Opticallimits

I'm considering to do some "fun" testing on Pentax Q. The system is very attractive for using C-mount lenses. However, these tend to be pretty bad on the average. Any recommendations ?

Computar 12.5mm f/1.3 - Here's some test notes on an E-P1 so you'll have to imagine what it is like with more sensor crop (~70mm f/7.1 equiv on the Q?). I got mine from here which seems to be less than ebay places although I haven't shopped around recently. Note for potential m4/3 users: it may be tricky to find an adapter that gets it close enough for infinity focus, but you can adjust the focus stops on lens to compensate to some degree.



At f/1.3 it suffers from reduced contrast. This clears up from f/2. Sharpness degrades as you go away from the centre, but this does improve a lot as you stop down. The extreme border of the image circle remains soft regardless. The lens exhibits blue/yellow lateral CA which is noticeable. I haven't observed any noticeable longitudinal CA so far.



Vignetting... the image circle doesn't fill the m4/3 sensor. It does expand slightly as you stop down. The three aperture blades do give triangular bokeh which gives its own character. As is, the lens doesn't do macro with a minimum focus distance around 40cm for not much magnification at all.



Distortion... in field conditions it seems to look like some barrel distortion at longer distances, noticeable on straight lines e.g. buildings. At close focus there was a hint of moustache. This really needs a test chart to nail.



Example of vignetting (also shows distortion):





f/1.3



100% crops from camera jpegs, centre and top right corner of building.





f/1.3 (note this was a bit over exposed as the camera ran out of headroom)





f/2.8





f/8 looks like diffraction has softened the centre slightly, but stopping down helps in the corner.





This is what it looks like with the bluebells at minimum focus distance. Not really close at all with the wide angle. How's the bokeh?





We're still at f/1.3 here. It's nice and round wide open in the middle, with a bit of outline. The shape does degrade at the edges (taken from top-right). The CA also impacts here. I haven't tried correcting it yet.

I was more thinking of something longer or wide than the 5-15mm. I think that this zoom lens is pretty good already so users may not be overly interested in something that overlaps here.



I haven't really seen something wider other than fisheyes. There seem to be a couple of good (on paper) 25mm and 35mm lenses.

However, I'm clueless whether -say- of the Tamron SP C-mount lenses is really decent. I reckon that most are as old as time itself. The Fujinon HF-XX-SA series seem to be rather attractive as well.

Fair enough. This one caught my eye as it has ok coverage for a bigger sensor, and relatively fast too.



I got the common cheap unbranded 25mm f/1.4 that's available everywhere, but all I can remember from that was really severe field curvature before I gave up on it.