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11-11-2010, 08:24 PM   #1
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How to make ANY non-A K mount lens into an A lens.

Let the discussion begin.

When I finish up getting everything worked out, I will post a full diagram.

I want to get your thoughts before I go and give it away.

11-11-2010, 08:30 PM   #2
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The challenge is the stop down lever which let's the camera set the aperture. On 'A' lenses, the lever is carefully calibrated and the aperture is set linearly proportional to the movement of the lever, on M and K lenses it is not.
11-11-2010, 08:35 PM   #3
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Oh my!
This sounds very exciting!
11-11-2010, 08:48 PM   #4
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One thing is for sure to add electrical contacts to indicate maximum and minimum aperture.

Ole has a nice point about linearity of lever movement however may be some of the lenses have linear moment and they can be the candidates for this.

can't wait longer for your experiment details

11-11-2010, 08:54 PM   #5
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Is the idea here that you could stop down the lens, and the blades would actually close down before you shoot, in order to get AV working properly?
11-11-2010, 10:47 PM   #6
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Results and preliminary diagram.

O.k., after mounting, unmounting, and remounting my 135 2.5 countless times, here is what I have come up with.

With the camera turned upside down and the lens removed, you can see the seven contact points. We will number them 1 through 7.

Pin 5 (the one that is NOT raised up) is the one that you have to ground to make the camera think you have an "A" lens.

Pin 1 is a required ground. If it is insulated, it makes the camera think you have a non "A" lens.

Pins 2, 3, 4, 6, 7 are the pins that dictate minimum and maximum aperture.

Since we have 5 pins that dictate the aperature settings, we can have 32 different combinations (2 to the power of 5)

So, since Pin 5 has to always be grounded, I will leave it out of the list of aperature modes.

To ground Pin 5, all you need is a small piece of aluminum foil and a piece of clear packing tape.

To insulate the other pins, you just use a piece of packing tape for each pin.

Make sure the pieces of tape aren't overlapping or else the lense will catch them and you will have to start over.

Here are the supported modes by insulated pin numbers when looking at the camera upside down.

none - min 1.2, max 22

2 - min 2.4, max 22
3 - min 1.7, max 22
4 - min 1.7, max 32
6 - min 2.4, max 45
7 - min 1.4, max 22

2,3 - min 3.5, max 22
2,4 - min 3.5, max 32
2,6 - min 4.5, max 45
2,7 - min 2.8, max 22

3,4 - min 2.4, max 32
3,6 - min 3.5, max 45
3,7 - min 2.0, max 22

4,6 - min 1.3, max 16
4,7 - min 2.0, max 32

6,7 - min 2.8, max 45

2,3,4 - min 4.5, max 32
2,3,6 - min 6.7, max 45
2,3,7 - min 4.0, max 22
2,4,6 - min 1.7, max 16
2,4,7 - min 4.0, max 32
2,6,7 - min 5.6, max 45

3,4,6 - min 1.2, max 16
3,4,7 - min 2.8, max 32
3,6,7 - min 4.0, max 45

4,6,7 - min 1.3, max 16

2,3,4,6 - min 2.4, max 16
2,3,4,7 - min 5.6, max 32
2,3,6,7 - min 8.0, max 45
2,4,6,7 - min 2.0, max 16

3,4,6,7 - min 1.4, max 16

2,3,4,6,7 - min 2.8, max 16

I will post some pics tomorrow since my battery died while I was testing my 135 2.5 -22 at the closest mode the camera supports which is 2.4 - 22.

Last edited by cyclone3d; 11-11-2010 at 11:00 PM.
11-11-2010, 10:51 PM   #7
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QuoteOriginally posted by paperbag846 Quote
Is the idea here that you could stop down the lens, and the blades would actually close down before you shoot, in order to get AV working properly?
On the DSLRs you can already stop down the lens in full manual mode with the green button (on my K10D anyway).

I would think that most of the film cameras have that ability as well.

This is to get everything working except for AF and auto zoom.
11-11-2010, 11:10 PM   #8
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QuoteOriginally posted by Ole Quote
The challenge is the stop down lever which let's the camera set the aperture. On 'A' lenses, the lever is carefully calibrated and the aperture is set linearly proportional to the movement of the lever, on M and K lenses it is not.

This is the main reason why it's not a good idea for a lens with pK mount to pretend to have pK-A mount. Let's say the camera believes the lens, and tries to pull the lever to the appropriate aperture (for a pK-A lens), the actual aperture in the lens is still wrong.

Added: I can't remember exactly, but I think with pK lenses, the movement of the lever is proportional with the diameter of the aperture; while with pk-A lenses, the movement of the lever is proportional with the area of the aperture.


Last edited by SOldBear; 11-11-2010 at 11:39 PM.
11-11-2010, 11:28 PM   #9
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QuoteOriginally posted by SOldBear Quote
This is the main reason why it's not a good idea for a lens with pK mount to pretend to have pK-A mount. Let's say the camera believes the lens, and tries to pull the lever to the appropriate aperture (for a pK-A lens), the actual aperture in the lens is still wrong.
The 3 fully manual lenses I have... A Tukumar Bayonet 135 2.8, Takumar Bayonet 135 2.5, and a Sears 50mm 1.7, all look like they are pretty linear in their aperature movement.

And from looking at all my lenses, it looks like the minimum and maximum place the aperature arms are should be the same for every lens.

I'll do some real testing when it is light out again.
11-11-2010, 11:45 PM   #10
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Any lens?
Love to see what you can figure out for M42 preset lenses.
11-12-2010, 06:02 AM   #11
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I have modified a ricoh 50 mm f2 lens to full A operation and can confirm first hand that the aperture control is very bad

I drilled the lens mount with the appropriate contact pattern for the apertures and used a spring loaded CPU chip contact pin for the A pin

Although all the controls worked the linearity of the aperture ( perhaps lack of linearity is more appropriate) caused exposure errors that were as bad as the k10 metering in the first place. I have previously posted these results. In my opinion it is a waste of time. Go out and use the lenses as opposed to sitting in your workshop damaging them

this has been discussed previously at length

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/117613-convert...dding-pin.html


https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/4893-replacing-lens-mounts.html
Attached Images
 

Last edited by Lowell Goudge; 11-12-2010 at 06:16 AM.
11-12-2010, 06:13 AM   #12
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QuoteOriginally posted by xjjohnno Quote
Any lens?
Love to see what you can figure out for M42 preset lenses.
Hence why the post title says "K mount".
11-12-2010, 10:07 AM   #13
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QuoteOriginally posted by Lowell Goudge Quote
I have modified a ricoh 50 mm f2 lens to full A operation and can confirm first hand that the aperture control is very bad

I drilled the lens mount with the appropriate contact pattern for the apertures and used a spring loaded CPU chip contact pin for the A pin

Although all the controls worked the linearity of the aperture ( perhaps lack of linearity is more appropriate) caused exposure errors that were as bad as the k10 metering in the first place. I have previously posted these results. In my opinion it is a waste of time. Go out and use the lenses as opposed to sitting in your workshop damaging them

this has been discussed previously at length

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/117613-convert...dding-pin.html


https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/4893-replacing-lens-mounts.html
I hadn't come accross that other thread.

However, after doing some testing with my 135 2.5, it it pretty dead on at both ends, but the exposure gets pretty far off in the middle of the aperture range, causing quite a bit of overexposure.

BUT... when using it as an A lens, but in M mode, the color reproduction is a whole lot better then when using it as an M lens.

Could the multi-segment metering have anything to do with this?

I can live with having to make a chart of how much I have to change the exposure at the different F-stops if it is going to give me better color.
11-12-2010, 12:47 PM   #14
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QuoteOriginally posted by cyclone3d Quote
I hadn't come accross that other thread.

However, after doing some testing with my 135 2.5, it it pretty dead on at both ends, but the exposure gets pretty far off in the middle of the aperture range, causing quite a bit of overexposure.

BUT... when using it as an A lens, but in M mode, the color reproduction is a whole lot better then when using it as an M lens.

Could the multi-segment metering have anything to do with this?

I can live with having to make a chart of how much I have to change the exposure at the different F-stops if it is going to give me better color.
metering does not impact color other than what ever happens as the result of over and under exposure. if you get the exposure correct, the color will be the same, it is all abot getting the exposure correct. it's that simple.

Note also, you can make a similar chart of the metering accuracy in M mode and the correction necessary, which is why i did not bother going further, as my whole reason for trying this was to get more accurate metering in manual, than my K10D provided, only to find it was much worse.

see the attached chart

to make the metering chart all yo need to do is have a uniformly lit surface, take photos with the camera's metering, and plot the greyscale value as a function of aperture.
11-12-2010, 04:28 PM   #15
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How can you make M and K into an A lens?They still won't do open aperture.They'll keep the same they're dialed at.Unlike an A len like my A 50mm f1.7.Even at f22 which would look pitch black stopped down, it it only do that once I fully depress the shutter
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