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03-23-2012, 02:39 PM   #1
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Super Takumars Contacts / Foil Paper, and other fallacies

I have a large collection of Taks, Super Taks and SMC Taks and never had any problem focussing or getting focus confrimation from my Kx or K5, except when I stop down to about f/8, f/11, etc. And this is only when there is not plenty of sunlight. I have heard about people using aluminum foil between the lens and the camera. Can anyone explain me what is the problem with those lenses, or maybe I have it and I have not noticed it. I do have to adjust EV+- with most of my lenses manual or AF. In fact, everytime I shot against the light I do that. I appreciate your input. Pepe

03-23-2012, 02:56 PM   #2
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My understanding is that you need to short some of the pins so that the camera knows that there is a lens attached. I'm unsure why it under exposes about 1.7 stops (for my k200d) when there is no lens (or it thinks there isn't...)... I don't have this near as much in manual - it seems to meter with the usual slight under exposure as it does with my auto lenses. in Av mode though, I either have to dial in a +1.7 EV comp, or short the pins with foil to get the typical exposure.
03-23-2012, 02:58 PM   #3
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QuoteOriginally posted by Pepe Guitarra Quote
I have heard about people using aluminum foil between the lens and the camera. Can anyone explain me what is the problem with those lenses
The foil is placed in between the lens (bottom flange) and the contacts on the body - this shorts the contacts and allows for CIF to be activated/used.
03-23-2012, 03:07 PM   #4
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With Takumars or M42 the problem is some of them do not cover the contacts or even after covering the contacts does not make a meaningful comunication to the camera due to paint insulation, so the camera thinks it has an M42 or no lens. Now there is no problem with that at all unles you want a Catch-in-Focus, other then that it will do every thing as you said focus confirmation etc. You might have to make some EV compensation as well. But if you use Alufoil or any thing like that or a flange type adapter (that has bare metal) your camera will have meaningful communication between the contacts (not to your lens, don't be confused) and you will get everything you were getting before plus CinF (with the right setting of course). Now according to my experience, you may also not need any EV comp.

03-23-2012, 03:48 PM   #5
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My experience is the following: I have a Takumar with flaked paint on the mount, so it has become conductive (bare metal).This is equivalent to using aluminum foil. The camera thinks I have an A-type lens on, and sometimes also thinks that it is set at f/2.8. Also, in green button metering, it stops down the aperture, doing that sound characteristic of K-mount lenses and which is inutile. I have covered the paint etches with nail polish and now everything is fine again.
03-23-2012, 05:46 PM   #6
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QuoteOriginally posted by pezmaker Quote
My understanding is that you need to short some of the pins so that the camera knows that there is a lens attached. I'm unsure why it under exposes about 1.7 stops (for my k200d) when there is no lens (or it thinks there isn't...)... I don't have this near as much in manual - it seems to meter with the usual slight under exposure as it does with my auto lenses. in Av mode though, I either have to dial in a +1.7 EV comp, or short the pins with foil to get the typical exposure.
You shouldn't be using m42 lenses in Av mode. Period. They will expose much more accurately in M mode, with the green button to take a reading.

Av is designed to meter wide open, and calculate the exposure for the aperture you set in camera based on that. Since you can't set the aperture in camera, it will only work wide open, and even then it won't be as accurate because the camera hasn't a clue what the actual aperture size is.
03-23-2012, 05:54 PM   #7
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QuoteOriginally posted by Philoslothical Quote
You shouldn't be using m42 lenses in Av mode. Period. They will expose much more accurately in M mode, with the green button to take a reading.

Av is designed to meter wide open, and calculate the exposure for the aperture you set in camera based on that. Since you can't set the aperture in camera, it will only work wide open, and even then it won't be as accurate because the camera hasn't a clue what the actual aperture size is.
While that may be true, my experiences have been that as long as I close down to the aperture I want manually, if shorted, I get pretty close to normal exposures. My helios 44-2 has the preset aperture and I just focus wide open, slide it down, and take the shot in Av mode - when I'm shorting the pins, it appears to be metering about the same as my auto lenses. My taks and vivitar have the auto/manual switch, so again compose/focus wide open, flip the switch and fire the shot, and again, when pins are shorted, it seems to expose as normal.

To be honest though, I don't use them in Av mode much because of the foil "trick" being a royal pain to always be redoing as i'm changing lenses about, and generally just use M and green button.
03-23-2012, 06:32 PM   #8
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QuoteOriginally posted by Philoslothical Quote
You shouldn't be using m42 lenses in Av mode. Period. They will expose much more accurately in M mode, with the green button to take a reading.

Av is designed to meter wide open, and calculate the exposure for the aperture you set in camera based on that. Since you can't set the aperture in camera, it will only work wide open, and even then it won't be as accurate because the camera hasn't a clue what the actual aperture size is.
I don't think this is the case - I am sure that in "AV" mode if the pentax body does not get an aperture reading or the aperture data from the lens that metering is activated in real time, no matter what lens is attached - meaning that live "Zone" metering is happening as long as the body has not went to idle.

'Correct Me If I Am Wrong"

03-23-2012, 06:50 PM   #9
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...related to catch-in-focus and then only on a limited number of older dSLR bodies.

Shorting the contacts may signal that an A-contact lens is present, but that is actually a bad thing. My Jupiter-9 has paint that is mildly conductive and fools my K10D into thinking that it is controlling the aperture. As a result, Av mode is a crap shoot as is green button metering. Screws up the exif too.


Steve
03-23-2012, 07:00 PM   #10
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QuoteOriginally posted by stevebrot Quote
...related to catch-in-focus and then only on a limited number of older dSLR bodies.

Shorting the contacts may signal that an A-contact lens is present, but that is actually a bad thing. My Jupiter-9 has paint that is mildly conductive and fools my K10D into thinking that it is controlling the aperture. As a result, Av mode is a crap shoot as is green button metering. Screws up the exif too.


Steve
What you have described is physically impossible. The A contact is supposed to be recessed on the body, a simply conducting base does nothing, because it cannot project into the space where the pin is recessed. If your k10 does this then it will also do it with K mounts. Check and see if someone has installed a wrong pin
03-23-2012, 08:01 PM   #11
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takumar w/ dslr in AV mode

I don't agree about using tak in AV mode. Doing this and zone focusing (e.g., setting lens at f/16 and focus at hyperfocal distance) is a very fast way to do street photography--particularly if using lenses of FL 35mm or wider. It is the usual way I use my Tak 28mm f/3.5, and I prefer it to using K or even A lenses. I simply adjust the +/- e.v. to account for the apparent scene average brightness--if it is very different than zone V.
03-23-2012, 08:09 PM   #12
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QuoteOriginally posted by Philoslothical Quote
You shouldn't be using m42 lenses in Av mode. Period. They will expose much more accurately in M mode, with the green button to take a reading.
I must disagree, at least with my K20D (which has a reputation for misreading). I find no more inaccurate readings with screwmount lenses than with MF bayonets, assuming I'm metering a neutral-tone centered subject. And the only issue I've seen with the contacts is that they must be covered by a conductor for CIF to work. My metal-tape-enhanced lenses usually don't fool the camera into thinking they're something else -- although sometimes I get a readout of f/2.8 instead of F--. [/me hums a few bars of IT DON'T WORRY ME]

Last edited by RioRico; 03-23-2012 at 08:15 PM.
03-23-2012, 08:30 PM   #13
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Newer models than yours also require a conductive lens mount, or shorting contacts though other measures, in order to properly stop down to meter with the green button. I've had to lightly sand several M type lenses, extension tubes, and such in order to get this working with my K-r. I'm pretty sure it's the same with the K-5 and K-x, not so sure about the K-7.

Interestingly, with some metal mount m42 lenses, I've had to insulate the contacts from the lens to prevent it trying to stop down, which results in the aperture control mechanism sliding and the mirror flopping briefly. Again, this is with the K-r, and it doesn't afflict all models.

As for the Av issue, it's not really something that's deniable. Several DSLR models, at least, are inaccurate by 1-2 stops, usually underexposing, when using m42 lenses in Av. K-x, K-r and I'm pretty sure K-5 are among them, but again, I know less about the K-7. Despite its similarities to other models, it seems to handle things a bit different, and there seem to be less K-7 users reporting this kind of thing (maybe, that's how it seems). Sure, you could correct for this with EV compensation, but that's at least as much hassle as hitting the green button to take a reading anyway, so what's the point? The same cameras that exhibit this issue are usually accurate to within about half a stop when using M mode and green button, as Pentax instructs us to do.
03-23-2012, 10:05 PM - 1 Like   #14
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QuoteOriginally posted by Lowell Goudge Quote
What you have described is physically impossible. The A contact is supposed to be recessed on the body, a simply conducting base does nothing, because it cannot project into the space where the pin is recessed. If your k10 does this then it will also do it with K mounts. Check and see if someone has installed a wrong pin
Lowell,
Perhaps I can send you a photo of the top LCD showing aperture setting when the J-9 is mounted? As for somebody installing the wrong pin...it would have to have been a factory job. I bought my K10D new in '07. As for the pin being recessed...you are correct. The A pin is only supposed to have continuity when an A lens is mounted and aperture ring is in the A position. On some lenses the pin retracts. On others there is an internal switch that breaks the circuit.

So...how/why does this happen? Hard to say, but these are the facts with my setup:
  • I own dozens of lenses, both M42 and K-mount and the J-9 is the only lens that has this behavior
  • Even so, it is VERY sporadic and unpredictable and has caused lost shots before I noticed that things did not look right in the viewfinder
  • At one point I put a multimeter across the lens base from one side to the other and the unbroken finish passes current, though with some resistance. None of my other M42 lenses do this.
As a result, I am unwilling to state that there is no camera logic gated by conductivity outside the A contact with the K10D.

Back to the discussion...

Shorting the contacts does not improve meter performance on the K10D or K20D when used with non-A contact lenses. Been there, tried that several years ago when the rumors first started. The Kx00D series may be another matter however.

I have not tested the K-5, K-r, or K-x, but I have tested the K-7 and conductive base does not change meter performance in Av mode. M mode works equally well (meaning very good) with both conductive and non-conductive bases. The K-5 is supposed to have the same meter logic as the K-7.

As for Av mode...All, except (by all reports) the *istD, may suffer from poor metering in Av mode. It depends on lens and aperture when metering.

Rico is correct...M42 and non-A contact K-mount should behave identically (except for my Jupiter-9 and it is possessed) on K10D and K20D and the K-hyphen models. Again the Kx00D models may be different.

Regarding street photography using Av mode and the ST 28/3.5...It does not surprise me that Av works great for you with minimal need for compensation. My personal research has indicated that most of the metering issues occur at f/3.5-f/4 and wider. I regularly shoot my Tamron 70-150 with the standard PK mount using green button only and no compensation. Works great.

One more thing before I go to bed...Pentax is not the only brand with meter issues using vintage lenses. Poor stop-down meter performance is a problem across brands. You just don't read the complaints from Canon and Nikon owners here.


Steve
03-23-2012, 10:22 PM   #15
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QuoteOriginally posted by Philoslothical Quote
nterestingly, with some metal mount m42 lenses, I've had to insulate the contacts from the lens to prevent it trying to stop down, which results in the aperture control mechanism sliding and the mirror flopping briefly. Again, this is with the K-r, and it doesn't afflict all models.
These are interesting observations regarding the K-r. Legacy behavior traceable back to the Kx00D series, perhaps? I am not sure what you mean by the aperture control sliding and the mirror flopping. On the K10D, the aperture actuation lever is triggered regardless of what lens is mounted at exposure time and with green button and with DOF preview. For non-A lenses, it simply goes full-travel. My mirror never "flops".

I would be more concerned if the camera shows an aperture setting in the display in Av mode rather than F-- (foo?). That would indicate that the body thinks it is setting the aperture and the movement of the aperture actuation will be less than full travel. The shutter speed would be totally bogus as well. (I do remember some folks who were using M42 lenses on K100D in M mode by shorting the A-contact, setting the aperture to say, f/5.6 on the body, and setting the ring at f/5.6 on the camera, using the green button to meter wide-open, and stopping down using the A/M switch just before exposure. Lots of trouble, if you ask me.)


Steve
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