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Gelatin ND filters, or similar, for Bolex


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I'm doing some shooting soon on a Bolex Rex-5, with 250D. Among other things I would like to shoot outdoors in daytime with the same filmstock and therefore need to use ND filters. At this stage I don't have a matte box for the Bolex, and can't find screw-in glass filters for the Kern 16mm lens I've got. 

Can I use gel ND filters such as the Kodak Wratten ND filters? Can these filters be cut with scissors to fit into the Bolex behind-the-lens filter holder? Kodak also sells "Optical filters" -- are these similar to gels? I will be using a Kern Rx 16mm and a Nikon 50mm on the turret.

Thanks for any advice!

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From what I remember, there was a template that you could use, so by cutting around it, with the gel filter held between the two halves, you got the correct size.  I kept the protective tissue on the gel while doing so, so it wouldn't be damaged. I just used sharp scissors.

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gelatin filter lots tend to pop up in eBay every now and then. they are pretty cheap when purchased this way (old stock or ones with small portion cut out of them previously) . I purchased all the gelatins I'll ever need this way couple of years ago, I think I got 30 or 40 or something for the same price than one new costs

Edited by aapo lettinen
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Thanks guys. I was thinking buying old gelatin filters might be a bit hit and miss but if it's a matter of getting a whole stack for a small price, and going through them for the usable ones, then that's a good solution.

Now, with a dark ND in place, I'm anticipating that it's going to be difficult to see much through that Bolex viewfinder! Is it possible to pull the filter out, in between shots for focusing etc, then slide back in and hit run? I know this will fog at least a few frames. But does anyone know if it will potentially fog the whole film compartment?

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The gap for the filter holder is a small slot that leads to the front surface of the prism. It can only allow a bit of light to possibly bounce around and hit the frame of film being exposed in the gate, but if the shutter is closed it shouldn't fog anything. So if you only remove the filter between takes you should be fine.

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That's a relief. I will get a heavy cloth and drape it over to minimise light getting in, just in case.

These filters are not easy to find. I've been looking for 0.9 and 1.2 ND which would be ideal (3 and 4 stops) but so far can only find second hand 0.6 (2 stops). The alternative is shoot on 50D.

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The pulling out of the filter holder regularly is going to add to the risk of dust or lint getting onto the filter and it will be difficult to check for it. A matte box really is necessary for serious filming.

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10 hours ago, Jon O'Brien said:

The pulling out of the filter holder regularly is going to add to the risk of dust or lint getting onto the filter and it will be difficult to check for it. A matte box really is necessary for serious filming.

I wouldn't have thought much of a problem with dust, unless it's a dusty environment. Any specks way out of focus and likely invisible at the gate.  No problem of course with bayonet models where the filter is enclosed on withdrawal, unless you then forget to insert 🙂

Unfortunately,  even with filters over the lens there's going to be difficulty focusing through the dark viewfinder of the Bolex. Maybe though with a matte box it'll be quicker to take off the filter briefly.

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Another thing you've probably thought already, half-close the variable shutter to reduce one stop.

Also... don't know if you are thinking of shooting closeups of non-actors, but I have found that giving them a bit of slowmotion, say 32 to 40 fps often helps.

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Shooting on 50D and putting in a 0.9 ND is sounding better and better, rather than try and use 250D. Or shoot in the shade and as the light is starting to fade in late afternoon.

I did think about closing the variable shutter down 1 stop Doug but I've not tried this before.

I know the interesting look they got in the opening battle scenes in Gladiator were filmed with a faster shutter, where mud flying up in the air had a 'staccato' look that heightened the drama of the action.

Do you know if a faster shutter will mean that pans or other movement will come out looking unusual?

Shooting at higher speed is a great idea too.

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10 hours ago, Jon O'Brien said:

Shooting on 50D and putting in a 0.9 ND is sounding better and better, rather than try and use 250D. Or shoot in the shade and as the light is starting to fade in late afternoon.

I did think about closing the variable shutter down 1 stop Doug but I've not tried this before.

I know the interesting look they got in the opening battle scenes in Gladiator were filmed with a faster shutter, where mud flying up in the air had a 'staccato' look that heightened the drama of the action.

Do you know if a faster shutter will mean that pans or other movement will come out looking unusual?

Shooting at higher speed is a great idea too.

I rather like that staccato look at times, but yes, panning does look jerky. Unless combining with slomo. But for fairly static scenes you don't notice any difference.

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