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Optlong Filters (L-Pro & L-Extreme) at f2.8 - will this work?

Optolong L-eXtreme Optolong L-Pro ZWO ASI533MC Equipment Filters
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Kieran Gunessee avatar
Kieran Gunessee avatar
Hello,

I'm after some guidance and advice as to how the Optlong L-Pro & L-Extreme will perform at f2.8 (if anybody has any experience of course)!

I'm planning to get a Samyang/Rokinon 135mm f2 lens for some widefield astro with my ASI533MC camera and would like to use my existing filters, but I've read conflicting information as to the performance of these filters at fast f-ratios.

On one hand, I've seen some less than ideal results on various forums, but on the other hand I've seen some great results on YouTube & other forum posts with similar setups.

I don't mind stepping up to f4 but I don't want to if I can help it, the extra light at f2.8 would be nice to have!

Thanks in advance.
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andrea tasselli avatar
andrea tasselli avatar
Right off the bat the L-eXtreme won't work well below f/3 but it works well at f/4. Problems are haloes & reduced transmission at f/ ratios below 2.8. L-Pro should work well up to f/2.8. Below that I do not know.
Manuel Peitsch avatar
Manuel Peitsch avatar
I have been testing both L-eXtreme and L-eNhance at f/2.2. As andrea tasselliwrites, the transmission is reduced, i.e. you'll need longer exposures anyway (like loosing 1 or more f-values). The more frustrating part is the level of halos one gets in the blue-green channels. Especially, if your field of view contains bright blue stars, you will have severe halos. While some of it can be removed during post-processing, it is very far from ideal. Therefore, I would opt for another dual-band filter. Incidentally, the Antlia ALP-T dual-band 5nmHighspeed filter I ordered arrived a few minutes ago.  As soon as the sky is clear again, I'll test it to see if the promised improvements are a reality. L-pro is fine indeed, and I have used it extensively with my f/2.2 setup.
Hope this helps.
Manuel
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SemiPro avatar
SemiPro avatar
Kieran Gunessee:
Hello,

I'm after some guidance and advice as to how the Optlong L-Pro & L-Extreme will perform at f2.8 (if anybody has any experience of course)!

I'm planning to get a Samyang/Rokinon 135mm f2 lens for some widefield astro with my ASI533MC camera and would like to use my existing filters, but I've read conflicting information as to the performance of these filters at fast f-ratios.

On one hand, I've seen some less than ideal results on various forums, but on the other hand I've seen some great results on YouTube & other forum posts with similar setups.

I don't mind stepping up to f4 but I don't want to if I can help it, the extra light at f2.8 would be nice to have!

Thanks in advance.

So a few things:

I know you asked about filters but at F2.8 you are going to have to become a grand master of fixing tilt and back focus. It probably won't be crazy-hard with a 1" sensor but if you want nice stars you are going to have to break out the tilt plates, shims, and allen keys. You may even consider shooting a shorter integration at f/4 just for nicer stars.

As mentioned above by @andrea tasselli the L-Pro should be fine. Its got some narrow band passes but not narrow enough to cause any issues.

For narrowband you have a few options: Buy something like the L-Enhance where the band shifting won't be as punishing with a wider band pass, or go for something like this: https://www.ontariotelescope.com/db5nm-hs2.html
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