Cheap Webcams

[bholmes]

Ross
Looking back at the photographs in you earlier post, how do you connect the webcam to a camera lens.

Regards

[rwilkinson]

how do you connect the webcam to a camera lens?

My original prototypes were made by screwing a plastic rear lens-cap (which includes the bayonet-fitting for the lens) onto a wooden batten, and drilling a hole in the centre, into which I could "bodge" the webcam's original lens-assembly (having removed the plastic lens elements):

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Then Brian made us some smart metal versions with a 1.25" hole in the back, into which a webcam with a "Mogg adaptor" will insert:

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(there is one of these in each of our BAS webcam loan kits)
The difficulty with this is making the lens fitting on the front: if it's a Pentax M42 or T2 mount lens then a standard thread can be cut, but if it's a bayonet-mount then you'll need to salvage the flange off the front of an old camera.
And you also need to include provision for an IR-blocking filter, otherwise you'll suffer from "fuzzy focus" and some very strange colours!

[rwilkinson]

This is a test from earlier this month, using my SPC880 colour webcam in RAW mode - here the camera outputs a stream of RAW monochrome (Colour Filter Array) frames in a .AVI stream, and I use the "De-Bayer" option in RegiStax to decode them back into colour.
However the decoded images look very green at first (since there are twice as many Green pixels as Red & Blue), so finding the colour-balance is quite fiddly.

Jupiter on 9-Dec, imaged with C8 and Barlow-lens (effective focal length around 7.5m). SPC880 webcam operating in colour RAW mode. Best of 200 frames stacked using RegiStax 5.1 and then processed in IRIS.

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Although the colour RAW mode should provide slightly improved resolution over the standard camera settings, I suspect that in practice the seeing conditions are more of a limit, and it's a lot less hassle to operate and process using the standard camera mode.

But when operating the webcam in Long-Exposure mode and imaging larger objects at lower magnification it should be better to use the colour RAW settings.

[rwilkinson]

Last night I revisited my experiment with operating my Philips webcam in colour-RAW mode (this produces much better calibrated long-exposure deep-sky images, but takes more processing).
Previously I'd struggled with the processing to get a sensible colour-balance in my planetary images (i.e. capturing AVI streams in non-LX mode), but last night I found a new combination of settings which provided realistic colours straight away.

In the SharpCap program there's an "SPC raw debayer" mode which displays the live image in colour, rather than the monochrome Bayer-matrix fed from the camera, which would look like this:

Bayer-matrix from webcam operating in "colour RAW" mode

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Then I eventually found the raw de-bayer controls in RegiStax6 (they are hidden in the "Pre-filter" menu!) which colour-converts the image stream on the fly, and speeds up the processing.

The "seeing" wasn't so good last night: there was a gusty wind, so it took me a few attempts to capture a 500-image stream without the planet being "blown across" my CCD.

Jupiter on 29-Mar-2014, captured with SharpCap from Philips webcam in colour-RAW mode on C8 operating at f/35.
Stacked in RegiStax6, then processed in IRIS.
(I've just realised that South is at the top on this image, as I was meridian-flipped from my usual imaging set-up)

jup_raw_29Mar14.jpg (12.78 KiB) Viewed 4297 times

So now I can leave my webcam in colour-RAW mode both for planetary and LX-imaging.