Pentax Full Frame and APS-c Lenses


With Pentax announcing that they will be releasing their DSLR with the same size sensor as 35mm film (know now as ‘Full Frame’) I wanted to try a test with some lenses designed for a APS-c digital image circle. Pentax refers to these as ‘DA’ lenses.  There are some lenses that are designed for use with either format these lenses are designated as ‘DFA’, I’m not interested in these for this purpose, as I know they will work as would older lenses from film cameras.  So back to the DA lenses.   It seems that the only lenses that can be considered to work with the larger format will be prime lenses (single focal length).  The zoom lenses designed for APS-c cause heavy vignetting and will likely need to be used in a crop mode rather than covering the entire full frame sensor.

Pentax SMC-DA* 50-135mm f/2.8 ED [IF] SDM ,  Pentax SMC DA 50mm f/1.8,  and the SMC DA 35mm f/2.8 Limited macro
An example of the extreme vignetting is this image taken with the DA*50-135 set at 50mm and f2.8

You can see that it doesn’t come close to covering ‘Full Frame’ with severe vignetting.  The situation is better at 135 stopped down to f4 but the vignetting is still heavy in the corners.

So moving on to the prime lenses where there is a much better chance of them covering the full image circle of the 35mm frame.  I should probably mention the fact that I used what I knew would be some bad film.  It was some very out of date Kodak 400 but because my primary objective was to test the lenses for their coverage I choose to use it.

First up is the DA 50 1.8 I took only 2 shots with it the first one at f4 and the second at f1.8 and it clearly covered the full 35mm frame with little to no vignetting in fact it seems perfectly suited to Full Frame.

With only a 24 frame roll of film my attention turned to what I was most interested in the DA 35 ltd a fantastic lens that I had hopes would work with the future full frame camera.  At f9.5 you can see there is no issue the lens easily covers the larger surface area without any vignetting.

Moving to f5.6 with the following images it can be seen that the lens works fine at this opening too.
PentaxMZ6_LensTest_Mar2015_007 PentaxMZ6_LensTest_Mar2015_011 PentaxMZ6_LensTest_Mar2015_020 PentaxMZ6_LensTest_Mar2015_021

So for the ultimate test I took some shots with the lens wide open which in this case is f2.8
PentaxMZ6_LensTest_Mar2015_008 PentaxMZ6_LensTest_Mar2015_010

The DA 35 ltd worked so well with my 35mm film SLR that I will have no hesitation using it again for film or with a future ‘Full Frame’ DSLR.  I had seen elsewhere on the internet that it didn’t work for 35mm film but that certainly contradicts my finding.  What vignetting exists I do not find at all objectionable and if you choose to it could be easily counter acted in software. The one caveat being that using the built in lens shade at full extension would certainly end up darkening the corners as its effect is even visible in the Pentax MZ-6 92% coverage viewfinder.

Similar things can be seen here DA 40 XS on film



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