Crop factors and mirrorless question
I'm intrigued by some of the mirrorless options coming out these days. I’ve seen some fantastic photos with the X100, NEX system, and others on Nikonians. The new X-Pro 1 and rumors of the OM-D are peeking my interest, too. These compact/larger sensor cameras could prove to be a valuable tool when shooting events where I need to get PJ-style shots without being too obvious.
Currently I use two DSLR’s: a D700 and D7000 – both excellent cameras as we all know. However, I do feel like a fish out of water when I use the D7000 due to crop factors. Sure, a 35mm has a similar FoV like a 50mm on a D7000, but it still has the distortion/curvature of a 35mm; anything smaller than a 50mm on my D7000 just feels awkward to me.
In researching this, I’ve read that – for example – a 35mm on a rangefinder such as a Leica doesn’t not have as much distortion as a 35mm on an SLR. This has something to do with how close the back of the lens sits in relation to the sensor (or film). I have never used a Leica or rangefinder, so I could be wrong. Please feel free to correct me if I am.
With this in mind, I’d like users of the NEX or X100 to tell me if the any Focal Length on either mirrorless has less curvature than a the same focal lenghth on an APS-C DSLR. If so, could you post a comparison? I think the x100 is 23mm, right? Could someone compare that to, say, a 24mm lens on a APS-C dslr? If the distortion is less, I think I can enjoy a mirrorless with an APS-C sensor. Otherwise, I think I'm in for a long wait for a full frame mirrorless to come out.
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#1. "RE: Crop factors and mirrorless question" | In response to Reply # 0aolander Nikonian since 15th Sep 2006Tue 31-Jan-12 04:51 PM
"a 35mm on a rangefinder such as a Leica doesn’t not have as much distortion as a 35mm on an SLR. "
This statement is baloney. If you're talking perspective distortion due to how close you are to a subject, it will be the same whether on a full frame SLR or Leica, and it will be the same for "equivalent" focal lengths on different format/sensor sizes. A 24mm lens on a APS-C DSLR will have the same "distortion" as a 35mm lens on a full frame camera if you photograph someone with the lens jammed in their face due to the fact the the distance to the subject will be the same in both cases for the same size image.
#2. "RE: Crop factors and mirrorless question" | In response to Reply # 1Tue 31-Jan-12 07:55 PM
Thanks for clearing that up - though somewhat aggressively. I wasn't sure about that statement myself, but had hoped it were true. Anyway, I'll stick with FF dslr's then. Sounds like I won't like the mirrorless for the same reasons I shy away from crop sensors.
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#3. "RE: Crop factors and mirrorless question" | In response to Reply # 2briantilley Nikonian since 26th Jan 2003Tue 31-Jan-12 08:38 PM
I think you may be barking up the wrong tree somewhat...
There are basically two types of distortion which can be seen in photographic images, the first being perspective distortion - the classically bad "big nose" appearance in a portrait. As Alan says, this is due only to the distance from camera to subject and the angle of the subject plane to the sensor plane. Perspective distortion does not depend on the camera format or the focal length of the lens - except that a wider lens might encourage you to get closer and thus amplify the distortion.
The other type is optical distortion, where straight lines near the edges of the frame are rendered as curves - this isn't formet-dependent either; it is governed by the optical design of the lens being used. The FX format doesn't automatically give you less distortion than smaller (or larger) formats. If you have a 24mm lens on your D7000 and a 35mm lens on your D700, one might have less optical distortion than the other, but any difference would be due solely to the design of the lenses. Similarly, a 13mm lens on a Nikon 1 camera might give more or less distortion than either of the others.
In short, there is no generic answer to your question - you'd need some practical testing to determine the distortion characteristics of any particular mirrorless camera/lens combination.
#4. "RE: Crop factors and mirrorless question" | In response to Reply # 3Tue 31-Jan-12 09:15 PM
Good to know. Somewhere I read that since the lens sits closer the the focal plane there was less distortion in equivelent lenses. Obviously someone was exaggerating - unintitionally making an overly ambiguous claim - about the benefits of a rangefinder. A quote from our favorite website to hate:
...For wide-angle lenses, allowing lens designers to make lenses whose rear elements can come very close to the image plane lets wide-angle rangefinder lenses be much smaller, sharper and have less distortion than SLR lenses...
I've read similar comments from other Leica & mirrorless users. This being the reason for my question. I knew I'd get the the "real" low-down here
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#5. "RE: Crop factors and mirrorless question" | In response to Reply # 4blw Nikonian since 18th Jun 2004Wed 01-Feb-12 12:21 PM
That statement is over the top. The lenses can be smaller, certainly. But more of the smaller also comes from not having to cram as much stuff in. A rangefinder lens is a manual focus lens, with fully manual aperture (ie no auto-stop down or full aperture viewing), no auto focus mechanism, no VR mechanism, etc. And rangefinders, with the exception of a couple, are nearly universally film cameras. Film grain is not sensitive to the direction of its activating light. Digital sensors are, so without pretty extraordinary measures, you get considerable light fall-off in the periphery, and this is more extreme the larger the sensor is. Again, an M7 doesn't care. An M9 does. And the M9 sensor actually tilts the outside sensors slightly toward optical center for this reason. It's one reason that the M9 sensor is so expensive. It is, moreover, not impossible to design telecentric SLR lenses to have very little distortion: the Sigma 12-24 is an existence proof.
If the claim is that Leica lenses are sharper and have less distortion, that's true. They also have significantly less function and cost dramatically more than most lenses to which they're being compared, so it is far from obvious what the contribution of the basic system design is and how much is simply a lot more engineering effort and cost being put into the end product. Also, note that rangefinder lenses are nearly universally primes, and most recent SLR primes are pretty damn good too. And even the expensive ones are half the price of the Leica equivalents, or less. As one example, the Nikkor 24/f1.4 is about $2000; the Leica 24/f1.4 is $7000. And while that Leica is a truly excellent lens, it's not as if the Nikkor is exactly a slouch.
If you want to stick to full frame, for whatever reason, that's your perogative. But there is no inherent difference in distortion between the formats, assuming that FOV is equalized. Try comparing, for example, the 24/f1.4 AFS on DX to the 35/f1.4 AIS on FX - you will find that the DX image has significantly less curvature of field, the same perspective "distortion" and significantly higher sharpness, at least wide open. Compare the 24 on DX against the 35/f1.4 AFS on FX and you'll find that they're about equal in sharpness, curvature of field and essentially identical in perspective.
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#7. "RE: Crop factors and mirrorless question" | In response to Reply # 5Sat 18-Feb-12 12:42 AM
I did a quick and dirty comparison between a 35mm 1.8 DX and a 50mm 1.4D. My conclusion? You're right. Once FoV is equalized the ONLY way I can tell which lens was which was by the DoF: obviously the 50mm @ 1.8 will be shallower than the 35mm.
To my eyes one image doesn't look any more "distorted" than the other. I imagine that if I staged a even more rigorous test and equalized the DoF, used a tripod, light meter, etc., I could produce images that you'd have to look at the exif to determine the lens used.
I've got some thinking to go do. Thanks everyone for the guidance, and correcting some obviously "distorted" information about lens distortion!
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#6. "RE: Crop factors and mirrorless question" | In response to Reply # 4ChrisPlatt Registered since 04th Jun 2011Wed 01-Feb-12 07:13 PM
I'm not sure the discussion has touched on the reason people are making that claim about rangefinder and/or mirrorless cameras. Those discussions all seem to address the retrofocus lens design necessary to get wide angle effects on an SLR. A retrofocus design being necessary because the rear element of a wideangle lens without the retrofocus group would be too close to the film plane/sensor and interfere with the operation of the mirror. The claim is that the retrofocus design introduces more barrel distortion. However, I expect modern lens designs have done a good job incorporating additional lens groups to counter that barrel distortion.
I really have no idea whether these claims are valid or were ever valid. Certainly, if you can eliminate the retrofocus group and any additional elements necessary to counter barrel distortion, the lens can be smaller/lighter, but would that really give them any advantage over a well designed (albeit much larger) DSLR wideangle lens with respect to barrel distortion?
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