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12-04-2015, 11:36 PM   #1
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The 67 300mm f4

Hey guys

Can someone please tell me what the 35mm equivalent field of view is (thats how my brain works) of the 67 300mm f4 mounted on a 645z would be?

cheers

Gav

12-05-2015, 12:57 AM   #2
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on the 645Z It would have an approximate 8.87 degree diagonal FOV, it would behave as 238mm lens in 35mm terms.
12-06-2015, 07:23 AM   #3
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Focal length is the property of the lens, not the lens mount, nor the sensor. ALL 300mm lenses will have the same field of view on the 645z's sensor, no matter which lens mount is attached to the lens.


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12-06-2015, 07:54 AM   #4
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The focal length and the field of view stay the same for any particular lens. What changes, when you change cameras, is the sensor (or film) size within that FOV.

The field of view of a 300mm 6x7 lens is about 16 degrees. Using the lens on a full-frame (35mm) camera would give you an image approximately the same as that of a 150mm FF lens. Using the lens on a 645z would give you an image approximately the same as that of a 190mm 645 lens.

In the last case, remember that a 645 digital sensor is smaller than a 6X4.5 film image. On a 645N or NII, the same 6x7 lens would give the approximate equivalent of a 240mm 645 lens.


Last edited by nparsons13; 12-06-2015 at 08:01 AM.
12-08-2015, 11:48 PM   #5
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240mm approx.
12-08-2015, 11:53 PM   #6
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QuoteOriginally posted by nparsons13 Quote
..... Using the lens on a full-frame (35mm) camera would give you an image approximately the same as that of a 150mm FF lens
Wrong. It would behave identically to any other 300mm lens on 35mm format. The image circle from a 67 lens is larger than what would be projected by a 35mm lens, but only the central a 36X24mm portion of the image circle would be recorded, not the full 56mmX70mm 67 format recording area the lens designed for. The Pentax M* 67 SMC 300mm f/4 ED [IF] lens with the correct 67>K adapter, when focused at infinity the optical center of the lens will be approximately 300mm away from the focal plane, the projected image will have an approximate 8 degree diagonal FOV on 36X24mm format*.

But in the case of the 645Z, you will only capture the central 44mmX33mm portion of the projected image circle, hence the slightly wider FOV and apparent decrease in focal length relative to 35mm.

* though truth be told, it isn't uncommon for telephoto lenses at and above 200mm to have their focal lengths vary by +/- 10mm of their stated focal length, sometimes even more than that. When doing panoramic photography it is important to know the exact FOV of your lens so you can accurately calculate the number of images you need to cover your subject.

Last edited by Digitalis; 12-09-2015 at 04:01 PM.
12-09-2015, 07:14 AM   #7
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Thanks for the correction, Digitalis. You made it much clearer. I should revise my field of view statement to say that the focal length stays the same, but the field of view changes with the type of camera (APSC, full frame, 645, 67, etc.).

I withdraw my comment and advise the OP to take a look at the clearest explanation of the differences in crop factors: The Crop Factor Unmasked - Articles and Tips | PentaxForums.com.
12-09-2015, 02:41 PM   #8
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QuoteOriginally posted by Digitalis Quote
Wrong. It would behave identically to any other 300mm lens on 35mm format. The image circle from a 67 lens is larger than what would be projected by a 35mm lens, but only the central a 36X24mm portion of the image circle would be recorded, not the full 56mmX70mm 67 format recording area the lens designed for. The Pentax 67 SMC 300mm f/4 lens with the correct 67>K adapter, when focused at infinity the optical center of the lens will be 300mm away from the focal plane, the projected image will have an approximate 8 degree diagonal FOV on 36X24mm format*.

But in the case of the 645Z, you will only capture the central 44mmX33mm portion of the projected image circle, hence the slightly wider FOV and apparent decrease in focal length relative to 35mm.

* though truth be told, it isn't uncommon for telephoto lenses at and above 200mm to have their focal lengths vary by +/- 10mm of their stated focal length, when doing panoramic photography it is important to know the exact FOV of your lens so you can accurately calculate the number of images you need to cover your subject.
thank you. That all makes sense. Before I asked the question I thought it'd be about 230mm so 238mm, i wasn't far off

I'm going to get one. I love the looks long lenses give. Just for personal use, I doubt I'd use it at weddings.

cheers

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