testing spot lightmeter

[quigon]

Hello, I want to test my lightmeter. Is there a forum where the topic was already dealt with?
Thanks
Luigi

[BrianShaw]

Testing for what aspect of spot metering - accuracy, precision, correct exposure recommendation? Which spot meter?

If I'm checking out a new-to-me meter I "test" by comparing meter readings with trusted meters on a large surface and not worrying about minor differences. But most often, I shoot a roll of film and look at the negatives. If the negatives are reasonably exposed then the meter is reasonably accurate. Others might be more scientific about testing and demand higher criteria than do I.

[quigon]

Thanks for answering
It's a Pentax digital spotmeter. I cannot test by comparing because I have no other trusted meters.

[BrianShaw]

Thanks for answering
It's a Pentax digital spotmeter. I cannot test by comparing because I have no other trusted meters.

I'd suggest shooting B&W film in "normal" circumstances and look at the negatives to see if they appear "normal". For me this works best with general coverage and incident meters. With a spot meter you'll need to be careful that your spot metering technique does not abnormally skew the exposure.

Some people find comparing meter readings to "Sunny-16" to be a good way to assess a meter. That depends on how accurate Sunny-16 is in your location, though.

Did it once work correctly or is this a meter of totally unknown accuracy?

[quigon]

It still works, but now and then I get mistakes (the problem may be with me). I've gone through a couple of papers which made my doubts increase (Ctein, Post Exposure and Exposure Metering by Jeff Conrad here they demolish the myth of 18% reflectance calibration).

[Bill Poole]

If you have a smart phone, you can download MyLightmeter Pro ($4) or other metering app and use it to compare with the Pentax. In my experience, the My Lightmeter ap agrees with my several other meters. Hope this helps.

[ic-racer]

Adjust the ASA dial so that a film renders a photograph of a uniform target 0.1 density when underexposed 4 stops.
BTW 0.1 density is 1/3 of a stop. So you can use the meter to check the negative.

[Ulophot]

Two things, depending on your preferred subject matter and light levels for photographing, and how detailed you wish to be.

Meter linearity is an important characteristic to test. That is, is it accurate throughout the range? If not, resulting anomalies may drive you batty. Therefore, I would add to the "test in normal situations," that you test your target in direct sunlight, exposing it by the reading and three stops over (to put it in the domain of textured white, Zone VIII in the zone System); in open shade, ditto, and either indoors (if applicable) or outdoors in very low light.

The film speed test mentioned above is also important, and I am attaching the notes I have on this, copied from where I don't recall.

229249

Feel free to post back with further questions.

[xkaes]

No need to get fancy. Some people on this board have a tendency to go overboard.

It's easy to figure out if it's functional -- i.e., working CLOSE to correctly.

Meter off a gray card in sunlight, a northern blue sky, or put a white, Styrofoam cup over the front and point it at the sun.

That won't tell you if it's PREFECT, but it will tell you if it's defective -- if it isn't close to the f-16 rule.

[Lachlan 717]

Accuracy of your shutter(s) will be a much weaker point in your process than your meter.

Perhaps look at calibrating them first.

[quigon]

Thank you for all suggestions. Some months ago, when I made tests for film (fomapan 100 classic, Stouffer step wedge, BTZS procedure) I got consistent charts (I suppose). It's when I use the data in the field -- using the pentax spotmeter to read a kodak grey card for shadows and highlights, setting the film speed, and finally reading the shadows for exposure -- that I get overexposed negatives. Should I try to reduce exposure by 1/2 a stop?

[Huub]

When i started using a spotmeter - a Gossen spotmaster in my case - the one issue i had was seeing how deep the shadows where. In other words: what dark spot should i meter to get good shadow separation without over- or under-exposing the negatives to much. Comparing the shadow reading with a one or two points in the picture that should be more or less average - grass, blue sky - helped a lot, in combination with the growing experience while making pictures.

You could reduce your exposure by half a stop or work around this and tell yourself for example that in stead of metering a point in zone III you are metering one in zone II.5. The crux is to find a way that works for you with your equipment and materials.

[LabRat]

If to eliminate any doubt, you can have it calibrated by Pentax in Colorado, or Richard Ritter (on here)...

Any new to user meter should be calibrated (if meter is still supported by maker or facility)...

The Pentax digital spot meter is a rugged meter that holds calibration well, but compared to another meter to gray card should give you an idea of it is off at all...

Steve K

[Doremus Scudder]

If to eliminate any doubt, you can have it calibrated by Pentax in Colorado, or Richard Ritter (on here)...

Any new to user meter should be calibrated (if meter is still supported by maker or facility)...

The Pentax digital spot meter is a rugged meter that holds calibration well, but compared to another meter to gray card should give you an idea of it is off at all...

Steve K

Steve,

Does Pentax in Colorado really work on the digital spot meters? If so, I'd really like more information about them; contact info, etc., for future reference.

Best,

Doremus

[LabRat]

Steve,

Does Pentax in Colorado really work on the digital spot meters? If so, I'd really like more information about them; contact info, etc., for future reference.

Best,

Doremus

Hi Doremus,
Back in '99, I was shooting on the street and a guy came up to me and asked me if I wanted to buy a lightmeter... He said he worked in theater and had an extra one used to measure "ranges" on stage... We met the next day and I paid him $25 for a nice one... But when I got home, I noticed the 10's digit was out... I could have lived with that, but I drove over to Quality Light Metric for an exam... George there told me he forwarded it to Pentax Service in Englewood CO to perform the service, and he didn't charge me anything for the forwarding, and provided the invoice from Pentax... (I still have the invoice somewhere...) They did a great job...

This was 20 or so years ago, but have heard Pentax services their products (binoculars etc) recently, but not sure if they still service lightmeters, but easy enough to contact them... And I read here Richard Ritter services them, so there are options...

Probably good to have 'em checked before too long goes by... ;)

Steve K