What focuser do you use with the C8 Edge HD ?

I am using a Moonlight Focuser.  The celestron reducer actually fits inside the focuser making back focus easy to manage.   If you intend on using an OAG it gets a little tricky on the 8 inch and  you need a thin OAG to pull it off but I am currently using that setup when I don't have the Hyperstar on.

Hi, I’m using the Moonlite focuser  specific for the Edge HD 8. The reducer fits up inside the focuser and this gives you the distance you need. It’s a great design. The Moonlite website is Focuser.com and you can find more details there or you can call and Ron (who is awesome) can walk you through it. I get great autofocus curves so I believe the mechanics are  spot-on.  The one trade off is weight, so check your total weight capacity. You might also have to get a small accessory  counter weight to add to the front of your mounting rail to get balanced in Dec.
I also use the ZWO filter wheel and OAG so I  know there is enough back focus !
One last thing, with this setup you just lock down the rear mirror and no more flop ! I get the same focus HFR before and after a meridian flip.
Best of luck and please let me know how it all turns out for you.
CS
Bob

I have the same setup as Bob. Edge HD 8, Moonlite focuser, ZWO OAG, ZWO EFW, and an ASI1600mm. I use this configuration both with and without the Celestron 0.7 focal reducer. With the 0.7 FR installed, back focus is within 2mm using the 1/4" spacer that comes with the focuser when the focuser is at the center of it's travel. If I remove the 0.7 FR I take out the spacer and again within 1 or 2mm. Works perfectly.

I focus at the start of the night by setting the focuser to the middle of it's travel and focus with the focus knob and a bahtinov mask, making sure that I end with a counter clockwise rotation of the knob (VERY IMPORTANT). Then lock the mirror. From there on the focuser does the rest. Easy peasy.

Happy to answer any questions you may have.

Best.
Tim

Rodolphe:

The Moonlite focuser consumes between 36.195mm and 49.276mm of back focus from the minimum to the maximum of its travel.  The travel is 13.081mm.  This is with the Celestron 0.7 Focal Reducer installed.  So, with the focal reducer, my imaging train is configured as follows:

Moonlite focuser - 42.7355mm (middle of the travel range)
Extension tube 1/4" (comes with focuser) - 6.35mm
ZWO OAG - 16mm
ZWO Camera adapter ring - 11mm (the black ring that came with your ASI1600 camera. I moved it to the other side of the EFW to help minimize vignetting)
ZWO EFW - 20mm
ZWO ASI1600mm - 6.5mm
Total back focus - 102.5585mm

The additional 3 are taken up in the travel of the focuser.

For use without the focal reducer, Moonlite includes a spacer that is inserted into the focuser in place of the focal reducer.  This spacer consumes an additional 32.04mm of back focus.  So, without the focal reducer, my imaging train is:

Moonlite spacer - 32.04mm
Moonlite focuser - 42.7355mm (middle of the travel range)
Extension tube 1/4" (comes with focuser) - 6.35mm
ZWO OAG - 16mm
ZWO Camera adapter ring - 11mm
ZWO EFW - 20mm
ZWO ASI1600mm - 6.5mm
Total back focus - 134.6255mm

The 1.3mm is taken from the travel of the focuser

The Celestron documentation says the back focus should be 105mm with and 133.35mm without the focal reducer.  When I first began imaging, I set the travel on the focuser to perfectly hit those numbers before doing my first focus of the night.  I did this by calculating the length needed in the travel and, knowing the step size from the motor as 0.00016" = 0.0041mm, calculated the number of steps to bring me to the exact length and set the focuser to that position before the initial focus.  In truth, now I'm lazy and I simply set the focuser to the middle of the travel for both.  Honestly, I can't see any difference.  I'm not sure that 1 or 2 mm is that impactful, but that is just my experience.  I would encourage you to experiment with your imaging train.

I hope you find that helpful.
Tim.

Hi  Tim
Many thanks for your explanations.
I just received the focuser and wait for a favorable night to test.
Will report back here afterwards.
Thanks again
Rodolphe

Celestron Focus Motor.

I was too cheap to get the ZWO EAF. Hehe. I wish now that I had. I hate the Celestron. CS & GB! Kip

After conversing with the owner of Moonlite I found out the only truly EdgeHD 8 compatible focuser Moonlite makes that fits the 8 with a Celestron 0.7x Focal Reducer is a custom made to order unit that is not available on their website. It costs ~$2300 USD plus shipping and must be ordered via email/phone. The focuser issues with the EdgeHD8 (mirror flop, alignment/binding, non-repeatability) is a frustration I have dealt with for three plus years until I recently switched to a refractor/EAF combo.

I hope to one day use my EdgeHD8 in f/10 mode and just deal with the it's focuser quirks. I would rather use a ZWO EAF because it has finer focus than the ill fitting Celestron unit. The Pegasus EAF has twice the refinement of the ZWO unit.

Search here on AB for an EdgeHD8 with a Moonlight…it'll tell you everything you want to know. They are as rare as a unicorn due to the notoriously tight back focus limits - most folks using Edge's use a 9.25 or bigger. Most are using 11's. Combine $2300 bucks and the money you could make selling an 8 would make a huge dent in the cost of the more common and effective EdgeHD11 that a Moonlite would work so much better.

CS & GB!

I'm using the ZWO EAF paired with a Celestron OAG and ASI174MM mini for my EdgeHD 8. I've been very happy with how everything performs and it's very easy to go back and forth between F7 and F10.