LPL c7700 strange circle in prints

Hello photofriends.

I've recently bought a LPL enlarger because i've restarted making analogue prints of my photo's taken with a mamiya 6.
In accordence of the steps written in 'Way beyond monochrome' i've started to calibrate de dichroic filters and have now noticed a strange cirkel in my print. You can see a scan as attachement.
I've done several tests with my enlarger, for example I used my 50 mm Apo Rodagon 2.8/50 and my componar-c 4.0/75. I also made a print without a neg in the enlarger (to exclude the step-wedge as source). Printed one with max Yellow as well as max Magenta. Nothing seems to help, the strange foggy-like cirkel remains. I've tried to messure densitydifferences on the easel (SWA2000 analyser, Ferm) which are minimal/neglectable. I even have replaced the bulb, since the one fitted had the bulb lose in its reflector (there was a Osram HLX 64627 EFP fitted, is this the correct bulb?).

When I examened the inner parts of the enlarger I noticed that the lens mounting ring has a large aluminium cirkel just around the thread of the lens and is further black painted. I serious doubt that this can be the raeson but still I've put black paint on the aluminium surface which is still drying.

I've also made a scan of the neg-less print, but in the scan this cirkel is hardly visible (I've probably printed it with to much density) in the original it can be seen.

Is anyone of you familair with this problem and can help me with a solution?

Kind regards

Guus

FotoGys said:

When I examened the inner parts of the enlarger I noticed that the lens mounting ring has a large aluminium cirkel just around the thread of the lens and is further black painted. I serious doubt that this can be the raeson but still I've put black paint on the aluminium surface which is still drying.

Click to expand...

Hi Guus

I had the same problem; stray light bounces off the bright metal and causes the ghost image. Your black paint should cure it but next time you use the lens mount the other way up, the paint will start to scrape off. Instead of paint, I use a washer-shaped ring of black paper cut from the light-proof bag from a pack of photo paper. This covers the bright ring and cures the problem.

Hope that helps!

Hello Richard,

I'am gonna wipe of the paint and make a paper cover, so I can try this out immediately. Let you know if it also workes for me.

Thanks for the fast reply and offered solution.

Kind regards,

Guus

Hi, did your enlarger come with a diffusion chamber (the metal and styrofoam thing) that mixes the light?

Jon

Hello Jon,

Yes the LPL c7700 has this diffusion chamber for mixing the light.

I've opened this chamber to look inside/clean it if necessary and the only remarkable thing I saw was the plastic bottomplate with glossy, angled sides on the inside and an even, pearl look on the outside.

Regards,

Guus

The 4x5 LPL's diffusion chamber bottom is a soft plastic (I suspect polyethylene) rather than the acrylic used in in cold light heads and other dichroic enlargers like Durst. It's thicker in its center than the edges to compensate for corner light falloff.

I went through three chambers before finding one that didn't have a high-density imperfection somewhere within the diffusion bottom plate. Each one that had this problem exhibited light spots on prints, since the "nodule" inside the plastic blocked light from reaching the negative in that area.

I suggest you examine the diffusion plate against an even light source and look for obstructive inclusions where your prints show the light circle.

Hello Sal,

the problem that can be seen in my prints are of the kind that there must be somehow extra light during exposure (phantom image), rather then the problem being caused by light blocking imperfections in the base plate as this would cause brighter spots in the prints rather then darker cirkels. I stil have to try out the paper ring on the aluminum cirkel on the lens plate as Richard suggested but will also check the diffusion bottom plate, just to eleminate any possible faults. Thanks for the suggestion.

kind regards,
Guus

Sal Santamaura said:

I went through three chambers before finding one that didn't have a high-density imperfection somewhere within the diffusion bottom plate. Each one that had this problem exhibited light spots on prints, since the "nodule" inside the plastic blocked light from reaching the negative in that area.

I suggest you examine the diffusion plate against an even light source and look for obstructive inclusions where your prints show the light circle.

Click to expand...

FotoGys said:

...the problem that can be seen in my prints are of the kind that there must be somehow extra light during exposure (phantom image), rather then the problem being caused by light blocking imperfections in the base plate as this would cause brighter spots in the prints rather then darker cirkels...

Click to expand...

In the negative-free image you attached:

(there was a url link here which no longer exists)

I see several areas that are brighter, not darker than the overall gray. Those are the defects I was attempting to troubleshoot. The dark circle wasn't even noticable on first glance; I only see it now after you've pointed it out for a second time.

I'm not sure what aspect of the enlarger / diffusion chamber might be causing that dark circle, but it's far less bothersome to me than the lighter areas. I'd work on those before worrying about the circle.

OK, I should have read you initial post more carefully. The dark circle really is obtrusive in your step wedge print.

I've never had this kind of problem with my 4x5 LPL enlarger. All my circular lensboards are all finished in black, inside and out. If you have one that's not, and black paint doesn't absorb enough light to eliminate the circle, perhaps some black self-adhesive velvet will solve the problem.

Sal Santamaura said:

In the negative-free image you attached:

(there was a url link here which no longer exists)

I see several areas that are brighter, not darker than the overall gray. Those are the defects I was attempting to troubleshoot.

Click to expand...

Hi Sal,

I see what you meen, there's an explanation for de bright spots in the scan which aren't visible in the original neg-les print:
To make the circle somewhat visible I had to scan with olmost max. contrast and hughe brightnes on a, over 10 years old, Primax scanner. That's probably why the not visibly printdesity differences in the original have become visible in the scan.

Hello everybody,

it took some time to be able testing the washer-shaped ring of black paper cut from the light-proof bag from a pack of photo paper as suggested by RH Designs. The results are amazing. Not only the foggy circulair ghost image disapeared but also the overall level of fog has disapeared. This is what I call the cure of more then just my problem, it's a hughe improvement.

Once again, thank you all for the suggestions and quick response.

Guus

Thanks for that tip. Apparently the newer lensboards are all black (my 670 VCCE was made around year 2000). I just took a look at an older lpl lensboard I got on ebay and it has the bright silver ring. I'll cut out a piece of black paper today for it.

Jon

Sal Santamaura said:

The 4x5 LPL's diffusion chamber bottom is a soft plastic ...
It's thicker in its center than the edges to compensate for
corner light falloff....a high-density imperfection somewhere
within the diffusion bottom plate.

Click to expand...

Same here but with a Meopta Dichroic. Prints had light
centers and darker edges and corners. Has one wondering
how much dodging and burning is going on due to those
poorly designed bottom diffusion plates. Dan