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  #1  
Old 25th August 2020, 02:11 PM
Nat Polton Nat Polton is offline
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Default Durst Comask

I have recently been given a Durst Comask masking frame.
No box or instructions. All seems quite straightforward really.
One puzzle though.
The two flaps nearest me Nos. 3 and 4 have a horizontal curve pressed into the flap doors, near the hinge.
I am assuming that the frame is complete, but cannot figure out what these two curves are for.
Can anybody throw some light on the situation?
Cheers.
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  #2  
Old 25th August 2020, 03:33 PM
Mike O'Pray Mike O'Pray is offline
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Nat I have one as well and cannot see the curve to which you refer but that is not to say that all Durst Comasks are exactly alike or I am in fact looking at the same Comask and seeing what you are seeing but not recognising the curves from your description.

Is a photo possible?

Mike
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  #3  
Old 25th August 2020, 04:28 PM
Nat Polton Nat Polton is offline
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Pictures of the ridge.

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The curve is at the pencil tip.
Cheers.
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  #4  
Old 25th August 2020, 07:29 PM
Nat Polton Nat Polton is offline
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I have puzzled it out at last.
The two cross bars can be removed. They look like pieces of retractable steel tape measure, sprayed matt black.
These two bars can be removed from their central location and fitted close to the set of hinges that have the curve pressed into the two flaps.
There are a couple of extra posts on the frame located were the curvy parts are.
The curve in the flaps is there to fit over the top of the bars.
By moving the two bars in or out of the different positions you can form the following masks.

All dimensions in inches.
6.5 x 4.5 .......... 2 windows
7.5 x 4.5 .......... 2 windows
4.5 x 3.5 .......... 4 windows

and of course the window on the other side for a bordered 10 x 8

Have a look at the pictures below.
It was all probably explained if a leaflet was included originally.
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  #5  
Old 25th August 2020, 08:45 PM
Mike O'Pray Mike O'Pray is offline
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Thanks Nat. I have got the two reversed-curved furrows now I look carefully. I hadn't really paid much attention to them until now and if I had I'd have remained puzzled forever as to why they are there. The reason being that my Comask which was secondhand and probably an e-bay acquisition has not got the two extra bars, I have the centre bar only

So I have dimensions 2&3 on your list but not dimension 1. Looking at the configuration it looks to me that in both our set ups the curve is large enough to allow some white light penetration from the side but I have never had any and when I think about it this has to be because the safelight only is in use from extraction of paper from the box to insertion of same paper into the developer so the gap is never a problem.

However if a person were to expose say sections 1 and 2 then have a break necessitating leaving the room or putting on the room light some white light penetrates the room and I suppose there is just some chance that white light then can penetrates the furrow.

Probably far better to open and close the door to the darkroom quickly rather than flood the room with light from the ceiling bulb.

Mike
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  #6  
Old 25th August 2020, 10:56 PM
Nat Polton Nat Polton is offline
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I have not used the frame yet, but it was the thought of the light creeping in as you yourself thought, that got me puzzling.
As I mentioned earlier the extra bars are made of spring steel, that looks exactly like that used for retractable steel rules.
I think they would be easy enough to make if you cut up a retractable steel rule that is getting a bit past its use by date.

I shall put up a couple close shots of the ends, and dimensions tomorrow.
A redundant rule, pair of scissors and spot of matt black paint and a bit of patience is all you need to make a pair of bars.

Cheers.
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  #7  
Old 26th August 2020, 11:09 AM
Mike O'Pray Mike O'Pray is offline
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Quote:
Originally Posted by Nat Polton View Post
I have not used the frame yet, but it was the thought of the light creeping in as you yourself thought, that got me puzzling.
As I mentioned earlier the extra bars are made of spring steel, that looks exactly like that used for retractable steel rules.
I think they would be easy enough to make if you cut up a retractable steel rule that is getting a bit past its use by date.

I shall put up a couple close shots of the ends, and dimensions tomorrow.
A redundant rule, pair of scissors and spot of matt black paint and a bit of patience is all you need to make a pair of bars.

Cheers.
Thanks Nat. How does your two cross bars detach from the middle where they form a cross that gives you 4 opening and then what do they fit to at the bottom to give you the two shorter frames than would be the case if they were merely detached from the middle to give you the two longer frames?

Mike
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  #8  
Old 26th August 2020, 02:53 PM
Nat Polton Nat Polton is offline
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There are four steel pins sticking up from the frame. They have the shape of mini flag poles with a button on top. The whole stud is only about 1/8" high. Difficult to see the shape of the head of each pin but if you run your finger nail up the side of each of the four studs you will feel a sort of click as the finger nail catches the wider head.
I have just measured the bars and they are made of the same springy steel as Stanley Powerlock 3 metre tape measures.
Curved and springy.
The notches in the ends of the bars slide under heads of the pins.
There is a notch on the side frame, either side plus a notch in the middle fixed frame.
This is duplicated for the middle and end positions.
I have arrowed the pins in the photos as it is difficult to see them otherwise.
The arrow sitting on the pink piece of paper points out how the notched bars fit under the pins.
As I said in an earlier post, there should be no difficulty in cutting a set of bars from a discarded spring tape measure using a pair of old scissors.
Good grounds for divorce if the missus catches you with her best dress making scissors.

Cheers.
http://www.film-and-darkroom-user.or...1&d=1598453504
http://www.film-and-darkroom-user.or...1&d=1598453504
http://www.film-and-darkroom-user.or...1&d=1598453504
http://www.film-and-darkroom-user.or...1&d=1598453504
http://www.film-and-darkroom-user.or...1&d=1598453504
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  #9  
Old 26th August 2020, 04:05 PM
Mike O'Pray Mike O'Pray is offline
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Thanks Nat for that very full explanation I have the pins on my Comask but couldn't work out how the cross bars attached as I don't have these bars but now I see the notches in the bars, it is clear. Since your last post I did a bit of measuring and had worked out that to replicate the 1:1.5 ratio of a 35 mm neg which is needed in the area to be exposed, the bars need to be about 20mm wide so it looks as if the bars are slightly lacking on width for this but do come close at about 13 mm to that 20mm width so as near as damn it the paper covers the whole negative at the right height and the width of the bars I suspect would avoid the need to trim the paper to even up the borders as a 20mm bar give a bigger border on left than the right

It might need careful drilling and hacksaw work to get a scrap metal curved notched correctly to fit the studs but should be doable

I have a Stanley metal tape that appears to be of the right width and maybe the right curvature. The only problem is that it is not scrap currently and is in constant use

Mike
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  #10  
Old 26th August 2020, 07:29 PM
Nat Polton Nat Polton is offline
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The metal strip has to be springy as the vee at one end slips under the head of the pin and the strip is then flexed to get the other end under the corresponding pin. Definitely has to be a piece of springy steel.
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