I used my AVX for 2 years before I had to service it. I got something like 8
of total backlash (according to PHD2). The AVX gears are anchored with set
screws, which loosened. I greased and reduced the gap between the gears as
much I dare and such that the gears still turned freely. I got something like
30 total back lash (which is good for a rank amateur like me). I found that
an eastward bias in the balance is essential, I could not get PHD2 to work
otherwise.
I had put 28 lbs on the mount intended for a maximum payload of 25 lbs. I used
an 8 Newtonian, a DSLR camera, an Orion 80mm short tube with Starshooter (?)
for guiding, and the original finder scope. I changed to a 50mm Orion finder
scope which has a built-in focuser and takes 1.25 eyepieces, and got rid of
the 80mm scope. This reduced the payload to 22 lbs.
-
Sent from Mail<https://go.microsoft.com/fwlink/?LinkIdU0986> for Windows 10
________________________________
From: az-observing-bounce@xxxxxxxxxxxxx <az-observing-bounce@xxxxxxxxxxxxx> on
behalf of Paul <emailpa@xxxxxxx>
Sent: Thursday, March 21, 2019 11:44:59 PM
To: az-observing@xxxxxxxxxxxxx
Subject: [AZ-Observing] Re: photography problems discussion
Good plan.
I put a camera ballhead on my AVX to take snaps of the moon and wide shots
of Orion for example. Never tried serious DSO work or extended time highly
accurate tracking with it. But it is light, fairly quick to setup & start
tracking and pretty accurate for how I use it, depending on alignment of
course.
IMO, I think your 1st step with AVX should be clean and regrease. If it
doesn't swing freely around the axes, then it will grab n slip during tracking.
-paul anderson
On March 21, 2019 12:21:14 PM Michael McDonald <mikemac@xxxxxxxxxxx> wrote:
Ive come to 2 tentative conclusions:
1) Expecting single pixel guiding (0.5 arc seconds) on an entry level mount
and in the light polluted environment of Chandler is unrealistic.
2) Mount manufacturers are selling snake oil.
Lets address #2 first since thats a provocative statement. In an effort
to figure out whether Im getting everything out of my (AVX) mount as it is
capable of, I went look to see what the manufacturer (Celestron) said about
its pointing and tracking specifications. When the answer turned out to be
nothing, I looked at other mounts specifications.
And with the exception of iOptron, Celestron, Losmandy, and Star Watcher
dont mention anything in the online specs about pointing or tracking
accuracy. iOptrons EC modules claim a PEC of less than half of an arc
second. Their non EC models claim a +/- 5-10 arc second tracking accuracy,
depending on the model (bigger models have the lower error). All of the
manufacturers are more than willing to tell you irrelevant info like the
diameter of the shafts. I assume they dont give tracking info either
because its a lot worse than theyd like you to believe or it varies so
much between units that the resulting number is meaningless.
There does seem to be some justification for the general assumption that
more expensive mounts are more accurate ones. But there doesnt seem to be
much, if any, objective data to back that assumption up. Is a mount twice
as expensive as another twice as accurate? Do all mounts in the same price
category have similar accuracies? Before I pay $2-4K for a new mount, Id
like some objective numbers that would give me the warm fuzzies that the
money was worth it.
So back to #1. Given that my AVX costs 1/3 of the low end iOptron CEM25EC,
I assume the AVX has at best the +/-10 arc second tracking accuracy. Thats
20X the 0.5/pixel I was hoping for. Not even close.
And an arc second is a lot smaller than I had appreciated. And it appears
that achieving tight enough mechanical tolerances to achieve sub arc second
tracking is hard, which equates to expensive.
So, given my tentative conclusions, what do I do? Well, Im not giving up
on getting the best images I can with what I have or reasonably can afford.
Im going to experiment with the changes I mentioned before (add the Barlow
to increase the guide scopes focal length, add the reducer to decrease the
main scopes focal length, remount the guide scope in a firmer location).
Im also going to start experimenting with binning. If my system truly
isnt capable of exploiting all of the resolution of my ASI1600, then that
high resolution would be better used by combining adjacent pixels into
larger super pixels at are more light sensitive, aka binning. By being
more sensitive, that will shorten my exposure times, putting less demand on
my systems tracking ability. And since Im just using the resulting images
on my computer monitor, I really dont need 4500x3600 pixels.
Time to find a clear night so I can try some of this out before having to
pack everything up for the AAMM next weekend.
Mike McDonald
mikemac@xxxxxxxxxxx
PS None of this is meant to disparage the AVX. It was designed to be an
entry level mount used primarily for visual observations and wide field
(Milky Way) photography. Its yours trulys fault for trying to use it for
something it wasnt really designed for.
--
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