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 Post subject: Using webcams
PostPosted: Wed Apr 06, 2011 9:04 pm 
I had an interesting chat with Dean after yesterday's meeting about the use of webcams.

He mentioned that he was using the webcam with an SLR lens. I have a couple of old Sigma zoom lenses (for Canon EOS) that are not compatible with the modern DSLR that I now have. It sounds like these would be ideal for sticking on the front of a webcam.

I've attempted to take some shots of the night sky using my DSLR but I can't get a wide enough angle to take constellation pictures and, when I zoom in on something, I just get streaks because of the earth's movement during the exposure. Now however, I have a EQ mount and scope so I guess I should get some motors, polar align and try again. There's a mount for a camera on top of the scope or I could try through the scope itself.

So my questions are :

1) would it be possible to borrow one of the kits sometime?
2) Dean, I've looked at the pictures in your album. Do you have any raw video I could download so I can have a play with Registax and other software?

Thanks,

Antony


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 Post subject: Re: Using webcams
PostPosted: Wed Apr 06, 2011 9:28 pm 
Hiya Antony, yeah sounds like those lenses would be perfect for use with a webcam... To get proper wide field images with the webcam though I just use the tiny lens that is attached to webcam when it arrives, this hives a wide enough view to fit most full constellations in. It's almost impossible using an slr lens as this tends to magnify your view to much ..... I have hundreds of raw avi streams ( mainly trial and error ones) and will send you a couple to get to grips with registax. I have found that using the webcam through the scope is futile unless your mount tracks properly and Is set up correctly .... However, this said when it is the images can be amazing ( see Ross' album in the gallery section) in order to get used to the webcam though I would try it with the original lens then the slr lenses first as this really shows what they can do and helps you grasp the settings etc..... I will be bringing kit no. 2 back next meeting which has everything you need including 3 different lenses to try, I'm sure you will be fine to borrow this and I can talk you through using it if you get stuck ....
Hope this helps.


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 Post subject: Re: Using webcams
PostPosted: Thu Apr 07, 2011 7:36 am 
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OK Antony, if you have a Canon DSLR, then you've got probably the best-value solution for astro-imaging! :)

But those zoom lenses are not ideal for astro-work: since they have more elements, they give dimmer images and more dispersion than fixed-focus lenses. So it's worth looking out for good-quality fixed-focus lenses on the second-hand market. If you get yourself a T-mount adaptor to go on your Canon, then you'll be able to use T2 mount lenses from any manufacturer.
And most 'scopes also have provision for T-mount cameras, so you'll be able to image through that too.

But your first purchases should be an RA drive motor and polar-scope for your mount, after which a whole range of possibilites will open up... ;)

I'll be co-presenting a talk on imaging Saturn at our 3-May meeting, and will be bringing along a couple of CDs of AVI images to use as demos - you'll be welcome to take one of these away afterwards to try for yourself.


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 Post subject: Re: Using webcams
PostPosted: Thu Apr 07, 2011 11:12 am 
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But it is still possible to get some interesting images when using a wide-angle lens on a fixed tripod.
Have a look at the section on the electronic equatorial in this IRIS tutorial:
http://www.astrosurf.com/buil/iris/tutorial2/doc11_us.htm

Remember that you need to use a wide-angle lens and to make each exposure short enough that there is no trailling.


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 Post subject: Re: Using webcams
PostPosted: Thu Apr 07, 2011 4:37 pm 
If i was you Antony I would concentrate on setting up the mount you have correctly and attaching the webcam 'piggy back style' to your scope. That way you can image and observe at the same time and you know your mount is tracking the target properly and you can expose for as long or short as you like knowing you wont get trails .... The reason I say this is that a mount like yours will be my next purchase before a scope of any kind as the mount will aid taking better images for me ...... Now, I'm sorry but I dont pretend to know a great deal about setting up mounts and as they say, if you cant swim stay out of the pool, so I'm not going to start telling you a load of jibberish. I'm certain some of the other members will be glad to help you with this though. Ross was kind enough to lend me a motorised mount of his that has improved my images somewhat in that it tracks well when i point it in the rite direction, (and at the correct polaris eh Ross, lol) and if you want to get good images of deep sky objects then long exposures and the mount tracking correctly are essential.....


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 Post subject: Re: Using webcams
PostPosted: Thu Apr 07, 2011 7:51 pm 
Motors and alignment scope ordered. That should help me to find things and keep them in view.


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 Post subject: Re: Using webcams
PostPosted: Fri Apr 08, 2011 10:47 pm 
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Antony,
Your Canon DSLR is better for constellations/deep-sky than a webcam. Webcams are the best for Planets and the Moon. Webcams can be modified for long exposures but they will still not match a Canon - Canons are incredibly low noise!
For constellations I use an old Pentax 28mm f/2.8 lens on my Canon. You will need an adpater to convert the lens to EOS but these are cheap on ebay (as are old Pentax lenses) - BTW they are not T-mount adapters that is something different. Ross is correct about zooms - avoid them. The other requirement will be a light pollution filter. The £25 SkyWatcher one is pretty good.
Good luck!


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 Post subject: Re: Using webcams
PostPosted: Mon Apr 11, 2011 3:02 pm 
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Whilst I concur with Dave's remarks about Canon DSLRs (and as you can see from looking at his images: http://www.deep-sky.co.uk/imaging/dslr/dslr.htm), I must say that you can't beat the Philips webcams for value-for-money (and you don't need to then pay more to have their IR-block filters removed either!)

And they are so versatile: I used the very same camera (and 'scope) to take this picture of Saturn:
http://www.boltonastro.org.uk/Gallery/displayimage.php?album=7&pos=17
and this one of The Owl Nebula:
http://www.boltonastro.org.uk/Gallery/displayimage.php?album=18&pos=18
just a couple of nights apart.

For the Saturn image, I had the webcam in Normal mode, and used a Barlow lens to get more magnification from the 'scope (a Celestron 8" SCT). But for deep-sky imaging, I use the webcam's LX mode, and fit a focal reducer to give me a wider field of view (and shorter imaging time).

And when I do use my DSLR (a Pentax - not as good for astro work as the Canon), it's mainly with lenses - from telephoto to wide-angle:
http://www.boltonastro.org.uk/Gallery/thumbnails.php?album=5
Attachment:
File comment: Imaging with DSLR and telephoto lens
k110d2.jpg
k110d2.jpg [ 108.96 KiB | Viewed 6603 times ]


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 Post subject: Re: Using webcams
PostPosted: Mon Apr 11, 2011 8:44 pm 
I have an EOS 400D but only one of the lenses is a prime (50mm f/1.8). I used it for some general shots on a fixed tripod so I could practice recognising some of the constellations. However, given that the sensor is not full-size, this gives a effective focal length of 80mm which isn't really a wide enough angle. The kit lens (18-55mm) is useless.

Additionally, this camera does not have the live view option and I have great difficulty seeing the stars through the viewfinder so focussing may be an issue. My scope (SkyWatcher Explorer 150P) does have a direct SLR connection if I buy some bits to connect it. It has a focal length of 750mm so with the 1.6x factor, I assume this would be equivalent to 1200mm.

The attraction of the webcam is that I will be able to see the image on a laptop and get the focus correctly set up. I can also stay in the kitchen where it is warm. It is also lightweight and cheap so if the cold and damp get to it, it won't cost £500 to replace.


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 Post subject: Re: field-of view calculator
PostPosted: Tue Apr 12, 2011 7:41 am 
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Antony, I find this free utility from the Astrononmical Society of Southern New England very handy:
http://www.assne.org/ccd.zip

You can enter the parameters of your telescope, lenses, webcam and DSLR sensors, and it will calculate the field-of-view of any combination.
You can then use any planetarium program to check how much of the sky you can fit in (the CdC program will actually display the field of view as a red rectangle).

Here's an example of it in use:
Attachment:
File comment: ASSNE "CCD" program showing the view of M31 using a DSLR and 200mm lens
fov.png
fov.png [ 16.56 KiB | Viewed 6592 times ]


Incidentally, my recent image of The Owl Nebula http://www.boltonastro.org.uk/Gallery/displayimage.php?album=18&pos=18 was taken with my webcam through my 8" telescope operating at around 700mm focal length - very similar to your Newtonian!


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