Does anyone know what the “back focus” distance is for these reducers? What’s
the proper distance from the male threads to the focal plane? Or don’t I
understand how they work/should be connected? Starizona’s SCT Corrector II
specifies a 90.3mm +/- 2mm. My EFW to ASI1600 sensor back focus is 37.5mm.
Means I’d need a ~2” adapter for the Starizona. But the Antares/Celestron/Meade
f6.3 reducer doesn’t say anywhere I’ve found.
Mike McDonald
mikemac@xxxxxxxxxxx
On Jun 2, 2019, at 4:09 PM, Jim Sellers <jsellersaz@xxxxxxxxx> wrote:
Mike, one experiment you my try is using a different focal reducer. I have a
Meade and Celestron f6.3 reducer/flattener. Both will fit directly to the
visual back threads of a Celestron telescope. I also have a Starfield 0.8x
reducer/flattener with a 2” / 48mm internal female thread on one end and a
42mm external male thread on the other end. Your welcome to borrow them if
you would like to see if they impact vignetting?
- Jim Sellers
Sent from my iPhone
On Jun 2, 2019, at 3:38 PM, Michael McDonald <mikemac@xxxxxxxxxxx> wrote:--
I went to find the specs for my Antares f6.3 reducer. They’re hard to find.
But I found one spot where it claims the reducer has a 1.5” image circle.
That should more than cover my 21mm diameter of my image sensor. So I’m not
sure why I’m getting such severe vignetting.
I don’t know if the spacing between the components of my image train are
correct. (I don’t even know how I hooked it all up for that test!) I’m
wondering the vignetting could be caused by either the tube connecting the
reducer to the EFW or maybe the filters themselves. I doubt the latter as
that spacing is the same as I always use it.
I don’t know how to determine if it’s the tube (Celestron #93633-A).
I’m open to experiments that might help me determine where the problem is.
Mike McDonald
mikemac@xxxxxxxxxxx
On Jun 1, 2019, at 2:47 PM, Michael McDonald <mikemac@xxxxxxxxxxx> wrote:
Hmm, I thought coma would exhibit as a radial effect. The stars on the left
side look like that could be the case. But the ones on the right look like
they’re more vertically oriented. Could it be collimation? Or a combo of
the two? Bad enough polar alignment so that rotation is showing up?
Operator error? Equipment mismatch? Lots and lots of possibilities. :-(
My reducer/“corrector” bites! If you don’t remember (and no reason you
should), it gives me images like this:
http://www.mikemac.com/Astrophotos/M42_L_2019-03-22_20_Bin3x3_60s_reducer.png
I wish I could find one that was 0.5X and would cover my ASI1600’s
17.6mmX13.3mm surface. That would give me an effective focal length of
around 700-800mm. And that would open up a lot of other targets! A
Hyperstar’s 290mm is way too wide. Plus I’d have to get a color camera.
Kaching!
Mike McDonald
mikemac@xxxxxxxxxxx
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