Testing contrast range of color mixing head (LPL7700): difference in contrast only at the extremes?

sterioma

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Hello,

For the first time I have an enlarger of my own that I have bough used: an LPL7700 (previously I was printing at a shared darkroom to which I don't have access anymore, so unfortunately I cannot compare with other enlargers).

To get a feeling of the range of contrasts available to me, I have made a series of 8 contact prints from a step wedge (Stouffer T2115), from 200Y all the way to 170M.
Honestly I have thrown in the "extremes" just of curiosity, expecting to see most of the differences in contrast around the "central settings" of Y and M, going by the "contrast grades" of the paper manufacturer suggesting to start around 60Y and end at 130M (there are no specific settings for the LPL so I am extrapolating a bit from other enlarger brands such as Durst and Meopta).

If you see the scan below, nothing much changes around the central settings (60M to 30Y looking largely the same?).

Just curious if this "unexpected" (something wrong with the enlarger head)?
My next step would be to create more steps in the gaps between 170M and 100M, and 60Y and 200Y respectively because that's where, it seems, the real difference exists.

Paper is Fomaspeed Variant RC (I repeated the same experiment with Fomabrom Fiber Base and the results are virtually identical). Paper is around 2 years old.

All steps have the same exposure (32' at f4) and identical development (they were all exposed in series, kept in a black paper envelope when waiting and then all dropped in the developer at the same time. I have tried to minimize the difference in the developer when moving them over to the stop bath 2/3 at a time).


 

MattKing

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sterioma

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That's interesting, thanks for the link. Ilford lists quite a few more enlargers than Foma. I wonder how transferable are those numbers (my range is actually 200Y to 170M which is not quite the same as Kodak) but it is worth a another try (I do happen to have some Ilford paper that I use for contact sheets, i could try that too).

If we assume that LPL is similar to Kodak, i would have thought the difference between grade 1 (50Y) and grade 3 (25M) to be more pronounced. My 60Y and 30M look quite similar.
 

ic-racer

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These are the ISO(R) values estimated from the posted images:

30Y = 150 GR 00
60Y = 150 GR 00
120Y = 225 GR 000

Looks like a smooth progression with Magenta (though one grade off).

170M = 90 GR 3
100M = 105 GR 2
60M = 120 GR 1
30M = 135 GR 0
10m = 158 GR 00

Can you see the yellow filter moving smoothly?

Does the Magenta filter totally cover the opening at 170?

Is the developer exhausted?
 
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sterioma

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Thank you, this is helpful.

ic-racer said:
Can you see the yellow filter moving smoothly?

Does the Magenta filter totally cover the opening at 170?
Click to expand...
I haven't got much experience peeking inside an enlarger, but from what I see the filters move up and down completely. There are a few screws that I suppose allow to finely control the height of the filters up and down although there is no mention of it in the user manual that I have.

One thing that occurred to me: is it possible that the halogen lamp is not of the right colour? Maybe it's a touch on the warm side, so the light is overall "too yellow"? I am not sure how I would test this. I cannot say that it's visually very warm, but it's hard to tell if it's the "right" colour.

ic-racer said:
Is the developer exhausted?
Click to expand...
I use Moersch Eco 4812 that lasts for a long time even at working solution. I am able to reach maximum black, and the print seem to start developing at the expected rate (they are fully developed at 2.30m). I can mix a fresh batch just in case next time.
 
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sterioma

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I have ordered a new lamp in the mean time (A1 231 100W), just to exclude that the current one is not of the right type or has aged. At least, I'll have a spare one once the current one fails.
 
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MattKing

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sterioma said:
I have ordered a new lamp in the mean time (A1 231 100W), just to exclude that the current one is not of the right type or has aged. At least, I'll have a spare one once the current one fails.
Click to expand...

FWIW, I always advise people to order two lamps - if the one in the enlarger fails, its replacement is already at hand.
Unless of course you are happy to have the one currently in the enlarger serve as your backup.
 

Doremus Scudder

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Some random thoughts:

The color temperature of your bulb shouldn't really have much effect on the extremes of the contrast range since the filters are the larger factor determining what the spectrum of light is that reaches the paper. However, in the middle ranges close to no filtration at all, lack of blue light being produced by the bulb would definitely show up as reduced contrast. Let us know if a new bulb makes a big difference here.

If there is a lack of blue light in the emission spectrum of your bulb, then exposure times at the maximum magenta setting would be quite long; extra time would be needed to make up for the small amount of blue light being transmitted. This does not seem to be the case with your test, so maybe there's something else going on.

If you really want to see the extremes you can get from the paper, try exposing your step wedge with Wratten #47 and Wratten #58 filters (blue and green respectively). These are the standard color-separation filters. I have found that I get significantly more contrast with a #47 than I do with max magenta on my color heads.

You don't mention your print developer or your developing time. There may be more variability there than you think, especially if you are underdeveloping your prints.

At some point, it's not really important what filtration setting you need to use to get a particular contrast range from the paper as long as you can get the full range of contrast somehow.

Best,

Doremus
 
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sterioma

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Update test, with fresh developer (Moersch Eco 4812 at 1+14), new bulb and my most "fresh" paper (llford RC MG V).




As I was having trouble developing multiple strips in one go without issues, I have decided to create a rough mask with a cardboard and simply move the step wedge across a single piece of paper. Unfortunately I have not managed to keep the table aligned all the times but it probably gives enough information.

There is maybe a marginal improvement compared to my previous test, but 170M (max magenta) is probably still a bit too soft?
 
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Sirius Glass

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If one uses split grade printing, then one does not need to be concerned with grades.
 

ic-racer

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Looks pretty good. Make some prints and see how it goes.
 
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sterioma

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Out of curiosity, I have bought a pack of graded fomapan paper (Fomaspeed N 311, which is a grade 3) to see what a "nominal" grade 3 would look like. In the mean time I have also done a side by side test of my current Moersch eco developer against a freshly mixed E-72.

Here's what I have found by contact printing a few more test wedges:

1. The Moersh developer mixed per instructions (1:14) is indeed a bit soft compared to E-72 1:2 (I think I've read that you can also mix the Moersch eco 1:10 for a bit more contrast, so I could try that; however it's getting difficult to source that developer in UK at reasonable prices, so I am tempted to just mix my own E-72 for a bit).

2. Fomaspeed VC glossy paper needs around 120M filtration with my colour head and developed with fresh E72, to reach the equivalent of a graded 3 fomaspeed paper (170M is my max, so I probably I can just about reach grade 4 if needed). This is by visual inspection comparing a few test wedges at 10M increments (I don't have a reflection densitometer).

I would like to settle on the equivalent of grade 2 as my "normal" filtration level, but I am not sure how to calculate what grade 2 is now that I have a fixed point with grade 3 (unfortunately Foma only sells grade 3 and 4 for their graded papers). I find it hard to just "count" the steps and map them to ISO R, as I am not sure which steps I should ignore (just the pure black and pure white, or "just off white" and "almost black"?, etc...).

I am tempted to arbitrarily just declare "60M" as my grade 2 and be done with it. Thoughts?
 
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ic-racer

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Seems like that developer is on the soft side, but just add extra magenta and start printing. If you have negatives that won't print with your magenta at maximum, get some higher contrast developer just for those or get the #4 paper. Otherwise you will likely be fine for most of your prints.

Most VC papers indicate they are about Grade 2 with no filtration with the paper's specified developer. But I'd not worry about that because you have already figured it out with your own equipment and developer (declare 60M as grade 2).
 

MattKing

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With my old Ilford Multigrade 400 light source, which intentionally only went up to an indicated grade 4, I added a below the lens filter holder and sourced a grade 5 filter for it. On the very rare occasions I needed more than the Multigrade system offered, I added the grade 5 filter to the light path and set the light source to grade 4.
 
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