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Minimum Focus Distance K-5 vs K-1

kasperbergholt
Posted 09/05/2023 - 08:24 Link
I currently use a Pentax K-5 and the Pentax SMC DA 35mm f/2.8 lens for a documentation and archival project for Wikipedia and a archival site called Radiomuseum on audio vacuum tubes.

The K-5 is in pretty bad shape, so I'm planning an upgrade to full frame. E.g. the Pentax K-1. Will the macro objective work fully on a full-frame camera? The minimum focus distance is around 14 centimeters on the K-5. Will that change if mounted on a K-1?

Thanks in advance,

Kasper
-- Kasper Bergholt
Posted 09/05/2023 - 10:10 - Helpful Comment Link
Hi Kasper,

I have a K-1 and the HD version of the DA 1:2.8 35mm Macro Limited lens. A fantastic lens I used on my K-50 till that camera broke. I've just tried it on the K-1 in 'Full Frame' mode at the minimum focus distance, it works fine, there is some vignetting but aside from that is works well.

Attached is the image I took, partof your post, handheld at f5.6, I expect the degree of vignetting will vary with the f stop used.

Comment Image


Of course in 'Crop' mode there will be no vignetting.

Hope this helps.

Regards
Mike
Lubbyman
Posted 09/05/2023 - 16:24 - Helpful Comment Link
The DA 35mm macro is designed for Pentax crop sensors, not full frame. However, as MikeInDevon has shown above, it will cover a full frame sensor but with light drop-off outside the area of the crop sensor. The minimum focus distance will not change, it is a property of the lens not the sensor or camera. So the alternatives with a K1 would be:
1. Use the full frame image and either put up with the drop-off or correct in post-processing.
2. Use the central, crop-sensor area of the image, either by in-camera 'crop mode' or by cropping in post-processing. The result will be the same as you would get with your current K5.
3. Acquire an FA 50mm f2.8 macro. This gives almost the same field of view with a full frame sensor as the DA 35mm gives with crop sensor (i.e. if something fills the frame on your K5 + DA 35mm at minimum focus distance, it will be close to filling the frame on a K1 + FA 50mm at minimum focus distance). The minimum focus distance will be a few cm greater, that is a consequence of the longer focal length and both lenses being designed so that minimum focus distance gives a 1:1 image.

Steve
kasperbergholt
Posted 12/05/2023 - 13:56 Link
MikeInDevon wrote:
Hi Kasper,

I have a K-1 and the HD version of the DA 1:2.8 35mm Macro Limited lens. A fantastic lens I used on my K-50 till that camera broke. I've just tried it on the K-1 in 'Full Frame' mode at the minimum focus distance, it works fine, there is some vignetting but aside from that is works well.

Attached is the image I took, partof your post, handheld at f5.6, I expect the degree of vignetting will vary with the f stop used.

Comment Image


Of course in 'Crop' mode there will be no vignetting.

Hope this helps.

Regards
Mike

Hi Mark - thank you for your reply & insights. It's definitely helps!

Does the minimum focus distance change when switching from full-frame to crop-mode?
-- Kasper Bergholt
kasperbergholt
Posted 12/05/2023 - 13:58 Link
Lubbyman wrote:
The DA 35mm macro is designed for Pentax crop sensors, not full frame. However, as MikeInDevon has shown above, it will cover a full frame sensor but with light drop-off outside the area of the crop sensor. The minimum focus distance will not change, it is a property of the lens not the sensor or camera. So the alternatives with a K1 would be:
1. Use the full frame image and either put up with the drop-off or correct in post-processing.
2. Use the central, crop-sensor area of the image, either by in-camera 'crop mode' or by cropping in post-processing. The result will be the same as you would get with your current K5.
3. Acquire an FA 50mm f2.8 macro. This gives almost the same field of view with a full frame sensor as the DA 35mm gives with crop sensor (i.e. if something fills the frame on your K5 + DA 35mm at minimum focus distance, it will be close to filling the frame on a K1 + FA 50mm at minimum focus distance). The minimum focus distance will be a few cm greater, that is a consequence of the longer focal length and both lenses being designed so that minimum focus distance gives a 1:1 image.
Steve

Thank you for your reply - very helpful & it definitely makes sense.

I would have thought the full-frame lens would be more expensive than my current 35mm.
-- Kasper Bergholt
Lubbyman
Posted 12/05/2023 - 14:38 Link
kasperbergholt wrote:
I would have thought the full-frame lens would be more expensive than my current 35mm.

In the UK, the 50mm macro (full frame) is 33% cheaper than the 35mm macro (crop sensor). I have no idea why!

Steve
jeallen01
Posted 12/05/2023 - 15:19 Link
Lubbyman wrote:
kasperbergholt wrote:
I would have thought the full-frame lens would be more expensive than my current 35mm.

In the UK, the 50mm macro (full frame) is 33% cheaper than the 35mm macro (crop sensor). I have no idea why!

Steve

Probably because they've made far more 50mm lenses than 35mm ones - the "benefits" of mass production of one lens that actually costs about the same to manufacture as another one of quite similar size & focal length but is sold in much fewer numbers?!
K-3 II, K-3 and a K-70 from SRS (having now relegated the K-30 /"K-50" to a backup body), & some Sigma and Pentax lenses (and a lot of old 35mm gear!)
Edited by jeallen01: 12/05/2023 - 15:21
RobL
Posted 12/05/2023 - 16:37 Link
50mm lenses seem cheaper generally, I guess it is to do with their glass configuration. The 50mm macro is a great lightweight lens for landscape, macro lenses tend to be sharpest at smaller apertures than conventional lenses in order to give increased depth of field in close-ups.
Edited by RobL: 12/05/2023 - 16:40
LennyBloke
Posted 12/05/2023 - 19:28 Link
RobL wrote:
50mm lenses seem cheaper generally, I guess it is to do with their glass configuration. The 50mm macro is a great lightweight lens for landscape, macro lenses tend to be sharpest at smaller apertures than conventional lenses in order to give increased depth of field in close-ups.

Wot Rob said....

...plus MPB have the FA version for 134: https://www.mpb.com/en-uk/product/pentax-fa-pentax-smc-p-d-50mm-f-2-8-macro if anyone is interested
LennyBloke
kasperbergholt
Posted 14/05/2023 - 16:23 Link
Hello again,

I've given it some thought over the weekend and done some research. I'm considering skipping the K1 and moving to the 645D instead.

I've created a new thread for this topic in the lenses section.

Thanks again for all the inputs
-- Kasper Bergholt

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