Poor man's centre filter

Hello:

 

I was wondering if a usable CF could be made by holding a clear UV

filter over a candle and getting a bit of smoke on it, very

carefully of course, then measuring the light absorbtion with a light

meter or enlarging meter.

 

Paying hundreds of $$$ for a slice of glass hurts, when 1/2 hr with a

candle may do the trick.

 

Any thoughts?

 

Thanks

Depending on how you plan to use the center filter, I have used a graduated 4x5 or 4x6" filter to offset the fall off from shifts or rises with a rail camera.

One of the most important considerations is determining IF you need the filter

at all. When I was using a 65 SA I had a CF and used it every once in a while

but did not find it necessary for a lot of my shooting. Right now my shortest

lens is a 75 mm SA and I find I have absolutelyno need for a CF at all. There

are certain lighting situation swhere I make careful use of a lens hood but that

is it. I have seen people discussin gthe use of a CF with lenses as long as 90

mm and again, have never seen the need for same.

 

I am sure there are lighting situations with 90 mm and 75 mm lenses where a

CF is needed just that I have not encountered them.

 

Ted

Rich,

 

If you are trying to duplicate a neutral density center filter for a wide angle lens, like a Schneider or a Rodenstock, without having to pay big $$$ for an offical filter, then I think your idea is clever and just might work.

 

Another alternative for you if the flame is not doing what you want would be to get a can of spray paint and give a sheet of glass a quick burst.

 

If the results are not good, simply wipe off the glass (if possible) or take a flat edge razor to the glass and redo it.

Although this might work if you work with B&W film, I would have low expectations for color transparency film. But it's inexpensive to test. I'm be interested to see how well it goes.

Wouldn't you be better off applying the filter at the enlarger stage? At least you wouldn't be messing up the negative. I don't think this technique should be used for color because of the chance that you would be degrading the image or color/density balance. Vapor products of a burning candle may absorb/reflect light in a non-neutral manner.

After spending all that moola on a camera, film, lenses, film holders, a loupe,

dark cloth, etc. I find it a bit silly to mess around with fire! You might get

burned. I would save a few dollars every month or week and ensure that

when you push the cable release your image has every chance possible to

be the best that it can be.

Richard,

 

Sounds more like you would be creating a graduated center diffuser along with a graduated center neutral density filter.

 

Since all you really would be doing is depositing a layer of soot on the central portion of the UV filter, not only would you have less light transmission but likely also a degraded image in the central area of your negative. Then again, maybe the soot particles would be so fine as to not degrade the image.

And then how do you handle an unintentional touching of the filter and how it may affect the image? The process you are talking about is dynamic and it (could) be constantly changing. No way in hell I would take a chance with my shooting with such a completely arcane solution as compared to a very well engineered and proven solution that works. You put an image on a transparency or negative and unless you are going to spend some big bucks to get image scanned to correct it, you are stuck with it. Goodness gracious, we all recognize that large format is expensive to begin with, why mess with it? If you need a center filter just get one even if it is in the used market. The reason that they are expensive is because they are not easy to manufacture and they work. I can see cutting corners with costs by tray developing versus a JOBO and old versus newer vintage lenses, but this one does not make any sense to me.

 

.

Richard

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I read a posting somewhere (not here) from an optometrist who is also a photographer, he decribed a very simple and effective method for creating a centre filter with equipment readily available. I vaguely remember use of a tinting solution that's used to colour optical glass, putting a drop in the centre and spinning it.

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I'll hunt around and see if I can find it. You may also like to ask a dispensing optician or similar?

Adding a little fuel to the "fire", I wonder if one could use one of photoshop's brushing tools (or something?) to create a dot pattern using an ink-jet printer on a gel filter to duplicate a center filter?

 

I have this vague recollection that center filters consist of a pattern of very tiny dots. If so, perhaps that's how one can still maintain focus, while also decreasing the amount of light.

If you want so strongly to venture into such rustic solutions here is a better way. Borrow a CF for your lens, take a transparency picture (1:1) of it on a light table (daylight corrected) and use the transparency in front of your lens as a poor man CF. (don't forget to return the real CF to its owner though...)

What if you borrowed a center filter and scanned it in to your computer, then printed it on transparancy film? Then you could cut it and attach it to a UV filter.....

Whatever transparency film one uses, it would need to be optically pure. Something like a 4x4 gel UV might be good. It's large enough for the printer to get hold of, but not so large as to be expensive.

Whatever you gain optically in purity with an UV gel you lose more than richly in the mediocrity of the scanning and printing process as opposed to the resolution power of the transparency film.