Condenser Enlarger Illumination "evenness"

[Jon King]

I recently purchased a Durst L138S enlarger with a condenser head. My previous enlarger experience has been with color heads with a large diffused light source, so this is new territory for me.

The bulb is a large (>4"/100mm dia)opal bulb. As I adjust the bulb location for the most uniform light distribution, the best I can do is to get the corners 1/3 to 1/2 stop dimmer than the center. Is this typical for condenser enlargers? I've read about light intensity variation with a condenser enlarger, but I've never seen any numbers to quantify the drop.

The 138 has seperate condenser combinations for 5x7, 4x5 and 6x9, the combinations I have tried. My enlarging lenses are 180mm/150mm/100mm for the corresponding formats. Results are similar for each setup.

Any suggestions, or am I doing ok with these results?

Thanks,

 

[Jon Shiu]

Hi, I don't know the answer to your question, but was wondering if you are measuring fall off with a negative in the carrier, and if that would make a difference?

 

[Ed Sukach]

In a "collimated" (read: with condenser lenses) system, the classic method of alignment is to remove the lens, and adjust the lamp so that the filament is in the best possible focus and centered. When the lens is replaced the illumination will be the most even.

It sounds (I'm sticking my neck in a noose a bit here - I am NOT familiar with the Meopta system) that the in-and out focusing (for want of a better description) is not quite at optimum - thus, a lot of fall-off at the corners.

 

[Jon King]

Jon, I measured with and without the 5x7 glass carrier - it made no difference.

Ed,

I vaguely remember doing something like that with a microscope lighting system. I'm guessing the concepts aren't too far off. The lamp stage can move in 3 dimensions, and moving the lamp out(away from the condenser) seemed to help with the corners.

I'm just not sure what 'good' is for a system like this. If this is as good as it gets, I'll stop messing with it and start using it. I'd evaluate it now by printing, except it is in the garage, and it is getting a bit cool at night to process prints!

Thanks,

Jon King

 

[Jon Shiu]

Okay, my idea was that the negative's base density would help prevent a hot spot from reflection or something, but you probably have no blank films to test with...

 

[Claire Senft]

print eveness of illumination

I use a Durst S45...a variation of the L138. I have not experienced uneven illumination. If you look at the diagram on the from of your enlarger head it shows the flat surface of the condensors facing down for the bottom condensor and up for the top condensor. This means that when the top condensor is installed the printing on the handle of the condensor will be upside down. Give it a try.

 

[wfwhitaker]

The correct choice of condensers will also depend upon the magnification desired. For a given format and lens focal length, there may be a couple of choices of condenser combinations for that reason. Make sure you're using the correct condenser pair for the magnification at which you're checking the illumination.

 

[Blighty]

I have used a couple of condensor head enlargers (only medium format) and have always experienced a little light fall-off at the edges. It's just a matter of giving a little extra exposure at the edges to compensate. Regards, BLIGHTY.

 

[Brian Bullen]

jking,
I'm not sure if this is possible with your enlarger but many years ago I had a condenser enlarger(beseler 23??) with a contrast filter holder directly under the lamp. In it I placed a piece of frosted glass to help diffuse the light and create more even distribution. Worked wonders and was very inexpensive. SatinSnow might even be able to help you out.

 

[dancqu]

I've read of the Omega B22, a 6x6, that it does well with 35mm. Dan

 

[dr bob]

On setting up my old Omega II, I had a bit of trouble getting even illumination with a 150mm lens, the proper extension cone, and a 4x5 carrier. The fall off was about one stop at the corners and edges. I finally traced the problem to the lamp position. I believe I remember that the “lamp source” (In my case it was a PH112, a standard size light bulb specially designed and frosted for enlarger use) should be focused on the entrance pupil of the lens with the condensers. (????)

There is still a fall off but it is even and only about a half stop which can easily be compensated by “edge burning” the prints when necessary. The abandoned farmhouse in my gallery in an example of a print from a full-size 4x5 negative with the enlarger set up as discussed above without edge burn.

Check your lamp position.

 

[lee]

ask Don Miller he has 3 138's.

lee\c

 

[GeorgesGiralt]

Be warned ;-)

Hi !
I own, and use, a Laborator 1000 which is the 4x5 version of the 138.
The specs claims for a 65 mm opal lamp for negs up to 6cmx6cm and 100 mm above. Unfortunatelly, these are not made anymore. (it seems one can find 110 V version of the 4" bulb, at old new stock prices...)
So I experienced severe light fall off even when using my C330 negs.
First, I asked Durst Italy for a copy of the manual, which they provided free of charge ! Wonderfull service ! It helped me figure what condenser pairs I needed when using a 80 mm lens or a 105 mm lens for medium format, and have the correct condensers regarding enlarging factor. This helped even lighting on the baseboard but does not come close to perfection. So I went out shopping and to my delight found that Philips produced a big (95mm dia) bulb which is a double enveloppe high voltage 150 W halogen bulb ! Upon inspection, I found that the outer enveloppe is even, has no markings, and quite perfectly round. I tested it and this get to the right side but not spot on. So I placed a sheet of tracing paper in the filter drawer (which is between the lamp house and the 45 degree mirror above the condensers) and .... BINGO ! light was as even as I can dream of ! (measured with a RH designs Analyser Pro) ...
So I went to the hardware store and bought a piece of glass used in fireplace doors to prevent the IR to cross ... I frosted it using engine grinding paste for valves, and here I am ... I have to add that this glass help keep flat the printing filters and help increase their life... (this is good because I am now unable to buy new ones, as Ilford has stopped making them.... (it seems they custom made the Kodak ones as well))
Oh, BTW, I own the color head for this beast and I was given the cold light head. I do not like the color head (I think it is un practical to use variable contrast paper with it) and the cold light head is really diffuse, only blue so not good for the VC paper I use.
hope this helps !

 

[Thilo Schmid]

The correct bulb for the 138(S) is a 300W Atlas 3/16 type with aprox. 7.5"x4.5".

You usually cannot prevent a little fall-off, but 1/3 stop seems too much. What is your exact condenser combination for which EL-lens at which aperture-setting?