Morte
I have an old Polish Krokus 67 enlarger from the 1980s in my home darkroom. It’s a simple but reliable piece of kit.
However, the opal lamp isn’t the brightest. That’s not a problem with small formats, but I’m currently doing a run of 24x30 enlargements on ADOX MCC, and with filter sheets in the drawer, I’m sometimes getting exposure times of almost three minutes. That’s incredibly annoying.
Now, you can of course replace such opal lamps. However, the one fitted isn’t labelled. The Krokus housing says something about 150 watts, but it’s not clear whether that’s just the circuit’s load capacity or the actual wattage of the lamp inside. I suspect it’s more likely a 75-watt bulb. But how do I find out? Without any labelling at all?
And assuming it is indeed a 75-watt bulb, would the (metal) housing actually withstand 150 watts without the thing starting to glow?
Alternatively, my only option would be to stop down (I use f/8) to shorten the exposure time, but that would result in shadows at the edges of the image, and that’s not ideal.
Does anyone here still know this device and have any advice?
Thanks and best regards
Morte
ErnstKluger
I’ve been using the same model for quite some time. I’ve really appreciated its incredible stability. The description ‘as sturdy as a railway track’ is certainly apt. The Opal lamp was a 100 W bulb. And I’ve always managed quite well with it.
Best regards, Ernst
Morte
The mystery has been partially solved:
After taking the housing apart and managing to loosen the bulb that was stuck in its socket, I discovered a barely visible embossed mark above the bulb’s thread. It is a 75-watt bulb.
To find a quick fix (i.e. more light output), the following idea occurred to me:
There is a frosted glass panel in the filter drawer. It is rather amateurishly secured on two sides with adhesive tape; it looks more like a transport safeguard than the factory-fitted state. Now, I don’t know enough about this: can’t you just remove this frosted glass pane? Is it needed as an additional diffuser, or isn’t the opal coating on the lamp sufficient for light scatter? The pane seems to absorb quite a lot of light, it seems to me.
bernhardmangelsgmxde
Just give it a go – I didn't have any problems with the enlargers I used without a diffuser on the condenser.
Urnes
Hi Morte,
If the enlarger is vignetting with the aperture open, start by adjusting the lamp properly. If I’ve understood correctly, you should be able to loosen the lamp socket and move it up and down along the centre rod; this should allow you to adjust the lamp so that it illuminates the image evenly when the aperture is open.
Regards, Sven.
Morte
Hi Urnes, I’ve already done that, but I’m not entirely convinced … In my experience, there are no problems at f/8 (the smallest aperture is f/4). Besides, people always say that image sharpness decreases at wide-open apertures. I’ve relied on that so far and everything’s been fine. It’s just a bit of a faff …
ThomasPauly
Is the condenser a single or double lens? With single-lens condensers, an additional diffuser is indeed required.
Morte
It’s a simple condenser. I’ve removed the diffuser and don’t get the impression that the light scatter has deteriorated. Of course, I haven’t tried it with a print yet.
Incidentally, Wikipedia states that the diffusion screen has become obsolete due to the introduction of opal bulbs. As I said, this is a sturdy but simple enlarger. Perhaps it was actually intended for use with standard (clear) incandescent bulbs. Unfortunately, I don’t have an instruction manual to check this.
bernhardmangelsgmxde
To check for vignetting, I’d try taking a grey print without a negative, using a f/5 aperture; if there’s no vignetting visible, it’s fine. I don’t think my Durst F30 had a focusing screen on the basic condenser either, and yet the illumination was still sufficiently even.
piu58
> making a grey print at just 5 when there’s no vignetting
With extra-hard paper, you’ll *always* see some unevenness in the exposure on affordable printers, at least to a small extent. This is much less noticeable in the final image, as it’s masked by the subject and balanced out by dodging.
Urnes
Hi Mort,
It depends on the lens. You’ll just have to try it out to see if an f/4 aperture isn’t actually sufficient. After all, the depth of field doesn’t need to be very deep for a sheet of paper. I’ve got lenses at home that you can easily use at a wide aperture.
I’d still switch to 150W, though. I find it easier to focus when it’s brighter.
Regards, Sven.
ErnstKluger
It’s a simple condenser. I’ve removed the diffuser and don’t get the impression that the light scatter has deteriorated. Of course, I haven’t tried it with a print yet.
Incidentally, Wikipedia states that the diffusing screen has become obsolete due to the introduction of opal lamps. As I said, this is a sturdy but simple enlarger. Perhaps it was actually intended for use with standard (clear) incandescent bulbs. Unfortunately, I don’t have an instruction manual to check this.
Hold on a moment, something’s not right here!
The Krokus doesn’t have a single condenser. It has the ‘brick’, which consists of two condenser lenses positioned in the condenser box with the appropriate spacers. Either you’re missing one half of it, which would explain some of your problems, or you’ve got it wrong. Just have another look carefully.
Regards, Ernst
Morte
Just for general information:
I have now produced a whole series of 24x30 prints WITHOUT the diffuser and haven’t had any problems whatsoever with sharpness, vignetting or anything else. The exposure time has been significantly reduced, and focusing at wide aperture has become easier thanks to the extra light. Overall, I’ve now arrived at an average exposure time of about 40 seconds, which works very well for me. I’m doing without a more powerful opal lamp for the time being, as otherwise I’d probably end up with very short, difficult-to-control exposure times for small formats.
One more comment on Ernst Kluger’s objection:
I think you’re right. The condenser is set into a round metal frame, which is black and looks a bit like the wooden packaging for Camembert in the supermarket (only about twice as thick). The whole thing does indeed resemble a briquette. I haven’t checked again to see if there are actually two condensers inside, but it looks like the factory standard. It must be right.
Thanks to you all for the advice!
Morte
