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Old 17-04-2012, 12:21 PM
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troypiggo (Troy)
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troypiggo is offline
 
Join Date: Nov 2008
Location: Brisbane, Australia
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matching NB filters to your gear?

I've recently been exchanging some emails with Astronomik regarding their narrowband filters as part of my halo problem. They've sent me out replacements now, so pending some testing, all good and happy there.

But in the email exchanges, they talked about the filters not being ideal for my setup, and when they sent me the replacements, they said the filters they have sent were selected for my telescope. Quoted below is the email exchange. They haven't yet responded to my last query for clarification.

What I don't understand is that they only have 12nm Ha, OIII, SII, Hb filters, and also a 6nm for Ha. They've sent me the exact same filter bandwidths that I had before. What is this selection for my telescope they're talking about? Is it a bit of BS/marketing dribble?

An additional concern of mine is that, like many of us, I use more than one telescope to image with. So if they've sent filters just for the scope with which I took the sample images I had to provide them with to assess the halos, what about my other scopes?

Is there some special formula for working out the best filters for each scope? I know there's good, bad, and ugly filter quality. But that's between brands, not within the actual product line of an individual manufacturer. I mean, I'm looking at Astrodons. I know they have 3nm and 5nm bandwidths. Is the selection of the bandwidth dependent on the optics? ie would one be better than other for 10" reflector vs 92mm refractor?

4/4/12:
Quote:
Hi there. Thanks so much for your time. Not sure what you mean about the Ha filter being hard to measure? And it not being the ideal filter for me? If I stretch the image I can clearly see the same style of small rings around Sirius. But what would you recommend as a more ideal filter? Do you mean a narrower bandwidth like 5 or 6nm?

On 4/04/12 1:41 AM, * Eric wrote:
Quote:
Dear Troy,


sorry to come back to you so late.


Your images show two kinds of Halo, best seen in the Sirius 5x1m Hb.tif.tiff image. The small rings are produced from our filters, the large reflection is caused by the MPCC.


The H.alpha filter is difficult to measure, it looks to me like it is a not ideal filter for your setup, the other filter can be replaced with improved filters more easy. We are going to send you a new set of filters as registered letter. There is a small invoice enclosed, that must not be paid, just for custom purposes.


Once you received the new filters, please send the old filters to
...The return should be done as registered letter.


Yours


Eric
...

Quote:
>Hi there. I am getting halos with my Astronomik narrowband filters and someone directed me to your page http://www.astronomik.com/en/news/as...r_halo_problem
>
>Your requirement to submit full sized, uncompressed images makes them too large to email, so I've provided links below to download them. They're about 16MB each. I have 1.25" Ha, Hb, OIII, SII narrowband filters, all bought somewhere around Feb-May 2011. I've also provided a Luminance filter shot for comparison. Each shot is a 5x1min exposure of Sirius, bias, dark, and flat calibrated, but no other processing applied.
...>I have attached reduced and stretched images just for demonstration.
>
>Images were taken on a 10" 1200mm f/4.7 reflector with a Baader MPCC and a QSI583ws. The luminance image shows, I think, that there are no reflections/halos caused by the MPCC.
>
>Serial numbers show up in this photo of the boxes:
...>My postal address is:
...
13/4/12:
Quote:
Thanks again for your help. I'm still confused by some of your comments below.

You mention the filters you have sent "are selected for my telescope." Firstly, like many astro-imagers, I have more than one imaging scope. I sent you images taken from just one of them. So hopefully the filters you sent are compatible with all of my scopes. Secondly, I wasn't aware how to select different 12nm filters. All of the online stores and even your website just seem to sell one type of 12nm Ha, one 12nm OIII etc. I'm not clear on how you selected specific filters for my scope. Aren't all of your 12nm filters the same?

On 12/04/12 9:34 PM, * Eric wrote:
Quote:
Dear Troy,
Hi there. Thanks so much for your time. Not sure what you mean about the Ha filter being hard to measure?
The diameters of the reflections need to be measured exactly.
And it not being the ideal filter for me?
The transmission may not be at the optimum position for a f/4.7 reflector.
If I stretch the image I can clearly see the same style of small rings around Sirius. But what would you recommend as a more ideal filter?
The filters we have sent, are selected for your telescope.

> Do you mean a narrower bandwidth like 5 or 6nm?

No. The smaller the bandwidths, the more precise the transmission should match the optimum. When you receive the filter, let me know if you are satisfied. I know that our current filters are better then nearly all other filters on the market.

Yours

Eric
...
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