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01-31-2009, 01:05 PM   #1
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Medium Format 6 x 7 on K20 Sensor

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?

01-31-2009, 01:57 PM   #2
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QuoteOriginally posted by Jewelltrail Quote
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?
are you saying that the field of view from a 165mm lens on a K20D is identical to the field of view on your 6X7?
01-31-2009, 02:41 PM   #3
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QuoteOriginally posted by Jewelltrail Quote
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?
Well, ofcourse a 165mm lens will act precisely as a 165mm lens - wherever it got connected too. Apart from different field of views, there is no difference between that lens used on different format cameras.

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... But that should also be possible to a good degree with your 67 lens, provided the adapter has some sliding action?
Ben
01-31-2009, 02:48 PM   #4
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QuoteQuote:
Gooshin: are you saying that the field of view from a 165mm lens on a K20D is identical to the field of view on your 6X7?
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

01-31-2009, 02:58 PM   #5
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A 165mm lens on a 6x7 has the same horizontal field of view as an 85mm lens on a full frame camera and a 57 mm lens on an APS-C camera.
01-31-2009, 03:03 PM   #6
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Crop Factors

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

Last edited by Ole; 04-05-2009 at 02:31 PM.
01-31-2009, 03:14 PM   #7
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QuoteQuote:
Ben Edict: 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... But that should also be possible to a good degree with your 67 lens, provided the adapter has some sliding action?
I see I was responding to Gooshin, while you were responding to me--LOL. I am not sure I understand everything you say above. Are you saying you want to use Large Format lenses on the K20?

Also not sure about the stitching you mention, nor about the "sliding action" of the adapter. Please, help me out here by providing some more specifics. Thanks.
01-31-2009, 03:18 PM   #8
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QuoteQuote:
Ole:A 165mm lens on a 6x7 has the same horizontal field of view as an 85mm lens on a full frame camera and a 57 mm lens on an APS-C camera.
Thank you, and yes, your chart provides more clarity as well. It is good to have a firm grasp on the inter-relationships of the various formats--i think.

01-31-2009, 04:28 PM   #9
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Since the crop factor is so extreme, you are using only the center of the lens. A 6X7 lens is designed to evenly cover a 60mm by 70mm negative. You are only using the center 18mm by 24mm of that. The edges of a 24mm sensor should have absolutely no vignetting and should be extremely sharp because you are not using the edges of the frame.
01-31-2009, 05:07 PM   #10
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QuoteQuote:
Pentaxman: Since the crop factor is so extreme, you are using only the center of the lens. A 6X7 lens is designed to evenly cover a 60mm by 70mm negative. You are only using the center 18mm by 24mm of that. The edges of a 24mm sensor should have absolutely no vignetting and should be extremely sharp because you are not using the edges of the frame.
Talk about the "SWEET SPOT"! The K20's outward persona takes on a new life in this garb. Here is a shot of the badboy, with my Super Program for comparison. Please forgive me for using a P & S for this

Last edited by Jewelltrail; 11-28-2009 at 08:04 PM.
01-31-2009, 10:49 PM   #11
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Nice, now how about uploading some images so we can see how she drives?
01-31-2009, 11:53 PM   #12
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what a convenient thread - cause i was wondering if it was possible (read: if there were adapters) to stick the medium format lenses onto a K20D.... now i know it is possible... (not like i have any such things available anyway)
02-01-2009, 12:05 AM   #13
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How about details on the adapter please. Are they available on the market?
02-01-2009, 12:16 AM   #14
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Pentax 67 to K adapters available with a pentax tag or as a Chinese copy on ebay most often...
But a google search "67 to K adapter" should return relevant results.
02-01-2009, 04:12 AM   #15
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QuoteOriginally posted by Damn Brit Quote
How about details on the adapter please. Are they available on the market?

I found several adapters, genuine Pentax made: 6X7 to 645, 6x7 to 35, 645 to 35. Recently I bought a Hasselblad to Pentax 645 adapter. Now I can use Hassy lenses on my K10D too!
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