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06-08-2010, 01:44 PM   #1
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Another Spotmatic Meter

I have a Spotmatic and a Spotmatic F. I have just installed Wein cells in each (still going through battery eliminations). The meters on each of these read differently though. Using the same lens on each (Super-Takumar 50/1.4) they read drastically differently. On the Spotmatic I get an f11:1/500sec exposure at iso 400. Pointing at the same object I get f5.6:1/125sec with the Spotmatic F at iso 400. What's up with that? My DSLR, BTW, reads it as f11:1/125 at ISO 200.

06-08-2010, 01:59 PM   #2
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QuoteOriginally posted by dmccardle Quote
On the Spotmatic I get an f11:1/500sec exposure at iso 400. Pointing at the same object I get f5.6:1/125sec with the Spotmatic F at iso 400. What's up with that? My DSLR, BTW, reads it as f11:1/125 at ISO 200.
F/11 at 1/500 sec is the same exposure as F/5.6 at 1/125 (same ISO setting).

F/11 at 1/125 (ISO 200) is one stop more light (toward over exposure) than F/11 at 1/500 (ISO 400) or F/5.6 at 1/125 (ISO 400).

Assuming the DSLR is correct, your Spotmatic cameras are 1 stop toward underexposure. This is probably OK given film latitude.

To ensure the test is valid, you have to fill up the viewfinder with a scene uniformally lit (a blank wall for example).
06-08-2010, 02:19 PM   #3
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What I don't get is why I can't get bvoth Spotmatics to read f11 at 500.

So I just tested again...pointing both at a blank wall. On the F I got 2.8 at 60; on the Spotmatic I got 2.8 at 250
06-08-2010, 02:27 PM   #4
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QuoteOriginally posted by SOldBear Quote
F/11 at 1/500 sec is the same exposure as F/5.6 at 1/125 (same ISO setting).

F/11 at 1/125 (ISO 200) is one stop more light (toward over exposure) than F/11 at 1/500 (ISO 400) or F/5.6 at 1/125 (ISO 400).

Assuming the DSLR is correct, your Spotmatic cameras are 1 stop toward underexposure. This is probably OK given film latitude.

To ensure the test is valid, you have to fill up the viewfinder with a scene uniformally lit (a blank wall for example).
No, I think you got confused with the stops. f11:1/500 isn't the same as f5.6:1/125. However, f11:1/125 is the same as f5.6:1/500. Is that what your cameras are telling you, dmccardle?

06-08-2010, 02:28 PM   #5
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QuoteOriginally posted by dmccardle Quote
What I don't get is why I can't get bvoth Spotmatics to read f11 at 500.

So I just tested again...pointing both at a blank wall. On the F I got 2.8 at 60; on the Spotmatic I got 2.8 at 250
Hmm, sounds like something really is wrong. Same ISO and everything? Did they meter the same before you did this mod?

Does the Spotmatic F have EV compensation controls? That might be throwing you off if not set to neutral.
06-08-2010, 02:32 PM   #6
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The Spotmatic F I have had for a while. I have gotten good shots out of it. The Spotmatic I just got. I have yet to process anything from it. Couldn't find a battery locally, so I ordered the wein cell. As long as I was doing it it for one I thought I'd get one for the F as well.

Yes same ISO. No EV Comp that I am aware of.
06-08-2010, 02:44 PM   #7
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Consider this:
  1. You don't need to use a Wein cell in either of your Spotmatics. The meter is not voltage sensitive. A 1.5v silver or alkaline cell will work just fine.
  2. Meter calibration can be off and can also be adjusted
  3. It is not unusual for two cameras to meter the same subject differently
If you are near a camera repair place, take your cameras in and have them evaluated for repair. If there is an issue with the meter, they will tell you. The evaluation is usually free.


Steve

BTW...you are aware that Wein cells have a finite life span once "opened" regardless of use?

Last edited by stevebrot; 06-08-2010 at 02:52 PM.
06-08-2010, 02:44 PM   #8
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Try metering all cameras with any 2 of these fixed to the same value:
- ISO - set your dSLR to 400
- f/stop -
- shutter speed -

With ISO at 400 on all three, and aperture at f/5.6, say, then the shutter speed readings will be directly comparable.


500/5.6 = 250/8 = 125/11, all equivalent EV exposures

On the DSLR, are you in stop down manual metering mode? If you are in aperture priority auto, on a Pentax dSLR you'll get an under exposure reading - usually my camera requires + 1 - 1.5 EV exposure compensation.

The other thing you might try: swap the batteries between the spotties, and see if you can reproduce the difference.

One last bit: a classic test is to point at a clear northern sky (in the northern hemisphere) to take a reading.

06-08-2010, 05:35 PM   #9
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Yes...I am aware of the short life span of the Wein's and the fact that I do not "need" them. I just thought that I would try them out to see if I got more accuracy with "perfect" voltage.

No...I cannot swap batteries as each camera requires a different size.

Yes...I did match f/stop. See above. At 2.8 I got 1/60th with one and 1/250th with the other. I think that the 1/60th was certainly closer to correct (the spotmatic F, with which I have gotten good results).

So it seems that the Spotmatic is off by a considerable amount. Don't I just remove the rewind lever and adjust something through the hole?

PS...thanks for all of the advise on this...and please keep it coming.
06-09-2010, 06:44 AM   #10
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Are you accounting for the Spot F doing open aperture metering?
06-09-2010, 10:26 AM   #11
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QuoteOriginally posted by Blue Quote
Are you accounting for the Spot F doing open aperture metering?
I'm not sure that I know what you mean?
06-09-2010, 01:28 PM   #12
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QuoteOriginally posted by dmccardle Quote
I'm not sure that I know what you mean?
Actually, since you are using the Super Tak 50mm f1.4 rather than the S-M-C or SMC, it wouldn't matter. I didn't catch that the first time.
06-09-2010, 01:55 PM   #13
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QuoteOriginally posted by Blue Quote
Actually, since you are using the Super Tak 50mm f1.4 rather than the S-M-C or SMC, it wouldn't matter. I didn't catch that the first time.
Yeah...I wanted to assure equal results
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