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03-01-2020, 02:18 PM   #1
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Using APS-C lenses with a FF sensor

I currently own the K3-II and a range of 5, Sigma and Pentax lenses. In looking to the possibility of upgrading to the K1-II, I am concerned about the potential loss of image quality using my current APS-C lens stock. The K1-II brochure suggest that its FF sensor will be automatically cropped to cope with these lenses using an effective resolution of 15.36 megapixels, compared to the 24.32 sensor on the K3-II.
Since I will only upgrade my lens stock slowly, over a few years, will my continued use of APS-C lenses on the K1-II and the resulting loss of pixels result in a noticeable loss of image quality ?
I mainly shoot landscape and birds.

03-01-2020, 02:25 PM   #2
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Some APS-C lenses will work fine in FF mode, others no way (black borders) and a few are usable with some loss of sharpness or visible vignetting at the corners. With zoom lenses it may depend on the focal length used, too, but most of them won't work.

Using the K-1 in APS-C mode will reduce the resolution to the picture size of the K-5 series. This is often enough, depending on your own expectations. Prints up to DIN A3 format are possible at good quality with 300 dpi.

Remember the K-1 is in some aspects not as "quick" as the K-3! The AF is precise and the camera is a work horse, but the K-3 is in some details the newer design. Pentax worked for years at the FF model ... beginning before developing the K-3.

Do you know this page? https://www.pentaxforums.com/articles/gear-guides/full-frame-coverage-of-da-lenses.html

It's a good idea to start with a bundle of the K-1 and the D-FA 28-105/3.5-5.6 which is a nice, compact and light weight zoom with good resolution results and nice bokeh.

Last edited by Austro-Diesel; 03-01-2020 at 02:51 PM.
03-01-2020, 02:25 PM - 1 Like   #3
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QuoteOriginally posted by peso54 Quote
Since I will only upgrade my lens stock slowly, over a few years, will my continued use of APS-C lenses on the K1-II and the resulting loss of pixels result in a noticeable loss of image quality ?
Welcome to the Pentax Forums!

You will lose pixels and that may influence how large you can print, but you will gain better high ISO noise characteristics more similar to a K-5II. My suggestion would be to hold off the K-1ii purchase until you can also afford at least your basic quiver of FF lenses and keep the K-3II for use with your crop sensor glass.


Steve
03-01-2020, 02:34 PM   #4
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QuoteOriginally posted by peso54 Quote
I am concerned about the potential loss of image quality using my current APS-C lens stock
Unless you print large or crop your images in pp by a big margin, you wont see any difference. i used to use a Pentax *istDS, 6MP. For web use the quality is outstanding.

But I agree with Steve, above. No point switching to K1 unless you are going to use FF lenses.

03-01-2020, 02:43 PM   #5
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Some DA lenses cover the full frame image circle quite well, and a handful do so perfectly. Knowing which lenses you have would help the advice you get.

But as already stated above - stick with crop unless you plan to invest in some full frame glass.
03-01-2020, 02:48 PM   #6
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QuoteOriginally posted by peso54 Quote
The K1-II brochure suggest that its FF sensor will be automatically cropped to cope with these lenses using an effective resolution of 15.36 megapixels, compared to the 24.32 sensor on the K3-II.
You can set the K1 and K-1 II to not automatically crop, and depending on the particular lens you may see a lot of vignetting or very little with your DA lenses.
I use the HD DA AF rear converter 1.4x AW quite a lot with my D FA 150-450 on the K-1, and whilst there is some vignetting, to me it isn't a problem. I almost always crop in post to arrive at an acceptable final image which is better than having the camera crop. I should add that whilst I find the vignetting of the 1.4x TC only a minor issue others have described it as serious, so it's a YMMV issue I think.
Check the lens database, many of the DA lenses have information on their performance (vignetting) at various f stops, on a FF camera.

Cheers,
Terry
03-01-2020, 03:03 PM - 1 Like   #7
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Don't forget to browse the K-1 Laboratory, which provides image samples of a few dozen Pentax lenses mounted on the K-1.
03-01-2020, 03:09 PM   #8
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The lens you have to have for the K-1ii is the DFA 28-105 or the DFA 24-70. I wouldn't plan on buying a K-1ii without one or the other.

But tell us what ASP-c lenses you have and we can probably tell you how much you'll need to upgrade.

03-01-2020, 03:14 PM - 3 Likes   #9
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Wow, as a response to my first ever post on this forum I am so grateful (actually blown away) for all of your constructive advice. So thank you all ! The links included in some replies will serve for further research.

For the record current lens 'stock' is: Sigma 'Ex' 10-20mm 1:3.5 DC HSM, HD Pentax-DA 1:3.5-5.6 16-85mm ED DC WR, HD Pentax-DA 1:4.5-6.3 55-300mm ED PLM WR RE, SMC Pentax-D FA 100mm 1:2.8 100mm Macro, Sigma DG 1:5-6.3 150-500mm APO HSM, HD Pentax-DA 1.4x AW Rear Converter.

So as you se I'm heavily invested already and replacement will carry heavy cost. Having watched many YouTube videos of my favourite photographers I guess my best future 'investment' ought be in honing my skills, and resisting the FF urge.
03-01-2020, 03:33 PM   #10
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Well, the Sigma 150-500 DG and the Pentax D-FA 100 Macro will work fine. The DA 1.4x Rear converter may be useful with some limitations. The rest of the gang will not be meaningful usable in FF mode, as far as I know.

Go for a K-1 II (or a used K-1, there is no significiant difference) with a D-FA 28-105. And keep looking for a new or used Sigma 70-300 DG OS (no other one, no APO, no Tamron, only the Sigma DG OS), this tele zoom is quite good for the few bucks to pay, you may find a new one for about 170 Euros at eBay.

Last edited by Austro-Diesel; 03-01-2020 at 03:41 PM.
03-01-2020, 03:41 PM - 2 Likes   #11
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In my view.... the good news is the K1's are a 10 year camera.... so one can get a K1.... enjoy it and acquire lenses more suited to it over a few years as funds and circumstances permit.
03-01-2020, 03:49 PM   #12
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All of your lenses apart from the 16-85 will have some use. The Sigma covers the full frame circle to a decent level when near the long end, and the other lenses are still more than useful on the K-1. You would only need to swap the 16-85 for a 28-105 for a similar price and your kit is pretty much good to go. The 55-300 might not be so hot on FF but it will still be more than usable with slight cropping.
03-01-2020, 07:01 PM   #13
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You'd definitely need the DFA-105 or DFA 24-70. There is no replacement for the 16-85 although the 24-70, 100 macro and 150-500 would be good would probably be great start, and your DA 55-300 PLM is 75% of an FF lens. I've used mine extensively on my K-1.

For the Sigma 10-20 you'd need the DFA 15-30, so taken altogether that is a pretty good chunk of change. The minimum being the 15-30 and 28-105 just to maintain your current zoom range. So it would be expensive. Personally I knew I couldn't afford the 15-30 so I went with a Rokinon 14 2.8 and I can use the Sigma 8-16 at 15mm or 16 mm.

My report on the DA 55-300 is here if you are interested.
Good Value Zoom WR Recommendations - Page 2 - PentaxForums.com

Last edited by normhead; 03-01-2020 at 07:33 PM.
03-01-2020, 07:31 PM - 1 Like   #14
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I went from K5ii to K1ii. No regrets at all. Very low noise level alone is a such a plus.
One apsc lens I would miss is the Sigma 30mm f1.4 but I can use it in square crop mode.
I do have lots of older FF lenses. One of them is a Sigma 28-70 F2.8 (77mm filter thread version). Always thought it was a little soft. Great portrait lens. However on the K1ii I find it sharp from F2.8 and it is now my most used lens.
Can't justify a new FF 35mm f1.4 especially as I have many manual 30mm and 35mm lenses if needed. All are great on the K1ii albeit no AF.

Using the K1ii in manual mode is a delight especially as the top dial can be used in ISO giving three dials for speed , aperture and ISO.
03-01-2020, 10:29 PM - 1 Like   #15
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Dont forget the huge amount of manual lenses from the film aera
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