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02-01-2009, 08:54 AM   #16
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QuoteOriginally posted by stevebrot Quote
What do you mean, by "not meter correctly"?
...
Steve, Thank you for your thoughtful, detailed response. I'll try to respond later with the same civil clarity.

Until then here's a photo summary of what I'm trying to describe. I put a super-tak 50/2 (completely manual-aperture pin jammed in) on my K100d in Av mode and took photos of my computer screen at f/2 and f/16 (lens in manual f/stop mode), without and with electrical contact (Left & Right.) Here are the results, including the info shown in the viewfinder.


The exposures with contact are correct, while those without are not. All I did was adjust the aperture ring and press the shutter button. (No AE-L or Preview.)

I used a "flange-type" adapter to assure electrical contact as shown in the right column. I use such adapters to modify other lens types to K flange; Nikon, OM, etc.

Dave

PS I'm not completely certain it is only the "A" contact that needs to be shorted & will experimentally verify that.


Last edited by newarts; 02-01-2009 at 10:11 AM.
02-01-2009, 09:03 AM   #17
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QuoteOriginally posted by southy Quote
I have always wondered if anyone has tried the aluminum tape used in duct work (NOT duct tape). It is aluminum backed with adhesive, but is still fairly thin. The adhesive is fairly strong, I'm just not sure how easy it would be to remove the glue after a while, since it, like the nastier duct tape is meant to create a stronger seal with heat fluctuations. Maybe it is worth a shot with my vivitar 28/2.

-southy
Yes, it is worth a try for sure. Let us know the results please.

Dave
02-01-2009, 10:06 AM   #18
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QuoteOriginally posted by newarts Quote
That's a good idea & certainly worth a try.

If the aluminum foil tears & wrinkles too easily, one might use some thin steel or bronze shim stock. It looks like a ring with an ID of 41.5mm and an OD of 53-54mm would be about right.

Yes, those dimensions are ok; I cut such a ring from .001" steel shim stock & it works well on a super-tak 50/2, which, as Mike Cash says, is too small to cover the contacts unaided.

Dave
After looking at the camera mount, I think the locking pin would probably tear up tin foil unless it was held in while mounting the lens. Shim stock is probably a better long term solution.
02-01-2009, 10:20 AM   #19
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QuoteOriginally posted by Just1MoreDave Quote
After looking at the camera mount, I think the locking pin would probably tear up tin foil unless it was held in while mounting the lens. Shim stock is probably a better long term solution.
Good thought.

However, I did manage to get a still painful "paper cut" with the 1 mil shim stock; also, maybe it won't matter if the locking pin tears the foil-tape as the damaged area will preceed the contacts as the lens is twisted onto the mount. Maybe.

A test is called for! Yay! Another trivial task to add to my list!

I think we are homing in on a completely reversible, cost effective way to adapt m42 lenses to K mounts! (I'm pretty sure I have a solution to the notch cutting conundrum.)

Dave

nb. it turns out my DIL has some sticky-backed thin aluminum sheet she will share with me later this afternoon! Life is good! As others watch the Super Bowl, I will be gleefully playing with scissors an lenses!


Last edited by newarts; 02-01-2009 at 11:59 AM.
02-01-2009, 11:32 AM   #20
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Hes anyone tried/researched to do the shorting in/on camera?

What is exposed/seen when you remove camera mount? Are there any ordinary wires, or place on PCB where you could add some. Is there any hollow space in good location to house another switch? Something like discrete toggle push button:
Pushbutton switch for surface mounting Y - ELFA Elektronika interneta veikals

Sounds very exaggerated, but hey, who knows maybe there is a place almost meant for this, would mean no additional messing with any lens. Also would work on lenses whose base is not covering the pins. Unfortunately it involves dissasembling and modifying the camera, so recommended only after warranty.

Last edited by ytterbium; 02-01-2009 at 11:41 AM.
02-01-2009, 03:05 PM   #21
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So I did a quick test, I was out shopping and picked up some Aluminum Waterproofing Repair Tape,
I cut out a small, 1mm x 15mm or so arc to fit on the base of my lens (Vivitar 28mm/f2) as so:


It actually looks messier in the photo than it is. After trial and error, you need to be careful to not cover any screws, which will get caught by the contact pins and cause tearing. If the strip is short enough, it will not get caught by the retention pins for the locking mechanism. My lens also has a little bit of a "shoulder" that the k-mount adapter sits on. This part rubs with the camera portion of the mount, so if any tape or glue gets in there, it seriously bogs things down. Results with an x-acto knife would be much cleaner looking im sure. Excess glue cleans up with a little lens cleaner.

And the results,
Before: (f8)


After: (f8)


The sun did set a little between shots, but the difference is apparent. I took two shots each to double check that it was metering consistently for both configurations. Trap focus also works with the tape on there. There is a little bit of added friction from the tape when mounting, but it does not seem to get damaged or cause any gumming after about 20 mounts.

I deem it a success, and may do this to all my takumars, since I now have 30 ft of leftover tape
-southy


hrmm looks like i got a little bit of dust in there now, time for the next project

Last edited by southy; 02-01-2009 at 03:11 PM.
02-01-2009, 03:12 PM   #22
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Southy,

It looks like you've permanently mounted your adapter onto the lens? Do you know if things would work differently if you were screwing in each lens?

Do you still get good infinity focus, even at f/2?

Also, perhaps you could post a photo of the tape you're using. I'm don't think I'm familiar with that product.

I have to go to the hardware store soon to get parts to re-repair my faucet, so perhaps I'll get some.
02-01-2009, 04:27 PM   #23
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QuoteOriginally posted by newarts Quote
Steve, Thank you for your thoughtful, detailed response. I'll try to respond later with the same civil clarity.

Until then here's a photo summary of what I'm trying to describe. I put a super-tak 50/2 (completely manual-aperture pin jammed in) on my K100d in Av mode and took photos of my computer screen at f/2 and f/16 (lens in manual f/stop mode), without and with electrical contact (Left & Right.) Here are the results, including the info shown in the viewfinder.


The exposures with contact are correct, while those without are not. All I did was adjust the aperture ring and press the shutter button. (No AE-L or Preview.)

I used a "flange-type" adapter to assure electrical contact as shown in the right column. I use such adapters to modify other lens types to K flange; Nikon, OM, etc.

Dave

PS I'm not completely certain it is only the "A" contact that needs to be shorted & will experimentally verify that.
Thanks for the good response and excellent visuals. I will have to run a few tests myself. I tried this before using foil with the only noted difference being when the "A" contact was shorted along with all the other contacts. Perhaps it is time to re-run the test?

It would be really great if this does work (even if it does not make sense).

Steve


Last edited by stevebrot; 02-01-2009 at 04:41 PM.
02-01-2009, 05:04 PM   #24
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I will have to check later when the sun is out and I may have to test a different lens.

I just left the adapter on the lens for reference, it isn't permanently mounted.

Here is a picture of the tape I purchased:


Note this doesn't help if your lens is too small to cover the contacts, but then again neither would paint removal.

Unfortunately this lens is pretty soft at f2 at infinity, and I won't have time / sunlight to test a comparison with/without at f2 for a few days. The markings suggest that anything past 20 ft is infinity, but that is quite far off so indoor shots are out for now.
02-01-2009, 05:09 PM   #25
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QuoteOriginally posted by stevebrot Quote
Thanks for the good response and excellent visuals. I will have to run a few tests myself. I tried this before using foil with the only noted difference being when the "A" contact was shorted along with all the other contacts. Perhaps it is time to re-run the test?

It would be really great if this does work (even if it does not make sense).

Steve

I just did a few tests and it appears to me that shorting the "A" contact doesn't matter on the K100D. "A" is the fifth one from 6:00 clockwise looking at the camera, right?

on edit: it appears to me, based on Mark Robert's helpful web page (http://www.robertstech.com/matrix.htm) that only the first pin clockwise from 6:00 need be shorted. That's what seems to work for me.

Please let us know your results!

Enquiring minds want to know!

Dave

Last edited by newarts; 02-01-2009 at 05:36 PM.
02-01-2009, 05:21 PM   #26
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I just did a quick test metering out the window with my K10D with both my Jupiter-9 85/2 and my Auto-Rikenon 50/1.7 at f/2 and f/16 both with and without a foil strip firmly pressed across the contacts and got identical results for both lenses using both setups.

Av mode, "A" pin not detected. Both lenses with fully manual apertures. Stock Pentax focus screen. Focus at infinity.

f/2 @ 1/2000 sec (~2 stop underexposed)
f/2.8 @ 1/500 sec
f/4 @ 1/180 sec
f/5.6 @ 1/60 sec
f/8 @ 1/30 sec
f/11 @ 1/15 sec
f/16 @ 1/6 sec

f/5.6 - f/16 all appropriately exposed

These results mirror my previous experience.

Apparently there is a difference between how the contacts are handled between the K10D and the K100D. I had heard reports that Pentax-K and Pentax-M (both of which have conductive bases) meter correctly on the K100D. That may be why.

Southy...What body did you use for your test where you got such impressive results?

Has anyone tried this trick on K200D, K20D, or KM/K2000 bodies?

Steve
02-01-2009, 05:27 PM   #27
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I use a k100d with stock screen. I always have to dial in exposure comp in Av mode with my m42s.
02-01-2009, 06:15 PM   #28
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Tried this with a super-takumar 135/2.5 (my 105 isn't wide enough to cover the contacts)
The takumar definitely fits more flush to the camera, so I had to spend a lot more time cleaning excess glue off the lens before mounting, but had similar results. Didn't modify these pictures at all, sorry for the poor focus, I was going more for metering rather than sharpness. Upon further inspection, the tape doesnt even need to fit precisely between the takumar and the camera, but actually just needs to be on the beveled "shoulder" of the lens, because the lens barely touches the contacts on the camera body.

The results:

Tape on lens:


Before Tape (f2.5)


After Tape(f2.5)


So it actually works better on my 2 vivitars (200mm/f3.5, 28mm/f2) more easily than the takumars, but it still works. Just requires a little more patience. Again a little additional friction when mounting, but nothing to be concerned with. The glue cleans up fairly easily as well. And it looks like I made it harder for myself than I needed to.

One more note: This method works best if you mount the adapter to the lens, then the whole assembly to the camera. The less contact between the lens and camera, the less chance for the tape to get caught.

-Southy
02-01-2009, 06:35 PM   #29
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I repeated Steve's test with my K200D and 50mm SMC Takumar. As it's dark here, I settled for my white ceiling, illuminated normally by the various lights in the house. The camera was tripod-mounted, so the composition was identical between trials. ISO was set to 400 throughout.

The exposures in manual mode all seemed pretty reasonable to me, but due to the somewhat strange setup, this test is more about consistency between modes than exposure per se. (In my defense, exposure in manual mode for this lens has been fine so far for "real" pictures.)

In unmodified Av mode, there was severe underexposure.

Av mode:


f/1.4 - 1/750 second
f/2 - 1/750
f/2.8 - 1/500
f/4 - 1/250
f/5.6 - 1/125
f/8 - 1/60
f/11 - 1/20
f/16 -1/10

Manual mode:


f/1.4 - 1/180
f/2 - 1/180
f/2.8 - 1/125
f/4 - 1/60
f/5.6 - 1/20
f/8 - 1/10
f/11 - 1/6
f/16 - 1/2

Av mode with tinfoil shorting all contacts*:

f/1.4 - 1/180
f/2 - 1/180
f/2.8 - 1/125
f/4 - 1/60
f/5.6 - 1/20
f/8 - 1/10
f/11 - 1/6
f/16 - 1/2

The conclusion seems to be, shorting the contacts makes M and Av mode metering the same; without the short, Av underexposes quite a lot.

I wouldn't want to use tinfoil regularly, as it shredded significantly during the lens install process. I wouldn't want small conductive bits of metal floating around inside my camera.

I worry that the aluminum tape trick would have the same problem -- small, conductive, sticky bits would seem rather worse. On the other hand, southy says that this doesn't seem to be be a problem.

Reid

* Some people have wondered whether this lens is in fact wide enough to short the contacts -- it covers about 1/2 the width of them. On my cheap Vivitar which I did remove the paint from, and which seems to cover them about the same, the shorting was successful.
02-01-2009, 06:38 PM   #30
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QuoteOriginally posted by stevebrot Quote
I just did a quick test metering out the window with my K10D with both my Jupiter-9 85/2 and my Auto-Rikenon 50/1.7 at f/2 and f/16 both with and without a foil strip firmly pressed across the contacts and got identical results for both lenses using both setups....
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
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