TR
Hello everyone,
A while ago, I bought the Krokus 6x9 enlarger with a colour head, as I needed a compact yet sturdy ‘6x9’. Unfortunately, the filter values for the ‘two-filter method’ don’t seem to be documented. So far, I’ve only managed to find out that the filter values are supposed to correspond to those of Meopta or Agfa. For Agfa, I’ve found a table at Ilford for filtering with a single filter. However, I prefer to work with both filters. Can anyone help me and provide some reference values regarding the “two-filter method” for my camera?
Or compare them yourself: whether the same amount of light reaches the base plate with the two filters set can easily be measured using a lab exposure meter. But how could one measure the respective “colour value” or compare it with the Ilford gelatine filters (or those of another enlarger)? Would this perhaps be possible with a colour temperature meter? I could borrow something like that. Or is a measuring device of this kind required for correct filtering when making colour prints?
Regards,
Thomas
Tandemfahren
Hello Thomas,
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I had the same "problem" despite supposedly using the correct filter table. It inevitably ends up in fiddly, imprecise adjustments, and in my opinion, this is for two main reasons:
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1. Are the tables supposed to apply to every type of paper? That’s simply not possible. The actual characteristic curves and contrast behaviour of the papers vary too much.
2. The tables generally do not specify exactly which target density is supposed to remain constant with different filtering.
?? You could measure that, but you don’t have a table at all, do you...? :-(
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The simplest solution: manual split grade. It’s so simple that I regularly kick myself for not having done it this way all along.
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Basically, all you need to do is provide exposure for a test strip for each type of paper, using maximum yellow filtration, say in thirds (yes, that’s right, THIRDS. Set the timer to a scale of thirds).
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The exposure value that results in Zone VIII (simply compare with a grey scale) is your reference for this paper.
You then adjust the contrast using only the hard filter. That’s all there is to it. Doubling the magenta exposure corresponds to approximately one gradation step.
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(Of course, you don’t have to use Zone VIII as your target highlight density. Just choose a very light tone for which you have a reference.
Similarly, you can of course start with the shadows rather than the highlights – that is, with hard exposure – and ‘fill in’ the highlights with soft filtering, particularly with rather flat negatives)
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lots of colourful light and Frankgröße
TiMo
Hi Thomas,
I can only agree with the advice given by the gentleman above.
I spent ages trying to create a mixing chart for my Fujimoto too, but Splitgrade is easier. Especially if you don’t have a densitometer.
With Splitgrade, you also have the advantage of being able to dodge full yellow and full magenta separately.
Best regards, Tim
Wolfgg
Hello,
I also have a Krokus 69S with a GFA colour mixing head.
For the two-filter method, you could theoretically take the values for Durst here and multiply them by 2; the Krokus uses Agfa values:
http://www.silberbild.info/positiv/zwei-filter-methode/
The only problem is that the actual filter values for the Krokus aren’t that accurate. With 200Y, for example, I once measured a 30Y error using a colour analyser. I would definitely recommend split filtering, as it doesn’t require precise filters. It does take more time (you have to turn the Y and M in and out twice for every image), but the results are excellent if you test everything properly.
Regards, Wolfgang
TR
Hi everyone, and thanks for the advice. I’ve finally got round to replying today. I’d already suspected that there isn’t – and can’t be – a clear-cut definition. I’m no stranger to the term ‘split grade’. However, I asked the question because I work with a slightly modified form of ‘split grade’:
I look for the area in the image that, on its own (local contrast), requires the harshest gradient (e.g. a wall texture at grade 4), and this is my first exposure. I then re-expose all other parts of the image separately at 0 (and sometimes also at 5). This saves me time and effort, as well as test strips. However, whether the wall texture in the example looks best at grade 4 or perhaps 5 is something I can only estimate at the start, and the two-filter method would be ideal for quick ‘switching’.
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Now I’ve come up with something else: For the first exposure, I simply use the magenta control (yellow remains at 0) and have to somehow measure out or test a pattern to see what the exact time extension or reduction factors look like with different magenta values, in order to just about reach the paper’s maximum black – for a specific type of paper, of course. Unfortunately, the extension factors given in the tables are useless. I’ll then also have to come up with a way to quickly obtain the extension factor from, say, grade 2 to 4 (i.e. to ‘skip’ a step). Admittedly, this isn’t as elegant as the two-filter method. On the other hand, I get a higher light output, which I’ll probably need anyway, as I only own the 6x9 condenser and it’s naturally quite dark.
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To assign the magenta values to the respective gradients (1–5), I will initially use the aforementioned Agfa values as a rough guide.
However, I don’t know exactly which filter setting corresponds to which gradient on my paper.
Are there any reference values regarding the respective exposure range? Something like this: Exposure range for Grade 5: 3 stops and Grade 00: 9 stops (always based on the Dmax just achieved)? Then I could use a transparency grey scale to assign the respective magenta setting on my head precisely to a specific gradient.
Tandemfahren
Hi Thomas,
I’m not quite sure I’m following you, but I suspect you haven’t quite grasped the principle of split grading.
You don’t need to abandon your line of thinking (which, in my view, is too complicated) – just give split grading a go, following the instructions to the letter.
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You won’t need to waste any more thought on gradation levels and the like; there are only ‘highlights’ and ‘shadows’ left.
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Just a quick note on the print runs for magenta and yellow: it depends on your filters and your paper; you’re better off forgetting about it (or just perform exposure on a few streaks with a transparency grey scale so your conscience is clear; that’s what I did too). Besides, you can’t use Dmax as a guide here, because every paper has a more or less pronounced shoulder, so it approaches Dmax asymptotically at best (not really, but something like that),
meaning your measurement scale has no defined end.
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It wasn’t long ago that I was fiddling about in exactly the same muddled way, and it got on my nerves. So don’t take my word for it – try it yourself!
You’ll see for yourself, and afterwards you’ll laugh at yourself for making it so difficult.
A Marian apparition is nothing compared to this!
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encouraging Frank size
