SEI Photometer

[William Whitaker]

Wrote Huw (http://www.huwswebthing.talktalk.net/sei.htm) to inquire about converting one of my SEI Photometers to LED. His reply was brief: "Will, I don't do this anymore, best of luck!"

"Best of luck!". Right!

Does anyone else do this conversion? I have two SEIs and would like to convert one of them to LED for reliability. It's something I'd actually like to use for its intended purpose of photography. Perhaps someone has a suggestion. Any of you electronic wizards familiar with LED design?

[William Whitaker]

Guess I'll ask Quality Light Metric if they can calibrate it. And keep my fingers crossed.

[Bill Burk]

What's "wrong" with the ones you have?

My selenium cell doesn't drive the needle up as much as it should, so I calibrated to other meters and then drew a line on a "screen protector" where the needle does come to.

[Jerry Bodine]

Will, I have an SEI that I bought at the first AA workshop I attended in 1966 (at a discounted price as a workshop participant) and it's still working fine. Also have a Gossen meter that at one point I thought should have its calibration checked. So I had the Gossen calibrated (it was off a little), and then compared the SEI to the Gossen. All is OK now. BTW, in case you're not aware, AA only used the SEI to get reflectance readings in terms of candles/ft^2, then mentally calculated the shutter/aperture settings from that as follows:

The shutter speed is the reciprocal of the c/ft^2, and the aperture is the square root of the film ASA (box rating). For example: if the reading is 200 c/ft^2 with ASA 64 film, then a shutter setting of 1/200 sec at f/8 would result in Zn V exposure. Then he'd adjust that for the preferred zone placement. That process came in handy for the "Moonrise" image when he couldn't find his meter in the rush to set up the camera, since he recalled (from experience) the c/ft^2 of the moon when at that position in the sky.

[William Whitaker]

What's "wrong" with the ones you have?

Fair question. I'm not sure that there's anything "wrong" with mine. I had wanted Huw's mod basically for reliability. Alternatively, having the existing meter gone over by QLM would just be to confirm that it's working properly. I could probably tell as much by comparing it to another known working meter.

I don't need to use the SEI, but wanted to be able to use it. They're heavy and a bit clunky. But they're so nicely made it seems a shame to relegate them to the shelf (or box). And besides, with 12x20 the additional weight isn't that noticeable...


AA only used the SEI to get reflectance readings in terms of candles/meter^2, then mentally calculated the shutter/aperture settings from that as follows:

The shutter speed is the reciprocal of the c/ft^2, and the aperture is the square root of the film ASA (box rating). For example: if the reading is 200 c/ft^2 with ASA 64 film, then a shutter setting of 1/200 sec at f/8 would result in Zn V exposure. Then he'd adjust that for the preferred zone placement. That process came in handy for the "Moonrise" image when he couldn't find his meter in the rush to set up the camera, since he recalled (from experience) the c/ft^2 of the moon when at that position in the sky.

That Ansel guy was a nerd. A cool nerd. But a nerd. ;-)