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02-01-2009, 06:54 PM   #31
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QuoteOriginally posted by rpriedhorsky Quote
The conclusion seems to be, shorting the contacts makes M and Av mode metering the same; without the short, Av underexposes quite a lot.
... where "a lot" actually appears to be ~2 EV, so one could also just set a +2 exposure compensation (the maximum, but enough, and for more control one could drop to M mode anyway).

That seems to me to be the least awkward of the solutions mentioned so far in this thread (for the K200D at least).

02-01-2009, 07:07 PM   #32
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QuoteOriginally posted by newarts Quote
Steve, you may want to check out Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography

It appears that the code for all contacts shorted is undefined as far as pentax codes go.

I suggest trying to short out only pin #1 (the first clockwise from 6:00). I think this may tell your camera that an f/2.8-f/16 lens is mounted (all other pins are seen as 0's.) This implies that maybe metering will be correct between f/2.8 and f/16.

Dave
The Roberts article was one of my sources in regards to how the pin codes work. From my reading of the contact mapping, the case for f/2.8-f/16 is all contacts insulated. All pins shorted would be f/1.2-f/22. That agrees with what I have seen if all contacts are shorted including the "A" contact on my K10D.

The data from your tests and others on this thread indicate that there clearly is a difference in how Pentax implements the contact logic between camera models and how that is applied to metering.

Steve

(Enjoy shorting your lenses! Wish it was as easy on my camera...)

Last edited by stevebrot; 02-01-2009 at 07:28 PM.
02-01-2009, 10:56 PM   #33
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QuoteOriginally posted by stevebrot Quote
The Roberts article was one of my sources in regards to how the pin codes work. From my reading of the contact mapping, the case for f/2.8-f/16 is all contacts insulated. All pins shorted would be f/1.2-f/22. That agrees with what I have seen if all contacts are shorted including the "A" contact on my K10D....
Maybe the difference is how the cameras handle shorting of the "Data" pin. The Roberts text can be misleading; when he's talking about the digital codes, he's referring to pins 2, 3, 4, A, 6, 7. Therefore, f/2.8-f/16 is represented by the following code:

(Data) (0) (0) (0) (A) (0) (0)

I find it makes a big difference if the (Data) pin, the first of the seven, is open or shorted.

Counting all seven pins, starting with the (data) pin the first one clockwise from 6:00, pointing the camera at my LCD screen results in the following exposure data:
0,0,0,0,A,0,0 shutter speed = 1/90sec
1,0,0,0,A,0,0 shutter speed = 1/20 sec = the correct exposure

It doesn't matter if pin A is open or shorted.

Last edited by newarts; 02-02-2009 at 08:04 AM.
02-02-2009, 07:57 AM   #34
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QuoteOriginally posted by ytterbium Quote
I did not see anyone mentioning, that shorting the contacts also makes Trap Focus work.

Otherwise camera fires always, when you press the shutter in both, AF and MF mode. Even if the subject is OOF (AF confirm not lit up) in AF mode.

As for metering. On my k100ds tried shorting the A pin with screwdriver. When doing so exposure is more or less correct and consistent (as much as it can be with such lenses..), when the pin is not shorted with some lenses i get up to 2..3 stops underexposure in Av and a little less in M.
Also, most of the time it is very unpredictable and you cant just always add 2 stops to get correct exposure. In Av even if you could, there is no headroom left for ordinary EV comp.

As for the price of M42 lenses. I think it matters for some more expensive takumars, zeiss and similar lenses, wich are real quality lenses. On the other hand you can see even such beauties as 31/1.8 ltd "raped" to get working on other mounts. Most of my M42 lenses for example, is just a cheap alternative to modern lenses in those focal lengths i use rarely. How much cheaper a 20$ smc takumar 55/1.8, or some 20$ 135/2.8 revuenon can get? It isn't anything that rare also, unless it is some new old stock, with box, caps and all the papers. Wheter you keep/sell the lens as a collectable or actually want to use it makes the difference.
good pick up.

actually it works like this

the first 6 pins starting from the lens locking pin are for automatic apature. pin 3 is recessed and therefore non A lenses don't short this pin when mounted. Origonal A lenses had a retractable contact that hit this pin when in A mode, later lenses had an internal switch.

the 7th contact is the lens data link, this provides lens info, focus info etc to the body. SHorting it to the mount makes focus status and trap focus work on manual lenses.

Also mike cash is right, many pentax lenses simply don;t cover the pins. My 35mm F2 is one of these, so why waste the time scraping off the paint.

02-02-2009, 08:10 AM   #35
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QuoteOriginally posted by Lowell Goudge Quote
...
...mike cash is right, many pentax lenses simply don;t cover the pins. My 35mm F2 is one of these, so why waste the time scraping off the paint.
The most reasonable physical solution I've found for this case is cutting a circular ring from shim stock large enough in diameter to touch the contacts & placing this ring over the base of the lens.

Or just forget about a physical solution and use a couple EV compensation - probably the best scheme.

Dave
02-02-2009, 10:26 AM   #36
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QuoteOriginally posted by newarts Quote
The most reasonable physical solution I've found for this case is cutting a circular ring from shim stock large enough in diameter to touch the contacts & placing this ring over the base of the lens.

Or just forget about a physical solution and use a couple EV compensation - probably the best scheme.

Dave
lazyness wins every time, I use +1.3 ev on the 35mm F2.

keep thinking shim stock, but .....
02-11-2009, 10:30 AM   #37
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QuoteOriginally posted by Lowell Goudge Quote
lazyness wins every time, I use +1.3 ev on the 35mm F2.

keep thinking shim stock, but .....
Not to regurgitate an old thread, but my laziness always means I forget to dial in the proper EV on my pictures, I often shoot of half a dozen frames before I realize theyre all too dark. The foil tape has been working without fail on my 28mm and 135mm such that I forgot it is even there. Again the 28mm focuses well past infinity so I will need to check if I have any on my 135/2.5 to post.
-southy
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