# Calculating Exposure Time



## PositiveDave

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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## gerry

Thanks Dave, That can save a lot of time and aggravation.


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## PositiveDave

It isn't rocket science but I got bored of explaining it three times a week.


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## splathead

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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## PositiveDave

Correct! I was just testing.


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## splathead

PositiveDave said:


> 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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## ole Jobe

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.


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## fajaryayat

so useful tips for beginner like me. thanks...


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## MotoskinGraphix

Would it not be better to have some sort of image? Even just a row of square blocks.


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## PositiveDave

MotoskinGraphix said:


> 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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## MotoskinGraphix

I liken myself to a fine wine and just get better with time!!!!


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## PositiveDave

I got corked along the line


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## 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.


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## MMACrypt

tagging for future use, thanks for the info.


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## red514

out da box said:


> 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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## norbac

red514 said:


> 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.


Ok, newbie here. So let's say I used a Stouffer or an Autotype calculator, obviously I need to rinse it to see how it washes out. Now my question is, should I just "dry" the rest with a towel or "something", and it will be ready to expose with the art and print right away?, obviously just covering it with tape like you said.

I'd appreciate any advice on the right procedure and or steps, and if possible a good place to get the calculators.


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## splathead

norbac said:


> Ok, newbie here. So let's say I used a Stouffer or an Autotype calculator, obviously I need to rinse it to see how it washes out. Now my question is, should I just "dry" the rest with a towel or "something", and it will be ready to expose with the art and print right away?, obviously just covering it with tape like you said.
> 
> I'd appreciate any advice on the right procedure and or steps, and if possible a good place to get the calculators.


Pat dry with paper towel. Don't rub. Pay special attention to the image. Make sure there is no water film left in the screen. Then let it sit until completely dry. I usually allow about an hour.

The tests can usually be purchased from the same place you buy your screens or emulsion.


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## norbac

splathead said:


> Pat dry with paper towel. Don't rub. Pay special attention to the image. Make sure there is no water film left in the screen. Then let it sit until completely dry. I usually allow about an hour.
> 
> The tests can usually be purchased from the same place you buy your screens or emulsion.



Thanks a lot Splat. 
When you say, "pay special attention to the image" what do you mean?. 

Just to make sure, the screen I run the test on, is later used for my printing right?. Obviously following your instructions to dry it, and then covering the test results with tape.


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## splathead

I mean not to let water dry in the image area. It could be mixed with dissolved emulsion and cause your image to not be as sharp. When you are patting the image down with paper towel, make sure no water whatsoever is left in the image area.

The test strips are placed in a corner of the screen. You would tape them off prior to printing.


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## norbac

Thanks again Splat, your help is much appreciated.


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## dd2

I wish I would have read the posting on the step test before I tried exposing film for three days..... did the step test and the first try on my logo came out perfect. This forum site is the best!! Thanks.


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## PositiveDave

dd2 said:


> I wish I would have read the posting on the step test before I tried exposing film for three days....


Exposing for three days is almost certainly too much


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## Yasirm86

PositiveDave said:


> I got corked along the line


hey i know im a bit late but i have a question...when i expose 1-8..starting at 1 minute and exposing each slot for 1 minute after that..im in the middle of doing it now and realized that when i expose 1 i do it for one minute and then move to the 2nd block and so on the 1st block will have been for a total of 8 mins or 36 mins?? highly confused!


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## dd2

8 minutes...


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## Yasirm86

dd2 said:


> 8 minutes...


I think I did it wrong lol I did 1 minute and then 2 minutes 3 minutes not 1 and then moved the bored and 1 moved the board lol


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## dd2

Yes, just move the board in 1 minute increments, so if you move it 8 times, your first section would have been exposed for 9 minutes. Good luck.


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## Yasirm86

dd2 said:


> Yes, just move the board in 1 minute increments, so if you move it 8 times, your first section would have been exposed for 9 minutes. Good luck.


It would be 9 minutes?? How did you get 9 I thought it would be 8 if I have 8 blocks


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## dd2

Yasirm86 said:


> It would be 9 minutes?? How did you get 9 I thought it would be 8 if I have 8 blocks


I am basing it on if your starting with the first section being exposed, and then you move it 8 times, there would be 9 sections total exposed. No matter, your going to be within 7 - 9 minutes total depending on your number of sections.... Once you figure out your optimum exposure- life will get easier and allow you to move on to other challenges. Just keep in mind that there are many factors involved with exposing (ie. type of light/ emulsion/ films). let me know if I can be of any help.


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## Yasirm86

dd2 said:


> I am basing it on if your starting with the first section being exposed, and then you move it 8 times, there would be 9 sections total exposed. No matter, your going to be within 7 - 9 minutes total depending on your number of sections.... Once you figure out your optimum exposure- life will get easier and allow you to move on to other challenges. Just keep in mind that there are many factors involved with exposing (ie. type of light/ emulsion/ films). let me know if I can be of any help.


Got you! Okay well the first attempt didn't come out so I'm redoing it


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## Yasirm86

dd2 said:


> I am basing it on if your starting with the first section being exposed, and then you move it 8 times, there would be 9 sections total exposed. No matter, your going to be within 7 - 9 minutes total depending on your number of sections.... Once you figure out your optimum exposure- life will get easier and allow you to move on to other challenges. Just keep in mind that there are many factors involved with exposing (ie. type of light/ emulsion/ films). let me know if I can be of any help.


no luck this is what i got...


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## Yasirm86

I did another image for 7 minutes and the halftones were all there but the image wouldn't go through....


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## dd2

What type of exposure system are you using? How far is the image from the light source? What type of emulsion? What type of films are you printing on and are you using ink jet or toner based printer? Are your images on your films opaque, meaning can you see light coming through when you hold the film unto the light?


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## Yasirm86

dd2 said:


> What type of exposure system are you using? How far is the image from the light source? What type of emulsion? What type of films are you printing on and are you using ink jet or toner based printer? Are your images on your films opaque, meaning can you see light coming through when you hold the film unto the light?


I'm using a unit with about 8 or 9 bulbs 15watts facing up with a glass on top the glass is about 7-8 upwards. I'm using a murakami hv emulsion not required to mix and i just started using water proof film ink jet printer well before I was doubling or tripling the image now it seems more darker with the waterproof film so I used one...


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## dd2

Are you using standard fluorescent bulbs or black light bulbs?


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## Yasirm86

dd2 said:


> Are you using standard fluorescent bulbs or black light bulbs?


I believe backlight bulbs


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## sallyfish

Nice for us, thank you very much. This is a good forum community.


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## kralgece

Yeah thanks for this, I'm going to try it out as I can't find another solution to calculating my times.


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## 2STRONG

great information i am about to try this now. only question is how do you decide which one is the exposure time. for example 5,6,7 look pretty close which would would i use????


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## PositiveDave

If your positive is good you should have the exposure latitude to go for the longer exposure, if it's a bit iffy, laser printer type etc. you have less wriggle room.


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## seyerwsm

This was my first attempt at coating a screen using ULANO QTX photopolymer emulsion.
- i didnt even degrease the screen but washed it THOROUGHLY!!!
(once again this was my test screen, so without degreaser was OK)

anyways, i had a ghetto foam (black sweater) under the screen and didnt even use a glass
(since i was only there for 3 minutes i figured id hold it down as best as possible.

now i marked my screen to 30 seconds, 45 sec., 1 min., 1min 15 sec..etc to 2minutes.
(PHOTOPOLYMER emulsion i read was fast acting and not recommended for SUN. Oh well, its all I had from a friend)

now i read its fast acting with the light process, 

My results were pretty good. 
the 30 seconds left out some stuff 
compared to the 2minute mark.
the 2minute mark alot of the emulsion pretty much almost fell right out, leaving a beautiful exposed screen.
the 1min and 30 second to 30 second part..is pretty much "OK" but nahh,
the 2min and 15 second mark is where i want to be.

once again, using ulano qtx photopolymer emulsion.
at 4pm...the sun wasnt too crazy..which was why i was shocked at the good results..

thanks for this post.


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