- Dec 21, 2002
- Large Format
dnmilikan said:Since I am beginning to use incident metering more then I once did, I have been thinking of using a densitometer to read filters as a more accurate means of determining the spectral response and filter factors.
Does this make sense? Has anyone done this?
David A. Goldfarb said:On the alleged superiority of acrylic vs. glass, I have a lot of 3x3" acrylic filters, mostly made by Ambico when they were trying to compete with Cokin. These come up fairly cheaply on eBay, so it's not too hard to accumulate lots of them, and there are many holders that will handle 3x3" filters, if that size is large enough for you. Voss, for instance, made a clip on 3x3" filter holder, which I use for all sorts of odd series sized lenses. I happened to acquire enough of the Ambico adapter rings (these are not so easy to find) when it was in regular production to make it worth while, though now I have several lenses that need a larger filter, so I'll have to find another system eventually.
In any case, I tested all my filters of various types once for flare, and while I found that even a cheap glass multicoated filter was better than a fancier glass single-coated or uncoated filter in supressing flare, the acrylic filters fell somewhere in between.
Acrylic filters can have other problems, such as ND and ND grads not being really neutral, and I'd be concerned that acrylic sheets not made for a specifically photographic purpose may not be optically flat.
Lex Jenkins said:Hey, Don, if it's not going off on a tangent too much, mind if I ask why you find yourself doing more incident than spotmetering these days?
This isn't a trick question and I don't have an axe to grind. I'm just often curious about the metering techniques we use.
Jorge said:It has to do with the thickness of the material and being able to read it with the densitometer probe. If the material is too thick you will have extraneous light going into the probe, plus the aligment of the sensor will not be the same as if it was a thin material, for which these instruments are designed.
Suppose you turn off all the lights to read the glass or acrylic filters, then at the same time you have light from the densitometer bulb escaping due to thickness.
Thilo Schmid said:Don,
I'm not sure what you expect from using a densitometer instead of a normal light meter for determining filter factors. Although a normal light meter might not exactly match the spectral sensitivity of your film, this is usually sufficient in practice. It is still photography and not rocket science!
dnmilikan said:...development times is based upon BTZS methods and procedures. BTZS utilizes incident metering...
dnmilikan said:Thilo Schmid said:If I were using a spot meter for my exposures, it would be a simple matter of metering through the filter. However when I am using incident metering I am not able to meter through the filter and must assign some exposure factor to the filter effects.
I did recognise that point. But what keeps you from using a spot- or normal reflective meter for determining filter factors "at home" as you would do with your densitometer? I can't belive that you do not even own one.
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