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06-16-2013, 05:30 AM   #1
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Whats the crop factor for a 6x7 lens on a APS-C K-mount camera?

Hi,

This question may have been answered on another forum post but I wanted to know what the crop factor would be for a 6x7 lens on a Pentax APS-C Camera?

I mean a full-frame lens has a crop factor of 1.5x on a APS-C, so what would be the crop factor for a medium format lens?

I tried searching online and even looked at the 6x7 to K mount Adapter's description but could not find it or maybe I didn't look correctly.

Please help!

06-16-2013, 05:48 AM   #2
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Focal lengthnisnfocal length. The only difference between a 6x7 lens, over a 645 lens or full frame is the image circle the lens projects.

Now if you are actually comparing the field of view between different formats that is a different issue. Consider the ratio of the diagonal of the frames to do this
06-16-2013, 05:53 AM   #3
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The crop factor should be a bit more than 3.8. (60mm / 15.7mm) .... but I suspect if you mount, for example, a 50mm 6X7 lens on a APS-C camera, the "35mm equivalent" will still be "75mm" (1.5 crop factor). It is the "6X7 equivalent" that would be "190mm" (3.8 crop factor).
06-16-2013, 06:24 AM   #4
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QuoteOriginally posted by Lowell Goudge Quote
Focal length is focal length. The only difference between a 6x7 lens, over a 645 lens or full frame is the image circle the lens projects.
Eg:

Tak 6x7 105mm on a P67: FOV = c.50mm (in 35mm terms)
Tak 6x7 105mm on Pentax LX: FOV = 105mm (in 35mm terms)
Tak 6x7 105mm on Pentak K5: FOV = c.150mm (in 35mm terms)

Pentax-M 100mm f/2.8 on Pentax LX: FOV = 100mm (in 35mm terms)
Pentax-M 100mm f/2.8 on Pentax K5: FOV = c.150mm (in 35mm terms)

Clearer?

06-16-2013, 06:37 AM   #5
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QuoteOriginally posted by 2her0ck Quote
Hi,

This question may have been answered on another forum post but I wanted to know what the crop factor would be for a 6x7 lens on a Pentax APS-C Camera?

I mean a full-frame lens has a crop factor of 1.5x on a APS-C, so what would be the crop factor for a medium format lens?

I tried searching online and even looked at the 6x7 to K mount Adapter's description but could not find it or maybe I didn't look correctly.

Please help!
Here is a comprehensive field of view table:

https://www.pentaxforums.com/forums/pentax-lens-articles/93714-field-view-tab...d-645-6x7.html
06-16-2013, 06:51 AM   #6
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Lowell is correct.
The focal length tells you how it will behave. A 100mm 6x7 lens adapted to APS-C will behave exactly like a 100mm APS-C lens on an APS-C camera.

[/enddiscussion]
06-16-2013, 07:14 AM   #7
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It looks like everyone is telling OP the same thing, just in slightly different ways.
06-16-2013, 11:29 AM   #8
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Lowell is right.

Focal length is focal length. A particular focal length on APS-C will have the same FOV regardless of the format the lens was originally designed to service.

I might add one caution regarding using medium format lenses on small format cameras. You may be disappointed with the results and with the experience in general. The performance standard for absolute sharpness for the larger formats is somewhat lower due to different design goals. Add in the extra weight and bulk and slower maximum apertures and you will likely be wishing you had a lens designed for a small format.


Steve

06-16-2013, 11:45 AM   #9
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In another explanation, saying using APSC camera give you a "magnification" factor of x1.5 is wrong. The focal length is same, just FOV different.
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