Different makes of filters comparisons?

[Physopto]

Has any one compared the different makes of filters. By this I mean actually bought the same say LRGB filters and the compared the results with another makers filters. I hear so much on paper but not seen actual comparisons. Astrodon are so expensive compared to say Astronomik, but are they any better?

Thanks in anticipation.

Derek

[ollypenrice]

I've had a few comparisons. I've processed a few guest images with Astrodon LRGB and was mighty relieved to find I was more at home with my Baaders! I didn't get on with them but that was just on a couple or three projects and I'm a subjective image processor. Some very big hitters love them.

I have both AD 3nm Ha and Baader 7Nm Ha. On some targets the AD blows the 7Nm out of the water on contrast. On other targets there is not much difference except that the AD stars are tiny - as in truly tiny.

As for Astronomik, I had their 13 Nm Ha with free haloes and the replacement with smaller haloes and three of their Aurora flatfield panels with fall-to-bits cables and I'm out of there. Sorry about that but a large sum of cash for a fall-in-bits 14 inch panel is not funny.

Olly

[Physopto]

Hi Olly,

Thanks for the answer. I have Astonomik filters, a full set. My NBs are all 13nm. I have had to contact them about halos. They have said that they will exchange my NBs except the Hb as they do not make that one anymore (only clip filters for cameras now). I can live with that. I was very disappointed getting halos, as I was told that the second gen filters were clear of that problem. Apparently the latest ones are better. Time will tell. They are saying that the new type of filter for LRGB won't be ready for some time. Also that these will not have a cross over in wavelengths, i.e. a sharp cut off with small gap. That is a shame as I have a problem with halos in the normal red and blue as well, so I will have to wait for replacements. I'm no expert as still learning and don't get much chance to get out with the rig at present. So the only images so far have been of the Horsehead, spoilt by the halos. I have one of their flat field panels so hope that keeps working!

So any information such as yours is welcomed.

Thanks,

Derek

[perfrej]

Incidentally, the Astrodon filters are, as I understand it, float glass base, while the Baaders are polished glass. This will put the Astrodons at a disadvantage as the f-number gets lower and the angle of incident of the light rays decrease. Again per my understanding, the Astrodons are coated and then cut, while Baaders are cut then coated making them (the Baaders) more resistant to moisture ingress along the edges. This is information that came my way when I was considering the options for my next camera (hopefully) which requires 60mm square filters. I have seen a picture of a delaminated Astrodon filter, but I am sure it is a rare occurence.

I have one set of Astrodons in my QSI and they have been reasonably good to me. I also have a set of unmounted Baaders in my other camera, and they have also been good to me. Both sets have been used with low f-numbers. The next set will be Baaders due to the fact that they are polished and more attractively priced.

ALl the best,

Per

[Physopto]

Thanks Per,

I'll get back to you on this ASAP. I'm on the IPad at present. Very interesting.

Derek

[Physopto]

Hi Per,

 I have sent off a general enquiry to Astrodon about their filters. Asking in particular how they are made. I'm not asking for any secrets just general information.

I also see that they make Fused Silica filters. Expensive even in 1.25 inch but if made from the correct grade of fused silica, are guaranteed not to introduce birefringence. That is something I had to pay particular attention to when in physics research. It also means that the filters have to be polished and cannot not be made by the float method, as they are cut from a boule. I will let you all know their answer or lack thereof of in due course.

I have just heard back from Astronomik's Eric-Sven Vesting. He has kindly said that he will send out  new type  replacement narrowband filters to replace my Ha SII and OIII set and that after I receive them I can send back the old halo affected ones. I cannot complain at all about that service, excellent! Unfortunately I cannot get a new Hb as they are discontinued for other than DSLR clip filters, shame about that!!!

If you are going to require 60mm²  it must be some camera!!

Well wife's chomping at the bit, got to go back to gardening.

Regards,

Derek

[sloz1664]

I have a new set of the Astronomik 6nm Ha Oiii & Sii and are relatively halo free on my WO star 71 and my AA 80ED Triplets.

Steve

[Physopto]

Thanks for that Steve. I just got an answer back from Astrodon about their filters. If I get permission to put it on here I will. But I have asked them first. Only fair and correct.

Derek

[perfrej]

Derek, filters are 60 x 60 mm Camera is FLI Nicroline 50100. It will take a few months before I have the means readily available, but then...

Look forward towards seeing a reply from Astrodon about their manufacturing process. The images and information that I have do not come from the horse's mouth...

/per

[Earl]

i hnd bad halos with baaders, not so good with astronomik, and minimal with astrodons, this is however is target specific, and i also feel F ratio and ccd also play some part.

others have not had these issues which makes it a bit of a headscratcher overall.

[Physopto]

Well hi everyone,

I have just had confirmation from Don Goldman of Astrodon. He has given me permission to publish his email answers to my questions. So I am including my questions first and all of his emails back to me as it sets the correct scene. He was very open and honest in his answers. So I must say thank you to him publicly.

Date: Thu, 28 May 2015 11:23:52 +0100
Subject: coating of filters.
 
Hello this is just a general  enquiry as to how you coat and finish your
filters.

I have a set of Astronomik filters which have caused problems with Halos
and am looking around at other makes to replace them. I have been
informed that your filters are on float glass. Also that they are coated
then finished to size, not cut to size then coated. Some one has
indicated that he had seen de lamination of the filter coating some time
in the past. I find that a bit hard to understand as I am a physicist
and have previously coated Cadmium Telluride substrate with pure gold to
produce Ohmic contacts. The only problem I had then was to prevent the
gold rubbing off as it was done at room temperature and not at increased
temperatures.

So what I would like to know is are your filters  ground and polished
then coated or are the cut after being coated.  They are expensive but I
am interested as I just cannot waste my time acquiring images, to later
find out that they are being degraded by problems with either halos or
because of artefacts caused by the finish/flatness.

I am also interested in finding out if you use fused silica at all, as
it if treated properly during the cooling stages  it does not introduce
birefringence.

Thank you for your help in advance,
Sincerely
Dr D O Brown

On 28/05/2015 4:27 PM, Astrodon wrote:
> Dr. Brown,
> 
> Yes, there are many rumors floating around.
> 
> Our LRGB, narrowband and photometric filters are all either ion beam or magnetron sputtered hard-oxide coatings on fused silica.
> 
> We have always coated large 1/4-wave substrates and cut/cored the filters to size, so they are coated to the edge and do not require edge sealing, being hard coatings.  We have done testing to show that cutting filters from large plates does not cause any degradation in performance or physical properties, such as flatness, bowing, etc.
> 
> Others coat individual, pre-sized substrates, which, due to beam shadowing from the holder in the coating chamber leaves an uncoated rim near the edge that needs to be blocked in the filter wheel, especially for narrowbands.
> 
> We had 2 bad batches of narrowband filters in our corporate history from a former manufacturer (large, world-class optical coating company!)  that had delamination problems (ca 2009) out of the thousands that were sold.  Even though the number of affected filters was small, it was an embarrassment.  That filter manufacturer was replaced over two years ago and no further incidences have been reported.  All of the delaminated filters were replaced free of charge, as we offer a 5-year limited warranty specifically for delamination. The customer is only required to incur the cost of shipping the filter to us.
> 
> Our LRGB filters have the bandpass and blocking layers all on one side and a high quality hard A/R coating on the other.  This essentially eliminates internal reflections that cause ghosting (haloes) around bright stars, which Astronomiks are/were known to have.  The transmission in the bandpass achieves >98%T with this design.
> 
> Our narrowbands are guaranteed to exceed 90%T at the specified emission line right on the box.  In fact, our latest 3 and 5 nm narrowband filters in the past two years are approaching 97%T.  The narrower bandwidths than our competitors means that our contrast will be significantly higher, bringing out fainter detail in the same amount of time.  Since the signals are so high, you don't need to take longer exposures with our lower FWHMs. Not one of these newer filters has ever delaminated.  This is why the filters are expensive.  One competitor's 7 nm H-a filter varied from about 86 - 70%T at the H-a emission wavelength, but they are priced significantly lower.  My goal from the founding of the company was to produce the highest performing astronomy filters, even if we are the most expensive.
> 
> I hope that this helps.
> 
> Best Regards,
> 
> Don
> 
> Don Goldman, Ph.D.
> President
> Astrodon Imaging
> Roseville, CA 95661 (USA)
> www.astrodon.com (commercial site)
> www.astrodonimaging.com  (personal astro image gallery)
> skype  astrodonrgb

Date: Thu, 28 May 2015 17:51:31 +0100
Subject: Re: coating of filters.
 
Dear Don,

Thank you for your very complete answer to my query. It goes a long way to answering my questions and the concerns of others who have answered my questions on line.

With your permission I would like to pass on your answer to "Stargazers Lounge" members here in the UK. If you prefer me not to do so I fully understand and will not pass on the email. In any case, I will do nothing unless I get your permission.
It would do you no harm I think, to dispel unfounded gossip.

Again many thanks for the answer. I will probably be looking towards purchasing your filters in the near future.

Many Regards,
Derek

On 28/05/2015 6:55 PM, Astrodon wrote:
> Hi, Derek,
> 
> Certainly.  We stand behind the quality of our filters.  Please post your initial inquiry along with my reply, if you don't mind, to put it in perspective.
> 
> Thanks.
> 
> Best Regards,
> 
> Don
> 
> Don Goldman, Ph.D.
> President
> Astrodon Imaging
> Roseville, CA 95661 (USA)
> www.astrodon.com (commercial site)
> www.astrodonimaging.com  (personal astro image gallery)
> skype  astrodonrgb

I have included every thing so that there are no misunderstandings.

 Derek