Index matching

Anyone have any foolproof methods for index matching sheets of PFG-01 roll film to glass? For 4×5" sheets I’d used both mineral oil and lamp oil with decent success, although I detest the messiness of it.

I’ve been working on the final Minas Tirith hologram and the last sticking point (as it were) was getting a 5×7" hologram done using 5% TEA solution. For lesser concentrations of TEA I was quite happy with sandwiching the film between two pieces of glass and shooting at ~56 degree angle.

Unfortnately at 5% I couldn’t get a fully dry piece of film no matter what I tried. Even a final hair-dryer treatment didn’t help and the film would stick to the glass and shift during the exposure, resulting in ugly black blobs. A sure sign of film movement.

I tried a couple of mineral oil matched shots last week and couldn’t avoid some movement even with 30-45 minute settling times. This really sucks because I’m burning 5×7" film every time, as well as burning a few hours every morning with nothing good to show.

Yesterday morning I tried lamp oil and had better results after just a 30 minute settle but the image was off-center enough that I decided to try another shot in the evening (these days I only have time for one attempt in the morning). Unfortunately the evening shot moved. Perhaps I wasn’t careful enough when applying the film or rolling out the fluid. I’m not entirely sure though. It could also be that for the morning shot I was using freshly TEA treated film which had been relaxed by the soak and hadn’t re-curled fully to its original shape. In other words, it was flatter than normal. On the other hand, the second piece was just as curvy as usual and perhaps this was causing more tension.

This morning I soaked another two pieces of film, left one to dry and blow-dried the second. I taped down one end of the film (emulsion side up), applied tape to the sides, put about 1ml of lamp oil on the plate at the first end and used a brayer roller to squish the film down and force the oil out the other end. Because of the tape on the sides, the film was held down after the roller passed and I only needed to give the tape a going over with my finger to make sure it was adhering to the glass. I then put another strip of tape down to hold other end of the film to the glass. I let this settle for 40 minutes and ended up with a bright clean hologram. This one’s a keeper and will go to its new owner on Monday.

Sometime this weekend I’m going to try the second piece of film and see if I can refine my methods. I can see a few potential problem areas:

1) Maybe I’m not allowing enough settling time at 30 minutes.
2) Maybe I’m not squeezing enough of the oil out, causing number 1.
3) On this morning’s shot I noticed some small dust grains between the film and glass. It may be that this is happening more often than I think and that those grains are causing cappillary action and long-term movement of the oil. I need to switch from using paper towels to clean the glass and clean both the film and glass with some kind of lint-free cloth before index matching.
4) I will definitely need to refine my application methods. If the film is curling on the long axis, perhaps I could leave out the side tape and squeeze out the oil with a squeegee, tape down the second end, clean up the oil and then tape down the sides. This might allow me to get more oil out and provide a tighter bond.

If anyone has any recommendations for this combination of 5×7" PFG-01 (roll) film and index matching, I’m all ears.

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

Author: Michael Harrison

Husband, Programmer, Irish dancer, tinkerer, astronomer, layabout (as much as possible)

6 thoughts on “Index matching”

  1. Is your film holder only clamped on two edges? I have successfully shot 4×5 film mounted in between 5×7 glass as well as 4×5 glass.

    The glass is clamped on 4 sides; My plate holders is a simple channel with a couple of holes dilled/tapped, and attached to the table with the option of a single post mounted in the center, or 2 posts mounted near the ends. The channel represents the “bottom” edge. The sides get clamped with 1 bulldog clip each on the left and right sides, and the top gets an extra clamp for good measure. Sometimes I can leave out the top clamp, but again it’s there “for good measure.”

    I have not found a need to settle for for more than say 2-3 minutes (for exposures that last up to 30 secs.)

    I agree that the parifin lamp oil is a MESS! I gave up on it.

    1. My index matching plate is a single piece of glass and is held in an L-shaped plate holder. It’s held in place with two thumbscrews on each side.

      I only need the really long settling times when index matching. When I use my sandwich holder (which I can only use at lower TEA concentrations) my settling time is typically 15 minutes. I might be able to go shorter but found 15 minutes works and I don’t like to experiment too much with the larger film. It gets expensive pretty fast.

      1. when i index my film, i use white spirits with glass and emul in contact, then tape down all edges, DAVE

        ps if your using it as a H1 you will have to compensate for delta in replay angle

  2. After these attempts I’ve continued refining my index matching methods and I’m two for two. I made a hologram this morning with the second piece of film that I’d TEA treated yesterday and the final hologram is nice bright and clear.

    On the other hand,

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.