Basing exposures on incident readings without adjustment will in some conditions result in underexposure, just as it would when using a gray card, unless compensation is made. The problem, as described by Davis, is as follows:
Originally Posted by bmac
"... although the meter's dome is designed to transmit 18% of the incident light, the normal pointer of the meter's calculating dial is fixed at the midpont of the normal 7-stop range. In other words, the meter cell assumes that the world is bathed in a 5-top range of uniform, shadowless light, but the calculating dial assumes that the cell's readings relates to the real world whre shade and shadows are every present and where 7 stops is the norm."
What to do when determing landscape exposures for B&W negatives by incident reading? Quick and dirty answers below.
1. Base your exposure on an incident reading in the shadows, but double the EFS (effective film speed).
2. Base you exposures on a highlight incident reading, but halve your EFS.
3. Base your exposure on an average of shadow and highlight incident reading, using normal EFS.
Sandy, that is very good information. I guess I need to stop worrying about what my brain is telling me is right or wrong, and concentrate on what prints best.
Thanks for all your help with this.
AZO and other graded paper blue light source
Pet store fluorescent lamps for marine tanks come in a variety of phosphors. Some mix long wavelength blue with other visible light, and others made for coral peak at 420 nm blue.
I am going to try them some time in a cold light box for a monochromatic lens I want to use for an enlarger (since there's not much point in using it for a camera!). Of course I will have to make an effort to equalize the light across a light box, but for contact printing I would hope that's more forgiving.
For example, Coral Sun Actinic 420 or Arcadia Marine Blue Actinic for linear 18-48" lamps, and SunPaq 420 nm Actinic for 65 and 96 W compact fluorescent. The latter will require special ballasts. The former should use whatever T8 ballast matches the standard phosphor in that size/wattage.
I woul avoid the high output (HO) ones because they usually have a specialty ballast.
I have not tried these yet, so don't break the bank yet.
According to my local, small-town electrical supply store R-40 standard base bulbs (yes, you do not want the mogul base), are a normal item. I was told they should not be hard to get and they should not be expensive. I recall paying less than $20 last time I bought one. Will try to check with the store next week and see what the current price is.
Michael A. Smith
Last time I checked, either Home Depot or Lowes's carried R-40 bulbs.
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The highest wattage I have found locally is 120w, but I think that should do fine for now.
I was unable to locate a retail outlet for the R40 300 watt lamp in my city. I finally located one at a electrical wholesale outlet. The cost was substantial in my estimation (above $25 as I recall).
I still contend that a mixture of fluorescent BLB and conventional fluorescent would probably be more efficient then the R40 bulb. The cost to fabricate a light source of this type would be more expensive then the R40 lamp, however.
I also believe, based upon testing by Sandy King on his Pyrocat dev, that a mixture of fluorescent BLB and conventional fluorescent (for the visual componant) would also provide higher effective contrast from a Pyrocat dev. negative then the R40 lamp. This gain would probably be on the order of .30 density units at the peak densities most are using on their Azo negatives.
The reason that I think that this would be true is that the Pyrocat stain is more actinic to UV then it is to light in the blue spectrum. The BLB fluorescent emits primarily in near band UV(A) whereas the R40 lamp provides it's primary exposure componant in the blue band insofar as use with Azo is concerned.
Azo is much more sensitive to UVA then it is to blue light.
Azo & Flourescent light
Originally Posted by Donald Miller
I found this post very interesting. Have you tried BLB flourescent light with Azo? Do you have any idea how much wattage would be required to make a feasible light source? I own a custom lighting business and could easily fabricate a prototype unit to play with. I certainly wouldn't mind having a light source that throws less heat than a 300 watt incandescent bulb! I am going to be at a workshop with Michael Smith and Paula Chamlee next weekend and when I return home could work on this.
I have worked with a single F15T8BLB and found that it exposes Azo much more rapidly then a 300 watt R40 lamp. I exposed a 4X5 neg and found that the coverage at 16 inches from the lamp to neg provided enough beam spread to easily illuminate an 8X10 negative (although I haven't exposed that large a neg with the single lamp). The problem that exists is that the BLB does not emit much visible light and that hinders burning and dodging. Possibly using a BL designation bulb (eliminating the Woods filter) may improve the visible light emission. I haven't tried that yet.
My exposure times with the BLB were on the order of 15 seconds at 16 inches removed. Whereas the R40 times were above 1 minute for the same negative. (light wattage reduction of 20 orders of magnitude and shortened exposure time of 4 orders of magnitude).
Insofar as the number of lamps, that would depend on the size of the negative that one would be exposing. I have thought of using 4 each F15T8BLB in conjunction with 2 each T8 cool whites (or similar) to expose my 12X20 negs. I would imagine that one would want some diffusion under the lamps to assure even coverage (depending on the lamp arrangement). I figured that this would require 3 electronic ballasts at about $25 and change each (my cost) The lamps would be about $55 (total) my cost. Then there would be the enclosure cost.
If you decide to play with this, please inform me of your results.
Thanks and regards,
I went out and got the highest watt r-40 bulb I could find. 250 watt. I could not find a frosted one and when I hung it up-about 3 ft above the sink-the illumination was not consistent. even after leaving it on for a while, so I returned it and got abother. The new one had the same problem, so I returned this and guess what the new one had the same problem. Is this normal, and will it print evenly?
Technological society has succeeded in multiplying the opportunities for pleasure, but it has great difficulty in generating joy. Pope Paul VI
So, I think the "greats" were true to their visions, once their visions no longer sucked. Ralph Barker 12/2004