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Webcam question

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Keep seeing different posts and articles about barlows , f'numbers focal reducers etc.....now im confused. Want to do some lunar / planetary imaging with my webcam. At the mo I have the meade 2x telenegative barlow. Do I need a 4x ?? and what about a focal reducer :) :)

Thanks in advance


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Hi Chubster,

Generally when webcamming the planets you want the highest focal length/ f number that your scope or the 'seeing' will permit. Your 2x Barlow will do the job just fine, a 4x Barlow will not come into focus in a Newt like yours when you are using a webcam.

Focal reducers lower the effective focal length for a wider field of view but again most (all?) cannot achieve focus in a Newt when using a webcam.


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This is a tricky subject :)

I reckon that you need to go for at least F20 and higher to sample the image enough to get truly hi res lunar/planetary images, given good conditions and equipment. If you look at the stuff Damian Peach and others did with the Toucam you'll see they often used F ratios of over 30! Getting there with an F5/F6 Newtonian is another matter. some Newts have no problem with focussing, but others do. The Skywatcher Newts can use 4x Barlows but some "might" need modification. The ones with 2" focusers can however be easily and cheaply adapted to work, if anyone's interested please pm me.


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The F ratio is the focal length divided by the diameter of your lens or mirror, however, the apparent focal length can be increased or decreased by using Barlows and focal reducers and this changes the effective F ratio.


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My suggestion follows the lets use what you have route.

I had a Toucam, a 10mm EP 8" F5 New (totally Rubbish for planets - when compared to SCT's and refractors etc). I also had a projection tube.

I put the 10mm EP in the projection tube, made an adapter out of some plastic tube and masking tape. and got the Toucam to slide in the end of the projection tube.

The beuty of that is that there wasn't a barlow in sight, I could create a larger image scale by sliding the toucam further out of the projection tube - thus increasing the size of the planet on the chip.

In case you having trouble with that, think of a torch. Shine it at a wall from the distance of say 3 feet. You'll get a circle of light a certain size. Move the torch away from the wall and the circle of light gets bigger.

Hope that helps... it worked a treat for me!


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