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07-16-2018, 05:29 AM - 2 Likes   #1
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Adding "contacts" to M-series and equivalent lenses with copper tape

I always wanted to add some sort of A-funcionality to my older, pre-A series, lenses, to get better exposure accuracy in Av-mode, acces to the PTTL-flash etc.. Common aluminium foil never worked for me as it is too fragile and I do not want its scraps inside my camera. But I found 3 mm self adeshive copper tape, tried it and voila! It works much better. Just by placing two small strips on the lens base I can "code" f 1.4, f 1.7, or f 2.4 as its max aperuture. It is work in progress and I wasn't able to replicate the usual contacts patterns of say five pins for a given lens (I was too impatient maybe). But the foil stays on the lens and the trick works for all my camera bodies.


Yes, I know this will never transform my lenses into A-series lenses, mainly because the aperture in all older series works differently and exposure are off when one stoppes down the lens. But seems good solution for lenses that I often use wide open (like M 75 - 150, M28, Rikenon 55/1,4, Rikenon 28/2.8). However no problem to find one correct combination of aperture value in say f 4.0 - 5.6 range and exposure compensation for automatic modes per lens.
Moreover I still use Pentax Kr which gets crazy when the battery gets weaker and no-A lens is used (shutter fires every time any button gets pressed).

Interestingly I still do not see aperturture value on the camera, but it works OK and gets stored in the EXIF (this is consistent).


The tape is ridicously cheap. 30 meters of 3 mm width version from China costs sometimes less then 1 USD (shipment included). No clue how it is available locally in Europe or US, but one can easily find it under copper tape/copper foil online shipped from China.

I will post few photos of the "modified" lenses in a few days when I go back home.

07-16-2018, 06:25 AM   #2
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QuoteOriginally posted by Piotrek K Quote
I always wanted to add some sort of A-funcionality to my older, pre-A series, lenses, to get better exposure accuracy in Av-mode, acces to the PTTL-flash etc.. Common aluminium foil never worked for me as it is too fragile and I do not want its scraps inside my camera. But I found 3 mm self adeshive copper tape, tried it and voila! It works much better. Just by placing two small strips on the lens base I can "code" f 1.4, f 1.7, or f 2.4 as its max aperuture. It is work in progress and I wasn't able to replicate the usual contacts patterns of say five pins for a given lens (I was too impatient maybe). But the foil stays on the lens and the trick works for all my camera bodies.


Yes, I know this will never transform my lenses into A-series lenses, mainly because the aperture in all older series works differently and exposure are off when one stoppes down the lens. But seems good solution for lenses that I often use wide open (like M 75 - 150, M28, Rikenon 55/1,4, Rikenon 28/2.8). However no problem to find one correct combination of aperture value in say f 4.0 - 5.6 range and exposure compensation for automatic modes per lens.
Moreover I still use Pentax Kr which gets crazy when the battery gets weaker and no-A lens is used (shutter fires every time any button gets pressed).

Interestingly I still do not see aperturture value on the camera, but it works OK and gets stored in the EXIF (this is consistent).


The tape is ridicously cheap. 30 meters of 3 mm width version from China costs sometimes less then 1 USD (shipment included). No clue how it is available locally in Europe or US, but one can easily find it under copper tape/copper foil online shipped from China.

I will post few photos of the "modified" lenses in a few days when I go back home.
If you want the aperture control from the camera, simply make the pin contact with 3rd (concave) contact on camera mount. I modified my M 50/1.7, as well as Revuenon 55/1.2. After that you should always leave aperture ring of the lens at max f number. Believe, it works
07-16-2018, 06:29 AM   #3
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QuoteOriginally posted by Medex Quote
If you want the aperture control from the camera, simply make the pin contact with 3rd (concave) contact on camera mount. I modified my M 50/1.7, as well as Revuenon 55/1.2. After that you should always leave aperture ring of the lens at max f number. Believe, it works
With the caveat that certain lenses do not have linear aperture mechanisms, and there will be some issues with exposure accuracy with AE.
07-16-2018, 09:04 AM   #4
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This has been tried before by more than one forum member, but never with fully favorable results. The best utility was that metered exposure settings would be accurate and that they could be used for full manual exposure in M mode using a combination of aperture ring on the lens and minimum aperture on the camera.


Steve

07-16-2018, 09:31 AM   #5
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QuoteOriginally posted by Digitalis Quote
With the caveat that certain lenses do not have linear aperture mechanisms, and there will be some issues with exposure accuracy with AE.
...qualified a bit to say that very few lenses without "A" contacts on the mount have a properly calibrated aperture mechanism. It is rumored that some late production M-series lenses are that way, meaning that a standard amount of movement of the aperture actuator results in the appropriate change in relative aperture (f-number or fraction thereof). Unusually this requires a cam mechanism specific to the iris size.


Steve
07-16-2018, 10:48 AM - 1 Like   #6
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This blog page by Mark Roberts has been around for ages:
Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography

The downsides of this "modification" is well noted in the posts above. The other caveat is that the metal tape will wear or come loose at some point and potentially end up in the lens or mirror box. The tape should be inspected each time the lens is mounted or dismounted.
07-16-2018, 11:12 AM - 2 Likes   #7
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I've got aluminum "speed tape" on the bottom off a 3rd party lens that was anodized from the factory. Seems to be working quite well, but it's also a large piece that shorts all contacts together.

In any case, I don't really get it; why not just run the lens in M mode, use the DoF preview function of your DSLR, and check the light meter "needles" to see what the camera's light meter is reading? I find it to be a pretty accurate way of metering a scene with my non-A lenses. And having it on the shutter button collar on my K-5 II means this function is quick to access/find when needed.
07-16-2018, 11:38 AM - 1 Like   #8
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Well, such a tape seems to be much more wear resistant compared to anything I tried before. YMMV but it gives some advantages for wide open shooting in semi-auto modes including matrix metering. For 1 Australian dollar it seems OK for me.

07-16-2018, 09:25 PM   #9
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QuoteOriginally posted by pres589 Quote
In any case, I don't really get it; why not just run the lens in M mode, use the DoF preview function of your DSLR, and check the light meter "needles" to see what the camera's light meter is reading? I find it to be a pretty accurate way of metering a scene with my non-A lenses. And having it on the shutter button collar on my K-5 II means this function is quick to access/find when needed.
Because, depending on lens and set aperture, exposure may be wildly off. My K-3 works pretty well for stop-down metering with several lenses and not so well with others. Hacking the mount contacts is seen as a way to fool the camera into metering properly. It can work pretty well from the metering end of things, but automatic aperture control by the body does not work so well.


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07-17-2018, 02:53 AM - 1 Like   #10
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QuoteOriginally posted by pres589 Quote
I've got aluminum "speed tape" on the bottom off a 3rd party lens that was anodized from the factory. Seems to be working quite well, but it's also a large piece that shorts all contacts together.

In any case, I don't really get it; why not just run the lens in M mode, use the DoF preview function of your DSLR, and check the light meter "needles" to see what the camera's light meter is reading? I find it to be a pretty accurate way of metering a scene with my non-A lenses. And having it on the shutter button collar on my K-5 II means this function is quick to access/find when needed.

I have one lens with an anodized mount (Porst 55/1.2) that I use copper tape on and the only reasons I use it is to allow the camera to meter (green button) and give me focus confirmation...

Last edited by pepperberry farm; 07-17-2018 at 09:16 AM.
07-17-2018, 06:24 AM - 1 Like   #11
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I've not noticed inaccurate metering via stop-down & checking. I didn't figure that could be a thing that could happen. Seems odd that it would, honestly.
07-17-2018, 08:29 AM   #12
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QuoteOriginally posted by pres589 Quote
I've not noticed inaccurate metering via stop-down & checking. I didn't figure that could be a thing that could happen. Seems odd that it would, honestly.
The aperture lever on the basic K or M lenses only has to open and close the aperture blades. All of the precision was in a slot on the mount and a bar that moved along with the lens's aperture ring. The camera followed that bar. Look at a Pentax K or M lens, and the lever moves in a straight line, because that's exactly how the camera's arm moves. The camera arm was also just open-close.

The KA mount was designed to be compatible but also add camera body aperture control. The new cameras could move the arm in precise increments. Pentax then designed new lenses with aperture levers that moved the blades in precise increments as well. Those levers move in an arc. If the aperture arm moves 0.1mm, all KA lenses should move their blades by the same number of stops.

When the camera is tricked into thinking a lens is a KA lens, it will move the aperture lever 0.1mm, but there is no guarantee that the blades will move by the same number of stops at all. You may get lucky within a certain range, like how -40 degrees is the same in C or F scales. Or the lens might have the right kind of aperture movement, which would still work fine as a basic K mount. But not all lenses will work properly.
07-17-2018, 09:11 AM   #13
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Knowing that a specific lens at a specific f-stop won't provide the same amount of light transmission as another lens at the same specific f-stop, it starts getting kind of academic anyway, to me. Select the f-stop that you think is appropriate, meter, and shoot. That lens on that body in that situation is going to do its thing. Different lenses would act differently anyway. I read the meter in the scene/situation and shoot based on my gut crossed with what the light meter is telling me or vice-versa.
07-17-2018, 09:55 AM   #14
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QuoteOriginally posted by pres589 Quote
Knowing that a specific lens at a specific f-stop won't provide the same amount of light transmission as another lens at the same specific f-stop, it starts getting kind of academic anyway, to me. Select the f-stop that you think is appropriate, meter, and shoot. That lens on that body in that situation is going to do its thing. Different lenses would act differently anyway. I read the meter in the scene/situation and shoot based on my gut crossed with what the light meter is telling me or vice-versa.
That's why there is stop-down metering with the green button. If you want continuous metering while you fiddle with the dials and aperture ring use the DOF stop-down metering on the high-end bodies (K10D/20D, K-7, K-5 series, K-3 series, K-1 series). The wet-dream solution would be for Ricoh (or whoever) to "un-cripple" the K-mount. That's not going to happen.
07-17-2018, 10:02 AM   #15
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I don't believe having an un-crippled k-mount is as good as stop-down metering due to my previous mention of each lens having a different light transmission-ability per f-stop. My Kalt 28 f2.8, stopped down to f8, probably passes a different amount of light than my Pentax M 28 f2.8 (recent purchase!) at f8. It seems like a semi-educated guess on the part of the camera. Stop-down metering with the green button, in my experience, can fluctuate at times with no apparent change of scene. I'd rather read the meter myself while checking the scene and make my own estimation of what the settings need to be.

Shot a lot of bands in a bar "back home" with either that Kalt 28 k-mount lens or my M 50 1.4. Became wary of green button metering alone and got to like the DoF-preview method instead. I do use a K-5 II which I think does help as you've mentioned and I've mentioned previously.
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