Astronomik Filter Halo Story [Deep Sky] Acquisition techniques · Joey Conenna · ... · 13 · 702 · 10

This will be long, TLDR: Myself and at least a few other competent imagers have had recent issues with Astronomik Deep Sky RGB filters and Astronomik's customer service. Buyer beware.

I will preface this by stating that I am not looking to bash a vendor here, merely share a recent experience which could assist those who are looking to make costly purchases. I have had many mixed emotions regarding this ordeal, but will attempt to keep this respectful. I also invite others who have experienced the same issues to chime in.

In early October 2024 I was in the market for a set of 50mm unmounted filters to pair with a QHY600M camera and an Astro-Physics 110GTX refractor / 110TCC reducer for widefield imaging. After doing much research on user opinions and experiences, it appeared that Astronomik filters had a strong reputation for good performance, and were backed by a halo free warranty. This warranty is really what sold me over buying another budget brand which makes statements that they do not offer returns for filters that produce halos (Antlia). I figured my purchase was quite low risk based on the very limited user reports of halos with Astronomik filters and the company's openess and willingness to apparently stand behind their product with a 10 year warranty. So I went ahead and purchased direct from Astronomik. At the time, this also saved me a little money versus buying from a local vendor, but in retrospect this was a mistake.

Upon receiving the filters in mail I noticed that the Green filter had a strange circular blemish on the glass and that the L2 filter had a small scratch near the edge:



I contacted Astronomik and they promptly requested to try cleaning the G filter with some water and cotton. Thankfully, the blemish was removed with some iso alcohol and kimwipes. Astronomik also promptly sent out a replacement L2 filter. Within a week I was ready to install the filters and get on to imaging!

Upon first light on M45, I noticed something that I was honestly not expecting: there were very obvious halos showing on the G and B filters:



After seeing this, I tested the rest of the filters. It appeared that R had the very slightest of halos, that I would not have otherwise recognized if I had not seen those in G and B. L2, and SHO filters showed no halos in my test images.

I tried flipping the filters as I have read that sometimes orientation can eliminate halos, but it did not make a difference. So I contacted Astronomik again shared the issue I had come across and provided the data. It is now early November time frame. Astronomik replied and stated that they believe the issue is the 110TCC reducer interacting with the filters that is causing the halos. They state that they have another customer with the same camera and telescope/reducer showing the issue, and that they will look into the issue.

At this time I had tracked down another user of the 110GTX and Astronomik filters here on Astrobin, and asked them how their LRGB images were looking since I only noticed them using Astronomik SHO. They replied that they too had the same ugly halos for G and B, and that they were in contact with Gerd who was giving them the runaround.

In the meantime, I decided to try the 110FF Field Flattener for the 110GTX to try and rule out the 110TCC reducer as the culprit. Sure enough, it as well showed halos:



I sent an email to Astronomik relaying the info from my experiment. They eventually responded that they are trying to investigate a new coating process to solve the issue, but it is very difficult due to this being associated with using a niche piece of gear. Again they pointed the finger at the Astro-Physics glass.

Given that there were some periods of no response after my emails, I decided to continue my investigation.

I removed any reducer/flattener at all and instead connected only the camera/filterwheel to the 110GTX telescope using extension tubes, to rule out any interaction with correcting glass near the filters as the culprit. The halos still appeared:



I sent this data to Astronomik for review. I did not hear back about it.

The next night, I placed the camera/filterwheel on my trusted 10" F/4 Newtonian and Paracorr II, which is a known quantity to me that does not have halo issues when imaging with a set of (Antlia) mono filters. The halos still appeared, which to me absolved the Astro-Physics glass.



I as well sent this data to Astronomik for review. I did not hear back about it.

It is now mid December and I really just want to get on with imaging if possible. After much thought, I decided to buy a new set of Chroma LRGB filters to see if they too show halos with my camera and rig.

To my relief, using the new Chroma LRGB filters showed no halos present where the Astronomik's had:



It was a relief to finally have all of the evidence pointing to Astronomik's filters themselves as being the cause of the halos in my images, and that I had a filter set I could rely on to image with!

I sent this data to Astronomik, hoping to maybe open their eyes to the possibility that their filters may actually be to blame and that perhaps there could be a QA issue in their fabrication lab since this appeared to contradict reports of their great performance. I did not hear back.

Instead, one day I randomly got a shipping notice from Astronomik, which I assumed were the replacement filters mentioned previously in an email. I am expecting to receive at least an RGB set as a replacement, but instead only received B and G filters. This would be fine... but the new filters came with a curious "XT" designation. From Astronomik's website, it appears that instead of the normal 1mm thick filters, XT filters are 0.3mm thick!

Upon testing, the XT filters do initially appear to be an improvement from the originals, however they still show a slight halo though it is more tight and embedded within the star's light scatter:



Note that halos arising from internal reflection within a piece of glass have a diameter that scales down with smaller glass thickness, which matches the data.

Glass_Thickness = [(Halo_Diameter * F_ratio) / 2 ]* 1.5

I am not sure where this formula is originally derived, and received it from the other user who had been dealing with these halos as well. Using it I found that in each image the formula pointed to a piece of glass approximately the thickness of the filter that was in place, either 1mm or 0.3mm.

So, even though the XTs may improve on the original's halo issues, they are a completely different thickness which makes them far from parfocal with the other Astronomik filters, and also require different backfocus spacing compared to the other Astronomiks that are 1mm thick. Also it makes me wonder if them sending me thinner filters was just an attempt to make the halos smaller and hope they would be less noticeable?

I promptly sent Astronomik data from my experiment as I usually did and requested a return.

Finally after some time, in late January Astronomik admitted that they were at a loss as to why my filters are showing halos for myself and some other customers with the same equipment, and they agreed to take back the Deep Sky RGB filters (and XT replacements) for a return. I then requested to return the L2 and SHO filters as well, but they refused stating that there is nothing wrong with them and that I could still use them.

Because filter thickness is critical on a relatively fast full frame imaging system, I cannot use the L2 and SHO filters unless I use them with other 1mm filters.

It is one thing to have a defective product, and not know what the issue is, but a company should also be evaluated on how they handle when their products fall short. I appreciate that for most imagers these filters have provided a great value proposition and many have tested well in the field. But when the filters do not test well, it is clear how Astronomik will handle it: offer a refund on the cheaper part of the set and let the customer eat the financial loss of return shipping and selling the remaining set of filters at a loss.

I appreciate that Astronomik did respond to my inquiries, albeit at a frustratingly slow pace, and that they at least made an attempt at producing some kind of replacement. However I feel compelled to share this story, at the very least to encourage others to purchase from a dealer who would be willing to accept back defective product in a prompt manner.

Thank you for coming to my TED Talk.

-Joey

I'm the other person that Joey refers to in his post.  I had an almost identical parallel experience as he did with Gerd and Astronomik. Months of intermittent communication with most of my emails being ignored, a half resolution at great expense to myself, bizarre claims that the filters were perfect and that it was Astro-physics fault.  After we proved that it had nothing to do with Astro-physics (which by the way I spent a ton of time with Roland Christen trouble shooting and him running ghost analysis, reviewing data, etc after the Astronomik claims) Gerd changed his mind and started blaming QHY cameras.  As of the final message I received from him (he has ignored me now for over a week) he still maintains that it is the fault of QHY. 

Like Joey, I ended up spending over $5,000 on a full set of Chroma's, which completely resolved the halo issues.  Even when presented with the mountain of evidence, data and testing from myself and Joey (of which Joey was exceptionally meticulous and diligent with) Gerd still wants to blame something else other than his filters.

It has truly been one of the more bizarre, incomplete and disappointing product and customer service issues that I have had in this hobby.

I will add, that this is the second full set of Astronomiks that I have owned, both the 50mm Deep Sky series.  My other set never had a halo issue, the set in question does.  For many people, like myself prior to this experience, Astronomiks have been excellent filters.  I have recommended them many many times to people, as their MaxFR filters pair nicely and the cost is reasonable for a full set.

It's not just myself and Joey however, Gerd indicated that there are about a dozen other people with halo issues.  After several months of exchanges and my diligence to follow-up, Gerd has offered to refund my RGB filters.  He has refused to refund my SHO filters, because they are not defective.  As Joey pointed out... we buy filter sets that are the same thickness to ensure backspacing requirements are maintained, so without the RGB filters, my Astronomik SHO filters are no longer usable by me.  I will be selling these filters at a loss, paying for the return shipping on the RGB to Europe from USA.  Basically, I will get the lower cost part of my purchase refunded (RGB) while I eat the most expensive part of the set (SHO) and the international shipping costs both ways.

Due to this experience with Astronomik, I also put their filters in the "Buyer Beware" category.  If you do decide to get Astronomik, which by all accounts are great for the vast majority of people, I HIGHLY recommend that you buy them from a reputable dealer and not direct from Astronomik.  Test the filters out while you have a return window and make sure they are good.  Probably, they will be!  But if not, you want to have a safe and reliable method for return and refund.  I do not believe that buying direct affords this same protection.  Through his actions and lack of transparency and communication, it felt to me like Gerd just hoped that I would quietly go away if he ignored me enough. 

I am more than happy to elaborate on anything that I have stated, so please do not hesitate if you have any questions or would like any clarification. 

Clear skies,

-Chris

First, I derived the formula:  Glass_Thickness = [(Halo_Diameter * F_ratio) / 2 ]* 1.5 and it is correct (unless the system is VERY fast).   The "correct" relationship is Glass Thickness = T = nFD/2, where F is the focal ratio, D is the spot diameter, and n is the index of refraction for the glass.  Since n is typically ~1.5, that's how you get the formula that the OP posted.

I've been trying to understand the halos coming from my ASA600 using Chroma filters.  I originally wondered if a double internal bounce within the filters could be causing the issue however, the refractive index of glass decreases with increasing wavelength, which would mean that the blue halo would have to be on the outside and the red halo would have to be on the inside.  Below is a photo showing what the halos look like in RGB.  So...that blows that theory!   I've also used these filters on my 20" CDK and never saw this problem so it's not the filters.

Longer wavelengths diffract at a larger angle than shorter wavelengths but I can't think of anything in the system that would cause this sort of diffraction pattern.  The sensor would produce a rectangular grid modulated by a Sinc() function formed by the square pixels and that's not what we see here.  So that blows that theory.

So, I'm left scratching my head over whether this could be due to the field flattener optics.  I don't have the prescription so I can't ray trace it.  The test for that is to make an adapter to mount my camera at the correct BWD without the reducer to see how it looks.  Since the scope is in Chile, that's going to take a while to try. 

I'm open to any other ideas so let me know if you've seen something like this.

John

Hi @John Hayes

John Hayes:
which would mean that the blue halo would have to be on the outside and the red halo would have to be on the inside.

IF the R,G and B subs were made in blocks, that is first all the Red then the Blue, etc. Could then possible changes in atmospheric conditions such as seeing (refractive index of air) and/or change in altitude have caused enough shift so that the red and blue would have swapped places?

I'm very sorry to hear the various problems you are encountering with the ASA600. I've recently secured a place at Obstech and would like to decide between a CDK24 and ASA600 so have been following the posts made by Mark and you. The choice to include a flattener to protect the filters from dust made perfect sense to me.

I hope you will be able to find the cause of the halo's and solve this problem very soon.

I bought Astronomik 2" Deepsky RGB filters about four years ago and I've never seen halos with my C925 Edge with 0.7X FR. So maybe something has changed in the manufacturing process since then. I'd really like to see how any of these filters are made with the vapor deposition process or whatever it is. I also have a 2.5nm Antlia OIII filter which also has no halos, though Antlia seems to be hit or miss for halos and I just got lucky. Perhaps someone who has the right skill set and equipment could do a cross section of a halo producing filter vs. one without and see what the technical difference is. These manufacturers must know more about this but I'm sure they don't wish to give away their trade secrets. I guess there is only so much they can QC when they are made - getting out under the stars is the only true test. Perhaps they should have an incidence angle test not just a band pass cert, as per John Hayes' argument. I also have some Chroma LRGBs on a GSO 16" RC and again no halos. I would put Chroma everywhere if I had the budget.

Good luck.

John

Here is a fascinating paper on filter halos:  https://www.researchgate.net/publication/365687384_Understanding_Filter_Induced_Star_Halos

A big take away that I found in it is that most halos are caused by filters being slightly off-band rather than anti-reflective coatings.  One reason perhaps why flipping filters makes no difference for most people.  There is a correlation between filter cost and how robust the off-band blocking is as it requires more layers to achieve better blocking.  I tried to have this conversation with Astronomik, however they did not wish to entertain (at least with me) the possibility that some of their filters were off-band.  I am not privy to how they test their filters for QC, but I would assume that band blocking could be tested on the bench.  Anyway, the vast majority of halo discussions are surrounding anti-reflective coatings and how they should be oriented, but AR coatings causing halos seems to be more rare.

Chris White- Overcast Observatory:
I thought I would post a followup on the resolution of my situation.

Thanks for the information! It is useful to everyone buying filters and you never know how good a company is until you have an issue. I still cannot understand how companies think they can get away with less than perfect customer service in  a day where forums and reviews are the standard. I have no doubt that Gerd will lose more than he saves as a result of this episode and this thread but the sad part is that he will likely never know just how much business he has lost so may not modify his policies.

For my part, I have a set of Astronomik filters that are about two years old (the high speed set) and they have been just fine. Clearly I bought mine before the QC issues began. I will probably sell them and get Chromas, not because they are bad but because I would like to have 3 nm instead of 6 nm and only Chroma makes those in high speed filters.

Bill McLaughlin:

Chris White- Overcast Observatory:
I thought I would post a followup on the resolution of my situation.

Thanks for the information! It is useful to everyone buying filters and you never know how good a company is until you have an issue. I still cannot understand how companies think they can get away with less than perfect customer service in  a day where forums and reviews are the standard. I have no doubt that Gerd will lose more than he saves as a result of this episode and this thread but the sad part is that he will likely never know just how much business he has lost so may not modify his policies.

For my part, I have a set of Astronomik filters that are about two years old (the high speed set) and they have been just fine. Clearly I bought mine before the QC issues began. I will probably sell them and get Chromas, not because they are bad but because I would like to have 3 nm instead of 6 nm and only Chroma makes those in high speed filters.

I really don't get it.  We proved early on that the filters were faulty. Simply removing the filter shooting through an empty carousel resolved the halo...  I guarantee that if he had just taken care of the situation as soon as the basic trouble shooting was out of the way that I would continue to praise the virtues of Astronomik in any relevant conversation.  All companies have QC or service issues, there is no way to have 100% perfection.  But how issues are handled, speaks volumes.   I'd wager that if Joey hadn't gotten the run around he would never have considered starting this thread! The QC issue would have been a blip, and we could just say that "I had a bad copy, but no worries, the manufacturer took care of it..."

I ended up with Chroma, which was absurdly expensive, but went that way based on their reputation for taking care of their customers. I have heard that some of the budget filters, like Antlia are getting better as well...but since this was a remote site I didnt want to risk any more down time due to these kinds of issues.  Maybe in the future i'll look at them for my backyard or something.