# built own exposure unit to replace yudu... problems shooting sceens



## personalazeit (Nov 5, 2009)

I've been successfully using a yudu unit as just my exposure unit. I've been good until my images get too big for it. So my husband built me a light box over the weekend. We couldn't afford the metal halide bulbs so figured we'd be fine with the same but bigger. There are 6 Philips 25 watt 24" T8 fluorescent bulbs. They're about 8" below the glass, which is clear. (the yudu glass is a little opaque)

This am I will do a test to calibrate exposure times. It did good with a very simple large image... but, halftobes  not good. I have read several posts with regard to halftones so keep in mind I've successfully been using my yudu even for halftones.

The image I have is full of different halftones, from 10% of black to 90% of black. Printed with accurip on Epson blackmax system. Using Lpi of 60, and dpi of 800. Before doing an exposure test, I just did what I always did on the yudu. On the 305 screen, yellow mesh, for 2 minutes. The screen completely washed out. For kicks, I had another pre coated 305 screen handy and did 4 minutes. Here's my key sticking point... most of the image is acting over exposed. The 90% of black part of the image completely washed off the screen.

I'm even washing screens of with a shower nozzle. Do have a pressure washer but didn't seem necessary.

Before I used the yudu successfully I spent time on the phone with kiwo. They have me successfully using polygon one-coat with no diazo. Is this my problem?

I have pictures of everything, just need to get to my laptop to upload.

Any thoughts in the meantime? I'm out of emulation and busy reclaiming screens to start all over. Emulsion will be here soon.


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## personalazeit (Nov 5, 2009)

Finally the pictures...

One is the new exposure unit, the others are the 2 screens with halftones not working at all, one is definitely under exposed, the other over exposed, but either way, not working. Did a step test and with a regular step test, the exposure unit works great at 1 minute and 30 sec to 2 minutes depending on the white or yellow mesh. But when I try halftones, no good. There is also a picture of the yudu, just to see the differences between the 2 visually. Mine is definitely bigger so I can fit the whole screen over light (that was my problem in the first place).


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## InkedApparel (Mar 18, 2009)

what are you using to get good contact from the film to the glass? any weight? you need to have possitive contact between the film and the glass......also halftones need less burn time than say a solid. how opaque are the films...if you hold them up to the light , can you see throught the films?

Inked


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## personalazeit (Nov 5, 2009)

I don't have a vacuum system, but we cut a very heavy piece of plywood and covered it in 3 mil garbage bag, then on top of that I don't know how much weight, but LOTS! It's basically the same thing I was doing with the Yudu. Today for example, the screen did not shoot very well, it was under exposed. So I grabbed another screen and did it on the Yudu and it was back to normal. Just trying to figure out the differences between the 2. From what I can tell, the lights in the Yudu are closer to the glass, the inside is coated with a reflective siding on all the walls and the glass is opaque. Those are the 3 obvious things we are thinking of changing next, but if it's not the problem, don't want to bother.

So less time with the halftones??? That's good to know then. I'm only washing these screens off in the shower and the halftone area is washing right off... but again with this new unit. I didn't try the same film with the yudu yet. My films are printed from the epson blackmax ink system, they are very black, not see through at all.

Thanks!
Tracey


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## selanac (Jan 8, 2007)

Personalazeit,

You need a thick glass about 1/4" and 20 lbs of weight on top of your screen. Also need a really dark piece of material over all of that to keep the light out. 

The glass should be NON-UV.

Also, your screens look like they're under-exposed. Try 5 minutes, then 6 if that doesn't work. 

The Flourescent Bulbs should be Un-coated Black Lights, not white flourescent. Grow lights work too.


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## macumazahn (Jan 11, 2007)

That looks like you glass may be the issue. I had the exact same problem with my home built metal halide unit. I asked for glass with no uv coating at the store but that wasn't what I ended up with. I will second the notion for good contact for the film positive as well that was another issue I also had. Use 1/4 inch glass at least, half inch would be better though. I actually ordered a low iron custom glass tabletop that fit my design perfectly and have been humming along relatively well. Halftones are tough anyway so once you get everything dialed in it will still be a learning experience on a home built unit. Just keep trying


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## personalazeit (Nov 5, 2009)

Got my new bulbs today, so excited! BUT not sure if I'm fixed yet, don't have any spare screens to try. First thing I noticed... the new bulbs are 18 watt (which I wasn't paying any attention to). They are T9 18 watt un-coated uv blacklights. So, when we yanked the old (new) ones out and put these in, there is a huge difference between this and the yudu. Not bright at all? Is this normal? The ballists I'm using were 15 watt, should that make a HUGE difference in brightness or not much??? Like I said I haven't shot a test screen, but I guess I've never seen a black light like this before. This making me even more curious, I took the yudo completely apart because I had to know what it has in it that has been working fine all this time? The details written directly on the bulb are: T8 15 watt FSL T8 15W/765 YZ15RR ROHS so I'm going to do some internet searching to see what that is. The are only 4 of those, 18" in the Yudu. And a screen shot of 1 min. 30 sec on a white 110 screen is always perfect. The under shot screens you're looking at above were done on the newer unit that isn't working. I will try to test a screen this weekend, but those are my details thus far! 

Thanks everyone!!! Will keep you posted!


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## Bob Wellen (Jan 25, 2011)

Hope this doesn't get confusion. first move the lamps up to about three inches from the glass. Wrap the wood in some black cloth to make sure that there is not light refraction. Weight the wood to emulate a vacume frame. Look up either bulb tronics or wester quartz on the web. Call them and get lamps that have a pectral range of between 360 and 420 nanometers. that will expose your emulsion a lot better and a lot quicker. If your using the proper emulsion you should be ab le to shoot it completely without closing down finer copy or halftones. My opinion is that if you have to lower the exposure thime to hold copy then you are compromising the emulsin to begin with. Try Murakami HVP. It is photopolymer and with the addition of diazo it becomes water and discharge ink resistant.


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