Need advice on super-portable frac

[Stu]

26 minutes ago, Louis D said:

It took some fiddling to get it to work.  Technically, it should just insert up into the focuser tube and not change back-focus, but the AT72ED focuser's baffling is narrower than the normal 2" opening, so even my 2" diagonal doesn't insert all the way in.  For the specifics of my setup:

This particular FF is M48 threaded on both ends and does not change the focal length, so the focus point doesn't change.  Since it needs about 128mm of backfocus for the 72ED scopes, I put it on the front of my 2" diagonal's filter threads.  However, this proved to be a bit too much and resulted in overcorrection.  Because I have a GSO 2" star diagonal with SCT threads on the input barrel side, I was able to get a SCT to M48 adapter from Agena Astro that replaces the front barrel.  I then screw the 15mm extension that came with the field flattener into the M48 threads of the adapter and then thread the flattener in to the extension.  It's not quite perfect, but it's darn close.  It does require another 20mm or so of back-focus over the GSO diagonal alone.  If your focuser allows 2" tubes to be inserted into it without limitation, there won't be any change to your back-focus.

The spacing between the FF and the eyepiece fieldstop must remain constant across eyepieces, so you'll need to parfocalize your eyepieces for best correction.  Most of my eyepieces have the fieldstop at, or very close, to the shoulder, so this isn't much of an issue.

That's really great info Louis! Well worth bearing in mind if I get another fast frac. Thanks!

[Louis D]

Just now, Stu said:

That's really great info Louis! Well worth bearing in mind if I get another fast frac. Thanks!

It's sort of like adding a coma corrector to a Newt.  Once you see what's possible in field correction, you can't imagine how you lived without it.

[Chris]

it does sound very handy, only made more complex by the specifics of your particular scope. 

I wonder how the overall cost and ease stacks up against similar sized Quad refractrors? This might be an interesting debate in it's own right for another time.

[BGazing]

Splashed on a 71FL Borg. YOLO. 

DSV-M mount incoming...and will find some decent photo tripod. 

Any suggestions re eyepieces? I have none i shorter FLs, ES 82 are fairly cheap atm.

[iPeace]

5 hours ago, BGazing said:

Splashed on a 71FL Borg. YOLO. 

DSV-M mount incoming...and will find some decent photo tripod. 

Any suggestions re eyepieces? I have none i shorter FLs, ES 82 are fairly cheap atm.

Carpe Diem

[BGazing]

Well, a little update.

What a lovely little scope. It weighs nothing. Feathertouch focuser is such a delight, really makes me wonder whether I should replace stock C8 focuser with a FTF one.

Pinpoint stars and some FC (as is to be expected), but also short focal length exposes budget EPs more than those a tad better. Only tried it with ES 24 (68 deg) and Synta gold 15mm so far (ES 4.7 and 8.8 82 deg will arrive soon). Double cluster and Pleiades looked awesome. Both me and my friend spent more time looking through it than the C8 and his newton, such a fun thing to use. Both of us even saw (or rather, we imagined seeing) some hint of something...nebulosity perhaps, around some of the Pleiades stars. But the sky was, I think, not good enough for that. Still makes me wonder if we suffered a joint hallucination or autosuggestion.

[iPeace]

Pictures!

[BGazing]

Here it is...

[iPeace]

39 minutes ago, BGazing said:

Here it is...

Excellent.