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Archive 2013 · Cropping A7R to match longer focal length on Micro 4/3?

alexands
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p.1 #1 · p.1 #1 · Cropping A7R to match longer focal length on Micro 4/3?

I currently have the OM EM-5 and the Panasonic 35-100 lens (equiv of 70-200 on full frame).
I'm considering selling these and buying an A7R with the 24-70 f4 OSS lens. What I'm wondering
is if I crop an A7R image shot at 70mm to the equivalent field of view as the Om EM-5 at 100mm (200mm equiv),
will they be comparable in terms of resolution. So, when cropped will the extra megapixels of the A7r make up
for the shorter focal length. I'm not sure how to compute this...can someone explain?

Dec 04, 2013 at 11:39 AM

aleksanderpolo
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p.1 #2 · p.1 #2 · Cropping A7R to match longer focal length on Micro 4/3?

A7R's sensor is 4 times the size of m4/3. If you crop it to m4/3 size it will be ~9MP

Dec 04, 2013 at 11:52 AM

alexands
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p.1 #3 · p.1 #3 · Cropping A7R to match longer focal length on Micro 4/3?

Ok, thanks. But what if I only want to crop the a7r image enough that I get the equivalent of 100mm (or 200mm full frame equivalent) on the om em-5?. Would my resolution end up being less than that of the m 4/3 file? Basically I'm trying to figure out the following - if I get rid of my 35-200mm on the micro four thirds camera, can I simply make up for the reach by cropping the image shot with the a7r and 24-70 lens.

Dec 04, 2013 at 12:16 PM

millsart
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p.1 #4 · p.1 #4 · Cropping A7R to match longer focal length on Micro 4/3?

Ummm maybe obvious, but why not buy either the 70-200 f4 when it comes out for the A series, or, just get an adapter and use any of the wide range of high quality, and rather affordable, 100-200 manual focus primes/zooms that exist ?

Then your getting a true 200mm equiv FoV with the full resolution of 36meg

Dec 04, 2013 at 12:27 PM

sebboh
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p.1 #5 · p.1 #5 · Cropping A7R to match longer focal length on Micro 4/3?

alexands wrote:
Ok, thanks. But what if I only want to crop the a7r image enough that I get the equivalent of 100mm (or 200mm full frame equivalent) on the om em-5?. Would my resolution end up being less than that of the m 4/3 file?

yes, if you crop the a7r at 70mm to make it an effective 200mm angle of view you will have substantially less megapixels (~5mp) than the omd shooting a 100mm (200mm effective) lens. if your crop the 70mm on an a7r to a 140mm aov you will end up with a ~9mp image. if you crop the 70mm on an a7r to a 100mm aov you will end up with ~16mp image.

Dec 04, 2013 at 12:33 PM

alexands
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p.1 #6 · p.1 #6 · Cropping A7R to match longer focal length on Micro 4/3?

Great, thanks! That answers my question. I was evaluating options for a minimalist kit. My em-5 plus Panasonic 12-35 and 35-70 weigh in at a total of 1095g. I was hoping that with the a7r plus 24-70 (891g) combined with some cropping I could have an equivalent kit. But it seems that I would lose out above 100mm (full frame equiv) if I went with the a7r and just the 24-70mm. I guess I'll do a search for high quality 200mm primes and see if there are any really light ones.....

Dec 04, 2013 at 12:57 PM

millsart
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p.1 #7 · p.1 #7 · Cropping A7R to match longer focal length on Micro 4/3?

Sadly, for all the advantages of FF cameras like the A7r, smaller sensors like m4/3 will always retain an advantage when it comes to the crop factor and being able to give more effective reach with smaller/lighter glass.

Its like the old saying of cheap, fast, well made....pick any 2, because you can't get all 3

A7r is great if you want resolution, huge dynamic range, subject isolation ability etc, but if your goal is also to be able to get a lot of reach while not carrying heavy glass, its not gong to happen really

Dec 04, 2013 at 01:12 PM

alexands
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p.1 #8 · p.1 #8 · Cropping A7R to match longer focal length on Micro 4/3?

I guess this would be an advantage of a super high mega-
pixel camera - you could crop to greater extents and still end up with reasonable resolution (without having to carry a lot of heavy glass). Sebboh, how did you compute those numbers?

Dec 04, 2013 at 01:18 PM

millsart
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p.1 #9 · p.1 #9 · Cropping A7R to match longer focal length on Micro 4/3?

alexands wrote:
I guess this would be an advantage of a super high mega-
pixel camera - you could crop to greater extents and still end up with reasonable resolution (without having to carry a lot of heavy glass). Sebboh, how did you compute those numbers?

Really is no free lunch, and even when you've got really high MP sensors, as previously stated, once you crop it down your giving up about 4x the pixels to get a 2x crop. Same principle of if you want to double the resolution you need 4x the pixels. Its why going from 24 to 36 megs really isn't that huge. You'd need to move to 96meg to double the resolution over a 24 meg camera essentially.

Of course when your cropping your not getting the real focal length either. Framing a shot to fill the VF with a real 200mm lens, vs filling a quarter of the frame with a 50mm lens, and then cropping it down to the 200mm FoV isn't going to look the same.

I mean, you can get those little digicams with 1000mm equiv lenses, but they are using a tiny sensor and have something like a 12x crop factor, so your real focal length is less than 100mm on them.

Cropping can work in some cases, but its not as simple as just getting a high rez sensor and using a quarter of it.

Dec 04, 2013 at 01:24 PM

alexands
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p.1 #10 · p.1 #10 · Cropping A7R to match longer focal length on Micro 4/3?

Interesting and thanks....

Dec 04, 2013 at 01:32 PM

sebboh
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p.1 #11 · p.1 #11 · Cropping A7R to match longer focal length on Micro 4/3?

Dec 04, 2013 at 02:10 PM

alexands
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p.1 #12 · p.1 #12 · Cropping A7R to match longer focal length on Micro 4/3?

Thanks for the explanation sebboh....

Dec 04, 2013 at 02:24 PM

alexands
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p.1 #13 · p.1 #13 · Cropping A7R to match longer focal length on Micro 4/3?

It seems that there is logic in being invested in more than one format - full frame and micro four thirds as each has its advantages. I was worried that my micro four thirds lenses would be antiquated because of the a7r, but I'm no longer concerned because long lenses for the a7r will always have to be much bigger than those for the micro 4/3 and the larger sensor will not compensate. On that subject, my canon L lenses have all held their value as well....seems that lenses are a good investment

Dec 04, 2013 at 09:31 PM


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