Using APS-C lenses with a FF sensor

**dwalt** · 03-05-2020, 03:26 PM

Originally posted by peso54

Thanks to all contributions, fascinating to have his combination of expert knowledge and expereince to draw on. My overall take out is that apart from 2 of my current APS-C lenses, the sigma 10-20 and pentax 16-85, all others will give acceptable results, or even great results as shown my norrmhead. I am a bit perplexed about why sigma would need to modify my 150-500 mount for a K1 since the mount is the same as the K3 II (unless my ignorance is showing.........again).
So I do remain tempted to make the upgrade and in time get 1 or 2 of the FF lenses recommended.
Just loving the pentaxian community, thanks again.

It is the part of the Sigma body around the mount. It is a bit too thick so that when you attach the lens to the K1, it scratches the K1 body.

See this thread: Sigma Lens Repairs for Damage to Pentax K-1 Mark II - PentaxForums.com

**Derek** · 03-07-2020, 04:23 AM

If you're using an APS-C lens on a K-1 II in crop mode, you're not always restricted to 15mp. Pixel shift works just fine on many scenes, albeit fairly static ones.

**sbh** · 03-07-2020, 10:39 AM

Instead of crop mode, there is also the possibility to crop in post. Depending on the lens, it might be possible to crop to more than 15.3 MP.

I don't know the image circles of the OP's lenses. On the 60-250 you can easily crop to more than APSC, perhaps 20 or 24 MP without losing much quality in the corners. The 17-70 on the other hand doesn't give much more than APSC, it goes black pretty quick.

TerryL · 03-07-2020, 02:50 PM - **1 Like**

Originally posted by peso54

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.

Get the K1 and a used FA 43.

Last edited by TerryL; 03-07-2020 at 03:11 PM.

gatorguy · 05-11-2020, 07:05 PM

I'm sure someone has tried and commented on the Sigma 17-50 on the K1, but I've missed it. In the back of my mind I vaguely recall someone saying it caused their camera to lock up, or perhaps I didn't. ??

Anyone?I have a K1 coming later this week and can check myself then but the lockup is something I'd want to be aware of if it's "a thing".

**clackers** · 05-12-2020, 06:53 PM

Originally posted by gatorguy

I'm sure someone has tried and commented on the Sigma 17-50 on the K1, but I've missed it. In the back of my mind I vaguely recall someone saying it caused their camera to lock up, or perhaps I didn't. ??

Anyone?I have a K1 coming later this week and can check myself then but the lockup is something I'd want to be aware of if it's "a thing".

I tried mine just then, Gatorguy, and it autofocuses without complaint.

But it vignettes badly at all focal lengths, though.

gatorguy · 05-12-2020, 07:14 PM - **1 Like**

Originally posted by clackers

I tried mine just then, Gatorguy, and it autofocuses without complaint.

But it vignettes badly at all focal lengths, though.

Much appreciated Clackers. Your comment about vignetting is equally as informative. I'll set that one to the side then, for K70 use only.

**Lowell Goudge** · 05-12-2020, 07:27 PM

What you give up in resolution, you gain in high iso performance. It’s your choice

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03-05-2020, 03:26 PM	#31
dwalt Loyal Site Supporter Join Date: Sep 2016 Location: Big Sky, MT Photos: Albums Posts: 217	Originally posted by peso54 Thanks to all contributions, fascinating to have his combination of expert knowledge and expereince to draw on. My overall take out is that apart from 2 of my current APS-C lenses, the sigma 10-20 and pentax 16-85, all others will give acceptable results, or even great results as shown my norrmhead. I am a bit perplexed about why sigma would need to modify my 150-500 mount for a K1 since the mount is the same as the K3 II (unless my ignorance is showing.........again). So I do remain tempted to make the upgrade and in time get 1 or 2 of the FF lenses recommended. Just loving the pentaxian community, thanks again. It is the part of the Sigma body around the mount. It is a bit too thick so that when you attach the lens to the K1, it scratches the K1 body. See this thread: Sigma Lens Repairs for Damage to Pentax K-1 Mark II - PentaxForums.com

03-07-2020, 04:23 AM	#32
Derek Site Supporter Join Date: Jun 2008 Location: Terrace, BC, Canada Photos: Albums Posts: 122	If you're using an APS-C lens on a K-1 II in crop mode, you're not always restricted to 15mp. Pixel shift works just fine on many scenes, albeit fairly static ones.

03-07-2020, 10:39 AM	#33
sbh Site Supporter Join Date: Oct 2012 Location: Black Forest, Germany Photos: Gallery Posts: 849	Instead of crop mode, there is also the possibility to crop in post. Depending on the lens, it might be possible to crop to more than 15.3 MP. I don't know the image circles of the OP's lenses. On the 60-250 you can easily crop to more than APSC, perhaps 20 or 24 MP without losing much quality in the corners. The 17-70 on the other hand doesn't give much more than APSC, it goes black pretty quick.

03-07-2020, 02:50 PM - 1 Like	#34
TerryL Pentaxian Join Date: Jan 2018 Location: Virginia, USA Photos: Albums Posts: 850	Originally posted by peso54 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. Get the K1 and a used FA 43. Last edited by TerryL; 03-07-2020 at 03:11 PM.

05-11-2020, 07:05 PM	#35
gatorguy Moderator Join Date: Feb 2015 Location: Central Florida Photos: Gallery Posts: 6,092	I'm sure someone has tried and commented on the Sigma 17-50 on the K1, but I've missed it. In the back of my mind I vaguely recall someone saying it caused their camera to lock up, or perhaps I didn't. ?? Anyone?I have a K1 coming later this week and can check myself then but the lockup is something I'd want to be aware of if it's "a thing".

05-12-2020, 06:53 PM	#36
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	Originally posted by gatorguy I'm sure someone has tried and commented on the Sigma 17-50 on the K1, but I've missed it. In the back of my mind I vaguely recall someone saying it caused their camera to lock up, or perhaps I didn't. ?? Anyone?I have a K1 coming later this week and can check myself then but the lockup is something I'd want to be aware of if it's "a thing". I tried mine just then, Gatorguy, and it autofocuses without complaint. But it vignettes badly at all focal lengths, though.

05-12-2020, 07:14 PM - 1 Like	#37
gatorguy Moderator Join Date: Feb 2015 Location: Central Florida Photos: Gallery Posts: 6,092	Originally posted by clackers I tried mine just then, Gatorguy, and it autofocuses without complaint. But it vignettes badly at all focal lengths, though. Much appreciated Clackers. Your comment about vignetting is equally as informative. I'll set that one to the side then, for K70 use only.

05-12-2020, 07:27 PM	#38
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,888	What you give up in resolution, you gain in high iso performance. It’s your choice