Filter slides

[Mokusatsu]

I'm thinking of getting a 2" filter slide, something like the Moonlite one, to pair with my 20" Skywatcher Dob. Ideally one with a dew heater element built in.

https://focuser.com/products/focusers/crayfords/filterslide/filterslideA.jpg

Does anyone have any recommendations? Are there any local suppliers or is ordering direct from Moonlite (or others) in the US the only option?

[gaseous]

I can't offer any advice sorry, but I'd be interested to hear if you have any success as I've got the same scope.

I looked at a filter slider like these (as the "outside" mounted slider I have won't allow me to reach focus), but I thought it'd clash with either the spider vane or the inside of the curved focuser mounting plate.

Also, I assume you'd either have to use it without the light shroud, or be putting your hands through the spider vanes to slide it.


Good luck!

[astro744]

There is also Astrocrumb. See http://www.astrocrumb.com

[gaseous]

Yeah, the Astrocrumbs sure are a nice looking unit. Unfortunately, for some reason Skywatcher have placed the spider vanes in such a way that one of them is directly above the focuser draw tube, so any filter slider would need to run at 90° to the Astrocrumb images.

[Mokusatsu]

I exchanged some emails with the astrocrumb guy, who quickly pointed out that as the Skywatcher spider lines up with the focuser a slide cannot be used.

Probably the easiest mod would be to move the plate that the focuser is installed on just enough to clear the spider vanes. We'd need to drill four new holes, tap a thread into them, and cut a new notch in the eyepiece plate to clear the spider vain. Only question is whether I could do it with the required degree of precision. It's not like I can stick that whole thing in a drill press vice.

Is this something a machinist would be equipped to do?

Edit: on further consideration, it shouldn't be a difficult thing to do, a jig could be built to facilitate precise hole drilling, and cutting out the notch would be 15 minutes with my Dremel. :)

I'll continue to exchange emails with Astrocrumb guy, and see if we can figure out a technical solution.

Any other 20" Skywatcher owners interested in a purchase if we figure it out, i.e. for group buy purposes?

[Allan]

I faced the same issue on a previous Orion dob. The fix is quite easy by rotating the spider veins 45 degrees in orientation. That gets them clear of the focuser so you can install the filter slide under the focuser.

I have the Moonlite slider on my dobs. It is a high quality machined aluminium and black anodised slider. The Astrocrumb is a timber slider. It is nice but not anywhere near the quality of the Moonlite.

[gaseous]

Looking at my UCA here, and I'm not exactly sure how you can rotate the spider vanes to make this work, unless you can rotate them yet keep the secondary mirror in the same orientation somehow. Otherwise if you rotate the spiders, you'll be rotating the secondary as well, which'll put everything out. Same goes for slightly shifting the position of the focuser mounting plate so the focuser clears the spider - you'd also have to slightly rotate the secondary mirror somehow, while not moving the spider, to keep the optics aligned. Or am I missing something simple?

[gaseous]

Actually it seems like the secondary could be possibly rotated and refixed in position with the locking nut, so it may be feasible if you feel like cutting into metal to rotate the spider - bit beyond my skillset judging by all the areas that seem to need adjusting.

[aperturefever]

I have been using the Astrocrumb for years now. Works a charm and the woodwork on the storage box is sensational. Highly recommended.

[gaseous]

Mokusatsu, did you end up having any success with your filter slider venture?

[gaseous]

Mokusatsu, I've found that a 4 position 2" external filter slide will reach focus in a 20" skywatcher dob with the lens of a GSO coma corrector screwed into the end of it. No chance with the lens from a Baader MPCC though.