Mercury Vapour exposure unit:

[vrooooom]

Oooh, DIY numchucks with your vacuum frame.

[Andymac]

Originally Posted by steve w

that is a sweet vacuum frame, looks brand new! If it rotates it's solar capable, just cut a hole in the roof.

[steve w]

it rotates.
do I need those wood blocks, or is the cord lone enough?
those were in there already.

[vrooooom]

We just use a piece of string. Works just fine. I hadn't seen the blocks before.

[Andymac]

burn em.

usually you just have a piece of cord that leads back to the vacuum source. drape the cord over the frame to help the air evacuate. Not sure why the wood. It must be a Chicago thing.

[Tom]

I got a 400w metal halide flood light today. Largest wattage I could get locally so Il be building my exposure unit around this.

The info sheet on my emulsion says a 1000w MH lamp will expose a screen in 500-530 light units at a distance of 120cm. Am I correct in saying my 400w will expose in 800 light units?

How many seconds is 10 light units?

These are suggested exposure times on the info sheet btw, I know some trial & error is needed, I just want to do as little as possible

Thanks.

[Andymac]

there is no correlation between light units and seconds until you set the apperature of the unit and set it up in a fixed position. then you can time the counting light units and get an idea of how many per second.

But if you move the light, it will change. That's the whole point of the integrator.

Measure your biggest image

Take diagonal of that 1.5 x this is your minimum distance of light bulb to glass. (for point light sources. if you had multiple lamps it could be shorter, with fluorescent it is only 4-6")

Do a step wedge test with some good film, standard coating, and time intervals. EVERY setup will be different. Your glass will change the time from the next guy.

At about 5 ft. I get (with 1k lamp, 2&2 Murikami pro dual cure on yellow) initial startup from cold 15 minutes. Once the lamp is warm it takes 9-10. white mesh is quicker by 1/3 (9 yellow = 6 white approx)

A 400w lamp will be slower. If you don't have big screens and you set it up to burn closer, your times will be less.

Don't be afraid to modify your times as you get into this. Don't expect to nail the perfect exposure on the first or second go. BUT-if you put your time into testing, and your setup and technique stays constant after your first tests, you will HAVE A PERFECT EXPOSURE EVERY TIME. FOR EVER. (except when it screws up....)

[Tom]

Thanks for the reply Andy. The diagonal of my largest screens is 40". So this is the minimum distance from bulb to glass so is it okay to have this as my fixed distance or should i go a little further?

I cant go the 120cm the emulsion info sheet recommends as i have very limited space for this unit. Im building a box with glass top. Il be using weight for good contact for now but would like to eventually build a vacuum lid.

Thanks,
Tom.

ps. Anywhere in Europe I can get your book (save on p&p

[steve w]

the diagonal of your biggest IMAGE, not screen

[Andymac]

sorry, i corrected that. 1.5x but you can cheat on that a bit. It's mainly so you don't get a hot spot in the centre, or bad undercutting at the outsides.

Re the book - not at the this time. Postage is outrageous.