Questions about SEI spot meter.

I got a cheap SEI spot meter from that auction site. Missing the calibration meter but I'd read of the led mod that makes that meter redundant. Clever me. Except that the guy selling the led mod, Huw Ferris, isn't doing it any more it seems.

Has anyone else built an led conversion for it?

The bulb still works. Once I manage to get a battery fitted, I'll use a dmm in place of the missing ammeter (?) to get a calibration close to my Gossen. Assuming there is something for the dmm to measure,

fwir, the black dot is for negatives and the white dot is for slides because, as one review said: 'It was built for people that knew what they were doing'.

There is at least a 7 stop difference between the black and the white dot. Why?

If a photographer knew what they were doing, all they'd need would be an EV number and they could sort the rest out from there.

John51 said:

fwir, the black dot is for negatives and the white dot is for slides because, as one review said: 'It was built for people that knew what they were doing'.

There is at least a 7 stop difference between the black and the white dot. Why?

If a photographer knew what they were doing, all they'd need would be an EV number and they could sort the rest out from there.

Click to expand...

The SEI is calibrated differently than modern spotmeters.

A modern spotmeter is calibrated to give a middle gray tone. Because negatives should be exposed based on a reading of the darkest area you need to retain detail in, and slides should be exposed based on a reading from the brightest tone you need to retain detail in, the middle gray reading is rarely used as-is. Instead, you meter the dark tone then give a couple stops less exposure than it indicates (so it renders as black, but with detail); or you meter a white tone and give a couple stops more exposure (so it renders as white, but with detail).

The SEI is designed to let you do a dark-tone or light-tone reading without having to correct the reading!

If you can get your hands on a copy, there is a very detailed description of the SEI in the book "Exposure Manual" by Jack Dunn and George Wakefield. The 4th edition is the latest and most common, but it was published in the early 1908s so you'll have to find a used copy. The book's authors helped design the SEI, and the book tells how it works and how to use it in great detail.

It's great fun. You don't have to take it apart.

Lacking reliable ammeter and selenium cell, you can just position a standard light in front of the eyepiece and adjust the internal bulb to match that.

The standard light could be anything, I happen to have a 100 foot-lambert source.

But it doesn't matter what the light brightness is, you could Jerry rig a pocket-sized LED into a box with translucent screen... and compare the reading with your Gossen. Take it and run with it.

I get it now. Choose enough light for detail in the desired shadows (negs) or not too much light for the desired highlights (slide).

I took the tube with the bulb out and shone my phone torch through it. Found something that had the spot be white, adjusted the internal nd filter and the spot was dark. So I'm confident that apart from calibration, the innards are working ok.

Without the bulb tube, a D cell fits. With the bulb tube, not quite. I've just ordered an AA to D converter and the plastic shell looks to have enough meat on it to be turned down (or sanded/filed) to fit inside the tube.

Good fun up to now, definitely a 'fondle me' piece of kit. Nice to know that calibration can be done easily.