PDA

View Full Version : x box , cheapest webcam astrocam recorder ?



mtumut
10-29-2006, 09:47 AM
I am still trying to find the cheapest data recorder of a astro web cam. Astronomers take super quality pictures with webcams . I want to do the same but directing the lens to nature. Naturally you have to take minutes long exposures for to grap the may be 100 megapixel. I found sherlock holmes traces of a data recorder , they say x box records the video. x box units cost 55 usd used. Do they work for my mission , are there even cheaper formulas ?

Best ,

Mustafa Umut Sarac

JoeVanCleave
10-29-2006, 10:44 AM
I'm probably the wrong person to answer your question, but here goes. My understanding, through reading a few of the articles in Sky & Telescope, is that dedicated astronomical CCD cameras for amateur use are a bit more sophisticated than a mere web cam, especially regarding resolution. And they have dedicated software that run the camera through a PC, usually a laptop for portability. And professional astronomers are using CCD's much more sophisticated than the type advertised in Sky & Telescope for amateurs. I would doubt that a professional would use a webcam, and there's no webcams that I know of with 100 megapixel resolution; in fact, a CCD of that resolution is very expensive, if available at all.

If you are interested in the "cheapest" solution to adapting a CCD camera as a digital capture device for scenic photography, an el-cheapo digital camera is still your cheapest solution. I purchased a "Jam Cam" about 5 years ago, for 20 USD at Fry's Electronics; I'm sure by now the selection is much better for cheap cameras.

The problem with finding high-resolution camera sensors on the cheap is that their manufacture is the most expensive part of the whole package. It's getting a grid of photo transistors on silicon with very few defects, and doing it inexpensively. It's easier to manufacture logic chips, since their transistors are not compacted into a grid like memory is. One sub-micron particle on such a memory array during manufacture can kill the entire row of cells; not necessarily so with logic chips.

Silicon real estate is expensive, and goes up with the square of the area. There are probably image sensors being manufactured for use in surveillance satellites where one entire 8" silicon wafer contains one rectangular image sensor. These would be on the order of hundreds of megapixels in capacity. But the yields would be tremendously low (i.e. how many at the end of the manufacturing line that work with a minimum of defects) and these would cost hundreds of thousands of dollars per sensor - a price that large governments and research institutes can afford, but you and I probably can't.

I also know that many consumer-grade CCD cameras use what's known as a "masking ROM", which is burned in at time of manufacture with a memory map of the defects present in the CCD; the masking ROM then works to buffer the output signal from the CCD and 'fill in' the missing pixels with an approximation of the average of the pixels surrounding the defective cell. This is a great idea, since it improves the manufacturing yield - or rather, it allows the use of otherwise defective chips. But as CCD's age, further pixels will start to die - which the masking ROM hasn't been programmed to compensate for. Which is why, after a few years, your digital camera or video camcorder starts to show pixels, especially if you cap the lens or shoot in a dark scene.

Back on topic, I'm sure you can figure some cheap method of adapting a web cam to scenic picture taking, but it isn't going to be hundreds of megapixels, astronomical quality imagers.

moot
10-29-2006, 12:30 PM
Joe, actually they are doing a lot of work with plain webcams. They are not, however, getting multi-megapixel resolution. I think what mtumut is referring to are planetary images, and the quality is not the result of fabulous resolution, but of overcoming the distorting effects of atmospheric turbulence. The images are recorded through a USB port using a PC, and any laptop would work. The image resolution is actually quite low, usually less than one megapixel.

What is typically done is to take video sequences with the webcams, then use computer programs (e.g. Registax) to filter the sequence, throwing out the images where the atmosphere caused fuzziness, and saving the images that happened to be taken during fleeting moments of stability. Once the best images are separated out, they are then automatically aligned and stacked. Noise decreases roughly as the square root of the number of images one combines, so if you stack 100 images you get an image with only 10% as much noise as an individual frame. Some of the best images are stacks of hundreds of individual frames. The resulting stacked image is then processed using Photoshop or some similar program to improve contrast, color saturation, etc. Despite being relatively low-resolution images, the results can be incredibly good. Amateurs with small telescopes now take some of the best planetary images available, except those taken from space.

Mtumut, what may not be apparent is that there isn't much point in going to higher camera resolution, since the webcam resolution is capable of capturing pretty much all the detail the telescope can resolve. Remember that these images are of objects only tens of arcseconds across, and the ability of the telescope optics to resolve fine detail is limited. When you point a webcam at a scene on earth, however, the limited camera resolution will be immediately apparent.

You might get what you want with a good digital camera and "stitching" software used to make panoramas. Assume that you would normally use a short focal length lens and maybe a 10 megapixel sensor to record a scene. If instead you use a longer lens and maybe four images (with the same sensor) to cover the same scene, you will get (approximately) four times the resolution. The longer the lens and the more images you combine, the higher the resolution of the resulting image, up to the limit of lens resolution.

This image is an example of that technique: http://www.tawbaware.com/maxlyons/gigapixel.htm

mtumut
10-29-2006, 01:46 PM
This is the strongest idea i have ever found. megapixels were my headache and i m seeing nightmares since it is widely available. Now I need a digital cam with tele lens very cheap and high quality.
I can pay 30 or less. Which camera do you advise ?
Finally I survived from data recorders or something else. May be it can be stacked more than one picture per frame and than all stitched.

Best ,

Mustafa Umut Sarac

moot
10-29-2006, 10:35 PM
This is the strongest idea i have ever found. megapixels were my headache and i m seeing nightmares since it is widely available. Now I need a digital cam with tele lens very cheap and high quality. I can pay 30 or less. Which camera do you advise ?

That's impossible for me to say. I would suggest that you can always get more performance for a given cost by buying used equipment, and probably buy locally to reduce or eliminate the cost of shipping. I'm not familiar with the different stitching software packages, but I suspect you can find programs that will do what you need available for free download. There is a lot of information on the Internet, in fact there are several links from that site. Good luck, and let us see the results of your efforts!