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ANTLIA 3.5nm filters: Thoughts so far

Earlier in 2020, after experiencing terrible star halos around Mag 5 and above stars with my Optolong 7nm filters (don't get me wrong, they're value for money but my goals in astrophotography changed) I was thinking that: If i'm gonna spend sleepless nights shooting for the stars, it'd better be worth it. Getting bad data given my harsh light pollution was always an instant put-off.

Thus, I decided to make the jump to Ultra-narrowband filters at a whoppping 3.5nm.

There are many filter makes in this industry, some of which are bloody expensive. As the saying goes "You get what you pay for!", such is true in this field. Rarely do you get really good quality equipment at a super affordable price-and I mean it.

The basic rule of thumb for those who are new to narrowband imaging is: The narrower your bandpass is, the better it is. This essentially makes sure that whatever data that's collected by your sensor is purely signal emitted from the depths of space and not unwanted photons such as light pollution. I had been using 7nm Ha, 6.5nm OIII, 6.5nm SII 1.25 inch Optolong filters with my old QHY 183M. While it worked (and earned my two amatuer astrophotography image of the day), I just wasnt too happy with the Signal-to-Noise-Ratio (SNR) of my images. Not to mention, stray light was already creeping into my subs at 300s exposures!

Just look at the beautiful lamp post nearby

Thus, I decided to upgrade these filters to an even narrower bandpasses.....but I had a problem: Money. The narrower the filters (bandpass), the harder and more intricate it is for these makers to manufacture, plus the demand for these filters are mainly observatories or serious imagers who already probably own $20,000 worth of equipment. Chroma and Astrodon are a couple of filter makers which have earned their reputation in making really good quality filters: such that star halos around even the brightest star are minimal or even absent (Users please chime in here as I've only based this off online reviews!)

What is so attractive about Antlia filters is that they were able to market 3.5nm Narrowband filters at approx. USD 300 a piece- a far cry from USD 600 for 3.5nm filters form Astrodon. There has got to be a catch aint it? I was not willing to spend tons and tons of sleepless nights just for data ruined by my filters, it is just not logical. Hence, I decided to take a leap of faith and bought the entire filter set.

I purchased 36mm unmounted versions of the filters, since I was to install it with my QHYCCD electronic filter wheel. Mo from Astroungu was so kind to have it ship to me direcly from Antlia itself, as the Covid situation was rapidly evolving in Aussie. (Shipping from China to Singapore would end up being faster than compared to shipping from Australia, surprise surprise) The customer service agent, Melisa Liu also kept me in check about the shipping updates. Once again kudos to these wonderful people who have provided me so much support during this period.

If you've read everything up till now, you really deserve a cookie (but seriously, thanks for the attention, I've always aspired to be a product reviewer for magazines)

The filters arrived in a well packed parcel, complete with tons of tape. No one will ever bother ripping it up apart, seriously. It came enclosed in three transparent acrylic boxes with magnetised covers: how cool is that! Opening up the paper wrapper itself revealed the gorgeous cyan, violet and yellow hues of the glass surfaces. They look something like this from the Antlia website, and I mean it quite literally:

Next: installing the unmounted filters! WARNING: The following image contains a cracked filter, it's been 2 months and I still haven't heard from Optolong ever since :(

For those who are interested, these are the postions of the filters

  1. Antlia 3.5nm Ha

  2. Antlia 3.5nm OIII

  3. Antlia 3.5nm SII

  4. Optolong Luminance

  5. Optolong Red (the crack happened during an imaging session, I only discovered it a day after...)

  6. Optolong Green

  7. Optolong Blue

Ever since the installation, there has been nothing but clouds...........typical of every new equipment. However, I managed to grab some data for different targets, via all three Antlia filters.

Note: all images are stacked and calibrated in DeepSkyStacker, with 240s of sub exposures, autostretched in Pixinsight

From left to right: Ha, SII, OIII in NGC 6188

Close up view of SII channel in NGC 6188

Close up view of OIII channel in NGC 6188

OIII in NGC 3576

From left to right: OIII and SII in NGC 3372

Close up view of OIII in NGC 3376

Close up view of OIII in NGC 3376

Verdict? There isn't any halos or ringing around the brighter stars in these few targets, espcially so in the OIII and SII channels. These filters have not yet been properly reviewed, thus I hope that this simple amateur review will kick off more reviews of these filters with other different targets!

My next major project will focus on the Sadr region in the constellation of Cygnus. Of course, any new data collected will be updated here, so watch this space!

Hope you enjoyed this mini review :)

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