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Calculating Exposure Time

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Calculating Exposure Time
Calculating Exposure Time
(without a step wedge)
Published by PositiveDave
January 11th, 2010
Default Calculating Exposure Time

It's easy to determine the optimum exposure time for a system even if you don't have an exposure calculator such as the Stouffer strip. Commercial exposure calculators are neutral density filters that allow specific percentages of the light to pass through so that you get a range of exposures from one experiment. This can be achieved in a less elegant but more practical method.
Standardise all your variables:
Thickness of emulsion
Emulsion type
Exposure difference
Temperature

Take a coated screen and cover all but about an inch with a piece of card, expose for a minute.
You may have a good idea what the exposure should be, you can alter the range given in this tutorial to suit your system.

Move the card over an inch and expose for another minute:

After a few minutes you will have a screen with a range of exposure on it:

When washed out it may look something like this:


1&2" have washed out, 3&4" are underexposed, 5" is OK, 6 is probably safe.
If you haven't got a reasonable range, just go back and do it again.
Your light source will deteriorate over time so you should repeat at regular intervals and if signs of underexposure occur.
It will be a good idea to have a positive with some text on to check for overexposure, when the open areas are filling-in you are overexposing.
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Old January 11th, 2010 Jan 11, 2010 1:53:17 PM -   #1 (permalink)
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Default Re: Calculating Exposure Time

Thanks Dave, That can save a lot of time and aggravation.
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Old January 11th, 2010 Jan 11, 2010 3:06:51 PM -   #2 (permalink)
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Default Re: Calculating Exposure Time

It isn't rocket science but I got bored of explaining it three times a week.
hent likes this.
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The Following 10 Users Say Thank You to PositiveDave For This Useful Post:
Aswang (April 3rd, 2011), cyandev (October 27th, 2012), JBYoungdahl (January 11th, 2010), madray (November 26th, 2011), raphskie (August 18th, 2011), rednax17 (September 2nd, 2011), Rodney (January 11th, 2010), sunnydayz (April 7th, 2010), thestitchwitch (August 5th, 2010), titopot (April 6th, 2011)
Old February 17th, 2010 Feb 17, 2010 10:24:42 AM -   #3 (permalink)
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Default Re: Calculating Exposure Time

Hey dave, isn't that last image backwards? #1 has received the most light, so why would the emulsion have washed out?


2/19/10 Update: So as not to confuse new readers of this post, Dave corrected the image, but changed his numbering sequence. In the last image, #1 has received the least light, so the emulsion completely washes out. #8 has received the most light.
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Last edited by splathead; February 19th, 2010 at 11:49 AM..
 
 
Old February 17th, 2010 Feb 17, 2010 11:01:28 AM -   #4 (permalink)
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Default Re: Calculating Exposure Time

Correct! I was just testing.
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Old February 17th, 2010 Feb 17, 2010 11:37:45 AM -   #5 (permalink)
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Default Re: Calculating Exposure Time

Quote:
Originally Posted by PositiveDave
Correct! I was just testing.

Hehe. trust me, I got a headache just trying to figure out if I was right or not.
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Old February 21st, 2010 Feb 21, 2010 12:51:00 PM -   #6 (permalink)
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Default Re: Calculating Exposure Time

Thanks, Dave. I also have a 1" strip of film with 1" squares with 10%-90% halftone dots in 10% increments as well as a solid area. This tells me the dot pattern I can hold on different meshes, coatings. God Bless.
 
Old April 7th, 2010 Apr 7, 2010 9:58:44 AM -   #7 (permalink)
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Default Re: Calculating Exposure Time

so useful tips for beginner like me. thanks...
 
Old April 12th, 2010 Apr 12, 2010 3:40:58 PM -   #8 (permalink)
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Default Re: Calculating Exposure Time

Would it not be better to have some sort of image? Even just a row of square blocks.
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Old April 13th, 2010 Apr 13, 2010 12:23:51 AM -   #9 (permalink)
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Default Re: Calculating Exposure Time

Quote:
Originally Posted by MotoskinGraphix
Would it not be better to have some sort of image? Even just a row of square blocks.
You want the advanced class
It's helpful to have some lines/text to diagnose over-exposure and under cutting problems but you should really get something like an Autotype calculator which has everything on the same small film.
If you get a Stouffer or an Autotype calculator, put it on each screen you make. Your light source deteriorates with age (don't we all).
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Old April 13th, 2010 Apr 13, 2010 4:59:22 AM -   #10 (permalink)
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Default Re: Calculating Exposure Time

I liken myself to a fine wine and just get better with time!!!!
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Old April 13th, 2010 Apr 13, 2010 5:44:31 AM -   #11 (permalink)
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Default Re: Calculating Exposure Time

I got corked along the line :-)
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Old April 13th, 2010 Apr 13, 2010 4:32:07 PM -   #12 (permalink)
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Default Re: Calculating Exposure Time

I dont like the idea of putting am exposure test image on every screen. Every so often, yes. Taping off screens and image areas is a pain and extremely time consuming. The less to tape the better.
Plus once you've got it dialed in, it's dialed in until you change something.
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Old April 22nd, 2010 Apr 22, 2010 8:36:35 AM -   #13 (permalink)
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Default Re: Calculating Exposure Time

tagging for future use, thanks for the info.
 
Old April 22nd, 2010 Apr 22, 2010 9:03:22 AM -   #14 (permalink)
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Default Re: Calculating Exposure Time

Quote:
Originally Posted by out da box
I dont like the idea of putting am exposure test image on every screen. Every so often, yes. Taping off screens and image areas is a pain and extremely time consuming. The less to tape the better.
Plus once you've got it dialed in, it's dialed in until you change something.
true but the test strip isn't very big and is easily covered with a piece of wide masking tape. I haven't experienced this yet but from what i've been reading regarding exposure units, the lamps will degrade over time. i don't think it's that important to use the strips on every screen but at least 1 screen a day. If you do run into issues then use it on every screen until the issue is resolved. I feel these test make a big difference when dealing with fine detail and high mesh counts, for those types of jobs i'd like the strips to be used on every screen.
 






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