Pentax 645z Aperture closing fully

Unregistered User · 10-18-2020, 02:18 PM

Hi!

When taking a shot at, lets say f/5.6, the aperture first goes to f/5.6, the shot is taken, the aperture then closes fully before opening fully.

This also happens when you check the depth of field by twisting the ON/OFF switch past ON.

Is it normal that it closes fully like that? My K-1 or any other camera I have does not do this...

See video: (1080 120p)

Youtu.be

Last edited by Unregistered User; 10-18-2020 at 02:28 PM.

**kaseki** · 10-18-2020, 05:38 PM

Originally posted by Tjompen1968

Hi!

When taking a shot at, lets say f/5.6, the aperture first goes to f/5.6, the shot is taken, the aperture then closes fully before opening fully.

...

My guess is that the iris is controlled by a stepper motor, and it is always helpful in such control circuits to remeasure step counts from one limit to the other. Proving that the limits can be reached can also be a form of self test.

Unregistered User · 10-19-2020, 12:42 AM

Originally posted by kaseki

My guess is that the iris is controlled by a stepper motor, and it is always helpful in such control circuits to remeasure step counts from one limit to the other. Proving that the limits can be reached can also be a form of self test.

But every shot? Ok.

Does yours do the same?

Sandy Hancock · 10-19-2020, 12:49 AM

I just checked mine. Exactly the same, so I would presume it's normal

Unregistered User · 10-19-2020, 01:00 AM

Originally posted by Sandy Hancock

I just checked mine. Exactly the same, so I would presume it's normal

Thank you. Makes me relaxed again =)

Bob L · 10-19-2020, 02:42 AM

A theory (and only a theory).......
The aperture is stopped down by the motor against the tension of the return spring. Allowing it to open fully again after the shot is simply a matter of removing the force applied by the motor. By fully stopping down after the shot, the spring is tensioned to its maximum and this may ensure that the aperture snaps back to fully open. Smaller format lenses may not require the same return forces.

Sandy Hancock · 10-19-2020, 04:59 AM

There is definitely a difference with the 645 aperture actuation. The FA645 lenses, when unmounted and in the "A" position are wide open, while K mount lenses from the A series onwards are fully closed.

Unregistered User · 10-19-2020, 05:05 AM

Originally posted by Sandy Hancock

There is definitely a difference with the 645 aperture actuation. The FA645 lenses, when unmounted and in the "A" position are wide open, while K mount lenses from the A series onwards are fully closed.

I did not notice that... Must check =)

What I do have found is that I can use the aperture ring to set the aperture and still have fully open aperture before shooting and also have the feedback to the camera which aperture I have choosen on the lens.

I guess this has something to do with why it closes before opening.

Unregistered User · 10-19-2020, 12:38 PM

So I took my A 35mm and put on f/8 on the aperture ring. Now it acts exactly as I had expected, closing to f/8, taking the shot and then opening fully without this weird closing down act.

Unregistered User · 10-20-2020, 05:45 AM - **2 Likes**

Talked to the workshop, the behavior is normal. The K-1 has a separate step motor for the aperture that goes in two directions. The 645z has a motor that only goes in one direction and that also used by the shutter.

All things good.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
K-30 mirror doesn't return fully to default position after aperture solenoid repair	RayeR	Pentax K-30 & K-50	6	03-18-2019 02:54 AM
K-x aperture problem: always fully stopped down on DA lenses	amrocha	Troubleshooting and Beginner Help	4	11-03-2011 03:47 PM
Optio A36 Fully powers up, then fully powers down.	PicturePlant	Pentax Compact Cameras	6	08-11-2011 11:45 AM
Aperture ring not closing	Glauco	Troubleshooting and Beginner Help	15	07-12-2011 07:51 PM
K200D not closing the aperture	j-pol	Pentax DSLR Discussion	6	07-20-2009 08:43 AM

10-18-2020, 05:38 PM	#2
kaseki Loyal Site Supporter Join Date: Dec 2017 Photos: Gallery \| Albums Posts: 1,138	Originally posted by Tjompen1968 Hi! When taking a shot at, lets say f/5.6, the aperture first goes to f/5.6, the shot is taken, the aperture then closes fully before opening fully. ... My guess is that the iris is controlled by a stepper motor, and it is always helpful in such control circuits to remeasure step counts from one limit to the other. Proving that the limits can be reached can also be a form of self test.

10-19-2020, 12:42 AM	#3
Unregistered User Guest	Originally posted by kaseki My guess is that the iris is controlled by a stepper motor, and it is always helpful in such control circuits to remeasure step counts from one limit to the other. Proving that the limits can be reached can also be a form of self test. But every shot? Ok. Does yours do the same?

10-19-2020, 12:49 AM	#4
Sandy Hancock Moderator Site Supporter Join Date: Feb 2012 Location: Adelaide Hills, South Australia Photos: Gallery \| Albums Posts: 11,275	I just checked mine. Exactly the same, so I would presume it's normal

10-19-2020, 01:00 AM	#5
Unregistered User Guest	Originally posted by Sandy Hancock I just checked mine. Exactly the same, so I would presume it's normal Thank you. Makes me relaxed again =)

10-19-2020, 02:42 AM	#6
Bob L Senior Member Join Date: Mar 2016 Location: La Vienne (86), France Posts: 223	A theory (and only a theory)....... The aperture is stopped down by the motor against the tension of the return spring. Allowing it to open fully again after the shot is simply a matter of removing the force applied by the motor. By fully stopping down after the shot, the spring is tensioned to its maximum and this may ensure that the aperture snaps back to fully open. Smaller format lenses may not require the same return forces.

10-19-2020, 04:59 AM	#7
Sandy Hancock Moderator Site Supporter Join Date: Feb 2012 Location: Adelaide Hills, South Australia Photos: Gallery \| Albums Posts: 11,275	There is definitely a difference with the 645 aperture actuation. The FA645 lenses, when unmounted and in the "A" position are wide open, while K mount lenses from the A series onwards are fully closed.

10-19-2020, 05:05 AM	#8
Unregistered User Guest	Originally posted by Sandy Hancock There is definitely a difference with the 645 aperture actuation. The FA645 lenses, when unmounted and in the "A" position are wide open, while K mount lenses from the A series onwards are fully closed. I did not notice that... Must check =) What I do have found is that I can use the aperture ring to set the aperture and still have fully open aperture before shooting and also have the feedback to the camera which aperture I have choosen on the lens. I guess this has something to do with why it closes before opening.

10-19-2020, 12:38 PM	#9
Unregistered User Guest	So I took my A 35mm and put on f/8 on the aperture ring. Now it acts exactly as I had expected, closing to f/8, taking the shot and then opening fully without this weird closing down act.

10-20-2020, 05:45 AM - 2 Likes	#10
Unregistered User Guest	Talked to the workshop, the behavior is normal. The K-1 has a separate step motor for the aperture that goes in two directions. The 645z has a motor that only goes in one direction and that also used by the shutter. All things good.