First Light SPC900 Webcam

[MarkS]

Tonight was my first attempt at using a webcam and also Registax.  The webcam was on the Celestron C11 with two 2x barlows to get the magnification.  I stacked 130 frames out of the 500 recorded.



In my ignorance, I'm not sure which way up it should be ...

[Carole]

Well done Mark if this is your first time using a webcam.

I am still struggling on my 4th attempt to get anything in focus, see my other posting.

Carole

[Ian]

looking good Mark. The focus looks good and the resolution is there in the detail. I think it would take more aggressive processing. Some sort of deconvolution or high pass filtering will help. Did you play with the wavelets in Registax?

[JohnP]

Excellent first light Mark... Did you use an IR filter..? Also did you check RGB align in Registax... I'm really glad you got this - Society members have not posted too many images of Mars which is a shame. I'm guilty but I no longer have a standard webcam - all my are modded & I can't do short exposures with them....

Looking forward to seeing more,

John

[MarkS]

John, 
Yes I used an IR filter because I removed the original webcam lens.  I also needed to align the RGB in Registax because the raw frames showed obvious colour fringing, but why, I'm not quite.

Ian,
I've never used wavelet processing - I'll try some experiments with it.  However, I did perform some mild deconvolution outside Registax but I'm always wary of introducing artifacts.  But the image does look clean enough to be a bit more aggressive.

I've still got 7 more AVIs of Mars to process.  But I know one was wrecked by a freight train going past!

[Ian]

colour fringing is an atmospheric effect, because of the really high focal length you're using you'll see it much higher up than normal. It's not objectionable in your image, but it is still a little blue bottom left...

Registax is set up nicely to allow you to play around with wavelets without having a clue about what you're doing. With your understanding of signal processing, you shouldn't have any trouble with it. Most of the time I just play around with the sliders until I get something I like the look of

Sounds like Railtrack could do with checking their tracks. If trains are getting between your scope and Mars, there must be a bl***dy big bump in the track. And to think they only replaced that track a year or so ago

[RobertM]

Hi Mark,

That's pretty good, infinitely better than my latest attempt in the windy conditions last week.  Maybe I should use an IR/UV blocker to - would it make much difference ?

What barlows did you use ? I used a single x2 (f20) but all the best SC images seem to be taken at f30-40.

Robert

[Ian]

Robert, it depends on the number and strength of the refracting elements in the image path. Prime focus with a newt won't need an IR block as IR is focussed at the same place as visible light. Correctors, barlows, focal reducers, refracting objectives all put the IR way out of focus compared to visible light.

I wouldn't get hung up on UV filtration. Glass is largely opaque to UV and CCD response drops off substantially in the blue, let alone UV. Have a read of some of the amateur attempts to image Venus in UV...

[Rick]

In my ignorance, I'm not sure which way up it should be ...

Standard orientation for observations of the Moon and planets has South at the top and West on the right. This is the way a standard astronomical refractor presents its image to the observer.

You can find a whole lot of Mars maps on the BAA Mars Section's website at http://www.britastro.org/mars/maps.htm

[Mike]

Very nice Mark.

[RobertM]

Thanks Ian, that's saved me a few pennies that I can put towards some other bits.

[Fay]

Really nice image Mark. You really do try hard & it is paying off.

Fay

[MarkS]

I've processed one of the other AVIs, done a bit of colour balancing (by assuming the ice cap is white) and some wavelet processing.  I've also flipped it round so it's displayed with the standard orientation mentioned by Rick.  Thanks for that site Rick - there are some very useful maps there.

The result (on the right) is quite a lot better:


Damian Peach has a very similar view from a couple of months ago (but his one is far better!!):
http://www.damianpeach.com/mars07/m2007_11_05rgb01_dp.jpg

Robert, two Barlows turned my f10 scope into an f40.  I just used a couple of cheapish Celestron ones I bought for my previous scope.  However, I might try eyepiece projection next time.  Also if your conditions were windy, the seeing was probably poor.

[Ian]

now that is much better. If you're feeling brave you could push the processing even further, but I would probably call the result over-processed.

As far as stacking barlows is concerned, I don't think it's quite as clear cut as that. The strength of the barlow is also related to the distance the barlow lens is from the CCD. And also the distance between the barlows if you've got a stack. If you know the apparent size of the disk, you can work out the plate scale and the actual focal length of your instrument.

If you've got Maxim DL, and an image of a star field, it'll work it out for you (after it's worked out what bit of sky you're looking at). Clever stuff, that is.

[MarkS]

Ian, yes I tried it with more aggressive processing but it did result result in an over-processed look.  I prefer to err on the side of caution.

You're right about your comments on the Barlows.  I hadn't thought of that.
Doing a rough calculation:
Mars is approx 15-16 arcsec in diameter at the present time
My image is 160 pixels across.  Therefore I'm getting 10 pixels/arcsec.  i.e. 1 pixel is 0.1 arcsec.  Usually, on my Canon, the pixel spacing is approx 0.55 arcsec but on the SPC900 they're slightly smaller:  5.6 microns against 7.1 microns
Therefore the SPC900 would normally give 0.44 arcsec/pixel.

So that combination of Barlows and webcam seem to be giving a factor of around x4.4