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FL-D 49mm Photography Filter

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Date: 9-9-2003
Price: Not for sale yet, but you may use a normal 49mm photo filter for this application.  For possible sale details see body of text.
Design: Contrast enhancement filter, designed for photography use.
Description: 49mm filter good for 2-inch eyepieces.

The Review

At the fifth annual Star Walk program in Quanah , Texas at Copper Breaks State Park I was fortunate enough to utilize a very surprising filter. It is a common photographic filter used to enhance the light curve on subjects lit under flourescent lighting while utilizing daylight film emulsions. The common terminology is an FL-D filter. Of course they come in the common 49mm size which is rather awkward for astronomy use but good for photography. The nice thing is that Sirius Optics Inc. of Kirkland Washington is making a rather limited run of these filters available for the amateur astronomy sector and if I know them well, they will be very professionally manufatured. I believe they could be available by early September but a check at http://www.siriusoptics.com/contact.htm  would be prudent.

The most important and unusual aspect of the filter is the seemingly miraculous way it brightens and yet increases the contrast of the surface features on Mars. The initial impression I had was the planet lost some of it's ruddy tan color and the dark maria stood out well. In comparison to a Wratten #23A the contrast was increased and the planet was not dimmed drastically like the light red filter usually does. This was a boon to the smaller 8" aperture I was using. The Polar hood was still well defined but the most striking thing was the dark mare jumping out at me.

The star party was populated by over 30 experienced amateurs and each one that I talked with commented about the increased detail in the filter. Most were very surprised. The initial effect of the word of mouth in the Dallas/Ft.Worth area was to run out and buy up all the local camera shop supplies. The only problem is the 49mm filter will only work on a 2" barrel EP with a step down 49-48mm ring and no Barlow. (the step down ring is too large to allow it to fit inside the Barlow). I am anxious to have my Sirius Optics filters so I can use them with a Barlow and the 1-1/4" format filter to work with my smaller but more powerful orthoscopics and plossls. This should prove to be a great combination.

This is an example of never knowing where the next big thing will come from. Who would have guessed? For those out there with a curiosity to see Mars at it's best in a smaller aperture, this is the key! My advise is to get the filter when it becomes available and before it is gone.

Submited by - David Ryle

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