Filters, what are the differences in quality, and what are I payingfor?

[Rocket Stars]

Im getting a filter drawer, and a better adapter setup for my hyperstar setup. 

Currently Im dabbing with a altair GPCAM 3 178c. But hoping to upgrade to 183 mono in near future. 

First, Im looking what size to get. Should one go for 2” to be future prof? Seems sensors are getting bigger at more ”afforable” prizes. Also in the future, i will get a filterwheel and a reducer for my edge 8. 

Baader has a special set for Highspeed optics. So Im wondering if multiband filters will work with my 178color camera? Or any other ”normal” filters? 

In essential, what is the difference? 

Alot broader filterqueation. What is the difference in quality between the brands? Astrodon seems to be the best of the best. To pricy for me. But why are they better? 

I can pay for good equipment. But I like to know why and what Im spending money on. 

[wimvb]

For good filters, it's not what they let pass, but what they block. Eg, if you have a 3 nm narrowband filter with 99% peak transmission and 1% transmission off band, then you still get a lot of unwanted light in. This is simply because 1% of all those photons that should be blocked make it through. But if the filter has 93 % peak transmission and only lets 0.01% through off band, that filter is much more light pollution proof. Then there is hardness. A quality filter will have hard, durable coatings, that can "take a beating". Less expensive filters may look good on paper, but the coatings can be less dense and have poorer adhesion. This is impossible to see when you buy, and may only show after a few years of use. Finally, there's the back side of the filter. This needs a high quality anti reflective coating in order to avoid reflections.

Filter makers spend a lot of time doing product development and quality control. They want to be paid for their efforts. In short, quality costs, and you get what you pay for.

As for multiband filters, I'm not convinced yet that they are time savers. In general, Sii, and Oiii are much weaker than Ha in a nebula. So you may want to use longer exposures for these wavelengths. Also Ha is more moon-proof than Oiii, and you can gather Ha when the moon is too bright for Oiii. If you only have an osc camera, a multiband filter may be ok, but I wouldn't expect the same results as for separate filters and a mono camera.

Decide what you want, and what you are willing to spend, and shop accordingly. 

[ollypenrice]

I'm not sure that the multiband filters would work with the steep light cone of F2. Certainly check that first. I've never tried them myself.

My experience of the expensive Astrodon 3Nm Ha versus the less expensive Baader 7Nm is that the Astrodon gives tiny stars and higher contrast in the nebulosity. The difference is considerable. On the other hand, for LRGB I'm perfectly happy with the Baader.

The cheapest RGB filters are absorption filters. They are OK at entry level but certainly not as good as the interferometric ones. As you are aware, the angle of the incident beam at F2 is difficult for filters to handle.

Olly

[Rocket Stars]

20 hours ago, wimvb said:

For good filters, it's not what they let pass, but what they block. Eg, if you have a 3 nm narrowband filter with 99% peak transmission and 1% transmission off band, then you still get a lot of unwanted light in. This is simply because 1% of all those photons that should be blocked make it through. But if the filter has 93 % peak transmission and only lets 0.01% through off band, that filter is much more light pollution proof. Then there is hardness. A quality filter will have hard, durable coatings, that can "take a beating". Less expensive filters may look good on paper, but the coatings can be less dense and have poorer adhesion. This is impossible to see when you buy, and may only show after a few years of use. Finally, there's the back side of the filter. This needs a high quality anti reflective coating in order to avoid reflections.

Filter makers spend a lot of time doing product development and quality control. They want to be paid for their efforts. In short, quality costs, and you get what you pay for.

As for multiband filters, I'm not convinced yet that they are time savers. In general, Sii, and Oiii are much weaker than Ha in a nebula. So you may want to use longer exposures for these wavelengths. Also Ha is more moon-proof than Oiii, and you can gather Ha when the moon is too bright for Oiii. If you only have an osc camera, a multiband filter may be ok, but I wouldn't expect the same results as for separate filters and a mono camera.

Decide what you want, and what you are willing to spend, and shop accordingly. 

Good info, Thank you. 

I vill certenly check If a dualband will work with hyperstar. Since you cant have a filterwheel with that set up. Makes such filter Intresting. Plan is however to get a cooled mono CAM in the near future. 

Sound like astrodon is a long term goal. But astronomin, baader ect. Will be a very good start. 

[Rocket Stars]

11 hours ago, ollypenrice said:

I'm not sure that the multiband filters would work with the steep light cone of F2. Certainly check that first. I've never tried them myself.

My experience of the expensive Astrodon 3Nm Ha versus the less expensive Baader 7Nm is that the Astrodon gives tiny stars and higher contrast in the nebulosity. The difference is considerable. On the other hand, for LRGB I'm perfectly happy with the Baader.

The cheapest RGB filters are absorption filters. They are OK at entry level but certainly not as good as the interferometric ones. As you are aware, the angle of the incident beam at F2 is difficult for filters to handle.

Olly

Exellent info! 

I cant remember Where, But have heard that broader filters, 7-12nm works with hyperstar. The narrower not so good. 

Im certenly not sure of that it is correct. 

Having right filters is important. And they are not cheap. So Im trying to do the best decission as possible. 

[wimvb]

3 hours ago, Rocket Stars said:

I cant remember Where, But have heard that broader filters, 7-12nm works with hyperstar. The narrower not so good.

that is correct.. The transmission peak of a nb filter shifts towards the longer wavelengths for oblique rays (ie low f-numbers).

[gorann]

18 hours ago, ollypenrice said:

I'm not sure that the multiband filters would work with the steep light cone of F2. Certainly check that first. I've never tried them myself.

My experience of the expensive Astrodon 3Nm Ha versus the less expensive Baader 7Nm is that the Astrodon gives tiny stars and higher contrast in the nebulosity. The difference is considerable. On the other hand, for LRGB I'm perfectly happy with the Baader.

The cheapest RGB filters are absorption filters. They are OK at entry level but certainly not as good as the interferometric ones. As you are aware, the angle of the incident beam at F2 is difficult for filters to handle.

Olly

I have both a 7 nm and 3.5  nm Baader Ha fillter and I have the impression that the 3.5 nm is quite a bit sharper but I have not tested them side by side or the same night. So it could be that the difference between Baader 3.5 nm and Astrodon 3 nm is rather small and not worth the big price difference.

[wimvb]

3 hours ago, gorann said:

So it could be that the difference between Baader 3.5 nm and Astrodon 3 nm is rather small and not worth the big price difference

Depends on whom you ask of course:

https://astrodon.com/products/astrodon-narrowband-filters/

AfaIk, there's only one manufactuter of 3.5 nm filters. But I could be wrong.

Are there any independent (bench) tests of nb filters? 

[gorann]

33 minutes ago, wimvb said:

Depends on whom you ask of course:

https://astrodon.com/products/astrodon-narrowband-filters/

AfaIk, there's only one manufactuter of 3.5 nm filters. But I could be wrong.

Are there any independent (bench) tests of nb filters? 

I should check my filters with a spectrophotometer, we have a few of them where I work. Just have to remember to do it.

[ollypenrice]

8 hours ago, gorann said:

I have both a 7 nm and 3.5  nm Baader Ha fillter and I have the impression that the 3.5 nm is quite a bit sharper but I have not tested them side by side or the same night. So it could be that the difference between Baader 3.5 nm and Astrodon 3 nm is rather small and not worth the big price difference.

For a subjective comparison I once imaged the same object at the same time with the same model of camera but at two focal lengths and resolutions. In a Tak 106 at 3.5 arcsecs per pixel I had the Astrodon 3nm Ha and in a TEC140 I had a 7nm Baader at 1.8"PP. Under normal circumstances - ie with the same filter in each rig, the TEC would give considerably tighter stars and more structural detail in nebulosity. In this case, though, the images looked remarkably similar. The Astrodon filter had lifted the subjectively perceived image quality as dramatically as that. I'm afraid I don't have the original data any more but am confident in my recollection because it was so surprising.

Olly

[Rocket Stars]

A very Intresting discussion! 

Regarding tests. I have not seen any real comparisons between manufacturers. 

Most reviews are very subjektive, to say atleast!