This is not a thread to debate or explain physics. This is a thread which hopefully can become a resource for lens selection for so called crop sensors.

The other day I was involved in a discussion about "85mm" lenses, and the differences between the characteristics of a certain FOV lens on "full frame", compared to how it looks on a crop sensor. A "native" lens can be designed to perform just like it´s other sized sibling, but when one is into vintage lenses / lenses that can be used on multiple systems it gets far more complicated! Lately I´ve been thinking a lot about lenses that work across different camera systems and the different qualities that are exhibited, depending on the size of the sensor. I´m not thinking so much about the obvious depth of field related changes as to how the overall feel of the image and subtle optical imperfections alter the image with the same lens used on different systems. I´d like to think of aps-c or s35 as base sensor / imager size over "full frame", at least for us who have video as the main area of camera usage, however, many lenses where designed for "full frame" and although the differences on s35 and aps-c can be rather small, I find the differences increase exponentially the smaller imager you put it on.

Hence I have come to search for vintage full frame lenses which will exhibit appealing qualities on a gh2 or a blackmagic design cinema camera. Now, what is appealing to me might not be appealing to you, but I will try to define my own criteria and I hope you can supply yours and add to this thread.

I have been building two main sets of vintage still lenses after ditching my canon fd´s (they were not getting the use to justify having them). For one, I have been buying c/y zeiss optics and I have been adding m42 mount lenses as I have come across them or found some interesting aspect which could fit in with the rest. The c/y´s will no doubt be a mainstay in my arsenale for years, however the ultimate reason why I pulled the trigger on the full set was the advent of the metabones speedbooster – I much prefer how they look on a slightly bigger sensor over a smaller one and I have high hopes for the speedbooster. The reasons for the preferred vicinity to "native sensor size" are:

1. less pronounced CA. I have become a bit allergic to aberrations of late.
2. nicer transition to OOF areas, wide open or stopped down.
3. More obvious contrast/microcontrast "sweet spot". (I think this is down to a slightly larger FOV)
4. Usability wide open, much in line with the criteria above. A lens which looks sharp in the center on full frame or aps-c might just look soft on a smaller sensor because there´s less contrast between edge and center.

With the m42´s it´s different. I like very much how they look on the gh2 AND f.i. the fs700 or BMD, so I find them extremely useful for video, across systems. So what is it I´ve been looking for?

1. Low(ish) contrast
2. Pleasing (sort of neutral) OOF and bokeh, also when stopped down.
3. good price / performance ratio.
4. great CA control
5. reasonable color match
6. good distortion control / flat focal field

I have mainly been searching through lens databases (on possible candidates), comparing sample images.

Now, this set consists today of the following lenses:

20mm flektogon f2.8 29mm meyer optik, pentacon f2.8 37mm Mir-1b f2.8 50mm Pancolar f1.8 58mm Helios f2 135mm meyer optik orestor f2.8 200mm meyer optik orestegor f4

I´m still looking to add a few but for the ones I have / I´ve had I can say the following:

20mm flektogon - I prefer the f4, as it´s tack sharp wide open. (f2.8 needs to be stopped down to 4-5.6) 29mm Meyer optik is sharper / has less blooming (coma) than the pentacon wide open.. maybe half a stop brighter as well - otherwise they are remarkably similar - both useful wide open. Bokeh can be both expressive and sort of neutral depending on where you place the focal field / subject and f-stop. 37mm Mir is a great "normal" lens on the gh2. Too slow? No. Just right. I want to add a macro ring to help out close focusing. Great value for money and beautiful OOF transitions thanks to the 10 blade aperture. 50mm pancolar - a bit too low in contrast to fit the others well. Not a fan of it´s bokeh. 58mm helios f2 - rock´n roll short tele on the gh2. Wonderful out of focus rendition and also nice transitions thanks to the round aperture. 135mm meyer optik - beautiful and tack sharp tele. Notoriously nice OOF / Bokeh rendition. Low in contrast and needs a push in post to match most of the other lenses. 200mm meyer ... - used it very sparingly so far. Not super sharp wide open. Not a preferred lens on gh2 sensor.

In general, I´ve had some issues with mechanics in cold conditions (needed to clean out and lubricate some helicoids) but they have been put to very good use already. I traded away a 35mm flektogon which I felt was a tad harsh in contrast in comparison to the others anyway (great lens tho). Another thing which is down to physics - the wider the lens, the more restless / harsher the bokeh is. The performance of a certain FOV does not quite match what you´d get on a larger sensor but this will only be a problem in case you are looking for really wide lenses in which case you are better off with native lenses anyway. The difference is mainly where you place the camera. (between different sensor sizes).

Note: I believe it´s difficult to switch lenses with acute focal fields between different sized imagers and not get very differing results.. For my m42 set I´d normally not use all for one production but choose a few depending on priority, like f.i. one or two wides, one or two tele´s to contain the slight differences in coatings, color e.t.c. However, they match remarkably well despite transgressing manufacturers and brands. I´d guess it´s because they are in the vicinity of one lineage of optics manufacturing.

Samples to follow.