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visual vs AP filters?

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#1 Danzup77

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Posted 29 November 2012 - 03:09 PM

I have recently just heard someone say filters for viewing wont work well for AP for different reasons (I cant remember) but one was that you have to refocus every filter change. Is this true and if so can someone please explain? I mean I would still want the filters I currently have anyway for observing but not exactly looking to purchase a complete second round just for AP any time soon.

Thanks as always everyone

#2 SMigol

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Posted 29 November 2012 - 04:38 PM

A lot of it has to do with that your eyes are most sensitive to green wavelengths and insensitive to infrared. Thus, many filters that are optimized for visual use do not take the step of adding an IR or UV resistive element and will take steps to widen the green frequency pass to improve your ability to see. I believe OIII filters are most significant in this difference.

FWIW, I recently swapped out a LPR filter that was for visual use for an AP optimized one for my DSLR. I can immediately tell the difference in better contrast.

#3 CounterWeight

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Posted 29 November 2012 - 07:06 PM

Hmmm I've been saying that since I started ;) There are a lot of reasons to use imaging filters for imaging - First and foremost is they work much better, or in my humor I'd say they work. A more detailed reason has to do the way each manufacturer goes about it, some are bandpass type filters and other use wavelength shifting to increase contrast. No right or wrong way for visual and each types have advocates. But for imaging you want something that is a bandpass type.

As far as the refocusing though I'm uncertain what you mean by the question. Refocusing for filters is more something you find in the monochrome CCD and LRGB filters or narrowband Ha, SII, OIII - and even then there are filters that are par focal meaning you don't need to refocus.

One shot color imaging you only need a good LP filter depending on what you are imaging with and how bad the light pollution might be... If you are in true dark skies - great! you don't even need that.

What type of CCD or camera are you thinking of using?

#4 Danzup77

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Posted 29 November 2012 - 09:06 PM

Thanks guys, Im just using my D90 (because thats what I have), but I have filters for observing Lumicon OIII, H-Beta, DGM NPB and Lumicon UHC all in 2" format. And although I dont go above and beyond with AP its somewhat bothersome to know I will have to spend yet another small fortune for AP filters lol. I mean it is what it is and if thats the case then so be it but I just had no idea. Learn something new every day I suppose.

#5 SMigol

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Posted 30 November 2012 - 01:24 AM

If you want, you can try stacking a UV/IR filter with your existing filters to see if it makes much of a difference. I tried it with the Baader Moon and Skyglow (a visual filter) and it worked well to control a bit of star bloat. it's a small fix while you gather gear.

#6 Wouter D'hoye

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Posted 30 November 2012 - 01:50 AM

Hi,

If you're currently using a D90 you don't need the UV-IR filter since that's already built in in the camera. The use of OIII and H-alpha filters primarily meant for visual use would still be a compromise. Because these filters aren't designed for imaging. The main reason the use imaging filters is that they are designed for this purpose. One important thing is their behaviour regarding reflections and halos. Something that would hardly ever be an issue with visual filters.

Kind regards,

#7 Danzup77

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Posted 03 December 2012 - 07:15 PM

Thanks for the replies guys. Wouter as far as the AP filters where would I find them? I dont even know where I would look because as I search around they seem to be primarily for CCD AP or filters just for visual. Also, what format are they made in 1.25 - 2"? Again, not looking to do this anytime in the near future but just trying to re-gain my bearings lol.






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