Timing/Evaluating the UV exposure for the 'archaic' print processes

KenS

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Since my retirement I have 'taken more' to making prints using the 'archaic print processes' under my home built UV light source. Timing the required exposure becomes somewhat "risky" when using the 'peeking' to see if the exposure time
has been 'adequate'. So.. I 'invested in a battery-powered UV exposure 'light meter' ... a little more $$ than I expected,.. but has proven to have been a 'worthwhile' investment.. no more 'peeking' and chancing the loss of good 'registration' after checking to see if the 'density' is 'adequate. The total UV illumination 'dose' is provided as a 'numeric' value... and I know when the print exposure has been adequate for the process. My 'personal tests that it works just as well when using direct sunlight as a UV light source.

Ken
 

mark

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Can you please explain how this works? I'm interested.
 
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KenS

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mark said:
Can you please explain how this works? I'm interested.
Click to expand...


go to www,LightMeasure.com to get all the information you need

Works like a 'charm' in the 350 to 400 nm

Ken
 

MattKing

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KenS

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mark said:
Can you please explain how this works? I'm interested.
Click to expand...

Mark, There is a sensor 'placed' close to the paper onto which you have applied the 'emulsion' and the wire 'plugged into and 'connected' to the "unit' that is placed outside' the 'whole' setup. The sensor reads the 'amount' of the UV light (on a continueous basis) that the sensor (AND the back of the negative that has been laid on top of the 'emulsion'and over-time records the 'amount' of UV radiation over time. Usually, the proper exposure time has been 'acquired'by 'testing'.. the same manner that you may use for getting the correct exposure time for a 'standard' B/W print under your enlarger. However the UV 'recorder is reading the 'total amount' of the UV radiation (over time) that the film side of the negative that has been placed 'emulsion side down' onto the hand applied UV sensitive 'emulsion' on the paper. It can also be used if you are 'relying' on the UV part of the spectrum emitted by the sun when outside in the back yard.
The sun's 'natural' UV radiation is what gives YOU that summer 'sun tan' that helps to prevent further 'damage' to the skin over 'time'

Ken
 

MattKing

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If I understand these correctly, unlike the light meters we use typically in photography, which measure the intensity of light, these measure the accumulation of total UV exposure.
They are sort of like a rain gauge for UV, instead of water.
 
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KenS

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MattKing said:
If I understand these correctly, unlike the light meters we use typically in photography, which measure the intensity of light, these measure the accumulation of total UV exposure.
They are sort of like a rain gauge for UV, instead of water.
Click to expand...

Matt,
"Well said" sir..
You could not come up with a better 'analogy' I now wish I could have expressed the 'how' as "easily" and "readily"
 

Vaughn

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It measures both the amount of incoming UV light and the total dose (the total amount of incoming UV over time).

I have one -- quite useful when dealing with different UV light sources. It will get one pretty close. One of the 'archaic' processes I use does not allow for peeking at a printing-out image to judge exposure.
 
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KenS

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MattKing said:
If I understand these correctly, unlike the light meters we use typically in photography, which measure the intensity of light, these measure the accumulation of total UV exposure.
They are sort of like a rain gauge for UV, instead of water.
Click to expand...

You got it "Right on the nose" feel free to give yourself a "Pat on the back". Different "Alt 'emulsions require "significantly" different exposure times and this unit/meter it saves all the "peeking"

Ken
 

Vaughn

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MattKing said:
If I understand these correctly, unlike the light meters we use typically in photography, which measure the intensity of light, these measure the accumulation of total UV exposure.
They are sort of like a rain gauge for UV, instead of water.
Click to expand...
They do measure the intensity of the UV light. In the images of the meter, the figure in the upper right ("In") is the intensity of the UV light. These meters are relatively cheap...one reason is that they are not calibrated...I think the word would be precise instead of accurate. They give repeatable results, but do not try to match one meter to another, or use them to determine the actual amount of UV present.
 

MattKing

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Vaughn is correct.
What I should have said is that "unlike the way we typically use light meters in photography, which concentrates on measuring just the intensity of light, these meters are used more frequently to measure the accumulation of total UV exposure - sort of like a rain gauge for UV, instead of water."
Another analogue (pun intended) - sort of like using a flash meter to meter the total, cumulative exposure from several "pops" of a studio strobe (for those who have done that).
 
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KenS

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" Think of something like 'volume/amount over time' rather than having to open the contact frame every now-and-againto see if the exposure has been 'long enough' (in time). i am NOT interested in purchasing a 'second' meter...

I'd much rather put some time and effort into 'using the information' that my meter provides 'as is'. I'm not convinced that any official 'calibration' is going to add 'convenience/accuracy to make my efforts worth while.

I.O.W.. You gotta dance with girl that you 'brung' to the event

Ken
 

Vaughn

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I bought the meter knowing its lack of calibration -- as calibration is not generally needed for our purposes. It can be a very slight matter when communicating with others on personal exposure times, comparing types of exposure units and changes in exposure due to alterations in the process, etc. Unlike our light meters, it cannot be calibrated to a set standard. Which is probably why the fellow who made them did not give the Intensity (In) reading any units. And he is quite open about this in literature.

The other thing to be aware of, and I would not call it a significant problem, is that different alt processes respond to different wavelengths (in the UV portion) to different degrees, and different light sources have peaks at different parts of the UV portion of the spectrum. All this means is that when using the meter to gauge the exposure on a new set of lights, there may not be an exact one-to-one correlation between two different types of light sources (such as sunlight, BL tubes, and Merc vapor). This can be taken to the extreme by matching LEDs specifically to a process, where a much higher percentage of the measured UV light is effective -- compared to a more broad UV spectrum light source.
 

ProfessorC1983

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What I'd be interested in is whether, in theory, a gauge like this can be used to determine some sort of consistent relationship between UV exposure for alt process vs. traditional enlarger exposure for silver gelatin, to give roughly the same density of image for a given contrast grade? For example, if I have a negative that I know prints out exactly the way I want it traditionally at e.g. (just making this up) 12 seconds at f/11 under a #2 filter, would it in theory be possible to derive some sort of equation where I know that I should give it roughly X minutes under a given UV light source? If so, I could see a lot of value in a gadget like this.

I understand there are probably too many variables -- the process being used, exact emulsion chemistry, application thickness/technique, wavelength of the source, etc. -- to generalize the relationship, but just within the context of my own work it would be priceless (at least in terms of silver nitrate!) to have a ballpark for how much UV exposure a given negative needs. Currently I have nothing better than total trial and error each time, which results in numerous wasted prints before I can zero in on an appropriate range.
 

Vaughn

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My negatives for alt processes are exposed and developed for a particular alt process, so testing with a silver print would not be very effective.

You did point out one big difference between this meter and one that is used under the enlarger to meter for a silver print -- the UV meter measures just the light striking the negative where as the latter measures the light passing through the negative.

What might be possible is to put the negative on a piece of glass, hold the glass over the meter and shine your UV light thru the neg to the meter. If you measure the UV through a middle gray area, you might be able to work out a starting exposure time for future negatives after a couple test prints .

Get a UV densitometer if you want to really nail it down.
 

koraks

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To an extent, this could be done, but as Vaughn points out, the issue is that the contrast of many alt processes is fixed and also deviates from the range in which variable contrast silver gelatin papers sit. The exception would be carbon transfer which has quite some flexibility in adjusting to a certain negative, although here as well optimal results tend to require negatives that are beyond the range of what you'd want for silver gelatin.

Add to this, when using silver gelatin paper, you're generally using either a contact printing setup or an enlarger and that introduces a range of variables such as the type of paper and contrast grade selected, intensity of the light source, distance between light source and print, condensors used, etc. etc.

All considered, it seems like an endeavor that doesn't have very clear benefits. If you want to achieve predictability, I'd simply figure out what exposure gives dmax for your chosen printing process and light source and combine that with the contrast the negative needs to have for the desired tonal scale in the final print. No comparison between printing processes needed; just some experience with the alt. process of your choice. As Vaughn states, if you want to make things measurable, a UV transmission densitometer can be useful, but it's not absolutely necessary (back in the old days, they didn't exist, and excellent salted paper prints, carbon transfers and cyanotypes etc. were produced all the time!)
 

ProfessorC1983

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Thanks to both! Makes a lot of sense. And yes, my ultimate goal is to develop a better understanding of how to produce negatives that are best suited for e.g. salted paper, kallitype, etc. But I still have a lot to figure out in both my printing and shooting technique, so right now there are many dependent variables and it's challenging to make significant progress without a lot of random trial and error. I suppose I was asking if there were a way to "shortcut" this process by using silver gelatin as a faster/cheaper way to get data which I could then extrapolate to the slower and more expensive processes, but it sounds like there's not much of a linear relationship there to begin with. Which only means there's more fun to be had and more perfectly good paper to "ruin".
 

koraks

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The "nice" thing with processes like kallitype and salted paper is that the exposure can stay the same; you only need to expose just enough for dmax (taking into account b+f of your film). From there it's a matter of making negatives with the right contrast. Experience goes a long way here. I can usually decide right away by looking at (through) a negative if it'll work for say, salted paper, and then just give it the standard 11 minute exposure which happens to be the sweet spot with my uv unit. Mostly it comes out first time right.
 
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KenS

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Surviving on my pension income, I cannot 'really' afford 'Commercial' B/W printing papers any more.. after 'forking out' for both 4x5 and 8x10 inch films... thus the 'main' reason I have 'taken' to mix my own "alternative/archaic" emulsions..for printing. While it is NOT as 'fast' as the silver/gelatin B/W printing, but 'somehow' I find it much more 'satisfying'.

Ken
 
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