Jan 17, 2012

Various and Sundry Things

I've had a few things that I've been meaning to talk about and they've been hangin' around on my back burner for a little while now.  I enjoy the mechanical and technical aspects of imaging as much as the actual images, so that's what I'm going to talk about this time out.  First I want to give a little love to Ed Thomas and his company Deep Space Products.  I've had occasion to interact with Ed on a couple of different things in the last couple of months and I've come away with a much better astro-life as a result.

Active Cooling for the Edge HD!!
Cooling Fans installed on my
11" Edge HD telescope
First - if you own an Edge HD telescope or one of the regular Celestron Schmidt Cassegrains that have the new tubes featuring vents at the back - you just have to get yourself a set of TEMP-est fans from Deep Space Products.  The picture here is of the fans as they are installed on my 11" Edge HD scope.  They're a pretty nifty design.

A fan installs on each side, replacing the stock vents that come with the scope.  The fans themselves have a micron filter to help keep dust out of the scope.  There is a 12 volt plug on each side (2.5 mm), and either of the plugs can be used to power both fans.  The fans are connected together from inside the tube by a plug that is supplied with the fans.  One fan blows air into the telescope, and the other fan blows air out of the telescope.  Installation took me all of about ten minutes and is accomplished with nothing more than a single Phillips head screwdriver.

  • Using the screwdriver, loosen the screws holding the stock vents onto the telescope and remove them.
  • Remove the stock vents.
  • Plug the connecting power cable into on of the fans, and thread it into the scope behind the mirror.  The mirror surface itself isn't exposed here, so it's pretty much impossible to screw this up. 
  • Seat the first fan into place and hold it.
  • Tip the scope to the side so that the fan is at the top of the scope...and the power cable drops toward the bottom. 
  • Fish the power cable through the second vent and connect it to the second fan.
  • Seat the second fan in the vent.
  • Tighten down the screws.  Be gentle when doing this so as not to crack the fan housing.
  • Connect to a 12 volt power supply.
It's really that simple.  It took me as long to write that as it will take you to do it once you get your fans.  I know what you're thinking.  "But Mike, do they work?"  In my ever humble opinion, yes they do.  Without the fans installed I put a thermometer inside of the OTA and put it outside to measure how long it would take for the scope to reach equilibrium.  On that chilly December night there was a 16ºF temperature difference from my home and the outside temperature.  That's right, I used the phrase chilly December night and 16ºF in the same sentence.  Just one of the many perks of living in Arizona my friends.  We call that "winter".  But I digress.  It took the telescope 145 minutes to get within 2º of the outside air.  Note that the outside temperature dropped 4º in that time for a total differential of 20ºF.

That's all fine and good, but what did it do with the fans?  Let's just say it did better.  When I placed the telescope outside the next night with the fans installed there was an 18ºF difference between the inside and outside temperature.  The telescope was within 2º of equilibrium at the 90 minute mark.  Note that the outside temperature dropped 6º during that time for a total differential of 24ºF.

To summarize:
  • Without Fans:  145 minutes to cool a total of 20º
  • With Fans: 90 minutes to cool a total of 24º
The best part of the whole thing?  You can use the fans while you're observing so that they keep up with continued drops in temperature as the night progresses.  Even though I ended my tests at around 9pm each night, the temperature drops another 15º to 20º by sunrise the next morning and you want the telescope to keep up with the temperature for optimum viewing and imaging.  In both short and long exposures taken with the fans running I can see vibration evident in the images.  Focus remains as sharp as if the fans weren't running at all.  But the fans aren't my only interaction with Ed as of late

Hypertune is the real deal
If you've been following for any length of time, you know that I've had some seriously frustrating equipment issues since mid summer.  In an effort to prevent the irresponsible purchase of an Astro Physics AP900 with all the trimmings, I took my Celestron CGE mount to Deep Space Products for a Hypertune.  The results have been astounding.  No, it didn't turn my mount into an AP900 or other high end offering, but it's vastly improved for my uses.  Nothing is more demanding on a mount than deep sky astrophotography.  Okay, maybe dropping the mount out of an airplane is more demanding, but I'm talking about legitimate use here.  When I got the mount back from Ed, it was like it was all brand new again. 

The first night home I set it up in my backyard to test everything out and started the tried and true Celestron two star alignment.  The first star - Vega - was just inside the outer ring of my Telrad when the scope stopped its slew.  With the second star - Fomalhaut - the mount placed the star on the CCD chip and asked me to finish up the alignment.  This was a promising start, but nothing spectactular.  Ed had mentioned that when he took the mount apart, that both axes were cross threaded.  He said it was common for CGE mounts to have one of them cross threaded - but he'd not seen both of them in the same mount.  He indicated I could now expect better go-to performance once the scope was aligned. 

Dutifully, the Celestron hand controller asked if I wanted to add a calibration star and I opted to do so.  I always opt for the calibration stars.  In this case it selected Aldebaran.  I waited with baited breath as the scope slewed all the way around to the other side of the sky and placed Aldebaran about 5 arc minutes from the center of the CCD chip.  Nearly perfect.  Subsequent calibration stars were all placed on the crosshairs superimposed over the center of the image in Maxim DL.  I was ecstatic at this sort of performance.  Autoguiding has become a true pleasure as well.  Graphs are now nice and flat with only occasional guiding corrections.  The shot of the double cluster shown below is a testament to the guiding the CGE now routinely provides.

NGC 869 & NGC 884
Captured with a Vixen ED80SF on my CGE Mount
12 x 120 seconds

Celestron's All Star Polar Alignment
What is that you ask?  It's a nifty little tool built into more recent versions of the Celestron firmware for their Nexstar hand controllers.  Essentially, the controller pays attention to the amount of slewing that you have to do in order to center the alignment stars as you go through the initial setup.  Once this is complete, it can use that information to calculate how far off the polar alignment is for the telescope.  The hand controller will even show you how much it has calculated if you navigate through the menu structure to Align -> Polar Align -> Display Alignment.  It will tell how far off in azimuth and altitude it has calculated that you are based on the initial alignment.  Too good to be true?  I wondered about it myself.

When I setup an imaging session, I never put an eyepiece into the telescope.  I do all of the alignment via CCD camera and screen.  Within Maxim DL, I turn on crosshairs and have a continuously downloading image being taken as I go through the alignment process.  While taking constant 1/2 second exposures at 4x binning, I nudge the telescope with the hand controller keys until each star is centered on the crosshairs.  Using this method I estimate that each alignment star is somewhere around 5 to 10 arc seconds from the center of the imaging chip.

I've been using the All Star Polar Alignment routine for awhile to image via Hyperstar at f/2 and 560mm focal length.  I've always worked on the assumption that the routine would be 'good enough' for this type of work and it has been.  However, as I move into imaging at  longer focal lengths I want to expand my skills and take up drift alignment to get really accurate polar alignment for long exposure imaging.  Being the inquisitive type of person that I am I wondered if it was necessary.  I mean, let's quantify just how accurate is the all star polar alignment routine?  With the help of Ray Gralak's PemPro software I set out to do just that.  I also use the routine in this software for drift alignment.  It measures how far off the pole your mount is as well but it does it by tracking a star in the same method as a normal drift alignment.

So I setup the mount and did Celestron's All Star Polar Alignment, getting the alignment as close to perfect as possible before switching over to PemPro and its measurement tools.  So cut to the chase Mike, how well does it work??  My assessment is that it works really, really well.  Below are the screen shots taken of the azimuth and altitude measurements.  The azimuth in my official test was accurate to within 7.5 arc minutes and subsequent follow up tests have all been under 10 arc minutes of the pole.  The altitude axis was only .5 arc minutes off, which is understandable since that variable doesn't really change more than about 1/2 degree between my usual observing sites.  For long exposure and long focal length photographic use this is probably not close enough and a drift alignment is necessary to refine it even further.  However, for short focal lengths and wide angle imaging, it's quick and easy and better than is necessary.  For a visual observer, I don't think you'd even see any drift or rotation until several hours had passed on the same object.  My vote:  Celestron's All Star Polar Alignment is a really useful tool.  If your firmware has it, you should use it.  If it doesn't, you should upgrade your hand controller if it's possible.

All kinds of good things happening lately in my astro-land.  More on that next time though.