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10-09-2014, 04:44 AM - 1 Like   #1
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Pentax dslr: apsc costs more than one stop (relative to full frame)

It's obvious when you think about it.

Put a 1.5x tc on a lens and you take it for granted that you are going to lose slightly more than a stop. Put extension tubes on to magnify another 1.5x - same. Crop factor is no different - there is no free lunch. If you think your classic 70-200 f2.8 is giving you 105-300mm and f2.8, you too have been successfully ...... what word should I use here, brainwashed? gulled? confused? led astray... you decide! by camera and lens marketings smoke and mirrors. You can't multiply the focal length by the crop factor and NOT multiply the aperture by the crop factor . As
"it breaks the math".
Your 70-200 f2.8 equates to 105-300 f4.2!!!

Sorry.

10-09-2014, 04:56 AM - 1 Like   #2
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Um... so what?
10-09-2014, 05:05 AM - 2 Likes   #3
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?? By that logic, how many stops does micro 4/3 "cost" compared to Large Format 11 X14 inch ?
10-09-2014, 05:15 AM - 6 Likes   #4
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Internet misinformation like that just makes things harder to understand for beginners.

Crop factor is an irrelevance. People who regularly switch between different formats will be aware of differences in angle of view and depth of field from personal experience. People who only ever use one format don't need to worry about it.

The assertion that, say, a 50mm f/2.0 lens on "full frame" would become a 75mm f/3.5 lens on APS-C is just plain wrong. It would still be a 50mm/2.0 no matter what camera it was mounted on. The f-stop is the ratio between the lens's focal length and physical aperture size, and using the lens with a different sensor size doesn't change that.

The notion that manufacturers should advertise their lenses with maximum f-stop values based on depth of field rather than exposure is simply moronic.

10-09-2014, 05:22 AM - 4 Likes   #5
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Or just take pictures. Who seriously gives a rat's arse about this nonsense?
10-09-2014, 05:24 AM - 1 Like   #6
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Exactly. Equivalence is not even about focal length, it is about field of view. Field if view is more than just focal length, since it also depends on image circle diameter and canvas (film plane or sensor area). Focal length is a lens property, completely independent on where it is mounted.
That being said, Pentax is still making FF lenses for APSC cameras. I would like Pentax to make some truly APSC lenses, which make use of the crop sensor advantages. Like Sigma with 18-35mm f1.8, or Fuji with 56mm f1.2, 23mm f1.4 and similar lenses. Not because crop "loses due to equivalence", but because faster lenses can be made for smaller sensors more easily (which is why we don't see f1.4 lenses on 67 cameras), and because Pentax needs a couple more primes that are faster than f2.8, since f2.8 is an aperture for zoom lenses these days.
10-09-2014, 05:28 AM - 3 Likes   #7
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The focal length of the lens does not change and nor does the aperture. If I put my FA 135/f2.8 on my K-01 it tells me that it is a 135mm lens and - wide open - it gives the appropriate exposure for f2.8. The "crop factor" crops the area that the light falls on. It does not reduce the intensity of light coming through the lens (as it would if it reduced the aperture). To put it another way, every lens produces an image circle and the brightness of the image is determined by the size of the aperture. A larger aperture gives a brighter image. But the brightness of the image is usually the same across the entire image circle (the exception is where there is vignetting if the image circle is too small for the format). You can crop that image circle to any size you want. If the lens if f2.8, any section of it will still be f2.8. That is the physics of it. No smoke and mirrors.
10-09-2014, 05:29 AM   #8
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If depth of field at a given aperture is all that matters, Tony Northrup should come clean and insist we all shoot 8x10 plate cameras.
What a crock.

10-09-2014, 05:35 AM   #9
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QuoteOriginally posted by Dartmoor Dave Quote
Internet misinformation like that just makes things harder to understand for beginners.

Crop factor is an irrelevance. People who regularly switch between different formats will be aware of differences in angle of view and depth of field from personal experience. People who only ever use one format don't need to worry about it.

The assertion that, say, a 50mm f/2.0 lens on "full frame" would become a 75mm f/3.5 lens on APS-C is just plain wrong. It would still be a 50mm/2.0 no matter what camera it was mounted on. The f-stop is the ratio between the lens's focal length and physical aperture size, and using the lens with a different sensor size doesn't change that.

The notion that manufacturers should advertise their lenses with maximum f-stop values based on depth of field rather than exposure is simply moronic.

Couldn't have put it better myself so I won't bother
10-09-2014, 05:36 AM - 1 Like   #10
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QuoteOriginally posted by marcusBMG Quote
You can't multiply the focal length by the crop factor and NOT multiply the aperture by the crop factor
Oh no, the crap factor again ! All that you do by using a FF lens on APS-C is to crop to the middle of the frame. Focal length and aperture do not change, no matter what the sensor or film size. It is only if you try to be clever and swap for a lens which gives the same field of view - necessarily one of a longer focal length - that things differ.
10-09-2014, 05:38 AM   #11
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One other thing, equivalists always talk about f-stop. What about t-stop? Would anyone make the claim that on a smaller sensor the t-stop must be multiplied by crop factor? Since t-stop has more to do with light transmission and less with aperture/DoF
10-09-2014, 05:40 AM   #12
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The funny thing with crap factor is that they ignore that the same factor give the smaller format a higher maximum magnification and hence, thinner DOF at that magnification at the same angle of view.
So not only is it moronic defining maximum aperture from DOF, but the proposed "equivalent" lenses are indeed NOT.
10-09-2014, 05:51 AM - 2 Likes   #13
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Tony Northrup got similar responses. I (and he) never said that the focal length or aperture of the lens changes. I (and he) are saying that if you want to think in terms of full frame equivalence then its both aperture and focal length that need to be multiplied by the crop factor. And the fact is that many do - only yesterday I pm'ed a fellow forum member who had written that a classic 135mm f2.8 would give 200mm!! at f2.8!! And the fact is that many don't appreciate the effect on DoF.
But at the end I agree with Dartmoor Dave that if you don't switch formats you shall just be familiar with the Dof and FoV on the format you use and thats all you in practical terms need - well put mate. But your first comment is just wrong, this is maths not misinformation, and your last comment misses the point: they advertise in terms of full frame equivalence. Bridge cameras are probably the worst offenders - check for yourself. Lenses marked being eg 28-400mm (equivalent) f2.8 except of course they're not! They're 6.5-80mm f2.8 OR 28-400mm f14 (I have assumed 5x CF) described as full frame equivalent.
This is not confusion it is enlightenment.

Last edited by marcusBMG; 10-09-2014 at 05:56 AM.
10-09-2014, 06:01 AM - 1 Like   #14
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The whole equivalence thing doesn't make much sense to me. It is useful if someone happens to shoot both on full frame and another format and can't remember how his lenses function on one format versus the other. What it doesn't seem to mean much is with regard to actual photography, particularly landscape photography. Assuming you want everything in focus, you have to be stopped down quite a bit -- more on full frame than on crop camera. In that sort of situation, "wide open equivalence," which seems to be what everyone refers to is meaningless. If I am shooting at f8 or f10 on a K3 because I need the depth of field, equivalence just tells me that I need to be stopped down even more on full frame to get the same depth of field. But doesn't everyone already know that?
10-09-2014, 06:04 AM - 1 Like   #15
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QuoteOriginally posted by marcusBMG:
And the fact is that many do - only yesterday I pm'ed a fellow forum member who had written that a classic 135mm f2.8 would give 200mm!! at f2.8!! And the fact is that many don't appreciate the effect on DoF.
The real fact is that most people don't care much about stupidly shallow depth of field. Most people who take photos in the real world want their shots to be in focus, so *more* depth of field is actually better.
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