#1  
Old 26-07-2010, 05:56 PM
Bolts_Tweed (Mark)
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Location: Banora Point NSW
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Astrodon Lum FIlter question

Gday

Am I the only one with this problem???

I have found that if I shoot say 5 min RGB subs with the astrodon filters and I then shoot a luminosity image I cant get the half flux diameter down to anywhere near what I get in the RGB - I have reduced the exposure down to say 30 seconds as an experiment and still the 1/2FD is 60 to 75% or larger than the RGBs - Sry this is using an ST8300 and a AP130EDT or a Televue np101is so I am fairly confident with the optics performance.

After much experimentation I am at an end - I know I should email Don Goldman but I thought I would check if anyone has a similar experience.

In extreme frustration I am going to try turning the filter around next weekend just in case they are directional but I cant find any reference to cirectionality on Dons website.

Anyone have any ideas or similar experiences - I am looking forward to a LRGB image instead of HaRGB for a change. I am keen to have a crack at the IFN in Apus this weekend and Ha just isnt going to help too much.

Mark Bolton
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  #2  
Old 26-07-2010, 06:29 PM
Bolts_Tweed (Mark)
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Damn - I think I can answer my own question. I just found this below in the fine print on Dons homepage

*********************************** *******************
The Clear (no near-IR blocking) may produce bloated stars if your optical system has poor near-IR focus. Use the near-IR-blocked Luminance filter in this case. The Clear filter is likely a better choice for reflectors, such as Ritchey-Cretiens, rather than refractors or camera lenses.
*********************************** ***********************************

So with a refractor , even a good one, they reccommend the IR blocked Lum filter to avoid bloating - I know I should have known this but it may be a warning to others considering Astrodon E series for these big chips. Save buying 2 Lum filters like I am going to have to

Mark Bolton
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  #3  
Old 01-08-2010, 05:38 PM
astrospotter (Mark)
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AstroDon will reply and Don makes wonderful filters

If you submit a question to Don he will reply. Wonderfully connected with his market. Perhaps that is why he has been so responsive in pushing the state of narrowband filters. They are costly but as has always been true, you get what you pay for. I have the Luma that does cut out IR and am happy with it although I am by no means very experienced to date.

I have been toying with trying his red one that is meant to be used to cut out all common narrowband lines so you can make a star mask that works well in fairly strong nebulous regions.
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