NEW Optolong 3nm Dual-Band L-Ultimate Light Pollution Filter

[FLO]

The new Optolong 3nm Dual-Band L-Ultimate Light Pollution Filter has been revealed 🙂 

 

[thomasv]

Interesting.

" this filter is not suitable for fast ratio systems ". Wonder if it's possible to quantify this a bit more precisely, what f number should be the limit? I know it's not a hard limit, but what would be still acceptable, is there any guideline?

Thanks.

[Steve Ward]

"Cuiv" has done some great videos recently on filters ... worth a watch ... 😉

 

https://www.youtube.com/c/CuivTheLazyGeek/videos

[Phillyo]

I asked this on Facebook. F4 or slower. 

[900SL]

One wonders which superlative they will use for the successor. The L- Fandabidozo perhaps?

[Adam J]

On 18/08/2022 at 13:15, thomasv said:

Interesting.

" this filter is not suitable for fast ratio systems ". Wonder if it's possible to quantify this a bit more precisely, what f number should be the limit? I know it's not a hard limit, but what would be still acceptable, is there any guideline?

Thanks.

If it's made correctly with the correct centre wavelengths, two of which you need to get right on a duel band filter then it should work down to about F3.5-F4 range. But let's be frank if recent independent testing of optolong L-extreme filters is anything to go by at 7nm then I am going to take some convincing that they are capable of producing an even more precise product as required at 3nm. Given that then personally I would be looking at F5 and higher as it gives more room for error unless and until people prove them at faster F-ratios. 

It's worth remembering that while technology has moved forward until recently only Astrodon and Chroma would attempt 3nm filters at all and those are single wavelength filters. Duel band is much much harder to get right. 

Am sure FLO and others would replace it if something was wrong. But unless you have a spectrometer or some other kind of filter to perform a side by side comparison with it's going to be difficult to know how it's performing. 

Looking at Baader they have been forced into binning their filters into three rather than two bins as pre civs YouTube vid. The reason for that he actually gets a little wrong though. The are not binning as such they will be optimising for three different f-ratio ranges. Basically if you design the filters to work over a narrower range by having three filters bands as opposed to two, the result is that you have gained some tolerance in your centre wavelength as it now no longer has to work from F1.8 all the way to F3.5-4. I also suspect that they will now test individual filters as opposed to testing filter wafers before cutting them up. A sensible solution. 

Adam

Edited August 20, 2022 by Adam J

[FLO]

On 18/08/2022 at 12:18, FLO said:

Introductory price!

Order the new Optolong 3nm Dual-Band L-Ultimate Light Pollution Filter before midnight 20th Sep to save £40 🙂 

One week remaining 🙂 

[Dark Raven]

Shawn Nielson made the review

Some halos apparently still persist on bright stars.

[powerlord]

No one here got theirs and imaging yet ?

I decided to go for it. I also plan to try some relatively silly experiments - like trying it on the asi1600 mono in front of my 6nm Ha and Oiiis... less Ha for sure, but should still get the benefit of 3nm... Obviously main use will be with my OSC cameras and 6D though.

[Adam J]

Halos are on carbon stars, there is probably a harmonic of the two primary wavelengths in the near IR that is causing IR light to be allowed through from deep red carbon stars. The scope will not correct at those wavelengths and so it's very out of focus...so not really a halo as such. 

[Lee_P]

I've got one, just need some clear skies!

[Phillyo]

57 minutes ago, Adam J said:

Halos are on carbon stars, there is probably a harmonic of the two primary wavelengths in the near IR that is causing IR light to be allowed through from deep red carbon stars. The scope will not correct at those wavelengths and so it's very out of focus...so not really a halo as such. 

This happens with the Antlia ALP-T 5nm filter too.

[powerlord]

So I wonder if an IR block filter would stop ? like the built in window on my asi2600

[Adam J]

2 hours ago, powerlord said:

So I wonder if an IR block filter would stop ? like the built in window on my asi2600

It's possible. 

[Lee_P]

There was a brief gap in the clouds last night, which allowed me to get an L-Ultimate subframe to compare with L-Extreme. You can download them here if you're interested: https://drive.google.com/drive/folders/15ikNeCfVpr32ba2F3JtSjYx0WjJ74QO0?usp=sharing

They're just two minute subs, taken from Bortle 8 skies using an Askar 130PHQ. To my eye there's not much difference; the L-Ultimate's stars are perhaps slightly tighter, and the frame a tad cleaner? But really hard to tell. Hopefully the differences will become more evident once I gather more data and make some integrated stacks.

[powerlord]

ooo. will do. i reckon it'd be on something like the oii on the squid where I'd hope to see a difference most obvious ?

stu

[Lee_P]

I'm integrating a decent stack of L-Ultimate data right now, and Askar have sent me a Colour Magic 6nm to test too -- watch this space for a dualband shootout!

[Lee_P]

Screengrab of L-eXtreme (left) and L-Ultimate autostretched data. Eight hours of integration time for each. L-Ultimate looks noticeably cleaner, has tighter stars, no halos, and happily lacks a green gradient that's present in the L-eXtreme data. So far the L-Ultimate is looking like an appreciable upgrade.

[StuartT]

This is all interesting. I have been toying with upgrading my L Extreme to the L Ultimate. The former has given me some very nice results, but the halos are annoying. It would be nice to have a tighter bandpass.

BUT I had exactly the same thoughts as @Adam J - we know Optolong don't have the best quality control there is, but with a 7nm filter you can afford more margin for error. But at 3nm, I'd be very concerned that my filter might miss one (or heaven forbid both) centre lines completely! It would be great to seem some spectroscopy tests, I guess, before parting with this much cash

Edited November 5, 2022 by StuartT

[Adam J]

On 06/10/2022 at 19:18, Lee_P said:

Screengrab of L-eXtreme (left) and L-Ultimate autostretched data. Eight hours of integration time for each. L-Ultimate looks noticeably cleaner, has tighter stars, no halos, and happily lacks a green gradient that's present in the L-eXtreme data. So far the L-Ultimate is looking like an appreciable upgrade.

Honestly I would be keen to split out the blue and green channels as the right image looks very red although I see better ha contrast in the right hand image I am worried that it appears to have less colour variations possibly indicating less OIII signal. Could be processing but a side by side oiii comparison will tell the story.