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05-14-2022, 11:44 AM   #16
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QuoteOriginally posted by Lowell Goudge Quote
Maybe the is a difference between minimum focus distance and minimum working distance.
Minimum focus is to the film plane minimum working is to the front element.
. . .
I hadn't thought about that. When I re-checked my lens just now, minimum focus distance is approx. 30.5cm and working distance is approx. 19cm.


QuoteOriginally posted by gofour3 Quote
I have the first 1976 version, same as yours, it has 0.3 as well for the MFD.

Phil.
Thank you, Phil.

05-14-2022, 02:48 PM - 1 Like   #17
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QuoteOriginally posted by pschlute Quote
Is that on all of them John ?
Peter - I only have the one copy now with a tiny 'ding' on the filter ring, I can't remember who I sold my perfect copy to
05-15-2022, 11:16 PM   #18
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also, Pentax may consider the minimum focus distance to include the additional depth of field from not only maximum lens focus on the scale, but also from stopping down the lens completely.
05-16-2022, 07:04 AM   #19
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QuoteOriginally posted by dkpentax Quote
also, Pentax may consider the minimum focus distance to include the additional depth of field from not only maximum lens focus on the scale, but also from stopping down the lens completely.
That would be a bit cheeky... and at minimum focus would the DoF really bring the minimum focus distance appreciably closer?

05-17-2022, 10:40 PM   #20
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QuoteOriginally posted by dkpentax Quote
also, Pentax may consider the minimum focus distance to include the additional depth of field from not only maximum lens focus on the scale, but also from stopping down the lens completely.
The few pieces of official Pentax literature I've seen all list the MFD as .3m. But measuring stopped down is an interesting idea.

I've never thought about that before: Do claimed MFD ratings apply to a lens when shooting wide open?
My own eyeballed measurements were taken with my lens at f/2.8.



QuoteOriginally posted by Jonathan Mac Quote
That would be a bit cheeky... and at minimum focus would the DoF really bring the minimum focus distance appreciably closer?
When I tried a quick measurement at f/22, MFD seemed about 27cm. But it was difficult to distinguish sharp and unsharp at f/22, so there's probably a bit of wiggle room.

Using default criteria, DOFMaster claims a near depth of field limit of 24.3cm at f/22 with a subject distance of 30cm for a 28mm lens using 35mm film format.
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