Re: [APML] RG200 Hypering -- Densitometer Readings

[Philip Perkins <philip@astrocruise.com>]

Gil,

Welcome to the black art of hypering! :)  The first thing about hypering is 
that there is no such thing as a set temperature that applies for 
everyone.  I don't think anyone has yet offered an explanation for this but 
my own view is that there are a number variables with each set up (such as 
actual temperature, stability of temperature, quality of forming gas, 
degree of evacuation of oxygen and water vapour from chamber, atmospheric 
pressure, actual pressure of forming gas).  With the high temperatures that 
we use, of 50 C or even higher, chemical reactions happen very quickly and 
these variables make a much bigger difference to results than if we used a 
lower temperature.  I believe that if we used 40 C instead we would see 
much greater consistency, and even more consistency if we used 30 C.

For example, my hypering times with all 'Kodak genre' films, are around 8 
hours at 50 C, whereas I believe that Bobby Middleton's times are around 5 
hours.  That's a very big difference for exactly the same result and 
there's no reasonable explanation for it (other than my conjecture 
above).  The only way to determine hypering time with your set up is to do 
some test runs at different times.  If it were me I would do three runs at 
4 hours, 6 hours, and 8 hours.  This assumes that the temperature is held 
strictly at 50 C.  Temperature makes the biggest difference of all to 
hypering - if you are off by even a couple of degrees C it will make a very 
noticeable difference to results.  Since you are going 2 hours at 55 C and 
see no sign of density increase it could be that your setup will need times 
not unlike mine, which is 7 - 8 hours at 50 C.

Don't be confused by others who say "I hyper for x hours and my film comes 
out perfectly"..  the time with your setup could be completely different - 
that's the black art of hypering! :)

The other thing about temperature is to be rather careful of it - I would 
say that 55 C is definitely too high.  I was once told by Brad Wallis that 
colour film emulsion starts to liquify at temperatures much above 60 C.  I 
would back it off to 50 C as soon as you can and keep it accurately 
regulated with a Lumicon probe.

Check your procedure and equipment to ensure that there are no problems 
with it (there have been several descriptions on APML in the past - try the 
archives at http://astro.umsystem.edu/apml/search.html  and search on 
'hypering procedure'). When you have a procedure you are happy with, then 
stick to it rigidly to ensure that your results are consistent.

In terms of knowing when the film is accurately hypered, the generally 
accepted yardstick is that the transmission density of hypered film should 
be 0.1 over base compared to unhypered film from the same batch, processed 
at the same time.  How do you measure that?  It's a problem that I 
struggled with for some time and after I had some success I wrote the 
following article which may help a bit:
http://www.astrocruise.com/densmeas.htm

It's better to be under hypered than over and after some experience I found 
that film delivering the best results was only 0.06 or 0.08 over base - the 
number doesn't have to be that accurate as long as you are not over 
0.1.  In the first place it can help a lot to get a sense of what correctly 
hypered film looks like, compared to the unhypered control.  I am sure 
there would be people willing to send you samples - I am certainly willing, 
though bear in mind that my samples will be subject to the vagaries of the 
air mail postal service from the UK.  Always compare hypered / unhypered 
strips on a light box - it's not enough to hold the film up to the light - 
often you can't see any difference that way.

You already tried to get your film measured at a photo lab - that's exactly 
the right thing to do.  However I came across the same problem as you - 
they use a Kodak densitometer which generates the RGB values you mention 
and I could find no-one who knew how to translate those readings into the 
greyscale density readings.  In the end I had to give it up.  There are 
greyscale densitometers around - it's worth raising a query here on APML to 
see if anyone might be able to help.

--Philip


At 09:42 09/02/02 -0800, you wrote:

>I've recently started hypering my film, and have found that it would 
>appear that I don't know what I'm doing. :-)  The several rolls of hypered 
>RG 200 that I've had processed have all come back with the base looking 
>like there was no fogging whatsoever.  My setup is a Lumicon 600 tank with 
>the hand pump.  I'm hypering the film in the cannister.  The first couple 
>of rolls I hypered at 55C for 2 hours (I do not yet have the regulator 
>probe, so the tank gets a little warm).  The second  set I hypered at the 
>same temp for 2 1/2 hours.  All rolls appear as if no hypering has been 
>performed.  I took the film to a local processor that has a densitometer, 
>and they read the following:
>
>R=0.37  G=0.70  B=0.92  For the second roll, R=0.37 G=0.73 B=0.93
>
>The calibration strip returned the following: R=3.01  G=2.96  B=2.97
>
>The folks at the lab couldn't tell me what and/or if these numbers had to 
>do with the information that I'm seeking: how much above non-hypered film 
>were my test strips -- perhaps a case of speaking two different languages, 
>or my not knowing what's what...  On APML and in other resources, it seems 
>that the discussion is always around ND steps above clear.  Is that what 
>these numbers show, only split out into RBG values?  Do I need to have a 
>non-hypered roll processed and measured for comparison?  Is it necessary 
>to combine the RGB values above to get to a proper "combined" value to 
>determine the proper level of base fog?  On the subject of measuring the 
>amount of base fog, does anyone know where I might acquire a calibrated 
>test strip?  Typically, how valid are test values from one film lot to the 
>next?  Do I need to be concerned about the variation, or is that variation 
>typically small enough to effectively ignore.
>
>Whew... Lots of questions.
>
>-- Gil


Philip Perkins - philip@astrocruise.com
Wiltshire UK & Luberon France
Astrocruise - http://www.astrocruise.com


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