PhilippReichmuth
Hello forum,
I’ve managed to pick up an Ilford Roller (aka Durst Comot) for €2. Now I’m wondering whether I should use it for film development as well as the paper processing I’d originally planned, if I only have one or two rolls of black-and-white film to develop and don’t want to go to the trouble of starting the machine up. I use a Paterson Multitank 3, Super System 4. In principle, rotary processing should be feasible with this; after all, Paterson also offers its own rotary processor (Auto-Colortherm).
I have the following questions regarding this:
- What is the density of the rubber lid in practice during rotation? I’ve just run half a litre of water for 20 minutes, which went well; are there any empirical values for longer periods of rotation?
- How much liquid needs to go into the tank? For tilt development, it holds one litre; unfortunately, the figures for rotation aren’t listed. It’s likely to be slightly more than with Jobo, as the tank is a bit wider at the top and a few extra decilitres will probably rotate along with it.
Thanks – Philipp
cfb_de
Hi Philipp,
First of all: I don’t rotate it. I only use my tin can roller for papers, though I did have to part with more than two tokens for it. Congratulations on your purchase!
You’ve already checked whether the lid stays tight. I’d take the small residual risk.
Regarding the fill levels:
You’re absolutely on the safe side if the tank is half full. Just assume the tank is a cylinder, measure the height and radius. The volume of the cylinder is given by pi*r²*h. Half of that, and the thing is half full.
It becomes more accurate (and better reflects reality) if you only calculate the section of the cylinder that you need.
To do this, wind a (developed) film onto the reel as you always do. This is now located somewhere on the outside of the tin. Draw a line across the inside of the film (i.e. the last section inside the reel). This line intersects the arc of the tin. You determine the length of the line using a set square (place the perpendicular edge at ‘0’ on the reel’s ridge; that’s the easiest way).
Together with the can’s radius, this line forms an isosceles triangle (twice the radius, once the “line”). From this, you calculate the angle formed by the two radii (law of sines) and thus obtain the area of the circular sector via (“angle” sin(“angle”)*(r²/2). Multiply that by the height of the tank to get the required volume. If you calculate the lengths in centimetres, the result conveniently comes out in ml :-)
Adjust for minimum developer quantities if necessary; in any case, add a bit extra for ‘safety’ and a good night’s sleep.
Hope this helps, best regards,
Franz
PhilippReichmuth
Hi Franz,
Thanks. During my lunch break, I worked out an approach using something like ((\pi * angle/360) - (sin(angle)/2)) * r for the arc. It does make sense, and it matches your approach using radians:(Just need to add a bit for the overhanging part on the lid and for the liquid in the spiral.
Which way round should I insert the spiral? Intuitively, I’d insert it so that the liquid spirals inwards rather than outwards, or am I wrong, or does it make no difference?
Philipp
cfb_de
Hello Philipp,
As I said before, I don’t rotate it. But off the top of my head, I’d also guess it rotates in a ‘clockwise’ direction.
On the other hand, it can’t be that critical, because ‘proper’ rotary processors alternate the direction of rotation.
But – as I said – I don’t rotate it; I’m just guessing here.
Best regards,
Franz
Wolf_XL
Hi Philipp,
I’ve been using the Durst Comot for film development for at least twenty years now – 90% of the time with a Jobo 1236. No problems so far...
I usually rotate with combination processes where the tilt development time would exceed 15 minutes. As this usually involves high dilutions, reducing the developer volume is generally out of the question for my applications – the minimum amount of developer concentrate would simply not be met... When determining the amount of developer for rotation, I would, on the one hand, use this value as a guide and, on the other hand – though this is my subjective opinion – ensure that, with the developing tank lying flat, the liquid level roughly corresponds to the radius of the tank.
