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A LITTLE BIT OF HISTORY: Development of the solenoid in Pentax cameras
Posted By: photogem, 06-27-2019, 01:50 AM

A little bit of history about the development of the solenoid in Pentax cameras up to the K-70:

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. This solenoid was driven with 6VDC (rated with 4,5VDC) by the solenoid-driver, impuls was 6.45V.

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.



The next drawing shows this early SLR solenoid (i.e. not yet DSLR!):


It has 3.4mm bobbin-size (versus 4mm bobbin-size for the later DSLR-solenoids). It looks almost similar to the DSLR solenoids but aside of a tiny differenz in bobbin-size it has a slightly different holding force and often me and others have found polarisation to be opposite to the later introduced DSLR solenoid.

Data Japan-made "SLR" solenoid:
- Operating Voltage DC: 3 - 6V
- Coilresistance: 30 ohms
- Attraction force: 2,2 N min
- Backtension: 0,8 N
- Operating stroke: 2mm


4. A very different solenoid was used in many other MZ/ZX such as the MZ5 bodies:





4. With the introduction of the Pentax *ist D came the made in Japan white DSLR 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.


The next drawing shows that this new introduced Japan solenoid for DSLR bodies had now 4mm bobbin-size instead of 3.4mm:


As mentioned, this difference of 0.6mm is hardly noticable but this is why aside from another small difference in holding-force and often opposite polarisation the early SLR solenoids with 3.4mm bobbin-size sit slightly bent when installed into a DSLR body! This new DSLR-solenoid made in Japan (also for ALPS) It had a live-timespan of remarkable 100.000 actuations!


Data Japan-made "DSLR" Solenoid:
- Operating Voltage DC: 3,6 - 7,2 V- Coilresistance: 30 ohms
- Attraction force: 2,5 N min
- Backtension: 1,0 N
- Operating stroke: 2mm


When Shinmei moved production to China, difficulties started!

The material of the body changed to green colourand instead of using PTFE (teflon) it was now made out of PET. The alloy of the plunger changed as well.
PTFE (teflon) is a very good bearing material, it is used as well for bearings in turntables. This bearing was patented by W. Firebough. He describes the bearing very well in This interview. I could verify the amazing bearing qualities myself. When one inspects a heavy used Japan-solenoid closer against one made in China, one can tell the difference, PET is worn off much quicker.

This China made solenoid was first tried in the flash circuit of the Pentax K100D, K100D, K200D, K-m, K-x and K-r but as far as I know mainly in those delivered to Europe.
Rated voltage was now 3,7 - 7.5V (impuls 8.32V) but live-time was drastically lower: 20.000 actuations.


Data China-made solenoid
- Operating Voltage DC: 3,7 - 7,5V
- Coilresistance: 30 ohms
- Attraction force: 2,8 - 3,0 N min
- Backtension: 1,2 N
- Operating stroke: 2mm


Here you can see the measurements on a Pentax K-30


The next drawing shows the datasheet of the green China-solenoid:

The dashed (----) line shows the 30ohms version used for Pentax. The lower live-time of 20.000 actuations is due to PET instead of PTFE used in the early Japansolenoid.

Some claim (without prove, because it cannot be proven) that the voltage used for the Chinasolenoid would be more in the region of 2.5V because it releases smoothly at 2.5V. That's a lot of nonsense because none, the early Japan made SLR, the next Japan made DSLR solenoid nor the China made version work well with just 2,5V/DC! They do work with 3V but are driven with 6V in the SLR Pentax cameras and 7.2V in the DSLR Pentax cameras.
If one studies the curve for holding-force one can see this very clearly! I have done tests with 3V, 6V and 7.2 Volts. Measuring release-time (and thus holding-force) can be done from 5V - 9V. If one compares different solenoids it just is important that the applied voltage is the same for all solenoids one compares! The applied Vpp since the Pentax *ist-D is exactly 8.32VDC. Earlier pre DSLR bodies such as the MZ50 had 6VppDC. The solenoid is driven by a transistor (BJT/SOT23) and protected by a simple diode, which some mistake for a resistor or chip-resistor. This diode looks almost identical to an SMD-resistor, and yes, it resists into one direction (infinite ohms) but not into the other (zero ohms)
Nevertheless, it is a good idea to resist such chips were you don't want them or were they just don't belong to.

Some repairshops quote that they exchanged a chip-resistor but following the circuit very closely I just could not find any. It wouldn't make sense either, because if one studies the curve and quick response the solenoid has to actuate, any resistor would basically block any quick response. The solenoid does depend mainly on "surge-power", i.e. milli-amperes delivered quickly and not on voltage. If one studies the curve, one can quickly find out, that there is a range which is best for minimum holding-force. I challenge anybody who insists on some chip-resistor to prove it to me. I am curious for the outcome. And should I be wrong, I will happily "throw my hat" on the ground and apologize!


While the China-made solenoid was tested in the flash-circuit, the solenoid used for aperture-control remained still the white made in Japan unit!
This test-period went on for about 6 years (the K100D was introduced 2006, the K-30 introduced 6 years later in 2012).
So 6 years without trouble, enough time to use it for the aperture control.

This photo shows the green China solenoid for the pop-up-flash in a K200D:



And here built out:



But this change turned out to be the beginning of difficulties, due to several reasons described here as well:

The plunger of this solenoid often remained closed/stuck! The diaphragm/blades/aperture of the lens could not open and this led what is now often called "aperture problem", "dark-image-syndrom", "dark-exposure-problems" etc.

For quite a long time it was not yet clear that the cultprit was just the solenoid! 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 (!) Ricoh/Pentax realized that it was just 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 since a long time in China, the plants in Japan closed, so no chance to go back to this Japan-made solenoid!


Some early KS-1's, K-S2's and many K-50's as well of course K-500's still used the earlier China-made green solenoid and thus some of them failed and still do fail.


As far as I can tell the green solenoid now used in the Pentax K-70 is superior to the early version!
And yet: The holding force is still stronger, it does not fire as quick as the white made in Japan-Solenoid!

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



Very different to the surface of a solenoid modified by filing or sanding:

The surface of the alloy which is hurt by sanding or filing starts to corrode and can actually rust pretty bad.



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.

Beware of those green China-Solenoids now being sold on ebay, aliexpress and other sources,
those are even inferior and were NOT MADE FOR DSLR but for Lenovo DVD-drives:



You can see, the 2 pins facing sideways are missing! They have again a too strong holding force.
They were constructed for a very simple "press-button-open-tray" circuit.


Beware also of blue-coloured China-Solenoids from ROM-Drives:
Wrong impedance (15ohms)! Danger of serious damage of the powersupply which is a socalled "solenoid-driver".

Again: Beware of green solenoids which are filed/sanded!
Further information why you should avoid this you can study HERE


Some companies offer modifications "in weight, structure and/or surface"
Well, if you sand of file, you change all three aspects of course.
But that's not the solution, to me more of a disimprovement




Last edited by photogem; 02-28-2021 at 03:56 AM. Reason: New info added by Photogem
Views: 12,166
12-28-2020, 09:13 AM - 1 Like   #46
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QuoteOriginally posted by photogem Quote
Not really:
Larger bodies, more weight and more expensive.
Read here what I wrote about this issue:
Buying a new camera body - Page 4 - PentaxForums.com
But do you have evidence that the "Japan" solenoid is still in production?

---------- Post added 12-28-20 at 09:26 AM ----------

QuoteOriginally posted by photogem Quote
It is not the technology which is wrong, it is just the solenoid which since China-manufacture was not perfected yet!
I keep hearing that it was slightly improved for the K-70, yet still fails, just not as quickly. The argument that Teflon should be used seems quite convincing, but I don't see evidence that Shinmei is willing to change materials or open a new production line for a Teflon solenoid - or that Ricoh is willing to shell out to make this happen for Shinmei, or take production into their own hands (patents?).

---------- Post added 12-28-20 at 10:06 AM ----------

QuoteOriginally posted by photogem Quote
Larger bodies, more weight and more expensive.
Between the K-70 and KP, I'm struggling to find evidence of this. The KP weighs 703g with battery and card, the K-70 688g, a difference of 15 grams, or 2.1%. The KP may have a lighter flash unit (GN 6 rather than GN 12). Battery life almost exactly the same. The extra size of the KP is mostly in the prism housing, which has nothing to do with solenoid vs. stepping motor.

Do we know the unit cost of a solenoid vs. a motor?

12-28-2020, 11:24 AM   #47
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This is not a thread of KP vs. K70.
This is a thread about the history of the solenoid within Pentax cameras.
So lets not continue this type of discussion here, if so, another thread.

Anyway:

I think we might see the K3III and can compare weight etc.
I have the KP but feel the K70 is better in my hands.
Optically I prefer the KP and I kept it against the K70 for other features.

QuoteOriginally posted by Breakfastographer Quote
But do you have evidence that the "Japan" solenoid is still in production?
Who claims this?
Not me!
03-04-2021, 09:31 PM - 1 Like   #48
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Exact datas added, showing clearly the difference between:

- early SLR solenoid (made in Japan, white PTFE Body)
- DSLR solenoid (made in Japan, white PTFE Body)
- China made solenoid (green PET body)
03-05-2021, 05:37 PM   #49
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QuoteOriginally posted by photogem Quote
Exact datas added, showing clearly the difference between:

-1. early SLR solenoid (made in Japan, white PTFE Body)
-2. DSLR solenoid (made in Japan, white PTFE Body)
-3. China made solenoid (green PET body)
and only cameras with the last one {#3} seem to have aperture control failures?

03-11-2021, 07:39 AM   #50
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Why the alternative solution is to use the AA batteries, where is possible, instead of the lithium one?
03-11-2021, 11:15 AM   #51
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QuoteOriginally posted by reh321 Quote
and only cameras with the last one {#3} seem to have aperture control failures?
No..... #1 as well but the opposite:

#1 = a bit to little holding force (compared to #2): Plunger slips sometimes to easely away from the permanent magnet: Overexposure
and.... it can lead to misalignement of the complex aperture/shutter/mirror-up mechanism!

#2= correct holding force: Never any failures

#3 = too strong holding force: Plunger sticks to the magnet, cannot release anymore: Underexposure


QuoteOriginally posted by Andrea K Quote
Why the alternative solution is to use the AA batteries, where is possible, instead of the lithium one?
This solution works only for a short time.
Not a permanent solution!
03-11-2021, 06:50 PM   #52
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QuoteOriginally posted by Andrea K Quote
Why the alternative solution is to use the AA batteries, where is possible, instead of the lithium one?
The answer may be buried in photogem's last post

QuoteOriginally posted by photogem Quote
#3 = too strong holding force: Plunger sticks to the magnet, cannot release anymore: Underexposure
If AA batteries provide less 'drive' to the solenoid, the situation where it delivers "too strong holding force" may be delayed - but it is just delayed.
I got an AA holder almost as soon as I got my K-30 ...... but the failure did develop, so now I use the K-30 only on occasion, and then with a lens having an aperture ring so that I can control aperture at the lens, since the body can no longer control it - I am basically back to my first Pentax, a ME/SE, a true K-mount camera which had only what we now know as 'M' and 'Av' modes.

Last edited by reh321; 03-11-2021 at 06:58 PM.
03-11-2021, 10:36 PM   #53
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QuoteOriginally posted by reh321 Quote
The answer may be buried in photogem's last post
What is buried (i.e. hidden) in my last post?

QuoteOriginally posted by reh321 Quote
If AA batteries provide less 'drive' to the solenoid, the situation where it delivers "too strong holding force" may be delayed - but it is just delayed.
You forget, that from all Pentaxbodies with the green China-Solenoid only those can use AA batteries:


K-30
K-50
and
K-500


K-S1, K-S2 and K70 can't use AA's.


This thread is about the history/development of the solenoid in general.

AA batteries in the K30/K50 delay the problem but don't solve it!

For those who can do it, money is better spend for the solenoid and DIY


Last edited by photogem; 03-14-2021 at 01:08 AM. Reason: K500 added
03-12-2021, 04:33 AM   #54
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Also k-r supports AA batteries
03-12-2021, 05:14 AM   #55
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QuoteOriginally posted by Andrea K Quote
Also k-r supports AA batteries
Yes, but the K-r has the Japansolenoid!


With the K-r you use Eneloops or similar for a different reason, the solenoid in the K-r never fails!


So it does not belong into this discussion regarding pushing a stuck green Chinasolenoid to some more life again.
03-12-2021, 06:44 PM   #56
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QuoteOriginally posted by photogem Quote
What is buried (i.e. hidden) in my last post?
It is "hidden" because it is just a few words, so those few words can become 'lost' amongst so many total words.
03-13-2021, 01:27 AM   #57
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QuoteOriginally posted by reh321 Quote
It is "hidden" because it is just a few words, so those few words can become 'lost' amongst so many total words.
That's a lot of gobbledygock!

Andrea asked (I corrected it a bit so):
QuoteOriginally posted by Andrea K Quote
If one can, is using AA batteries instead of lithium a possibility?

My answer was very straight, clear and yes .... short, because no more useless words were needed:
QuoteOriginally posted by photogem Quote
This solution works only for a short time.
Not a permanent solution!

If Andrea would not understand, I'm sure: He would tell me.

So: I don't need spoonfeeding nor crutches
03-13-2021, 06:05 AM   #58
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QuoteOriginally posted by photogem Quote
That's a lot of gobbledygock!

Andrea asked (I corrected it a bit so):

My answer was very straight, clear and yes .... short, because no more useless words were needed:


If Andrea would not understand, I'm sure: He would tell me.

So: I don't need spoonfeeding nor crutches
To my understanding, {of your original words} those gave the most accurate and concise answer to Andrea's question, a question which others may have wondered about as well.
We don't need even more words on the subject - you may add even more, but I am done.

Last edited by reh321; 03-13-2021 at 06:23 AM.
03-13-2021, 09:21 AM - 1 Like   #59
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QuoteOriginally posted by photogem Quote
That's a lot of gobbledygock!

Andrea asked (I corrected it a bit so):



My answer was very straight, clear and yes .... short, because no more useless words were needed:



If Andrea would not understand, I'm sure: He would tell me.

So: I don't need spoonfeeding nor crutches
I admire your patience, as far as i can see : if not a completely new solenoid drops down from heaven there is nothing more to say. I fiollowed your recommandation and think of selling my kp, because fior my needs the k30 is almost just as good
03-14-2021, 01:07 AM   #60
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QuoteOriginally posted by reh321 Quote
To my understanding "your original words gave the most accurate and concise answer" to Andrea's question,
a question which others may have wondered about as well.
Well: If.... to *YOUR* understanding.... *MY* answer was... as you wrote now
"the most acurate and concise answer" to Andreas's question:

What "may others have wondered about as well"???
About what?

Before you wrote:
QuoteOriginally posted by reh321 Quote
The answer may be buried in photogem's last post
which is just nonsense. Nothing was buried!

QuoteOriginally posted by reh321 Quote
We don't need even more words on the subject - you may add even more
Oh, you are so polite... well, with your permission:

QuoteOriginally posted by reh321 Quote
.... but I am done.
Excellent idea!
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