JCDowdy Posted January 3, 2015 Share Posted January 3, 2015 I recently ran across a filter I have not heard of before: Sky's the Limit 2" Venus U Premium High Transmission filter The listing specifies a Schott RG610 substrate but listing images show a transmission plot that is not consistent with that glass. Anyone ever heard of this filter before? Link to comment
colinbm Posted January 3, 2015 Share Posted January 3, 2015 Another strange one ?Further down the listing it has "The ground and polished piece of optical glass that is used as a base for the filter coating. Schott B270, HB610 or RG610."The filter ring thread spec is a strange one too, M46 x 1.86mm ??Col Link to comment
enricosavazzi Posted January 3, 2015 Share Posted January 3, 2015 I did not google around, but there seems to be something wrong with the filter size. An M46 filter ring is not wide enough to contain a standard 2" filter blank. These blanks are usually mounted in M48 rings. The transmission spectrum visible in the picture of the data sheet seems similar to the Asahi Spectra XRR0340:http://www.asahi-spectra.com/opticalfilters/uv_broad_bandpass_filter.html See also http://savazzi.net/photography/uvpassfilters.html#asahispectra for samples with the XRR0340 filter. Link to comment
Andrea B. Posted January 3, 2015 Share Posted January 3, 2015 By dealing directly with the manufacturers and suppliers in China and keeping our overheads low in the UK we are at the forefront of the bargain price supply chain. It had to happen that eventually there would be cheap Chinese knock-offs of the Baader Planetarium and other such filters.But I see no mention at all of how the IR suppression is achieved. Are there dichroic coatings? Buyer beware unless you have a way to verify the transmission. Link to comment
nfoto Posted January 3, 2015 Share Posted January 3, 2015 Well, knock-offs they might be, but cheap they are not. Hence an understandable wish of having better data on the filter spectral performance. Link to comment
Andrea B. Posted January 3, 2015 Share Posted January 3, 2015 Oh man did I ever misread the price !!!It is indeed very expensive. Yarg!!!£249 = US$381 = €318 These days the Baader U is running around $350 in the US.I don't know how anyone is going to be able to afford this UV hobby anymore. Link to comment
enricosavazzi Posted January 3, 2015 Share Posted January 3, 2015 It is indeed expensive enough to be a remounted Asahi Spectra filter. The copper-color is a dielectric coating. The original Asahi Spectra XRR0340 is copper-colored on one side, black on the opposite side (which probably shows the color of the ionic substrate, very likely a U-340 or equivalent). Link to comment
JCDowdy Posted January 3, 2015 Author Share Posted January 3, 2015 The transmission data sheet in the accompanying images and the appearance of the filter are consistent with a UG-11 type dichroic red rejection filter. However, the filters of that type (DUG-11) that I have handled appear much redder, like the Asahi Spectra XRR0340. Link to comment
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