[Clavius]

Overall, unless you happen to have the larger format lenses anyway and want to use them to save cost, probably not. Admittedly you would be using the centre of a larger image circle, which does have some benefits of course (avoiding the issues lenses have in the corners of the frame) but the fact is that larger format lenses are not necessarily higher resolution per unit area covered than a lens natively made for the smaller format, and often actually lower resolution per unit area covered. The very best ones are perhaps as good per unit area as a lens made for a smaller format, but no better, and most are not even that good. It is hard to make a lens that covers a large area and simultaneously has high unit resolution across that large frame. The fact they are intented to be used with a larger area of film or sensor compensates for this issue and you can get better results in the final result purely because you are using most of that large image cirlce with a nice large area of film or sensor. However, you lose this advantage by using it on a smaller format via an adaptor.

So, in short, you are probably better off using a lens built for the format you are using unless you happen to have the larger format lenses already or are looking for the 'character / personality' achieved by a specific larger format lens (some people like the feel of specific lenses).

You certainly are not getting any extra reach this way. A 400mm lens is a 400mm lens, regardless of how large its image circle is.

Thanks for the explanation. Next to my K5, I also have a film 645 with a pair of lenses that I use now and then. It came with the 645 to K adapter, but I never bothered using it.

[Ed Hurst]

Some of the 645 glass performs well on smaller formats. Which 645 lenses do you have?

[Clavius]

Some of the 645 glass performs well on smaller formats. Which 645 lenses do you have?

The 75 and 55 2.8, I really like them though. I would love to use a 645D.

[Ed Hurst]

I think you will find them both competent performers on your K5, but probably no better than lenses of equivalent length made for the smaller format (and perhaps not as good). Why not try them and see?

Now if you had said you have a 645 A 35mm, or a 120mm (A or FA) or 150mm FA or the 300 f4 I would have said expect to be very pleased! A couple of the 67 lenses likewise would be every bit as good as a first rate smaller format lens.

[jogiba]

With a 6x7-K-mount adapter and Pentax 1.7x AF adapter fast 67 lenses like the 165mm F2.8 will AF on Pentax DSLRs and the K-01.

[Ed Hurst]

Did you say they will autofocus? I think not :-)

[Clavius]

With a 6x7-K-mount adapter and Pentax 1.7x AF adapter fast 67 lenses like the 165mm F2.8 will AF on Pentax DSLRs and the K-01.

Sounds fun to experiment with!

Please don't get this the wrong way, but that contraption looks absolutely hideous.

[excanonfd]

Did you say they will autofocus? I think not :-)

Actually, yes. AF is being performed by the Pentax F AFA 1.7x adapter, not the lens. You would have to bring the lens to near focus then the AFA 1.7x adapter can AF the rest of the way.

Sounds fun to experiment with!

Please don't get this the wrong way, but that contraption looks absolutely hideous.

You think so, too? Buy a camera without a viewfinder and end up emulating a viewfinder by attaching a big black funnel around the LCD screen... Each to his own, I guess.

[SkiBum]

6 months down the road now and I'm curious how the 6x7 and 645 lenses have been doing on your dslrs. I've seen amazing images from the 67 lenses when shot on film...but I'm curious about digital. Whenever I see these great shots, I automatically crop them in my mind to how my K5 would see the image. How have these lenses faired for you?

[ohce]

I would like to know as well. I am seriously considering this approach if the 67 or 645 lenses could improve IQ.
If someone could provide 100% crop shots side-by-side comparison would be great. Same camera, same frame, same focus point and same aperture.
Thanks

6 months down the road now and I'm curious how the 6x7 and 645 lenses have been doing on your dslrs. I've seen amazing images from the 67 lenses when shot on film...but I'm curious about digital. Whenever I see these great shots, I automatically crop them in my mind to how my K5 would see the image. How have these lenses faired for you?

[Smolk]

I think you will find them both competent performers on your K5, but probably no better than lenses of equivalent length made for the smaller format (and perhaps not as good). Why not try them and see?

Now if you had said you have a 645 A 35mm, or a 120mm (A or FA) or 150mm FA or the 300 f4 I would have said expect to be very pleased! A couple of the 67 lenses likewise would be every bit as good as a first rate smaller format lens.

I agree. I tested the A 35mm against three K 35mm lenses (M 2; M 2.8; M 24-35mm) and found the 645 lens was sharper and had nicer rendering. The A 120mm is the lens I use on a more regular basis with the adapter because it is Makro and very sharp.

The A 75mm performed quite well but was a tad less sharp than the SMC Takumar 85mm I also had at the time, although the Takumar always had to be corrected for over- and underexposure, whereas the 645 lens could just be used without any adaptation (with aperture-priority in both cases). Still, that lens is no slouch: see [link dead and removed; see next post].

[Smolk]

the review link appears to be dead. Here's an image though for border performance:



And here for the centre:



Tables from SLR lens review. Of course sharpness is not the make all end all.

[Sigmoid]

I recently purchased a 6x7 lens (400 mm f4 Tak, with non-rotating foot) and it came with a "Cirrus" brands adapter to fit K-mount.

Has anyone else used this brand of adapter? It seems to work OK except that the body sits a few degrees (perhaps 5?) out of level when everything tightens up. The only adjustability I can see is that the adapter has four blades and can be attached to the lens in four orientations 90 degrees apart. I don't see any way to fine tune the rotation.

Any ideas?

Thanks,
Sig

[Smolk]

I think you will find them both competent performers on your K5, but probably no better than lenses of equivalent length made for the smaller format (and perhaps not as good). Why not try them and see?

Now if you had said you have a 645 A 35mm, or a 120mm (A or FA) or 150mm FA or the 300 f4 I would have said expect to be very pleased! A couple of the 67 lenses likewise would be every bit as good as a first rate smaller format lens.

I tested both lenses on the K-x with the Pentax adapter. The 75mm is good but a tad less sharp than the SMC Takumar 1.8/85mm was. However, I did not have to dial in any compensation, unlike said Takumar, so it was much more user-friendly and the difference was not all that noticeable. My 645 A 35mm was in fact sharper and nicer than 3 equivalent lenses for Pentax, but then again, that is a really nice lens. I would not use 645 lenses however, apart from the A 120mm because it is a Macro lens which I have used for some product photos. The 645 A * 300mm was sharper than the K version, but I was always afraid it would damage the camera because of its weight....

In the end, it is about practicalities, as long as IQ is not too starkly different. I'd use 135 lenses on a 135 or APS-C camera.

[drougge]

I recently purchased a 6x7 lens (400 mm f4 Tak, with non-rotating foot) and it came with a "Cirrus" brands adapter to fit K-mount.

Has anyone else used this brand of adapter? It seems to work OK except that the body sits a few degrees (perhaps 5?) out of level when everything tightens up. The only adjustability I can see is that the adapter has four blades and can be attached to the lens in four orientations 90 degrees apart. I don't see any way to fine tune the rotation.

I have their 645 to K adapter. It also mounts the lens slightly rotated. This has never bothered me, because I don't have any lenses with non-rotating feet.

What has bothered me with it was internal reflections. It really needed to be flocked. After doing that it was fine. (Originally I used a piece of black sock, later I bought flocking material on ebay. Performance was fine with the sock too.)