So, it's been a month since I updated this thread on my saga.
Scope 1: WO Z73 - had star issue, sent back for refund in Jan.
Scope 2: WO Z73 - same issue, lesser degree (I couldn't believe it!), sent back for refund in Feb.
I worked with the second vendor and provided images. I sent the images to WO for evaluation. The vendor asked me to mask the front of the scope. I 3d printed printed two masks. One had a 76mm hole and the other had a 66mm hole. Front of scope was 86mm across at the dew shield. I repeated taking images on a clear night. No mask... slight inverse diffraction spikes, 76mm mask...less inverse diffraction spikes, 66mm mask. I asked about loosening the screws a 1/4 turn to relieve pressure but the images with the masks lead the vendor to believe it wasn't overly tight lens. I was still on the fence but wouldn't do it without instruction.
I sent the scope #2 back to the vendor for a full refund. Since they were out of WO73s and I didn't want to wait on back order I decided to get something different. Fool me once... fool me twice, I didn't want to waste another month trying again.
Scope 3: Astro-Tech AT72EDii arrive mid-Feb.
Scope arrived a few days later. First night out... I can see no hint of the inverse diffraction spikes. You know I was really looking hard too! The WO Flat73a fits the Astro-Tech so that was a plus. I didn't have to sell it on a classified a lose a few bucks.
Edit: William Optics Zenithstar 73 vs. Astro-Tech AT72EDii
I thought I'd share a few things I noted between the two scopes since over the past two months I've become more than familiar with them. I'm by no means an expert and this is only my second telescope but other newbies might find this useful when making their decision on a wide field refractor.
- Both arrived quickly from the various sellers. Both were double boxed in thick cardboard and had ample thick closed cell foam protects the good stuff.
- Both scopes are similar in size and weight. Powder coating and anodizing on both is excellent.
- Threads where the field flattener screws in were smooth on both scopes. They're also the same as I'm using the WO FLAT73A with my new AT72EDii.
- AT72EDii is $150 cheaper. That may be important for some. It's apparent in some of the extras that come with the WO73.
- WO73 came with a set of 50mm adjustable guide scope rings.
- WO73 came with a handle that could be added to the top of the main rings (if they were slid apart). The handle is a nice touch but moving the rings apart a couple inches makes the scope less packable.
- WO73 has a thumb screw lock for the extendable dew shield
- Both have a nice extendable dew shield lined with felt so it slides in/out smoothly and maintains position easily.
- The dovetail under the AT72EDii is shorter at 6" or 150mm long. I don't recall exactly but I'd estimate it was either 7" or 7.5" long (177mm or 190mm).
- Not signficant (for me at least) because you might need risers and a longer dovetail to get a proper balance with a camera hanging off the back.
- I bought a 9" dovetail and it looks to be the perfect length. I 3d printed a 20mm riser block to put between the scope rings and dovetail.
- The dual speed focuser on the AT72EDii comes with a push on plastic cover vs. the WO73 has a screw on aluminum cover.
- I actually prefer the push on since I trouble threading the alumunium one in the dark. Those threads were super fine.
- Both have 10:1 dual speed rack and pinion focusers.
- 2.5" for the WO73 and 2" for the AT72. I can't notice a difference visually but that's what the websites say.
- Both very smooth and a dream to focus. I don't know how I'm going to enjoy focusing the SCT ever again!
- The WO73 has their built in Bahtinov mask. I really liked that feature. It was handy for storage being right in the cap.
- I wish all manufacturers had this but it's probably patented by WO.
- Both scopes accept 2" eye pieces and have a nice attachment for them.
- Both scopes have FPL-53 glass.
- No spurious color halos or fringing.
- Both produce excellent flat images (when paired with the flattener).
Well, that's my informal review after spending a couple nights with the AT72EDii and a couple months with the WO73. Even though the AT72 is cheaper.. that's largely made up for with some of the extras that WO includes. For me there essentially equal in cost performance and I definitely would have stuck with the WO73 if I didn't have the optical issue around the stars. That said... I think I'll be perfectly happy imaging with my new Astro-Tech. Hopefully, this is one that I'll pass on to the kids one day.
Edited by psuaero, 27 February 2020 - 02:28 PM.