Sinar Booster1 metering

[Chris Bronson]

I recently acquired a second-hand Booster1 probe (525.11) to take advantage of the film plane metering capabilities of the Sinar backs.

One issue is puzzling me. When I am metering a 18% grey card with the probe, I am getting a +1EV difference compared to the reading I am getting with a Minolta Spotmeter F. The difference is consistent (+/- 0.1EV) across all the DB lenses I tested.

To all Booster1 users on APUG: are you experiencing a similar metering shift with your probe?

Thanks

Chris

 

[David A. Goldfarb]

Are you accounting for bellows factor?

 

[Chris Bronson]

All measurements were made with focus to infinity.

 

[David A. Goldfarb]

Sounds like a calibration issue, presuming there aren't other factors like the angle you are using with the spotmeter. Transmissive loss is another factor, but I'd expect that to be within 1/3 stop with modern lenses. Doesn't the booster have a calibration dial on it? I haven't used the Sinar Booster I, but I have a Minolta Booster for the Flashmeter series, and I thought most of these had a gain control on the booster.

 

[Chris Bronson]

The Sinar Booster1 is factory calibrated and has no gain dial as the Minolta Booster does.

 

[MattKing]

By chance has the ground glass been replaced on the camera?

 

[Chris Bronson]

The Sinar Booster1 meters on the film plane. There is no ground glass between the lens and the probe.

 

[MattKing]

The Sinar Booster1 meters on the film plane. There is no ground glass between the lens and the probe.

Thanks Chris. I clearly had it confused with something else.

 

[Captain_joe6]

Matt, I believe you're thinking of a Gossen attachment that consisted of a fiber-optic 'wand' that one pressed against the ground glass in order to get a reading. Foolishness, all of it.

I can't figure out why your booster would read a higher reflectance than the spot meter by itself, its usually the other way around. Another possibility that comes is some sort of flare in the optics of the spot meter, but that shouldn't be enough to cause a 1ev difference, and almost certainly not in a consistent way. It may also be, now that I think of it, that the meter is entering a different mode when the probe is plugged in, and perhaps that mode is set to compensate 1ev over reflected direct metering. Just a thought.

All the same, meters disagree all the time. Trick is to have one that is consistent and to trust that it works well all the time. It could be outside ISO spec by 200%, but if its consistent and linear, it wouldn't matter at all.

 

[Chris Bronson]

Thanks. One other factor could be the light comming back in from the ground glass. The use of some sort of dark cloth is necessary to block the backlight.

I agree with you Patrick. It doen't really matter as long as the readings are consistent and linear. I am mainly trying to find out if all Booster1 probes have this shift or if it's just mine.