My sick Takahashi

[atalas]

Peter If your talking about the distance needed for the artificial star I think Its 20 x the focal length but If you can go longer to be on the safe side.

Cheers

Louie

[Starkler (Geoff)]

Originally Posted by Exfso

When I rotated the toucam, the oval image rotated as well on the laptop, I reckon if it was objective problems the image would not have moved.

I dont want to scare you, but im thinking the opposite would be the case.
If the toucam is moving in relation to a fixed astigmatic objective, the astigmatic image would rotate on the screen.

If the astigmatism is in the toucam, it wouldnt rotate at all.

Im sure there is another explanation.

[atalas]

Hi Geoff, you could be right but I think that the astigmatism would reveal Its self at the eyepiece at 200 x . I could see how turning the camera will revolve the image but If you take a scope and turn It upside down you still see the same orientation through the eyepiece.

Cheers

Louie

[Stephan]

>The two really oval piccies were taken at over 500x with toucam, the other >two at about 200x

For a useful star test your need a magnification of at least 3x the aperture (in mm) but 4x to 5x are better. Your star test images with the 200x are not really meaningful.

If you use the webcam at 500x again, take one star test image (of the inner focus) then rotate the webcam and take another image. Repeat this with the outer focus. This will reveal if the webcam ccd-chip is not flat or if the telescope optics has astigmatism.

Stephan, I have already done this and confirmed that as I rotate the webcam, the oval picture rotates as well. The higher the magnification, the more the oval shape is prevalent. I will try and get a still picture through my digital camera and my artificial star and see what transpires.

Cheers

[RB (Andrew)]

Originally Posted by Exfso

Stephan, I have already done this and confirmed that as I rotate the webcam, the oval picture rotates as well. The higher the magnification, the more the oval shape is prevalent.

Cheers

So does this mean the fault is in the webcam or the telescope?

As near as I can tell, if the oblong image rotates when I rotate the webcam, it is not the optics but the webcam, sounds logical to me. It it were the optics, rotating the webcam would not make any difference to the position of the oblong image, at least that is my thinking. I actually have the scope set up in my shed with my artificial star some 20 metres away, no webcam, no diagonal, and just allowing the scope to become ambient, but as far as I can tell at present through the soup, the star image is round as it should be. Stay tuned.

[elusiver]

update exfso??

el

Been out of town a few days, not had a chance as yet to do anything. Will probably use Rumple's proper star up in the flinders ranges for a test.