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Old 14-10-2015, 11:18 AM
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Which LRGB filters?

Struggling to find which would be the best LRGB filter set to buy. I'm after something with no halos and suitable for use with a highly-sensitive CCD coupled with a refractor.

Astrodon, Astronomik and Baader all allege zero halos, but in every case I can find examples of images with halos. Tricky part is that some of the photos might have been taken with older versions of the filters, I'm not sure.

I'm happy to pay for the Astrodons if they give me no halos and the others will, but I definitely don't want to fork out the money and find that I get them.
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Old 14-10-2015, 11:24 AM
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I have been using Astrodon Gen II filters on a few different scopes and have been very happy with them wrt halos and general performance.

Cheers,
Rick.
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Old 14-10-2015, 12:27 PM
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Thanks Rick
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Old 14-10-2015, 01:13 PM
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I use Baader Planetarium's.

They're meant to be parfocal, but, I thought I'd put it to the test since I've resolved my RoboFocus issues.

Last night, I decided to run autofocus on each filter on the same star at the same temperature (639 units according to the RoboFocus).

All 7 filters (LRGBHαSIIOIII) came to focus within 2 counts of each other. Quite impressed! My microstep/pause and step/size are both set to 4. I seem to be hitting the CFZ quite well with those settings, but, the next night there's dodgy weather, I will change both to 2 and redo my V-curves and then run my autofocus test on each filter again to see whether the numbers vary wildly or not.

H

Last edited by Octane; 14-10-2015 at 02:30 PM.
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Old 14-10-2015, 02:14 PM
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I like Astrodons as well. I have used Baader and they are good and a bit redder than Astrodons. Astrodons seem to be parfocal and 1:1:1 colour combine. Baaders that I had (about 5 years ago now) were not 1:1:1 colour combine.

I did not notice halos from either except on the brightest of stars where I think its unreal to expect zero halos from any maker.

Greg.
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Old 14-10-2015, 05:21 PM
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Thanks H & Greg, appreciate your feedback.

Being parfocal is reasonably important, as I typically like to do RGB all on the same night, but I do plan on setting up automated focusing in the near future, at which point it will become less important: I'll probably refocus after every frame anyway, certainly at every filter change.

Greg's comment about expecting halos on brighter stars regardless of maker concerns me; maybe I'm expecting too much.

I'll post up some 100% crops of recent captures and see what you guys think. Maybe this is about as good as it gets and I need to look for a processing solution rather than hardware.
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Old 14-10-2015, 05:59 PM
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Lee I am using Astrodons too. I have only seen halos on real bright stars and that is not very often. It almost never happens on the RC but does occassional happen on the FSQ. The spacing between filters and the imaging window could be the actual cause there. Feel free to take a look through my gallery for confirmation.
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Old 14-10-2015, 06:49 PM
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Hi Lee,

I have very limited experience with RGB filters, so I probably should keep quiet...however, I have found Astrodons to be vastly superior in keeping halos in check in narrowband imaging (comparing to Astronomiks).

Having said that, it might be not entirely fair to compare 12nm with 3nm ( http://www.iceinspace.com.au/93-770-0-0-1-0.html) and results may or may not translate to RGB.
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Old 14-10-2015, 07:23 PM
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Thanks Paul and S... the Astrodons certainly are getting the thumbs up.

Attached is a star whose apparent magnitude is 8.686, as captured in my recent effort on NGC 300. As you can see there's a reasonable halo on both the blue and green filters, red not so much.

Could I expect better performance from the Astrodons, or is this simply to be expected?

Edit: Based off Paul's NGC 253 with stars of a similar mag, looks like I could expect better performance with the Astrodons.
Attached Thumbnails
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Last edited by codemonkey; 14-10-2015 at 07:57 PM.
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Old 14-10-2015, 07:41 PM
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The notion Astrodons are 1:1:1 is rather fanciful as all they are doing is leaking signal from R to G and G to B which simply gives you less saturated colours.

The basic physics was established by Helmholtz well over 100 years ago.

That is not to say they are not good filters...they are excellent....but the 1:1:1 exposure times is not a good reason to purchase a set.

Don's narrow band filters are rather awesome...sadly with the current debased $A... in both price and performance, but if you are ultra-serious I can think of none better.
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Old 14-10-2015, 07:50 PM
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Lee "Wormsy" Borsboom

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Thanks Peter. Have to agree about the 1:1:1 factor, it doesn't rate for me at all. I'm happy to take subs of different lengths, as I'll probably do anyway due to changing sky conditions.

That said, if they get rid of those halos it'll be worth it. It's not so bad when it's just a star on background, but it's bugging me when there's a (for example) mag 9 on my main subject... I can't unsee the halos.
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Old 14-10-2015, 07:58 PM
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The 1:1:1 doesn't meant anything, really. We use sophisticated processing software which allows to set weights, quite easily. Furthermore, each of us has a creative bent and will allow RGB weights in our images which please our senses.

H
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Old 15-10-2015, 11:46 AM
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Looks like I'll be getting the astrodons then. Thanks everyone for their input.

Funny thing about this hobby, I always seem to end up buying the things I considered way too expensive initially.
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Old 15-10-2015, 03:00 PM
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Yes I suppose that is true that 1:1:1 may not be important but I went through a phase in imaging with a Tak BRC250 where it became very difficult to get reliable colour combines and that was with Baaders. I got weird posterisations in blue very often. That stopped when I switched back to Astrodons. I see very occasionally but now its rare and usually a processing error beforehand black clipping the histogram.

So there can be a real issue there if the colour is skewed in the basic data.

One way is to measure weights required to match a G2V star and then weight your coloured filter exposure times appropriately.

Just from recall Baaders were 1:.7:1.2 RGB weights. So you would take less green and more blue subs.

Here is the blurb from Astrodon. There are more benefits to 1:1:1 than mentioned.

http://astrodon.com/e-series-lrgb.html

I have used Custom Scientific, Astrodon Gen 1 and 2, Baader, Astronomik Gen 1. Astronomik are quite good but only up to 6nm for narrowband. Astrodons are also parfocal with their narrowband filters which is a huge plus as I focus in Luminance then image in narrowband and focus is spot on. Its hard to focus a narrowband filter by itself. I got a dodgy Baader 7nm Ha filter once also that gave salt and pepper spots in the images. Astronomik sold me 1mm thick filters without spacers to make them fit the bog standard 3mm filter holders and a couple got wrecked and then Gerd got some spacers made up and charged a US$100 for them. Bits of square plastic. Didn't leave a good impression. Don (astrodon) has always been super helpful and I've met him up at the Gold Coast and he's a great guy.

As far as bleed from other the other colour filters his website says the opposite. I imagine there is always some crossover otherwise you could miss a slice. But in my experience I get less filter related imaging problems using Astrodons than any other filter mentioned. They simply do their job without further attention apart from a cleaning. They also seem pretty tough.

Greg.
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Old 15-10-2015, 04:28 PM
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I have no problems with my Baader filters.

Posterisation can't be because of the filters. It'd be a processing problem.

PixInsight has sophisticated colour calibration and background neutralisation routines, not to mention LinearFit which helps get colours balanced.

I know Astrodon's are the bees knees, but, I can't justify the expense when my Baader's are performing so well.

H
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Old 15-10-2015, 05:09 PM
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Quote:
Originally Posted by Octane View Post
I know Astrodon's are the bees knees, but, I can't justify the expense when my Baader's are performing so well.
Right on, if I didn't have issues with my old type 2 Astronomiks I wouldn't either. I'm inclined to fork our the big bucks simply because it seems that I'll be less likely to get issues and I'd rather not get a set of Baaders then find out out I have the same issue and then end up buying Astrodons anyway.

I've seen examples of both with halos, so I'm not sure what to trust... in the absence of more concrete evidence I'm relying on the fact that every person here who owns the Astrodons has nothing but good things to say, and there's only one in here vouching for the Baaders.
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Old 15-10-2015, 05:24 PM
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Hi Lee,

I think the size of halos may also depend on the optics, in particular with refracting telescopes

For example, my doublet does not focus all light equally; say when I focus for red colour, blue will be quite out of focus and spread out, thus even with 3nm filters with longer exposures and bright stars, signal very slowly builds up around the stars. No filter surpasses 100% of the unwanted signal. For that particular reason, in spite of being pure "narrowbander", in the future I would like to move to a quality triplet.
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Old 15-10-2015, 05:36 PM
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Lee "Wormsy" Borsboom

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Good point S. I'm reasonably confident it's not a focus/correction issue with my triplet though; the stars look in focus and of a similar size. With my previous doublets you could easily see, using a bahtinov mask, that the focus was off, but I don't get this with the Esprit 120.
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Old 15-10-2015, 06:56 PM
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Quote:
Originally Posted by codemonkey View Post
Good point S. I'm reasonably confident it's not a focus/correction issue with my triplet though; the stars look in focus and of a similar size. With my previous doublets you could easily see, using a bahtinov mask, that the focus was off, but I don't get this with the Esprit 120.
I am confident your triplet will deliver with Astrodon's .

I was just thinking of possible reasons as for why some images acquired with Astrodon's might have some halos too.
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Old 15-10-2015, 08:25 PM
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Lee "Wormsy" Borsboom

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Quote:
Originally Posted by Slawomir View Post
I am confident your triplet will deliver with Astrodon's .

I was just thinking of possible reasons as for why some images acquired with Astrodon's might have some halos too.
Ah right, sorry, I misunderstood your angle there. Fair point.
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