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Forum: Pentax K-1 & K-1 II
06-26-2016, 07:59 PM
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Following up on my previous post, an example from yesterday showing flare handling and the largely absent purple fringing of the Voigtländer. Taken at f/8.0 straight into the late afternoon sun, extremely bright highlights on the water, with very minimal post-processing - just enough to lift the shadows/left side a tiny bit. I focused rather close, so already the swimmer is way behind the focus plane. The DoF scale is rather 'generous' by today's standard. Highlights which are close to the focal 'plane' show next to no fringes, further out, there is some weak red outlining. Unfortunately, I did not have the HD-DA15 with me to compare, but this looks more than adequate to me, including contrast. Using RawTherapoee's tone mapping, this cleans up nicely with just a little brightening of the trees above the reflection but overall good contrast.
(Exif incorrectly shows 50mm as I forgot to set FL).
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Forum: Pentax K-1 & K-1 II
06-24-2016, 05:47 PM
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Maybe not the best ultra wide angle lens around technically, I nevertheless completed my planned (preliminary?) K-1 wide-angle set with a lens so far not mentioned here: A new Voigtländer Color Skopar 20mm f/3.5 arrived from Hongkong yesterday. The others are an F28 f/2.8 and a Tamron 17-35mm f/2.8-4.0 (excellent range for city/town, more useful than my 8-16mm on APSC was), and currently a rarely used Samyang 8mm fisheye, but that might get replaced, just need to figure out with which one. Together with the D-FA28-105mm, I have a fairly competent minimal landscape set for hikes without much weight.
The Color Skopar is in almost all respects the exact equivalent of the DA 15mm ltd. on fullframe so loved by many as shown in https://www.pentaxforums.com/forums/122-lens-clubs/86234-15mm-limited-controls-my-mind-club.html when it comes to the compromises made in its design. It's a tiny, well-built ultra-wide lens intended mostly for landscape use with the aperture closed down a few stops and, important for me, extremely flare-resistant. The main difference to the DA15 is lack of auto-focus. To compare details of the two, I used FF shots from the CS20 scaled up 200% and APSC crop shots from the DA15 scaled up 300% for the same apparent size on screen. As expected, the field of view on the CS20 on FF is slightly wider than the DA15 on APSC, but the DA15 would just cover the same angle if you cropped manually.
Even though the optical construction is fairly different, the two seem to render in a very similar way. Both have excellent center sharpness and contrast throughout their aperture range, but require ~f/8 for the corners to catch up when you need them. Even the character of the dominating aberrations are the same: strong field curvature and significant coma. Chromatic aberrations are very similar in magnitude, just color-wise the CS20's contours are purple whereas the DA15's are red. Nothing to worry about with either lens though. I'd say the CS20 is slightly more prone to purple fringing than the (HD-) DA15, but I'll confirm that with some other subjects. From a first look, the close-ups from the CS20 look even better than from the DA15. Colors are slightly warmer than the (HD-) DA colors.
So why bother and not continue to use the DA15 in crop mode? The CS20 on FF definitely delivers in terms of additional detail and, using the full sensor, should also help with dynamic range. The manual focus of the CS20 has a nice long throw which makes the depth of field scale easier readable than the DA15's, which often is more important to me than AF as I shoot the DA15 mainly manually focused. One difference which really bothers me is that unlike most of my other primes (F28, DA35, F50/1.7, D-FA50, DA70, D-FA100), the CS20 needs 52mm filters:( and so far I don't have any 52mm ND filter.
I chose the Color Skopar over chasing a M20 f/4 as I could get a brand new lens for not much more than I would have had to pay for a beaten M20mm f/4 currently, and because it is available without having to spend a lot of time searching. Maybe I keep my eyes open to complete the 49mm threaded prime set. The f/2.8 Pentax lenses (A,FA20) are already bigger and all three (M/A/FA) don't seem to enjoy the same flare resistance as the CS20, as far as I can tell from published sample pictures and reviews.
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