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08-17-2012, 05:16 PM   #106
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QuoteOriginally posted by excanonfd Quote
Thank you, that worked very well. Following the instructions you've provided, I was able to get my Tamron Adaptall-2 02B 28/2.5 with a PK/M adapter to work like an A lens. No green button to meter and no "F--" to worry about, an excellent modification!
Whoa! If this lens is not an 'A-series' compatible lens, you do have one more chore....

While the A-series and newer, Pentax had to standarize the rotation of the aperture lever between lens. If the body knows the min & max aperture, then to get to an intermediate f/stop, the body allows the lever to move <X> degrees of arc to reach that aperture.

This standardization didn't exist with the 'M-series' and old lens. For those lens, the body just released the aperture lever all the way every time and when the lever hit the f/stop set on the lens, it had the intermediate f/stop. What this means in practical terms is that when your body is set to (for example) f/8 and your M-series lens is set for f/8, it may not stop all the way down to f/8. You will get overexposure. The amount of overexposure will vary between lens and between f/stops on a specific lens. The good news is the overexposure will be consistent at each f/stop on a specific lens.

With this in mind, you need to take some test shots and record the overexposure at each stop. Then using this record, you can use the +/- exposure adjustment button to dial in the needed change.

This discussion happened in another thread and had to do with P-TTL flash exposure using a M-series lens, but the findings are valid for non-flash photography too:
https://www.pentaxforums.com/forums/pentax-flashes-lighting-technique/190819-high-speed-sync-flash-manual-non-lens-2.html#post2021062

If you use this trick to mount an A-series lens or newer on extention tubes, you don't have this issue because, again, the aperture lever action is standardized.

08-17-2012, 11:08 PM   #107
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QuoteOriginally posted by JimJohnson Quote
Whoa! If this lens is not an 'A-series' compatible lens, you do have one more chore....

While the A-series and newer, Pentax had to standarize the rotation of the aperture lever between lens. If the body knows the min & max aperture, then to get to an intermediate f/stop, the body allows the lever to move <X> degrees of arc to reach that aperture.

This standardization didn't exist with the 'M-series' and old lens. For those lens, the body just released the aperture lever all the way every time and when the lever hit the f/stop set on the lens, it had the intermediate f/stop. What this means in practical terms is that when your body is set to (for example) f/8 and your M-series lens is set for f/8, it may not stop all the way down to f/8. You will get overexposure. The amount of overexposure will vary between lens and between f/stops on a specific lens. The good news is the overexposure will be consistent at each f/stop on a specific lens.

With this in mind, you need to take some test shots and record the overexposure at each stop. Then using this record, you can use the +/- exposure adjustment button to dial in the needed change.

This discussion happened in another thread and had to do with P-TTL flash exposure using a M-series lens, but the findings are valid for non-flash photography too:
https://www.pentaxforums.com/forums/pentax-flashes-lighting-technique/190819-high-speed-sync-flash-manual-non-lens-2.html#post2021062

If you use this trick to mount an A-series lens or newer on extention tubes, you don't have this issue because, again, the aperture lever action is standardized.
At first I thought it was my K20D (known for it's unreliable metering) but it was much too consistent - always overexposed at all aperture value except when wide open and by almost the same amount at each setting. I thought about taking the camera out to shoot at all aperture range but it was just too warm this afternoon. Adjusting ev values is a necessity when shooting with a K10D or a K20D, it isn't all that different when shooting with the modified M type lens.

Thanks,
09-14-2012, 09:27 AM   #108
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Here's a set in Australia:

Rare Pentax PKA Mount Triplus P/AF Extension Tubes Set 36mm 20mm Macro Close Up | eBay
09-14-2012, 09:45 AM   #109
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QuoteOriginally posted by excanonfd Quote
At first I thought it was my K20D (known for it's unreliable metering) but it was much too consistent - always overexposed at all aperture value except when wide open and by almost the same amount at each setting. I thought about taking the camera out to shoot at all aperture range but it was just too warm this afternoon. Adjusting ev values is a necessity when shooting with a K10D or a K20D, it isn't all that different when shooting with the modified M type lens.

Thanks,
I've never understood why anyone would call the K20D metering inconsistent. I find it very predictable and accurate compared to my K-x.

Anyway, I have a manual Kiron that overexposes progressively as it stops down (on both my cameras). If I want correct exposure, I meter wide open and count clicks to set the exposure. JimJohnson's post is the first time I've heard the explanation for this consistent and progressive error.

09-15-2012, 02:29 AM   #110
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QuoteOriginally posted by vonBaloney Quote
Here's a set in Australia:
Hmm... 7 contacts but no AF shaft? Odd... 7 contacts and Ricoh contact? Also odd.
09-15-2012, 05:18 AM   #111
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QuoteOriginally posted by Moo Quote
Hmm... 7 contacts but no AF shaft? Odd... 7 contacts and Ricoh contact? Also odd.
No, that's what they are all like, pretty much.
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