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10-09-2010, 12:12 PM   #1
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Converting K/M lenses by adding an A pin?

Is there a way to add the Pseudo-A facility of K/M lenses on the lens side? In other words, apart from creating the pattern for the aperture coding, can I solder/glue/mount a conducting ball to the lens mount in the place of the A pin? It wouldn't matter that it is not retractable.

The tin foil solution to shorten the A pin on the camera mount is a little bit annoying in long term use with loads of lens changes.

Has anyone experience in this field?

Please let me know,

Vranx

10-09-2010, 12:14 PM   #2
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What would be the purpose of this?
10-09-2010, 12:26 PM   #3
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To pretend an A lens to a recent camera body allows multi-segment metering, P-TTL, full EXIF information etc.

Of course, the diaphragm mechanism is not affected (linear vs. proportional), but here's an example:

The Porst 1.2/50 mm lens does not need any conductiong pattern just the blank metal of the lens mount. With an A pin, metering and EXIF information in Av and M modes would be expanded and on a pre-A body the lens works the same as before the modification.

Normally one puts a piece of conduction foil over the pins, the camera thinks an A 1.2 lens is attached and by using an exposure factor, the photographer can adjust the metering to the actual speed of his lens in use. By creating the code pattern AND the A pin on the lens barrel, one could get rid of the crunbly foil solution.
10-09-2010, 02:20 PM   #4
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I believe that Lowell Gouge has posted at length on this subject and may even have modified some lenses. If he does not dive in to this thread, it might be worth pinging him.


Steve


Last edited by stevebrot; 10-09-2010 at 02:30 PM.
10-10-2010, 01:02 PM   #5
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I don't think it can be done with a lens. Check the last paragraph....

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10-10-2010, 04:10 PM   #6
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conductive foil over the A pin may work but it can be difficult to do because the pin is recessed; the foil may not contact the recessed pin. You'll know you are successful when the e-wheel works and F-- is replaced by F1.2 or something.

I had good success by adding foil under the camera's lens mount ring to short circuit the A pin. Just remove the screws, lift the ring, place the foil, and replace the ring. It is easy and not dangerous.

When this is done the camera thinks all lenses are A type....I have found no practical downside to this modification.

Turn the e-wheel so the view finder indicates an f-stop as low as it will go, then set the actual f-stop you will use with the lens' aperture ring. The camera will meter correctly and p-ttl will work.

Dave
10-10-2010, 04:15 PM   #7
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QuoteOriginally posted by newarts Quote
snip
edit: this works with K/M series lenses, but not M42 and other lenses that don't short the data pin with their mount:
https://www.pentaxforums.com/forums/pentax-beginners-corner-q/83348-p-through...ml#post1209537

Last edited by Eruditass; 10-11-2010 at 06:41 AM.
10-10-2010, 05:24 PM   #8
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I modified for test purposes a Ricoh 50mm F2 and added the aperture coding and an "A" pin to evaluate whether it was worth making my K mounts KA lenses

I did this largely because of the very poor metering of the K10 and to get p-TTL flash

While the modification worked, and by this I mean I could control the aperture by the body, the movement of the aperture on non A lenses is not the same as A lenses. Overall, wide open metering was OK but as you stop down there were errors in exposure up to 2 full stops and except for the novelty of having aperture control , metering was actually worse than a K lens on it's own using the green button. The problem is that K lenses have the aperture lever change the diameter of the aperture linearly. KA lenses have the lever change the area linearly. That is a huge difference

In short it is not worth damaging a good lens over

10-10-2010, 06:32 PM   #9
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QuoteOriginally posted by Eruditass Quote
Unfortunately, this doesn't work on the K-x, as I stated here:
https://www.pentaxforums.com/forums/pentax-beginners-corner-q/83348-p-through...ml#post1209537

On mine, I need to short the data pin, which means my AF lenses won't work. Shorting the aperture pin makes M42 and other lenses act like M-series for me.
I know that shorting the K-x's data pin enables catch-in-focus. And yes, it disables AF....I guess that if the data pin is shorted, the camera thinks the lens is not AF.

Unfortunately our results differ regarding shorting the data pin to make p-ttl flash function properly; it fails to do so with my K-x. I just tried it with a manual, non-A lens.

Perhaps some menu setting is necessary to make p-ttl work with the data pin alone shorted?

I just experimented carefully with my K-x. To make p-ttl work properly I found it necessary to short circuit the A pin (from underneath the camera's mounting ring - I've never been successful shorting it from above the ring - perhaps conductive paint would work?)

I also shorted the other pins, including the Data pin by laying aluminum foil over them when mounting the lens-this was necessary because the lens I used did not have a an electrically conductive base- this step is not needed if the base of the lens used is electrically conductive like K mount lenses.

You'll know you are successful when "F--" in the viewfinder is replaced by something like "F2.8". Then turn the ewheel so the f-stop indicated in the viewfinder is as low as it will go - adjust the actual f-stop with the lens' aperture ring.

I tested for success by taking two flash photos, one at f3.5 and one at f22 with no other changes; they were exposed identically. This was not possible when the data pins (but not the A pin) were shorted .

Here's the camera mount pin designations:

You say "Shorting the aperture pin makes M42 and other lenses act like M-series for me."... how is that different from not shorting the A pin?

Dave
10-10-2010, 07:27 PM   #10
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From memory:

When I don't short the A pin, I see F--. When I do short it, I see F numbers in M mode, but don't get matrix, P-ttl, Tv, etc. It's like an M-series lens.

When I short the data pin (with the A pin), I get matrix, P-ttl, Tv, etc. like an A-series lens. I have not tried only the data pin.

edit: d'oh, this is for M42 style lenses that don't short the data pin with their base. If you are using an M-series lens, it will already short the data pin, and the above method will work.

Last edited by Eruditass; 10-11-2010 at 06:41 AM.
10-11-2010, 12:47 AM   #11
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As I have made clear in my second posting, I am aware of the difference of the linear (A) and non-linear (K/M) diaphragm actuator design. The point is, I am not interested in changing this and I am not interested in controlling the lens from the camera body.

My only goal is to find a more solid solution that does not use a piece of foil over the cameras' bayonet mount, but the lens will be still used in Av or M mode anyway. I still want to keep control ;-)

@newarts/Dave: That is an interesting solution even it is not on the lens side, but is there a risk that the foil moves and falls inside the body? Did you use a foil ball or just a thin adhesive layer? How often can you change a lens befor the foil is worn or compressed enough to call for a replacement?
10-11-2010, 05:13 AM - 1 Like   #12
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QuoteOriginally posted by Vranx Quote
...
@newarts/Dave: That is an interesting solution even it is not on the lens side, but is there a risk that the foil moves and falls inside the body? Did you use a foil ball or just a thin adhesive layer? How often can you change a lens befor the foil is worn or compressed enough to call for a replacement?
I did this a couple years ago with a K100D. The foil under the mounting ring lasted more than a year ( I took it out to try conductive paint which I never got around to.)

I used the foil-under trick last night on my K-x; I plan to leave it in place.

I used no adhesive or ball, just a piece of foil larger than the pin diameter; the mount ring clamps it in place. There is no risk of its falling out.

Here's a photo summary of the procedure on a K-x:


Dave

Last edited by newarts; 10-11-2010 at 06:34 AM.
10-11-2010, 05:17 AM   #13
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The reason for working on the camera side rather than the lens side regarding the A pin is one of convenience; I've not found a reliable, easy way to modify a lens base to push/short the A pin. Trying to place a ball of foil over the A pin has never been possible for me.

If the lens being used has a shiny conductive base, it will short the other pins; if it is not conductive, put sticky-backed foil on the lens base or remove the finish from the base to make it conductive.

Dave

Last edited by newarts; 10-11-2010 at 04:04 PM.
10-11-2010, 05:21 AM   #14
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QuoteOriginally posted by Eruditass Quote
From memory:

When I don't short the A pin, I see F--. When I do short it, I see F numbers in M mode, but don't get matrix, P-ttl, Tv, etc. It's like an M-series lens.

When I short the data pin (with the A pin), I get matrix, P-ttl, Tv, etc. like an A-series lens. I have not tried only the data pin.

We agree then. At least the A pin as well as the data pin must be shorted. The other pins tell the camera the lens' max/min aperture, so it doesn't matter much which, if any, of them are shorted...shorting/non-shorting the appropriate pins on the lens might let EXIF report the correct lens (but not the actual f-stop for the photo).

Dave
01-28-2012, 08:37 AM   #15
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mod for K-5

Hi,

I am trying to do this mod on my K-5.

Turn out that the mount ring and the contact pin A act as a "punch" and cut out a hole on the foil (kitchen aluminium foil).

Should I use a ticker foil? I think the same thing will happen. There is just no space/gap between the hole on the mount ring and the rubber/plastic ring that surround the a pin.

Maybe K-x and older pentax camera have a bit more tolerant/gap on the mount ring? I have a feeling that I am not doing this correctly.

I am thinking of file the hole on the mount ring (for the A pin) a tinny bit bigger using a round diamond file. But before I do this "destructive" action, would like to hear some advise from people who have done it correctly.

Thanks in advance.

-kkx
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