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01-09-2012, 09:10 PM   #1
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Does this work ?

Can anyone confirm that this mod :
http://www.robertstech.com/matrix.htm

from this thread :
https://www.pentaxforums.com/forums/do-yourself/73144-how-make-non-lens-work-like-lens.html

works with digital SLRs ?

01-09-2012, 11:23 PM   #2
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Works, sort of.

The lens will communicate min and max f-stop information and the camera will show the f-stop and allow to set it via the camera. It will also be included in the EXIF data. You will be able to use all the other camera modes (Tv, TVa, P, Sv), P-TTL flash, and pattern metering.

The problem is that all exposures except the extreme open and closed, will be off, sometimes more than one stop so you'll have to compensate in different amounts for every f-stop.

The reason being that all manual aperture lenses have their aperture lever moving proportionally to the diameter of the aperture while the A, F, FA and DA move proportionally to the area of the aperture.
01-10-2012, 04:45 AM   #3
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QuoteOriginally posted by demp10 Quote
Works, sort of.

The lens will communicate min and max f-stop information and the camera will show the f-stop and allow to set it via the camera. It will also be included in the EXIF data. You will be able to use all the other camera modes (Tv, TVa, P, Sv), P-TTL flash, and pattern metering.

The problem is that all exposures except the extreme open and closed, will be off, sometimes more than one stop so you'll have to compensate in different amounts for every f-stop.

The reason being that all manual aperture lenses have their aperture lever moving proportionally to the diameter of the aperture while the A, F, FA and DA move proportionally to the area of the aperture.

Ah ha !...Very logical and well written explanation...Thanks for that.

I believe I might attack one of my crappy lenses and try it out. That'll be fun.

Cheers
01-10-2012, 06:52 AM   #4
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QuoteOriginally posted by demp10 Quote
The reason being that all manual aperture lenses have their aperture lever moving proportionally to the diameter of the aperture
Not quite all...
M 50/2, M 28/2.8 (version 2), and M 80-200/4.5 (version 2) are oddities, and probably some third-party lenses don't fit the pattern either.

01-10-2012, 09:10 AM   #5
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QuoteOriginally posted by Moo Quote
Not quite all...
M 50/2, M 28/2.8 (version 2), and M 80-200/4.5 (version 2) are oddities, and probably some third-party lenses don't fit the pattern either.
That's correct. There are a few late M lenses that behave like A. There are rumors that Pentax run out of parts late on their production and used parts from the A version. Who knows.
01-10-2012, 09:22 AM   #6
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Noooooooo! Now folks are going to start drilling these jewels. Snif.
01-10-2012, 02:50 PM   #7
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QuoteOriginally posted by crewl1 Quote
Noooooooo! Now folks are going to start drilling these jewels. Snif.
Sellotape.

01-10-2012, 03:09 PM   #8
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QuoteOriginally posted by chromo Quote
Sellotape.
Yes and a bit of aluminum foil to short the A pin that is recessed. Until of course you gum up all the contacts and the A lenses don't work any longer
01-12-2012, 06:46 AM   #9
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QuoteOriginally posted by demp10 Quote
Yes and a bit of aluminum foil to short the A pin that is recessed. Until of course you gum up all the contacts and the A lenses don't work any longer
Er I would put the tape on the lens. Then the body contacts don't see the sticky side.
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