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  • Welcome to the new site. Here's a thread about the update where you can post your feedback, ask questions or spot those nasty bugs!

Protecting the members from the "Imaging Technology" section

Doug Kerr

Well-known member
Hi, Asher,

I ask that you consider modifying the forum software so that posts to the "Imaging Technology" section would not be listed on a basic search for new or yet-unread posts.

Those few (if any) who are interested in the matters to which that section is devoted can easily go directly to that section every so often to see if these is anything there of interest to them.

This way the much larger fraction of the membership that is not, in general, interested in such matters will not have their daily "menu" diluted by items of no likely interest, which I have heard somehow impedes the general good.

Best regards,

Doug
 

nicolas claris

OPF Co-founder/Administrator
Doug
although I don't understand all your posts, they are fully part of photography's world and have to stand in front, like other matters.
It is very easy to ignore if some of OPFers do not wish to read.
your threads are most of the time to the very first importance and do bring light (when understood!).

One cannot be protected from knowledge!
 

Doug Kerr

Well-known member
Hi, Nicolas,

Doug
although I don't understand all your posts, they are fully part of photography's world and have to stand in front, like other matters.
It is very easy to ignore if some of OPFers do not wish to read.
your threads are most of the time to the very first importance and do bring light (when understood!).

One cannot be protected from knowledge!

Thank you.

Best regards,

Doug
 

Asher Kelman

OPF Owner/Editor-in-Chief
The correct approach is to consolidate threads that can go together when you discover such an affinity. At the same time we have to post more photographs.

I will do my part!

Asher
 
I agree with Nicolas, Doug. I start reading your threads and I do eventually get lost and not understand, but there are some of us here that do understand and should not have to hunt to find this information. I have no problem with it being grouped with everything else. You are not talking about planes, trains and automobiles, you are talking about cameras and lenses and it definitely has a place here.

I actually appreciate that you post them; just a little annoyed at myself that so much of it goes over my head.

:)
Maggie
 
Doug.. i generally read your posts and do get confused at times. i generaly poke the recent posts button and see whats new. if your tech posts didn't show up i probably not look somewhere else for them.
With all the ISO/ASA discussions, i am looking forward to your explanation of the Weston and GE ratings for their classic light meters. :) I have an old Weston Master II (actually i have a couple) and an old GE and their take on film speed is interesting. http://www.westonmeter.org.uk/speeds.htm
 

Doug Kerr

Well-known member
Hi, Duke,

With all the ISO/ASA discussions, i am looking forward to your explanation of the Weston and GE ratings for their classic light meters.

One concise discussion of that is here:

http://en.wikipedia.org/wiki/Film_speed#Weston

I have an old Weston Master II (actually i have a couple) and an old GE and their take on film speed is interesting. http://www.westonmeter.org.uk/speeds.htm
Nice reference. Thanks.

I never had either a Weston or a GE, but my father had a GE. My guess is that he got it in perhaps 1947 or so, which I think is when he got interested in photography. He used it with his Argus C-3.

Of course we're having fun. That why other people get so pissed off.

Thanks.

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi, Duke,

With regard to this note:

http://www.westonmeter.org.uk/speeds.htm

I call attention to this passage:

Up to the Master IV the scale on the dial is in cd/ft2 - foot candles, now known as Lumens.​

This is a real mish-mash of units and dimensionalities.

Indeed, in the Weston exposure meters of that era, the meter itself read in cd/ft² (a unit of luminance, as befits the basic role of the instrument as an incident-light meter).

The foot candle, however, is a unit of illuminance, corresponding to 1 lm/ft².

And the lumen (lm) is a unit of luminous flux. (It is one factor in the unit lm/ft², which is equivalent to the footcandle.)

Note that I present "footcandle" as one word (not customary) rather than the more customary foot-candle, because the latter suggests that the unit is the product of the candle and the foot, and it is not.​
In fact, the footcandle, in terms of the candle, is essentially the candle•steradian/ft² (more precisely, the candela•steradian/ft²; the candela is the SI version of the candle, but they are for all practical purposes the same unit.

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi, Duke,

With further regard to the Weston exposure meters, that same note says:

After the IV, Weston started to use arbitrary numbers. With the baffle open, the scale is from 0.2 to 50 and with the baffle closed, 25 - 1600.​

I only have the manual for the Weston Master V. I can't relate what I see there with the above. I will work from the manual.

In it, the scale with the baffle open runs up to 10, and with the baffle closed up to 16. Note that I don't say "0-10" or "0-16". There is a "0" at the bottom of both scales, and that is presumably the meter "zero point", but since the scales are logarithmic (more about that in a moment), as far as the units of the scale are concerned, this "meter zero" is actually minus infinity in both cases.

As I hinted above, my reverse engineering indicates that this scale is logarithmic in luminance. It seems as if the meter actually reads about Bv +3.8.

What that amounts to in cd/m² depends on the reflected light calibration constant used in this meter, but assuming some nominal value, at the top of the "low" scale (10 units) that is probably 250 cd/m² and at the top of the high scale (16) it is probably about 16,000 cd/m².

Ah - here's the manual for the Weston Master 6.

Yes, its two meter ranges are 0.125-32 and 16-2000.

I'll jump through all the layers of reverse engineering. It seems that the meter indications are probably in candles/ft² (candelas/ft², cd/ft²).

Oh, duh! It says that on the dial!​
Maybe some other model has meter ranges of 0.2-50 and 25-1600.

I'm about Westoned-out for one night.

But thank you for asking.

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi, Duke,

It is in fact the Western Master Universal Exposure meter, Model 715 (ca. 1939) that has meter scales of 25-1600 and 0.2-50!

I have not done any further reverse engineering of that machine.

It uses the exposure index in terms of the "Weston film rating". It works with aperture on the basis of f-number, but the manual gives equivalences for other aperture systems evidently still in use during its era.

The manual is, by the way, quite detailed.

Best regards,

Doug
 
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