omega lens cones produce reflection

[quigon]

Hi everybody.
Last year I bought an Omega enlarger at a reasonable price. Now I'm fighting with lens cones. I use both 135 and 150 mm lens and luckily manage prints with a single lens cone (the one for 135 mm lens). What I've been unable to suppress is an annoying reflection created by the lens cone. It seems that the flat surface of the inside of the cone creates a white circle all around the projection of the negative on the easel. I've tried without the lens cone (mounting the lens directly behind the bellows) and the reflection vanishes.
Any idea? Have all the Omega cone users the same problem?
Luigi

[R.K]

I have Omega enlarger and I never had problems with lens cone. But mine cones are black inside. Are you cone black? ore maybe you have some chromium plated lens mounting ring.

[photog_ed]

I suspect the problem is caused by reflection from the underside of the negative carrier, after reflecting from the lens or unpainted lens cone. The early negative carriers were bare aluminum on top and bottom. If you are worried about this illuminated ring (I don't think it will affect your enlarged image), you could paint the inside of the lens cone and the underside of the negative carrier black is was done on later carriers.

[Jac@stafford.net]

To make sure there is no light-leak from under the negative carrier, I suggest adhesive black flocking paper (https://www.edmundoptics.com/lab-production/general-tools/65-20quot-x-26quot-2-sheets-non-adhesive-flock-paper/)on the negative holder facing the lens side, and another flocking paper on top of the carrier facing the light source. It will not only stop light dead, but its minor depth will help seal the junctions.

All you need is the paper and a razor, such as an X-Acto (http://www.xacto.com/products/cutting-solutions/knives) knife to trim. It's easy, almost a pleasure to use.

I have used the stuff for decades. It is really dead, non-reflective. I do not recommend paint because it wears off, chips on negative carriers. (Though for non-contact surfaces I do recommend only one particular flat-black paint: Testors spray #1249 with primer)

[quigon]

Here are two images to show the effect (hope it is visible) and the inside of the cone that is matt painted black
177582177583

[Mark Sampson]

I've seen that forever- but I have never seen any effect on any of my prints. I gave up trying to figure out where it comes from.

[Bill Burk]

You would see it when you photograph several prints for display on the web and flip through them - because the ring of additional density may be camouflaged by any single print... but revealed if seen in sequence.

I agree, it would be light reflected off the back lens surface, shone onto the back side of the negative carrier which is near the image plane, so it is sharply imaged around the negative.

[Jerry Bodine]

When I bought my Omega 5x7 enlarger new in the late '60s and saw the negative carriers were bare aluminum, I immediately took them to a local processor and had them all dipped in an anodizing tank that applied a durable flat black color to all the surfaces. I think the most important surfaces are the edges of the format cutouts, as enlarger light can reflect off these surfaces and produce a slight additional density at the edges of the printed image.

[photog_ed]

Now that I see your photo of the effect, it must be something else, but I'm not sure what. I assume you're worried about the large-diameter ring that is well outside the image.