Walk me through lamp adjustment on the Durst 138

I've been reading Jens Jensen's article on enlarger light sources (http://www.durst-pro-usa.com/pdf/COLIMATED%20LIGHT%20VS%20DIFFUSED%20LIGHT.pdf)

On page 16 he talks about focusing the lamp filament: "Adjusting the lamp is done visually and only requires that you know what to look for."

My question is, what am I looking for?

The logistics of my setup are as follows: Thorn 300W bulb, 200 over 130 condensers, and a 90mm Apo Rodagon lens. I primarily print 6x6 negatives 6.5" x 6.5" or 9.5" x 9.5"

So far, I have adjusted the lamp the get the most even amount of light. I use an enlarging meter and test prints of a middle grey tone to confirm this. That's the extent of it. Reading the article makes me feel like I'm missing something.

Can anyone walk me through their process? I'd appreciate it!

Thanks.

Here's the manual. Page 12 is what you want. It sounds like you've done it right. That's how I adjust the lamp on my 606 too, by visually checking it, and w/ a light meter used in different places on the image shined on the baseboard w/ some white paper on it.

My guess is that he means uneven illumination or light falloff.

http://www.durst-pro-usa.com/pdf/manual/L138S_manual.pdf

Hello Momus, thanks for taking the time to respond. I've never seen the lamp filament that Jensen refers too. I suppose that's because I'm using a frosted bulb. I've only ever used frosted bulbs in my enlargers. When I get into the darkroom next I will look try and see if it's there. Otherwise I suppose I'll just be content with even illumination and get to making prints instead of fussing over technicalities.