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06-27-2019, 01:50 AM - 20 Likes   #1
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A LITTLE BIT OF HISTORY: Development of the solenoid in Pentax cameras

A little bit of history about the development of the solenoid in Pentax cameras up to the K-30:

The legendary patent named "Automatic Camera Shutter" was applied for July 30, 1968 and granted Jan. 4th, 1972.

You can down load the patent HERE


1. The first very simple solenoid I have found in the Pentax ME and ME-Super.


No permanent magnet yet but only a plunger and an electro-magnet to induce the magnetic force to pull the plunger:



It was in 1983 that Pentax introduced its first SLR which offered fully automatic exposure ("program") mode when coupled with a matching Pentax-A series lens:
The Pentax Super-A (Super Program), followed by the Program Plus (Program-A) in 1984.



This was the first time solenoids where used the way we know it until today up to the Pentax K-70.

2. A very nicely built and sophisticated solenoid:






Not yet a rare-earth-magnet as later used but an alnico-magnet, i.e. an alloy mainly of al-uminium, ni-ckel, co-balt, invented by T.Mishima 1931 in Japan:



Backside:



The solenoid in action:





The force of this alnico magnet pulled a kind of cap connected to the leaver which moved the aperture-mechanism and kept it in place.
Taking a picture, the two coils acting as an electro-magnet receive 3 Volts DC from the cameras battery ( 2 x 1,5V SR44 or 1 x 3-V CR1108).
Those 2 coils cancelled the magnetic force of the permanent magnet and the top-cap opened, the leaver moved. Impedance was 14,3 ohms.


The electro-magnetic coils:


The partnumber given was G-100:


This partnumber G-100 remained the same at least up to the Pentax K20D and K200D, possibly later on as well but I have not yet seen a service manual of those.
Samsung named it G-100 as well in the GX1, GX2, GX10 and GX20.


The next solenoid as we know it was introduced in some the MZ-Series (MZ50, MZ6, MZ7 and a few others up to the analoge *ist). It looks identical to those used in the later DSLR bodies and had almost the same impedance. But its holding-force and body thickness was slightly different. Some which I and others had found had opposite polarity as well but others applied it with success in DSLR bodies, so it looks like that there were different versions used. Another type of solenoid was used as well for example in the Pentax MZ5/n. But Pentax didn't keep it up later on.

3. Here a photo showing the 3.rd version of a solenoid, this one I took from a MZ50 tested in a K30:


One can see, the plunger tilts slightly in relation to the round part of the leaver which it moves.

4. With the introduction of the Pentax *ist D came the made in Japan white solenoid which never failed in any of those bodies up to the Pentax K-r:


The manufacturer of those solenoids was Shinmei, Japan... also manufacturing similar solenoids for ALPS and Matsushita.

When Shinmei moved production to China, difficulties started. The material of the body changed to green and instead of using PTFE (teflon) it was now made out of PET. The alloy of the plunger changed as well. This solenoid was first tried in the flash circuit of the Pentax K100D, K200D, K-m, K-x and K-r but as far as I know mainly in those delivered to Europe. The solenoid used for the aperture was still the white made in Japan unit. The test period of this China made green solenoid was about 6 years (the K100D was introduced 2006, the K-30 introduced 6 years later in 2012). So 6 years without trouble, enough to use it for the aperture control:


5. The green made in China solenoid:




But it turned out to be the beginning of difficulties, due to several reasons described here as well the plunger of this solenoid often remained closed, i.e. it stuck the diaphragm of the lens could not open and this led what is now called "aperture problem", "dark-exposure-problems" etc.

For quite a long time it was not yet clear that it was the solenoid alone, the complete "diaphragm-control-block" was exchanged or possibly just the whole camera because exchange of the block was very work+time intensive. But then due to all the research mainly here in this forum (!) Pentax realized that it was the solenoid itself. It was about Dec. 2015 that Ricoh started to modify the solenoid. The made in Japan solenoid was no longer available, machines were already a long time in China, the plants in Japan closed.


But some early KS-1's, K-S2's and many K-50's still used the earlier China-made green solenoid and some of them failed.


As far as I can tell the green solenoid now used in the Pentax K-70 is superior to the early version!

Close-up photos show a very nicely machined plunger with a very smooth surface:


Very different to the surface of a solenoid which was filed and sanded:

and thus starts to corrode/rust very badly.

With the introduction of the Pentax K7 Pentax developed a new design, using a robust stepper-motor instead of a solenoid.
This design was used until now in the following DSLR Pentax: K7, K5, K3, KP, K1 and also in the K-01. HERE you can see it in the K-01.


Last edited by photogem; 07-09-2019 at 01:18 AM.
06-27-2019, 03:21 AM   #2
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Very interesting! Thank you for posting this history of the development of the solenoid.
06-27-2019, 07:26 AM - 1 Like   #3
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QuoteOriginally posted by photogem Quote
A LITTLE BIT OF HISTORY: Development of the solenoid in Pentax cameras
A nice piece of reverse engineering and analysis. Thanks for posting!

I am frequently amazed at the content of Pentax Forums and the many talented members.

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06-27-2019, 11:38 AM - 1 Like   #4
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Excellent. Thanks for sharing this information. I confess, I wouldn't have expected to find the solenoid development interesting... but I enjoyed reading this

06-27-2019, 11:47 AM - 1 Like   #5
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The best part is the pictures, which makes sense since this is a photography forum, but photos do a much better job of conveying information than words.
06-27-2019, 01:39 PM   #6
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Link broken?
06-27-2019, 01:41 PM   #7
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QuoteOriginally posted by monochrome Quote
Link broken?
Which one, Paul? The two patent-related links at the top of the post are working for me...
06-27-2019, 05:24 PM   #8
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QuoteOriginally posted by BigMackCam Quote
Which one, Paul? The two patent-related links at the top of the post are working for me...
Itís good now.

09-24-2019, 01:04 PM   #9
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Is there any place that we can purchase the "NEW" green solenoid for repair of our K30, and how would we know we got the NEW solenoid
09-24-2019, 10:25 PM   #10
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QuoteOriginally posted by hnikesch Quote
Is there any place that we can purchase the "NEW" green solenoid for repair of our K30, and how would we know we got the NEW solenoid
I had wondered too and tried but hitherto no success.


And yet, the "MODIDIED" (I would not call it new) green Chinese solenoid has sometimes failed as well in just the same way those of the K30/K50 failed, but to a much smaller percentage. (Same for K-S1 and K-S2)

As we know, the quality of manufacture of the white made in Japan solenoid is just superior and thus I recommend to find this one!
09-25-2019, 12:06 PM   #11
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Does the istD use a white solenoid for the pop up flash and if it does can I use it repair my K50?
09-25-2019, 06:46 PM   #12
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QuoteOriginally posted by martym Quote
Does the istD use a white solenoid for the pop up flash and if it does can I use it repair my K50?
As far as I can remember yes.
You can use any solenoid from the istD up to the K-r but at least in Europe most Pentax from the K100D up to the K-r use already the green solenoid in the pop up flash but the white one for aperture control.
09-28-2019, 09:02 PM   #13
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Incidentally, that mechanism still works correctly in my "Super Program" which I purchased in 1983, "retired" in 1995, but still use periodically.
10-06-2019, 01:41 AM   #14
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Well, this mechanims with a Japan-made solenoid still works without any problem in any DSLR body prior the K30 (and except the K7 which has the new design with the stepper-motor). It works as well without problem in those SLR bodies but as said, it slightly different.
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