How do you focus a webcam on a telescope?

[Alienfox]

OK, so last night was nice and clear for a few hours last night, so with converted webcam , telescope, laptop and wzAstroCapture runing I point my scope at the sky using one of the stars of Ursa Minor as a point of reference, nothing, I cant see athing?  So I point it at a window across the street, it works no problem.  I then tink that maybe is because I am not focused on the stars so they are just to blurry to pick up, my question is how do you focus on such a small point of light using this sort of setup, if I inset a 25mm eyepiece and focus using that and the switch over to the webcam will that work?

Thanks.

[Ant]

First thing to remember is that the field of view on a webcam is quite small.

What's in the field of view of a 25 mm EP won't necessarily be on the chip. Both the EP and webcam will have a different focus point. The webcam will be much closer to the scope than the EP.

So....

1. the finder needs to be very accurate, or use a high powered EP (10mm or below) and make sure that the object is as centred as you can.

2. Pop in the webcam, wind the focuser all the way in. Then slowly start to move the focuser out, while watching on the laptop screen. Turn the gain up, it'll be very noisy, but for this it doesn't matter. If the gain is right up, then an out of focus star (even if it's slightly out of the field of view) will still start to appear.

You may find that you cannot reach focus with a webcam (common problem with Newts) with some form of modification.

The easiest way is to wait till the moon is about, and use that. Much easier to find and get on the chip, plus once you've definately got the object in the chip you can find focus and once you've found focus, mark the position in some way (I used a lead pencil to mark the draw tube).

Cheers

Ant

[RichM63]

You are asking a lot from a relatively small telescope and a webcam designed for video chat, there is generally just not enough light hitting the chip for stars to register as sharp focus.

Webcam use is best left to bright objects such as the Moon, Jupiter and Mars if you are lucky.

As per Ant, find and mark the infinity focus point if you can.

At the moment Jupiter would be the target of choice with a webcam. Turn the gain right up and focus on the moons as bright points of light, then reduce the gain (a lot) don't touch focus, the planet will be in focus but will zip accross your screen from top left to bottom right, so you need to practice chasing it to keep it centered.

You will also have 'seeing' problems with what looks like a boiling effect, this is the same for any kit.

Stars with a cheap webcam tend to look like noise when processing the video, in fact the noise often looks better than the stars.

[JamesF]

Yup, start with the Moon.  There's a much greater margin for error with such a large target.  During the day you could try focusing on something quite distant to get a rough idea of the correct position of the focuser with the camera.  As ant says, it can be quite different from that with an eyepiece.

James

[knobby]

Also try focusing on something distant in daylight with an EP , pop webcam in and count how many turns of focuser til focused ...

[wayland]

I have found that a X2 barlow lens working in conjunction with a webcam makes focusing easier. Often with newts the focusing range does not allow the webcam to achieve focus. i.e. the focuser hits the stop before a good focus can be achieved. The barlow will focus and can be modified so the webcam does also. 

[Waldemar]

If yoiu can see the windows across the street with your webcam, that means the lens is still on it.

If you  directly mounted the cam on your scope with the lens still on the cam, you will not be able to see anything. Impossible to reach focus . Two options:

#1   take the lens of the webcam, so you can see the sensor and use your telescope as the camera lens.
#2   Use an eyepiece and use ep projection on the webcam.

 

Waldemar