Coronado BF15 dies....resurected!

[Merlin66 (Ken)]

After seven years my BF15 (from my SM60) finally died......
I was testing an ol' IOM etalon and borrowed a Lunt 1800 filter; I couldn't help but try it on the SM60. Majic! Wonderfully bright and detailed surface and proms.
When I went back to the BF15 I thought I'd gone blind - the solar disk was very faint by comparison (similar to the difference between single and double stacking). What!!!!!!!!!!!!!
A closer look at the ITF element revealed the dreaded heat rust syndrome - Bumma! All my BF filters are always kept in sealed Tupperware with Silica Gel.

Mr Maier to the rescue. I bought one of the ITF replacement filters ( H-alpha ITF Blocker, 0.69 Dia x 0.125 inches) for testing a couple of years ago (to compare with the Baader 35nm as an ITF replacement) and quickly did the change over.
http://maierphotonics.com/656bandpassfilter.aspx

The view was now as bright as the Lunt with the same visible details!!!
Hopefully the Maier ITF will last as long as the original.

[alocky (Andrew lockwood)]

Hi Ken,
I have a Coronado 60 in my house that has a suspect blocking filter as well. I might put my own Lunt one on to check it, but what external signs are there that the bloom has grown on the filter?
Cheers
Andrew.

[OICURMT]

Originally Posted by Merlin66

Mr Maier to the rescue. I bought one of the ITF replacement filters ( H-alpha ITF Blocker, 0.69 Dia x 0.125 inches) for testing a couple of years ago (to compare with the Baader 35nm as an ITF replacement) and quickly did the change over.
http://maierphotonics.com/656bandpassfilter.aspx

The view was now as bright as the Lunt with the same visible details!!!
Hopefully the Maier ITF will last as long as the original.

Sooo... I have to ask the question.

As the Maier filter is inexpensive, Is there a DIY possibility to convert a cheap 1-1/4" diagonal to a BF for Solar use?

[Merlin66 (Ken)]

Andrew,
It's easier to see the "Rust circles" if you actually remove the ITF first.
It's not the "fungus" type problem you can have with the Lunt......
I do have some images of the typical burn out circles...
OICURMT,
Unfortunately the blocking filter is made up from a couple of elements...
The upfront element is the ITF which suppresses the IR energy, the final element is the critical part - a very tight (about 8A) narrowband filter.
You need the final narrowband element to make an effective blocking filter.

[h0ughy (David)]

Ken,
did you manage to take some images of the filter before and after?

[Merlin66 (Ken)]

David,
I can take one for you, but the attached image from my "rogue's gallery" shows the rear surface of the heat circle damaged ITF.
I also, for comparison show the typical fungus problem on the Lunt ITF....

[h0ughy (David)]

yes that brings back memories - i had the craze for the venus transit?