Making my first digital negs

[sanking]

Ben,

I have printed a couple of the calibration sheets and the print densities seem to vary just a bit even with the same machine printing at different times. At 50% the colors are identical, or almost so. At 100% I got the following readings from the two sheets. These are UV densities.

PK 3.09--3.18
Y 2.59--2.65
LK 1.63--1.73
C 2.26--2.25
M .91-- 94
LC .99 --1.07
LLK .67 --.74
LM .41 --.41

One of the sheets was printed in late August, the other was printed three days ago.

Sandy

It would be interesting to see how much these machines vary. Sandy and Ron-San have printed QTR calibration sheets for me from their 3800's, for a project I'm working on (slowly). If anyone else would like to print one and send it to me I'll measure that too. PM me for the specs.

Ben

 

[sanking]

I use a MAC and don't what GUI is, but I do know how to adjust the internal curve of the profile. But how does one determine how to tweak it except by trial and error? My experience is that if the curve does not linearize output one is better off just dumping it and creating a new curve using the method Ron outlines.

Sandy

What about simply adjusting the curve within the
QTR profile? I find those curve adjustments very predictable and easy to work with, just like an .acv curve in PS. In the curve creation tool GUI, just enter the number pairs in the curve field under the gray curve tab. Then there's no need to make a whole new curve when tweaking. Sorry if I've misunderstood the problem.

 

[Colin Graham]

Sorry Phil, it didn't occurred to me until late that a Mac might be different than XP that I'm on, but here's a screen shot of the graphical user interface (GUI) for the curve creation tool. (The curve entry here has end quotes and a 100;100 pair, just was longer than the field window allowed to view all at once.)

Sandy, I know the curve adjustments aren't completely literal in practice, but I've never used any UV blocking methods that have been. That isn't to say that there aren't any of course, I just haven't used them, so maybe I don't know what I missing as far as that goes. I have noted that with QTR the actual curve adjustments seem relatively mild compared to what the measured samples seem to indicate are needed.

 

[Ben Altman]

Ben,

I have printed a couple of the calibration sheets and the print densities seem to vary just a bit even with the same machine printing at different times. At 50% the colors are identical, or almost so. At 100% I got the following readings from the two sheets. These are UV densities.

PK 3.09--3.18
Y 2.59--2.65
LK 1.63--1.73
C 2.26--2.25
M .91-- 94
LC .99 --1.07
LLK .67 --.74
LM .41 --.41

One of the sheets was printed in late August, the other was printed three days ago.

Sandy

Then there's the question of how accurate/repeatable the UV measurements are... I usually move the patch around and take several readings to get an idea of a good average, but even so I'm not too sure that the readings are really accurate.

However, a good profile to my mind should use the ink densities at the low end of the scale to build up density, if possible. Weird dot-gain things happen at high ink densities - I've seen 100% patches that were lighter than 90% patches, for instance.

Which reminds me - another parameter to add to my earlier list is the screening algorithm used, as that seems to change the curve too. I've found that the complicated ones have glitches, often at the 50% mark. So I've been using the Ordered dither, which has the additional advantage of loading faster.

Ben

 

[sanking]

My densitometer appears to give very repeatable results. I just did a random check of some of the high densities for the two calibration sheets that I had previously measured and none of the readings were off by more than log 0.02, and most of them were identical.

I alsos move the the aperture around over the step to make sure I am getting the same reading, and if not I use an average. You will see the same type of variation in sensitometry with film.

Sandy King

Then there's the question of how accurate/repeatable the UV measurements are... I usually move the patch around and take several readings to get an idea of a good average, but even so I'm not too sure that the readings are really accurate.

However, a good profile to my mind should use the ink densities at the low end of the scale to build up density, if possible. Weird dot-gain things happen at high ink densities - I've seen 100% patches that were lighter than 90% patches, for instance.

Which reminds me - another parameter to add to my earlier list is the screening algorithm used, as that seems to change the curve too. I've found that the complicated ones have glitches, often at the 50% mark. So I've been using the Ordered dither, which has the additional advantage of loading faster.

Ben

 

[donbga]

I'm curious, has anyone ever successfully used someone else's QTR profile for digital negatives?

Colin,

I can't speak specifically about QTR curves, but I can tell you from my own experience that curves for alternative processes are not universally transportable.

I've found that curves made with the same model of printer and OEM ink aren't always reliable and that different UV light sources have a major effect on the final print.

The nice thing about using QTR curves that Ron has created is that it does provide some framework and starting point for someone to start [struggling] with.

Don Bryant

 

[donbga]

I use a MAC and don't what GUI is, but I do know how to adjust the internal curve of the profile. But how does one determine how to tweak it except by trial and error? My experience is that if the curve does not linearize output one is better off just dumping it and creating a new curve using the method Ron outlines.

Sandy

I personally find the PC interface, QTRgui, to be really slick, a much better way to use QTR than how the Mac version operates.

Don Bryant

 

[sanking]

My experience in conducting carbon and pt/pd workshops at various locations is that the curves are very portable, assuming that all of the chemistry, materials and conditions are as close to identical as possible.

The UV light source could clearly have a major impact on results so that is definitely something you have to consider. My BL tube bank prints almost identically to the BL tube banks at the Formulary. But most sources put out less radiation with time so you also have to keep age of the bulbs in mind. I have a good friend whose print time for palladium is in the 30+ minute range with digital negatives using a NuArc 26-1ks. My times are about three minutes with the Amergraph ULF-28, and slightly longer in printing with NuArc 26-1ks at workshops. I have to figure my friend has a very old bulb since everything about his working procedures are similar to mine for palladium.

Sandy King

Colin,

I can't speak specifically about QTR curves, but I can tell you from my own experience that curves for alternative processes are not universally transportable.

I've found that curves made with the same model of printer and OEM ink aren't always reliable and that different UV light sources have a major effect on the final print.

The nice thing about using QTR curves that Ron has created is that it does provide some framework and starting point for someone to start [struggling] with.

Don Bryant

 

[pschwart]

Sorry Phil, it didn't occurred to me until late that a Mac might be different than XP that I'm on, but here's a screen shot of the graphical user interface (GUI) for the curve creation tool. (The curve entry here has end quotes and a 100;100 pair, just was longer than the field window allowed.)

Sandy, I know the curve adjustments aren't completely literal in practice, but I've never used any UV blocking methods that have been. That isn't to say that there aren't any of course, I just haven't used them, so maybe I don't know what I missing as far as that goes. I have noted that with QTR the actual curve adjustments seem relatively mild compared to what the measured samples seem to indicate are needed.

Thanks. I'm using a PC, but when I tried to enter number pairs into the curve field QTR threw errors. I'l try again -- it would definitely be useful to be able to do this.

 

[sanking]

Ben,

I think all of the things you mention would be important to include in the profile description. In addition, specific processes would need other information.

With carbon, for example, we would need a specific protocol about tissue formula, method of sensitizing, etc.

If I ever get that perfect carbon profile for the 3800 to put on Ron's web site my goal will be to include every bit of information that I consider important.

Sandy

Sandy has a couple of great ideas in this thread:

- Get the QTR profile close (and smooth), so it is doing most of the work by adjusting the way the printer lays down ink. Then use a routine like Charthrob to make a fine-tuning curve in Photoshop, which can adjust for the minor variations between machines, batches of wet materials, photographers, etc. This should be quicker than trying to get the QTR profile perfect.

- Put a lot of info. in the QTR profile text file itself so self and others know how to use it, and what for. Maybe we could figure out a standard format for this - here's a starter list of what should be in there:

Printer
Negative substrate
Ink-set or subset of inks
Embedded ICC profile of image file
Whether profile prints from positive or inverted image file
Process (i.e. Carbon, Ziatype, Gum, whatever)
Intent (long or short scale, shadow or highlight detail, whatever)
Mixture (contrast agents)
Paper type and preparation
Light source
Other process controls (humidity, whatever)
Post-processing (toning etc.)

What am I forgetting?

Ben

 

[Ben Altman]

Ben,

I think all of the things you mention would be important to include in the profile description. In addition, specific processes would need other information.

With carbon, for example, we would need a specific protocol about tissue formula, method of sensitizing, etc.

If I ever get that perfect carbon profile for the 3800 to put on Ron's web site my goal will be to include every bit of information that I consider important.

Sandy

OK, so how about a line-item called "process-specific information"? That could also cover such things as development info. for an Azo/Lodima print. And we'd need a line for printer settings (i.e. uni- or bi-directional printing etc.). Including my earlier thought about the dither, the list now looks like this:

Printer
Negative substrate
Ink-set or subset of inks
Embedded ICC profile of image file
Whether profile prints from positive or inverted image file
Dither
Printer settings (uni- or bi-directional, etc.)
Process (i.e. Carbon, Ziatype, Gum, whatever)
Intent (long or short scale, shadow or highlight detail, whatever)
Mixture (contrast agents etc.)
Paper type and preparation
Process-specific information
Light source
Other process controls (humidity, whatever)
Post-processing (toning etc.)

Amazing how many variables there are, and I'm sure there are some we have not thought of. Keep the suggestions coming!

Ben

 

[donbga]

The UV light source could clearly have a major impact on results so that is definitely something you have to consider.

Sandy King

This is the largest single factor that I've experienced that makes a big difference, judging by the results of printing on 4 different UV printers.

Don

 

[PVia]

Well, this is a great discussion.

I especially like the idea that complete info accompany a profile whenever one is posted, especially the exposure equipment and exposure units, and possibly a sunlight equivalent. Is there such an equivalent?

So, Ron has related (in his Pd pdf) that he exposes for 75 units. So I'm wondering what that may be in sunlight exposure. I've heard that UV equipment (such as the NuArc) take longer than a "full sun" print, but have no experience in that area. Anyone?

I know that there are too many variables (geography, time of year, etc) but just wondering about a ballpark guesstimate?

 

[donbga]

Well, this is a great discussion.

I especially like the idea that complete info accompany a profile whenever one is posterd, especially the exposure equipment and exposure units, and possibly a sunlight equivalent. Is there such an equivalent?

So, Ron has related (in his Pd pdf) that he exposes for 75 units. So I'm wondering what that may be in sunlight exposure. I've heard that UV equipment (such as the NuArc) take longer than a "full sun" print, but have no experience in that area. Anyone?

I know that there are too many variables (geography, time of year, etc) but just wondering about a ballpark guesstimate?

You can use a UV light integrator to measure exposures outside.

Don Bryant

 

[sanking]

That is about the only way to relate indoor exposure unit times to exposure times outside.

Simply too many variables in the intensity of outdoor radiation to even offer a ball park comparison figure.

Sandy King

You can use a UV light integrator to measure exposures outside.

Don Bryant

 

[PVia]

That's what I figured, but thought i'd take a shot anyway.

Besides, a few test strips and you're close to being there...I don't think there'd be any appreciable difference besides exposure time between a UV unit and pure sunlight...some minor contrast difference maybe.

 

[PVia]

I tried a test strip on a negative made with Ron's QTR palladium profile today.

Now this is all very unscientific, as I'm using the sun, which here in So Cal is absolutely bright, full blue sky, no clouds for 10 months out of the year. Taking into account time of day and season, I believe you can be pretty accurate in making prints requiring a UV source in this particular location, not Dick Arentz to 4 decimal places accurate, but enough to make some beautiful prints ;-)

Ron's profile definitely gave more UV blocking density than my first test, and although the strip was about a stop too light, all the tones are there and well distributed.

Just thought I'd pipe in with an update. When I'm finished with my tests, I'll compile the results with the variables mentioned in this thread. Since I'm using the sun in a particular geographic location, maybe this won't be perfectly helpful, but at least the trials of someone trying different profiles and curves with a particular printer will at least light a path for another newcomer to follow or at least learn a little bit from.

 

[donbga]

I tried a test strip on a negative made with Ron's QTR palladium profile today.

Now this is all very unscientific, as I'm using the sun, which here in So Cal is absolutely bright, full blue sky, no clouds for 10 months out of the year. Taking into account time of day and season, I believe you can be pretty accurate in making prints requiring a UV source in this particular location, not Dick Arentz to 4 decimal places accurate, but enough to make some beautiful prints ;-)

Ron's profile definitely gave more UV blocking density than my first test, and although the strip was about a stop too light, all the tones are there and well distributed.

Just thought I'd pipe in with an update. When I'm finished with my tests, I'll compile the results with the variables mentioned in this thread. Since I'm using the sun in a particular geographic location, maybe this won't be perfectly helpful, but at least the trials of someone trying different profiles and curves with a particular printer will at least light a path for another newcomer to follow or at least learn a little bit from.

Well given the fact you don't have access to a UV light integrator, I would suggest using an incident type light meter to make measurements of ambient light levels. My guess is that incident meters are probably somewhat sensitive to UV radiation and using a incident meter may provide you with some way of bench marking outdoor light for exposure analysis.

As I recall, southern California has air pollution to one degree or another which could be a factor in the amount of exposure you can expect on any given day as well as seasonal variations changing the intensity of UV radiation. Additionally sunlight has a wider band of UV specta which may make actinic sensitive emulsions gain speed and contrast compared to exposure units used indoors which will affect the way digital negatives print.

Hopefully you are printing digital step wedges to analyze your results.

Don Bryant

 

[Loris Medici]

Sun Exposure Calculator (based on UV Index)

Paul, see this:

Dead Link Removed

 

[PVia]

Loris,

That's a really interesting worksheet...so, you put in your normal time and step wedge info under known conditions, and put in the new UV index and it interpolates from there?

Do you use this sheet in your regular work?

Thanks! I'll play around with it...

 

[Loris Medici]

Thanks, I just designed it when it occured to me that UV index can probably be used for estimating exposure times for UV sensitive processes under sun, as long as you have a weather station reporting it at 1/10 scale (say... like UV Index = 7.2), web sources say it's a linear index so I just make a simple ratio calculation to find the new exposure time.

Unfortunately I haven't tested it because I do my exposures in the evenings, under UVBL lightsource. But the idea seems logical / plausible. I was looking for someone who can try this and see if it works for them. Can you do that for me? (I have no sunlight in this season...)

Regards,
Loris.

Loris,

That's a really interesting worksheet...so, you put in your normal time and step wedge info under known conditions, and put in the new UV index and it interpolates from there?

Do you use this sheet in your regular work?

Thanks! I'll play around with it...

 

[sanking]

Loris

Have you considered adding other key components to the callculator, such as latitude, declination of the sun, altitude, and time of day?

Sandy

Thanks, I just designed it when it occured to me that UV index can probably be used for estimating exposure times for UV sensitive processes under sun, as long as you have a weather station reporting it at 1/10 scale (say... like UV Index = 7.2), web sources say it's a linear index so I just make a simple ratio calculation to find the new exposure time.

Unfortunately I haven't tested it because I do my exposures in the evenings, under UVBL lightsource. But the idea seems logical / plausible. I was looking for someone who can try this and see if it works for them. Can you do that for me? (I have no sunlight in this season...)

Regards,
Loris.

 

[PVia]

At the moment, I have no source for UV Index with accuracy to one decimal point.

 

[Loris Medici]

Sandy, that's irrelevant since UV index is based on the total UV energy (in watts) reaching the soil (based on a specific criteria) and is calculated geographically (taking into account the altitude too). According to my idea, all you need is a weather station nearby that measures UV Index, which you can use as a UV lightmeter. (I happen to have one just 500 yards away from my residence http://www.enka.com/weather/)

Regards,
Loris.

Loris

Have you considered adding other key components to the callculator, such as latitude, declination of the sun, altitude, and time of day?

Sandy

 

[sanking]

Loris,

Thanks for explaining that. I was not aware that the UV index included all those factors.

Sandy

Sandy, that's irrelevant since UV index is based on the total UV energy (in watts) reaching the soil (based on a specific criteria) and is calculated geographically (taking into account the altitude too). According to my idea, all you need is a weather station nearby that measures UV Index, which you can use as a UV lightmeter. (I happen to have one just 500 yards away from my residence http://www.enka.com/weather/)

Regards,
Loris.