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4 Days Ago   #1
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Question about compatibility of APSC-designed lenses with K-1

Greetings; new member here, but four-decades-long Pentax owner, both film and APS-C digital, with about a dozen Pentax lenses.
I recently bought the Pentax DA 20-40mm f/2.8 Limited zoom, but the Ricoh/Pentax website says that it's an APS-C lens (vs. the DFA 24-70mm f/2.8 lens, which it says is designed for FF cameras as well as APS-C). I'm planning to buy a K1 II camera soon, and am wondering what happens when one of these APSC-designed lenses is put on the K1. What problems are there? thanks for the patience, as I'm sure this has come up previously in this forum (but I didn't find it in a quick search)..

4 Days Ago - 1 Like   #2
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Welcome to the forums!
It will vignette (i.e. your corners will be black or you will see a black circle surrounding the image). You can avoid this by using the crop mode.
4 Days Ago   #3
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Welcome aboard. The link below will answer most of your questions........................................I hope.

Pentax K-1 Lens Compatibility Guide - Articles and Tips | PentaxForums.com
4 Days Ago   #4
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As far as I know, by default the camera will use up to 15MP downsampling when cropping APS-C when DA lenses are connected. Optionally, you can enable the use of the entire sensor area.
I heard SMC PENTAX DA 50MM F / 1.8 seems to be without vignette. While this may not be the case..


Last edited by Martin Stu; 4 Days Ago at 09:26 PM.
4 Days Ago - 2 Likes   #5
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See also this article for tests of each DA lens:

Full Frame Coverage of DA Lenses: Comprehensive Test - Gear Guides | PentaxForums.com

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3 Days Ago   #6
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In the end , if the image looks good, you've found a good lens.
I own a K-1, but use the DA 21, DA 40 LTD , DA 40 LTD, and DA 18-135 regularly, and often without using crop mode, because the vignetting is minimal to nonexistent with those lenses, and I usually compose knowing I will crop in post.
3 Days Ago   #7
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QuoteOriginally posted by cometguy Quote
Greetings; new member here, but four-decades-long Pentax owner, both film and APS-C digital, with about a dozen Pentax lenses.
I recently bought the Pentax DA 20-40mm f/2.8 Limited zoom, but the Ricoh/Pentax website says that it's an APS-C lens (vs. the DFA 24-70mm f/2.8 lens, which it says is designed for FF cameras as well as APS-C). I'm planning to buy a K1 II camera soon, and am wondering what happens when one of these APSC-designed lenses is put on the K1. What problems are there? thanks for the patience, as I'm sure this has come up previously in this forum (but I didn't find it in a quick search)..
@BruceBanner showed some images and commented on using this lens in K-1 FF mode. You may look for these posts.
3 Days Ago   #8
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Welcome to the forum cometguy. Have you been able to catch a glimpse of Neowise? Members have posted some great shots.

2 Days Ago - 1 Like   #9
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QuoteOriginally posted by Apet-Sure Quote
Welcome to the forum cometguy. Have you been able to catch a glimpse of Neowise? Members have posted some great shots.
Yes, I've been able to see the comet on numerous nights. I only have a K10D (but am getting a K-1 Mk II soon) so I don't have the astrotracker feature and I just bought an iOptron ProGuider Pro clockdrive to mount my camera on (but it arrived in bright moonlight so haven't had a chance yet to really test it -- though it tracks stars well (I've tested it in moonlight, but no good pics of the comet).
Attached is a photo that I took of the comet before moonlight, perhaps 10 days ago, taken with my K10D camera and my DA 12-24-mm f/4 lens on a tripod (no tracking), exposure 20 seconds wide open; this photo is interesting because I caught a meteor up near the bowl of the Big Dipper, as well as the comet just above the central tree (taken overlooking the Atlantic Ocean from Gloucester, Massachusetts).
Attached Images
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PENTAX K10D  Photo 

Last edited by cometguy; 2 Days Ago at 01:18 PM.
2 Days Ago   #10
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Nice, @cometguy . You'll find that on the K-1 that DA12-24 works from 17mm onward.

BTW, if you still use your film cameras, that's a good way to test your lenses for yourself.
1 Day Ago - 1 Like   #11
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QuoteOriginally posted by clackers Quote
Nice, @cometguy . You'll find that on the K-1 that DA12-24 works from 17mm onward.

BTW, if you still use your film cameras, that's a good way to test your lenses for yourself.
I do still use my LX occasionally. So the K-1 sensor is supposed to be the same size as the area exposed on 35-mm film?
1 Day Ago - 1 Like   #12
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QuoteOriginally posted by cometguy Quote
I do still use my LX occasionally. So the K-1 sensor is supposed to be the same size as the area exposed on 35-mm film?
Yes the full frame sensor is the same size as the slr negative

QuoteQuote:
Sensor Size 35.9 x 24.0 mm (35mm full frame)
Read more at: https://www.pentaxforums.com/reviews/pentax-k-1-review/specifications.html#ixzz6U5p7h4mU

Last edited by aslyfox; 1 Day Ago at 02:25 PM.
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