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gtewks

Joined: 15 Mar 2014
Posts: 21

 Posted: Sat Dec 30, 2017 7:32 pm    Post subject: Olympus OMD M1-ii "high res" for macro Just got my Olympus OMD M1-ii today (MFT camera). This camera has what's called a "high res" option whereby it shifts the sensor around over 8 photos to produce a 80mp image (then downsized to 50mp). To me this seemed like a great way to increase my ability to magnify my macro shots (with cropping to around 24mp). This combined with the 2X crop factor I'll get using my Sigma 150 FX macro (with adapter),,, it seems like I could be looking at an equivalent 4:1 macro rig while still having a 24 mp image to work with. Am I missing something or does this sound like it will work? (still waiting on my lens adapter so I cannot test the theory just yet).
Lou Jost

Joined: 04 Sep 2015
Posts: 3062

 Posted: Sat Dec 30, 2017 8:09 pm    Post subject: You want to crop out a 25Mp chunk of that effectively 50Mp image. Those megapixel numbers are areas, not lengths, so half the megapixels does not give you half the field of view of the 50Mp image. 50Mp = L*w = L*k*L where L and w are the sensor dimensions in pixels, and k is a shape factor which describes the proportion between the length and width. K is a cosntant for any given sensor format. Now you want to find out what the length M would be for a 25Mp image on the same sensor. So we have L^2 = 50/k . Similarly M^2 = 50/2k. So the ratio (L/M)^2 = 1/2 and so L/M = 1/SQRT(2). So your new field of view will be your original MFT field of view divided by the square root of two. This implies that your "crop factor" in relation to a full frame camera is not 4 but 2*1.414 = 2.8_________________Lou Jost www.ecomingafoundation.wordpress.com www.loujost.com
elf

Joined: 18 Nov 2007
Posts: 1363

 Posted: Mon Jan 01, 2018 1:15 am    Post subject: Crop factor is a figment of a marketer's dream
enricosavazzi

Joined: 21 Nov 2009
Posts: 1112
Location: Stockholm, Sweden

Posted: Mon Jan 01, 2018 3:11 am    Post subject:

 Lou Jost wrote: You want to crop out a 25Mp chunk of that effectively 50Mp image. Those megapixel numbers are areas, not lengths, so half the megapixels does not give you half the field of view of the 50Mp image. 50Mp = L*w = L*k*L where L and w are the sensor dimensions in pixels, and k is a shape factor which describes the proportion between the length and width. K is a cosntant for any given sensor format. Now you want to find out what the length M would be for a 25Mp image on the same sensor. So we have L^2 = 50/k . Similarly M^2 = 50/2k. So the ratio (L/M)^2 = 1/2 and so L/M = 1/SQRT(2). So your new field of view will be your original MFT field of view divided by the square root of two. This implies that your "crop factor" in relation to a full frame camera is not 4 but 2*1.414 = 2.8

Also remember that with smaller pixels your CoC is smaller, so you need to open up the diaphragm between one and two stops to compensate for diffraction and get a similar sharpness. This implies that your DoF also reduces.

During the last month or two, I have been testing photomacrography lenses with the E-M1 Mark II, and found that many lenses good enough on a full frame or APS-C sensor of similar pixel count simply don't cut it on Micro 4/3, because of the smaller absolute pixel size. I don't know how the Sigma 150 behaves on Micro 4/3, but as a rule-of-thumb, you should not go past f/5.6 at 1x at 20 Mpixel native resolution (unless you are willing to give up sharpness for DoF), or f/4 in 50 Mpixel mode.

I just finished testing a very sharp lens (Printing Nikkor 105 mm A), and there is a detectable loss of resolution, due to diffraction blur, even from f/2.8 and f/4 and even in 20 Mpixel mode. If you do a systematic test of your lens on Micro 4/3, you should start from f/2.8 and go up to f/5.6 or f/8. The choice of a suitable resolution target is also important, and is discussed in several threads on this site.
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Pitufo

Joined: 21 Jun 2015
Posts: 213
Location: United Kingdom

 Posted: Wed Jan 03, 2018 2:18 pm    Post subject: gtewks - I'd be really interested in seeing your real world results. I am considering getting something similar to shoot myxos in the field - maybe the cheaper E-M5 mk II or mk III (soon to be released). I will start another thread to see if anyone can post photos of myxos taken with focus-bracketing MFT cameras. EDIT: New thread started here http://www.photomacrography.net/forum/viewtopic.php?t=36226
Lou Jost

Joined: 04 Sep 2015
Posts: 3062

 Posted: Wed Jan 03, 2018 3:01 pm    Post subject: I don't think they will work so well at high m. Reversing a native MFT lens to get auto stacking at higher m is feasible, but the working distance is very small with MFT lenses. Maybe putting a reversed non-MFT lens, or an objective, on an MFT lens and focus bracketing with the non-reversed lens would work with shallow subjects (I have done some experiments with this) but you can't get deep stacks._________________Lou Jost www.ecomingafoundation.wordpress.com www.loujost.com
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