Base for starting exposure test (yeah another one)

[Gilligan]

Ok... as you guys know, I'm extremely ignorant to coating screens and exposing them.

Well... I need to get a job going and I decided to go for it.  I coated 3 screens with Chromaline blue... 2 passes on the shirt side followed by 1 pass on the squeegee side (rounded edge).  It went ok... no mess, does that count for anything.

Now I'm gonna expose using a vacuum storage bag and a 400w metal halide bulb (technically on a HPS ballast).  I'll put the light about 4' above the screen (in it's stock hood... it was a grow light given to me).

What I'm wondering is what do you guys think my exposure time will be?  I don't have an exposure calc or anything.  With the vacuum bag I'll have a hard time doing a exposure test by uncovering at intervals.  I do have a fixxon sample pack that came with a sample of half tones and text exposed on one of their films.  Not sure if that could be useful.

Any advice to get me a decent exposure as quickly as possible... I promise I'll fine tune it later.  The design I need to print is only 20 toddler shirts 2 color spot color with EXTREMELY loose registration (no colors touching).

[prozyan]

4 feet is quite the distance.  30-36" would be more in the neighborhood.

As for your exposure time, anything I threw out would be a total guess.

[Gilligan]

Yeah, you are right... my math was wrong.  I'd thought it seemed far but I didn't put pencil to paper, just off the cuff in my head at 1am

So 3' distance not 4'.

Honestly, your guess will probably be a LOT better than my guess.

[tpitman]

You need to crack your wallet for the $7 or so for a Stouffer scale from Victory Factory or anyone else who sells them. Takes the guesswork out of calculating exposure times. Or ask Andy to rouse "Step-Wedge Man" from his premature retirement, although serious alcoholic fortification is strongly advised before looking upon the dazzling visage of Step-Wedge Man . . .

[Fresh Baked Printing]

Here's a video from Roger Jennings that explains the step wedge thing pretty good"

http://youtu.be/29g2uHkdC_c

[bimmridder]

To find a good distance, (starting point at least) take the diagonal of the area you are exposing and try that

[Frog]

Ok... as you guys know, I'm extremely ignorant to coating screens and exposing them.

Yeah we know, but we have also seen that, as in other facets of the process, you will listen (at least sometimes)

As noted, your initial distance was much greater than necessary, and greatly affects time. Doubling the distance quadruples the time, tripling it increases it nine
fold. I guess the time is a factor of the distance difference squared. Here is a simple table from one emulsion to use just to see the distance/time relationship.

DISTANCE FACTORS
20 inches /50 cm.    0.25                   44 inches /110 cm.     1.21
24 inches /60 cm.    0.36                    48 inches /120 cm.    1.44
28 inches /70 cm.    0.49                    52 inches /130 cm.    1.69
32 inches /80 cm.    0.64                    56 inches /140 cm.    1.95
36 inches /90 cm.    0.81                    60 inches /150 cm.    2.25
40 inches /100 cm.  1.00                    72 inches /180 cm.      3.2     

That said, I do have experience with 400 watt bulbs, though used with the proper ballast, along with a similar Chromaline emulsion.
At 26", a yellow 160 coated similarly to your description, achieving the "glisten" described in Douglas Grigar's article on the Home Page, exposures were in the 90 second range.

So, with all of this, and the information on how to perform a manual step wedge test (or a one step calculator version), as a starting point for you, I'd pick a range  that halves and doubles my numbers. Remember that each mesh requires testing and adjustment.

And, as Tom brought up, remember that though he will not do your grunt work,  Step Wedge Man is watching you!

[Gilligan]

Hello inverse square law.  Well familiar with it from all other aspects of my life (video, photo and stage lighting).

In a sense the more distance I have the more "latitude" I have?  Is that right?  If I am close enough to expose at 1 minute than 50 seconds would be fairly under and 1:10 would be fairly over.  But if I need 3 minutes to expose than 2:50 is significantly less under exposed and 3:10 is significantly less over exposed... am I correct in assuming that?

In a sense that will be better for me, starting off right (more room for error)?  I know it's not a fix for doing it right... but I could use all the leeway I can get.

Btw, Andy... I do listen... my wallet just doesn't cooperate sometimes.  You think it's tough running one business, try spreading yourself thin across several.  Bank accounts went from being 900, 1500, 150 one day to 900, 8k, 4k the next day!  Of course all that money is already spent somewhere... just have to find the best place to put it and budget till next set of invoices come in.

[3Deep]

Couple things here vaccum storage bag? I,m thinking will bounce some of your light not being really clear #2 double coat with the round edge is going to give you a very thick screen (EOM).  Not having proper vac and light will cause you some undercutting with what your doing now, I would use the sharp edge to coat 1/1 until I got a better setup.

You know you can build a exposure unit for a few dollars and use blacklights or hang a photoblub over top with a pc of glass pressing your film down tight to the mesh.

[Gilligan]

Well... from what I've seen that vacuum bag looks pretty slick and tight.  Sure it might not be AS transparent as glass... but then again it's much thinner so maybe that offsets some of it?

He was using a foam pad in the back of the screen but it was being sucked down so hard that he just stopped using it.



Here it is in action:

vacuum top.wmv

[Gilligan]

I just realized I can easily do the stepped exposure test with my setup (I changed the way I WAS going to do it and never revisited the idea again).

So what would be best to print out as an exposure calculation film?  Anyone got a file they wouldn't mind sharing?

[Fresh Baked Printing]

I just realized I can easily do the stepped exposure test with my setup (I changed the way I WAS going to do it and never revisited the idea again).

So what would be best to print out as an exposure calculation film?  Anyone got a file they wouldn't mind sharing?

Ulano sells an exposure kit. I have this one from them:

[Gilligan]

Just seems pricey... I'm sure it's good I just wish there was a PDF that one could print and accomplish the same results.

Yeah, I'm cheap, what can I say!

[Frog]

I just realized I can easily do the stepped exposure test with my setup (I changed the way I WAS going to do it and never revisited the idea again).

So what would be best to print out as an exposure calculation film?  Anyone got a file they wouldn't mind sharing?

With a manual step wedge test, you need no special film for exposure, just one of your typical films, perhaps with various sizes of a simple type like Arial starting really small, like 4 pts.The advantage of a manual test with your own film is that you are testing what you will actually be using, rather than a more perfect professionally produced film.

So, the film, and a piece of cardboard or other opaque material to slide (or a series of overlapping strips) and seven or so measured marks, and you're good to go. On a yellow 160, I'd go from 30 seconds to four minutes to get a wide range of visual guidelines.
Then you can fine tune it in with another test in the sweet spot.

[Gilligan]

The advantage of a manual test with your own film is that you are testing what you will actually be using, rather than a more perfect professionally produced film.

That was one of my thoughts also... a professional calculator only shows you EXACTLY what's up IF you can match their quality and transparency.  I mean if we are worried about what my vacuum bag will transmit vs glass then difference in transparent films will be "drastic" also.  Then lets not even begin to talk about vellum(sp).

Thanks, I'll give giving this a whirl tonight... we shall see!