Antlia ALP-T

Formats

  • 2″ Mounted (48mm thread)

Spectral Transmission

Yellow line is published transmission. Color fill is my independent verification with the filter I tested.

Physical Characteristics of 2″ Filter

  • Filter mount thickness: above threads: 5.02mm; including threads: 7.2mm
  • 48mm threads with 0.75mm spacing
  • Minimal knurling only on top
  • Dual bandpass narrowband filter
  • Inner retaining ring does have notches for easy filter disassembly with a spanner
  • Width of the glass filter without the filter mount is 46.46mm

Real World Tests

Bortle 8, Stock Canon T7, 464mm f.l., f/5.4, ISO3200, 36 min. integration (6*6″). Open full-size image in new tab.
Bortle 8, Full Spectrum Modified Canon 60D, 464mm f.l., f/5.4, ISO3200, 36 min. integration (6*6″). Open full-size image in new tab.

Comparisons to No Filter

Before Image After Image
Stock Canon T7 - No filter vs. Antlia ALP-T

Before Image After Image
Full Spectrum Canon 60D - No filter vs. Antlia ALP-T

Bortle 4 Comparison to Astronomik L2 Luminance Filter

Before Image After Image
Full Spectrum Canon 60D - Astronomik L2 vs. Antlia ALP-T - Bortle 4

Reader Rating10 Votes
75
Pros
5nm bandpasses provide excellent contrast and tight stars
No halos on bright stars
Published transmission very close to my measurements
Cons
Expensive
Currently only available in 2" format
95
Purchase from:
  1. Hi Nico,

    The top two images for the Antlia ALP-T both have the same caption, “Bortle 8, Full Spectrum Modified Canon 60D, 464mm f.l., f/5.4, ISO3200, 36 min. integration.” Should one of them be for the stock Canon T7? (The total integration time is the same but the exposure time/number of exposures is different.)

  2. I’m sorry if I missed this, Nico, but is there a list of criteria you use to score the filters, and is the scoring for each filter available? (I’m sure you mentioned this, but I can’t find it.) I thought this might help me (or others) decide on a particular filter based on those criteria that are most applicable.

    1. Ha, good point. No, I’ve never published the criteria I use, but I should find a place to add that somewhere. Thanks for keeping me on my toes. This WordPress theme came with the ability to give my reviews scores, so I thought I might as well. My criteria breakdown is: 70 pts. performance (based on the constraints of filter type: light pollution, narrowband, etc.), 10 pts. value/cost, 5 pts. formats available, and 5 pts. physical characteristics/packaging. So for this filter. My score breakdown is 69 on performance (1 pt. off for possibly slightly lower [OIII] transmission than advertised), 10 on value, 1 on formats, and 5 on physical/packaging. It mostly lost points just because it’s only available in 2″ format and not 1.25″ or clip-in. I did list ‘expensive’ as a con, but honestly the value of this filter is still amazing if you look at the competition, so I didn’t take points off there.

      1. Great! Thanks so much for taking the time to explain, Nico. That’s a big help to get a sense of where the others’ lost points as well. Very helpful!! Thank you again.

  3. Does the ALT-P filter need to be installed in a specific direction? If so what would be that direction? Gold side towards what?

      1. ok thanks, that’s how I have it too since its the only way I can have it in ZWO filter drawer. Antlia did tell me direction doesn’t matter, but I also found a post by them in 2020 saying their Ha and Oiii filters should have gold side to scope, which seems odd to have directionality concerns with their Ha or Oiii filters, but not having it with a dual narrowband filter.

  4. Does it really matter going to a low Bortle zone with the availability of these filters?
    What’s the advantage?
    if theres is one, which filter would be best?
    I have a trip coming up to a Bortle 3 zone. I just don’t know if it’s worth it!!

    1. Hi Rafael,
      I wouldn’t suggest doing just filtered exposures from a Bortle 3, but mixing exposures from one of these filters and unfiltered (or IR-Cut) exposures can give you the best of both worlds and get a nice result quicker. The dual narrowband filter will give you much higher contrast and detail on the nebula and without filter will give you good star color and reflection nebula (if there are any in the scene). I wouldn’t say that one filter is particularly better than the other when it comes to Bortle 3. Personally, I’d probably just go with the L-eNhance since it’s the cheapest of the three I looked at.
      Nico

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Final Score