D100 photography

[Dindsy]

Hi There,
The other night I tried taking photo's of the moon with my D100 attached to my Skywatcher 6". I came acros 2 significant problems and got pretty crap results. this is the second go I've had and no luck.

Problem 1. The image I see when my D100 is attached is smaller than when I just attach the EP.

Problem 2. I can't seem to get it focused. at first i thought it just couldn't get in/out far enough to enter focus but more testing showed it comes more or less into focus and then shifts out of focus when i trun the focus knob.

The set up is: The EP is inserted into the camera adapter, the camera adapter is connected to (wait for it) the camera, just like a lens would, and then the whole assembly is slid into the EP socket(?) on the scope.

Shutter speed is handled manually because the Aperture doesn't function with the adapter in place and not a lens. I use a chord to trigger it to reduce wobble

Any idea's.

thanks

[iceman (Mike)]

Hey Dindsy,

1) What you see when looking through the eyepiece is the magnified image. The magnification is worked out by the focal length of your scope / the focal length of your eyepiece.

When you use a DSLR at prime focus (I assume you weren't using a lens on your DSLR, or an eyepiece in the telescope), you are using the telescope as a long focal length lens - ie: 800mm or 900mm, or whatever the focal length of your 6" newt is.

If you use eyepiece adapters with your DSLR (or simply point it into the eyepiece), you can do afocal photography with a lens on your DSLR, and then you can photograph the magnified view that the eyepiece gives you.

If you want to photograph the moon, the best results will be achieved by:
1) Using a ToUcam webcam at prime focus (or with a barlow) to take magnified images of certain parts of the moon
2) Use a low-power eyepiece and your camera with lens to do afocal images of the moon, where the whole of the moon fits in the FOV of your camera.


2) Regarding focus, most 8" and 10" newts won't come to focus at prime focus with a DSLR. The mirror needs to be moved up the tube, or you need to get a very low-profile focuser, as there's not enough in-focus. I'm not sure if your 6" has the same problem?
If the focus is changing, it could be the weight of the DSLR changing the focus. Try tightening the locking knobs on your focuser so the focus doesn't change.
What type of focuser is it? R&P or crayford?

Hope I've helped a bit.

[Dindsy]

Hi Iceman,
I think I got that bit about the prime focus mirror having to move out of the tube. THe thing is I am using the Eyepiece to maginify the image. The Eyepiece fits into the Bintel camera adapter which conencts directly to the camera. So, the camera is essentially looking directly into the eyepiece.

I'm not sure what sort of focuser it is.

One thing to not is that the eyepiece is now in the adapter so it is further out of the OTA than it would be normally. So that will upset the focal length somehow. But I assume it should still work since the adapter is made for it.

[astro_south (Andrew)]

Dindsy

You need to remove the eyepiece or put the lens back on the camera. The light rays coming out of the eyepiece are parrallel. The camera needs diverging light rays (usually the job of the lens which converges the rays which eventually become diverging) and through focusing you align the sensor to the corresponding focal plane of your subject. Having the eyepiece in the optical train will mean it will be impossible to focus the image in the camera.

This may not completely fix your focusing problem and you may still require an extension tube, but at least you will see some change in the image when turning the focus knob.