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10-01-2014, 02:59 PM   #1
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Pentax K1000 and ASA dial problem

Hello all.

I'm new to this forum, but a Pentax user for many years.

I found a K1000 on a cupboard at home, long forgotten in there, and with plenty of mold and all kind of nasty "things".
I had to disassemble it to perform a deep clean, plus fix the mirror spring not working propertly.

Everything was fine, but now, after reassembling it, I found that the ASA dial doesn't seem to show the correct ASA value.

For example, I take one of my DSLRs and set the ISO to 100, f/5.6 and speed to 125, and it says that exposure is correct. But now, when I go back to the K1000, I set the exact same parameters, but the photometer tells me that the image will be underexposed. I change then the ASA and set to 400, the the exposure seems to be correct.

So I think the problem is some kind of dial disalignment, but according to the k1000 technical manual (http://www.pentax-manuals.com/markroberts/k1000_man.pdf) everything is correct and in place, so I'm here stuck. I can just deduct 300 to the ASA value and that woulld do the trick, but I would like to make it work properly. Any idea?

The battery I'm using is a LR44 1.5v freshly purchased.

The objective I tried was the original jpanese on, the 50mm one, and also a Zenitar 50mm. Both of them I got the same exposure measurements.
The mirror, prist and lenses are prefectly clean.

Someone would help me resurrect this lady?
Thanks in advance.

10-01-2014, 04:09 PM   #2
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It could be the meter. Some meter circuitry will degrade over time. My suggestion would be send it to Eric.
10-01-2014, 04:34 PM   #3
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It may be that you were off a bit when you did your reassembly.

BTW...do you have the service manual?

http://www.pentax-manuals.com/manuals/service/servicemanuals.htm


Steve
10-01-2014, 08:34 PM   #4
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Sometimes when a camera with cds cell meter sits around the meter cell dies. Look at the manual to see how to calibrate the meter. The circuitry allows for a fair amount of adjustment, but you may find it is too far gone. Good luck.

10-02-2014, 01:36 AM   #5
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Original Poster
I will take a look at the cell.
Thanks for the advice.
10-02-2014, 07:55 AM   #6
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Original Poster
Hi.

Just saying that I found what the problem was.

Let me briefly explain, so anyone else with the same problem can understand what is going on, because it can be either a very easy to fix problem, a DIY fix up to a true nightmare.

The K1000, to show the exposition, uses that small needle. This needle is placer between two "magnets" that vary their magnetic power according to the electrical power passing by the wires connected to them.
One of the magnets is connected to the light receiving cell, so when the light reaches this cell, the magnetic power if the upper magnet, increases it's power, moving the needle up.
The second magnet is connected to the speed and aperture switches, so when the aperture and/or speed is increased, the second magnet power is increased, and the needle moves down.

So now, if you have another SLR and you know that the exposure is correct in such camera, then point it to somewere where is light. Now set the ASA/ISO, speed and aperture to a value where the exposure is correct.
Now with your K1000, set the same parameters, and point to the same point.

If the K1000 needle says "overexposed", then the light receiving cells are wrong because it is receiving more electricity than it should, and this is probably because the resistors are not offering enough resistance.
If the needle says "underexposed" then the speed and/or aperture switches are wrong. The explanation is similar to the previos one.


In either case, there are two solutions:

1) The easy one: turn the ASA dial in the K1000 so the exposure is compensated. (I will give and example later) This can solve the problem if the maladjustment is little, for example, you use ISO film 200, and the K1000 requires set to 500 or 600 or whatever. But if the maladjustment is huge, then you will probably don't have enough ASA in the K1000 dial to compensate. In this case, you will have to go to 2), or just "deal with it".

2) Physically repair the camera: this requires to purchase new electronical components. You can do it yourself, it's not hard at all, but you will need a soldering machine and watchmaker tools to unscrew the camera screws. It is possible that the problem are the cables or soldering being in bad shape, so before purchasing or unsolder something, check out the cables.


Whatever, you can access the K1000 technical manual here: www.pentax-manuals.com/markroberts/k1000_man.pdf which will guide you to all the process to dissasembly and reassembly the camera, as well as an in depth description of this problem

So now an example: my camera is using right now an Fujicolor C200, which is a ASA 200 color film
I take one of my SLRs that I know the metering is correct, for example, a Zenit 122k. I meter the light in the neightbor's window, and at ISO 200, f/5.6 and speed 125, the exposition is adecuate.
Now I set the exact same parameters in the Pentax, but I it says me that it's underexposed. S I know now that the speed or aperture switches let pass too much electricity to the "magnet", so it's power is increasing, atracting the needle to the lower side.

Of course, it could be either the speed/aperture switches allowing to pass too much electricity, or the light metering not allowing to pass enough electricity, but according to the K1000 technical manual, it's likely the resistors lose their efectivity over time, letting pass more electricity than expected.

Now, to solve the problem in my camera, I changed the ASA dial to trick the camera, increasing the ASA, and making it to compensate the difference. With my camera, increasing ASA by 600, the problem is solved, and since I'm not going to use film with more than 2600 ISO (2600 + 600 = 3200, which is the maximun ASA allowed by the K1000 dial), then the problem for me is solved. I just need to remember to increase 600 to the film ISO and then put the correct number in the K1000 dial. So basically, right now my camera says ASA 800, but it is really ASA 200.



I hope this helps for anyone else with similar problems.

Cya.
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