Is My L-Extreme Genuine ?

[Millsy]

Ok so I bought an L-Extreme duo band filter secondhand.
To be honest I expected more. It was ok but I dont see much difference than I did with my Zwo Duo Band.

I was expecting the earth to move and wow to come next but it didn't happen. Now all this has left me with that feeling of, did I get duped ??

It looks easy enough to do, screw out the retainer ring and pop in inferior glass but how do you know ??

Is there a way to test my little shiny circle of mirrored glass or is there some teltail marking I can see that will at least put my mind to rest ??

[bojan]

You have to use spectrometer (a simple one made with cheap diffraction grating (100 l/mm) will do the job) and BASS Project s/w (https://groups.io/g/BassSpectro)...
By comparing the published and obtained transmission curves you can put your mind to the rest (or not).
The process is partly described here (https://www.iceinspace.com.au/forum/showthread.php?t=153419&highlight=Rocolax&page=2) .

[Millsy]

Thx Bojan
Appreciate the reply.

[JA]

Hi M,

Looking at the transmission curves , roughly lined up below, you can see that the transmission in both Ha & OIII is similar for both filters at around 90%, with the ZWO having a much broader OIII bandwidth and a slightly wider Ha bandwidth. Depending on your local sky conditions (light pollution) and the spectrum of emissions from the target you might not notice that much difference.

Where there is sometimes some differences seen between filters is in halo effects, especially noticeable around bright stars/objects which are related to coatings and optical precision of surfaces.

You could only really know if there are differences with a true back to back comparison of the filters on the same night, same object using the same gear. Of course, as Bojan suggested (Hi Bojan), you could always try to test the transmission spectrum for the filter using spectral analysis gear.

Best
JA

[bojan]

Something like this (https://www.ebay.com.au/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=gemology+spectroscope&_sacat=0) may help...

[Startrek]

I started using OSC Dualband filters just over 3 years ago with my ZWO2600MC under both Bortle 8 Sydney skies and South coast NSW dark skies Bortle 3
Bought the ZWO Duoband ( Ha 15nm and Oiii 35nm ) and used it for 9 months with mixed results , no so good under Sydney skies
Then upgraded to the L Extreme ( Ha 7nm and Oiii 7nm ) which resulted in a significant improvement overall from the ZWO , but with halos around the larger stars
Last year I upgraded to the Antlia ALPT OSC Dualband golden filter ( Ha 5nm and Oiii 5nm ) and it’s been a game changer especially in heavy light polluted Sydney skies . Work’s unbelievable well too in dark skies

To answer your question, yes the L Extreme should make a significant improvement to the ZWO Duoband under all types of skies , at least that’s my personal experience
I image with Newts from 900mm to 1280mm focal length

Hope the above helps

Cheers
Martin

[Millsy]

Thank you for the link and feed back. Very much appreciated.

[ChrisV]

I started with the STC duo band, and then went to an optolong l-extreme (but haven't gone to the more recent 3nm bandpass type duo filters). It was a big improvement. I noticed two things that improved my images.

1. The Ha versus OIII (on the R versus BG splits) differed to each other alot more with the l-extreme. So they were separating better.
2. But the main thing was that the noise on the OIII (and the Ha, but this signal is usually large) was a heck of a lot less due to the narrower bandpass.

I can't show anything to prove this as I slacked off and stopped putting up my images on astrobin about the same time I swapped to the l-extreme. So all very subjective ... but I believe it, and you have to believe something