Another
gorgeous night! It was a little warmer,
although I was still fighting dew, just not as much. Because of the end of Daylight Savings, I got
to get started at 6 instead of 7, which was awesome. Also, Orion comes up an hour earlier
now. Since the first quarter moon was so
high, I decided to grab a video on that before I got started, and I also
grabbed a video of it on the guide scope with the QHY5, but it didn’t have good
enough contrast to get a nice shot, even after messing with the gain, exposure,
and gamma as much as I could. I guess I
could’ve thrown my neutral density filter on, and it wouldn’t have changed the
focus because it screws onto the end of the extension tube, which just slides
inside the guidescope, but oh well.
Daylight Savings Time seemed to be
causing issues with the telescope as well; it wasn’t quite getting on stars
quite right. So I replaced the alignment
stars and calibration stars, and that seemed to work, so I started imaging
Stephan’s Quintet. I got two images in
when I needed to do a meridian flip, so I did that, but then PHD started having
fits. During calibration, it was giving
me non-orthogonality errors, so I ran the guiding assistant to see if it would
help. It didn’t, and the manual said it
might be due to bad polar alignment. RA
was the main problem. I figured maybe
the time change would affect the polar alignment somehow, so I started re-doing
the polar alignment, but then I accidentally touched the RA cable, which caused
it to jump when it shorted. So then I
had to re-align completely. I left the
camera attached so that I could do fine alignment using BackyardNikon’s Frame
& Focus feature, which uses live view.
At ISO-3200, I can see not only the stars I usually use for alignment,
but even the precise goto stars show up no problem, since the D5300 will adjust
the shutter speed & ISO to see something. But
its guesses as to where Vega and Altair were terrible; I actually had to go get
the Telrad since it was not even close.
When this happens, it’ll usually correct itself out as I add stars, but
it was consistently guessing terribly, which it shouldn’t have been because I
was polar-aligned still from the previous nights. So then I shut it down and restarted
completely, and it was getting even worse, not even making it close to
Vega. I even tried putting it an hour
ahead and back in Daylight time, but the result was the same. Basically, it looked like RA wasn’t going far
enough; dec was pretty close. It was
either stopping too soon, or not spinning the gears as fast as it thought it
was. It might have been my imagination,
but sounded less aggressive than usual when it was moving. After trying various things, power cycling,
unplugging and replugging, changing the time, etc, it was still not
working. So I went inside to warm up and
have some dinner (I brought leftovers, but Bob cooked some brats that
he shared), and then I packed it up and left by 11:30. It’s weird that it worked in the first part
of the evening; it went to the moon from the home position, all the way in the
south, with no issues, and also went to Stephan’s Quintet on the east side of
the meridian with no issues. It even
went over to Fomalhaut, the polar alignment star I’m using, just fine. It wasn’t until I hit the cable and made it
jump. The cable also got hit a few more
times as I was re-situating it. Oh,
also, it seemed to take longer than normal to find the switch position in
RA. Bob suggested that maybe
it’s time to send it out to get hypertuned, and maybe they can do the Bennett
mod while they’re at it. He said he
knows someone who had their Celestron mount tuned with a guy named Dr.
Clay. It’ll cost some money, but will be
cheaper than getting a new mount – the CGE mount’s original price is
$3,000. A quick look online shows a site
called Deep Space Products that does it, including the Bennett mod (although
you have to supply the kit), for $505 (so $855 total with the Bennett mod
kit). That sounds pretty good to me if
it’ll save me the headache of the cabling issue and these other issues I’ve
been having. I can also get a dual Losmandy-Vixen
ADM dovetail attachment put on there for another $110, which I was talking to
Bob about last night – he thinks I should get a refractor sooner rather than
later, like before I get a deep sky camera.
Seeing the results from just my guidescope, I’m inclined to agree. There are a lot of issues shooting with the
SCT, and another one is possibly cropping up – mirror shift. It’s not a big deal to re-focus for each new
target and after a meridian flip – it only takes a minute, especially now with
BackyardNikon – but it might be the cause of the drift I still see. Even with guiding, the image slowly moves
across the frame, and that movement shows up in pretty much every other
frame. My RMS error isn’t too bad in PHD
(about 2 arcsecs), although sometimes when I’m moving the scope at slow speed,
it is a little sticky in dec, I think.
(Although, it’s my RA error that is the larger of the two – I do have
some backlash). I haven’t done the
mental geometry, but it seems to be moving in the same direction each time –
not the same camera direction, but the same sky direction. This might indicate the mirror shifting as it
tracks across the sky in RA. There are
two fixes I could do: use off-axis guiding (in which case, I’ll probably need
to get a more sensitive CCD, but I might not, I’ll have to test), or send the
scope off too for a hypertune (I could get a spring put behind the primary to keep it from shifting, since I can’t
lock the mirror on this C11).
So, a disappointing end to an
otherwise spectacular weekend. But it
was a great weekend! And I got some
sleep last night.
