Going mono: advice on filter set selection - Forums

Topic starter

Aug 21, 2022

Hi all,

I've been using OSC cameras only (EOS 6D & ASI 178 MC) since I've re-started astrophotography four years ago, first with a Samyang 135, and then with an ESPRIT 100 ED. I've definitely not yet exploited that relatively modest gear to its fullest, but I feel it's time to spend some money ;)

I'm thinking of finally buying a dedicated astro camera, namely an ASI 2600 MM. For the filter wheel, I'm looking at the ZWO EFW 7x36 mm V2. The only filter I own today is an Astronomik L2, with which I had no problems, so I'm simply thinking of going for an RGB set from that brand + eventually H-alpha 6 nm.

Now for the questions to the experts

- The ZWO FW is relatively cheap. Are there any known issues with it?
- What about the filters themselves? Are there significant differences between brands for the RGB filters? For H-alpha, Baader has a 3.5 nm "f/2 Ultra-Highspeed" version that sells for ~the same price as the 6 nm Astronomik. Is that any good?

CS,

Frédéric

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TakFan

Aug 21, 2022 · Edited: Aug 21, 2022

Dear Frédéric,

I am using the 2600MM-PRO with ZWO FW 7x & new 36mm Baader Filter UNB (for slower focal lenght). The Ha results in Halos. Using on an TSA-120 with reducer, flattener and extender from Takahashi.

And I was told to go for Astronomik instead. Didn't listen to the advice, though .

The EFW works fine for me.

CS
Dirk

Frédéric Auchère

Topic starter

Aug 21, 2022

Dear Frédéric,

I am using the 2600MM-PRO with ZWO FW 7x & new 36mm Baader Filter UNB (for slower focal lenght). The Ha results in Halos. Using on an TSA-120 with reducer, flattener and extender from Takahashi.

And I was told to go for Astronomik instead. Didn't listen to the advice, though .

The EFW works fine for me.

CS
Dirk

I suppose I should stay away from the Baader and stick to Astronomik then.
Thanks for the feedback!
F

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Alfonso Caschili

Aug 21, 2022

I have been using the 2600MM with the Zwo EFW 7x36v2 and the Astronomik LRGB + SHO 6nm filters for about a year and half now and am perfectly happy with the filters. The Efw is ok, had to tape it all over to prevent light leaks but besides that it has worked flawlessly.

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Frédéric Auchère

Topic starter

Aug 21, 2022

Alfonso Caschili:
I have been using the 2600MM with the Zwo EFW 7x36v2 and the Astronomik LRGB + SHO 6nm filters for about a year and half now and am perfectly happy with the filters. The Efw is ok, had to tape it all over to prevent light leaks but besides that it has worked flawlessly.

Light leaks? Ah, good to know, thanks for the tip!

F

Andy Wray

Aug 21, 2022

The main thing on the ZWO filter wheel is to set it to unidirectional mode. In that way it more accurately positions the filters and matches your flats. It may take longer to change filters, but it is worth it.

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Frédéric Auchère

Topic starter

Aug 21, 2022

Andy Wray:
The main thing on the ZWO filter wheel is to set it to unidirectional mode. In that way it more accurately positions the filters and matches your flats. It may take longer to change filters, but it is worth it.

One more good piece of advice

How long does it take to move from one position to the next? Also, as I may not buy 7 filters at once, I suppose it would be better to load the empty positions with dummy masses to keep the mechanism balanced. Any recommendations for that?
F

Frédéric Auchère

Topic starter

Aug 21, 2022

Andy Wray:
The main thing on the ZWO filter wheel is to set it to unidirectional mode. In that way it more accurately positions the filters and matches your flats. It may take longer to change filters, but it is worth it.

One more good piece of advice

Leonardo Landi

Aug 21, 2022

Anyone uses Optolong filters? I have the complete LRGB+Ha OIII and SII and works great. I'm waiting for the 3nm 31mm filters

Mark Abbott

Aug 21, 2022

I’m no expert but I recently purchased a mono camera (294mm) and went with Astronomik deep sky RGB and narrowband filters. I’m very happy with them and they seem to be a good bang for the buck.

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Frédéric Auchère

Topic starter

Aug 21, 2022

Thanks Mark & Leonardo! The Optolong 3nm seems interesting for its price. Any feedback on that one?

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Andy Wray

Aug 21, 2022

Frédéric Auchère:
I suppose it would be better to load the empty positions with dummy masses to keep the mechanism balanced. Any recommendations for that?

No need to worry about that ... the mechanism is more than capable of coping.

Andy Wray

Aug 21, 2022

Frédéric Auchère:
One more good piece of advice How long does it take to move from one position to the next?

A couple of seconds.

Brent

IOTD Staff

Aug 21, 2022 · Edited: Aug 22, 2022

Bottom line up front: parfocal filters, it matters.

background: the glass thickness influences back focus, so if you have one brand of LRGB filters and another brand of narrowband, the required back focus may be different! and that does not make for happy imaging.

I have gone astronomik all the way... now.

I wanted to save money on the LRGB filters and went with ZWO filters there, and astronomik for narrowband.

I wanted RGB stars for some of my narrowband images and quickly realized, how significantly different the back focus was. I do image on fast systems ( f/4 newtonian, and f/2.2 hyperstar) where this effect may show up more. shooting at f/7 the effects may not be as strong, not sure?

This can also influence focus on off axis guide (OAG) scopes and keeping them in focus as you change filters.

if you want a technical deep dive - I did a video on dichroic filters, figuring out where reflections come from, and how/when to think about bandwidth for narrowband. because I do a good bit of fast optics I settled on the MaxFR filter set.
https://youtu.be/DW081qgoPUU
and
https://youtu.be/rtFX92dZE_w

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Brent

IOTD Staff

Aug 21, 2022

I also talked with Gerd Neumann from Astronomik last week - he was recommending the 'deep-sky' RGB filters rather than the type 2C.
they have slightly different band pass than the 2C RGB filters.
Astronomik Deep-Sky RGB Color Filter

Andy Wray

Aug 22, 2022

Brent:
This can also influence focus on off axis guide (OAG) scopes and keeping them in focus as you change filters.

I'm not sure I understand what you mean by the above? An OAG would be placed before the filters in the imaging train and as such would not be affected by them

Wei-Hao Wang

Aug 22, 2022

Andy Wray:
I'm not sure I understand what you mean by the above? An OAG would be placed before the filters in the imaging train and as such would not be affected by them

If your filters are not parfocal, you need to refocus after you change filter. This will push your OAG out of focus.

Andy Wray

Aug 22, 2022 · Edited: Aug 22, 2022

Wei-Hao Wang:
Andy Wray:
I'm not sure I understand what you mean by the above? An OAG would be placed before the filters in the imaging train and as such would not be affected by them

If your filters are not parfocal, you need to refocus after you change filter. This will push your OAG out of focus.

I think I get the point now, but not sure it would have any appreciable affect on the OAG. I have non-parfocal filters and it has absolutely no affect on my guiding.

kuechlew

Aug 22, 2022

Andy, you're imaging with 800mm focal length while Wei-Hao Wang images at up to 3500mm focal length. Focus plane is quite a bit smaller and the OAG may loose the stars at very slight focus shifts.

Clear skies
Wolfgang

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Chris White- Overcast Observatory

Aug 22, 2022 · Edited: Aug 22, 2022

Andy, you're imaging with 800mm focal length while Wei-Hao Wang images at up to 3500mm focal length. Focus plane is quite a bit smaller and the OAG may loose the stars at very slight focus shifts.

Clear skies
Wolfgang

Critical focus zone (cfz) is determined by focal ratio, not focal length (and does vary slightly by bandwidth). I don't know what scope Wei Hao is using but a 3000mm f10 scope is more forgiving with focus than a 500mm f5.

With my edge scope I was able to mix 1mm and 3mm filters. The oag camera was set to focus right in the middle. So it was never perfectly focused but stayrd the same between the two filter thicknesses. I could not get away with this on my shorter refractor.

To the OP:
I use chroma and astrodon now, but if I was to buy filters again, I'd go with the astronomik deep sky rgb and the max fr for narrowband. Much more affordable and proven performers.

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Rouz Astro

Aug 22, 2022 · Edited: Aug 22, 2022

Frédéric Auchère:
Hi all,

I've been using OSC cameras only (EOS 6D & ASI 178 MC) since I've re-started astrophotography four years ago, first with a Samyang 135, and then with an ESPRIT 100 ED. I've definitely not yet exploited that relatively modest gear to its fullest, but I feel it's time to spend some money ;)

I'm thinking of finally buying a dedicated astro camera, namely an ASI 2600 MM. For the filter wheel, I'm looking at the ZWO EFW 7x36 mm V2. The only filter I own today is an Astronomik L2, with which I had no problems, so I'm simply thinking of going for an RGB set from that brand + eventually H-alpha 6 nm.

Now for the questions to the experts

- The ZWO FW is relatively cheap. Are there any known issues with it?
- What about the filters themselves? Are there significant differences between brands for the RGB filters? For H-alpha, Baader has a 3.5 nm "f/2 Ultra-Highspeed" version that sells for ~the same price as the 6 nm Astronomik. Is that any good?

CS,

Frédéric

*I recently have a detailed comparison of 3nm vs 5nm here:
https://astrogeartod...astronomik-6nm/

CS
Rouz
https://www.rouzastro.com/

Wei-Hao Wang

Aug 22, 2022

I am also looking around for filters. It's interesting to hear that Baade NB filters produce halos. Can others confirm?

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Rouz Astro

Aug 22, 2022

Wei-Hao Wang:
I am also looking around for filters. It's interesting to hear that Baade NB filters produce halos. Can others confirm?

*I have a 3.5nm from a 3 years ago, it did suffer from halos.

CS
Rouz

Wei-Hao Wang

Aug 22, 2022

Rouz Astro:
Wei-Hao Wang:
I am also looking around for filters. It's interesting to hear that Baade NB filters produce halos. Can others confirm?

*I have a 3.5nm from a 3 years ago, it did suffer from halos.

CS
Rouz

Thanks! It's very important to know this.

On the other hand, on Baade's website:
https://www.baader-planetarium.com/en/blog/new-cmos-optimized-baader-filters/
there seems to be some updates in their filter formula lately. Has anyone tried their latest batch of NB filters? Any improvements?

I am seriously consider Baade because it appears to be the only manufacture that offers all the filters I want with equal thickness. My size and filter type requirement is kind of special, and Baade is the only one who has all. However, if there are halo issues, I will reconsider this.

Rouz Astro

Aug 22, 2022

Filters being parfocal isn't necessary.
Even if they are, you telescope is not "parfocal" unless you use a reflector only system like a pure RC or Newtonian (no correctors).

I mix 1mm, 1.1mm and 3mm all in the same filter wheel.

while that is extreme, mixing different 1mm or 3mm filter brands will not be a huge issue for the OAG.

In any case, its always best to calculate offsets between filters if you don't want to refocus (NINA does that).

I would never assume perfectly parfocal no matter what.

CS
Rouz
https://rouzastro.com/

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