Modification of a K24/2,8 to "A"

klaus123 · 06-03-2013, 10:45 AM

Hello

During the last day I modified a manual K24 to Auto-Mode

Using a K7 it can be adjusted fom 2,8 to 22 (as it should) and exposure is OK at 2,8 and needs to be adjusted by minus 0,5 step for each step the aperture is closed (means F8 --> - 1,5). Without this correction it causes over-exposures the more you close the aperture. It is caused by a lack of linearity in these old lenses but I think that is something I can use.

BUT- The results on my K01 are surprisingly inconsistant..........

More Details at http://klaus-takes-pictures.blogspot.de/

lytrytyr · 06-03-2013, 10:59 AM

Interesting, but in terms of lost resale value on the K24,
the cost of your time working on it,
and the non-linearity you mention,
wouldn't it have been better just to buy an A24?

yusuf · 06-03-2013, 11:03 AM

I wish some Chinese manufacturer comes up with readymade mounts, would be a lot easier. Thanks for sharing

Adam · 06-03-2013, 01:37 PM

Originally posted by klaus123

Hello

During the last day I modified a manual K24 to Auto-Mode

Using a K7 it can be adjusted fom 2,8 to 22 (as it should) and exposure is OK at 2,8 and needs to be adjusted by minus 0,5 step for each step the aperture is closed (means F8 --> - 1,5). Without this correction it causes over-exposures the more you close the aperture. It is caused by a lack of linearity in these old lenses but I think that is something I can use.

BUT- The results on my K01 are surprisingly inconsistant..........

More Details at http://klaus-takes-pictures.blogspot.de/

Right, the levers on K lenses are linear while those on A lenses are logarithmic (or vice-versa), so the conversion isn't quite that trivial, unfortunately.

Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)

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lytrytyr · 06-03-2013, 01:58 PM

Just to fix a baseline,
was the K24 exposing properly before the conversion?

These old lenses often have sticky blades.

stevebrot · 06-03-2013, 02:38 PM

Sorry to say, but this modification is a crime, particularly considering the amount of information on this site and many other places on the Web counseling that it will not work.

Steve

aurele · 06-03-2013, 02:58 PM

Originally posted by klaus123

Hello

During the last day I modified a manual K24 to Auto-Mode

Using a K7 it can be adjusted fom 2,8 to 22 (as it should) and exposure is OK at 2,8 and needs to be adjusted by minus 0,5 step for each step the aperture is closed (means F8 --> - 1,5). Without this correction it causes over-exposures the more you close the aperture. It is caused by a lack of linearity in these old lenses but I think that is something I can use.

BUT- The results on my K01 are surprisingly inconsistant..........

More Details at http://klaus-takes-pictures.blogspot.de/

You are such a barbarian to have mutilated such a nice lens....

kakapo · 06-03-2013, 04:10 PM

Originally posted by stevebrot

Sorry to say, but this modification is a crime

Which I committed on a much cheaper Five Star 28mm acquired on Ebay

It works decently enough on my K-01, but under some lighting condition the camera goes nuts with its non-stop stop down/open up squinting act.

06-03-2013, 10:45 AM	#1
klaus123 Senior Member Join Date: Apr 2011 Location: Germany Posts: 238	Modification of a K24/2,8 to "A" Hello During the last day I modified a manual K24 to Auto-Mode Using a K7 it can be adjusted fom 2,8 to 22 (as it should) and exposure is OK at 2,8 and needs to be adjusted by minus 0,5 step for each step the aperture is closed (means F8 --> - 1,5). Without this correction it causes over-exposures the more you close the aperture. It is caused by a lack of linearity in these old lenses but I think that is something I can use. BUT- The results on my K01 are surprisingly inconsistant.......... More Details at http://klaus-takes-pictures.blogspot.de/

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06-03-2013, 10:59 AM	#2
lytrytyr Pentaxian Join Date: Nov 2011 Photos: Gallery \| Albums Posts: 4,310	Interesting, but in terms of lost resale value on the K24, the cost of your time working on it, and the non-linearity you mention, wouldn't it have been better just to buy an A24?

06-03-2013, 11:03 AM	#3
yusuf Pentaxian Join Date: Nov 2008 Location: Palo Alto, CA Photos: Gallery Posts: 2,497	I wish some Chinese manufacturer comes up with readymade mounts, would be a lot easier. Thanks for sharing

06-03-2013, 01:37 PM	#4
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,608	Originally posted by klaus123 Hello During the last day I modified a manual K24 to Auto-Mode Using a K7 it can be adjusted fom 2,8 to 22 (as it should) and exposure is OK at 2,8 and needs to be adjusted by minus 0,5 step for each step the aperture is closed (means F8 --> - 1,5). Without this correction it causes over-exposures the more you close the aperture. It is caused by a lack of linearity in these old lenses but I think that is something I can use. BUT- The results on my K01 are surprisingly inconsistant.......... More Details at http://klaus-takes-pictures.blogspot.de/ Right, the levers on K lenses are linear while those on A lenses are logarithmic (or vice-versa), so the conversion isn't quite that trivial, unfortunately. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

06-03-2013, 01:58 PM	#5
lytrytyr Pentaxian Join Date: Nov 2011 Photos: Gallery \| Albums Posts: 4,310	Just to fix a baseline, was the K24 exposing properly before the conversion? These old lenses often have sticky blades.

06-03-2013, 02:38 PM	#6
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Sorry to say, but this modification is a crime, particularly considering the amount of information on this site and many other places on the Web counseling that it will not work. Steve

06-03-2013, 02:58 PM	#7
aurele Veteran Member Join Date: Jan 2011 Location: Paris, France Photos: Albums Posts: 3,217	Originally posted by klaus123 Hello During the last day I modified a manual K24 to Auto-Mode Using a K7 it can be adjusted fom 2,8 to 22 (as it should) and exposure is OK at 2,8 and needs to be adjusted by minus 0,5 step for each step the aperture is closed (means F8 --> - 1,5). Without this correction it causes over-exposures the more you close the aperture. It is caused by a lack of linearity in these old lenses but I think that is something I can use. BUT- The results on my K01 are surprisingly inconsistant.......... More Details at http://klaus-takes-pictures.blogspot.de/ You are such a barbarian to have mutilated such a nice lens....

06-03-2013, 04:10 PM	#8
kakapo Junior Member Join Date: Mar 2013 Photos: Albums Posts: 41	Originally posted by stevebrot Sorry to say, but this modification is a crime Which I committed on a much cheaper Five Star 28mm acquired on Ebay It works decently enough on my K-01, but under some lighting condition the camera goes nuts with its non-stop stop down/open up squinting act.