Hi
Just figured out that there are 2 generations of Baader's solar continuum filter, which I use routinely for white light imaging. To reduce the chromatic abberation of my 127mm FH refractor I used a G-Filter. A friend borrowed me a Solar Continuum Filter for testing. I was quite shocked when I first tried it out and got this result (rearranged today):
As many people make very good photographs using this filter it was apparent that I did something wrong. I decided to scan the filter in a spectrophotometer (we have one in the lab).
Aaa-Ha! There is the advertised peak at 540nm (10nm half bandwidth as promised), but there is an additional huge leak transmission in the near infrared. And my DMK41 is quite sensitive for this light. And my FH lens will not focus this light properly, which explains the low contrast. I decided to combine Baader's filter with a IR-block filter and that is the result:
And this combination yields this type of solar image: ...
Lesson learned: Combine Baader's filter with a IR block (or better L-Filter) and all will be fine. You just need to know that. I used the combination IR-block + Solar Continuum routinely. But last week the story got another twist:
As I'll give the filter back to the owner I needed to order my own one. Scanning it in the photometer gave a result which I feel is worth reporting:
The new filter (bought July 2015) had no IR-leak transmission at all!
And it does not need any additional IR block filter to deliver good solar images:
There appear to have been (at least) 2 generations of the filter. The design of the barrel is similar, even the product number indicated on the barrel is identical. However, the old filter barrel is a bit thicker than the new one. If the new barrels always contain new filter glasses is not known to me.
Conclusion: There are 2 generations. The old one requires an additional IR block filter and the new one does not. Both do an excellent job, but the old one only when combined with an additional filter. I feel this info is important especially for those who have older filters or buy a filter on the second hand market.
Hartwig
2 generations of solar continuum filter out there
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Re: 2 generations of solar continuum filter out there
Good analysis and useful information there Hartwig!
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Re: 2 generations of solar continuum filter out there
Very interesting indeed! yes we knew that it leaked IR and for some scopes a IR cut filter was absolutely necessary with it, but we didn't know Baader had corrected this. This is excellent news indeed for anyone buying a new one in the future.
Alexandra
Alexandra
Re: 2 generations of solar continuum filter out there
Hi Hartwig,
very interesting, thanks for posting it
cheers
Marcello
very interesting, thanks for posting it
cheers
Marcello
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Re: 2 generations of solar continuum filter out there
Hi Hartwig,
This is very good news Baader finally solved this long standing problem.
Thanks for sharing with us the information !
This is very good news Baader finally solved this long standing problem.
Thanks for sharing with us the information !
Christian Viladrich
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
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Re: 2 generations of solar continuum filter out there
Thanks Hartwig I will test my filters with an IR cut if the sun ever comes out here.
Re: 2 generations of solar continuum filter out there
Finally, great news . I had this problem of additional wavelengths in IR, because i didn't want to buy another filter. I think a lot of the reasons and saw the plot of transmission and know what's going on. Do You know price of new SC compare to older one, is it the same? The differce between these filters is only barrel? Any differences (new sentences, words, pictures) on the packaging?
"The first drink from the cup of natural science brings atheism, but at the bottom of the cup waits God." – Werner Heisenberg