Best filter for my field flattener? - Forums

Topic starter

Jul 4, 2020

Hi!
I'm super new to this but I ordered a eqm-35 mount along w/ a WO Z61ii refractor and the field flattener that goes along w it ( https://www.highpointscientific.com/william-optics-adjustable-flat61-for-z61-p-flat61a?utm_source=google&utm_medium=cse&utm_term=WYO-P-FLAT61A&gclid=CjwKCAjwrvv3BRAJEiwAhwOdM2nAviprO-OVv87esl6caU9t98aKYmzzuomUaM5WdK0oM5qwl-PCPxoCWX8QAvD_BwE )

Do 2" filters work with this & which filters do you recommend for someone in a class 9 looking to shoot nebulae?

Thanks all!

matthew.maclean

Jul 4, 2020

Yes, it looks like your Flat61a has a place to screw a 2" filter into if you take the back cap off the flattener (there's a picture of it on the WO site). You might want to note it appears on the WO site that there is an alternate 61r that has a larger FOV and a rotator built in too. It seems like both are made to work with the Z61.

I assume you are planning to use a DSLR? Astro-modified?

Bortle 9 will be difficult (I live under Bortle 7 skies on the rare occasions they aren't covered by clouds...), so you might have to be a bit aggressive with the filtering. It may take some trial and error to discover what works best for you. A number of companies make dual-band, "UHC" style filters that work well. I have a Baader UHC-S which is good for me, but it passes fairly wide bands (around 35nm I think). Sky-tech (Altair) also makes one called "tri-band" that is similar and is good (I have a "clip-in" version of it for Canons). Optolong has one called L-enhance that you might look at (haven't tried it but it is popular). And I just see in looking it up that they are advertising a new one called "L-eXtreme" that has very narrow pass bands (7nm), so it is essentially two narrowband filters put together. https://agenaastro.com/optolong-l-extreme-dual-bandpass-light-pollution-reduction-imaging-filter-2.html
These are a trade-off. The more narrow the band pass, the more they will isolate the nebula content, but the less "natural" the surrounding star colors will probably look.

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psdoty

Topic starter

Jul 4, 2020

Thank you so much for your reply! So I assume the 2" filters have an m48 thread because according to the site, that's what is allowed to be threaded to the flattener
I think this gives a better description. https://williamoptics.com/new-adjustable-flat61-for-z61
Or do I buy specifically an m48 style filter? not too sure

matthew.maclean

Jul 4, 2020

Any standard 2” filter should work fine (they all should use an M48 thread). For whatever reason, they are called 2”-filters even though they aren’t exactly two inches. Agena Astro has a helpful page explaining a lot of the thread nomenclature that might be useful:
https://agenaastro.com/articles/guides/miscellaneous/astronomy-threads-explained.html

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