Grove Creek's Internet Controlled Celestron C14
Click here for the LIVE Weather Status Page
Images taken with telescope Building Details
Grove Creek's famous vintage C14 (the 5th every made) is installed on a Astro-Physics GTO-1200 mount and pier, in our Middle Observatory - one of three buildings at the Grove Creek Observatory complex. The visual limiting magnitude at Grove Creek is 7.37 (Bortle Sky Magnitude Rating: 21.7). The mount has a hardware 2.14 arc second hardware periodical error, which has been software trained down to 0.55^secs - well below the pixel threshold of the CCD camera. Even though you would think that there would not be any movement at all with such a low PE, this is still not possible due to atmospheric refraction, the RA movement not being uniform across the sky and wind. Finally, it is near impossible to polar align a commercial mount to within arc second tolerances, which can cause declination drift after 20 minutes. Due to these factors, unguided exposures are limited to 4 minutes on this telescope, at zero degrees declination (the greatest area of movement). However with CCD imaging, users can easily take multiple images and stack them to simulate one long exposure or use autoguiding. The C14 will reach up to 21st magnitude on a moonless night, with a signal to noise ratio of 12, with a 240 second exposure.
How light travels through a C14
Extensive pointing error mapping and specially designed primary mirror locks, ensures the pointing error is within +/-2^minutes tolerance. Large SCT's are known to suffer from "mirror flop", due to the very heavy (and thicker in the older C14's) primary mirrors, which are normally only stabilised via a single manual focus knob. This has been eliminated with our system by locking the primary mirror in 3 places and adding an automatic external auto-focus temperature controlled focuser. Replacing the standard 8 x 30 viewfinder, a GStar EX deep sky video camera is installed as a live electronic viewfinder that can capture up to 10th magnitude! It also enables remote syncing on a known star using a fixed laser, in the rare case that the telescope looses it's known computed position of the night sky. Click here for details about using lasers legally for this purpose.
Research conducted by users of Grove Creek's C14 Telescope include vital work with NEODyS - the search for Near Earth Objects (609 observations, as of June 2010 alone!) - The International Astronomical Union Minor Planet Center (which Grove Creek Observatory is officially designated as E-16), where the C14 is responsible for several discoveries of minor planets, including one asteroid named as "Grove Creek" - in honour of this facility. Thousands of variable star observations have been conducted by members of the American Association of Variable Star Observers - AAVSO (including 6 supernova discoveries) and general CCD imaging of interesting objects.
THE C14's CCD IMAGING SYSTEM:
SBIG ST-8XME Class 1 CCD camera. Providing a field of 14' 22" high x 21' 39" wide, with an image scale of 1.69^sec/pixel @ BIN 2x2. We lock this camera at BIN 2x2 as this is closer to the desired pixel ratio of 1.5^sec for any telescope combination and to provide twice the sensitivity. The larger the pixels (just like grain on old 35mm film) the more sensitive the CCD camera is. This CCD camera is kindly on loan by Wheaton College in the USA, who operate another internet telescope at the facility. The camera must be returned next year and we need help to replace it.
SBIG CFW10a 10 position filter wheel with Red, Green, Blue and Luminance colour filters and Sodium II, Hydrogen Alpha and Oxygen III narrow band filters. The LRGB filters have IR and UV coatings.
Optec NextGEN WideField 0.50X NGW focal reducer running the C14 at f/6.2. This provides nearly twice the field of view and 50% shorter exposures, than the native f/12 focal ratio of a standard C14, as well as a better CCD pixel match with the reduction in focal length from 3,910mm down to 2,200mm.
Optec TCF-S 2" Temperature Controlled Auto-Focuser so we never have to focus the telescope! In fact, it will even focus the C14 automatically during an exposure. The TCF reads a temperature probe on top of the telescope, which has previously been trained to change the focus when the tube gets colder (contracts) or gets warmer (expands) - which is why the initial focus can change over a nights use.
HOW TO TAKE COLOUR IMAGES ON THE C14 TELESCOPE:
Available Filters for the C14 and SBIG ST-8XME
1-Red, 2-Green, 3-Blue, 4-Luminence, 5-Sodium II, 6-Hydrogen Alpha, 7-Oxygen III
(A luminance filter is a clear filter that blocks infra-red and ultra-violet light, for better colour balance)
Transmission Curves: RED=600nm GREEN=520nm BLUE=400nm
Astronomik Type2c Click here for a full LRGB response chart
With these filters, you can take true colour images of objects with high
block IR at ~1150nm.
The exact ratio multiple, using a huge average of GTV calibration stars with our optical/CCD setup on the C14, is as follows:
RED = 0.86 GREEN = 1.00 BLUE = 1.45 L = 1.00
The Kodak KAF-1603ME imaging chip in the CCD camera, has different sensitivities to different coloured objects through the telescope. As you can see in the below Quantum Efficiency chart below, RED (600nm) is a lot more sensitive at 80% QE, compared to Blue (400nm), which is only 45% QE. These differences are normal for any type of CCD camera. Also, colour response depend on the type of filters you are using (transmission curve) and to a lesser degree, the type of optics. Grove Creek staff have spent many hours measuring and averaging over a hundred of special pure white (GTV) spectral stars, to obtain the exact colour ratio for you. Not one setup is ever the same - responses can even differ as part of the manufacturing process of the same model chip. Therefore, you can depend on these ratios to give you true colour images.
SBIG ST-8XME CCD wavelength response.
Example: Peak response is @ 650nm. This is why a lesser exposure through red is required.
Compare this to blue, which only peaks @ 55% and thus requires a longer exposure to match.
Using the filter ratios of RED=0.86 GREEN=1.00 BLUE=1.45 - you multiply your exposures, in seconds, by these ratios. For example, if you were taking a 5 minute (300 second) colour exposure you would use the following exposure times, through each colour filter:
300 x 0.86 = 258
seconds for RED
300 x 1 = 300 seconds for GREEN
300 x 1.45 = 435 seconds for BLUE
300 x 1 = 300 seconds for LUMINANCE
The Luminance filter is a clear filter with the same UV and IR blocking coatings that the colour filters have. You need a luminance exposure as part of the colour merging process. It is always the same exposure as the green. To remove thermal noise, you need 3 Dark Frames. Using the above example, take a 300 second dark frame for your luminance and green exposures, a 258 second dark frame for your red exposure and a 435 second dark frame for your blue exposure. Then reduce these dark frames from your 4 images. Using astronomical imaging or other image processing software, you then merge the L R G B dark subtracted images to create a single colour image. For different exposure times, always round off to the closest second.
Important Note: Some software packages allow you to change the levels and/or ratio of the raw images for each colour channel. Always ensure all your images are set to the same level (or ratio set to 1:1) in the colour combine function. Never use this feature as you have already taken the raw images using perfect ratios. Using the ratio method with your raw images have many advantages over taking the same exposure for each colour. If you were to do so, you would need to "stretch" the channels to match. This introduces noise - especially to the less sensitive channels, like blue and the end result will be very poor.
CLICK HERE FOR AN EXAMPLE LRGB 240 sec IMAGE OF M27
HOW TO AUTO-GUIDE YOUR IMAGES ON THE C14:
The SBIG ST-8XME has a separate guide chip, located at the top of the main imaging chip. The guide chip is only seen when in the autoguiding functions of the software. As the pixels are smaller, always use Bin2x2 or even BIN3x3 (if you can get away with it) for the GUIDE CHIP as some objects may not have bright enough guide stars in the field. Below, is the physical layout of the 2 chips, inside the CCD camera:
Main imaging and guide chip layout (compliments SBIG)
mount can perfectly track the sky against the planet Earth's rotation, without some
trailing. The C14 at Grove Creek has an exceptional mount and does
not require guiding for exposures under 120 seconds, if the wind is low. We
always set our guiding rate to correct around 5 seconds exposure. This is enough
to find almost any faint guide star and it is also important that you NEVER
autoguide under 1 second exposures, as you will correct for seeing, not real
Filters 5-7: Deep Sky Narrow Band CCD Filters:
Astronomik Sodium II Hydrogen Alpha Oxygen III
New wide 12nm bandpass and transmission up to 99%.
(Click on the above filter name link, for full filter product information)
These filters provide stunning details that can not be seen with normal filters for imaging emission lines of nebulae.
HOWEVER, IT IS OFTEN DIFFICULT TO FIND GUIDE STARS,
SO ALWAYS DO A GUIDE TEST FIRST. IF FAIL, TRY MOVING THE IMAGE!
You can also substitute the Red, Green and Blue channels with our narrow-band filters, to create "Hubble Palette" false colour images:
Narrow Band Transmission Curves (click charts for full size)
Substitute: Sodium II for Red Hydrogen Alpha for Green Oxygen III for Blue for Hubble Palette
CLICK HERE FOR AN EXAMPLE OF A 900sec EXPOSURE OF NGC2070
Grove Creek's Middle Remote Internet Controlled Observatory
One of the 2 remote control roof motors
In December 2007, Jim Lynch paid for the motorisation of the roof and the building was completed and fully automated by Steven Williams. The roof motors support 24VDC battery backup, so that when mains power is lost, a "keep-alive" relay will trigger the roof to close automatically, via a 24VDC backup battery which is charged when the mains is on. When mains power returns, the relay is released and the roof can be opened again. Two motors control the roof, one on the north/west for the western half and the other on the south/east for the eastern half. They can also be operated on-site with a wireless remote control, up to 40 metres range. A strobe light and Piezo alarm is used to warn local staff in case of automatic roof movement.
We use a model KT-5220 USB relay device from Ocean Controls, that has 8 relays which remotely control both the roof and the electrical astronomical equipment. It also supports 4 input sensors to detect the open/close status for each side of the roof, which are triggered by magnetic reed relays (the same type used with household alarm systems). The Live Weather Station and Boltwood Cloud Sensor is streamed to the Middle Observatory, from the server in the main observatory. When armed, this will trigger the roof to close automatically in case of adverse weather conditions. When the input sensors detect that the roof has physically closed, the unit is programed to automatically power down the telescope and accessories, saving considerable electricity costs.
Above: The USB Relay Control System and PC Software Interface.
An internal live WebCam (shown above/left) and a external night-vision security camera (shown above/middle at night) are in place, along with motion detection back-to-base alarm system, as well as an armed guard, who lives 100metres north of the facility, to safeguard the observatory and monitor the telescope position. When the C14 is online, the top/right image shows our Live C14 G-Star Night Sky camera, which is used as an electronic viewfinder with a 9.5° x 7° field of view, as well as for remote syncing with our fixed laser installed on the telescope. The image updates every 10mins when the telescope is online, via our live weather status page.
The Weather Station and Boltwood Cloud Sensor - Protecting the Middle Observatory:
The wireless Weather Station showing sensors (Cloud Sensor at top) and receiver system.
We use the Oregon Scientific, model WMR918, wireless professional weather station (shown above) to safeguard the remote observatories. With software written by Andrew Mattingly, weather data is streamed over our LAN to close the roofs automatically, if adverse weather conditions are present. The Boltwood Cloud Sensor is the white angled tube, shown on top of the weather mast - this device provides live cloud data on our web site and will automatically close the roof, if very overcast conditions are present or the slightest sprinkle of rain is detected. Although the weather station also measures rainfall, the problem is that the rain detector only triggers after 1mm of rain - therefore the Cloud Sensor is essential to ensure the equipment does not get wet. Only Grove Creek staff are permitted access to open and arm the observatories. We do not allow 3rd party telescope projects access to roof controls.
Via a separate serial interface, the weather station also provides the Trunkey Creek area with helpful online weather information and detailed historic data. Greg Ford has been instrumental in implementing this important community service for the local community, where the nearest weather station is 62kms away at Cowra. For this, we use the FreeWX Weather Software to upload useful weather data in a graphical form every 10 minutes to our Online Weather Web Page, as well as graph data from the Cloud Sensor. In addition, we also have a very sensitive G-Star wide field night sky video camera that also uploads to our weather web page every 5 minutes.
The data from Grove Creek's Weather Station can also be DISPLAYED LIVE on your own local PC, if you have a permanent internet connection. It updates the graphs every 10 minutes by grabbing a very small data string from our web server. Here is a sample screen grab of the output of the FreeWX web client software, freely available to download and use:
Would you like the graphical program that updates
LIVE from our weather station on your desktop?
Click to download the FreeWX web client for Windows unzip and install.
(Read the enclosed readme.txt file to setup for Grove Creek)