Why webcams for planetary, and not DSLRs?

[SteveL]

Just curious why webcams tend to be used for planetary imaging and not DSLRs. Can anyone explain it to me?

[GazOC]

You need a high signal to noise ratio, a web cam can fire off 10 FPS onto a hard drive for minutes at a time.

[Kaptain Klevtsov]

And a DSLR can't.

The useable image only covers sufficient pixels to need the webcam chip size, and bigger and its so faint that its no good. Instead of storing all the black bits of the DSLR image, you just use the much smaller chip to reduce the amount of "waste" data that you are collecting.

Captain Chaos

[MartinB]

And smaller pixels on a web cam so better resolution. Also I suspect (but might be wrong) that the web cam chips are more sensitive given they were designed for low light enviironments.

[barkis]

And smaller pixels on a web cam so better resolution. Also I suspect (but might be wrong) that the web cam chips are more sensitive given they were designed for low light enviironments.

Martin, does that mean my Canon digital camcorder would make a good imager? Not that I would want to, just curious.

Ron.

[Vega]

I thought the main reason for webcamming (using video) was that you can catch those precious few moments (frames) when Saturn is less obscured by the earth's atmosphere. A single DSLR shot will more than likely will be taken when the planet is totally distorted as it 'wobbles' in the atmosphere.

Matt

[bengriffin]

I may be totally wrong here, being new to these things, but there are basically 2 approaches to imaging: long exposure / slow shots and short exposure / fast shots with image stacking.

The challenge with slow shots is going to be drift - your telescope needs to track very very carefully in order to prevent motion blur on your image over a long exposure due to vibrations or poor tracking.

The challenge with fast shots is noise - as you have to use a very high iso setting (as set with webcams) there is much more noise to any given image.

I would imagine that using a very high iso setting (eg 3200) and relatively fast shutter speed would be pretty similar to using a webcam, but the larger sensor pixels on the webcam would be more sensitive to low light.

As with anything, it's always an issue of trade offs.

[brianb]

And smaller pixels on a web cam so better resolution. Also I suspect (but might be wrong) that the web cam chips are more sensitive given they were designed for low light enviironments.

Very little difference these days ... they're all about 50% efficient in turning light photons into electrons captured, and modern high pixel count DSLRs have tiny pixels too.

The big "down" for high res, long focal length imaging with DSLRs is the mechanical vibration from mirror & shutter. Webcams have no moving parts, therefore no vibration ... and you can take many hundreds of images in rapid succession. The stacking software will then picj out the sharper ones, rejecting those ruined by seeing distortions, wind vibration etc, and stack them to get an acceptable signal to noise ratio.

The video mode on DSLRs (those that have it) is something of a compromise in the way in which images are processed & stored - even with a web cam, capturing "raw" helps a lot. And the large pixel counts on DSLRs is a major "down" when imaging planets, as your flash card (or disk) rapidly fills with images which are mostly black sky ... the lower resolution (in pixel terms) of the webcam can be a big plus here; there's little point in imaging Jupiter more than 250 pixels in diameter, as that represents an image resolution of 0.2 arc secs, which is beyond what the atmosphere is likely to let you resolve, however big your scope is and however good the optics are.

[arad85]

Pixel size is around the same. My DMK21 is 5.6um pixel size, the 450D 5.2um size. The advantage of webcams is it is easy to get a LOT of uncompressed images of the planet quickly. Important if you're dealing with something that rotates quickly such as Jupiter and you want to stack lots of images.

If you're using a DSLR, typically, you'll be using it as a webcam in live mode. As Brian says, 99% of the sky is black and you'll be left with whatever processing artefacts the live view provides. It is possible, just I've not seen as good pics with a DSLR as with a webcam...

As to sensitivity, the sensors in use on the preferred webcams are more sensitive than those in general use. They are typically the Sony line of CCD and are chosen (by planetary imagers) as they are more sensitive than normal CD devices.

[MishMich]

You can use a DSLR for planetary imaging if you connect it to a laptop and capture the video stream. It is like using a webcam. To get a useful image you need to set it to zoom mode, and that transmits slightly higher resolution than VGA, but not as high as a high resolution webcam.

This was done with a DSLR:

as was this:

Which whist not brilliant, are better than anything I have achieved using a webcam to date.

You can use anything with a sensor that you want to, if you are prepared to mess about with it. I have started using a CCTV camera connected to a HDD/DVD recorder. There is no reason I can think of why you couldn't use a camrecorder - provided you were happy to remove the lens and connect it to the telescope. I'd do it myself, if I could find one cheap enough to warrant messing about with it.

M.

[yesyes]

hmmmmm....

That reminds me. I should have an old Hi-8 analogue camcorder somewhere still. Sounds like a project for a cloudy night... ;-)

[daz]

Wow!

I think this breaks the record for "Old Thread Resurrection"!!!

[MishMich]

bizarre - I never noticed....

M

[Moses_C]

Hi all, i suppose i'll be breaking the record again in 2012..

I'm new to astronomy (my Celestron C5 would be arriving somewtime around next month..yeah, that new) and would like to know beforehand, is a DSLR iso better than a webcam?

From what i understand by the above comments, pixel size isnt a problem, file size would favour webcam....but what about ISO performance? Can my Canon 550D be used to do everything (or at least..) a webcam can do? I've just recently realized that even serious astronomers almost always use a webcam of some sort to do imaging and video...

Thanks to all who will help out with this topic. Also, i believe this thread will be informative to many others, for many more years to come.

[michaelmorris]

The problem with taking images of bright extended objects such the Moon, Sun and the nearby planets is that turbulence in the Earth's atmosphere distorts the image, leading to different areas of the image being in or out of focus and the shapes of features being distorted over time scales of fractions of a second.

One technique for getting around this problem is to take 100s or 1000s of images and use software to align each frame then average out the brightness values for each pixel on the picture. To prevent smearing due to rotation/movement of the body you are imaging affecting the image and atmospheric turbulence, one needs to take a large number of frames in a very short time. This technique is called 'lucky imaging'.

Certain makes and models of webcam and high frame rate industrial video camera that have very sensitive (large pixel) CCD imaging chips, high frame rates (10 to 60 frames per second) and low-noise electronics, are ideal ways of capturing these type of data.

Special software such as Registax or Avistack will automatically select the sharpest frames, align them, then stack the best frames to produce an image based on the average pixel value for each pixel.

I hope this helps.

[michaelmorris]

Oops - double post.

[iwatkins]

Holy thread resurrection Batman!!

Anyway, maybe some of the info. is now a bit out of date...

Some Canon DSLRs can now have their LiveView imagery captured. E.g. On my 7D, I can use the APT software to grab thousands of frames as individual images without having to flip the mirror and open and close the shutter. Or you can grab a video using just the centre of the sensor. Both cases acts similar to a webcam.

Cheers

Ian

[michaelmorris]

Some Canon DSLRs can now have their LiveView imagery captured. E.g. On my 7D, I can use the APT software to grab thousands of frames as individual images without having to flip the mirror and open and close the shutter. Or you can grab a video using just the centre of the sensor. Both cases acts similar to a webcam.

I totally agree, some DSLRs now have very advanced video capture and nice high frame rates. They also have the huge advantage that you only need one camera for both planetary/lunar imaging and for DSO imaging.

In the past, the disadvantages of using DSLRs for astrovideo capture has been poorer low light sensitivity (when compared to a CDD webcam/video chip) and data compression of the video stream. I would be interested to know how the performance for planetary imaging of the latest DSLRs compares to such webcams/video cameras as the Phillips SPC900NC and the TIS DMK21 .

[iwatkins]

I do think that dedicated astro cameras are probably still more suited and easier to use. But for what they can do, they are expensive, but that is just down to volume of sales I guess.

But if you have a recent DSLR, it is becoming easier to use them for planetary as well as DSO. With software like APT it gets easier still.

I would suggest the later DSLRs are now better than the SPC900, as many can do higher frame rates.

I guess a dedicated camera for a particular role is always going to be better than a DSLR, but DSLRs can now do it all in a single body.

Cheers

Ian

[michaelmorris]

I certainly think that if you already have a DSLR with video/liveview capability it's worth dipping your toe in to planetary imaging with your DSLR first before moving on to more specialist kit.

[Moses_C]

Thanks very much Michael and iwatkins

Both your replies really cleared all the wondering and doubts i had earlier...

Ya, i shall just stick with my 550D for long time to come, and get one of those astronomy softwares to assist it...great advice and explanation from both of you.

Cheers!

[sanmatt]

This thread has given me hope!

I have a Nikon D90, and that has live view and video. So it ought to be possible? Anyone care to hazard a guess on how I might be able to actually do it and with what sort of settings I should use? I can pinch my sons laptop too. And I can hook up the DLSR to the scope, but I have to use the 2X Barlow or else I cant focus.

Thanks

[Moses_C]

This thread has given me hope!

I have a Nikon D90, and that has live view and video. So it ought to be possible? Anyone care to hazard a guess on how I might be able to actually do it and with what sort of settings I should use? I can pinch my sons laptop too. And I can hook up the DLSR to the scope, but I have to use the 2X Barlow or else I cant focus.

Thanks

Hi there..

I'm not sure how to do it on a Nikon, but I suppose its pretty close to a Canon...

I suppose you already have the necessary accessories to attach your DSLR... i.e. the T-Adapter (probably with 2x barlow, as you say) and Nikon T-Ring. Then with a bit of experimenting your new setup, maybe you'll be good to go..:p

Hehe..hope it helps a tiny bit...

Maybe you can try asking elsewhere like DPReview or some other photography site, where there may be other D90 users far more experienced than i am..

Oh btw, I've yet to receive my C5...looking forward to it. :)

Clear skies!

[Hugechris]

Has anyone had any success using movie capture via USB from a canon 1100D for planetary imaging?