50mm Comparison: Voigtlander 50mm f2 vs Nikon f1.8s

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EricTheAstroJunkie Contributing Member • Posts: 691
50mm Comparison: Voigtlander 50mm f2 vs Nikon f1.8s
1

Disclaimer: if you're looking for autofocus based performance comparisons this is obviously not the thread for you.

So as some may have come to notice/realize, I'm not the biggest fan of some aspects of the S lenses when it comes to my particular usage (almost entirely astrophotography). I really love the 50mm focal length for my nightscape imaging and since the Z cameras have been released I've really been looking for a high performing, but not massive in size/weight lens in the 50mm range. As soon as the 50mmS came out I bought one and used it for astrophotography, it was a disaster, the lens was badly decentered, it had terrible coma, terrible LoCA, and mediocre sharpness (it obviously should have failed every QC metric reasonable for lens release). This on top of the really poor focus by wire implementation by Nikon really turned me off the 50mmS. I used the lens long enough that it fell outside the return window and after the Sigma Art 40mm was released I basically banished the 50mmS until I sold it. The Art 40mm (IMO) is the benchmark for all lenses wider than 100mm when it comes to lens performance, it is the sharpest, most aberration free lens available of the many many lenses I have tested. Unfortunately it is also massive and heavy. I really loved the 40mm and vowed I'd never sell it because it was so good. It just kinda sucked to use adapted via the FTZ due to its unwieldy size/mass.

Fast forward to the last few months, the Voigtlander 50mm f2 APO has been on the market for a little while, I've been kind of following the reviews for it. By most measures it appears to be one of, if not THE best performing 50mm lenses on the market in terms of image quality/resolution. It also has the advantage of being small and lightweight and completely manual (astrophotography not requiring AF afterall). I've previously owned and used the bigger brother, 65mm f2 APO, also a wonderful lens. I sold the 65mm because I wanted a little more reach and ended up with the fantastic 85mmS. My girlfriend has been using the 50mmS for some nightscape imaging and I've been waffling on giving it a try again, her copy doesn't have the awful decentering/LoCA/Sharpness issues mine had. I noticed a 50mm APO pop up for sale recently so I figured I'd grab it and do a comparison between her 50mmS and it.

So for the initial part of this comparison I wanted to put the lenses through a optical performance test, I did not want to introduce more subjective things at this point so I'm using a great astrophotography program called PixInsight for this portion. PixInsight can open the raw files in a non-debayered, linear (true RAW) state with absolutely no software manipulation (like curves/stretches, color balance, lens profiles, etc). The software is also capable of doing image analysis in this true raw state, analysis that measures stars full width half maximum (FWHM, star size) as well as eccentricity and create contour plots as well as 3x3 mosaics of the image frame so it's easy to compare basic lens performance. What this part of the comparison does is look at coma and lens sharpness/star rendering/resolution.

So the basics of the test were both lenses were tested back to back with consecutive exposures at f2, f2.2, f2.5, and f2.8. For most intents and purposes lens performance past f2.8 (especially for astrophotography) is fairly consistent these days. Most lenses tend to top out at f4-ish in these areas and since I do astrophotography I'll never use these lenses stopped down past f2.8. All exposures were 15 seconds and ISO 800 on my tracking mount so as to ensure proper exposure and complete lack of star trailing. Every exposure was focused centrally on a bright star using a Bahtinov mask to ensure precise focus (spoiler alert, both lenses have not insignificant focus shift when stopping down). I chose a random star field with stars that weren't so massive as those tend to alter the FWHM measurements in some cases, I tried to do the exposures as quick as possible to limit the differences in sky brightness/atmospheric conditions/etc that would also alter the results.

I'll put my thoughts in subsequent posts so as to not alter the initial perception of the following images. Each image has 4 elements, 2 are 3x3 mosaics of the exposure showing central, middle-edge, and corner stars of the exposure, 2 are FWHM contour plots of the exposure. The left mosaic and top contour plot are for the Voigtlander, the right mosaic and bottom contour plot are the 50mmS. In terms of the plots, they are measure star size a relation to pixel size and lens sharpness/resolution capabilities. In a perfect lens world these contour plots would be perfect bullseyes, with a small FWHM taking up the central area and falling off to the edges and corners with larger FHWM values. Obvious a huge number of lens defects can cause this to not be the case, I'll talk about what I saw in subsequent posts, but what you want to see is mostly a bullseye with the center being DARK falling away to lighter shadings towards the corners/edges.

f2:

f2.2:

f2.5:

f2.8:

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