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01-26-2020, 04:54 AM   #1
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How to detect aperture block failure on Pentax K-S1 (and K-S2)

How to detect aperture block failure on Pentax K-S1

(How to do it with your K-S2 you best read HERE, because it is the same as for the K-70)


This is a step-by-step tutorial on how to identify the dark-exposure-problem on the Pentax K-S1 which uses a solenoid for aperture control.
If the aperture control (diaphragm control) doesn't work any more, then in almost all cases the solenoid driving the aperture control is stuck.

This problem started with the introduction of the Pentax K-30. If you want to know more about details and the history,
read here: History of Solenoid
There are older Pentaxbodies which use the same technology but the problem of a stuck solenoid never touched those,
but just in case this ever would happen, it is the same procedure:
All *ist DSLR bodies, K10D, K20D, K100D, K110D, K200D, K2000/m, Kx, Kr and Samsung equivalents

Method 1 with kit-lens or any other AF-lens without A-ring:
(such as DA 18-55, DA 18-50,DA50, DA35 many Sigma/Tamron lenses etc.)

a) Set the mode-dial of your K-S1 to AV-mode:



b) Set aperture "wide open":

for example: - DA 18-55: f3,5 (at 18mm) - DA 18-50: f4,0 (at 18mm) - DA 50: f1,8 - D-FA50macro: f2,8 (the one I chose here)



c) Take a photo:


This photo should be dark/underexposed!



Next step:


d) Set aperture "full stopped down" for your given lens:

for example: -DA 18-55: f38 - DA 18-50: f36 - DA 50: f22 - D-FA50macro: f22:


e) Take a photo(if necessary use the flash if daylight isn't bright enough):


This photo should be fine!




The test shows you that the solenoid doesn't need to actuate when the lens is fully stopped down, that's why this photo is alright!
But with the lens wide open the solenoid has to actuate but can't because it is stuck.

If you done the test this way, you can say with 99,9% certainty, that the solenoid is stuck and needs to be replaced.


Method 2: Using Live-View mode with any A or AF lens with or without A-Ring:
(such as DA, DA-L, FA, F or A and those of other manufacturers with A-ring)

If you use a lens with an A-Ring set it on A!

This is best done with a prime lens, such as DA50/2,4, DA35/2,4, F/FA50/1,7/1,4
or any other which allows a good view into the front of the lens to see the aperture blades.

This photo shows the F50/1,7 set on A:




a) Set the mode-dial to any mode such as AV, TV, TAV or P:

b) Turn your K-S1 (switched ON) so you can see into the front of the lens!

c) Now press the Live-View button:



If the aperture in your lens moves to f4, the solenoid works alright:






But if the aperture is fully closed,
the solenoid is stuck and damaged:






Often (but not always!) you can still take photos in LV (Live-View)!
But photos taken through the OVF (Optical-View-Finder) are underexposed!


This is due to the solenoid actuating twice plus the important fact that the mirror is up as soon you activate LV!
This drains more power (mA) from the battery.
So as soon as you press the shutter-release-button, the mirror goes down and this sudden stop of holding the mirror up allows some extra power and thus the solenoid often (but now always) now actuates this second time.

But because the solenoid was stuck the first time metering was not perfect:
Metering was done full stopped down instead of f4,0! So you get some kind of alright photo but it isn't really correct!

You cannot you check the function of the solenoid in M-Mode and preselect aperture!
In M-Mode the solenoid is not used by the camera!
But all the other parts of the complex aperture control mechanism are used, this is the reason why manual lenses and green button metering does work.


When the K-S1 is open, you cannot check the solenoid functioning as one can with a Pentax K30/50/500!


But you have to change the solenoid with a functioning one. As long as you have warranty on your K-S1 you better send it in
because if you apply DIY you lose warranty!
But if outside of warranty, then you best do it yourself, the tutorial you find HERE.
It is pretty straight forward and the solution with using the white made in Japan solenoid is by far the very best.


Of course in most cases filing/sanding the plunger will work kind of but why you better stay away from this you can read here:
Why you shouldn't file/sand the plunger of the green China-solenoid but replace it


This thread is not for discussion or commentaries!

Any discussion, commentaries etc. please post here:
Dark exposure problems on K-30 or K-50? Discussion Thread - PentaxForums.com


Last edited by photogem; 01-26-2020 at 10:04 AM.
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a-ring, aperture, aperture control, control, da, dark photos, dark pictures, diaphragm control block, k-s1, k-s2, lens, mirror, pentax, pentax k-s1, photo, solenoid
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