DURST CLS 501 head filters and light field

[Serg Lavrenchuk]

I have a practical question - what is real density field unevenness obtainable with Durst 501 CLS heads?
We were trying to play with it changing lamps and mixing boxes.

With Durst Test neg printed 0.7/0.7/0.7 we get 0.7 in the middle and -0.15D and -0.10D at left and right sides. Actually we see denser and more “blue” circle from lamp reflector + lamp filament in the middle on the grey print. That is with 66N mixing box + dif2 installed.


And the second question about DURST CLS 501 head I = in the manual for 1200 enlarger Durst write that 130 uits filtration on CLS501 head is about 195 CC units (about x1.5 conversion should be applied). Tests with color meter shows that 100 filtration on Durst CLS501 is about 100CC. Also general recommendations by Ilford for BW Multigrade paper advice filtrations for general contrast values (Grade 00 to 5) for Durst 0-130 heads that are generally more or less accurate (at least not x1.5 times wrong).

Looks like in the manual Durst wrote some unadequate information about “more dense filters” ?

 

[AgX]

There are several different units used on colour heads indicating filter density.
There is the engineering one (desitometric density) and at least 4 units used by 3 manufacturers.

 

[ic-racer]

Light intensity at the perimeter of the enlarger's projected image is influenced by many things such as magnification, lens construction, aperture, in addition to mixing box design and distance from the negative. For example the diagram shows this lens can obtain 80% (roughly 1/4 of a stop) at the corner of the frame at f11 with a low magnification. Whereas at f5.6 at large magnification, the relative illumination at the corner of the frame is less than 30% (a little less than 2 stops).

 

[AgX]

The same time vignetting at taking to some extend can be compensated by vignetting at enlarging.

 

[Serg Lavrenchuk]

Do you think Durst in CLS501 actually used densitometric but wrote in the manual not correct info?
For me now that is the only explanation.
Another way I can't explain why Ilford recommendation for "Durst max 130 filtration" lets say 10Y / 69M for Grade 4 are working with CLS 501.

There are several different units used on colour heads indicating filter density.
There is the engineering one (desitometric density) and at least 4 units used by 3 manufacturers.

 

[AgX]

In my notes I read that Durst filter units are 1.3-1.7 x densitometric density..
That I wrote that range indicates that I learned of different values in past.

 

[Serg Lavrenchuk]

Thank you. My lack of specific education tricks me. I really got out of my mind that lens might be an issue actually (don't know why).
Somehow It was stopped down heavy to f22 from f5.6 and I decided that 105 APO lens should be more or less linear at these settings.
Magnification was about x5 what looks like a minimum of optimum range.

May I ask for your advice. Actually two
- Do you think some blueish color from filament and circle from lamp glass on the 0.7/0.7/0.7D grey print is a real limit of CLS 501 color path?
- 0.05D difference between left and right part of the image should be searched in the lens or mixing box influence?

 

[Serg Lavrenchuk]

In my notes I read that Durst filter units are 1.3-1.7 x densitometric density..
That I wrote that range indicates that I learned of different values in past.

I would make a measurement of +30Y +30M +30C filtration. Would it reduce exactly one stop the light intensity?
I think with 1.3-1.7 x-factor that test would give noticeably bigger influence for exposure time. Would post results soon.