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01-21-2017, 10:06 AM   #1
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SMC-A 20mm f2.8 distortion correction help

Hello, all--

Pro, new to Pentax (bought K-1 and traded in Nikon gear). I shoot a lot of artwork and installations for artists, galleries and collectors. I am using brand new Pentax FA 50mm f2.8 and 100mm f2.8 macro lenses for artwork, and acquired a pristine SMC-A 20mm f2.8 lens on eBay for wide angle architectural views. I am finding, however, that the 20mm has horrible distortion--barrel distortion in the center, and pincushion-type distortion at the edges (I was shooting all images at f/11, on a tripod). Sadly, there is no lens correction profile in Photoshop CC or Adobe Camera Raw for this lens, and I am not finding any profiles for it online. It seems to not be a very common lens, but has a solid reputation as a sought-after piece of glass. Anyone else here have distortion problems with this lens, or know of a source for a correction profile? Any help appreciated.

Thanks in advance.

01-21-2017, 10:59 AM   #2
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Hello there, from Durham (across the pond from you )...

I don't know of any existing profile for that lens. However, with some effort you can create your own using Adobe's Lens Profile Creator. You'd need to print out (or have printed) a large calibration chart that Adobe supplies.

It's a bit of a hassle, but once you're set up to do this, you'll never be short of a lens profile again

Take a look at this link and scroll down to "Adobe Lens Profile Creator":

Digital Negative (DNG), Adobe DNG Converter | Adobe Photoshop CC
01-21-2017, 11:40 AM   #3
LHK
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QuoteOriginally posted by slow_shutter Quote
Hello, all--

Pro, new to Pentax (bought K-1 and traded in Nikon gear). I shoot a lot of artwork and installations for artists, galleries and collectors. I am using brand new Pentax FA 50mm f2.8 and 100mm f2.8 macro lenses for artwork, and acquired a pristine SMC-A 20mm f2.8 lens on eBay for wide angle architectural views. I am finding, however, that the 20mm has horrible distortion--barrel distortion in the center, and pincushion-type distortion at the edges (I was shooting all images at f/11, on a tripod). Sadly, there is no lens correction profile in Photoshop CC or Adobe Camera Raw for this lens, and I am not finding any profiles for it online. It seems to not be a very common lens, but has a solid reputation as a sought-after piece of glass. Anyone else here have distortion problems with this lens, or know of a source for a correction profile? Any help appreciated.

Thanks in advance.
Well, I have this lens and also the FA 20/2.8, for which a lens correction profile is also absent in LR (I'm still using Version 4). The easiest way around is to "borrow" from the competition. I'm using the lens correction profile of the Nikon 20/2.8 lens, which works pretty good.

Lutz
01-21-2017, 12:01 PM   #4
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a) You can download the latest CameraRaw or check the release notes to see if it includes the lens profile of the FA 20mm. This is for adobe, other softwares have different lens profile databases
b) You can look for tutorials on how to make your own lens profile
c) You can try to photograph in such angles that the distortion is least visible. (This is a good idea even if you use lens profiles and digital corrections)

With the latest version of Lightroom you have automatic CA correction that is not part of a lens profile, so you can use that function with any lens. Distortion correction also has a manual option, so you can play with it and memorize which values work for that lens.


Last edited by Na Horuk; 01-22-2017 at 12:00 PM.
01-21-2017, 08:47 PM   #5
dms
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I do (a simple correction) w/ photoshop quite easily--presume similar for Lightroom. Done so for maybe 6 of my lenses. If zoom--then do it at a few FL's, the correction is essentailly linear with FL (e.g., +6% at 20mm, +3% at 30 mm, 0% at 40 mm, etc.).
-- I Photograph a rectangle--I use a window frame, or the venetian blinds behind the window. Then open the file up in software and find the lens correction amount that corrects the distortion.
-- Lens correction amount should be a single value independent of f-stop, and it seems to be good for all distances (anyway infinity to moderate distance).
-- By this method a mustache type distortion would need a second order correction as well (maybe warp in photoshop) but I haven't needed this.
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