You are currently viewing archive for August 2011
Posted by: Tom How
Another busy couple of days at the New Forest Observatory over the bank holiday weekend working on the mini-WASP astrophotography array.

First job was upgrading the automatic computer-controlled dome rotator on the Pulsar 2.2m telescope observatory. Our first prototype used two 0.5Nm torque stepper motors. Whilst this proved that the idea worked, they didn't quite have the speed or torque required. Greg purchased some 2.2Nm Nema 23 hybrid stepper motors designed for CNC use, and looked very beefy and up to the job.

I wired up the new motors to the Stepperbee controller board and proved that the motors worked in the study. We then did all the metal-work required to mount the new motors in place of the old motors.

After some problems with earth-loops and truculent computers we got the new motors working properly with the observatory computers. My software runs on the the observatory computer and communicates with TheSKY to fetch the telescope position and sends the required signals to the motor controllers. A solid state compass provides closed loop positional feedback.

The motors easily slewed the dome at 3 or 4 degrees per second. We were able to run it even faster, but it is a bit terrifying at high speed - we don't want to lob the dome into the next garden! Here is a video of the system in action. I was very pleased with the speed!

This activity managed to use up most of Sunday afternoon. The skies looked very promising, so we set out to try some imaging. Whilst Greg concentrated on setup work in the old South Dome, I ran the mini-WASP array in the North dome, working my way through various problems, but was able to grab a few dozen frames of some nice targets with both cameras operating in parallel. Bed about 3am.

After a late start on Monday we tidied up a few problems and set to work with some stolen sheets and shirts to try and get a decent flat field. The best arrangement consisted of a couple of layers of white shirt attached to the Sky 90s with elastic bands pointing at the open telescope dome slit. A large thick white sheet was draped over the entire dome slit - providing a double diffused light source which provided a decent flat. Calibration with these flats and some bias frames removed all of the vignetting on the images from the previous night.

Next job is to look at the gigabyte or so of FITs files and see if there is a decent image lurking in them!

Posted by: Tom How
I've had an epic weekend of work and partying to celebrate the launch of the New Forest Observatory mini-WASP telescope facility: Probably the most advanced amateur wide-angle astrophotography facility in the country.

The mini-WASP system is named after its big brother, the Super-WASP system. Mini-WASP consists of two wide field refractors with two 10MP Starlight-Xpress CCD cameras and filter wheels. Eventually the system will boast 4 such cameras and scopes. Under this array of imaging equipment is a Paramount ME equatorial telescope mount on a custom aluminium pier. The rig is housed in a 2.2m Pulsar Optical observatory dome.

I turned up at Greg's around 11am on Saturday. After trying out some software I'd written to synchronise the 4 cameras and 4 computers, we erected Greg's new 6m by 4m marquee. This was kind of fun with only two chaps and no clue how it went together. Much of the remaining afternoon was spent tuning the automatic dome rotator system and generally making preparations for the following day's party.

During the evening we has a lucky bonus of some clear skies. I set to work in the observatory about 9pm to polar align the Paramount using a rather humble webcam and a copy of K3CCDTools: Despite the simple tools, I got the job done. Beneath deteriorating skies we were able to grab a few long exposure frames to validate the polar alignment. This test culminated with both cameras running automatically in parallel for the first time.

Sunday was party day. We got up fairly early (some earlier than others) and I collected Little Pete from the train station at the god-forsaken time of 9.15am. The morning was spent cooking and preparing for the guests who started to arrive around 11am. The rest of the afternoon vanished in a blur of activity: Cooking, eating, talking etc. As chief astro-engineer geek, I made sure lots of would-be astronomers got their hands on the Paramount joystick control for a test drive.

We had to endure one of Greg's powerpoint lectures, but were rewarded with a lot of superb puddings, one of which was more densely packed than a neutron star with yummy things. Surely gravitation pudding collapse was only averted by "ice-cream degeneracy pressure"? After discussion with my old physics professor, Brian Rainford, the solution to the cosmological "Dark Matter" problem was found in Helga's chocolate fondue.

After people left we reversed the process by dismantling the tent, tidying lots of stuff up, driving home and collapsing in bed.

A very successful weekend, and very enjoyable. Hopefully it won't be long before Greg dazzles us with his first completed mini-WASP image.

New forest observatory party

New forest observatory party

New forest observatory party

New forest observatory party

New forest observatory party

Most of the photos by Pete because I forgot!
Posted by: Tom How
In an ideal world, we'd all have our telescope observatories at the top of mountains with totally uninterrupted views in any directions. For those of us who do not have a handy mountain in the back garden, we have to contend with trees and houses getting in the way. This creates a hard limit on the objects we can use for Astrophotography. It would be nice to have a perfect horizon, but most of us cope by patiently waiting for the required target to arrive in a region of clear sky. British astronomers have lots of patience!

Most of us modern astronomers use computerised star chart programs. Such software allows you to enter the horizon limits in each direction and create a local horizon line (yellow on the chart) above the zero degree horizon (grey on the chart).

With the installation of my new homemade telescope mount combined with the passage of time, my map of the local sky has changed. The annoying huge tree to the south east has grown, whilst pruning has created some gaps in other areas. As it was cloudy today, I decided to recreate my horizon map.

This is a simple yet time-consuming task. You have to slowly move the telescope around the sky, using the scope to locate the line between the sky and the trees/houses. The telescope mount tells us at which altitude the telescope is pointing. This information is recorded around various points of the sky - the job only takes a hour or two.

Then is is a case of entering this data into your planetarium software (Skymap wins an award here for dreadful such a dreadful interface) and use the resulting plot when planning your observations. When it is dark, it is very easy to suddenly find yourself shooting images through a tree and wondering why the stars like so odd. With a decent chart setup it is easy to avoid silly mistakes.

Here we can see my plots in each direction. As it happens, most of my astrophotography is done in the north east, as this does the darkest sky. Many interesting objects appear in the south as well, but I can usually only track these for a couple of hours, so it is harder to get a decent image.

Category: Astronomy Images
Posted by: Tom How
Finally the skies cleared last night to allow a bit of astrophotography. Still learning the foibles of my own homemade GEM mount, but hopefully we are starting to get somewhere. This is 9 x 1200s exposures combined and stretched a bit. Art 285 camera with Astrodon 6nm Ha filter on a F5 8 inch newtonian. The full resolution version has an image scale of around 1.33 arc seconds per pixel.

NGC 7380 is the open cluster of stars discovered by Willian Herschel's little sister Caroline in 1787. Of course, they wouldn't have spotted much of the nebulosity in the region - the is is catalogued in the Sharpless catalgoue as sh-142.

The major problem with the data is the horrific star shapes. Although the scope is guiding ok in RA, the DEC guiding is still rubberbanding all over the place. More work required.

Click here for the full sized version

ngc 7380
Posted by: Tom How
Yet another visit to the New Forest Observatory today. That is my third trip out to the New Forest this week to setup the automatic telescope dome rotator. Telescopes, metalwork, computers and electronics: My favourite type of project. This has been an extremely satisfying way to spend a few summery days off. Who would lay on a beach when there are toys to be played with?!

Greg's setup uses an array of 4 telescopes atop a Paramount ME German Equatorial Telescope mount in a 2.2 metre Pulsar Optical telescope dome. The slit aperture is about 630mm. This means that the dome slit aperture needs to be aligned with the scopes to within a few inches to avoid problems. Constant visits (nearly every 10 minutes) to the dome would be needed to keep manually moving the dome slit aperture into the correct position. Clearly some kind of automated dome rotation system was going to be required to reduce user error and allow a modicum of sleep.

Actually the real reason is to give Greg one less thing to moan about in his ongoing crusade against the German Equatorial Mount.

Most commercial dome rotation systems have a couple of major failings: Either they aren't integrated, or they cost far too much! The standard dome rotator supplied by Pulsar optical falls down on both fronts. For the best part of a grand you get a motorised dome rotator that isn't integrated to the telescope. For unattended imaging this is useless. Other computerised systems do exist, but not for less than 2000. This type of project is the sort of thing I thrive on so I was desperate to try a bit of astronomy DIY. Once Greg saw a bit of demo simulation software I created, he was willing to cough up for the parts to make it a practical reality. A fool and his money?

The trigonometry needed to calculate the required dome slit azimuth from the telescope pointing data is long and involved - but computers are good at calculations. I knocked up a bit of software that fetches the pointing data from TheSky via ASCOM to calculate the required dome slit azimuth. The software interfaces with a couple of large stepper motors to actually move the dome.

Finally I got some Tom How metal work onto the NFO mini-wasp system in the shape of two stepper motor brackets. I think my rude metalwork compliments the precision finish of the Paramount quite nicely. I'll leave it to Greg to apply the red paint.

Once we'd got the metalwork sorted the software side worked after the usual tweaking. With any drive dome system you can always expect some slippage in the transmission and motor stalls - therefore we've used a solid state compass mounted in the top of the dome to provide positional feedback.

Below is a short video of the system in action. Greg is sitting on the floor with the video camera. At the beginning of the clip you can see the telescopes on the left pointing out of the dome slit aperture. The telescope mount is then moved to a slightly different part of the sky. After a few seconds you can see the dome slowly rotate to the correct place. You can here the thud-thud-thud action of the motors.

Of course, now Greg wants more powerful stepper motors. His excuse is to help it run past any sticky parts on the circumference. In reality I think he just wants to see the dome slewing around as fast as the Paramount itself.

All in all, a fine way to spend a few warm summery days. Here is the video of Tom How's patent dome rotator! Through the door of the observatory you can see the NFO South Dome.

Posted by: Tom How
Filled up many pages of the astronomy notebook today.

First up was the dome rotation project for the New Forest Observatory. A couple of broken things to fix in the stepper motor controller and everything is up and running again in my workshop. I need to get back down to the NFO again this weekend and see if Greg and I can get it to work in situ and link it up to the telescope itself. If this can be made to work it will make Greg's life much easier - the mini-wasp system is a fairly tight fit to the dome aperture.

Automatically rotating a telescope dome so that the slit points where the telescope is looking is a lot more complicated than you might expect.

Happy that the stepper motors are working, I've left them tracking a a long test and turned attention to the guide camera which was having a lot of problems with random noise. I've taken things apart. Changed the earthing. Removed a few unused components and generally fiddled about. I got it working ok on the laptop running on batteries. Plugging in the laptop power made the noise much worse.

Encouraged, I put it back in the observatory and carefully switched everything back on, one thing at a time, until the whole system was operating. The frames from the guidecamera now look much better.

Like many of these things, I'm not entirely sure what I've done, but I'm hopeful it has worked.

The guide camera is a simple webcam adapted to take long exposures and remounted in a special case that allows it to work with my homemade off axis guider.
Category: Astronomy Images
Posted by: Tom How
I have managed a very short exposure of M16 Eagle Nebula between the clouds. Clear skies are in short supply this week. We have no moon - which is known for creating clouds. I'm on holiday this week. More clouds created. And Greg in the New Forest has got his new equipment almost up and running. Many many clouds created!

A couple of clear hours last night enabled me to test the fixed up guide camera under the skies. I knew the clouds were coming so I ran off 10 x 120s frames of the M16 region. This is a very bright emission nebula and star forming region made famous by the classic Hubble shot of the "pillars of creation".

The camera had a 6nm Astrodon Hydrogen Alpha on it and I operated the camera in 2x2 binning mode to get lots of signal in short time.

The result was somewhat better than I expected for only 20 minutes of exposure time.

The guide camera isn't working properly. Very noisy - so much so that the guiding software kept loosing the guidestar with predictable results.

M16 Eagle Nebula

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