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09-03-2015, 07:57 PM   #31
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QuoteOriginally posted by monochrome Quote
Good grief - is there anything you don't know?
I am bored.

This issue of the Spotmatic battery requirements has been an irritant to me for some time. I knew the bridge was unbalanced, but also knew that most users had few if any problems with available silver cells (e.g. 387S). Throw in the fact that Eric offers calibration of Spotmatics to the 1.55v cells and we have yet another puzzlement. Today, I finally spent some time with the available manuals at pentax-manuals.com as well as doing a careful read of the thread linked above.

The meter in the Spotmatic F, as noted above, is different and more similar to that in the K series cameras and is a whole 'nother beast. That being said, the pdf for the SP F at pentax-manuals.com has schematics for all variants as well as interesting summary tagged on affirming that the meters are "relatively immune" to battery voltage variations.


Steve

09-15-2015, 05:36 AM   #32
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Well, a Spotmatic (the original model) is on the way, sans batteries... and I will be shoving in a suitably sized 1.5-ish volt cell and checking the metering against a K-5 to see how things roll. If there's a consistent offset, I'll adjust accordingly when I set the film speed. If not, then it's Sunny Sixteen (and associated rules) all the way and we'll see how THAT goes. Good thing the film I've been buying still has the exposure guides printed on the inside of the packets!
09-15-2015, 05:47 AM   #33
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QuoteOriginally posted by pathdoc Quote
I'll adjust accordingly when I set the film speed. If not, then it's Sunny Sixteen (and associated rules) all the way and we'll see how THAT goes.
Sunny 16 can help in spotty light scenes, since it is related to incident light rather than reflected light. It can moderate a "bright spot".
09-15-2015, 07:55 AM   #34
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QuoteOriginally posted by stevebrot Quote
I am bored.

This issue of the Spotmatic battery requirements has been an irritant to me for some time. I knew the bridge was unbalanced, but also knew that most users had few if any problems with available silver cells (e.g. 387S). Throw in the fact that Eric offers calibration of Spotmatics to the 1.55v cells and we have yet another puzzlement. Today, I finally spent some time with the available manuals at pentax-manuals.com as well as doing a careful read of the thread linked above.

The meter in the Spotmatic F, as noted above, is different and more similar to that in the K series cameras and is a whole 'nother beast. That being said, the pdf for the SP F at pentax-manuals.com has schematics for all variants as well as interesting summary tagged on affirming that the meters are "relatively immune" to battery voltage variations.


Steve
Unbalanced or not this a shot with the SPF, "new battey" and slide film.



I think it's fine.

09-15-2015, 08:38 AM   #35
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QuoteOriginally posted by Cuthbert Quote
Unbalanced or not this a shot with the SPF, "new battey" and slide film.
Looks good. Which "new battey" are you using?

(Actually, maybe forget that, because the plain old Spotmatic will want a different one from the F, won't it?)
09-15-2015, 10:29 AM - 2 Likes   #36
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QuoteOriginally posted by pathdoc Quote
Looks good. Which "new battey" are you using?

(Actually, maybe forget that, because the plain old Spotmatic will want a different one from the F, won't it?)
I wrote it previously, it's a standard Varta PX625, I also have a SP1000 but I still have to change the battery.

In short, don't worry, shoot a test roll and be happy, 90% of the stuff you read on the net are mental masturbations of people who stay in front of the computer for too long and shoot too little.

Another shot of the SPF, the Varta battery, the Tak 50mm f1.4 and Agfa 100:


Last edited by Cuthbert; 09-17-2015 at 12:14 PM.
09-22-2015, 11:42 AM   #37
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Well, it arrived, and just for the fun of it I'm shooting the first roll sans metering, sunny sixteen and associated rules only (as described in the film packaging - yes, modern film still includes the basic pictorial guide inside the cardboard box!). It's a very different beast to hold than any of the other cameras I've owned so far, but by far the biggest mental "gear change" required after several months of using Takumars on the K-5 is remembering to leave the lens on auto and use the metering switch on the camera to stop it down!
09-23-2015, 09:48 AM   #38
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Okay, results. I put in an "InfiniCell" SR41W/392 cell, rated at 1.5 volts.

Using my SMC Takumar 55mm f/2.0 lens on both the Spotty and my K-5, I aimed at the same general area on my office wall (as close to the same spot as I could get every time). The lighting is practically all artificial, and the testing was completed within a few minutes, so I don't think natural lighting variations had any effect. The lens was wide open. I used centre-weighted metering on the K-5, with the green button in manual mode. Using spot metering on the K-5 made about another half-stop of difference SOMETIMES, depending on exactly where I pointed the K-5.

At 200ASA, the Spotty wanted 1/60 and the K-5 1/125.
At 400 ASA, the Spotty wanted 1/125 and the K-5 1/250.
The same relations were maintained at 800 ASA and 1600 ASA, which is where the Spotmatic quits.

Given that I cannot easily obtain film slower than 200ASA (200 and 400 are all I can easily get in the stores where I am), I did not think it practically worthwhile to continue the test at lower speeds.

CONCLUSIONS FROM THIS BRIEF TEST: With the InfiniCell SR41 or 392 cell, the Spotmatic would overexpose by one stop at every ASA setting, and I should set the ASA one stop faster than is on the cartridge.

I will subsequently test it against the Pentax P3 and/or P30T, so as to compare film camera against film camera and report back when this is complete.

ETA: I have a Pentax ME immediately to hand, and under the same conditions as above it renders the following results:
200ASA - agrees with Spotmatic (1/60)
400ASA - wavers between 1/125 and 1/250. I give 1/125 the benefit of the doubt here, especially considering that at...
800ASA - Agrees with Spotmatic (1/250)
1600ASA - Agrees with K-5 (1/1000)

Make of this what you will. The P3/P30T test will be the decider.


Last edited by pathdoc; 09-23-2015 at 10:02 AM. Reason: Additional data
09-23-2015, 11:02 AM   #39
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QuoteOriginally posted by pathdoc Quote
Okay, results. I put in an "InfiniCell" SR41W/392 cell, rated at 1.5 volts.

Using my SMC Takumar 55mm f/2.0 lens on both the Spotty and my K-5, I aimed at the same general area on my office wall (as close to the same spot as I could get every time). The lighting is practically all artificial, and the testing was completed within a few minutes, so I don't think natural lighting variations had any effect. The lens was wide open. I used centre-weighted metering on the K-5, with the green button in manual mode. Using spot metering on the K-5 made about another half-stop of difference SOMETIMES, depending on exactly where I pointed the K-5.

At 200ASA, the Spotty wanted 1/60 and the K-5 1/125.
At 400 ASA, the Spotty wanted 1/125 and the K-5 1/250.
The same relations were maintained at 800 ASA and 1600 ASA, which is where the Spotmatic quits.

Given that I cannot easily obtain film slower than 200ASA (200 and 400 are all I can easily get in the stores where I am), I did not think it practically worthwhile to continue the test at lower speeds.

CONCLUSIONS FROM THIS BRIEF TEST: With the InfiniCell SR41 or 392 cell, the Spotmatic would overexpose by one stop at every ASA setting, and I should set the ASA one stop faster than is on the cartridge.

I will subsequently test it against the Pentax P3 and/or P30T, so as to compare film camera against film camera and report back when this is complete.

ETA: I have a Pentax ME immediately to hand, and under the same conditions as above it renders the following results:
200ASA - agrees with Spotmatic (1/60)
400ASA - wavers between 1/125 and 1/250. I give 1/125 the benefit of the doubt here, especially considering that at...
800ASA - Agrees with Spotmatic (1/250)
1600ASA - Agrees with K-5 (1/1000)

Make of this what you will. The P3/P30T test will be the decider.
There's something you didn't consider in your test: the Spotmatic has a plain average lightmeter, while the ME is strongly centere patterned meter with a peculiar pattern...rarely my Spotmatic agrees with other cameras.
09-23-2015, 11:59 AM   #40
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QuoteOriginally posted by Cuthbert Quote
There's something you didn't consider in your test: the Spotmatic has a plain average lightmeter, while the ME is strongly centre patterned meter with a peculiar pattern
I accept this - I simply offer up the ME findings as additional data and because, out of the two other cameras I had immediately available, it is far more comparable in technology to the Spotmatic than the K-5 is.

In your opinion, should I repeat the test with the K-5 set to matrix metering?

The P3 and the P30T ought to have the same basic sensor and metering pattern as each other, unless someone can tell me they changed things radically between models, and I have the P3 loaded with 400ASA film plus a 200ASA cartridge (awaiting processing) that I can put into the P30T to tell the DX coding what to do. This will be a much more limited range test, true; but as these are the only two film speeds I can easily get hold of, it makes no practical difference what the results are at higher or lower sensitivities. I'm not exactly sure how the camera interprets things inside, but I still have a feeling it's closer to the Spotmatic than the K-5. Correct me if I'm wrong.

ETA: With the K-5 set as before, except matrix metering on, results are UNCHANGED from above.

Bizarrely enough, when I had an FA50/f1.4 on, set it to aperture priority to make sure the camera couldn't change that on me and ran the same test, it agreed with the Spotmatic. When I ran it in manual mode with f/2.0 set on the aperture ring, it agreed with the previous findings above. Using the f/2.0 55mm Takumar, it makes no difference whether I use Av or M mode.

Truly the ultimate arbiter will be to shoot a roll relying on the Spotmatic's metering, with the sensitivity set per the film box, and see what happens. I suspect, but cannot prove, that the Spotmatic is telling me what it wants best for film and the K-5 is telling me what it wants best for its sensor/processor, but I don't have the time to do a direct head-to-head shoot of exactly the same subjects and I will settle for being pleased (or displeased) with what the Spotmatic serves up. If everything's overexposed, I'll know what to do next time.

Last edited by pathdoc; 09-23-2015 at 12:14 PM. Reason: Additional info
09-23-2015, 12:22 PM   #41
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If you test it against an evenly illuminated wall you may find that average or cecenter weighted should be same
Now try changing the light on the wall or location, not just the ASA/f/speed settings, you are taking one point all the time
09-23-2015, 12:28 PM   #42
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I don't have that flexibility, unfortunately, either in lighting or in time. I wanted a reasonable, practical set of variables that could easily be controlled, right down to using the same lens in all cases (thank God for the M42/K adapter). If I get time, which is at a premium with a young family and busy job, I might do a more exhaustive test out in the field, but the weather is shifting at the moment with variable cloud and sun, which means I might not be able to rely on constant light throughout the experiment. As things are, I can bring the P3 and/or P30 to my office any day I want and know the lighting conditions are going to be close enough to the same to be of no real difference - film has more latitude than the ambient-plus-artificial light changes I get during the day. Science has its basis in reproducibility, and uncontrolled (and worse, uncontrollable) variables are the curse of good science.

On this occasion, I consider the fact that I have established a linear and predictable relationship between my DSLR and the Spotmatic to be a definite bonus. My worst fear, which is that results would be all over the shop, is unfounded. The ultimate practical test (a full roll of film) is yet to come. That trumps everything.
09-23-2015, 12:53 PM   #43
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That you are within a stop over then you are in ideal range particularly for most all C41 and b&w film.
09-23-2015, 02:35 PM   #44
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QuoteOriginally posted by titrisol Quote
If you test it against an evenly illuminated wall you may find that average or cecenter weighted should be same
Now try changing the light on the wall or location, not just the ASA/f/speed settings, you are taking one point all the time
Yes this is correct, but the OP can't do that the best solution is to shoot a roll of film and see the results.

I would start with C41 colour, if positive he can try with the E6.

Also there are other reasons besides the battery that might cause an error in the lightmeter, oxidiation of the CdS is one thing.

However, another difficult to meter shot with E6:



And anther C41 one:

09-23-2015, 04:48 PM   #45
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I don't shoot slide film and doubt I could get it anyway, so it's C41 or nothing. I can try asking them to do two runs with and without exposure correction at the printing phase.

ETA: P3, loaded with 400ASA film and with the Takumar 55/2.0 mounted, wants 1/125 - i.e. agrees with Spotmatic (and I retried the Spotmatic immediately after with the same lens and settings, and it still agrees with yesterday's figures). I will try again tomorrow with the P30T with a 200ASA cartridge in it, but I think I know what the answer is going to be.

Right now, the fact that a quick check against two other film bodies supports the Spotmatic's readings tells me that I should trust it.

Last edited by pathdoc; 09-24-2015 at 03:57 AM.
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