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Filters and halos, what is the answer?

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#1 blueman

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Posted 31 August 2012 - 01:55 AM

I have been doing Astrophotography for over 6 years. I started out with inexpensive cameras like the Meade DSI 1,2 and 3 using both OSC and Mono. From the begining I realized that I preferred Mono and my first set of filters came with my Meade DSI II Pro. For the next five years I had several cameras and many brands of filters, some inexpensive and some not so inexpensive. But I always fought with halos on bright stars for years.
I finally bought a SBig ST-2000 and got LRGB and Ha, O-III and S-II filters for that. I tried three different brands, all had halos. I finally bought Astrodon Gen2 LRGB filters for it when they came out and for the first time I did not have halos.
Well, time went on and I bought a bigger chip and sold the ST-2000 with the filters and wheel and bought an FLI ML8300 camera and filter wheel. FLI was giving a break on their LRGB filters when you bought the entire setup, so I got those. First thing I noticed was HALOS, big ones and they were all over my images. I had the CCD window replaced because the word was this was the cause, but this did not fix anything. So I bought Astronomik filters and the halos were still there and just as bad. I then bought Baader filters and they were better by far, but still halos on stars brighter than Mag 6.5.
Finally, I bought a set of Astrondon Gen2 "E" filters for it in LRGB, they were not cheap, but I remembered that the ones that I bought for the ST-2000 worked great and no halos. So, sure enough, put the Astrodon filters in the wheel and NO HALOS.
The point of this is, I did not learn from my prior experience and I went through sets of filters and other things AGAIN, when I knew better. Why, because the other filters were less money.
Well, I have to tell you something. Compared to all the money you spend on the camera & filterwheel, scope, guiding setup, mount and laptop computer not to mention software, well the filters are not that expensive as far as percentage of cost. However, they are the only thing that really matters in the end when dealing with halos.
So, if you are tired of halos, save your money and buy a set of Astrodon Gen2 filters. I bought mine used from Tony Hallas and as he said "I would not think of using another brand of filters".
I do not work for Astrodon and have no affiliation or interest in the company. I am just one of many amatuer astrophotographers trying to take pretty pictures.
Blueman

#2 Konihlav

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Posted 31 August 2012 - 03:13 AM

great Blueman, I really appreciate your post! It's wonderful when people are up to make a reflection - to say, I was wrong, to ever admit it. Your case is even more "funny" as you did not learn from your previous experience ;)

but anyway, this happens (me too).

I also do not work for Astrodon, but I had many filters from Don Goldman, re-measured them many times (on my blog) and I simply can't recommend anything else. All else is piece of garbage. Period.

You are pretty right about how many $$$ people spend on telescopes and mounts but do not pay attention to the very important parts (filters, CCD camera etc.). But I gave on trying to "open eyes" to people buying narrow band filters. I always say how much you improve your SNR with 3nm over 5nm, but people do not understand it. So be it. I would repeat myself, that people understand that 10" scope gathers more light then 6" scope. The same analogy works for th 3nm vs 5nm (7nm) filters in favor of the narrower.

Congratulations again! I am happy for you.

BTW my current imaging setups:
(i) MII G3-11000 with integrated 5pos FW, Ha 5nm Astrodon, LRGB Gen2 I-series 50mm round unmounted (compact and still lightweight)
(ii) Atik 460EXM with SXFW 7pos 1.25", 3nm Ha, 3nm OIII, 3nm SII, LRGB Gen2 E-series 1.25" mounted

this is what I find ultimate after doing research on cameras and filters during last 3-4 years :)

BTW ultimate guiding camera will be on the market hope in few months and I ordered already 2 pieces and will sell my two guiders (Atik 16ic, MII G1-0300) then.

#3 freestar8n

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Posted 31 August 2012 - 03:30 AM

I use astronomik type 2c LRGB filters with a c11 at around f/6 and have not noticed a problem with halos. Can either of you provide examples that compare a similar scene, with the same imaging configuration, using astrodon vs. Astronomik 2c filters?

I think the early astronomik filters had a problem with IR leakage - but I believe it has been addressed with the 2c version.

It's essential that any comparison images be with identical setups (camera, OTA, filter spacings) because there are many factors that conspire to create halos.

Frank

#4 NorthBoundTrain

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Posted 31 August 2012 - 04:09 AM

I am glad you finally got filters that work for you Blueman!

I decided on Baader Planetarium Ha/LRGB when I upgraded, and find they work very well.

I can't say I agree with you though Konihlav, that anything aside from Astrodon are "All else is piece of garbage. Period."

But everyone is entitled to their opinion I suppose right?

Anyhow, I hope the filters continue to work well for you Blueman. I think a lot of us learned the hard way, through blood, sweet, tears & money. Eventually though with enough research and trial and error we all get to that place where we are happy & having fun. To me that's what it's all about anyhow. :)

#5 jmasin

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Posted 31 August 2012 - 08:09 AM

I also do not work for Astrodon, but I had many filters from Don Goldman, re-measured them many times (on my blog) and I simply can't recommend anything else. All else is piece of garbage. Period.


well there ya go... :rimshot:


Blueman,

I'm glad you posted this, from the standpoint of technically it is good to know when someone has found a set of equipment that works well and eliminates problems.

As far as spending $$, everyone does what they can, when they can. It's always a balance of what equipment, what cost etc. I think it's most typical to upgrade pieces of equipment at different times since not many have the funds to simply buy six-figures of equipment outright (not claiming anyone in this thread does, just making a point)... so yea, some end up with expensive mounts and cheap scopes (been there), expensive scopes and bargain cameras (I'm there now), etc. But that's how it goes.

#6 alpal

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Posted 31 August 2012 - 10:30 AM

Pavel,

All else is piece of garbage. Period.


Hi Pavel - you have very strong opinions.
I would say that a bad workman always blames his tools.
I've seen some people take better pictures with a DSLR camera & no filters -
than other's who have very expensive telescopes,
CCD cameras & every filter you could name.

Apart from that some people just don't have $1,000 to spend on every filter -
in the same way that we don't all drive Ferrari's.

#7 troypiggo

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Posted 31 August 2012 - 12:21 PM

Alpal - in this instance, at least in my experience as per below, you can blame the tools.

I found the halos only an issue on my narrowband filters. They're caused by reflections inside the filter glass between each face. Of course you're not going to get this with a DSLR, and it's also only noticeable on really bright stars. So yes, you may have seen good images taken with other gear, or gear that does produce halos but not noticeable because there weren't any bright stars in the shot.

And as in my case, when I did take a shot that had excessive halos, I considered it ruined and wouldn't post it online. Perhaps that's why you haven't seen many posts with them in. People may not be happy to put them out there.

Here's some shots from my Astronomiks:
http://www.iceinspac...19&postcount=14 The halos we're talking about are probably most evident on the Hb shot in this link. They're the small ones immediately around the star, starting as a bright donut around the star maybe two star diameters wide, then next ring slightly dimmer 4 diam wide and so on. They're incremental steps of brightness rather than gradual fading.

The big (about third to quarter size of frame) halos, as I understand it, are not caused by the filters but by other optics in my imaging train - probably the MPCC.

Happy ending to the story, the filters were replaced. While the halos in the replacements were negligible, I had already started down the path of swapping over to Astrodons anyway - more for the 3nm bandwidth. So sold the Astronomiks to a friend who is more than happy with them.

#8 blueman

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Posted 31 August 2012 - 12:33 PM

Hi Troy,
Thanks for posting the photos using the Astronomiks filters, these show the same thing that I experienced. I did not keep the Astronomiks filters long. I did not have that many images with them, but I will see if I can find some. The Narrowband filters haloed badly and I wrote Astronimiks in Germany and the owner of the company sent me a new Ha filter with new coatings that was to be the new generation of their filters. I used it, but though it was improved, the halos were still there.
Blueman

Alpal - in this instance, at least in my experience as per below, you can blame the tools.

I found the halos only an issue on my narrowband filters. They're caused by reflections inside the filter glass between each face. Of course you're not going to get this with a DSLR, and it's also only noticeable on really bright stars. So yes, you may have seen good images taken with other gear, or gear that does produce halos but not noticeable because there weren't any bright stars in the shot.

And as in my case, when I did take a shot that had excessive halos, I considered it ruined and wouldn't post it online. Perhaps that's why you haven't seen many posts with them in. People may not be happy to put them out there.

Here's some shots from my Astronomiks:
http://www.iceinspac...19&postcount=14 The halos we're talking about are probably most evident on the Hb shot in this link. They're the small ones immediately around the star, starting as a bright donut around the star maybe two star diameters wide, then next ring slightly dimmer 4 diam wide and so on. They're incremental steps of brightness rather than gradual fading.

The big (about third to quarter size of frame) halos, as I understand it, are not caused by the filters but by other optics in my imaging train - probably the MPCC.

Happy ending to the story, the filters were replaced. While the halos in the replacements were negligible, I had already started down the path of swapping over to Astrodons anyway - more for the 3nm bandwidth. So sold the Astronomiks to a friend who is more than happy with them.



#9 blueman

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Posted 31 August 2012 - 12:50 PM

Hi Frank,
To be honest, I disliked the halos so much and the halos were so bad with the Astronomk filters, that I did not take many images, just test shots and I am not sure that I still have them.

I have more images using the FLI filters that have the halos, but again not so many of the same object with the same setup using the Astrodons. In fact I have been working to take mostly images of objects that I have not captured before or at least not in years.

As far as comparing images, well that is tough. When I realized that bright stars meant big halos, I framed my images to eliminate bright stars.

I can tell you that I have taken only two images with the new Astrodon Gen2 E fitlers, but one was the Western Veil and that was one object that I did try to take earlier with other filters and the halo around the bright star was very bad. I will see if I still have that one, but I do not have the same setup at all. Since then I have a new TEC-140, ML8300, AP .8x reducer and I do not even own the AT8RC or the WO 80mm f/6 Lomo objective telescopes that I used then. So I am not sure the comparison would meet your criteria.
Blueman

I use astronomik type 2c LRGB filters with a c11 at around f/6 and have not noticed a problem with halos. Can either of you provide examples that compare a similar scene, with the same imaging configuration, using astrodon vs. Astronomik 2c filters?

I think the early astronomik filters had a problem with IR leakage - but I believe it has been addressed with the 2c version.

It's essential that any comparison images be with identical setups (camera, OTA, filter spacings) because there are many factors that conspire to create halos.

Frank



#10 bill w

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Posted 31 August 2012 - 01:18 PM

i've had trouble with astronomik filters as have others
my understanding is that they've improved things and that you can return filters with halos as described above.
have done very well with filters from baader, astrodon, and custom scientific
though extremely bright stars will give some hale no matter what

#11 rigel123

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Posted 31 August 2012 - 03:26 PM

I'm an Astrodon convert, will probably go to their NB at least for OIII. My Orion HA and SII seem fine, the OIII gives me funny looking stars and not sure why.

#12 alpal

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Posted 31 August 2012 - 04:57 PM

Troy,

Happy ending to the story, the filters were replaced.


Hi Troy
Well that says it all - there were Astronomic filters with this fault & they were replaced.
OK - in that case a worker can blame his tools.
Thanks for the photos of the problem.

I just bought a Baader H-alpha 7nm, 2 inch filter yesterday.
On the side of the box is written " No halos, NO reflections."
If the filter has noticeable halos I will return it to the supplier.
In this case I would not call the filter rubbish as Pavel implied but faulty
& to be returned for a refund or replacement.

I too would like a full set of Astrodons but I will
work with what I have for now.

#13 mikeschuster

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Posted 31 August 2012 - 07:36 PM

Bummer about going through sets of filters again. FYI, I have had good luck with Astrodon H-a 3nm. 40 minute subs with mag 2.2 Gamma Cygni in the field. No halos with the FSQ-106EDX and the QSI 683. Small spikes yes (microlens), small blooms yes (HSR overflow when binning), but halos no.
Regards,
Mike

#14 alpal

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Posted 31 August 2012 - 07:54 PM

I got a free set of filters with my QHY9 mono purchase to get me up & running.
A photo of the transmission curves is here:
http://i262.photobuc...wRGBfilters.jpg

Notice there is a gaping hole between Green & Red.
That will be not much good from a dark site but from a city
it will at least get rid of some sodium emission which is at 568 & 589 nm.
It won't stop mercury emission.

see graph here of light pollution:
http://www.eso.org/~...zenit_paper.htm


My new Baader 7nm Ha filter will be interesting to try too.
I hope to post some test pics soon & we'll see.

#15 blueman

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Posted 31 August 2012 - 07:59 PM

The Baader filters have a great bandwidth coverage, the colors are rich and well balanced. But halos on biright stars are a problem, at least for me. The NB Baader filters were OK, except O-III has halos, pretty big ones. I have flipped the filter but have not tested then since. The Ha and S-II seemed OK, so it could be the fliter needed to be flipped. I will try to take a test image with the O-III this next month.
I did flip the LRGB filters to see if the halos were improved, but they were still there on bright stars. They were much better than FLI or Astronomik filters that I used, but still there were halos.
Blueman

I got a free set of filters with my QHY9 mono purchase to get me up & running.
A photo of the transmission curves is here:
http://i262.photobuc...wRGBfilters.jpg

Notice there is a gaping hole between Green & Red.
That will be not much good from a dark site but from a city
it will at least get rid of some sodium emission which is at 568 & 589 nm.
It won't stop mercury emission.

see graph here of light pollution:
http://www.eso.org/~...zenit_paper.htm


My new Baader 7nm Ha filter will be interesting to try too.
I hope to post some test pics soon & we'll see.



#16 BlueGrass

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Posted 31 August 2012 - 08:53 PM

Floyd,
Hello. Don in his FAQ on the website says orientation shouldn't matter. I was under the impression that was why Baader keyed the edge of their filters though...?

#17 buckeyestargazer

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Posted 31 August 2012 - 09:00 PM

Floyd,
I have Baader filters and am generally pleased with them. I am wondering if the quality of the scope's optics affect halos around stars? I now have an APM LZOS 115mm apo refractor that has excellent optics, and I've noticed that the stars don't seem to give halos, or at least less.

Take a look at this image: M109 and PHAD

Do you consider there to be a halo around Phad in this image? Sometimes I'm not sure what constitutes a "halo" in a star like this that is so bright.

#18 blueman

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Posted 31 August 2012 - 11:13 PM

Hi,
Well, I think the TEC-140 has good optics. But more than that, I went from halos to no halos. That to me is pretty absolute. If this were the first time that I had this experience, then I would maybe consider the optics. But this is the second time that Astrodon Gen2 filters cured all halos and that was with different scopes and cameras.

In your image Phecda does not have hard edged halos. That is very good when you consider it is Mag 2.41, so you seem to not have halos. Hard edged halos are caused by reflection and they have a definitive round structure with a hard edge. It is possible that the Baader filters I bought new a bit over a year ago had a problem. I have no real way of knowing. But I did try to put the filters in the wheel with both sides toward the camera, but still there were halos.

This is a crop of the Veil a 10 minute image with the Astrodon Gen2 blue filter. The star is SAO70467 a Mag 4.2 star. With the Baader blue and green filters particularly, I got a large hard edged halo with stars brighter than Mag 6.4.
Blueman

Floyd,
I have Baader filters and am generally pleased with them. I am wondering if the quality of the scope's optics affect halos around stars? I now have an APM LZOS 115mm apo refractor that has excellent optics, and I've noticed that the stars don't seem to give halos, or at least less.

Take a look at this image: M109 and PHAD

Do you consider there to be a halo around Phad in this image? Sometimes I'm not sure what constitutes a "halo" in a star like this that is so bright.

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#19 blueman

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Posted 31 August 2012 - 11:14 PM

The Baader filters that I bought new had no markings on the edges. I bought 7 filters at the same time, LRGB, Ha, O-III and S-II. None of them were marked for direction.
Blueman

Floyd,
Hello. Don in his FAQ on the website says orientation shouldn't matter. I was under the impression that was why Baader keyed the edge of their filters though...?



#20 blueman

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Posted 31 August 2012 - 11:20 PM

I personally wrote the owner of Astonomik in Germany and complained about the filters. I was told they were working on new coatings. They sent me one Ha filter, but it was not really better, still haloed badly. I was never offered a refund or replacement for the set. I bought a complete set new and sold them with the replacement Ha filter as a bonus.
I have nothing against any of the filter manufacturers. I am only stating what I have experienced. If your experiences differ from mine, then that is fine. :)
My thoughts on the Baader filter would be they are #2 on my list, they are good and have good saturation, but they do halo.
Blueman

i've had trouble with astronomik filters as have others
my understanding is that they've improved things and that you can return filters with halos as described above.
have done very well with filters from baader, astrodon, and custom scientific
though extremely bright stars will give some hale no matter what



#21 freestar8n

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Posted 01 September 2012 - 02:14 AM

To be honest, I disliked the halos so much and the halos were so bad with the Astronomk filters, that I did not take many images, just test shots and I am not sure that I still have them.



OK - well I guess I'll provide an example of a "bad filter" halo with Astronomik 2c filters at f/5.7 on a c11.

Since people are touting Astrodon, please look at his FAQ on how to identify the cause of halos here.

Based on the f/ratio and spacings you should be able to confirm the cause of a given halo. Combining images with data on the f/ratio and spacings would help identify the filter as the cause - otherwise, as that web page points out, the halos will be independent of filter manufacturer and more linked to the ccd.

I looked at my own images and found some evidence of halo and mottling artifact around a long exposure image of Merope, which is a typical halo stress-test for filters - and I think many people should have such images. The one below is from a stack of 5m exposures and has been stretched to enhance the halo and mottling. The halo has a diameter of 220 pixels, which at f/5.7 and 6.45 um per pixel translates to a spacing of about 4mm - which roughly agrees with the distance from the ccd to the cover slip - and does not correspond with any filter spacing that I know of. I think the mottling is caused by a microlens reflection from the Sony interline chip on the sxvf-h9 ccd.

In summary - I did find evidence of a halo in a particularly challenging image situation, and based on Astrodon's own write up I conclude it is not related to the filter.

I recently bought Astrodon Sloan filters and had a good impression of them being top notch - and I now see he has an improved version of them and the ones I have are outdated. Nothing wrong with that - it's great to see improvements. But at this point I don't see solid evidence that the improvements made to the Astronomik LRGB filter sets in the 2c version did not in fact solve any halo problem they may or may not have had.

I would prefer to see concrete evidence that the filters are the cause, similar to Astrodon's write up, that include calculations of the halo size that links them to the filter location. Note that Astrodon's write up has an error because he surprisingly ignores the index of refraction in the filter thickness - and each thickness should be replaced by the "reduced" thickness, t/n, where n is the refractive index, or about 1.5.

Note that my halo - and the mottling - are much more evident in the blue than r, or g - which is consistent with Astrodon's conclusion that the enhanced blue reflectivity of silicon ccd's could make the halos more prominent in the blue. This doesn't confirm it - but it's at least consistent with his write up and explanation.

Frank

Attached Files



#22 Konihlav

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Posted 01 September 2012 - 03:53 AM

buckeyestargazer: your scope is F/7 (!) therefore much, much less prone to halos than say my F/4.3 scope.

freestar8n: I pretty much agree.

alpal: I am chep too, for my 50mm round I selected 5nm instead of 3nm because I am not able to spend $1000 on filter but I am able to spend $600. So my 1.25" are 3nm set and 50mm are 5nm set.

as I understand we are all on budgets, there's only Baader 7nm Ha filter that is very good and that I recommend for tight budget beginners. But for the other two emission lines there's unfortunatelly not much to choose from so I recommend to save money for at least 5nm Astrodons :) I also purchased one filter by one, not all in one order :)

#23 NorthBoundTrain

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Posted 01 September 2012 - 06:38 AM

there's only Baader 7nm Ha filter that is very good and that I recommend for tight budget beginners.


I am sorry but there is nothing "beginner" about the 7nm Baader or any other filter in their line. Just because you don't like them ( for whatever reason ) dose not make their entire line garbage. MANY seasoned imagers use the Baader Planetarium line with fantastic results.

Edit- Let me be clear here I am not arguing that Astrodon filters are not good, they are. All I am saying is that they are NOT the only line of filters on the market that are good.

#24 BlueGrass

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Posted 01 September 2012 - 07:52 AM

It does seem, based on Don's testing results and the use of various optical setups, that halos may just be a fact of life for a specific CCD, scope type and given FL and FR? Also, I'm not clear what's the effect on reducing halos using a specific band pass?

#25 BlueGrass

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Posted 01 September 2012 - 07:56 AM

These were for the 2". For my set of the 36mm Baaders used in the ST8300 CFW5/CFW8 series, they were marked for direction.






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