RA-4 paper sensitivity and exposure time

[dkonigs]

So I've just finished my first attempt at RA-4 darkroom printing, using a dichroic enlarger and Fuji Crystal Archive Super Type II paper (i.e. the only kind you can actually by in cut sheets). Overall, I'm quite pleased with the results. The main thing that concerns me is exposure times. This paper seems to be far more sensitive to light than the B&W paper I've used previously.

I was printing a 35mm negative with a 50mm enlarger lens. I had the lens stopped down to f/8 and had a 2-stop ND filter screwed onto it. My exposure times were still only in the 7-9 second range, and the image was dim enough that it was actually hard to make it out while exposing. Is this time range normal/okay? Should I crank it up to f/11 and/or add more ND to bump the time up? (And if I consider using cyan for that, how do I convert dichroic filter added ND into terms of "stops" so I can compare/choose an appropriate value?)

FWIW, the book "Color Photography" by Henry Horenstein mentions that color paper experiences reciprocity failure if the exposure is too long and that I should keep my exposure within the 8-20 second range. I never expected to be bumping up on the short end of that range. That being said, does this guidance still apply today?

 

[138S]

paper seems to be far more sensitive to light than the B&W paper I've used previously.

Yes, approx 3x faster

Lambda photo printer machines may have some problems to print FB BW paper, it can be overcomed, but some tricks have to be used with FB because machines are designed for faster RA-4 paper.

 

[Mick Fagan]

I have not used the current crop of RA4 paper, but in another life I have used plenty of RA4 paper from very small 12cm x 15cm paper through to 1.8m x 6m colour prints. When doing mural sized prints, exposure times would sometimes be around 6 minutes through to 15-20 minutes, depending upon density of the negative and what was required.

In my home darkroom if a printing time was too short, be it B&W or colour negative (RA4) then I added neutral density to the head to make the printing times longer and/or more manageable. To add neutral density you need to add all three filters in the colour head, then add the filtration required for correct colour.

If for instance you have a correctly exposed and colour corrected print, using say: C00 M77 Y92 and an exposure time of 10 seconds at f/8 and find this too short a time. You can add a stop of exposure by adding 30 units of all three colours into the head. Then your filter settings will be: C30 M107 Y122 and at f/8 your correct time will be approximately 20 seconds.

To get another stop of exposure time, you will need to add 60 units of all three colours to the colour head. This would then be C60 M137 Y152 and an exposure time of 40 seconds, approximately.

Exposure time increases are approximate as the filtration won’t be exact, but if you are careful they will be very close.

If you do your test prints at or around whatever time you are working with, whether that is a very short time or a very long time, then your colour will not change. However if you move from 8 seconds to say 80 seconds, then a small filtration adjustment will mostly be required. This however is par for the course when doing enlargements as density changes and slight variation of colour, will most likely be what you will need when printing larger prints.

A quite large print will usually have a slight difference in density than a smaller print. This is mostly a size thing, because if you have a lightly coloured skirt that is 35mm top to bottom in a small print, then enlarge it so that it is 150mm top to bottom, your viewing perspective of the colour and the density of that colour changes somewhat.

One tip for colour printing: you adjust the M filter to control magenta and green, you adjust the Y filter to control blue and yellow.

To control red and cyan you make a density change. Making a print darker will add red, making it lighter will add cyan to the image. Once you are very close with your colour balance, the exposure changes that make a print more red or more cyan, become more obvious. The cyan/red difference is not a huge thing and is not readily noticeable, but it is there when you are virtually on the money.

Mick.

 

[koraks]

Is this time range normal/okay?

Yes, and as long as you have a reasonably consistent timer, this is perfectly OK. I myself currently use a diy led light source with a timer that does tenths of a second and my exposures are around 3 seconds at f/8 for 35mm onto ca 5x8.5" small prints. Works perfectly fine.

 

[Tom Kershaw]

Yes, and as long as you have a reasonably consistent timer, this is perfectly OK. I myself currently use a diy led light source with a timer that does tenths of a second and my exposures are around 3 seconds at f/8 for 35mm onto ca 5x8.5" small prints. Works perfectly fine.

What enlarger are you using with your DIY LED head? - I've started to look into these as I recently needed to buy some new 300W ELH halogen lamps and realised how expensive they had become.

 

[138S]

I have not used the current crop of RA4 paper, but in another life I have used plenty of RA4 paper from very small 12cm x 15cm paper through to 1.8m x 6m colour prints. When doing mural sized prints, exposure times would sometimes be around 6 minutes through to 15-20 minutes, depending upon density of the negative and what was required.

In my home darkroom if a printing time was too short, be it B&W or colour negative (RA4) then I added neutral density to the head to make the printing times longer and/or more manageable. To add neutral density you need to add all three filters in the colour head, then add the filtration required for correct colour.

If for instance you have a correctly exposed and colour corrected print, using say: C00 M77 Y92 and an exposure time of 10 seconds at f/8 and find this too short a time. You can add a stop of exposure by adding 30 units of all three colours into the head. Then your filter settings will be: C30 M107 Y122 and at f/8 your correct time will be approximately 20 seconds.

To get another stop of exposure time, you will need to add 60 units of all three colours to the colour head. This would then be C60 M137 Y152 and an exposure time of 40 seconds, approximately.

Exposure time increases are approximate as the filtration won’t be exact, but if you are careful they will be very close.

If you do your test prints at or around whatever time you are working with, whether that is a very short time or a very long time, then your colour will not change. However if you move from 8 seconds to say 80 seconds, then a small filtration adjustment will mostly be required. This however is par for the course when doing enlargements as density changes and slight variation of colour, will most likely be what you will need when printing larger prints.

A quite large print will usually have a slight difference in density than a smaller print. This is mostly a size thing, because if you have a lightly coloured skirt that is 35mm top to bottom in a small print, then enlarge it so that it is 150mm top to bottom, your viewing perspective of the colour and the density of that colour changes somewhat.

One tip for colour printing: you adjust the M filter to control magenta and green, you adjust the Y filter to control blue and yellow.

To control red and cyan you make a density change. Making a print darker will add red, making it lighter will add cyan to the image. Once you are very close with your colour balance, the exposure changes that make a print more red or more cyan, become more obvious. The cyan/red difference is not a huge thing and is not readily noticeable, but it is there when you are virtually on the money.

Mick.

Great explanation, thanks.

 

[koraks]

What enlarger are you using with your DIY LED head? - I've started to look into these as I recently needed to buy some new 300W ELH halogen lamps and realised how expensive they had become.

A durst 138s, I think it's the old/original model.
But it'll be much quicker, easier and cheaper if you just find a replacement bulb for your enlarger. The led option is tricky, highly customized and highly complex if you want to do it even halfway right. It's not an off the shelf solution by far.

 

[Tom Kershaw]

A durst 138s, I think it's the old/original model.
But it'll be much quicker, easier and cheaper if you just find a replacement bulb for your enlarger. The led option is tricky, highly customized and highly complex if you want to do it even halfway right. It's not an off the shelf solution by far.

I have no immediate plans to convert over to LED heads but it seems to be something that several people have now done, and Heiland electronic have their solutions (for a price).

 

[BMbikerider]

If your enlarger has the small bulbs such as the Osram A1/231 12v/100w I am not sure that you will be able to get an LED equivalent. I tried a LED bulb in my Meopta B&W and connected my digital timer to it and it only worked in a flashing mode, not a steady light The bulb was a non dimmable type so it should have worked unless my timer is unique you may also find that you have problems with that as well.

 

[koraks]

I have no immediate plans to convert over to LED heads but it seems to be something that several people have now done, and Heiland electronic have their solutions (for a price).

I haven't come across anyone who has done this with a RGB controlled light source and acceptable outcomes. I've seen people use white led bulbs with regular filters (I don't know about their results) and I've seen one or two people using off the shelf remote controlled RGB bulbs but with (in my eyes) poor results. I know about the heiland system and I bet it works fantastically (the price is fantastic as well).

 

[138S]

I've seen people use white led bulbs with regular filters

For RA-4 this works pretty well if the LED bulb is warm around 3500K and if it has high CRI. Not exactly the tungsten spectrum but good enough to do the job.

 

[koraks]

Yes, it should indeed work just fine. I haven't tried it myself, but I don't see how it would be impossible given the right color temperature and spectral continuity as you say. Of course, I chose a vastly more complicated way to make things unnecessarily difficult for myself...

 

[138S]

spectral continuity

Yes... usually RGB LEDs have spectral valleys between main colors that may have (or not, I don't know) an impact in the grading of hues.

A good test would be printing an IT8 transparent target on RA-4 to see the difference between tungsten and RGB LED, with the main colors well balanced then it should be seen how hues are graded.

If there is a difference then this can be worked in several ways, one is also including leds that fill the spectral valleys, another way would be using a high CRI warm white LED of continuous spectrum for the main illumination with additional RGB aid to adjust color.

What is clear to me is that RGB LEDs are good for BW, Split Grade, etc, and that High CRI warm white is good for both BW and RA-4, what I don't know is how RGB LEDs can work with RA-4.

 

[koraks]

what I don't know is how RGB LEDs can work with RA-4.

I've just documented my attempts here: https://www.photrio.com/forum/threads/craziness-using-leds-to-print-ra4-and-b-w.171911/

 

[halfaman]

Heiland LED conversion is tempting. Their heads are made of hundreds of lamps and give the same ammount of light regardless of the negative or paper size. Only one diffuser box is neccesary for any kind of enlargement. The problem is that it usually cost more than the enlarger itself.

 

[138S]

I've just documented my attempts here: https://www.photrio.com/forum/threads/craziness-using-leds-to-print-ra4-and-b-w.171911/

Thanks

 

[mklw1954]

Sounds right, I use Fuji Crystal Archive Type II paper. I always stop down to f11 and 15-20 seconds exposure time is typical for an 8x10 print from a 35mm negative including the maximum amount of the negative (18.75" between the paper in the easel and the bottom of the lens).

 

[DREW WILEY]

I'm very skeptical of LED sources being precise enough in spectral quality, or powerful enough if so configured, to be realistic for high-quality color printing yet. But continual experimentation that direction is inevitable. I once had a Durst color mural enlarger so bright that it would punch a 30X 40 inch Cibachrome print from a chrome original with a .90 density contrast mask attached in about 15 sec, which means it would have done it with current RA4 paper in about 1/10 second! If you gave the chrome 45 sec and removed it from the carrier, it might be faded! Darn thing doubled my utility bill, so I got rid of it and designed my own colorhead to run cooler.

 

[Tom Kershaw]

What was the wattage and technology of that Durst mural enlarger - halogen lamps?

 

[138S]

What was the wattage and technology of that Durst mural enlarger - halogen lamps?

The condenser BW type has a 300W Opal lamp, a lower power can be used for non mural prints.

Color head, halogen 1000W

 

[koraks]

I'm very skeptical of LED sources being precise enough in spectral quality, or powerful enough if so configured, to be realistic for high-quality color printing yet.

My skepticism has shrunk considerably since my more recent attempts that I linked to above. I think it is very feasible, in fact. Considering how far I got with cheap, off the shelf leds and -stumbling-in-the-dark software engineering, I think with more dedicated and systematic efforts quality and usability levels that are on par or even succeed regular light sources are well within reach. The technology is within reach; it's just that demand would be too small for many serious efforts to be taken in terms of development. Only Heiland and if I'm not mistaken Beseler have jumped into the gap so far - and there's not all that many more players in the enlarger market anyway.

 

[Tom Kershaw]

De Vere are still going but I presume mostly manufacturing colour dicroic heads.

 

[138S]

My skepticism has shrunk considerably since my more recent attempts that I linked to above. I think it is very feasible, in fact.

I also think it's quite feasible.

 

[DREW WILEY]

Human flight was also once considered feasible. It just didn't happen overnight. Quite a few crashes first, and even some thereafter. What I had in mind when making my own additive colorheads, which involved some very complicated halogen engineering, was not only improved efficiency relative to power consumption and heat reduction, but truly improved color accuracy too, and I doubt LED's are capable of any real improvement in that respect yet, or even equalling what you can already get right off the shelf in terms of halogen subtractive colorheads. But I applaud anyone trying. Even the Wright brothers didn't get it "right" the first time, attempting to fly. Mistakes and partial disappointments are just part of the necessary learning curve. But it all depends on one's quality expectations in the final print. Yes, you might get a full-color print; but before I believe in any such thing, I'd want to see just how fine-tuned you can get to a standardized color target. And it just ain't going to happen if the spectral peaks aren't spot on, as well as being totally controllable. But I have little doubt that within a decade or so, after a few commercial bellyflops, someone will finally come up with an LED system perhaps equal to what halogen dichroic filtration already did half a century ago.

 

[Lachlan Young]

All I'd add here is that there's quite a few films shot on film from the last decade that have quite extensively used LED for all sorts of lighting - and a fair number were traditionally colour timed (which would really show up any flaws in the spectrum) rather than scanned at an early stage. I don't think anyone would be able to immediately tell them apart from incandescent or HMI lit scenes. Not that the kit is cheap - look up how much a reel of LiteRibbon Cinema will set you back!