Gast
Hello,
I’ve got the Meochrom colour mixing head for my Opemus 5 enlarger. The Meochrom is still the old version without a ‘filter off button’ (to quote the manual ;-)… so the unit only has the knobs for the three filters.
If I turn all the filters to zero, are all the colours then turned out as well? That would make the most sense to me.
I would like to use the Meochrom with multigrade paper, specifically with Fomaspeed Variant III paper.
The paper’s data sheet also provides a table with filter values. Can these values be used without further consideration?
Or rather, how can I test whether the set colour values actually correspond to a specific gradient?
Can a Laborbeli Kaiser Trialux help me with this? The Laborbeli works by removing all filters/colours, then measuring the darkest and lightest areas where detail is just about visible, and subsequently displaying, amongst other things, the paper gradient.
Then I put the colours back in and measure again to get the correct exposure time. But how do I know that the gradient is correct? How can I verify this?
I hope I haven’t made myself too unclear or am thinking along completely the wrong lines.
Best regards
Carsten
MirkoBoeddecker
Carsten,
You’re quite right. However, we don’t have a table for a Meochrom 5 either.
But if you’re willing to do without your Kaiser to start with, then you can happily get on with enlarging away.
If it’s too soft for you, turn the magenta up until it’s right – if it’s too soft, turn the magenta down until it’s right.
Whether that corresponds to 1, 2, 3 or 4 is relatively unimportant.
If 00 magenta isn’t enough – add yellow until it stops getting softer.
Ultimately, you decide when the contrast meets your expectations.
It isn’t really important to know what the effective paper gradation was.
Best regards,
Mirko
cfb_de
Hi Carsten,
You’ve got almost the same kit as me. I use an Opemus-5 with a ‘modern’ Meochrom (= with a filter adjustment lever).
So: is the filter out when it’s on ‘out’? Unscrew the top and have a look inside. You’ll be able to see. On mine, I have to readjust the cyan filter (the previous owner didn’t need it either, and neither do I, but you want everything to be perfect, don’t you…).
It works fine for MG papers, of course. But you need to be aware of a few things: adjustment tolerances on these ‘extremely precise’ scales. Filter values also depend on the paper. And: Very important: these “time-corrected” filter combinations between magenta and yellow only ever apply to a single grey level!
It’s not for nothing that the unit of measurement “gradient” isn’t standardised anywhere and differs from manufacturer to manufacturer. Even twenty years ago, Tetenal “special” was roughly equivalent to Ilford “normal”. With fixed gradation and the enlarger I used most back then.
I use a Trialux as well. However, after the first twenty sheets of paper, I learnt one thing: you can forget about “measuring the gradient” with that thing. It’s nothing more than a mostly incorrect assumption (cf.: the gradient is relative, etc.).
I measure without a filter once to get a rough idea of the gradient (usually the thing shows far too little). Then I measure again with the “recommended” gradient and make a test strip. If that works, fine.
Since I usually expose entire rolls of film under reasonably consistent lighting conditions (and, incidentally, print a maximum of 15 exposures per 35mm strip), I stick with the gradient I’ve found, leave the filters screwed in, and then only measure three points.
Mirko, a silly question to finish with: What sort of halogen bulb goes in the Meochrom (grey, new, interference filter)? And: Are there any weaker ones available? I find it too bright and the extra dimmer is a nuisance in my makeshift darkroom. That’s where I usually keep the photo paper.
Best regards,
Franz
Gast
Hello Mirko and Franz,
Thank you for your replies.
From everything you’ve written, I can see that the gradient—that is, contrast—is a very subjective matter.
So far, so good.
Now I’ve seen various ways online of how to use the filters. As single filters (either just yellow or magenta) or as double filters (a combination of both colours).
Which makes more sense?
I find the single-filter method easier to grasp at the moment.
I think I’m a bit out of my depth when it comes to colour theory, or perhaps I haven’t quite got to grips with it all yet... or maybe I’m just making it too hard for myself to understand.
The less yellow, the ‘harder’.
The less magenta, the ‘softer’.
Is that right?
... and the impression of the photo’s contrast is what counts anyway... regardless of any specific values... OK.
Well then, I’m looking forward to seeing the first results when I get round to enlarging.
@Franz
Do the filters have to be completely outside the diameter of the mixing chamber’s opening?
In my case, the filters each protrude inwards a tiny bit.
When I remove the lid of the head, I can see the three filters each hanging from a lever with a slotted hole. The rods for the adjustment knobs are each fixed in the slotted holes.
However, the rods are always already fixed at one end of the slotted hole. That means, if the filters were to be outside the diameter of the mixing head, I’d have to file or mill out the slotted holes (whichever’s more convenient ;-)
But when I see how the linkage is attached – namely with miniature retaining rings – the very thought of tinkering with it gives me a mild panic attack. I wonder how they managed that in series production at Meopta? ;-)
Is the bulb just a standard halogen bulb? I can well imagine that. After all, the light is ‘processed’ in the mixing head.
If so, I can certainly imagine that there are also halogen bulbs with this base available for 75W or less.
Perhaps it’s worth asking the usual lighting manufacturers?
Regards
Carsten
cfb_de
Hello Carsten,
The double-filter method has the advantage that the exposure time remains the same for at least one grey tone in the print. Insert filters from, for example, Ilford work in the same way (i.e. they are also a combination of yellow and magenta filters).
The filtering works roughly as follows: Yellow = soft, None = approx. grade 2–3, Magenta = hard. The extremes that can be achieved depend on the filter density. With Amaloco Varimax (which apparently contains Varycon), I can’t quite reach the ‘hard’ limit with the Meochrom and have to use the grade 5 insert filter as well.
With mine, too, the filters protrude a tiny bit into the beam path. That doesn’t matter at all, as there are all three of them. Taken together, they act like a neutral density filter and darken the light beam—which is far too bright anyway—slightly. No tinkering is needed there.
Regarding the lamp: As I have to test my filtering anyway (every lamp has a different colour temperature, which also changes over the lamp’s lifetime), I have no problems with the following approach:
The previous owner had already fitted a dimmer to the power supply to the transformer. I calibrated this in steps and then created a separate filter table for each dimmer setting. Of course, I could simply have fitted a weaker lamp, but why should I remove the one that’s still intact when I have to test the filter values anyway?
What was more important to me was tinkering with the enlarger itself. It has been fitted with a new, now flat, base plate, and the column has also been given additional stabilisation. I built a sort of ‘inverted U’ out of aluminium profiles, bolted to the top of the column and the bottom of the base plate. Now nothing wobbles anymore and I can also use the filter drawer without any shaking.
Best regards,
Franz
Gast
Hi Franz,
I’ve got the hang of the gradient now.
I’d now like to put together a table based on test enlargements to compare the filter settings with the approximate gradient.
But if it’s all so subjective, I imagine that’ll be quite tricky.
Of course, ultimately it’s your own impression of the photo that counts, but I wouldn’t mind a bit of a helping hand to get started.
As I only got the mixing head yesterday, I’m keen to see what the new exposure times are like. Before, with the condenser and a 75-watt opal lamp, it was quite a relaxed process.
But having read a few articles here about the bright lighting from the Opemus colour mixing heads, I reckon my exposure times will change drastically too.
I’ve already thought about making the Opemus more stable. Your solution sounds good. I’d been thinking of something a bit more complex, for example.
I still have an old Beseler 23C here, which I want to spruce up a bit in the winter or whenever. The Beseler has two guide tubes and is very sturdily built as it is.
I like the principle of the two guide tubes. I’d been thinking of something like that for the Opemus too. That is, I’d place a column to the right and left of the actual guide column, connect these to each other, and then fit guides for the additional tubes on the Opemus. Plastic plain bearings would work very well for this, as they’d run beautifully on chromated tubes.
The guides are a fairly simple welded construction that you can either have a coating applied to or simply paint.
I would use plain steel for the material. I’m not worried about the weight, as the enlarger stands on a very stable base and, besides, all the joints would be bolted for easy dismantling. Luckily, I also have a stationary darkroom.
But perhaps I’m just using a sledgehammer to crack a nut. ;-)
Regards
Carsten
cfb_de
Hi Carsten,
I don’t have a dedicated darkroom and am using my bathroom for that purpose instead. The enlarger is usually kept in the least suitable room imaginable for the job: my bedroom.
That’s why weight was definitely a factor in my DIY project. But even if weight hadn’t been an issue, I would have solved it in the same way (albeit using 18/10 stainless steel). I consider the head’s guide on the slant to be sufficiently stable; the problem is the wobbly mounting of the slant. You simply can’t get it tight enough in all directions.
That’s why I made the frame; now I have a sort of ‘triple saw’. At the top, where my “frame” overlaps the sloping surface, I’ve attached it to the saw using a wing nut and lock nut, which allows me to adjust the head so it’s parallel to the base plate.
The lighting with the Meochrom is really great, by the way. For small formats I dim it down; this evening I made a 40x50cm projection onto the wall. The head was set to “full brightness” and I had an exposure time of just two minutes (projection onto 150x150cm) at f/8. However, you do need to block out the stray light from the colour head somehow (I quickly “converted” a large cardboard box for this purpose).
Perhaps of interest to others too: Quick adjustment of such an enlarger for wall projection: My door (=projection surface) is easy to adjust: using the door lock in conjunction with the hinges, you can adjust it in all three directions. This is done using a spirit level; I just check it afterwards.
Align the enlarger with a spirit level as far as possible. The tricky part of the adjustment is getting the negative plane parallel to the projection plane. To do this, with the door plumbed, I carefully plumbed my laser pointer, screwed it onto the tripod and screwed one of these ‘pattern templates’ onto the front. The part that creates a very symmetrical dot pattern. I traced the pattern onto a piece of wallpaper; now, based on the position of the ‘projection square’ on the patterned wallpaper, I can very quickly see whether I’m actually projecting a square image. If necessary, move the enlarger; all that remains is to correct the left/right deviation.
However, I’ve once again got myself worked up over the design flaw from Prerov: the filter drawer is at the *bottom* for wall projection. Every time you tilt it, the diffuser hits the condenser; using sheet filters (which I need to achieve maximum gradient) is out of the question – they fly mercilessly past your hand onto the floor when you change them.
Oh, and by the way: creating a table is easy if you use a grey scale and familiarise yourself with the ISO-R calculation for the paper beforehand. Then you can work out which filters correspond to which ISO-R for your paper. Meticulous people use a densitometer for this; I did it by eye. After all, I usually view my prints with my own eyes rather than with a reflected-light densitometer.
Best regards,
Franz
CarstenM
Hi Franz,
I kept my Duka in the bathroom for quite a while. But all that faffing about putting it up and taking it down really got on my nerves, so when I renovated my kitchen, I cleared an entire wall and fitted a kitchen worktop with base units there. I now have about 3 metres of space, and the enlarger is always there now without getting in the way.
The base cabinets hold the rest of the lab stuff – bowls, beakers, etc. The fridge with the beer, paper and chemicals is in there too. It’s all very practical, as before the equipment was scattered all over the flat.
Incidentally, I live on my own, so there are no issues whatsoever with using the kitchen. ;-)
I haven’t dared to try such large enlargements yet. If I were to do that, my doors would be completely unsuitable. They’re made of wood and have seen better days. In other words, some of them are already quite warped.
For large enlargements, I’d use a large board that I can hang up and attach three adjustable feet to level the board, resting against the wall. I can then level the board using a spirit level.
Tell me, Franz, how did you solve the problem of stray light on the Opemus? I find that a lot of light escapes, particularly around the negative stage. I have a metal stage and use glassless inserts.
As for filtering with the colour mixing head... there’s a very good course on sensitometry at the neighbouring online photo shop. I’ve read through it and will now try to put what I’ve learnt into practice.
Regards
Carsten
