Exposure Test when using a Vacuum Top?

[mimosatexas]

Just transitioning to a 1000w Metal Halide from my Fluorescent Tube exposure unit.  Due to space constraints and the desire to expose some pretty huge frames for certain projects, I would like to build a vacuum frame with a pivot so I can line up the screen while horizontal, then flip it vertical and open the shutter on the ballast.  This would also allow me to reposition the ballast to keep the proper 1.5x image diagonal as the distance from the frame.  Basically I'm going to make my own version of something like this: http://image.made-in-china.com/43f34j00YsDTfIqlVHkg/Large-Vacuum-Frame-Exposure-Units-SE-1624VG-.jpg

I had a few pretty basic questions, and just wanted to get others' opinions and any random advice on how to calibrate my exposure times or pitfalls of using the metal halide.

Questions:
1. Can I just use a step test by taping strips on the outside of the glass and pulling them every 5 or 10 seconds to lock in exposure time, or is there a cost effective way to really dial it in with some kind of gadget?
2. Any idea how long I should let the bulb warm up before exposing?
3. Any issues I should be aware of with these bulbs when it comes to leaving it on for too long?

Really just looking for any advice that will save me time and headaches.  I do not need help with the actual build (I build basically all my equipment and this is really basic), but if you have an unusual tip about that feel free to add it if you want.

[tpitman]

As for exposure times, get a Stouffer strip. They're cheap. Takes the guesswork out of the job. Victory Factory sells 'em. Others do too. Here's a link:

http://www.victoryfactory.com/tools.htm

4th item down. Seven bucks.

[mimosatexas]

Awesome!  Thanks!

[Gilligan]

Yeah, those are pretty cool.

Picked one of them up in a bundle of other stuff we got from a shop and we burn it on EVERY screen.

Great checks and balance and if you don't have a light integrator (we do) it will also keep an eye on your aging bulb and let you adjust accordingly.

We still do step wedge but we also put this guy in there and cover it at the point that we THINK we might be right... then not only do we have step wedge results we have a 2nd piece of data to confirm the 1st (if we were close with our guess).  This guy tells you how much to go up or down in your exposure depending on which way you were off.

[Frog]

If you are going to try a manual step wedge test without opening the frame, just make the exposed strips on your film wide enough to not need to worry about the possibly iffy edges.

If you're ever in NorCal, I would probably let my Olec 5k head and ballast and integrator go pretty reasonably, but I'm not dealing with crating or shipping heavy metal..

That's one of the reasons I have a surplus of Heat presses as well. (Sorry Dan, one is even for hats)

Oh, , I let my MH without an integrator warm up for 4-5 minutes. (2-3 is probably all it needs)

[blue moon]

make sure you have an integrator. Without one, your measurements will eventually become obsolete/irrelevant. . .

pierre

[mimosatexas]

I'd buy that Olec off ya in a second, and probably the heat presses too   I have two hat presses now, and use them for sleeves and labels 95% of the time, and they rock it out.  I've been wanting to add two more, but the only ones that have been coming up for sale in central texas have been the 20+ year old wood handled National's, and the 18 year old national I have is plastic crap compared to my 15 year old analog geo knight (I have a 15 year old 16x20 geo knight as well, and both presses are amazing...)

Whats the best source for the integrator?

How quickly do these bulbs age?  I go through about 40 screens a week right now, usually burnt in 4-6 separate sessions depending on how the jobs come in.

[Gilligan]

Those stouffer strips are a bandaid for a lack of integrator like I mentioned... But I LOVE having an intergtrator, set it and forget it!

[mimosatexas]

Sorry for my ignorance, but how does the integrator work or what does it do exactly?  Are all integrators the same or do I need a specific type or model?

[Frog]

The simple answer is that they measure light in units. That way, once you have an exposure dialed in, it will compensate for bulbs getting weaker or fluctuations in power, and stay consistent. Time may change, exposure will not.

Some are mounted in the head unit, and I assume that some have a sensor that can be mounted under the glass.

[mimosatexas]

I would assume that it doesnt really matter where the sensor is, as long as you dial in your exposure based on it being in the same place (so in front  of the glass may read more units due to the glass not blocking any UV, but regardless the amount of UV will be consistent over time?)

Does it simply read the amount of UV and display it, and you pull the screen off or close the shutter when it hits the ideal number, or does it somehow integrate with the actual exposure bulb or can be setup for some kind of auto shutter?  Since the Metal Halide I'm using isnt instant start, it would need to have a shutter, and being able to automate that closing would be awesome.

[Frog]

In the Olec, and I assume most units, it closes the shutter.
You will have to be clever and come up with a relay and spring or something similar, or just use it as an indicator and slide it yourself.

I used to really concentrate on the newbie /DIY stuff on forums, and have never seen someone get this sophisticated because, except as a labor of love, it's probably more trouble and expense than procuring a decent used commercial unit.

[mimosatexas]

I get a kick out of building my own stuff, and I still have enough random down time right now that it doesnt take away from my press making money.  I'll probably manually work the shutter assuming it doesnt take very long to expose a screen.  Any tips on which integrator to buy or what to look out for?  I found one use don ebay for $25, but the next cheapest is $170 so I'm a little weary...

[mimosatexas]

Just bought this: http://www.ebay.com/itm/181262544692

Not sure if it is a good deal or not, but it was only $25, and I can fix the power button in less than 5 minutes.  Anyone know if this was a good purchase?

[StuJohnston]

That model is a good one. Though I am not sure how it would work without being attached to an olec light source though. While I think that the vacuum frame diy isn't such a bad idea, they are not so easy to find used, I would still look out for a used olec al53. They seemed to be the exposure unit of choice for small offset shops that are either going out of business or going digital. I had made a manual MH unit before I got my olec and it worked well enough, but the olec was $250, with integrator. I paid about $200 for my ballast and MH lamp from a grow shop that was having a grand opening sale. I don't think that I could have beat $250 otherwise.

As for the original questions
1. Can I just use a step test by taping strips on the outside of the glass and pulling them every 5 or 10 seconds to lock in exposure time, or is there a cost effective way to really dial it in with some kind of gadget?

To get a good exposure, you need enough vacuum that you couldn't pull anything out from under the blanket. Try talking to your local supplier of emulsion and see if they won't give you an exposure calculator. I am actually considering buying a slightly more complicated one, but free is a good price.

2. Any idea how long I should let the bulb warm up before exposing?

I used to let it (my home made unit) warm up for 15 minutes, it was a 1kW lamp on 110 and I didn't want to try to guess how little time I could get away with after getting some under exposed screens

3. Any issues I should be aware of with these bulbs when it comes to leaving it on for too long?

I am guessing you are looking at grow lamps, which are meant to be left on for hours or days at a time, so no, not really any problems from leaving them on too long. Though you need to make sure your shutter material can take the heat. Conversely, turning off one of these types of lamps will kill their inertia or something that I don't fully understand, but they have to cool down completely to be able to reach full brightness again. With an olec, it's instantaneous and while I wouldn't recommended cycling a MH more than you have to, you can shut it down and turn it back on without delay as well.