Report: 08/07/2012 - Testing the Nexstar 4SE + PC control

[Cladinator]

It's been months since I've been able to pull out a scope and enjoy the sky. Mostly school, work, and bad weather have prevented me from enjoying my hobby.
I had my Nexstar 4SE fixed not too long ago after finding several problems.
I also recently learned how to use the PC control plugin on Stellarium to control the Nexstar so I wanted to give it a go to see how well it performed.

I set up around twilight in my back yard next to the bean field that's struggling to grow with a lack of moisture.
By the time I was set up there were plenty of decent alignment stars shining bright enough to get down to business.

I always use auto two star alignment to get the scope aligned. I chose Mizar and Arcturus.
The alignment was successful and so I connected the hand control to the RS-232 cable and plugged it into my PC and fired up Stellarium.

I did not have the success I wanted when using the PC control.
When I tried to use Stellarium to command a slew, the scope would just point directly north. I'm not sure why this was happening. On the screen, the Nexstar reticle even showed that it was pointing directly north (right next to Polaris). I don't know why it was doing this. As far as I know I was doing everything correctly.
I didn't waste too much time trying to figure this out. I tried using the PC control to slew to M10 and M12 in Ophiuchus. No joy.

Whatever. I disconnected and restarted the Nexstar and then got a new alignment.
I really wanted to tour Sagittarius. There are plenty of objects in there that are close together. The scope wouldn't have to do too much work.

Successfully, I found 13 objects, two of which I had never seen.
My problem, was that the objects were too far outside of the field of view for my comfort.

I used my Hyperion Baader zoom MK III. At the 24mm setting that gave me a magnification of 55x.
I noticed the scope was usually slightly below the actual object. The error was probably slightly more than 30 arc minutes below the object and anywhere from 1-3 fields of view to the right (usually).
There were a few occasions where the object was in the FOV but it was only just in it.

My location was correct. My time was correct. My mount was level.
So I'm not really sure.
This is the first time the scope has been used since it was repaired so it is probably back to the original default settings.
Could the problem be backlash settings? I've never actually done anything with backlash settings so I'm not sure.

When aligning, the last movements should be right and up, correct? That's what I was doing.


The sky was fairly dark. I was able to see the faint nebulosity of the Milky Way stretch across the sky, something I can't see terribly often.
The bugs were a nightmare. They were biting me everywhere I didn't have bug spray (my hands).
There were these moths everywhere. They were all over my car. I had a bunch hanging out on my scope too.
The heat wasn't terrible but I was still pouring sweat. I didn't think the humidity was too bad but we've had nary a rain lately.

This is why I can't stand the summer for observing. My most successful observations were made while it was very cool/cold when the bugs were gone and the air was thin.

The objects that I saw were less impressive than what I remember. Objects were dimmer and I had a more difficult time focusing than in the past.

Finally, the objects:
-M8
-M10
-M12
-M17
-M20
-M21
-M22
-M23
-M24
-M25
-M27
-M28
-M54

I found M20 and M54 for the first time during this observation.
I could not see any nebulosity in M20. That was disappointing. The only reason I know I was looking at it was the configuration of the stars associated with the nebulosity. I think the 12" dob will probably allow more detail.
M54 is a nice dense globular cluster.

So there you have it. The scope performed OK. I want that alignment to be much tighter than it is. Even when it was "broke" I was getting decent alignments.
I also need to figure out what the deal with the PC control is. I'd like to get that taken care of mainly for things like public outreach. It would be a handy tool. I can't see myself using it too much because the computer screen kind of kills your dark adapted eyes even if you select "night mode" in Stellarium.

Please feel free to chime in if you might know how to correct the error in my alignment or if you are familiar with the PC control problem.

[bigjack]

Nice report. What version of Stellarium are you using. I'e used it to control my scope many times with no problems. Mine is the SynScan controller. Are you true serial or USB to serial as there have been many reported problems in that area.
Good Luck

[Cladinator]

Thanks Jack.
I'm using the most recent version of Stellarium (0.11.3).

I'm using a USB to serial. My laptop (like most) doesn't have a serial port.

I probably could have played with the PC control a little more but I didn't want to take away too much from observing.

I'm eagerly awaiting shorter days and cooler nights.

[Cladinator]

Does anyone know the best way to test backlash? Is it more of a trial and error? I'm not sure if this could have been a problem or not.

[sxinias]

Nick,

I generally use a 32 mm eyepiece for gotos with my 4SE as well as my other scopes. However, my experience with the 4SE mount is you should have the object well within the field for view. As far as the last two movement, I can never get that right but really see little difference...

Backlash can be a problem. You need to experiment with the settings and use the slew speed that is appropriate for you. I use 16x sidereal rate for my backlash settings but I am interested in photography, not viewing. For viewing, you probably want to use a higher slew speed. After I complete an alignment, I do a couple of gotos then use the replace alignment stars command and replace each alignment star with itself. After that, gotos are very accurate. I like the two star alignments because they are faster. I always do a calibrate goto if I have removed the OTA from the mount or moved it on the mount, am altering the weight of the scope, etc. Don't know if it does any good but can't hurt. I also use a 12mm reticle eyepiece for centering alignment stars and am thinking about going to a 6mm reticle eyepiece. Again, I am interested in photography and not viewing so I want as much precision as I can possibly get. Also most of my work with the mount is in the equatorial mode but I find the azimuth mode as accurate as the equatorial mode.

Joe

[Cladinator]

Thanks Joe.
I'm not very familiar with the fine-tune settings on the Nexstar. I will have to go through and experiment with backlash, calibrating, slew speeds, and replacing alignment stars.
The scope wasn't too far off but it was far enough out of the field of view at 55x that I'm concerned. It's probably nothing serious. The scope seems to be working well after the repair. I never once had a failed alignment.
It really could be as simple as the tripod sinking slightly in the soft soil after the alignment but it probably just needs to be fine tuned. I'm pretty sure it came back from Pasadena with a full factory reset.
I'm really looking forward to cooler, more comfortable evenings when the days are shorter so that I have more time to get these issues under control.

Despite a light coat of insect repellent, my hands and arms are covered with mosquito bites from this observation.