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filter for double star observations

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#1 darren8se

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Posted 04 October 2013 - 06:51 AM

ok today I aligned the finder with the Bressr AR127l and had a look at some distant objects against the bright background I could make out some CA I knew I would as id done a lot of reading on refractors,
so I was expecting some it wasn't all that intrusive infact I think it was more I was looking for it.

Anyhow as my main aim for this scope is to split doubles, will the CA be less visable at night against stars or more so ?? also ive read both threads on baader longpass and yellow filters now if im understanding it correctly,
they are more for Astrophotography than visual so now im confused for visual doubles what filter do you recommend ?? my choices are:
baader long pass
baader fringe killer
baader semi APO filter

I want to get as natural looking colour as I can for when I record my observations I like to record the colour of each component star so I would like a filter that is not going to add false colour to my view ...
sorry for rambling on so much
Darren

#2 Jon_Doh

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Posted 04 October 2013 - 07:19 AM

If you are just looking at stars a contrast filter works fairly well and renders a natural color.

#3 Illinois

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Posted 04 October 2013 - 07:52 AM

Never heard of it! I think some kind special to block bright star's glare like Sirius A and B

#4 darren8se

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Posted 04 October 2013 - 08:08 AM

If you are just looking at stars a contrast filter works fairly well and renders a natural color.

Do you mean a contrast booster filter ? If so will this reduce CA at the same Time ?

#5 Mike4242

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Posted 04 October 2013 - 08:23 AM

The filters you listed are for visual as well as photography. I think you'll get the most benefit from the filters when splitting uneven doubles where one component is much brighter than the other. The filter will reduce the CA around the bright component while also cutting down the glare. I haven't tried the 495 long pass, but I do own the Semi-Apo and the Fringe Killer. Personally, I prefer the Fringe Killer to the Semi-Apo. The Semi-Apo brings things back to a more natural tone, but I didn't think it was quite as sharp. When it comes to color contrasted doubles, my AR152, a 6" f/6.5 achro, does distort the color on white and blue stars. For instance the gold component of Albireo does indeed look gold, but the whitish blue component looks more of a washed out green blue color. However, your 5" should have less CA than my 6".

#6 darren8se

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Posted 04 October 2013 - 08:41 AM

The filters you listed are for visual as well as photography. I think you'll get the most benefit from the filters when splitting uneven doubles where one component is much brighter than the other. The filter will reduce the CA around the bright component while also cutting down the glare. I haven't tried the 495 long pass, but I do own the Semi-Apo and the Fringe Killer. Personally, I prefer the Fringe Killer to the Semi-Apo. The Semi-Apo brings things back to a more natural tone, but I didn't think it was quite as sharp. When it comes to color contrasted doubles, my AR152, a 6" f/6.5 achro, does distort the color on white and blue stars. For instance the gold component of Albireo does indeed look gold, but the whitish blue component looks more of a washed out green blue color. However, your 5" should have less CA than my 6".

Thanks for that info Mike very helpfull indeed i think i may just get the fringe killer for now and see how it fairs and in time grab a long pass as they are quite cheap so if its not good not a great loss unlike the fringe killer and semi APO that are a fair bit more expensive :-)

#7 russell23

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Posted 04 October 2013 - 08:59 AM

Darren, I have the Fringe Killer and the Baader 495 long pass that I just purchased and used the other night. If you just want to split the doubles and don't care about the color shift then I think the 495 longpass is the way to go. Albireo was a yellow-orange/white with the longpass vs. the natural gold/blue without a filter. Fainter stars appear white. Stars are really sharp with both filters, but the longpass really impressed me as a double star and deep sky filter with an achromat.

Dave

#8 Jon_Doh

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Posted 04 October 2013 - 09:28 AM

If you are just looking at stars a contrast filter works fairly well and renders a natural color.

Do you mean a contrast booster filter ? If so will this reduce CA at the same Time ?


Yes, it will reduce/eliminate CA at the same time as keeping the natural color. There is a thread here somewhere with photos. The downside to this is it dims the view and if you are splitting dim doubles it may not work. The solution would be to stack a fringe filter with a moon and skyglow. That combo reduces or eliminates CA while giving a truer color of the stars and only slightly dimming the view. A long pass filter will add a yellow cast visually, but works nicely for astrophotography.

#9 mikey cee

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Posted 04 October 2013 - 09:50 AM

I have both a Baader Contrast Booster and a Semi-Apo in my filter wheel on each side of the no filter position. Both filters appear identical on double stars. The airy discs are noticeably sharper and smaller. ;) Mike

#10 gdd

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Posted 04 October 2013 - 01:31 PM

I thought any filter is going to affect color balance. This link suggests that an aperture mask and using the lowest power capable of spitting the binary will do the best job of reducing false color:

http://rfroyce.com/r...actor spots.htm


Gale

#11 tlogan6680

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Posted 04 October 2013 - 08:51 PM

This will not help with CA, but to split hard, close doubles, I use a plain old yellow filter. try it on Rigel or the Lyra double-double and it will help with any scope-refractor, reflector, or cass.
Tom in ca

#12 jrbarnett

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Posted 05 October 2013 - 11:56 AM

The CA will be visible at night on brighter targets and/or at higher magnifications. I would expect CA in that scope on any target Magnitude 2.5 or brighter at any magnification above ~90x.

CA won't much affect your ability to split doubles, though, so I wouldn't worry about filtration. Filters improve aesthetics only, and in fact slightly reduce performance.

Regards,

Jim

#13 beanerds

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Posted 05 October 2013 - 08:23 PM

I agree Jim , I don't use filters at all with my Isatr achro , but I have played around with my 'Variable polarising' filter ( that is a must when using my Lunt Hershell solar wedge ) and that helps a lot with un-equal doubles like Rigel and Antares on in the lower settings .
I had both a 'Minus Violet' and 'Fringe Killer' but did like the un-natural tone they produced .
I would rather put up with a bit of CA .

Try a 'Vairable Polarising' filter , and if its not for you on doubles , these also tone the moon down a lot , stopping moon blindness . :lol:.

Brian.

#14 jrbarnett

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Posted 05 October 2013 - 09:01 PM

Good tip, Brian. I have used gentle ND and polarizing filters on Sirius and Antares with some success.

Regards,

Jim






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