How opaque is Portra?

Craig · Oct 30, 2007

I did a shoot at work today of some machinery, and I used that as an excuse to use the 8x10. I used Portra 400NC and when I was unloading the holders tonight I noticed that I had accidentially loaded 2 sheets into one side of the film holder.

Would the second sheet have been exposed through the first, or might it be OK? I hate to throw out 8x10 colour film if I don't have to!

GeoffHill · Oct 30, 2007

If its the same as 35mm portra 160vc, I looked through the leader and i'd guess its about 5 stops or so.

Thats an entirely unscientific test however.

Bruce Osgood · Oct 30, 2007

Craig said:
I noticed that I had accidentially loaded 2 sheets into one side of the film holder.

Would the second sheet have been exposed through the first, or might it be OK? I hate to throw out 8x10 colour film if I don't have to!

Other than the thickness of the film why wouldn't the top sheet be okay? So, I would develop both sheets and see.

Photo Engineer · Oct 30, 2007

The top sheet will be fine, but the bottom sheet will have no exposure to blue light. The top sheet absorbs all blue light.

Also, due to the other dyes and the thickness of the top sheet, the remaining layers of the bottom sheet will get about 2 - 5 stops less exposure.

PE

Craig · Oct 30, 2007

Would it be appropriate to consider the bottom sheet "unexposed" and use it for something else? If the blue is fully absorbed by the top sheet, I assume then that the bottom sheet would have only been exposed to red and green. Is 5 stops less exposure signifigant, or will be there some ghosting if I use this sheet for a different photo?

Photo Engineer · Oct 30, 2007

The bottom sheet can have a 'ghost' image on it of the brightest parts of the previous scene due to the extreme latitude of the film. Therefore it is most likely useless.

I have done this and the second sheet has always had some sort of 'ghost' on it. You might be lucky if the tonal range of the scene was narrow.

PE

Craig · Oct 30, 2007

Thanks PE. I think I'll toss the sheet, as I don't want to risk any ghost images.

Christopher D. Keth · Nov 20, 2007

Eh, the top sheet is pretty likely to be out of focus. Behind a camera lens, that extra sheet of film behind it could easily throw it out of focus, especially if you were on a wide-ish lens.

Craig · Nov 20, 2007

Christopher D. Keth said:
Eh, the top sheet is pretty likely to be out of focus.

Nope, the top sheet came out just fine. I didn't risk using the second sheet, so threw it away.

How opaque is Portra?

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