DTP


 
Lively discussions on the graphic arts and publishing — in print or on the web


Go Back   Desktop Publishing Forum > General Discussions > Images

 
 
Thread Tools Display Modes
Prev Previous Post   Next Post Next
Old 01-07-2007, 01:39 PM   #1
ElyseC
Sysop Emeritus
 
ElyseC's Avatar
 
Join Date: Oct 2004
Location: southeastern Iowa, in the technology corridor
Posts: 2,190
Default Newton's Rings (archives)

From our archives...
-------------------------------------------------------------------------------

From: Mac T
To: Alan R
Topic: Those darn newton rings!
Msg #15527, reply to #15507
Date: Tue, Oct 22, 1996, 7:14:24 AM

Newtons rings occur when light is reflecting back and forth between two surfaces that are very, very closeto each other (on the order of some fairly small multiple of the wavelength of the light itself), but not in complete contact (if I can remember correctly my physics from many decades ago). The light waves generate interference patterns seen as rings.

I've never used a drum scanner, but one can get the newtons rings effect on a camera or vacuum frame as well if drawdown is incomplete.

The solution is to get the two surfaces in complete contact. Everything from dust to static can cause contact problems.

But I suppose you knew that.

Sorry I don't have any ideas on how better to do that using your equipment.

-------------------------------------------------------------------------------
From: Marcus S-T
To: Alan R
Topic: Those darn newton rings!
Msg #15633, reply to #15579
Date: Thu, Oct 24, 1996, 1:10:31 PM

There are a number of ways to overcome the problem of Newton Rings, it all depends on the size of the film you start with and the degree of magnification you're going to give it. The idea is either to get total contact between the film and the drum, as in oil, or to prevent the intimate contact of the two surfaces by holding them apart on the tiny, transparent dry peaks of an aerosol applied laquer (hair spray or anti-newton spray). The problem with using the spray is that it restricts the degree of magnification. Above about a 4X enlargement you run the risk of the spray points becoming a visible part of the reproduction. If you're using cut film (5x4 and above) then another alternative is to use a dry starch powder (anti setoff powder). The beauty of that is it's a dream to clean off afterwards. It has to be a transparent, finely divided powder which is why starch works well.

For 35mm you really should be using oil - liquid paraffin. I have seen some some operators have success using a thick adhesive tape and making a mask around the edge of the frame on the side which will be in contact with the drum. The principle is that if you mount the tranny tight enough the centre of the frame will not touch the drum. The centrifugal force of the spinning drum also tends to throw the film out from the surface. THIS IS NOT A RECOMMENDED METHOD. You run the risk that you will get differential focus across the frame, also I'm not convinced that the method is any faster or easier than the proper use of oil.

If you're going to use an aerosol spray, then spray the main burst into the air and pass the back of the film through the droplets suspended in the air. This way the heaviest should have fallen out of the way and only the finest points, the least visible, will stick to the tranny.

Good luck

Marcus

==================================

From: Andrew R
To: Philip B
Topic: New to drum scanning
Msg #23452, reply to #23448
Date: Mon, Jul 21, 1997, 3:51:04 PM

-->Drum cleaning and care, dust management, mounting, batch scanning, anything! I feel as if we are reinventing the wheel.

There is defiantly a learning curve when first working with a drum. I've gotten a lot better at mounting film on a drum then day one.

Get drum tape! When I first started using my drum scanner, I used all kinds of tape. Drum tape leaves no residue on either the drum or film. It's easy to pull off but keeps the film in place well when the drum spins. You DON'T want a piece of film flying off the drum when it's going 1600RPM!.

As to mounting, while our drum can be removed and I found this to be easy to do when I first stated, I now have no problems doing the mounting in or out of the unit. I usually place a piece of tape on the one side of the short axis, line up that edge with the black mounting line on my scanner. Then I place a piece of tape on the opposite end. While applying pressure to the area of film near the first piece of tape, I rotate the drum until I get to the next piece and the film is then warped flat on the drum. This is CRITICAL. The film has to be flat from end to end. Next I place tape on the other sides. Therefore the film has tape on all four sides. This keeps air from moving under one side and buckling the film which will make the scan out of focus (in some areas).

As to dust, you don't have to be too anal about the drum. Yes it should be kept clean but if you happen to have a scanner with an internal light source for mounting like ours, you will see a lot of dust and such but it doesnt' show up like you would expect. Get a good film cleaner. We use some stuff called Pec-12. You can get it at better camera stores. It's expensive and smells but does a great job. I find that 90% of the dust is in or on the film, not the drum surfaces. If you don't oil mount but see newton rings, give some anti-newton ring spray a try.

I don't oil mount often, there's little need unless you have to enlarge past say 700-500%. Even then, it's up to you. Advantage is there's then virtually no dust and no scratches. Downside is that you have a mess to clean up.

There are supplies used to clean the drum (drum cleaner and lint free cloths), drum tape, special oils etc. I really like the disposal lint and static free cloths for both cleaning the film and the drum. Dust off is good to have as well.

We don't have a ColorGetter so I can't comment on the software.

Andrew

-------------------------------------------------------------------------------

From: Philip B
To: Andrew R
Topic: New to drum scanning
Msg #23465, reply to #23452
Date: Tue, Jul 22, 1997, 7:50:03 AM

Andrew

Thanks for such a detailed response.

Yes, I can see where a light source inside the unit for mounting would help.

Let's see. Drum tape, antistatic cloths, and PEC 12. I have the latter. Do you use it routinely or just for things like fingerprints? Where would I find the drum tape and the disposable dust cloths - specific brands?

So far we have not seen any newton rings, much to my delight. Perhaps we are not mounting the film tight enough to the drum? I assume too that the "depth of field" of the PMT is quite shallow - effectively zero?

I'm glad you mentioned oil mounting. I'd heard that one did this for extreme enlargements, and I guess I thought that it somehow preserved better sharpness in the scan. So the real benefit is dust and scratches go away?

Thanks again

Philip

-------------------------------------------------------------------------------

From: Andrew R
To: Philip B
Topic: New to drum scanning
Msg #23474, reply to #23465
Date: Tue, Jul 22, 1997, 12:13:13 PM

-->Where would I find the drum tape and the disposable dust cloths - specific brands?

Try drum scanner services

-->So far we have not seen any newton rings, much to my delight. Perhaps we are not mounting the film tight enough to the drum? I assume too that the "depth of field" of the PMT is quite shallow - effectively zero?

I usually see the rings on film that has clear areas (something shot on a white bkgnd). Yes there's VERY LITTLE depth of field but better scanners will allow you to adjust this.

Andrew

-------------------------------------------------------------------------------
This is an archive from the original DTP Forum. Please comment in an existing or new thread. Thanks.

   
__________________
Elyse
ElyseC is offline  
 

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Scanning & Newton's rings john_b Images 17 01-09-2007 07:58 AM
From the Archives Howard White The Corner Pub 7 08-21-2005 02:19 PM


All times are GMT -8. The time now is 08:36 AM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Contents copyright 2004–2014 Desktop Publishing Forum and its members.