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AT72EDII + 0.65X APEX?

Astro-Tech AT72EDII ZWO ASI533MC Pro Reducer Acquisition Deep Sky
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Phil Creed avatar
Phil Creed avatar
Anyone use the SHORT version of the Starizona APEX-0.65X? (the APEX-S) with an AT72EDII?

I've periodically given thought to replacing my AT60+0.8X with an AT72EDII (or equivalent) + 0.65X APEX-S.

Virtually the same focal length between these setups, with my existing 288mm @ f/4.8 vs. 281mm @ f/3.9.

Why entertain this idea?  Because…f/3.9.  That's pretty fast, and 2.3° x 2.3° with my ASI 533MC-Pro.  I'd get the same in 2 hours at f/3.9 as what I'd get in 3 hours at f/4.8.  That may not much for many of y'all, but giving my horrible NE Ohio weather and family+work commitments, time is more of an adversary than a luxury.

But I have not come across ANYONE who's done this, and don't care to run an expensive capability test.

So…anyone done this?

Clear Skies,
Phil
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Jeff Horn avatar
Jeff Horn avatar
SemiPro avatar
SemiPro avatar
At F/3.9 prepare to adjust back focus and tilt. Like, a lot. Can it do what you want it to do? Yeah most likely. You just need to be prepared to fine tune it. I  can not stress this enough. Tiny, almost unnoticeable star defects you see at F/4.8 will look like you are going to light-speed at F/3.9.

There is something to be said for vignetting, but with a 1" sensor I don't think that is an issue for you.

I would search around on astrobin for people using the ApexED-S and check out their images.
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Phil Creed avatar
Phil Creed avatar
I'm wondering if what I should do is get an APEX-S and then test it out on my AT60.   I'd get the same f/3.9 light cone I'd get if paired with the AT72ED-II, just with 234mm vs. 281mm focal length.

That way I'll at least know what I'm getting into before swapping the AT60 for the AT72ED-II.  What I don't want to do is part with both the AT60 and 0.8X for the unknown combo of AT72ED-II + 0.65X all at once.

It's tough for me to resist a (relatively…) affordable sub-f/4 with a refractor for imaging purposes.

Clear Skies,
Phil
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SemiPro avatar
SemiPro avatar
Phil Creed:
I'm wondering if what I should do is get an APEX-S and then test it out on my AT60.   I'd get the same f/3.9 light cone I'd get if paired with the AT72ED-II, just with 234mm vs. 281mm focal length.

That way I'll at least know what I'm getting into before swapping the AT60 for the AT72ED-II.  What I don't want to do is part with both the AT60 and 0.8X for the unknown combo of AT72ED-II + 0.65X all at once.

It's tough for me to resist a (relatively...) affordable sub-f/4 with a refractor for imaging purposes.

Clear Skies,
Phil

https://www.astrobin.com/h4t1r8/H/?q=ApexED-S&camera=
https://www.astrobin.com/fvdstw/C/?q=ApexED-S&camera=
https://www.astrobin.com/eu8s7n/?q=ApexED-S&camera=

Its tough to say because there are not a lot of people who use this on Astrobin it seems. These are the best I could find. What we are looking at here are the star shapes in the corners. They are certainly alright, and the perfectionist in me says that any defects are a result of of improper tilt or back focus adjustment just based on what I have seen from the more prevalent ApexED-L. I could be wrong though.

If you are going to go down then route then I do think testing the reducer first makes sense. Maybe you find you don't like the stars, or maybe ripping your hair out trying to adjust tilt and all that is not for you. As someone who deals in fast focal ratio there are definitely times where I wanted to see how far I could throw my telescope

Either way, better to just have to deal with potentially selling or returning the reducer than having to re-buy your current setup.
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