UV/IR filter (L-Pro or Astronomik L-3) + L-Extreme in the same optical train

Optolong L-Pro Optolong L-eXtreme ZWO ASI533MC Pro Equipment Broadband Deep Sky Help Needed
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Frank "Voloire" avatar
Frank "Voloire" avatar

Since I have an ASI 533MC Pro without any UV/IR filter, I was thinking of permanently mounting an Optolong L-Pro filter in the dedicated thread of an ASKAR SQA55 (Petzval design). I would then also use a ZWO filter drawer in the optical train to sometimes insert an Optolong L-Extreme filter when I need dual narrowband, or leave the drawer empty when I want to do pure broadband. Will this setup work? I also have an Astronomik L-3 filter, and I'm under a bortle 4 sky.

Happy new year and thank you!

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Doug Crowe avatar
Doug Crowe avatar

Not sure why you would want extra glass in your image train? If you have a filter drawer, wouldn’t it be just as easy to have a couple extra sliders and use a single filter depending on your target? Just my opinion.

Frank "Voloire" avatar
Frank "Voloire" avatar

Hey, thank you for taking the time. My biggest concern in swapping filters (I do it all the time) are basically the flats.
Since I have always the need of an UV/IR filter since the 533 get just a AR glass I was thinking to reduce the possibility of introducing dust mote and stuff while swapping the filters and then crushing into a "flat drama" so to speak :-)
But I got your point and it make sense to me.

CS

Rick Veregin avatar
Rick Veregin avatar

With the L-Pro there you will lose something like 5% to 10% of the light in Ha and OIII compared to use the L-eXtreme alone. The L-Pro also is not particularly great with halos and reflections, so doubling up filters is not the best idea, you may get reflections between them.

I know it is more expensive, but a filter wheel is a wonderful option. With the drawer option you probably want to have each filter in a separate drawer so you can easily slide them in and out quickly, with many filters this gets expensive too. Taking the time to unscrew and screw in filters increases the risk of dust and dropping them in the dark, etc.

If you ever think you want to expand your range of filters, for example the L-eNhance is an option I use as a strong LP filter, while the L-Ultimate is best for pure NB targets, or if you want to try SO sometime, which I do. So after using drawers I got a filter wheel and love it. Like you I hate doing flats: with the filter wheel get everything pristine once and then it stays that way. As I virtually never take my train apart, I have used wheel for 6 months and four filters so far and have never yet had to retake flats. It is so easy.

Rick

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Frank "Voloire" avatar
Frank "Voloire" avatar

Rick Veregin · Jan 6, 2026, 04:07 PM

With the L-Pro there you will lose something like 5% to 10% of the light in Ha and OIII compared to use the L-eXtreme alone. The L-Pro also is not particularly great with halos and reflections, so doubling up filters is not the best idea, you may get reflections between them.

I know it is more expensive, but a filter wheel is a wonderful option. With the drawer option you probably want to have each filter in a separate drawer so you can easily slide them in and out quickly, with many filters this gets expensive too. Taking the time to unscrew and screw in filters increases the risk of dust and dropping them in the dark, etc.

If you ever think you want to expand your range of filters, for example the L-eNhance is an option I use as a strong LP filter, while the L-Ultimate is best for pure NB targets, or if you want to try SO sometime, which I do. So after using drawers I got a filter wheel and love it. Like you I hate doing flats: with the filter wheel get everything pristine once and then it stays that way. As I virtually never take my train apart, I have used wheel for 6 months and four filters so far and have never yet had to retake flats. It is so easy.

Rick

Yop, I already use a wheel for the other scope even with the 2600mc: no-filter, l-qef and l-ultimate :-) On this other rig was thinking about a shortcut, but hey everyone of you is completely right. Dropped the “idea” :-) Manually switching and call it a day! Thanks for taking the time to answer everyone.

CS

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Armin Lukas avatar
Armin Lukas avatar

Under B4 sky, is there really an improvement with the L-pro filter? I think leaving the UV/IR filter in the image train and use the l-extreme for duo narrowband should be a good option. But there is some loss due on more glass in the optics.

The better option would be like Rick mentioned, to use a filter wheel.

CS

Armin

Guillermo (Guy) Yanez avatar
Guillermo (Guy) Yanez avatar

Hi. I own an SVBONY filter drawer that comes with two drawers right out of the box. You may order an additional one and have your three filters easily interchangeable. That said, you will need to get new flats after any filter change. The filter wheel that someone already mentioned may also be a great idea, even if it is a manual wheel (those are cheap). For me, the filter drawer works great.

Under Bortle 4, I would try the Astronomik L‑3, as I do not see any advantage in using the L‑Pro over the L‑3 under such dark skies. You could still compare both and see what works best for you. Broadband Optolong filters are great but may introduce halos in your images. Try the L‑eXtreme when imaging nebulas.

I would not recommend using two filters at a time, as there are always reflections that may cause more halos and distortions, and you will also sacrifice a certain amount of light‑gathering power by going that route.

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