Film has different density from lead to tail edge

[egorus]

Heidelberg Primesetter.
Lead edge density is less then tail edge.
10% dots on lead edge almost disappear (like as 3-4%).
Online processor is clean, chemistry is new.

 

[PDL]

On all films, or just the first of piece to run? Just curious.

 

[maxon]

New chemistry does not rule out the processor. Make sure you use the correct developer and parameters are checked - temperature stability, machine speed and recirculation pump condition being the most important. Expose a 50 percent raster rectangle full size to test uniformity ; cut, process, measure center and corners. Expose same job with machine in complete darkness, cut, then intercept the film sheet just before entering the online processor (you have to figure out how) and feed it backwards. Process, measure. If density now increases head to tail you should suspect the primesetter optics, could be dust or autofocus problem.

 

[maxon]

One more thing I've seen old film processors with worn out rollers and bushings unable to pull film smoothly, you may need to check dev section rollers and gears moving easily driven by hand. Again, the uniformity test I described will tell the drive system condition, look for banding and patterns indicating film is slipping or slowing down.

 

[egorus]

10% screen (on picture). Lead and tail edge.

On solid black:
lead edge film dencity - 2.88
tail edge film dencity - 3. 66

"Expose same job with machine in complete darkness"
How I would to see in the darkness?

 

[maxon]

You won't see much with 10%. Do a 50% grey test (or even 80) full area as advised because it will (mosy likely) rip as 45 degrees making artifacts more visible.
Did you check the processor ?

10% screen (on picture). Lead and tail edge

Just asking why do you measure density instead of percentage ? I have processed the picture you sent, they threshold as 6.1 and 2.6 percent respectively.

How I would to see in the darkness?

That's for you to figure out. I don't know what film processor or bridge conveyor you have. You may use a very dark green light to avoid fogging the film. I hope you understand why is it important to feed a sheet of film rotated 180 degrees.

 

[egorus]

Primesetter 74 and online processor Colenta.

 

[John W]

Go to be slipping in the machine during development. I suggest with lights on, ruin a piece of film but watch it carefully though the tanks. Usually, with a recirc pump down, the tailing edge would be the weaker density not stronger.
I'm guessing the film is slipping once past the dev tank and into the fix wash dry. so the tailing edge is getting more dev than the leading edge. Since it isn't streaky, then the slippage must be uniform. Or the dev temp heater is on too much during processing so hotter means more density.

 

[DonBlock]

You guys are killing me..... The optics are dirty, it's a very common issue.
Just be careful not to scratch the mirror or lens.........

 

[egorus]

DonBlock, You are right!

The optic was dirty.
We cleaned it.
Density became uniform and higher.
3.6 (before) -> 4.6 (after)!!!

There was one problem...
Dirty air bearings nozzles in laser head...
It overheats and makes a noise.

Can we clean them yourself?

 

[DonBlock]

egorus, the "air bearings" are actually Teflon pads that separate as the motor spins up creating a cushion of air for the motor as well as provide for braking when the motor spins down. I would not attempt to do anything with it yourself. You should look for someone who is qualified to work on that type of motor.

 

[egorus]

In Primesetter 74 installed Thermoelectric Cooler Tec 12703 30*30 mm.
It's right?
What are its electrical characteristics?
We have it crashes once a year...