Relining the Chromega light mixer

I’ve had my Super Chromega D Dichroic II for over twenty years and have never paid much attention to the light mixing chamber that sits above the negative carrier.  I don’t print color, so the change in light color from long term yellowing has never caused me much grief.  Lately, though, I’ve noticed that I am not getting even light distribution across the entire negative area when I print 35mm and it could be even worse with larger negative sizes.

I noticed that the central area of the diffusion screen on the bottom of the mixing chamber has become quite glossy in the center and tests have shown that it reflects the negative.  Well, actually, it reflects the white negative carrier which results in a band of brighter light around the outside edges of he 35mm frame.  I was able to remedy the problem by covering the diffuser with dull finish diffusion material (like the diffusion material used on studio lights) or by covering the top of the negative carrier with black paper.

Nonetheless, the diffuser and lining of the mixing chamber had become yellowed and the shiny spot in the center made me think it needed to be replaced.  Luckily, Omega sells a relining kit that can be purchased through B&H for $98.50.  I ordered it and it came this week.

The mixer is accessible by removing the front door of the Chromega lamp house.

The lining kit includes the foam pieces, diffuser, and instructions.

First, remove the six screws that hold the top on.

You may need to pry the top off using a small screwdriver at the corner.

Save the springy plastic “pressure loop”. It will be reused.

Remove the long pins that hold the top foam piece on.

Next remove the tight fitting front and back pieces.

The output diffuser can be removed by pushing up from the bottom.

The old liner is on the left and the new kit is on the right.

I used a razor blade to bevel the upper edge of the top foam piece.

The bevelling of the upper edge eliminates interference with the cover.

Install the long pins to hold the top foam in place.

Replace the pressure loop.

Finally, install the cover and secure it with the six screws. Be careful not to over tighten the screws.

I noticed the new output diffuser has a glossy surface on the bottom and a matt finish on the top, opposite from the old one.  This is problematic because the glossy surface reflects the white edges of the negative carrier resulting in uneven lighting of the negative.  As noted above, the reflection can be eliminated by covering the diffuser with a piece of dull diffusion material or by covering the negative carrier with black paper.  I intend to use the latter option, except I will paint the negative carrier black.  I sometimes use Ilford Variable Contrast filters under the mixing chamber and, since they are glossy, they would present the same issue as the glossy diffuser.  Making the 35mm negative carrier black will reduce the light output, but  that suits me fine since I often find myself having to use neutral density filtration to get long enough exposure times with faster papers such as Adorama RC.

Unfortunately, I neglected to make a color temp reading of the light output before relining the chamber, but the light looks whiter.  I wouldn’t be surprised if my prints showed slightly higher contrast for the same filtration due to the replacement of the old yellowed liner.

If you want to test the light distribution of your enlarger, just make a high contrast print (max magenta filtering or a #5 VC filter) without a negative in the carrier.  Ideally, the print should be a uniform gray tone from corner to corner.  If you see light fall-off toward the corners, you might try using a lens made for a larger format.  For example, I get more even light distribution using my Nikkor 80mm lens than I do with my Nikkor 50mm lens.

ZoneMaster II Button Replacement


           RH Designs ZoneMaster II

I have had an RH Designs ZoneMaster II enlarging meter for years that I use regularly.  A few weeks ago I noticed that one of the buttons had become unreliable.  I had to press it hard several times to get it to work.  Since I am in the US and RH Designs is in the UK, I decided to try and fix it myself.  As it turned out, that was not terribly difficult.

I should note that electronics has been both a hobby and career for me, so I am used to working on electronics circuits.  If you are not comfortable doing simple electronics repair work, you might not want to attempt this.  If you decide to go for it, you can reduce the risk of damage by using an anti-static wrist strap.


             ALPS SKHHBWA010

I can’t say precisely what button was used in the manufacture of the ZoneMaster II, but  ALPS makes a close match.  The ALPS part number is SKHHBWA010.  I ordered  from Mouser at $0.15 each plus a small shipping fee. To see an accurate picture of the switch you may have to click on the data sheet rather than relying on the representative illustration shown on the website.

The ZoneMaster can be disassembled by removing the four black Phillips head screws on the bottom and carefully separating the top and bottom of the clam shell box..  I recommend checking to make sure the power switch is turned off and then removing the battery.

Open Clam Shell Box

                                                  Open Clam Shell Box

The circuit board is held in place by three short Phillips Head screws, one in each corner.  Be careful not to accidentally damage the push-button power switch.  Jewelers screwdrivers come in handy at this point.

Circuit board removed from box

                                Circuit board removed from box

Carefully work the circuit board out of the plastic box and turn it over to see the buttons.  To remove the buttons you will need a small soldering iron (25-50W or so) and either a “solder sucker” or some solder wick.  Flip the circuit board back over and desolder the faulty button.  The molten solder can be sucked off with the solder sucker or soaked up with the solder wick.  Being too rough or using too much heat for too long can damage the fragile copper traces on the printed circuit.  After removing the solder, use small needle nose pliers or tweezers to work the pins loose so the button can be removed.

Faulty button removed

                                           Faulty button removed (yellow circle)

The new button is a match for the old faulty one and seems to require very similar operating force.  The “click” sound made by the new button is a little different, although certainly not enough to matter to me.

New button is on left, old on right

                                New button is on left, old on right

The hole pattern for the switch is rectangular, so it can be installed in two ways.  Since the pins are symmetrical, it doesn’t matter which way you install it.  Be sure to press it all the way into the holes on the circuit board and solder all four pins.

Reassembly is the reverse of disassembly.  Be careful not to strip out the holes in the plastic box when reinstalling the screws and remember to reinstall the battery before buttoning everything up.  It might not be a bad time to replace the battery while you have everything apart.

If everything went well, you didn’t ruin your very expensive enlarging meter.

Nothing is Ever Simple

In the process of adding older pictures to my website galleries, there was one I wanted to add but apparently lost the print.  So, today, I reprinted it.  The first print I made was of the wrong negative.  Duh.

The second print I made was great except for one tiny dust speck.  Rather than spot it, I decided to hunt down and destroy the dust particle.  It turned out to be stuck on the negative and would only come off after I used a moist Q-Tip on it.  I made another print and the speck was gone.  Success!  But, wait.  It didn’t look right.  Slightly crooked or something.  I straightened it up and made yet another print.  Still not right.  WTF?

I finally realized that I put the near perfectly symmetrical negative back in the carrier emulsion side up.  I don’t remember ever having done that before, but the emulsion side of TMax 100 film is quite shiny, so I didn’t notice it.

The five prints are pictured below with the first print (from the wrong negative) on the far right and the last (final) on the far left.  Look closely and you’ll see that two of the five are reversed.


Picture details:
TMax 100, 6×7 cm, RB-67 with 127mm lens, Developed in TMax RS, scan from 8×10 print on Ultrafine  VC Elite RC pearl Paper.  Shot in my very cramped unheated garage in December, 1998, long before I had a dedicated studio.

Lynnette, 1998

Lynnette, 1998