Split grade printing contrast

[ericdan]

Exposing paper to let's say:

10s @ 2.5
or
5s @ 0
5s @ 5

shouldn't that give me the same outcome?
I always find my exposure time at grade 2.5 first.
I then try a straight print at 2.5 and then do the same at 50% 0 and 50% grade 5.
The split grade alway looks more pleasing. It seems to have slightly more contrast, but still gives details in the shadows. (used MCC and MGFB papers)
How does that make sense when the combination of the two extremes should give me the middle. My starting point.

 

[Svenedin]

Unless you have an enlarger that has constant exposure times across all grades then your example above does not give 2.5. Exposures for grades 4 and 5 are double those of the lower grades (when using above or below lens Ilford filters).

 

[David Brown]

Split grade printing is more than just finding an exposure at a middle grade and then “splitting” into two equal halves. Start here: http://www.lesmcleanphotography.com/articles.php?page=full&article=21

 

[cowanw]

No, it does not always (?ever) work like that. For example my Zone vi enlarger has a time counter for light power and the blue is way faster than the green. I presume the blue bulb is more powerful. As well, the mixes which keep time constant are designed for one particular tone, say a certain grey and whites and blacks may be different. What can be said is that X units of blue and Y units of green will yield a particular result, however achieved. The problem is figuring out how to mix them (or how to separate them). it can be done but is not consistent lamp to lamp.

 

[pentaxuser]

Perhaps ericdan can tell us what filter system he uses? This might help us answer his question.

pentaxuser

 

[cramej]

Contrast filters and multigrade papers are not linear - they are logarithmic so "0" exposure + "5" exposure does not = "2.5" exposure and the resulting print will not look the same. Here is an excerpt from the Ilford paper on contrast control:

"CONTRAST RANGE
This section describes how MULTIGRADE papers give different contrast levels. For practical information on selecting contrast levels turn to the next pages.All chloro-bromide (black and white) emulsions are blue sensitive with a slight sensitivity to green light. To make an emulsion sensitive to colours in addition to blue, sensitising dyes need to be added.

MULTIGRADE papers are coated with an emulsion which is a mixture of three separate emulsions. Each emulsion is a basic blue sensitive emulsion to which is added different amounts of green sensitising dye. Thus, part of the mixed emulsion is sensitive mainly to blue light, part to blue light with some sensitivity to green light and part to both blue and green light. All parts of the emulsion have the same contrast. They also all have the same speed to blue light, but naturally, the part of the emulsion with only a small amount of green sensitising dye has a low speed (that is, is less sensitive) to green light.

When the paper is exposed to blue light, all parts of the emulsion react and contribute equally to the final image. This image is of high contrast because of the additive effect produced by three emulsions with the same speed and contrast. The resultant curve has a narrow exposure range and is thus of high contrast.

When the paper is exposed to green light, only the parts of the emulsion with the larger amounts of green sensitising dye react initially. This is because the three emulsions have very different sensitivities to green light. This image is of low contrast because of the additive effect produced by three emulsions with different speeds to green light, but with the same inherent contrast. The resultant curve has a very much wider exposure range and is thus of low contrast.

By varying the proportion of blue to green light, a contrast range between these two extremes can be obtained. The simplest way of controlling the colour of the light reaching the emulsion during exposure is by the use of filters: a magenta filter absorbs green light and transmits blue; a yellow filter absorbs blue light and transmits green. In this way, high and low contrast images can be made." https://www.ilfordphoto.com/wp/wp-content/uploads/2017/03/Contrast-control-for-Ilford-Multigrade.pdf
​

 

[cramej]

A good use of split grade printing might be this:

You have a landscape scene with detailed terrain, bright sky and clouds. You decide that you want the rocks/terrain/etc. to be nice and contrasty so you expose with a 5 filter but then the clouds lose detail. You can come back with a lower grade filter - say 2 or 3 - and expose for additional time to bring some detail back into the clouds, masking other areas of the print as appropriate. Split grade printing is about more than just combining differently filtered exposures to get a good print.

 

[ericdan]

Perhaps ericdan can tell us what filter system he uses? This might help us answer his question.

pentaxuser

Built in variable contrast filters on an LPL VCCE enlarger. Goes from 0-5.

 

[RalphLambrecht]

Unless you have an enlarger that has constant exposure times across all grades then your example above does not give 2.5. Exposures for grades 4 and 5 are double those of the lower grades (when using above or below lens Ilford filters).

that doesn't work.thereis no such thing as constant exposure across all grades. If you switch grades, the exposure needs to be adjusted; always.

 

[ericdan]

From reading through the links it seems that grade 5 should require twice the time grade 0 does.
That would mean all my prints using the above example are too thin and lack contrast. I observe the opposite though. My prints come out with about the right density and are more contrast than what I get with grade 2.5.

I do agree that at grade 5 the light beam looks much dimmer than at grade 0.

 

[RalphLambrecht]

Exposing paper to let's say:

10s @ 2.5
or
5s @ 0
5s @ 5

shouldn't that give me the same outcome?
I always find my exposure time at grade 2.5 first.
I then try a straight print at 2.5 and then do the same at 50% 0 and 50% grade 5.
The split grade alway looks more pleasing. It seems to have slightly more contrast, but still gives details in the shadows. (used MCC and MGFB papers)
How does that make sense when the combination of the two extremes should give me the middle. My starting point.

Correct; an overall print contrast achieved by split-grade printing can also be achieved with a single contrast exposure. the benefit of split-grade printing lies in being able to dodge and burn during the soft or hard exposure alone, getting the most out of highlight or shadow detail.

 

[Sirius Glass]

There is not a formula for times of split grade exposure. One must experiment and use whatever combination of filters and times work PLUS there is burning and dodging using different filters and times.

 

[Ian C]

Regarding post # 10:

Ilford’s comments on the difference between its low-range (00 – 3.5) and its high-range (4, 4.5, and 5) filters applies to its dyed-acetate filters. These comments don’t apply to the use of dichroic thin-film interference filters used in color-printing heads and variable-contrast printing heads for photo enlargers. Neither do Ilford’s comments necessarily apply to dyed-acetate filters made by other suppliers.

 

[pentaxuser]

So if split grade printing results in the same contrast as a single grade including decimal points of a grade then is there a mathematical way of working out what the equivalent grade is to the figures ericdan has given us for his split grade. Just to repeat it|: he has exposed 5 s @ grade 0 and 5s @grade 5. So what's the resulting equivalent in a single grade?

What isn't clear to me is what kind of a filtration is inbuilt with LPL VCCE enlarger. Is this a dichroic head which has discrete settings for grades 0-5 but not half grades or is it a kind of Ilford system with grade filters that act in a similar way. It sounds as if he simple turns a knob that give him grades 0-5 but that is my inference from what he has said which may be wrong.

pentaxuser

 

[cowanw]

http://store.khbphotografix.com/Variable-Contrast-VCCE-Module-for-LPL-4x5-Enlargers-LPL100461.html

If you've been using a Dichroic Color head for variable contrast printing, you know that you have to adjust the exposure each time you make a change in the filtration. That's not necessary with a VCCE lamphouse - the f-stop and exposure time stay the same no matter what grade is selected.

Elsewhere I found
The variable contrast filter module used dichroic yellow and magenta filters mounted with an attenuator in a small frame which fit in the slot on top of the lamphouse. The filter was calibrated for both Kodak Polycontrast and Ilford Multigrade papers. By raising or lowering the filter slide, the user had continuously variable filtration.

So the head must provide some mix of Yellow and Magenta that provides some neutral density to keep the times constant, similar to the kodak value 32y/42m for 2.5 in the Ilford sheet packed with the paper.
Which means that 2.5 at 10 sec has the dichroic filters part way in the path of the light.
O and 5 would have the filters all the way in for more filtration.
Assuming the values are the same as my LPL enlarger, in your example, it would be necessary for a 32Y filter for 10 sec to equal a 200 Y for 5 sec. And a 42M at 10 sec to equal a 170M at 5 sec.
This has not been my experience, Please try it and let us know.
Note as the bulb ages and gives off a different colour, the grades values at any one setting will change as the amount of blue and green light available from the bulb, and that can be filtered by the yellow and magenta filters, may change.

 

[Svenedin]

So if split grade printing results in the same contrast as a single grade including decimal points of a grade then is there a mathematical way of working out what the equivalent grade is to the figures ericdan has given us for his split grade. Just to repeat it|: he has exposed 5 s @ grade 0 and 5s @grade 5. So what's the resulting equivalent in a single grade?

What isn't clear to me is what kind of a filtration is inbuilt with LPL VCCE enlarger. Is this a dichroic head which has discrete settings for grades 0-5 but not half grades or is it a kind of Ilford system with grade filters that act in a similar way. It sounds as if he simple turns a knob that give him grades 0-5 but that is my inference from what he has said which may be wrong.

pentaxuser

I believe it’s the same kind of system as my Kaiser VPM 7005 multigrade enlarger. This is VCCE (variable contrast constant exposure). It uses dichroic filters to vary the contrast with a dial that runs from 0-5 and anything in between. In order to keep the exposure constant across the grades a neutral density filter is also employed. This is automatic and varies the light intensity in tandem with adjusting the grade dial. As far as I can remember from the last time I peeped inside my enlarger the neutral density is fully engaged at grade 0 (which actually reduces the light intensity) and then gradually wound out of the light beam as the grade dial is increased. This gives a relatively brighter projected image at the higher grades and hence negates the usual increase in exposure time (as with Ilford filters). As Ralph Lambrecht said though, this is only an approximation and some adjustment of exposure is usually also required. As I understand it, the VCCE is only constant for a particular grey tone and this probably won’t suit the whole photograph.

 

[K-G]

As a guide for contrast and brightnes variations for a certain paper with a certain enlarger/filter combination I made a chart with small prints , exposed with both combination filters and 0 + 5 filters . I varied exposure times for 0 and 5 filter settings to se the effect of dark and bright areas for both maximum and minimum contrast. In my own example ( se enclosure ) I used ADOX Vario Classic paper ( discontinued since a few years ) and my Leitz Focomat IIC with an Ilford 500 H head . The picture I chose is of my grandson as very small ( now ten years old ) and it was selected as it had a good variation of bright and dark areas. It takes some effort to make a chart like this, but it gives you a good feeling for the material you are working with. I hope you can se the filter settings and exposure times that are written close to each picture.
Karl-Gustaf

 

[pentaxuser]

I have to say "the plot thickens" i.e. things become more puzzling. Thanks to the very clear explanation given by Svenedin and mentioned by IanC I am still puzzled why ericdan is experiencing what he is experiencing. If I have understood the VCCE system then what ericdan did should be very close to 2.5 with either way unless I am missing something in terms of understanding how the VCCE system works.

ericdan, as a matter of interest what adjustment is required to your time settings to get the same print with the VCCE as you get at 2.5.

Of course this is purely an academic exercise because, if I have understood the VCCE system correctly it obviates the need for split grade exposure at all. The whole point of split grade is that using single grade exposure with the likes of Ilford filters can only get you discrete half grades at best, whereas two split grade exposures might result in the best grade of say 2.75 which is impossible with Ilford filters but not with VCCE.

pentaxuser

 

[MattKing]

The whole point of split grade is that using single grade exposure with the likes of Ilford filters can only get you discrete half grades at best, whereas two split grade exposures might result in the best grade of say 2.75 which is impossible with Ilford filters but not with VCCE.

This is not the whole point of split grade printing. The whole point of split grade printing is that it permits very fine control of contrast and, in particular, the ability to easily print different parts of scenes with different contrast, all in the same print.
It does not serve the interests of the OP well to try to duplicate a fixed grade 2.5 result by mixing high contrast filter and low contrast filter results. What will serve the interests of the OP well is to observe what the results are when he does that and other mixes, and use those observations when printing in the future. The filter grade "equivalencies" are a decent starting point, but they aren't particularly accurate.
The filter grade "equivalencies" are really most useful for those who are either coming from fixed grade papers, or are trying to duplicate an older, fixed grade paper.

 

[Sirius Glass]

So if split grade printing results in the same contrast as a single grade including decimal points of a grade then is there a mathematical way of working out what the equivalent grade is to the figures ericdan has given us for his split grade. Just to repeat it|: he has exposed 5 s @ grade 0 and 5s @grade 5. So what's the resulting equivalent in a single grade?

What isn't clear to me is what kind of a filtration is inbuilt with LPL VCCE enlarger. Is this a dichroic head which has discrete settings for grades 0-5 but not half grades or is it a kind of Ilford system with grade filters that act in a similar way. It sounds as if he simple turns a knob that give him grades 0-5 but that is my inference from what he has said which may be wrong.

pentaxuser

Dichroic heads allow one to set any value for Yellow or Magenta* [or Cyan] through the range continuously, therefore any contrast grade is possible not just the integer values and half integer values.


* Which according to the two letter troll is not a color.

 

[Svenedin]

I have to say "the plot thickens" i.e. things become more puzzling. Thanks to the very clear explanation given by Svenedin and mentioned by IanC I am still puzzled why ericdan is experiencing what he is experiencing. If I have understood the VCCE system then what ericdan did should be very close to 2.5 with either way unless I am missing something in terms of understanding how the VCCE system works.

ericdan, as a matter of interest what adjustment is required to your time settings to get the same print with the VCCE as you get at 2.5.

Of course this is purely an academic exercise because, if I have understood the VCCE system correctly it obviates the need for split grade exposure at all. The whole point of split grade is that using single grade exposure with the likes of Ilford filters can only get you discrete half grades at best, whereas two split grade exposures might result in the best grade of say 2.75 which is impossible with Ilford filters but not with VCCE.

pentaxuser

Yes, in theory with a VCCE head any contrast setting is possible but such control is also possible with a colour head and it may be that even finer control of contrast is possible with the colour head. I defer to printers who are vastly better than I am. What I can say is that a very fine line exists for certain prints in terms of contrast and exposure which may not be achievable with the 0.5 grade steps afforded by Ilford filters.

 

[Svenedin]

Also to say (I am on a mobile device and no facility is available to edit my most recent post) that the waters are muddied by what is really meant by “split grade”. Is it the use of two seperate exposures to achieve a “straight” print at an intermediate grade that is not achievable with fixed filters OR is it also called “split grade” when one burns particular areas at a different grade? I certainly burn at different grades to specific areas but I don’t split-grade for the bulk of the print -I don’t need to.

 

[cowanw]

http://theonlinephotographer.typepad.com/the_online_photographer/2010/09/lpl-co.html
Here is the how does it work story.
Maybe Ericdan will do the real world test for us.

 

[ericdan]

I have to say "the plot thickens" i.e. things become more puzzling. Thanks to the very clear explanation given by Svenedin and mentioned by IanC I am still puzzled why ericdan is experiencing what he is experiencing. If I have understood the VCCE system then what ericdan did should be very close to 2.5 with either way unless I am missing something in terms of understanding how the VCCE system works.

ericdan, as a matter of interest what adjustment is required to your time settings to get the same print with the VCCE as you get at 2.5.

Of course this is purely an academic exercise because, if I have understood the VCCE system correctly it obviates the need for split grade exposure at all. The whole point of split grade is that using single grade exposure with the likes of Ilford filters can only get you discrete half grades at best, whereas two split grade exposures might result in the best grade of say 2.75 which is impossible with Ilford filters but not with VCCE.

pentaxuser

I’d have to try that. Never

I have to say "the plot thickens" i.e. things become more puzzling. Thanks to the very clear explanation given by Svenedin and mentioned by IanC I am still puzzled why ericdan is experiencing what he is experiencing. If I have understood the VCCE system then what ericdan did should be very close to 2.5 with either way unless I am missing something in terms of understanding how the VCCE system works.

ericdan, as a matter of interest what adjustment is required to your time settings to get the same print with the VCCE as you get at 2.5.

Of course this is purely an academic exercise because, if I have understood the VCCE system correctly it obviates the need for split grade exposure at all. The whole point of split grade is that using single grade exposure with the likes of Ilford filters can only get you discrete half grades at best, whereas two split grade exposures might result in the best grade of say 2.75 which is impossible with Ilford filters but not with VCCE.

pentaxuser

Never tried figuring out the time adjustment it takes to get the same as a straight 2.5 print. I just noticed that I’m getting slightly more contrast with an overall density that’s about the same.
The enlarger must be compensating. It also has a switch I can flip to make it brighter for focusing. That must be moving the neutral density filter out of the way.
The head has three filters in total. They somehow rotate depending on what filter setting you turn the knob to.
Pretty interesting. Didn’t know this is not normal as it’s my first enlarger. Although that’s been a few years now.

 

[ericdan]

This is exactly what I have.
http://theonlinephotographer.typepad.com/the_online_photographer/2010/09/lpl-co.html
Thanks for the link!