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Old 01-03-2007, 08:10 AM
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White Rabbit
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Question about astro photography from a newb.

HI Guys/Gals.

I'm pretty new to amature astronomy having only bought my Meade ETX125 (shoulda got the meade 12" lightbridge but thats next ) at Xmas last year. I've been thinking of getting a web cam for the scope.

So here is my question.
If I buy a camera of some sort for the scope am I correct in assuming that my EP's cannot be used and that at the most I will only really be able to use a barlow? So I'm stuck with the normal magnification of the scope and can only increase this using a barlow? If so are there special EP's that can be bought that a web cam can fit into/onto.
I'm thinking about the Tocam web cam to start off with and if I enjoy that I may upgrade later to a DSLR.

Sorry that was more than one question.


Thanks
Sandy
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Old 01-03-2007, 09:04 AM
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When it comes to imagers, magnification is based on chip size. A smaller chip=greater magnification. For example, the Meade LPI is about the equivalent to a 6mm eyepiece, plenty of magnification for your ETX. On good steady nights you can add a barlow to the mix, giving you much more magnification. Hope this helps.

Clear skies,
Shane
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Old 01-03-2007, 09:08 AM
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[1ponders] (Paul)
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Hi Sandy.

If you are using an ETX then you should be able to fit the webcam at the straight through position and an eyepiece at the top and use the flip mirror to swap between the two. You may need to get a T adapter for the webcam to do this. You won't be able to use a barlow in this situation unfortunately. As for increasing magnification, you can use a barlow to increase but it would have to go where your eyepiece would normally go. Or you can use a technique called eyepiece projection (if you have enough range of focus with your focuse knob).

There are a number of ways you can do this. The easiest way is if your scope has a T thread at the back. If it does then you can use a Meade meade variable extender (or similar eg Orion). Using the variable extender you can get a considerable range of magnifications depending on the distance the camera is from the eyepiece and the eyepiece you use. This is not the same as afocal imaging. Have a look at the diagram below to get the idea. Just swap the SLR with a webcam. Oh and you will need the webcam T adapter for this as well.

Hope this all made sense.
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Old 01-03-2007, 09:10 AM
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[1ponders] (Paul)
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PS: for your situation you can ignore the eyepiece holder - visual back. I don't know if you can get one with a T thread anyway.
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Old 01-03-2007, 10:08 AM
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Thanks guys, thats very helpful. I take it the projection tube is to give you more focal length ie more magnification.
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Old 01-03-2007, 11:05 AM
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Basically yet. It is a bit like getting a torch (say an old fashion chunky dolphin torch) and standing 1 meter away from a wall. The wall represents the camera chip and the torch lens the eyepiece. The torch projects a circle of light onto the wall. As you move the torch further away from the wall the circle of light will get bigger.

Now if you changing to a torch with a different lens, like one of the newer led torches that have a smaller light circle at 1 meter, it's like changing eyepieces.
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Old 04-03-2007, 04:45 PM
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I'm using an ETX 105 to play with Astrophotography.
I have used a Webcam (Neximage) direct where the EP fits, I can also use the 2x Barlow.

I have also bought the Camera adaptor and mounted the SLR on the back.

The field of view with the Webcam is 7'45" x 5'20".
On the 125 the FoV wuold be reduced by (1470/1900).
The chip size on the Neximage is 3.6mmx2.7mm

With the D80 slr and the short T-mount the FoV is 49'x33' (the focal length becomes 1,640mm at F16. The chip size of the D80 is23.6x15.8mm)

For 35mm the FoV is 75'x50' with the same set-up.
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