In the Black and White Handbook by Roger Hicks and Frances Schultz, mention is made of the above. It fits over the lens of the camera and transforms the metering into incident metering.
The picture of it suggests that it is like the diffuser used under the enlarger lens for colour analysis. It also doubles as a lens cap.
Sounds like a useful accessory for those of us who are generally satisfied with our camera metering but need the benefits of an incident meter on occasions.
Can this still be obtained and at what price and does it come in different sizes for different lens? It's shown with a Nikkormat but I am assuming that it isn't Nikon specific.
Incidentally a very useful book for those looking for wide coverage of monochrome techniques but which is also very readable. Full of photos illustrating the content without once lapsing into "dryness"
Thanks for any contribution from those have any knowledge of this accessory.
Thanks for the kind words. The Expodisc is indeed still available, in many sizes, but in the process of being reborn the price has gone up very significantly. It's imported into the UK by (I think) Morco -- but a web search should find it. It's currently sold for setting white balance on d*g* as much as for exposure determination and there's a warming-filter version, but I believe the neutral version still works for exposure determination.
Originally Posted by pentaxuser
And while I'm at it I'll plug www.rogerandfrances.com...
I haven't seen the new Expodiscs, but have two from the original maker. The front piece is a sheet of clear plastic "pyramidal" diffuser, as often seen over flourescent lighting fixtures in the US. The back (lens side) is a milky white plastic. My understanding is that neutral density and color balancing filters are sandwiched between to provide an 18% neutral gray. In the originals, they were individually tested to meet specs.
It might work under the enlarger lens as you describe with some compensation, but the intended use was to shoot a frame in the camera through the Expodisc at the metered reading under the same illumination source as your subject. This is equivalent to a gray card shot under the same lighting as your subject and the resulting negative could be placed in the enlarger and read with a color analyzer for correct filtration and exposure. Likewise it can be used to set color balance for a digicam.
I mostly use mine to make pre-exposures for contrast control and to shoot even frames for zone system testing on rollfilm.
The originals are not threaded, but the plastic is sized to be a squeeze fit into standard thread sized. Mine are still fine for this after 20 years or so.
As Roger mentions, prices seem to have increased significantly. In part this could be explained by the much higher prices of the gel filters used for ND and color balance in the sandwich. I forget the specs, but the originals had very tight tolerances, a very small fraction of a stop.
The original maker died several years ago. I thought the family had decided to carry on making them, but don't really know who owns the rights and manufactures them now. I suspect increase overhead because of this may have also influenced the price rise.
The originals also had a 12 inch string leash attached so that you could hang it off your camera strap.
I have the same version as Lee, now apparently called the "Classic" and apparently being cleared out (in the US at least)
It came off the auction site and was supplied with a card giving the original densitometer readings of .00 Red, .03 Green and .00 Blue for colour and Transmission of 18% +/- 1/6 of a stop. It still works fine, but is now getting expensive to buy new.
I have two of these discs. The 52mm one and a 72mm one. I believe that the 52mm one is now discontinued. As 52mm was the filter size for around 80% of Nikkor lenses, I believe that was the reason it was made then and now discontinued.
The daughter of the inventor figured out the ExpoDisc had uses for determining correct white light values for the new wave of electronic cameras. She was right, it is brilliant at doing that. As a consequence, manufacture has shifted from the analogue manual focus system to the electronic auto focus systems. The new ExpoDiscs do come with a neck lanyard which is heaps better than the waxed string that both of mine came with.
Now to the question originally asked. The Wallace Expos Disc, can be used under an enlarger once you have referenced your analyser to a neutral grey.
I had letters and telephone calls between Bob Mitchell in America about this, in conjunction with his COLORBRATOR for colour negatives.
Bob was kind enough to send me one of his own thin plastic diffusers which I cut to size and installed in my swing in/out red filter holder. It transmits considerably more light than the ExpoDisc does. Experiments told me that the ExpoDisc works brilliantly under the enlarger, but you will need a strong enlarging light coming through, otherwise your analyser won't have enough light to get a correct reading.
I myself run the Jobo Color Star analyser, which is the original and very basic version of these analysers.
The "mitchell COLORBRATOR" is pretty much the best system I have had the pleasure of using to get correct colour printing colour negatives.
It is the invention of the late Bob Mitchell and is designed to get your system colour correct so that you can then evaluate all of your other negatives.
It comes with a colour negative that you insert and make a print with. From that print you use the supplied neutral grey card with the hole in it, to scan the colour print you have just made. You locate the equal colour square on the colour print to the card with the hole in and use that exact square to adjust your analyser to neutral, (or whatever).
I then had a perfect neutral grey and I also knew what density (or time) was required to make a colour print.
When out shooting I used the Wallace ExpoDisc on one frame in the light I was shooting under. Basically I used my Nikon F3 by puting the camera into A for aperture priority and just hit the shutter button. It didn't matter whether it was a fast or slow shutter, the camera is just recording a neutral grey across the whole frame.
Back in the darkroom I would put a neg in I wished to enlarge. I would compose it as I wished then replace that neg with the frame which was exposed with the ExpoDisc. Put the analyser probe under the easel and adjust the enlarger filters until the analyser was satisfied.
Then I just replaced the original negative I wished to use and exposed. Invariably the very first print of a session was 99% correct. That system is that good.
Bob Mitchell also had a "MITCHELL GRAY KEY" which he also sold. The idea of the Gray key was that this was a piece of material with a key ring hole that could always be carried by the photographer. It is basically a piece of Laminex which is about the same reflectance as any grey card. It is brilliant and works as well as the Wallace ExpoDiscs.
I bought the Wallace ExpoDiscs as they were/are a way to turn your camera meter into an incident light meter and also allow you to test shutter accuracy etcetera.
If I was starting out I would be very tempted to purchase the "mitchell COLORBRATOR" as well as the "GRAY KEY" as a way to get a quite good consistent system in your colour darkroom.
Last edited by Mick Fagan; 12-30-2006 at 12:17 AM. Click to view previous post history.
Reason: Error and spelling.
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Funny to see this thread! I was digging through a box of photo gadgets in the back of my closet the other day and found a 52mm ExpoDisc which I had forgotten about. I bought it years ago and could never make up my mind whether I really liked using it instead of a small grey card. The one thing I do recall, though, is that it didn't serve very well as a lens cover. It wouldn't stay on the lens when pressed into the threads, so I hung it around my neck when it wasn't inside my camera bag.
Thanks all for replies. Once again a question asked on APUG is a question comprehensively answered.
Roger I'll check out Morco.
Peter and others. Yes it looks as if the price has risen substantially and it's all about its digi application, as you'd expect nowadays.
I don't think that the price has risen at all.
The ExpoDisc was always extremely expensive. If you take into account inflation, the extras that you get with the latest version; very good and better neck strap holder and a DVD with how to instructions and many tips and hints. It's a better deal, relatively. :-))
All I got with both of mine were a sheet of paper and a piece of waxed string.