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  #1  
Old 28th February 2010, 02:27 PM
birdwall birdwall is offline
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Question Gossen meters

Hi there

I have an old Gossen lunasix exposure meter which seems to be accurate and reliable, but on the back there's a little legend which reads 'for incident reading set 50 ASA' Am I right in assuming this means set the film speed at half the usual value when using the diffuser? Even the instruction manual (which I obtained on-line from butkus) makes no mention of this.

Yours birdwall
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Old 28th February 2010, 02:51 PM
Mike O'Pray Mike O'Pray is offline
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Sounds as if they have missed "% of" after 50 and before the word ASA. There might be occasions when you should drop speed by half a stop but going to 50 ASA if you were using 400 ASA could be disastrous.

I can't work out why they would apparently pluck out of thin air the number 50.

Mike
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Old 28th February 2010, 06:12 PM
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What does the manual say? If you do not have one, which model is it?

The Lunasix 3 manual is here: http://www.butkus.org/chinon/flashes...3/lunasix3.htm (and various other meters here: http://www.butkus.org/chinon/flashes_meters.htm).
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Old 28th February 2010, 11:58 PM
lee l lee l is offline
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You set the meter for ASA 50 if you want to measure approximate Lux or footcandles using the chart for which that inscription is a heading. Set to ASA 50, read the EV off the meter dial after zeroing the meter needle. Then find that EV on the chart of which the 'with diffuser set ASA 50' is a part and read across the columns for equivalent Lux and footcandles. E.g. if you read EV 10 with the diffuser in place at ASA 50, that is approximately 5500 Lux or 500 footcandles.

Lee
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Old 1st March 2010, 12:18 AM
Mike O'Pray Mike O'Pray is offline
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Lee I think I understand what you have said but can you explain what use this would be if you have an ISO 400 film in the camera?

If the setting of 50 is simply an illustration of how the system for reading Lux and footcandles works then OK but it would seem that then synopsis of how it works hasn't made it very clear that it is just an example.

If the summary is a shortened version of a full explanation in the handbook then OK but that doesn't seem to be obvious from what birdwall has said or is it?.


Mike
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Old 2nd March 2010, 02:46 PM
lee l lee l is offline
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The chart on the back of the meter simply uses the 50 ASA setting to translate EV readings into approximate Lux and footcandle readings. This isn't commonly used in routine photographic practice. It's just an extension of the uses of the meter for reading in other units, and 50 ASA is the calibration point for which the Lux and footcandle numbers in the table on the back of the meter are correct. The translation from EV to Lux or footcandles would be wrong with the front dial set to another film speed.

This has nothing to do with setting the meter at a different film speed when using the incident dome. For photography, you use the film speed you prefer for a given film, which would be the same for both incident and reflected meter readings.

Some accessories that attach to the front of Gossen meters do require some compensation, but that's usually done with the compensation dial on the front of the meter. The accessories, for example the 15/7.5 degree selective metering attachment, have the compensation needed on a badge or stamped on the bottom of the accessory.

Gossen has a full set of manuals in English and German on their web site. Some may be found under a link to discontinued models.
http://www.gossen-photo.de/pdf/ba_lunasixf_e.pdf

The page describing the conversion chart is attached.

Lee
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Old 2nd March 2010, 03:23 PM
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Just to add to what Lee said, It should be remembered that photographic light meters don't give you a reading of the actual light level. They take the light level and do a series of calculations that translate the light level into camera settings based on film speed(ISO or EI) and where the particular meter manufacturer decides the mid point on the film curve should be (K factor for manufacturer).
Hence as Lee said, 50 speed gives actual light level readings with no calculations applied for camera settings.

My Minolta Spotmeter F will do the same except it must be set on 100 speed. From the output reading I can then lookup a conversion table to give cd/mē or foot lamberts. Not that I ever have as I wouldn't know what to do with a foot lambert if I had one.
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