[Andres]

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A while back I developed this table - hope it helps.

Ole! you're my newest hero! I love that table!

[Ben_Edict]

Gooshin, thank you for your question. I do not have a 6 x 7 camera, yet anyway. Thinking about your question I can see that mine is poorly worded.

First, to answer your question---no--the FOV for the 165mm lens cannot be the same on the K20 as on a 6 x 7 camera. The crop factor for the lens on the K20 is 1.5( in relation to FF) of course, and the FOV factor on the 6 x 7 (in relation to FF) would be less than 1 and directly related to its negative which is a good deal larger than FF.

I apologize for my error in reasoning in my original question and thank you for helping me to reason it through.

My question should be this: What is the FOV factor (a word, opposite in meaning to "crop" need be inserted here, before factor) for the 165mm lens on a 6 x 7 camera--I suspect it has to be less than one--somewhere near .5 if the digital negative of Medium format is 2x that of full frame?

Is this a better explanation of my question?

More succinctly:

165mm lens on K20= FOV of 247.5mm
165mm lens on FF = FOV of 165mm
165mm lens on 6 x 7 =FOV of___________ please fill in the blank

I think, your table at the end is the result of the ill-informed discussions about crop factors all around on the web. This is not aimed at you! But a 165mm lens produces a certain image circle. With different format sensors/film you make only use of part of that image circle. An APS-C sensor (as in our Pentax DSLRs) uses a tiny area from the middle. A 35mm camera (or full frame DSLR) takes out a somewhat bigger area and a 67 camera uses nearly the full available image circle. That's it. Nothing else.

Your last line "165mm lens on 6x7 = FOV...." makes only sense in comparisson to another film format. So a 165mm lens on a 67 camera gives you the FOV of a 85mm portrait lens on a 35mm camera.

Ben

[Jewelltrail]

Gary: How about details on the adapter please. Are they available on the market?

Yes, they are available here Adapter Fits Pentax 67 lens to PK with tripod mount - eBay (item 310115378652 end time Jan-20-09 02:06:01 PST) and I highly recommend them. There have been a couple of different versions out, but this one is of very nice quality. Not only does it have the built in tri-pod mount, but it blends in beautifully and complements fully, the K20. BTW, I put in an offer, $5 lower than the BIN price and it was accepted. I have seen adapters like this, but not as good, going for over $100 bucks elsewhere.

So far all of my pics are taken in low light--in doors. When I get outside with it I will post some shots, but they would be best appreciated in full resolution, something I can not do at this forum.

Also, not sure if it is the larger glass or not, but is seems easier to manually focus with this glass. I am using a $30 split prism, which is normally not bad, but it seems much better with this glass wide open (f2.8 on the 165mm).

Best of luck.

[Jewelltrail]

Ben Edict: I think, your table at the end is the result of the ill-informed discussions about crop factors all around on the web. This is not aimed at you! But a 165mm lens produces a certain image circle. With different format sensors/film you make only use of part of that image circle. An APS-C sensor (as in our Pentax DSLRs) uses a tiny area from the middle. A 35mm camera (or full frame DSLR) takes out a somewhat bigger area and a 67 camera uses nearly the full available image circle. That's it. Nothing else.

Your last line "165mm lens on 6x7 = FOV...." makes only sense in comparison to another film format. So a 165mm lens on a 67 camera gives you the FOV of a 85mm portrait lens on a 35mm camera.

Ben

Thanks Ben---I am aware of everything you say above. I made the little table simply to see what fov the 165mm gives on the 6 x 7 system. I thought my discussion showed an understanding of everything you say, but I do appreciate you giving your explanation as well. I know the fov of view comparisons only make sense in relation to one another--that is why I put them all alongside one another in my table. I tried to clear up the ambiguity I caused in my original thread with my response to gooshin. I know how tedious these explanation can get.

[calicojack]

<snip> What I am really interested in, is to use my K20 as a digital back on my LF gear. Stitching should be easy with a moveable back and the image size and resolution (provided the LF lenses stand up to this) would be unbelievable... <snip>
Ben

Wow, what a thought! Make up a back for my old field camera that I can mount my K10D onto, that will allow the K10 to be moved enough to cover the area of a 4X5 negative. Lets see, APS C is 16mm tall. That will have to be moved 6 times to almost cover the 4" height. APS C is 24mm wide. that will have to be moved 5 times to almost cover the 5" width. Then all that is left is to stitch 30 seperate exposures into 1. I guess the only possible real world use would be shoot in a studio. I bet the earth revolves too much in the time it would take to make 30 seperate exposures with 29 moves of the back to even think about an outdoor or live subject.
Interesting brain teaser though!
Brian

[er1kksen]

As long as the light isn't rapidly changing (as in, an exposure near mid-day on a cloudless day, or a uniformly overcast day) I would think that pulling off 30 exposures wouldn't be too problematic. If you've got a well-worked-out system I imagine you could work it at 1 exposure or so per second.

Still kind of limited, but think about... 400 megapixels? I can see where some people might have an interest.

And if you've got the time and resources to spare, it's just kind of fun.

[Jewelltrail]

Here is an indoor shot, incandescent lighting--white balance off a bit. The crop is 100 percent.

165mm f2.8 on K20 @ f11--3 secs--100 iso

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Last edited by Jewelltrail; 12-11-2009 at 10:58 AM.

[Ben_Edict]

Thanks Ben---I am aware of everything you say above. I made the little table simply to see what fov the 165mm gives on the 6 x 7 system. I thought my discussion showed an understanding of everything you say, but I do appreciate you giving your explanation as well. I know the fov of view comparisons only make sense in relation to one another--that is why I put them all alongside one another in my table. I tried to clear up the ambiguity I caused in my original thread with my response to gooshin. I know how tedious these explanation can get.

I apologize if I was too insisting on correct wording. You obviously know your way, but I have read som much nonsense about crop factors and miracleous focal length changes, that I jump at any posting about this issue... Sorry.

Ben

[Ben_Edict]

Wow, what a thought! Make up a back for my old field camera that I can mount my K10D onto, that will allow the K10 to be moved enough to cover the area of a 4X5 negative. Lets see, APS C is 16mm tall. That will have to be moved 6 times to almost cover the 4" height. APS C is 24mm wide. that will have to be moved 5 times to almost cover the 5" width. Then all that is left is to stitch 30 seperate exposures into 1. I guess the only possible real world use would be shoot in a studio. I bet the earth revolves too much in the time it would take to make 30 seperate exposures with 29 moves of the back to even think about an outdoor or live subject.
Interesting brain teaser though!
Brian

Brian, I ordered a back for my 4x5 from China and will see, how it works out. It would be a killer for studio work, but I can imaging using it for landscapes, too albeit perhaps not with the full 4x5 area. Two rows of four exposures seem to be doable to me, but experience will tell.

Ben

[calicojack]

<snip> but I can imaging using it for landscapes, too albeit perhaps not with the full 4x5 area. Two rows of four exposures seem to be doable to me, but experience will tell.

Ben

32mm High x 96mm Wide. Sounds like an interesting panoramic format. I'd love to see some results if you can get it to work.
Best of luck,
Brian

[Ben_Edict]

32mm High x 96mm Wide. Sounds like an interesting panoramic format. I'd love to see some results if you can get it to work.
Best of luck,
Brian

That's certainly true. First I have to await delivery of the adapter - then I will see, whether it works as advertised and finally I will use it. But right now the weather is, eh, poor... I am in the Alps in March and that will be the right place for playing with such a setup.

Ben

[baldeagle21b]

I have begun shooting medium format on the K20 via an impressive adapter made expressly for this purpose. The adapter is well-made, with a built in tri-pod mount for these rather heavy 67 lenses. So far, though the testing is still short-lived, the images are impressive. The bokeh, contrast, sharpness and 3-d effect are all top quality. I have only tested the 165mm f2.8, which is not known as one of the better 6 x 7s.

I wonder if anyone out there is also doing the same. And I have a question: Will someone tell me why a medium format 165mm lens appears to act precisely as a 165mm lens on the K20d crop sensor?

Interesting idea. Based on the discussion, I decided an to invest in an experiment also. Ordered the same adapter and a lens from KEH. It will be interesting to discover what I can do with this combination. Thanks for the suggestion.

[Jewelltrail]

Baldeagle21b: Interesting idea. Based on the discussion, I decided an to invest in an experiment also. Ordered the same adapter and a lens from KEH. It will be interesting to discover what I can do with this combination. Thanks for the suggestion.

Glad to be of help. If I can give anything back to this forum, which has given so much to me, then I am a happy camper.

Which lens did you pick from Keh? I have my eyes set over there too.

[baldeagle21b]

I chose a 150mm f/2.8 in EX condition, based upon its reasonable price, mainly. It arrived on Friday and it is in excellent condition, as are all things from KEH in my experience. Should give the K20D a very purposeful appearance with that big glass hung on it, I think.

[feverbeaver]

6x7 s-m-c Takumar 1:4.5 75mm on K10D.