The only question remains: is it worth of money and efforts and what special to look at? I mean in Na or He D3 lines. Valery, is WL worth the money, effort and risks? I am not sure but it it seems Na (or He) is at least as good as WL, with added benefits. I don't like heat getting inside my scopes ...

Thanks a lot Ken. Great results, not only the shift lets Na and He in but also keeps Ha at near full transmission. It also proves the minimum tilt is 30 degrees, a little more if we want full Na/He transmission. Meanwhile I tried my D-ERF (hold by hand) against some street lights, which I think are ...

On the other hand color glass has significant less quality than clear glass, so I think the tlilted clear glass will still be better than the non-tilted color glass. One issue with the clear glass is that it does not block completely the yellow-green light, less than 1% remains (one can check it in ...

Now I would welcome opinions about what is best for visual. Na or HeD3. I will go only with one of those. Na and HeD3 are so close, only 2nm (20A) apart (587.5 and 589.5) that we could think it could be possible that just one filter could reach both with extra tuning, but I think the blockers would ...

OK, Thanks Ken! Valery, I think you are assuming the D-ERF is made of red glass. That is the C-ERF that is made of red glass and then uses dielectric to refllect IR. The D-ERF is made of clear glass, it uses dielectric to filter everything below 610 and above 680. In fact I just checked my D-ERF hol...

Bob, you mentioned 800mm at CN. Can you confirm that? I will be using it with 1400mm which would make it only acceptable, not very good. Hi Pedro, That is the design focal length Mark Wagner provided - and he should know as the Baader telecentric units are made to be used with the Solar Spectrum li...

Thanks a lot Ken for the test. Unfortunately the results are disappointing. From what I found the shift in wavelength is given by: wf=wi x sqr(1-(sin(A)/n)^2) where: A is the angle n is the refractive index wf and wi the final and initial wavelengths I am not sure of the refractive index of the ERF,...

An excellent analysis! I especially appreciated the citation of Gene Baraff's work on the importance of using properly optimized telecentric lenses matched to the focal length of the objective - something generally not fully appreciated with these filters -- and why DayStar rightly does not provide...

Thanks a lot Merlin, that would be great. My current 180 D-ERF is already mounted at 2 deg to avoid reflections between ERF and etalon. We are lucky that tilting shifts wavelength to the blue, or else nothing could be done :-) Valery, the yellow glass filter does not reject all the heat as the Baade...

Well, 355mm for CaK seems a little too much. Resolution is linear dependent on the wavelength, so for the same aperture CaK (392nm) has 1.67x more resolution than Ha (656nm). Hey, I'm the guy who thinks 150mm Ha is much better then 90mm Ha, and that 200mm Ha is much better than 150mm Ha. But 355mm C...

Mark from SolarSpectrum told me this week: "I can make etalons from 390nm- 900nm with the setup I have. I have made Na filters." I am considering a Sodium (Na) filter, instead of a WL wedge. For a Na ERF I am considering a Baader D-ERF tilted enough to shift bandpass to include Na line. Ba...

Hi all, I am mainly a visual guy, I like to look through the eyepiece and discuss equipment, not so much photos. That is why double stack is more important to me. It is well known that double stack with two internal etalons works not as perfect as a internal etalon with an external etalon. However a...