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06-16-2010, 10:23 PM   #1
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Crop factor demonstration.

Here is a little demonstration of how the crop factor affects your photos.

I went out today with my old Ricoh KR 5 Super, and also took my K110D, both had 28mm lenses mounted. here are the differences. 28mm is pretty w i d e on film...I was standing in the same spot for both of these photos...

KR5 Super with 28mm lens.



K110D with 28mm lens



06-17-2010, 12:30 AM   #2
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If i'm not mistaken, you divide the FOV with the crop factor...meaning the APS-C pic will cover 60% (2 thirds) of the 35mm image.

That is quite a big difference.

In order to compensate this, one can get a wider lens . It might be interesting, Stratman, to show another picture in wich the difference is compensated.

Maybe after your post a lot of first time APS-C DSLR users will get FF cameras )
06-17-2010, 12:34 PM   #3
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Until they see the same demosntration using a telephoto lens.
06-17-2010, 02:40 PM   #4
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I just figured this will give a VISUAL explanation of how it works. I have never really seen one posted. I was out with 3 cameras yesterday, and decided to do a little test. It's pretty obvious the difference when you see actual photos from the same spot of the same subject.

06-22-2010, 06:49 PM   #5
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I hate the term CROP FACTOR. It is an obscenity, and quite misleading. Newbies think, "Ooh, I took this 200mm lens off a K1000 (full-frame film SLR) and put it on my Kx (half-frame dSLR), and now it's a 300mm lens!!" No, it isn't. It's still 200mm, but the half-frame sensor sees less of the projected image than does the full-frame film.

Do this: Take a magazine, select a picture, and cut it to 2 1/4 x 1 5/8 inches (56x42mm). That's the size of a 645 medium-format picture. Now cut a card to 36x24mm. That's the size of a full-frame 35mm image. Center the card on the picture and draw a line around it. Now cut the card in half, to 24x18mm. That's about the size of a Pentax dSLR sensor. Center the card on the picture and draw a line around it. Now cut it in half, to 18x12mm. That's about the size of a 4:3 System sensor, like those little Olympus and Panasonic babies, or a 110 film frame. Center the card on the picture and draw a line around it.

Ok, let's suppose the original 56x42mm picture was shot on a Pentax 645 camera with an 80mm lens. On it you've drawn smaller outlines. Each of those smaller views IS STILL THE RESULT OF THE 80mm LENS!! They're just much less of the image. The 645 diagonal (which is how coverage is measured) is ~1.6x the full-frame (FF) diagonal, but nobody says that an 80mm lens has a 1.6x crop factor on FF. It's just as misleading to say that a half-frame (HF) dSLR has a 1.5x crop factor compared to FF. Smaller sensors capture less of the image, that's all.

I want to find the b@stard who coined the term CROP FACTOR and torture them.
06-22-2010, 07:08 PM   #6
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QuoteOriginally posted by RioRico Quote
I hate the term CROP FACTOR. It is an obscenity, and quite misleading.
...
I want to find the b@stard who coined the term CROP FACTOR and torture them.
So, how do you like the term "focal length multiplier"?

I remember reading a blog article. The author said that if you attached a 200mm Nikon FX lens to a Nikon DX body, you had a 300mm lens. But if you attached a 200mm Nikon DX to a Nikon DX body, you had a 200mm lens because the lens was already DX format, you wouldn't have to apply the "focal length multiplier" factor!
06-22-2010, 07:41 PM   #7
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QuoteOriginally posted by RioRico Quote
I hate the term CROP FACTOR. It is an obscenity, and quite misleading. Newbies think, "Ooh, I took this 200mm lens off a K1000 (full-frame film SLR) and put it on my Kx (half-frame dSLR), and now it's a 300mm lens!!" No, it isn't. It's still 200mm, but the half-frame sensor sees less of the projected image than does the full-frame film.
While nothing you've said is untrue, it really misses the point of why the concept of a "crop factor" *does* have value if you're trying to understand the relationship between what kind of pictures a lens takes on one format versus another format. Sure, the result *on the sensor* is the same as as in your cropping example. But no one looks at the sensor. Even if they did, they wouldn't see an image. In order to see the image, you have to display it on screen or print it. And when you do that, lo and behold, the smaller cropped image gets magnified more, and therefore *does* start to resemble one taken with a longer focal length on a larger sensor in the one and only way that matters to most people: they show the same FOV. So while of course it isn't correct to say it actually increases the focal length, the distinction you are making just isn't relevant to most people, and making such big deal of just confuses the issue for them, IMHO.
06-23-2010, 05:04 AM   #8
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Focal Length is Focal Length is Focal Length... it is an inherent physical property of the lens that is unaffected / unchanged by what size sensor is "seeing" the image created by it. I would venture a guess that a fair percentage, if not a majority, of first time DSLR users (myself included) have no experience with 35mm film or FF DSLRs, and these focal length "equivalence" references back to 35mm only serve to confuse unnecessarily. I think we'd do well to familiarize ourselves with lenses of different focal lengths and how they work with our own particular camera sensors, whether they be full frame, APS-C, 4/3, etc. Just my two cents...

06-23-2010, 09:47 AM   #9
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Note I do agree with the above - if you have no reaosn to comapre to 35mm film, then the whole concept is not worth one's time. But if one *does* have reason to perform such comparisons (if only to be able to better understand books and articles written from a 35mm film perspective), then a *proper* understanding of the crop factor is necessary. The hard part is making sure people understand what it is is and what it is not. if people didn't already tend to have a preconceived notion of focal length equating to FOV, life would be a lot simpler, but for better or for worse, people have become accustomed to making that association, and somehow one has to find a way to work with that in explaining the behavior of "cropped" sensors. Maybe the best approach would be to first teach peopel to disassociate focal length from FOV. but the problem is, there's is virtually no support for that kind of approach - discussions of lenses virtually *never* revolve around the very practical concept of FOV, but rather this obscure physical property called focal length.
06-24-2010, 04:09 AM   #10
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QuoteOriginally posted by Marc Sabatella Quote
Until they see the same demosntration using a telephoto lens.
Which always makes me cringe inwardly, as the usual conclusion is often "APS-C is better for telephoto", quite stupid for the simple reason that FF pics can always be cropped to the same amount as APS-C (often with still superior IQ), negating the perceived telephoto advantage...
06-24-2010, 04:26 AM   #11
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QuoteOriginally posted by dlacouture Quote
Which always makes me cringe inwardly, as the usual conclusion is often "APS-C is better for telephoto", quite stupid for the simple reason that FF pics can always be cropped to the same amount as APS-C (often with still superior IQ), negating the perceived telephoto advantage...
Now that is funny!
06-24-2010, 04:57 AM   #12
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QuoteQuote:
Which always makes me cringe inwardly, as the usual conclusion is often "APS-C is better for telephoto", quite stupid for the simple reason that FF pics can always be cropped to the same amount as APS-C (often with still superior IQ), negating the perceived telephoto advantage...
That is not correct, because by cropping an already taken image one loose resolution (is like digital zoom) as oposed to the "optical" cropping in the case of crop sensors.
06-24-2010, 05:20 AM   #13
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QuoteOriginally posted by kytra Quote
That is not correct, because by cropping an already taken image one loose resolution (is like digital zoom) as oposed to the "optical" cropping in the case of crop sensors.
?

FF camera often have nearly the same pixel density than APS-C sensors (D700 being a notable exception).

Let's take the 5d mkII (3753x5634 for a 24.0 mm x 36.0 mm sensor) : if you crop the resulting 21MP pic to the 15.8 mm x 23.6 mm APS-C equivalent sensor size, you end up with (counting on fingers) 2470x3693 pixels (9.1MP), which is quite plenty enough...

Okay, it's a little bit less than a K10, but I'd trade in a blink anyway...

EDIT: And before someone gives the "bigger aperture" advantage for APS-C, let's consider that a f/2.8 200mm on APS-C is equivalent to a f/4.5 300mm on FF, DOF and FOV wise... And given that FF has better high-iso, the 1.5Ev light loss due to the smaller aperture is easily matched by the better high-iso handling.
So, identical photos can be taken with about the same price tag for lenses... The DA*200 is not that far below the DA*300 price, and you still end up with a slightly better 300mm with the FF solution...
Well, this leaves the body price discrepancy to explain to your wife...

Last edited by dlacouture; 06-24-2010 at 05:53 AM.
06-24-2010, 06:02 AM   #14
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Stratman you left out one difference. The photo from the digital would have to be smaller. Pretend that the sensor is film. Both "negatives" are in an enlarger. Both set for the same magnification. The cropped sensor "negative" will yield a smaller print.
06-24-2010, 06:22 AM   #15
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@dlacouture

What I said is true if you take similar sensors (lets's say Kx and D700 12Mpixels) - if you crop the D700 image you'll loose resolution whereas the Kx will maintain the 12 Mpix in order to achieve the same magnification. Furthermore, if you crop the K-x image you'll obtain an even better magnification with the same resolution of the D700 crop.

This is the reason behind pro-sport shooters (and by sport I don't mean chess or snooker) always using APS-C cameras whereas landscapers use FF and MF.
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