lens. What happens with half-frame vs full-frame is, the sensor area is cut in half and the frame diagonal is cut by 1.5x. What happens with our visual system is... more complicated, because we move our eyeballs around to synthesize a view that's both wide and tele with deep DOF. A camera just doesn't see like a human eye does. The trick for becoming a decent photographer is to learn to see like a camera. Practice, practice, practice...

Last edited by RioRico; 02-22-2012 at 08:47 PM.
02-23-2012, 03:22 AM   #12
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QuoteOriginally posted by RioRico Quote

.... forget that you ever heard of crap.factor. It is totally misleading.

.
And how about "Equivalent Focal Length"? I wish I knew, whoever coined that term.............
02-23-2012, 03:43 AM   #13
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QuoteOriginally posted by Stone G. Quote
And how about "Equivalent Focal Length"?
You really only need crop factor or equivalent focal length when you compare different systems. Once you're using a specific system, you can forget about all of it.

Why would one need it once one uses a specific system? Are you going to think "yeah, on FF I would have used 75mm instead of 50mm for this shot" or "on my P&S I would have used 6.3mm instead of 25mm for this shot"?
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