Imaging with a
Best of the early webcams was the Philips' Toucam. However, over the years Philips updated the webcam but only in its appearance - not its performance. They remained USB 1 devices to the end. When it comes to maximising frames per second they have been left behind not just by the specialist video cameras used by the experts (up to 60 frames per second for these guys) but also by more modern webcams. The Philips are no longer available new and perhaps the new king of the castle will be the Microsoft Lifecam Cinema with a potential for 30 frames per second. I have recently acquired one and decided to investigate further.
The Lifecam Cinema features an Omnivision HD chip (see below) with excellent low light performance. Pixel size is 3um square which means less telescope magnification is needed. The HD resolution (up to 1280x800) whilst somewhat overkill for planetary imaging is excellent for the Sun and Moon and does mean finding/centring planets is much easier.
Specification for the Omnivision Sensor
Modification for Astronomy
I am not going to repeat here the modifications needed for astronomical use. These are given in great detail on Gart Honis' webpage. Suffice it say the camera size is ideal and what we will end up with is an eyepiece sized camera. Don't forget to paint out the tiny blue LED on the circuit board.
My modded webcam mounted in an old eyepiece. Note a UV/IR block filter will be required.
Software - Taking
I tried both WxAstroCapture and SharpCap selecting the 1280x720 HD resolution. Both are similar and have the essential histogram display for checking over/under exposure. I settled on SharpCap as it offered the promise of 30 frames per second (fps) using the MJPG codec. This codec and frame rate did not appear as an option with WxAstroCapture. SharpCap was a bit flakey and liable to crash but I decided to go with it. I didn't achieve 30fps with Jupiter on my laptop - 20fps was the fastest possible for no dropped frames. In further tests my Quad Core desktop could indeed capture 30fps so it appears that maximum frame rate is down to the PC. However, 20fps is a big improvemnt and means 3000 to 4000 frames can be captured before Jupiter's rotation becomes apparent. The MJPG avi files produced are much much smaller than those saved under the YUY2 codec. I took a selection of both to compare. Quality looked similar - these are lossy compressions so neither is perfect.
Software - Processing
Registax6 had no issues with opening either type of avi file - YUY2 and MJPG. I could not persuade AviStack2 to read the MJPG files - "Codec not supported" message. This was despite following instructions to load the krsgravi DLL/DLM which is supposed to fix this. There is also a note that it can read any codec that Windows Media Player can play (the latter played them both) but no go for me in Avistack2. So Registax6 it is for processing.
Registax6 is starting to become somewhat bloated and suffers from overkill in my opinion. Where is the simplicity of earlier versions? I used it for the multipont alignment. Watch out for dust spots on the chip - flat fields would solve this.
I used a Celestron C8 Celestar - a classic from the past! No GOTO and simple spur driven RA drive. From the first tests, if Polar alignment is good (not easy with the Wedgepod - you have to kick the legs to adjust) then having no electric DEC drive is not a problem. What is definitely needed is a focus motor which of course it doesn't have.
With the small 3um pixels of the Omnivision chip a focal length of around 4 metres is sufficient. Rather than a barlow lens I use a 2x teleconverter bought on ebay for £2.56. It was a Japanese clone but even these are 4 element and on-axis images are good.
First image. Jupiter 2012 with Celestron C8 Celestar at f/20 - OK but not brilliant
Tried the Lifecam out on the Moon which produced some strange results. This was of course imaging over the full extent of the sensor. So I decided to take a flat (300 frames) and see what was going on. The following was the result:
There was a definite reddish tinge to both the left and right edges - a sort of reverse vignetting. As a first guess I thought it was amplifier glow? On second thoughts it is so regular I think the camera must have a built-in flat-field to correct for the deficiencies of the lens Microsoft provides. It does mean shooting extended objects would really need flats taking. These are somewhat problematical with lossy compressions. Possibly blurring the flat first to get rid of the lossy artifacts might work. More thought needed. It is not an issue with Jupiter.
After the problems with the Moon I returned to more tests of Jupiter - I wanted to see if I could get the colour balance a bit better and image the Red Spot plus some moons. There has been no colour adjustment of this image - colours as taken. The details of this Jupiter shot are on the image - it was the best 2000 frames from a 3000 frame avi..
Later the same night there was a transit of Ganymede plus Io was nearby. I was able to fit all three in the frame. This time best 1500 from a 3000 frame avi - there is less sharpening as wavelets seemed to mess up Ganymede's shadow.
Reasonable seeing and the promise of the Great Red Spot and its junior companion enticed me out on the 10th Decmeber - despite the cold!
Pushed my luck with a 4000 frame avi and selected out the best 1000 or rather Registax did. Auto colour balance this time got a slightly different result - seems a bit random.
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