I thought it would be a good idea to compare a few lenses which have very good to excellent UV transmission for presence of focus shift, sharpness in UV at F4 (or the maximum aperture of the lens if smaller than F4) as well as when stopped down to F8.
I have also added a third component – the lens capability when spanning two light spectra, in this case both UV & visible light (blue and green). Images were taken at F4 and F8 using my IDS2e filter.
The lenses which I tested:
1) 35mm F3.5 enlarger lens old model (Aico lens used but will also apply to other rebadged versions)
2) 35mm F3.5 enlarger lens new model (Also Aico lens tested – but same should apply to other rebadged versions)
3) Novoflex Noflexar 35mm F3.5
4) El-Nikkor 40mm F4
5) El-Nikkor 80mm F5.6
6) Kuribayashi 35mm F3.5
7) Soligor 35mm F3.5 (9xxxxx series)
8) Prinzgalaxy 35mm F3.5 (7xxxx series)
9) Mayfair Crystar 35mm F3.5
10) Leica Focotar-II 50mm F4.5
11) Coastal Optics 60mm F4 APO (my reference)
I used my Olympus E-PL5 to shoot with the various lenses (only Coastal Optics was shot with Olympus EM-5). Focus was done with no filter on the lens using light from my mini studio. The focus point was the 0 on my DIY Focus target. Visible images were lit by the mini studio and taken without filter, while the UV images were also lit by the mini studio using the Baader U filter. Any shift of focus from the 0 mark in the UV image is a sign that focus shift is present.
My DIY focus target was made from a print out from the web, and glued onto a tissue and Maltesers box. I also use this to do micro autofocus adjustments for my Sony LA-EA4 and A-mount lenses.
For the sharpness test, I used a Rudbeckia fulgida as the subject. Focusing was done using live view with Baader U filter on the lens and subject lit by Nightsearcher 365nm UV torch. Photos were subsequently taken using Quantum X2D as UV-light source, with lenses set at F4 or the maximum aperture of the lens. The same method was used for the IDS2e images.
All images have been cropped to 1280×1280, so click on images for larger pics.