[Ben-G]

Is there a real advantage, on K-1,* to buy used pentax 645 lenses and a Pentax Adapter K for 645 Lens (645 to K mount) or is, obviously, a convenient choice only for users that already own 645 lenses?


Pentax Adapter K for 645 Lens (645 to K mount) Reviews - Pentax K-mount Teleconverters and Adapters - Pentax Lens Reviews & Lens Database


Best regards

Ben-G

Now THERE's a good question. And a related one, what about the use of M42 lenses on the K-1?

[BarryE]

Is there a real advantage, on K-1,* to buy used pentax 645 lenses and a Pentax Adapter K for 645 Lens (645 to K mount) or is, obviously, a convenient choice only for users that already own 645 lenses?


Pentax Adapter K for 645 Lens (645 to K mount) Reviews - Pentax K-mount Teleconverters and Adapters - Pentax Lens Reviews & Lens Database


Best regards

Ben-G

Occasionally a question pops up in this forum that really makes me think. This is just such an example. Good one Ben.

[Docrwm]

On M42 the answer is yes, particularly for wide & UW lenses. If the cost of the 15-30 prohibits UW AF on FF the old mf lenses work a treat.

[chrism888]

I'd be very interested to know if any PF user has used a K1 with any 645 lenses and their imprecisions of the IQ, I'd have thought it ought to be very good

[blackcloudbrew]

Somewhere on this forum there are really good answers to this question. About 8 or so years ago when I discovered medium format, I got excited because I could pick up relatively cheap fast 645 lenses and with an adapter mount them on my K20d or later K-5. I was underwhelmed at the results. I recall around then reading that there are some design considerations involved. While the K-1 has a bigger sensor, it's not that much different IMHO than an APS-c. So, I'd expect similar underwhelming results on the K-1. There are some other things like 645 lenses don't get any faster than f2.8 and of course they are going to be fully manual on the K-1, there are just better matched optics out there. For that matter, I have also experimented with 6x7 lenses on K mount cameras and been similarly unimpressed. Can you do it, yes, is there an advantage? I haven't seen any.

Again, I recall some really good posts on this subject awhile back.

[pepperberry farm]

there's several shooters here that adapt medium-format lenses to our K-mount bodies, both Pentax 645 and Mamiya MF lenses...

and I cannot think of any reason to not try M42 lenses on your K-1, as long as you have the proper adapter...

[Fenwoodian]

there's several shooters here that adapt medium-format lenses to our K-mount bodies, both Pentax 645 and Mamiya MF lenses...

I have adapted the legendary Bronica SQ S 150mm f/3.5 lens to K mount and use it on my K-1. I like it so much that I currently own 4 such lenses.

This medium format lens was rated as one of the best bokeh lenses by the "father of bokeh" himself.

[photoptimist]

Generally speaking, lenses are optimized for their formats. That leads to three disadvantages to 645 lenses on FF:

First, optimizing a medium format lens for acceptable sharpness across the full width of the 645 frame generally means sacrificing some sharpness in the center. Thus, a 645 lens on a K-1 is likely to underperform a similar lens designed only for FF. That said, the total resolution of a decent MF lens on an MF camera may be higher than a FF-format lens on the K-1, but the K-1 throws away a lot of that resolution in cropping the view of the 645 lens.

Second, a medium format lens brings in a lot more light that's going to end up bouncing around inside the mirrorbox of the K-1. Contrast is likely to be lower unless one finds or creates a suitably restrictive lens hood (preferably a petal hood).

Third, the 645 lens will be physically larger and heavier than the corresponding or equivalent FF camera lens.

Unless you already have the 645 lenses or can get a really good deal on them, they won't be better than similar FF lenses.

[robgski]

Now THERE's a good question. And a related one, what about the use of M42 lenses on the K-1?

Yes, I have a few M42 lenses on my K-1 for years, no problems

[Wasp]

Older medium format lenses might not be as sharp as you would expect, especially when pixel peeping. They were perfect for film work when new, but times have moved on. Not worth it from where I am sitting, but I have never tried it. As I see it, buying a 645 lens and adapter will shrink the funds available for full frame lenses. The genuine Pentax 645 to K adapter is also very expensive AFAIK.

[Sagala]

Pentax K1 with
SMC Pentax-A 645 120mm F4 Macro


https://www.pentaxforums.com/forums/attachments/10-pentax-slr-lens-discussion/445357d1553360824-k1-645-lenses-_img4682.jpg
https://www.pentaxforums.com/forums/attachments/10-pentax-slr-lens-discussion/445356d1553360824-k1-645-lenses-_img0732.jpg

[torashi]

It depends on what you're looking for. I already had a 67 and lenses when I started trying out MF on 35mm and APS-C. I've used them with the corresponding Pentax and tilt-shift. 645 lenses are nice for perspective correction and plane of focus tilts. For example the A 35/3.5 and 135/4 LS (which I wish had an linked aperture adapter like the 67/645 one) which are the best performers I have. Second comes the A 45/2.8. I haven't tried the A 55/2.8. The A 75/2.8 and A 150/3.5 didn't impress me that much. Too much color fringing. Maybe the same thing others have noted.
Adding to the discussion, I wish there was a focal reducer and speed booster for K mount though (just an optical unit designed for the the K mount adapters would also be a great option). Now THAT would be a game changer. If we consider the 3:2 aspect ratio of FF to cover only part of the ~5:4 aspect ratio of 6×7, it's still 3,57 times more light. That's almost two stops (+1.78) extra light. That alone could justify the added size and weight. And it would preserve the look of those lenses. Since everything would be compressed, fringes and other chromatic aberrations would also be smaller and less evident. That would turn any 67 f/4 lens into an ~f/2.2 with almost the same FOV on both systems!

[blackcloudbrew]

Generally speaking, lenses are optimized for their formats. That leads to three disadvantages to 645 lenses on FF:

First, optimizing a medium format lens for acceptable sharpness across the full width of the 645 frame generally means sacrificing some sharpness in the center. Thus, a 645 lens on a K-1 is likely to underperform a similar lens designed only for FF. That said, the total resolution of a decent MF lens on an MF camera may be higher than a FF-format lens on the K-1, but the K-1 throws away a lot of that resolution in cropping the view of the 645 lens.

Second, a medium format lens brings in a lot more light that's going to end up bouncing around inside the mirrorbox of the K-1. Contrast is likely to be lower unless one finds or creates a suitably restrictive lens hood (preferably a petal hood).

Third, the 645 lens will be physically larger and heavier than the corresponding or equivalent FF camera lens.

Unless you already have the 645 lenses or can get a really good deal on them, they won't be better than similar FF lenses.

Thank you for weighing in here, this was the kind of info I was referring too.

[Ben-G]

Dear pentaxforumers,

[@dlh
@BarryE
@Docrwm
@chrism888
@blackcloudbrew
@pepperberry farm
@Fenwoodian
@photoptimist
@robgsky
@Wasp
@Sagala
@torashi
@blackcloudbrew]

thanks very much for yours gentle and precious responses and advice ...

...this is, sincerely, a great forum.


Best regards


Ben