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Done exposing???

Posted on Tue, 20 Apr 2004 at 22:24



Hi,

I'm fairly new to screening and I've only used a commercial exposing unit. I'm planning on making my own with 40W X 6 fluoresent bulbs (the really long ones) in a wood box. The frame will be 3.5 inches away form the light.

I know it's hard to guess the exact time from my descriptoin. Is there anyway by looking at the screen to tell when the frame is done exposing? Any guesses? Any suggestions?

Retarded queston, but I am suppose to use black lights if I can vs "cool white"?

Thanks

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Anonymous says: Ben, This will be very helpful, you can contact you're local Autotype dealer... Or contact me and I will assist. Vernie Dahl Exposure Calculator Working Instructions 1.0 100% 0.7 75% 0.5 50% 0.33 33% 0.25 25% NEURAL ...

Ben,

This will be very helpful, you can contact you're local Autotype dealer... Or contact me and I will assist.

Vernie Dahl
Exposure Calculator Working Instructions

1.0
100% 0.7
75% 0.5
50% 0.33
33% 0.25
25%

NEURAL DENSITY FILTERS
The filters allow increasing percentages of light to reach the dried emulsion

Step 1: Double the selected exposure time
Decide what exposure time would be the optimum for the
emulsion being tested. SUGGESTION: Use the current
exposure time that is being used to produce stencils as a
starting point. For Example: If the current emulsion being used
is exposed for 200 units, double this exposure time for the
calculator test (200 x 2 = 400 units).

Step 2: Expose the screen with the exposure calculator for the
selected exposure time.

Step 3: Washout the exposure calculator image and dry the screen.
Recommendation: Always thoroughly dry the screen before
deciding when the color change stops. A screen that is not
completely dry can give a false reading.

Step 4: Determine where the color change stops
The objective is to select the filter where 100% of the diazo
sensitizer has reacted with the light exposure to completely
harden the stencil. The selected filter is determined by where the color change stops. In the example below, the color of each filter gets lighter and lighter until the color changes stops at the 0.7 filter.

Color Change

1.0
100% 0.7
75% 0.5
50% 0.33
33% 0.25
25%

Step 5: Calculate the optimum exposure
Use the percentage factor of the selected filter where the color
change stopped x the original doubled selected exposure time used for the exposure calculator test. The optimum exposure in this example is 200 units because the color change stopped at the 0.5 filter (400 x 0.5 = 200 units optimum exposure).

1.0
100% 0.7
75% 0.5
50% 0.33
33% 0.25
25%

Color Change

1.0
100% 0.7
75% 0.5
50% 0.33
33% 0.25
25%

In the above example, the color change has stopped at
the 0.33 filter. The double selected exposure time
of 400 units times 0.33 equals the optimum exposure
time.

400 x 0.33 = 132 units optimum exposure

False Readings:

1.0
100% 0.7
75% 0.5
50% 0.33
33% 0.25
25%

If the color change stops at 1.0, this is a false reading. Not enough exposure time was selected for the exposure test. The doubled selected exposure time must be increased until the color change stops at either the 0.7, 0.5 or 0.33 filters. Only these three filter reading are acceptable for optimum exposure calculations.

False Readings:

1.0
100% 0.7
75% 0.5
50% 0.33
33% 0.25
25%

If there is no color change across all filters, this is a false reading. Too much time was selected for the exposure time. The doubled selected exposure time must be decreased until the color change stops at either the 0.7, 0.5, or 0.33 filters. If there is an overwhelming decrease in exposure time and there is still no color change, it is possible the emulsion has been exposed to light. Keep in yellow safelight conditions or in subdued light.

posted on: Tue, 04/27/2004 - 2:36pm
Anonymous says: for 30 bucks autotype se;ll a exsposure calculator real easy to use and your screens will be perfect.black lite bulbs are best hunt around some are stronger than others alsing ps every mesh is different ...

for 30 bucks autotype se;ll a exsposure calculator real easy to use and your screens will be perfect.black lite bulbs are best hunt around some are stronger than others

alsing
ps every mesh is different looking at the mesh is hard to tell and is like cooking a cake 12 inches tall and guessing if the center is done use a calculator there cheap an easy

posted on: Wed, 04/28/2004 - 6:48pm
Anonymous says: I'll also suggest an exposure calculator: the Image Mate Exposure Guide. Typical price is $10; free if you're really nice to your distributor. It's a 1/2" x 4" strip with 10 steps of increasing filters. ...

I'll also suggest an exposure calculator: the Image Mate Exposure Guide. Typical price is $10; free if you're really nice to your distributor. It's a 1/2" x 4" strip with 10 steps of increasing filters. A single exposure will tell you if you are correctly exposed, or how to correct the exposure time. You need to establish correct exposure times for each set of variables, assuming you're using one photoemulsion: mesh count, mesh color, coating procedure, & positive type. What people fail to realize, or instruct, is that if you use vellum positives, you need to place the calculator between the coated screen and a piece of vellum - so that the calculator "acts" like vellum.

Regarding light bulbs - they must transmit the proper wavelength/range of light in order to properly cure photoemulsions in the shortest time possible. Check with the bulb supplier, manufacturer, or specifications on the box. For optimum curing, bulbs should provide maximum output in the 350 to 450 nm range. Some fish tank/grow light bulbs found in pet stores will have this info on the box. I have had customers tell me they shot our PC 701, one-part emulsion, on fluorescent for as little as 30 seconds!

Marty Medvetz
Technical Manager
www.image-mate.com

posted on: Tue, 05/11/2004 - 9:27am

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