Calibrating Meters

[abhoan]

I am currently using a Hasselblad 500c with a Kiev TTL metered prism (yes, i am poor). I just started using it and I wanted to calibrate it before I go out and start shooting. I have a minolta IV flash meter and a Canon 5dmkii to make metering comparisons.

Now I don't have a grey card, would I specifically need one if I wanted to calibrate the meter? Or is there any other way for me to do this?

[ic-racer]

Look up "Zone I Exposure Index Testing"
Basically you shoot a target at Zone I, metered with the Kiev prism, at various exposure index settings on the meter. Choose the negative with a transmission density that is one-third of a stop more dense than a blank negative; use that one as your exposure index for your prism meter.

[Leigh B]

Forget all the zone nonsense. Go out and take some pictures.

On a nice sunny day, go find some nice scenics (urban or rural, whatever).
Meter the first one. If the reading seems reasonable for your film based on 'sunny 16',
shoot a three-shot series at exposures of -1/2 stop, nominal, and +1/2 stop (or -1, 0, and +1 if you prefer).

Do the same with the other three scenes.

Develop the roll and see how it looks. And you'll have some decent negatives to print.

- Leigh

[afrank]

You can customize your meter readings using the spot metering on the camera to read values on the usual shadow areas of subjects you shoot, i.e: Landscapes usually expose for the landscape and not the sy, the sky can throw off the meter.
While calibrating avoid white surfaces, its better to meter on brick walls or alike or surfaces that are not glossy. Use different setting of reciprocity to test whether the meter is working correctly, i.e: f4@1/60. f8@1/30.... etc for 1 low light situation, one medium and high (related to the min and max of your meter [my yashica tlr goes as low as f3.5@1/30 but my minolta slr can go down to f1.7@1/30] ).

Further testing can be done by making sure the components are working correctly using a volt/amp meter, i.e: Resistors have to be in the right range, photocells/cds/photo-resistors can go bad and give ~0.1 ohms readings on both light and darkness, ussually its around 4-10kohms o light and +1mohs on darkness.
You can also use 3v batteries or combinations of them to make the meter more sensitive to light, and change the resistances accordingly to calibrate (a variable resistor or potentiometer works best for this.) ussually there are various variable resistors in the camera, turn them with a flat screwdriver or scissors and see the needle move as current passes through it.

Good luck!

[Leigh B]

...there are various variable resistors in the camera, turn them with a flat screwdriver or scissors and see the needle move as current passes through it.

Can you think of any better ways to totally screw up the calibration of the camera?

[cliveh]

For the meter prism on my Hasselblad, I set to film speed and maximum lens aperture. It’s that simple.

[afrank]

Can you think of any better ways to totally screw up the calibration of the camera?

Nothing is beyond fixing, not if you know what you are doing. I just point in the direction, its easier to go about things once you know what to look for, of course it depends on how much calibration he needs. One of my cameras needed new CDS/Photo-resistors and I just gave it some extra EV range by changing from 1.5 to 6v using 2 cr1616 and compensating on the high end of the EV range with a bigger Variable Resistor on the post-CDS section of the circuit (this controls high light situations and wont mess with low light sensitivity.) After that is just a matter of tunning (move the variable resistors) up and down to let more current or less pass through the circuit as to the meter needle align with the markings.

As a side note, 2 photo-resistors/CDS in parallel allow more current(more sensitivity to light) and 2 in line decrease it.

Example:

http://www.willegal.net/photo/srt/sr...functional.htm

[cliveh]

Nothing is beyond fixing, not if you know what you are doing. I just point in the direction, its easier to go about things once you know what to look for, of course it depends on how much calibration he needs. One of my cameras needed new CDS/Photo-resistors and I just gave it some extra EV range by changing from 1.5 to 6v using 2 cr1616 and compensating on the high end of the EV range with a bigger Variable Resistor on the post-CDS section of the circuit (this controls high light situations and wont mess with low light sensitivity.) After that is just a matter of tunning (move the variable resistors) up and down to let more current or less pass through the circuit as to the meter needle align with the markings.

As a side note, 2 photo-resistors/CDS in parallel allow more current(more sensitivity to light) and 2 in line decrease it.

Example:

http://www.willegal.net/photo/srt/sr...functional.htm

What on earth are you talking about?

[afrank]

For the meter prism on my Hasselblad, I set to film speed and maximum lens aperture. It’s that simple.

I think he means to calibrate a meter that is not metering correctly even with the correct ISO and shutter/fstop settings.
This involves using the variable resistors that are meant for proper calibration. You can even use the batteries of you choice (no weird conversions necessary) given that the built in resistors give you enough playing space (4-50kohms).

[BrianShaw]

What on earth are you talking about?

No offense intended to "afrank", but: +1.

Please remember, Mr Frank, that many people here are not electrical engineers so that kind of advise could cause some to end up with a pile of scrap rather than a working meter.