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10-24-2011, 08:57 AM   #1
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Question about 67 mount lenses..

I'm currently looking into mounting a 165 f2.8 & adapter to my K-5.. but I am wondering about a few things..
A. 165mm is "165mm on 35mm/FF" correct? not "165mm on 6x7 format"
B. Will f2.8 be f2.8 on 35mm/FF or f2.8 on 6x7..
so will this simply allow more light/faster speeds?
All the 6x7/67/67II lenses are pretty huge, so I was wondering more about the aperture relevance than the focal length..
And for those with experience, which 67 and 645 do you have and use most?

10-24-2011, 09:10 AM   #2
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165mm is 165mm. f2.8 is f2.8. The reason it's so big is because it has to produce a larger imaging circle for the 6x7 frame.
10-24-2011, 09:19 AM   #3
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A. No, 165mm is 165mm on 6x7. And 165mm on APS-C when you mount it to your K-5.
However the field of view and depth of field will be very different between the two formats...The field of view of 165mm on 6x7 is roughly equivalent to 80mm on 35mm and about 55mm on APS-C.
So using the 165mm on the K-5 will have a much narrower field of view than on the original 6x7.

B. Yes. The physical properties of the lens can't change - it will still focus light at 165mm and have a diaphragm that opens to 1/2.8 of the focal length.
The only other possible factor is if the size of the adaptor and K mount is wide enough for the lens. Meaning that if the width of the K mount is less than the width of the lens diaphragm when wide open, you will lose a bit of light.

I've never used the 67 lenses on digital, but they work great on 6x7. Really good resolution and detail in general, but of course each lens is a bit different.
10-24-2011, 01:28 PM   #4
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67 Lenses on 35mm.

I remember reading a Pentax brochure when Pentax talked about the adapters for their various lens systems and the field of view on smaller film systems.

They said that when you mounted a 200mm 67 lens on a 35mm SLR that the field of view of the 200mm 67 lens was larger, so more wide angle, than a 200mm 135 format lens, so the lens had a an effectively smaller focal length. But they then went on to say that since the 135 format has a smaller surface area compasred to the 67 surface area, and you were only going to be using the central portion of the lens that the effecting focal length then became 200mm.

So a 200mm 67 lens will produce the same filed of view on a 135 format as a native 200mm 135 format lens would. So no effective field of view change from 67 to 135 format.

But when you mount it on an APS-C camera you wtill get the 1.5 crop factor because of the smaller surface area of the APS-C format compared to 135 format. So a 200mm 67 lens on an APS-C camera would have the field of view of a 300mm lens.

In confirmation to the post from Goddo31 the standard 67 lens was a 90 or 105mm lens, so a 165mm lens is a short telephoto which would have the same field of view as a 135mm lens on 645 or an 85mm lens on 135.

Regards

Chris Stone

10-24-2011, 02:00 PM   #5
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Thanks for the input! That's kind of where I thought it would land (80-85mm), now just wondering how one would stack up against a cheap 85 f1.4 from Bower/Samyang/Rokinon.
10-24-2011, 09:41 PM   #6
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QuoteOriginally posted by Chex Quote
Thanks for the input! That's kind of where I thought it would land (80-85mm), now just wondering how one would stack up against a cheap 85 f1.4 from Bower/Samyang/Rokinon.
No I don't think you get it still

You can't really compare the 165/2.8 67 lens on a APS-C DSLR to an 85mm lens.
Because the 165 is still double the focal length! 165mm vs 85mm.
If you use the 165 on its original format (ie. an actual Pentax 6x7 camera), only then will it have a similar field of view to an 85mm on your K-5.
So unless you are also shooting with a 6x7 camera, the comparison is meaningless.

Crop factor or using a lens on another format does not change the focal length.
10-24-2011, 10:24 PM   #7
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Ok, then how about this approach.... FOV of a 165mm 6x7 format lens CROPPED on an APS-C sensor would be a rough equivalent to ____ ?
10-25-2011, 12:33 AM   #8
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There is a useful chart showing the differences in field of view between formats floating around here somewhere, hopefully someone will find it.
165mm on APS-C will be roughly equivalent to ~165mm on one of the modern zooms, or relatively close to a 150mm prime.

But a 165mm lens on APS-C will have a similar field of view to the following lenses on other formats:
35mm film SLRs - ~250mm
Pentax 6x7 - ~500mm

10-25-2011, 06:36 AM   #9
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There are a lot of confusing posts on this thread, so let's review the situation.

the OP wants to mount a 165mmF2.8 lens origonally designed for a pentax 6x7 SLR.

the performance of that lens, in terms of exposure and focal length will be EXACTLY the same as any other lens of 165mm focal length and F2.8 aperture when mounted on his camera.

the aperture and focal length are physical optical properties and do not change as a function of what format sensor they are mounted on.

Also, mounting a 6x7 lens with an adaptor, will not cause a reduction of maximum aperture because any light that is restricted by the adaptor is light that would not be falling on the sensor area. This light however, and this depends on the adaptor, can cause terrible reflections and loss of contrast. Make sure that the entire interior of the adaptor you use is flat black, to minimize internal reflections.

As people have mentioned, the only difference that MAY need to be considered, is that if you are coming from the 6x7 world, the field of view is quite a bit narrower when using this lens, Specifically you have a crop factor of 3.2 compared to a DSLR, and therefore if you used this lens on your 6x7 to get a similar FOV you would want something like 51.6mm focal length.

If you have never used other than a DSLR, forget all discussions about crop factors FOV etc, 165mm is 165mm and F2.8 is F2.8.

As for sixe, this has been ansewered. THe rear and mount diameter are so big due to the image circle the lens projects, about 93mm in diameter.
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