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Saturday, 24 January 2009
Lots of colour was captured as well as lots of detail in the trapezium area. Amp glow is visible at the top left of the image as no dark frames were captured as they would have been if the prime aim was to obtain a still image rather than use the camera as an observation camera.
M1, The Crab nebula proved to be a different matter. The real time video image contained hardly any colour. 70 integrated Mintron frames were captured and summed by Astrovideo and in the final image, some colour had been detected.
This camera can never be as sensitive as the monochrome version due to the presence of the Bayer matrix colour filters in front of the pixels effectively excluding some of the light.
For comparison, below is a monochrome image of M1 taken with the Mintron MTV-23S85H-EX-R monochrome camera taken on the same night with the same scope. With both cameras the frame integration was set to 256 frames and an 0.5 focal reducer was used in conjunction with an IR/UV cut filtere
Saturday, 17 January 2009
The modified MTV-62V8H-EX colour camera was attached to a Skywatcher Equinox 80mm fluorite apochromatic refractor and focussed on the Orion nebula. The video stream was recorded to DVD at high quality with the camera set to 128 frame integration.
150 integrated frames were registered and stacked by Astrovideo to obtain the image here.
The next tests I do with this modified camera will be to make a side by side comparison with the unmodified camera.
This is a single integrated frame captured from the real time video stream and shows what is seen on the TV screen.
Friday, 16 January 2009
That notwithstanding, it is still possible to capture video frames and to combine them into quite pleasing still images even with quite modest equipment. This image of M27 was obtained with a Celestron Astromaster 130 Newtonian and a Mintron 23S85HC-EX-R monochrome, frame-integrating video camera.
I shall be testing the various Mintron cameras with a variety of telescopes of all sizes over the next few months and showing some of the results on this blog.
Thursday, 15 January 2009
First light was a test DVD recording and two directly captured images using an f/5 achromatic 80mm Orion refractor.
M42 & M43
Here is a snapshot of the TV screen showing what the live display is like. The nebula was a very pleasing live image. When 115 frames were integrated as shown above, the resulting image was quite good.
The telescope was mounted quickly on a Merlin AZ autotracking mount and an IR/UV cut filter was used. the Mintron was set to 256-frame integration. 30 minutes of DVD was recorded and Astrovideo was used to capture a frame every 5s for 55s and another image was captured at the same rate of capture for 60s. The frames were summed on the fly and were saved. The images were de-rotated and merged using Picture Window software. It would have been far better to have used an equatorial mount but I had very little time from my location to capture the data as I had been out earlier giving a talk to the Port Talbot Astronomical Society. The Merlin mount can be up and running in 3 minutes.
Since then, the Moon has been a more serious problem and the weather has been poor. The next tests will be done with an equatorial mount so that far more frames can be integrated to produce a final image. I shall use an Apochromatic 80mm refractor next time to image the Orion Nebula and a 10 inch f/4.8 Orion Europa Newtonian to attempt the Crab nebula. This will be done on the first clear sky without the Moon.
Wednesday, 14 January 2009
Video can be recorded on a DVD or video-tape and can be watched again in the future. The recording settings should always be set to the highest quality.DVD recordings give the highest quality, next is Super VHS which is almost as good as DVD. The poorest quality recordings are made on VHS video-tape. I prefer to record to DVD at the highest quality setting and then capture from the DVD playback video stream.
If a digital camera is placed on a tripod and set up in front of the TV screen displaying the live image it can be used to capture a screenshot that will be a reasonable image. If the ISO value is set low and the timer shutter release is used so that no shake is introduced into the camera, the shot will integrate several frames and avoid the raster scan if a cathode ray tube monitor is used.
Digital photograph of the screen of a CRT monitor displaying a video image of the Moon
Video can also be captured directly to a computer via a capture card such as the EasyCap USB 2.0 capture device.
This device connects to the computer via a USB 2.0 port and accepts composite or SVideo inputs.
PAL to VGA aspect-ratio correctionA problem I found with this device is that it does not allow for capture of PAL TV at 640 x 480 resolution. PAL resolution is the default capture size and this has a resolution of 720 x 576. The problem is that at this resolution, the aspect ratio of the image is distorted from 640 x 480 to the 720 x 576 PAL resolution. Thus circles appear as ellipses with the long axis being in the vertical dimension. Now, 640 is 0.8888 of 720 and 480 is 0.8333 of 576. To correct the aspect ratio of any image captured at the PAL resolution, even if the image has been cropped, you simply resize the image (making sure that the aspect ratio is not preserved) so that the horizontal dimention is changed to 0.8888 of the original dimension and the vertical dimention is changed to 0.8333 of the original dimension. This can be done in most image manipulation programs such as the Gimp, Paintshop Pro and Photoshop. Some capture cards allow capture to be made at 640 x 480 with no distortion of the aspect ratio of the objects in the image. This just has to be regarded as part of the image extraction process.
With one of these capture devices and the appropriate capture software your Mintron becomes a USB camera.
When long integrations of for example, 256 frames are used, the image is updated about every 5s or for 128 frame integrations the video image is updated about every 2.5 seconds.
I use the AstroVideo video capture software http://www.coaa.co.uk/astrovideo.htm which can be set to capture a frame every 5s (5000ms) for example and to align and sum them on the fly. The captured frames can be saved as an AVI that can be processed in Registax, or the summed frames as a FITs file either 16 bit or 32 bit deep or a BMP.
Sunday, 11 January 2009
Mintron Mintron MTV-23S85H-EX-R monochrome video camera (0.33 inch CCD sensor) 256 frame integration
Image of M1 the Crab Nebula captured from the video stream from the Mintron MTV-23S85H-EX-R camera with a 0.5 focal reducer and an F/4.8 10 inch Newtonian.
Image of the limb of the Sun in H-alpha light using a x3 Barlow and a Coronado PST H-alpha solar telescope. Image captured on Dec 6th 2008
These cameras can be used to capture bright or faint objects as these images show.
Thursday, 8 January 2009
In general, purpose-built astronomical cameras have 16 bit ADCs and produce output with 65536 levels of brightness.
This means that non-linear image processing can be used to brighten up the very faint parts of an image without oversaturating the brighter parts. The 16-bit depth allows this to be done with high precision.
There are many cameras that have been produced for other purposes such as webcams and surveillance cameras that typically have 8-bit output with 256 levels of brightness. This fine for display purposes as computer type monitors have 8-bit displays. The problem is that with only 256 levels of brightness, different real levels of brightness are contained within a particular band of the 8-bit data. Most of the cameras I use are 8 bit devices.
I will begin here with the 8-bit Mintron Frame-integrating surveillance cameras that can be set to synthesise long exposures by integrating up to 256 video frames in some models and which output a continuous video stream that is updated at a rate determined by the level of frame integration selected. For example, with the integration set to 256 then the image in the video stream is updated about every 5 seconds.
Images taken with the MTV-12V5HC-EX and an f/4.8 10" Newtonian
I was one of the first astronomers to use Mintron cameras about 10 years ago when I introduced them to my imaging group QCUIAG (an acronym for QuickCam and Unconventional Imaging Astronomy Group) http://www.qcuiag.co.uk/
Bev Ewen Smith at COAA in Portugal, with my help, developed some capture software called AstroVideo (works under Vista in XP SP2 compatability mode), that enables the integrated frames to be captured and saved in an AVI or to be saved as individual 32-bit deep FITs files as well as being registered and summed on the fly into a 32-bit FITs file. The program was my idea, Bev did all of the coding and I did extensive testing of the software. This program now has a large user base. I use AstroVideo for capturing data from Mintron frame-integrating cameras.