Baader Narrowband Filter issue?

[ChrisLX200]

Just a thought :

I have all 2 inch HAOIIISII + UV/IR(LUM)+RGB baader filters and used to them in ED80 with/without the FFR 0.85 and on GSO RC6" with/without the CCDT67 reducer and a combination of SBIG8300 or DSLR's (Canon 350D and Nikon D90).

In all cases whether there was extra glass (flattener - reducer) or not, there has been no halos at all.

Same goes for 2" IDAS LP2 which i sometimes use in combination with RGB + extra glass.

The only filter i have even seen halo from in bright stars is the UHC-S baader but that was a 1.25" filter (and i didnt even had an FFR at the time).

Also of all the images i have personally seen (not that many admittedly) either live or from the web's, where halos occurred the common factor is always the size of the filter being 1.25".

My reasoning could be utterly wrong but 90% of the times the word halo is mentioned it involves a 1.25" size filter

One of those statistical oddities, there are (probably?) 10x more users of 1.25" filters than 2".... maybe :-)

ChrisH

[silios]

One of those statistical oddities, there are (probably?) 10x more users of 1.25" filters than 2".... maybe :-)

ChrisH

Stats could of course be true!  ( math of any kind makes my head spin faster than a quasar )

Just found as well that it has been suggested earlier by lensman here http://stargazerslounge.com/topic/240649-baader-oiii-halo-suggestions/?p=2612018

If anyone uses 2" inch OIII and gets halos it would be nice to share with us in this thread.

[RikM]

Mine are all 1.25" and no halos here.

[silios]

Mine are all 1.25" and no halos here.

Mythbuster

What makes the subject even more hard to track down is that are there reports about every kind of brand (inc astrodons 3nm OIII and HA) producing halos, especially on cloudynights.

They usually conclude that the astrodons are the best in reducing the problem (on image trains that exhibit halos) but not solving it altogether.

Too many factors into play i guess..

[Kbramley]

mine are 2" and have halos, i will post up some cropped subs if I get chance later

[FLO]

I am far from convinced halos are an issue specific to Baader OIII CCD filters. Dichroic filters reflect (they are reflectance filters, it is how they work) so if there is something in front, reflecting back, you might see a halo. But, being Baader's largest UK astro dealer I want to be sure our customer's filters are okay so here's an offer:

If anyone has purchased a Baader OIII CCD filter from FLO and is experiencing excessive halos please email us an image. We will then arrange a free collection and replacement. 

HTH, 

Steve

[Robp]

Hi Steve,

I purchased the Baader OIII, Ha and RGB filters from you around last Christmas.

I do get bad halo's but only when using the OIII filter. I did some research when I first got them and came to the conclusion that this was just the norm and would have to be processed out.

This is a crop of a star from a NGC281 image with the HA filter, looks fine:

This is a crop of the same star with the OIII filter and Halo:​

Another OIII example from the Elephant trunk nebula:

I haven't had any issues with any of the other filters (including the Blue filter but I haven't used it as much as the OIII filter).

I have three items in the optical train that could be the problem, a Baader MPCC Coma corrector, the filter and a window on the CCD.

I also remember a thread earlier in the year when you replaced the OIII filter for someone that had bad halos, and they still had the same halo's with the replacement.​

Whilst I appreciate your offer to replace these filters I'm just not convinced it will make much difference (apart from giving you a truckload of used OIII filters!)

[steppenwolf]

Here are some thoughts to add to the mix and I invite comment as I have no empirical evidence but maybe the following deserves testing or, indeed shooting down in flames?

How about this for starters - light from an off-axis star is funnelled through the telescope in the form of a light cone. This means that it arrives at the filter at some angle of incidence. The unwanted wavelengths are reflected away from the filter where they may or may not get reflected back from the rear element of a coma corrector/field flattener/focal reducer. The wanted wavelength passes through the filter and the vast majority of the light falls on the sensor - however, the light hits the optical flat at a small angle of incidence and a small amount is reflected from the optical flat in front of the sensor back to the rear of the filter and finally reflected again by the rear of the filter, through the optical flat and on to the sensor. This *might* explain why so many of these halos are off-centre on the star image.

However, there are questions to be answered:-

1. Why the concentration on OIII filters?

2. Why are the halos sometimes offset toward the field edge and at other times toward the centre of the field? Martin's (Hograt's) are all over the place!

     a. Toward the edge of the field - reflection from a convex surface in front of the filter?

     b. Toward the centre of the field - reflection from the optical flat?

     c. Centred on the star with the star placed anywhere in the FOV - filter fault?

3. Does the problem really go away if the coma corrector/field flattener/focal reducer is removed from the light train?

I would love to get to the bottom of this issue both for myself and for others but with so many equipment combinations, this will require pooled resources. There has to be a proper explanation for what we are seeing and I am not totally convinced that these are filter 'faults' - caused by the fact that the filters work by reflecting, yes but not necessarily a 'fault' as such.

[ChrisLX200]

These filters are complicated things consisting of many extremely thin layers compounded to achieve the required rejection of specific wavelengths of light. I figure each company use their own techinque to accomplish this layering and some (apparently) work better than others. My Astrodon OIII doesn't produce halos using any of my gear, the Baader OIII does. (or did - I don't have it any more). I should think Baader research labs would be in an excellent position to investigate the phenomenon as they have the kit to run the proper tests, but as end users we are not.

ChrisH

[Robp]

I will try some subs without the Coma corrector to see if that makes a difference (looks like I might be able to get out tomorrow night if the weather reports remain the same).

It shows up pretty clearly on single subs so wont take to long to test. I don't have a mono camera without a window so wont be able to remove that from the equation.

Another option might be for someone who has a Baader OIII filter that doesn't halo to take one of the ones that does and give it a test in there rig?

That way if the filter works fine, you can tie it down to something within the rig. If the filter produces a halo then its a fault with the filter?

I'm happy to temporarily donate my filter to someone nearby in the interest of science  

[FLO]

Whilst I appreciate your offer to replace these filters I'm just not convinced it will make much difference (apart from giving you a truckload of used OIII filters!)

I don't believe all Baader OIII filters are prone to halos. We have been selling them for years (indeed we chose them because they were less prone to halos than what was, back then, a more popular competing brand). It was Baader's approach to filter design, in particular their focus on reducing reflections, that caused the other brands to rethink and redesign their offerings. 

But, if a handful have slipped through the QC net we want to find and replace them. Hence my offer

Steve

[MartinB]

Wasn't it Astronomic filters which were first reported as being a problem? I never had problems with my 1.25's but a 2" Ha did have halos. I thought they had addressed the issue but maybe not. What action did they take to try to cure the problem. None of my Baader filters produce halos. The fact that someone has one make of filter which produces halos and another make that doesn't isn't really relevant. I would be very surprised if nno one has ever had halos with Astrodon filters.

The whole situation is complicated by the commercial positioning of the filter makers. All of them are very heavily into hype, some more than others.

[MushroomBill]

Not sure if this helps but I had a similar issue with the Baader OIII.  Out of interest I tried shooting some images using all of the Baader NB filters (HA, OIII, SII and Hb) on a brighter star - can't remember which now.  I've attached a Ha shot from my 200p,  I could get similar results with the SCT and ED80 using two different CCD cameras.  

I believed that the following website offered the answer http://geoastro.co.uk/equipment/ghosts.htm

I seem to remember that the descriptions of the LRGB filters stated "no reflections" but the same line was missing from the NB filters...

[ChrisLX200]

Well that is a _very_ harsh test for any filter!

ChrisH

[RikM]

NO halos. NO reflections.

[Robp]

That is what my box says as well RikM 

If the filter was at fault, would it create a halo in front of a colour DSLR as well?

[physicus]

While all the evidence is being thrown on the table.... I got my Baader NBs on Amazon, but I'm pretty sure they're kosher. And I have serious halos, only with OIII, in the two configurations I've used with them (C9.25/fr/oag/fw/460 and 300mm lens at f4/fw/460). I don't normally give up without a fight, but researching the issue I quickly found so many pictures and reports out there that I, like Robp, assumed this was normal for Baader OIII filters, and perhaps some others. For the record, here's a nice strong OIII halo in the Veil (see link) (ignore the other aberations - this isn't my best optic). I can't access my main machine at the mo', but will check through some other examples. From memory, the eccentricity of the halo does for sure move depending on where in the frame it sits. Also that the eccentricity is stronger at the lower f numbers (but need to check that). I'd invest in another brand, but at the mo' don't trust any of them. After all, we're having this discussion - again.

https://flic.kr/p/wBJkYE

Post edit: this pic shows the eccentricity with position really well

https://flic.kr/p/yZ5aRi

[Steve 1962]

Just my two pennies' worth...

Here's a link to an image of the Pelican Nebula taken through my Baader Ha filter.

http://stargazerslounge.com/topic/249107-ha-pelican/

Note - no halos.

..and here's a stretched crop of the same image through my Baader Oiii filter.

I think I've worked out that these are reflections between surfaces which are about 2.5mm apart, so in my mind they must be caused by internal reflections within thin bits of glass .

I use the kit listed in my signature, and the only thin bits of glass in my train are the window on the CCD chamber and the filter. In my mind - the fact that there are no halos on the Ha image tends to rule out the CCD window.

I've just added a reducer to my scope to make it f3.6 and these  halos are now much worse than they were at f5. I think this is because the light cone is steeper and the angle of incidence at the glass surfaces is increased - therefore more light is reflected and the halo is bigger.

I've just ordered some Chroma 3nm NB filters from Bern at MA and plan some side by side tests with my Baaders to get to the bottom of this.

Steve

[FLO]

If anyone has purchased a Baader OIII CCD filter from FLO and is experiencing excessive halos please email us an image. We will then arrange a free collection and replacement. 

But, if a handful have slipped through the QC net we want to find and replace them. Hence my offer

So far only one person has contacted us, we are sending him another OIII filter for comparison but he lives in Poland so it might be a while before we know the results. Is there anyone here in the UK with a Baader OIII CCD filter (purchased at FLO) suspected of causing halos? 

Steve

[Robp]

Hi Steve,

I've sent you an Email, hopefully we can get to the bottom of this

[FLO]

I've sent you an Email, hopefully we can get to the bottom of this

Excellent, we'll send another for comparison  

Steve

[ollypenrice]

Olly, how do Astrodon filters get round the issue of light being reflected from their filters onto other optical surfaces?

I've no idea, Martin. Perhaps they still produce reflections and the haloes are created by other means. This is a very hard stretch of the Baader 0111 data for Outters 4 to show what we get with ours. (FSQ106N.)

Olly

[pyrasanth]

So far only one person has contacted us, we are sending him another OIII filter for comparison but he lives in Poland so it might be a while before we know the results. Is there anyone here in the UK with a Baader OIII CCD filter (purchased at FLO) suspected of causing halos? 

Steve

Hi Steve,

I have a 2" OIII filter which I bought from you & that causes the same issue of a halo on processing of the subs. I posted an example on the veil Nebula in this thread.

[FLO]

I have the same issue with the OIII filter on  my Celestron RASA even with the fast 2" Baader narrow band filters which were not cheap. See the attached image.

Veil-Nebula3_OIII.png

There is most definitely an issue. 

Hi Steve,

I have a 2" OIII filter which I bought from you & that causes the same issue of a halo on processing of the subs. I posted an example on the veil Nebula in this thread.

We are discussing the Baader OIII CCD filter Mark, not the Baader f2 Highspeed filters you are using with your f2.2 Celestron RASA. 

I also think a faint halo around the bright star at the centre of the Veil is not uncommon (dons tin hat and jumps in bunker). 

Steve

[ChrisLX200]

It's difficult to differentiate what is simply star 'flare' due to imaging a very bright star and what is a definite and troublesome 'halo' - particularly on all these different targets with stars of varying brightness and colour (and different exposures too). Bright stars will naturally cause flaring (light spreading out around the star) and I see that even with Astrodon filters - you'll see even _without_ any filters. The example in the very first image in this thread is an unacceptable 'halo' to my eyes, the example above of the Witches Broom is just what you tend to get anyway - possibly slightly worse but again, difficult to say it's a halo with any conviction. This is purely IMHO and underlines the difficulty in assessing the problem outside of a lab where consistent test conditions can be applied.

ChrisH