2 generations of solar continuum filter out there

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astrohardy
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2 generations of solar continuum filter out there

Post by astrohardy » Sat Jul 18, 2015 2:04 pm

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):

Image

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).

Image

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:

Image

And this combination yields this type of solar image: ...

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:

Image

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:


Image

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.

Image

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

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marktownley
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Re: 2 generations of solar continuum filter out there

Post by marktownley » Sat Jul 18, 2015 3:55 pm

Good analysis and useful information there Hartwig!
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Montana
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Re: 2 generations of solar continuum filter out there

Post by Montana » Sun Jul 19, 2015 2:09 pm

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

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Re: 2 generations of solar continuum filter out there

Post by Marcello » Mon Jul 20, 2015 11:53 am

Hi Hartwig,

very interesting, thanks for posting it

cheers
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Re: 2 generations of solar continuum filter out there

Post by christian viladrich » Mon Jul 20, 2015 5:51 pm

Hi Hartwig,
This is very good news Baader finally solved this long standing problem.
Thanks for sharing with us the information !
Christian Viladrich
Co-author of "Astronomie Planétaire"
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Co-author of "Astronomie Solaire"
http://www.astronomiesolaire.com/

Derek Klepp
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Re: 2 generations of solar continuum filter out there

Post by Derek Klepp » Wed Jul 22, 2015 9:09 am

Thanks Hartwig I will test my filters with an IR cut if the sun ever comes out here.

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matti_94
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Re: 2 generations of solar continuum filter out there

Post by matti_94 » Thu Jul 23, 2015 8:50 am

Finally, great news :D. 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?
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