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01-28-2012, 10:03 AM   #16
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QuoteOriginally posted by kkx Quote
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
the best way to achieve an A pin in this type of conversion is to use pins from am IC grid array mount. They are a little on the small side, so you need to be accurate in location, but they can work. The issue, as I posted earlier is the aperture movement is not the same, and the cama body holds the aperture open more than desired at medium apertures to make the mod work and get reliable and accurate exposure. In short, it just is not worth the time

01-29-2012, 05:25 PM   #17
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Thanks for the info.

I wasn't being clear, I was trying to mod the camera so that it will think all my MF lens are pentax-a lens. My main reason for doing this is to get p-ttl flash when using my old MF lenses.

For pentax-M lenses, I know the aperture will be wrong, will work out how to get around that when I am there. But I will mainly use this for my takumar M42 lens. So no problem there, I also get aperture recorded in exif, which is a bonus. Stop down metering will be more "painful" (meter at full open, then AE-lock, and stop down the lens etc, I use to this when I use MF lens on Canon, not very nice, but if I can flash to work correctly and exif, then this is the price to pay).

I kind of like the drill a second hole for pentax-m lens to mount in such a way that I still can control aperture fully manually.

Anyway, still can't manage to short the a-pin on my K-5. Camera still showing F--. Need to have another go tomorrow.

-kk
02-01-2012, 07:05 AM   #18
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QuoteOriginally posted by Lowell Goudge Quote
[snip] In short, it just is not worth the time
Too bad. It would be nice to have the convenience of an A seting on all those fine old K and M series lenses I own.

Tom G
02-01-2012, 09:05 AM   #19
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QuoteOriginally posted by 8540tomg Quote
Too bad. It would be nice to have the convenience of an A seting on all those fine old K and M series lenses I own.

Tom G
that was why I tried. I was OK with the *istD, because a) metering was reliable and consistent, and b) because it supported TTL flash.

I looked seriously into this when I purchased my K10D because the metering was a mess, and I lost TTL flash support.

In the end, although I successfully converted the XR Rikenon 50mmF2 to a KA mount by drilling aperture coding detents into the mount, and adding the A pin, the exposure accuracy was worse than the K10D metering alone, due to the difference in aperture movement.

IF i had a machine shop and infinite time to fabricate new aperture mechanizms to make the movement linear with area, then it would be a worthwile conversion. Since I (and I guess many others) have neither, my conclusion is a waste of time, but that does not mean a conversion linkage could not be made for each lens, just that it won't be me doing it

02-01-2012, 09:44 AM   #20
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Won't be me either Lowell.

Maybe there is a niche market here for someone with the appropriate skills and knowledge. There might be some money to be made converting all those millions of old Pentax lenses. I'd be willing to pay a hundred bucks or so to upgrade some of my old K and M series glass.

Tom G
02-01-2012, 11:48 AM   #21
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QuoteOriginally posted by 8540tomg Quote
Won't be me either Lowell.

Maybe there is a niche market here for someone with the appropriate skills and knowledge. There might be some money to be made converting all those millions of old Pentax lenses. I'd be willing to pay a hundred bucks or so to upgrade some of my old K and M series glass.

Tom G
Ok so tom, here's the question for you. If it was commercially available (assuming some bright person figures out the mechanism, for each K and M lens there is) would you send him your 200/2.5?

It's a tough call, not to mention third party stuff that preforms well like my Series 1 70-210F3.5 (version 1)
02-01-2012, 12:57 PM   #22
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Fascinating thread; I had been pondering how workable it might be to hack a lens into KA. Had to figure someone would have tried it already; thanks Lowell.

QuoteOriginally posted by Lowell Goudge Quote
If it was commercially available (assuming some bright person figures out the mechanism, for each K and M lens there is)
Well, not much point converting the lenses that carried on to the A-series with the same optical formulae. So maybe the task doesn't quite require infinite time. Oh, for an uncrippled K-mount DSLR...
02-01-2012, 01:08 PM   #23
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QuoteOriginally posted by baro-nite Quote
Fascinating thread; I had been pondering how workable it might be to hack a lens into KA. Had to figure someone would have tried it already; thanks Lowell.
thanks. as to workable it is basically the aperture mechanism, levers and cams that need to be reworked. If you look at how lenses go together, it is probably not technically demanding to come up with something new, it is just the time to do it for every variant you come across and getting the precision you need.
QuoteQuote:


Well, not much point converting the lenses that carried on to the A-series with the same optical formulae. So maybe the task doesn't quite require infinite time. Oh, for an uncrippled K-mount DSLR...
but it;ll never happen, the crippled K mount actually became a reality in the film days

fof me, it is not this as much as the loss of TTL flash that hurts, because pentax has a metering system that works through the green button, but no longer an accurate flash system for legacy lenses.

02-01-2012, 01:14 PM   #24
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QuoteOriginally posted by Lowell Goudge Quote
fof me, it is not this as much as the loss of TTL flash that hurts, because pentax has a metering system that works through the green button, but no longer an accurate flash system for legacy lenses.
Actually same issue for me; I'm happy enough using K and M lenses as is, otherwise. (Although I wish M mode were more configurable; would like to be able to control ISO from one of the e-dials.)
02-01-2012, 02:08 PM   #25
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QuoteOriginally posted by Lowell Goudge Quote
Ok so tom, here's the question for you. If it was commercially available (assuming some bright person figures out the mechanism, for each K and M lens there is) would you send him your 200/2.5?

It's a tough call, not to mention third party stuff that preforms well like my Series 1 70-210F3.5 (version 1)
I wouldn't be first in line Lowell and no the K 200/2.5 would not be the first lens I sent for the upgrade. Save the best for last.

However, if enough good word of mouth was heard around the Forum from folks I respect I would give it a try. I'd probably send the M 28/2.8 in first as I seldom use it and wouldn't be too upset if things didn't go well. If things did go well some of my better loved lenses would follow. I wouldn't want a butcher job though. I'd want some A type aperture rings to replace the originals so things not only worked but looked as they should.

Tom G
02-01-2012, 02:31 PM   #26
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QuoteOriginally posted by 8540tomg Quote
I wouldn't be first in line Lowell and no the K 200/2.5 would not be the first lens I sent for the upgrade. Save the best for last.

However, if enough good word of mouth was heard around the Forum from folks I respect I would give it a try. I'd probably send the M 28/2.8 in first as I seldom use it and wouldn't be too upset if things didn't go well. If things did go well some of my better loved lenses would follow. I wouldn't want a butcher job though. I'd want some A type aperture rings to replace the originals so things not only worked but looked as they should.

Tom G
Tom

now you're getting fussy. I think the conversion would be to modify the lens mount and add an aperture pin, plus modify the aperture lever mechanism, but it would leave the aperture ring with no A position, you would just have to remember to leave the lens in F22 or what ever.

I can't see having an A pin but any ways, since no one is offering, we don't need to worry.
02-01-2012, 02:41 PM   #27
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QuoteOriginally posted by kkx Quote
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).....
Thanks in advance.

-kkx
A couple things come to mind that might work for you. Steel shim stock maybe .001" - it is much stronger than aluminum.

BTW the aluminum strip shown in my photo earlier was two layers thick..

Silver conductive paint - it can be removed easily with nail-polish remover if needed.

Here's best of all I think - it doesn't matter where the A pin connection to ground is made; just be sure that the foil strip you use is long enough to clamp under the metallic surface of the mounting ring when you screw the mounting ring back onto the camera. Or you could stick a fine copper wire (like an individual strand stripped off a braided wire) through the A pin hole & clamped under the mounting ring.


Both my K100D and K-x have this mod & it continues to work well for me. It must not interfere with anything consequential because I haven't noticed anything & its been years I've used the trick.
02-01-2012, 03:31 PM   #28
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I use my Pentax-M 400 F5.6 often for birds and I like it stopped down to F8 to improve DOF and contrast and to decrease PF. I was getting tired using the green button all the time since one moment I was pointing to a sunny spot and the other to dark foliage. I really wanted to use TVa mode, set aperture at F8, shutter at 1/100 and let the ISO float.

The solution that worked for me was to tape a piece or aluminum foil on the A pin on the camera mount, making a depression using the tip of a pen for good contact, and cover with tape the pins that needed to give the correct pattern for the lens (F5.6 to F45). The lens has metal mount so it shorts the other pins. The camera reported the correct aperture range and I was able to switch to TVa mode. Exposure was correct at F5.6 but significantly off at all other F-stops.

I kept the lens aperture ring at F45 to simulate an A lens in the A setting and dialed the F-stops at the camera. When taking a picture the camera closes down the lens proportionally to the dialed F-stop but the camera thinks in terms of linear areas while the M lens closes in linear diameter.

To calculate the correction factor at any given F-stop in the camera, I built an Excel spreadsheet with linear diameter steps, converted them to areas, calculated the effective f-stop and its difference from the dialed one. The fix was to use exposure compensation for any given F-stop.

For that lens, expose at F5.6 needed 0 compensation. At F8 it was -0.5 (actual F6.6), at F11 it was -1 (actual F8) and at F16 it was -1.3 (actual F10).

Obviously the solution is practical only if you have a few favorite lenses and you want to use them all the time in other than manual or Av modes.
02-01-2012, 03:37 PM   #29
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QuoteOriginally posted by demp10 Quote
Exposure was correct at F5.6 but significantly off at all other F-stops.
Thanks for the info; very interesting. I was guessing perhaps the actuator displacement scales would converge as you approach minimum aperture. Did you test it out to f/45?
02-01-2012, 04:06 PM   #30
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Thanks for the suggestions, Newarts.

I manage to finally short the a pin using kitchen aluminium foil. Took a few tries.

I kind of did what demp10 have done. Use a blunt pin head to push the foil and make a doom shape before I clamp down the mount plate.

The contact works, but seems a bit "precarious", if this didn't last, I will remember to try the thin copper wire tricks. Sound more "stable" (easier to get a good contact).

Lowell is right, the exposure is not correct. So if anyone plan to do this, bare the limitations in mind.

I kind of get confused at first, but manage to work out that when in use flash I can either have (if I am using M42 lens or pentax-M lens that are not fully mounted, so aperture ring at lens still close down the aperture):

- correct f number in exif and use exposure compensation to "correct" things like demp10 did

or

- set aperture on camera to max, and set actual aperture on lens, which should give correct exposure

Strangely, for my vivitar 28mm f2, it works as expected at f2, f2.8 and f4. At f8 and beyond, I still need +1ev compensation. Will play around with this a bit more and see if my understanding is somehow wrong.

-kk
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