Filter choices for OSC imaging

[pmrid]

Recently saw reviews of the Antlia dual band filter ( https://www.testar.com.au/products/antlia-fast-golden-dual-band-filter?variant=42603934449889&currency=AUD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&utm_campaign=gs-2019-12-27&utm_source=google&utm_medium=smart_campaign&gclid=EAIaIQobChMIx7aMlsqa9wIVmX8rC h3Zfgp8EAQYBSABEgJOa_D_BwE) at $599 from Testar and wondered how users had found it compared with other choices. With a 5nm bandpass in both OIII and Ha, the Antlia certainly seems like a good choice for mid-level light polluted areas such as mine.

But I have also read some interesting discussions about the effect of focal ratios on the bandpass shift issue. I will be imaging mainly at F5 or F6 so I expect the impact to be minor. But, I’d appreciate any suggestions for alternatives that are perhaps not so bloody expensive.

[AstroJunk]

I have the OPTOLONG L-eNhance for use at f2 and it works very nicely. The L-eXtreme is too narrow and the Ha drops off entirely at hyperstar f-ratios. Being Tri-band, it really maximises the potential of our OSCs.

The attached photo is a test image under a 1st quarter moon which is pretty good all things considered - has no significant processing.

[pmrid]

Hi Jonathan. What got me started was the YouTube video by Cuiv “The lazy geek” entitled “OSC Narrowband filters - what to buy” and in particular the graphs and explanations starting around the 8 minute mark explaining how much signal is lost at very short focal ratios. I found it very interesting and it got me started in wondering about filters with very narrow bandpass.

[Startrek]

I use my L Extreme ( 7nm Ha Oiii ) with a 2600MC at both f5 and f6 under Bortle 8 Suburban and Bortle 3 dark site when moon is around and it’s a game changer
Started with a ZWO Duoband a few years back for a while but the L Extreme blew my socks off

Cheers

[pmrid]

Yes. The ZWO duo is a bit of a dud. With bandpass of a whopping 35nm in the OII/Hbeta) and 15nm in Ha, it does not give me the contrast I want. I have bitten the bullet (late last night) and ordered a L-Enhance with figures of ~25 (OIII and H-Beta) and ~11 (Ha) it’s not down there with the “Extreme” I admit but it will have to do.

[Retrograde]

I have the Antila dual-band filter (but have so far only managed to use it once due to the terrible weather in recent times).

One of things that attracted me was the claimed halo suppression around bright stars which seems to be a problem with filters containing tight OIII bands. Whether that holds true remains to be seen along with the claimed performance at low f-ratios.

I'm still new to processing these types of images but here are a couple of renditions of my first light with the filter. About 1.8 hours of exposure in Bortle 7 skies at f5.3.

[pmrid]

I’d love to see comparison shots with the L-Extreme and the Antlia - the 5nm version at least. The reviews of the Antlia are certainly glowing. Pity about the price!

[Startrek]

Images from last night with L Extreme under full moon in Bortle 3 skies
8” f5 GSO Newt
About 2 hrs of data
I’m super happy with the L Extreme and obviously don’t suffer from Star halos with the newt , so I can’t see myself upgrading to the “Golden” Antlia Duoband
I don’t think the slightly tighter bandpass will accentuate the detail my images from what the L Extreme is capable of doing at present.

Cheers

[pmrid]

Thanks Martin. With the images posted by Pete - of the same object but with an Antlia filter, I have the comparison I wanted. And thanks to Pete also, of course.

I will enjoy spending time with these.

[AstroJunk]

L-eNhance, Bortle 4, 98% Moon last night
110mins Esprit 100/ASI071 live stacked using the ASI Air

Stretched only - I've made no colour changes so you can see exactly what comes off the camera. It does the job pretty well I recon, I should have done some darks...

[pmrid]

Great Jonathan! That completes the trifecta of filters.
My l-eNhance is still in transit. I’m extra keen to get it into action.

[Nikolas]

That second image is a cracker

[Dave882]

The l-extreme is very useful when imaging Ha or Oiii rich targets and very effective countering the effects of full moonshine and city light glow. I’ve used it extensively with my scts at both native focal lengths and reduced to f7, f6.3 and f1.9 with the Hyperstar.

With regards to using l-extreme with the Hyperstar, I’ve never done the calcs but am persuaded by others that there is a substantial loss in effective aperture. However, that doesn’t mean it’s not still effective and it can still deliver good contrast with severe light pollution. Just need to be aware of the trade offs. I’ve recently purchased a dual band IDAS NBZ filter which is pre shifted for use with Hyperstar. Just haven’t had a good night to trial it yet.

In addition I like using the Optolong UHC filter to reduce light pollution and this fairly versatile for a variety of targets.

[AstroJunk]

Here's the Tarantula with the L-eXtreme at f2 and its isolated red channel. It's fair to say that this is largely an OIII object anyway, but the loss of Ha was more dramatic than I had expected.

[Retrograde]

Thanks Nik! That was actually my first processing attempt which I did by following a YouTube tutorial.

Nice pics everyone. Clearly on the subject of multi-narrowband filters it's horses for courses, depending on your scope type etc.

I also have an Optolong L-Pro for broadband objects but I'm not convinced it's that worthwhile. Whilst it reduces LP & associated gradients it still leaves some that need to be fixed in post-processing anyway, & affects the colour balance a bit (although less than most other comparable filters. It would mainly help to allow longer length subs without the sky background overwhelming the signal.

[pmrid]

I’m afraid I have to disagree with you on this. The Tarantula is the largest EMISSION nebula known which makes it a major Ha source. So your loss of Ha signal has been almost entire. Can I suggest you have a look at the YouTube video I referenced earlier. I found it a very interesting discussion and explanation for the phenomenon you are experiencing.

[dugnsuz]

Hi Peter - I've been using the 2" Antlia Dual Band 'Golden' filter with my 2600MC.


This gear marks a return to imaging after a 10 year drought, so I'm in no position to give anything but rookie opinions.


I'm enjoying the images from this filter - I attach recent Eta and Tarantula pics(please excuse processing and significant tilt issues at edges - yet to fix)
Eta is 26x600s and Tarantula 18x600s


Stars have slight blue haloing, but that's more likely an artifact from my dodgy PS skills.


I may be putting this filter up for sale soon though as I got the dreaded oil leak on the 2600MC sensor - ZWO will replace, but I'm using the 'opportunity' to move to the 2600MM sensor and therefore the OSC accessories will be for sale (all going well)


Cheers
Doug

[AdamJL]

It's pretty common with this filter, at least with refractors.



ha, same. I bought the QHY because of an oil leak on the 2600MC. Mine's all cleaned up now, but still... didn't give me a lot of confidence. The MM can have it as well.
I'm almost hoping it happens again so I can get it replaced by ZWO. When I had it happen to me, it was before ZWO said they'd replace the cameras, and Testar cleaned it for me instead.

[dugnsuz]

Thankfully my oil leak wasn’t as bad as some I’ve seen - slowly creeping towards sensor!!:(

[AdamJL]

Lucky. Mine was worse than that!

[pmrid]

Looking at the Antlia images Doug posted below, and comparing with my L- Enhance images, I am struck by the lack of “bloom” around the stars with the Antlia. I have been imaging with 2 different 72mm achromats so I expect some fringe effects but am surprised by the extent of it. I had expected that with the dual band filters, much of this would be avoided. It doesn’t look that way though.

Any tips on Photoshop processing it out?

[Retrograde]

Interesting - it looks like everything is just a little out of focus.

Given that each band is in a different part of the spectrum an achromat is likely to have some trouble I guess?

[pmrid]

Hi Pete.
yes, it looks that way but both images (2 different scopes) was focused by ASiair’s autofocus routine. Since each image was taken through a L-Enhance filter, where the bands are red(Ha) and Blue/green), and since the scopes are achromats, some CA is to be expected I suppose. So ASiair autofocus routine must prioritise one band over the other. Not much I can do about that I suppose.

[Astro_Girl]

Hi there,

Would you happen to have or are able to obtain a test shot of a bright star say Acrux 30 seconds plus exposure using the Antlia filter and post it here.

I am in the market for one but am interested to see what if any haloing is present.

Cheers,
Cheryl

[Sunfish]

Hi Peter,

I have used a little manual lense correction in PS Light Room developing to get rid of the coloured fringing. It works if used gently on one particular colour and you can choose which colour to work on . Blue fringing is particularly easy.

I am sure the same lense correction would be available in PS also. LR is easy for me.

[Retrograde]

It's not Acrux but here's a 100% crop of Lambda Centauri (which is still quite bright) with the Antila through my little ED65.
All that has been done is a basic stretch and crop (also added the full frame with basic stretch to give some context)

Hope this gives some insight,
Pete

[evltoy]

I’m so glad I found this thread as I’m currently trying to work out which way to go. If any of you guys can give me some direction that would be awesome.

I’m looking at getting both the L-eNhance and L-eXtreme (1.25”) to add to my filter collection which includes a ZWO Duo and a Baader Moon/Sky Glow. My gear is the asi294MC pro, SW ed80 & ed120 and a Celestron 8” SCT. My F-stop is no more than F6 and I don’t plan to go past f4 in the future. I live mainly in bortle 5/6 and my holiday area is 3.

Given that these filters are no good for Galaxies or Reflection Nebula's I would be instead using the SCT with the baader Moon/Sky glow or just the UV/IR filter with the 294MC.

My delimer is, is the L-eXtreme going to be worth it considering the narrow band pass of HA or do I get the L-eNhance 1.25” for the asi294 and another L-eNhance 2” for my unmodified DSLR to run on either the ed80 or ed120? Getting the L-eNhance 2” would allow me run 2 setups at a time.

What are your thoughts?

FYI – Cuiv just released a new vid 4 days ago with some interesting info on the filters we are talking about.

[pmrid]

A point to bear in mind is that both refractors you mention are achromats which means they are not as colour-corrected as a triplet or better. That means your dual-band filters are likely to show some bloom around stars. That’s because the red and blue components are not coming to best focus at the same place.

The Ha bandpass in filters like the Enhance is comparatively wide (about 20nm or so from memory; and the blue/green bandpass is even wider I think.) If you compare results with a mono ccd and discrete NB filters, the difference will be quite marked.

[evltoy]

Hi Peter

Thank you for the information you have provided, but I'm not sure if I have missed your point... I dont have a mono camera in my setup to compare.


I'm more asking would I be better off with 2x L-eNhance filters running on my ED80 & ED120 with the 294MC and DSLR (non-modified) at the same time

or

would the L-eNhance & L-eXtreme combo serve me better just on the 294MC only.

Another way to look at it... Will I get more benefit from having the L-eXtreme in my kit over being able to run 2 rigs at the same time with both on the L-eNhance

Cheers
Wayne

[pmrid]

I guess the suggestion I was making was that with the amount of $$ you’re looking to spend, you may want to consider the alternatives first - mono ccd and NB filters.


Peter

[evltoy]

Ahh ok. Nope mono camera/setup is out the question… don’t have the time or enough clear skies.

Also You couldn’t get a mono camera and NB filter secondhand for the cost of the 2 filters ($700).

[Hoges]

No one has mentioned using 2 separate filters - something like the Antila Edge at 4.5nm in Oiii and Ha - I know that it is not efficient using a OSC with single narrowbands, but wouldn't that be much more advantageous particularly for an acromat where you're only dealing with one wavelength at a time? Someone on FB posted their Ha and Oiii images recently which I downloaded to have a play with combining in photoshop elements and I found the results very pleasing - particularly having control over the different colors (PS elements doesn't have individual channels available).

[pmrid]

John, I recently started using AstroPixel Processor (APP) which includes the means to tease out individual NB channels from Dual-Band OSC image. You may find that a useful alternative to the method you propose.

[Hoges]

Cheers Peter. Yes, I did have a look at that a couple of weeks ago. Though doing it via software after the exposure, doesn't allow you to finely focus an acromat on only one wavelength at a time. Might be a complete waste of time but it's something I'll experiment with when the astro budget allows :) I did give the Lenhance filter a go on my Askar fma 180 the other night with a 98% moon was out - much more effective than I would have guessed: https://www.facebook.com/photo/?fbid=2165454150321033&set=gm.778646270165063