Pentax KX fast shutter speeds are all the same???

BradS · Jun 22, 2018

I was checking out a Pentax KX that I have owed since new. Running through the shutter speeds, it seems like the shutter speeds above 1/60 sec are the same speed. This is with the back open, pointing the camera up toward open sky, actually looking through the lens...not just "sounds about the same".
Of course, I thought that I must be delusional...so, I tried some of the other 35mm SLRs around here....there are a few. They all seem to behave as expected, one can actually see that the shutter open time is progressively shorter with faster shutter speed settings -- exactly as I expect.

Yes, obviously, the KX needs a CLA....but why, what happened? What could cause this?

(or, am I imagining a problem that doesn't exist?)

Sirius Glass · Jun 22, 2018

It sounds like it is time for a CLA. We could spend many days and type up the bandwidth speculating why but a competent camera repair man can tell after examining the camera. I hope that you get this camera up and running properly again. You were wise to listen to the shutter and to look through the back of the camera before you shot a roll of film.

BradS · Jun 22, 2018

Another side effect of this little experiment, I discovered that the Honeywell (Spotmatic) SP-1000 shutter doesn't even open completely at 1/1000 sec... so, two (Pentaxes?) (Penteces?) Pentax bodies for the repairman...<sigh>

BradS · Jun 22, 2018

Gremlins.

shutterfinger · Jun 22, 2018

Focal plane shutters have two curtains that should travel at the same speed. Shutter speeds are determined by the time lag between the first curtain release and second curtain release. This lag creates a slit that moves across the frame, the slower the speed the wider the slit, the faster the speed the narrower the slit. If all speeds above a certain speed have the same slit width then the second curtain is not releasing properly.
Pentax service manuals are available at
Dead Link Removed
http://www.pentax-manuals.com/manuals/service/servicemanuals.htm
Both the KX and SP1000 have horizontal travel fps. The curtains are on two spools each side with one inside the other. Dirt, wear debris, dried oil or grease is preventing the spools from turning freely and independently of one another.
Rubberized silk used for shutter curtains is usually .007 inch thick when new and the rubber coating will swell with age up to .025 inch thick depending on storage and climate the camera has been in.
Do some searching, you may be able to find a service manual for the KX but the internal differences of the KX, SP1000, Spotmatic are not that great.

Ces1um · Jun 22, 2018

BradS said:
I was checking out a Pentax KX that I have owed since new. Running through the shutter speeds, it seems like the shutter speeds above 1/60 sec are the same speed. This is with the back open, pointing the camera up toward open sky, actually looking through the lens...not just "sounds about the same".
Of course, I thought that I must be delusional...so, I tried some of the other 35mm SLRs around here....there are a few. They all seem to behave as expected, one can actually see that the shutter open time is progressively shorter with faster shutter speed settings -- exactly as I expect.

Yes, obviously, the KX needs a CLA....but why, what happened? What could cause this?

(or, am I imagining a problem that doesn't exist?)

My k1000 and km both do this as well. They have a focal plane shutter. After a certain speed the shutter doesn't close any faster, just the width of the slit in the shutter varies so as it gets narrower less is exposed per unit time. At 1/125 and up they all sound alike. When I have time I'll try and find a youtube video that explains it better- I just have to duck out right now to take the kids to the grandparents.

ic-racer · Jun 22, 2018

BradS said:
I was checking out a Pentax KX that I have owed since new. Running through the shutter speeds, it seems like the shutter speeds above 1/60 sec are the same speed. This is with the back open, pointing the camera up toward open sky, actually looking through the lens...not just "sounds about the same".
Of course, I thought that I must be delusional...so, I tried some of the other 35mm SLRs around here....there are a few. They all seem to behave as expected, one can actually see that the shutter open time is progressively shorter with faster shutter speed settings -- exactly as I expect.

Yes, obviously, the KX needs a CLA....but why, what happened? What could cause this?

(or, am I imagining a problem that doesn't exist?)

Focal plane shutters don't travel faster than the flash synch speed.

Theo Sulphate · Jun 22, 2018

So... we know sound means little here. It is the slit width, or time between first and second curtain.

You are saying that when you were looking at it with the back open, the slit width at 1/60 was the same as the width at all higher speeds up to 1/500? At 1/1000 it is capped (no slit)?

Time for CLA visit unless you are good at doing it yourself.

Chan Tran · Jun 22, 2018

How do you see the slit width really?

BradS · Jun 22, 2018

shutterfinger said:
Focal plane shutters have two curtains that should travel at the same speed. Shutter speeds are determined by the time lag between the first curtain release and second curtain release. This lag creates a slit that moves across the frame, the slower the speed the wider the slit, the faster the speed the narrower the slit. If all speeds above a certain speed have the same slit width then the second curtain is not releasing properly.
Pentax service manuals are available at
Dead Link Removed
http://www.pentax-manuals.com/manuals/service/servicemanuals.htm
Both the KX and SP1000 have horizontal travel fps. The curtains are on two spools each side with one inside the other. Dirt, wear debris, dried oil or grease is preventing the spools from turning freely and independently of one another.
Rubberized silk used for shutter curtains is usually .007 inch thick when new and the rubber coating will swell with age up to .025 inch thick depending on storage and climate the camera has been in.
Do some searching, you may be able to find a service manual for the KX but the internal differences of the KX, SP1000, Spotmatic are not that great.

Thank you!

This is not something that I'd attempt to repair myself but, I just wanted to understand what was going on.

shutterfinger · Jun 23, 2018

OK I'm reading the Asahi Pentax Spotmatic service manual in either of the links in post 5. I was mistaken, the Spotmatic uses two rods per curtain mounted close to each other. It also uses a slow speed governor to regulate the speeds.
The first curtain speed should be 14 ± .3 millisecond at 20°C , sensors at the edges of the image frame or 12.5 ± .3 millisecond with a digital tester whose sensors are 2mm inward from the edges of the frame. Adjust the speed of the first curtain to be .05 to .1 millisecond faster than the second.
The handy os calculator shows that that the curtain travels 2.57 millimeters per millisecond. 1/125 shutter speed is .008 second or 8 milliseconds therefore the curtain slot width should be 20.56 millimeters. 1/1000 is .001 second or 1 millisecond., therefore the slit width should be 2.57 millimeters. My eye was never good enough to see the slit width at that speed but setting up the test equipment and operating it is a piece of cake. Please correct me if the math is incorrect.
You can probably pull the top and bottom covers, flush the curtain rod ends and governor with https://www.homedepot.com/p/CRC-11-oz-QD-Electronic-Cleaner-05103/205021975 then apply a straight pin point drop of https://www.homedepot.com/p/CRC-11-oz-QD-Electronic-Cleaner-05103/205021975 to the rod ends and governor gear ends and have a correctly operating shutter without any further disassembly or adjustment.

BradS · Jun 23, 2018

shutterfinger said:
OK I'm reading the Asahi Pentax Spotmatic service manual in either of the links in post 5. I was mistaken, the Spotmatic uses two rods per curtain mounted close to each other. It also uses a slow speed governor to regulate the speeds.
The first curtain speed should be 14 ± .3 millisecond at 20°C , sensors at the edges of the image frame or 12.5 ± .3 millisecond with a digital tester whose sensors are 2mm inward from the edges of the frame. Adjust the speed of the first curtain to be .05 to .1 millisecond faster than the second.
The handy os calculator shows that that the curtain travels 2.57 millimeters per millisecond. 1/125 shutter speed is .008 second or 8 milliseconds therefore the curtain slot width should be 20.56 millimeters. 1/1000 is .001 second or 1 millisecond., therefore the slit width should be 2.57 millimeters. My eye was never good enough to see the slit width at that speed but setting up the test equipment and operating it is a piece of cake. Please correct me if the math is incorrect.
You can probably pull the top and bottom covers, flush the curtain rod ends and governor with https://www.homedepot.com/p/CRC-11-oz-QD-Electronic-Cleaner-05103/205021975 then apply a straight pin point drop of https://www.homedepot.com/p/CRC-11-oz-QD-Electronic-Cleaner-05103/205021975 to the rod ends and governor gear ends and have a correctly operating shutter without any further disassembly or adjustment.

Well...hmm...now you got me thinking. The bottom cover is easy enough but top cover looks a little more involved.I think I may download and study that repair manual too.

Thank you! You may have saved me a bunch $$$$

shutterfinger · Jun 23, 2018

BradS said:
Well...hmm...now you got me thinking. The bottom cover is easy enough but top cover looks a little more involved.I think I may download and study that repair manual too.

Well the advance has a small left hand screw.
Are you going to blame me if its a bust?

BradS · Jun 23, 2018

shutterfinger said:
Well the advance has a small left hand screw.
Are you going to blame me if its a bust?

Good heavens, no...

I have a Spotmatic in the junk box...If, after reading the repair manual, I decide to give it a go, I'll practice on the junk Spotmatic first....most likely the (very dear to me) KX is getting a trip to the professionals.

shutterfinger · Jun 23, 2018

I've had the covers off a Spotmatic and that's about it. Get the National camera repair manual as well as the factory one.
Ask questions with pictures if you run into trouble or need clarification.

Theo Sulphate · Jun 23, 2018

Chan Tran said:
How do you see the slit width really?

Don't blink!

Seriously though, a good way to infer that successively higher shutter speeds each produce a narrower slit, is to:

1. Choose widest aperture.
2. Open the back.
3. Aim camera at uniformly lit surface like a white wall.
4. Observe intensity of light coming through the shutter at each speed.

I find this works well during the day in a shaded room. For example, the light on the white wall gives a meter reading of 1/30, f/5.6, ISO 200 -- that's the intensity of light on the wall. So, at 1/60, f/1.4, when the shutter trips you'll see a nice bright flash. At higher speeds you'll notice it get dimmer and dimmer.

BradS · Jun 25, 2018

shutterfinger said:
I've had the covers off a Spotmatic and that's about it. Get the National camera repair manual as well as the factory one.
Ask questions with pictures if you run into trouble or need clarification.

I successfully removed and reinstalled the top cover on my practice camera!

That nut below the screw that turns the wrong way...it requires some sort of special tool. I improvised with two jewler's screw drivers and a crecent wrench. Is there a proper tool? If so, which do you recommend? and where might a fellow buy one?

shutterfinger · Jun 25, 2018

BradS said:
I successfully removed and reinstalled the top cover on my practice camera!

Congratulation on the success.

BradS said:
That nut below the screw that turns the wrong way...it requires some sort of special too

The one I had apart used a slot head screw.

BradS said:
Is there a proper tool? If so, which do you recommend? and where might a fellow buy one?

Use a Dremel with cutoff wheel and some sheet stainless steel or similar material and make one. I have at times used internal snap ring pliers when such a retainer was large enough.
big verity on both ebay and amazon, the local hardware or autp parts store may have them also.

oreston · Jun 26, 2018

Chan Tran said:
How do you see the slit width really?

A rough-and-ready way is to do what the OP did (firing the shutter while looking at the curtains with the back of the camera open and no lens mounted) but adding a flash unit into the process. At the highest electronic flash synch. speed (1/60 for the KX) you should of course see the whole of the frame illuminated by the flash as this is the highest speed at which the shutter curtains open completely to expose the entire frame simultaneously. As you increase shutter speed, you will see less of the frame illuminated at each setting, with the remainder blacked out. The illuminated portion equates to the slit between the two curtains, frozen (as it were) by the flash as it scans across the frame. At 1/125 (double the maximum synch. speed) around half the frame should be blacked out. At 1/250, twice as much again and so on. I find on my Spotmatics (basically the same shutter as the KX) this does break down at 1/1000, where often I don't see any illumination at all (or sometimes just the faintest slither at the left edge of the film gate as I'm viewing it) even though a test with window light alone confirms there's no capping.
Since the frame is 36mm wide, at 1/125 the slit should be around 18mm wide (ie half the width) if the shutter is working properly. At 1/250 it will be 9mm, at 1/500 4.5 mm and at 1/1000 2.25mm - though, as I say, often nothing is visible at 1/1000. I find it helps to mark off these widths with a pen on strips of white card and tape them to the top and bottom film rails (obviously aligning them to the edge of the frame).
I'm not claiming that this method is a substitute for a shutter speed tester, but it does enable you somewhat to "see" what's going on with the curtains at the higher shutter speeds and it can help to give a useful indication of how well a focal plane shutter is working.

Pentax KX fast shutter speeds are all the same???

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