Jump to content


Photo

Dip testing?


  • Please log in to reply
4 replies to this topic

#1 Zamir Merali

Zamir Merali
  • Basic Members
  • PipPipPip
  • 185 posts
  • Director

Posted 01 May 2007 - 06:53 PM

Hi
I have a few rolls of colour negative 16mm film that I would like to test before using. I have black and white developing chemicals at home. Can I use those to dip test the film? If not could I give a small clip from each roll to a still picture lab in my town with some specifications and expect them to test the film? Thanks for answering my questions.
  • 0

#2 Dominic Case

Dominic Case
  • Basic Members
  • PipPipPipPip
  • 1357 posts
  • Other
  • Sydney Australia

Posted 01 May 2007 - 07:38 PM

No. And no,no.

The main purpose of dip testing is to check if the base fog is OK or if the stock is suffering from age, heat or other deterioration. If you develop the neg in black and white chemistry you won't have any idea of what the base fog should be.

If you give the test strips to a stills lab: (a) they probably won't be able to handle 16mm and (B) the certainly won't be able to process motion picture neg which has remjet backing. The C41 stills process has no prebath or backing removal stages to remove this, so it will contaminate their developer tanks, rollers etc. They won't thank you for that.
  • 0

#3 Dan Salzmann

Dan Salzmann
  • Basic Members
  • PipPipPipPip
  • 1143 posts
  • Cinematographer
  • Paris, France

Posted 02 May 2007 - 04:35 AM

I've never had to do dip testing because I have always used fresh stock and have a few questions?

1. Is it essential to expose the film to be tested?
2. If so, what? A bracketed Macbeth and gray scale?
3. What info, recommendations does a lab supply with the test, if any?
4. If just the developped test is returned to me, what is the best way to interpret this strip of film?
5. How much film is reasonable to give a lab for a dip test?

Any suggestions highly appreciated. Dominic?
  • 0

#4 Jonathan Bowerbank

Jonathan Bowerbank
  • Basic Members
  • PipPipPipPip
  • 2815 posts
  • 1st Assistant Camera
  • San Francisco, CA

Posted 02 May 2007 - 01:45 PM

You don't have to shoot anything to find out what physical condition the film is in. Just cut off a foot or so of your roll and take it in for a densitometric scanning. That reading can basically tell you the condition your film is in and whether it's suffered any age fogging...or any other type of damage.

BUT, since you're probably still not sure what the stock you're using is going to get you, might as well shoot a test and get it developed to find out! :)
  • 0

#5 Dominic Case

Dominic Case
  • Basic Members
  • PipPipPipPip
  • 1357 posts
  • Other
  • Sydney Australia

Posted 02 May 2007 - 06:05 PM

1. Is it essential to expose the film to be tested?

No. As Jonathan says, you can tell a lot from a reading of the unexposed base + fog density. That is all that is usually done. BUT - it has to be processed! No-one can read the fog level on unprocessed film. Apart from not being what you want to measure, it's a physical impossibility (think about it.)

2. If so, what? A bracketed Macbeth and gray scale?

This will test your exposure meter and everything else as well. An alternative that is only possible with some labs is to have them expose a sensitometric strip on your stock. This will check all of the properties of the emulsion, and their process. But not every lab has a sensitometer, it would cost you, and it's probably more useful for obscure b/w emulsions, where there are more variables in the process.

3. What info, recommendations does a lab supply with the test, if any?

The lab will normally measure and report the red, green and blue d-mins (base + fog density). They may indicate if those values are normal or excessively high. But most labs will avoid giving a straight OK or NG verdict, as it's a gradual shift from good to bad. It depends on your requirements, whether you don't mind a bit more graininess than usual, the contrastiness of the scenes you are shooting, whther you choose to overexpose a bit to compensate, and a whole raft of other things.

4. If just the developped test is returned to me, what is the best way to interpret this strip of film?

Ask the lab - ut see above.

5. How much film is reasonable to give a lab for a dip test?

If you send in the whole can, the lab will remove what they need for you - usually it's only a couple of feet.
  • 0


Aerial Filmworks

Gamma Ray Digital Inc

Media Blackout - Custom Cables and AKS

Technodolly

Rig Wheels Passport

Paralinx LLC

CineLab

Ritter Battery

Wooden Camera

rebotnix Technologies

Opal

Tai Audio

Visual Products

CineTape

Glidecam

FJS International, LLC

Willys Widgets

Abel Cine

Broadcast Solutions Inc

Metropolis Post

The Slider

CineLab

Ritter Battery

Willys Widgets

Gamma Ray Digital Inc

Media Blackout - Custom Cables and AKS

FJS International, LLC

Glidecam

Aerial Filmworks

Technodolly

CineTape

Rig Wheels Passport

Tai Audio

Broadcast Solutions Inc

The Slider

Wooden Camera

Metropolis Post

Opal

Visual Products

Paralinx LLC

Abel Cine

rebotnix Technologies