[Aavso-photometry] Where do the professionals source

[Stan Walker]

Hi Arne & Michael,

There's obviously a major change from UBV filters with pm tubes to the more 
complex CCD filters. We used to buy filter glass directly from Germany and 
had no trouble with any sort of 'crud'. The original set made in 1965 was 
still going strong in 1990 and may still be in the unused photometer.

But some U glass bought in the 1980s caused some trouble as it appeared to 
be coated. This makes me wonder whether all of these commercial filters have 
some type of coating - anti-reflective or something - which is probably 
unnecessary. Or is it needed with CCD photometry where the filters are much 
closer to the focal plane and you're not just looking at one defocussed 
image?

Auckland is very humid but we had no trouble with filters except for the 
adhesive on some sets of filters that had come from Mt Stromlo. They 
replaced these very promptly and helpfully.

Maybe if this continues to be a problem the AAVSO could get into the filter 
making game and produce sets that don't cause problems. This was the way 
things were done in NZ and Australia in the 1970s with UBV photometry. But 
perhaps the manufacturers could be approached to see what 'improved' 
treatment of filters isn't working? The idea of throwing a set away each 
year is alarming in that the degradation must affect all measures during 
that year.

Regards,
Stan

----- Original Message ----- 
From: "arne" <arne at aavso.org>
To: "Michael Koppelman" <lolife at bitstream.net>
Cc: <aavso-photometry at mira.aavso.org>
Sent: Saturday, September 24, 2005 7:17 AM
Subject: Re: [Aavso-photometry] Where do the professionals source


> Michael Koppelman wrote:
>
>> I can do that, although I tried to clean it so it looks worse than it 
>> did. I can just send you the dang thing, too, if you'd like. It's of  no 
>> use to me anymore.
>>
>> Michael
>>
>> On Sep 23, 2005, at 12:21 PM, arne wrote:
>>
>>> Thinking about the actual paper, I was wondering if someone has one  of 
>>> the
>>> bad filters and would be willing to take a picture of it for me so  that 
>>> I
>>> can include a jpeg image in my presentation.
>>
>>
> I'd rather have an "unadultrated" filter picture if possible, if anyone
> can get me one.  Michael's cleaning results can be another useful
> picture, though.
> Arne
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