I've been using a set of homemade BTZS tubes made from ABS pipe. They work fine, except every now and then a 4x45 negative exhibits slightly higher density in the *center*. Edge density is fine.

Anyone have any idea how this can happen?

Let me stress that the density is in the center of the negative, and is not a 'streak' running width-wise across the negative. If you look at a negative, you'll a circular section (about 2" in diameter) of slightly higher density in the center of the negative.

A friend who has a Jobo couldn't explain it either.

Ideas?

BTW: HP5+ 4x5 sheets, Ilfotec HC 1+31, 7:30.

-- Ken Miller (andawyr@hotmail.com), September 06, 2001

Answers

Could it be your lens? that you need a center filter? If you are using some of the wide angle lenses and you are seeing higher densities in the center, and it is a circle then I say it is not the developing but the lens. If it walks like a duck, quacks like a duck, and swims like a duck...maybe it is a duck..:-))

-- Jorge Gasteazoro (jorgegm@worldnet.att.net), September 06, 2001.

Ken,

A few years ago a made a set of rollers and tubes for 8x10 negs from ABS. I had a similar problem, especially when longer development was required. My rollers allowed the tube to travel laterally while it was being rolled. A friend suggested that if the movement was excessive back and forth, the developer would slosh slightly side to side and in the middle their would be an increase in turbulence where the wave fronts met. He was a mechanical engineer, and I don't know if he really knew anything about fluid dynamics, but after I put a couple of stops on each end to hold the tube stationary while rolling the problem was eliminated. If you notice sideways "walking" of the tube this may be your problem.

-- James Chinn (Jim1341@dellepro.com), September 07, 2001.

Jorge:

The lens is a Roddenstock Grandagon-N 75mm. I have noticed some falloff around the ledges, but never excessive density in the middle. I've taken a reasonable number of shots with the lens, and have not noticed this center density in all the shots.

James:

I run the tubes in a fairly narrow container, and so they don't have a lot of movement left-to-right. However, I'll try and make sure that the rotation is a bit 'smoother', and that I don't bounce the tubes up and down too much (which may cause the sloshing you mention).

Thanks!

-- Ken Miller (andawyr@hotmail.com), September 07, 2001.

Ken i apologize for not reading the post abit more closely. I would agree with Jorge that it may be an exposure problem since you describe the density change in the middle of the neg. One other possibility could be film holders. I recently bought a 4 used riteway film holders and after using them had a couple negs with the same problem you describe but showing overexposure indicating some sort of a light leak. In any event once a narrowed it done to the offending holders the problem was eliminated. Just another possibility.

-- James Chinn (Jim1341@dellepro.com), September 08, 2001.

No problem James.

I'm starting to suspect that the 75mm is the cause. I was under the impression that you would only see fall-off if you did any sort of movements, but I guess that isn't the case; the fact that you can by center grads for the 75mm illustrate that point. Searching on Usenet yields lots of hits on just tihs subject...

I will, however, veryify that it's not the holders that are causing the problem. I'll take a test shot or two of a single-colored object (a wall) and inspect for fall-off.

We'll get there.

-- Ken Miller (andawyr@hotmail.com), September 09, 2001.