Re: Recent encoder discussion on CN


dvjbaja
 

Some thoughts on small, portable mounts.  The ultimate in portability and load carrying capability is the Rainbow Astro RST-135.  Not inexpensive, but innovative with lots of potential.  For short focus telescopes the odd periodic error curve from the harmonic drive is correctable with a small, separate guidescope.  Can be run in EQ, or Alt-az configurations.  I love alt-az for the convenience of operation, eyepiece placement, and the lack of the dreaded mount flip. It would carry a Stowaway with little effort and most likely a 130 f/6.  Another to consider is Rowan Astronomy Atl-az, which has all the machinist qualities of an Astro-Physics Mach 1, but in an Alt-az package for visual.  Soon to be motorized! It's actually about the size of an AP 400.   I love my AP gear, but look around, there are some very high quality products out there as alternatives as Roland and company consider their next offering.  

 BTW, as an American, I absolutely hate the flood of cheap Chinese mounts, telescopes, and CMOS astro-cameras on the US market.  They are good mounts and cameras overall plus very affordable for folks getting started. It would seem our American companies have had to counter the flood and go the high end premium route to maintain market share and profitability. As someone who has managed a $6B portfolio of desktop PC's across all price points, I understand this well.  It's a complex world.  

-jg


On Fri, Feb 26, 2021 at 5:34 AM weihaowang <whwang@...> wrote:
On Fri, Feb 26, 2021 at 11:16 AM, Roland Christen wrote:
If we ever decide to design a smaller portable mount, what would be most desirable? What's missing in the panoply of mounts today? Before you answer, I have in my right hand a 400 mount that weighs 12lb without the base. It has a precision gear set and can be fitted with absolute encoders that would allow it to track at sub-arc sec levels. I daresay that this mount can easily swing a C11 or a 140 refractor. Is there a reason for such an animal?

I love to see a portable mount from Astro-Physics. However, before you go ahead and design one, you may want to ask what kind of portability you are aiming at.

Portable with a car? Then I think Mach2 fits it nicely. Mach1 is even better I suppose, but there is a tradeoff in payload.

Portable for air travel? Then Mach2 is too heavy for that for most people. Even Mach1 may be too heavy. I think a compact design with 20lb of weight (including base and counterweight shaft) would be desirable for this. It will need a light-weight dovetail system.  The counterweight shaft needs to be thinner, and longer too, so people don't need to bring many heavy counterweights to the plane.  

For those who do this kind of portable imaging, do they need high-prevision absolute encoders?  I am not sure.  At least for me, I don't need.  A smooth PE curve with less than +/- 4" of amplitude will be sufficient for me (good enough for 5 minutes of exposures on 300mm lenses).  Even +/-8" would be acceptable if there is good permanent PEC.  The mount has to be rigid, in case the places we travel to is windy, but I think AP mounts are all good for this.  The polar scope may need some rethinking.  The current RAPAS may be a bit too bulky for such a small mount.  Finally, its power consumption needs to be as small as possible.

That's my wishlist for an air-portable mount.

Cheers,
Wei-Hao

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