| article: piggy back photography |
The name *piggy-backed* comes from the term when someone is riding on anotherones back.
In this case the camera (imager + additional optics) is riding on the telescope's back.
This usually means that you have to add more weight to counter-balance the camera.
The piggy-back adaptor below (to mount the camera) was included with my Starlight Xpress ccd camera.
Another way of piggy-backing is to ride on the counter-balancing axis of the mount.
This is only possible - for sure - if this DEC axis is turning with the tracking of the stars in DEC.
There are some mounts where the axis is fixed, but this is not the case with most of the equatorial mounts.
An advantage to the first way is that when the camera is on the counter-weights side you need less counter-weights.
Or at least not more.
The piggy-back adaptor below is home built out of cheap plumbing parts and a piece of wood.
Unfortunately it is almost hidden behind the two counter weights left and right of it.
Another homegrown adaptor for a 85mm f/8 and a 55mm f/4 in parallel.
With CCD cameras I use this method to take pictures with telephoto lenses from 45 mm to 650 mm.
It brings special advantages especially for deep sky work:
- Smaller focal length gives wider field of views - important for small CCDs and big objects like M31
- The main telescope can be used for accurate guiding (if necessary)
- Smaller focal lengths will show guidance errors or wrong tracking of the mount less severe or even not at all
- (Field rotation due to mis-aligning the mount to the pole will stay the same as with longer focal length!)
- Used telephoto lenses are cheap compared to telescope optics and can be bought second hand much easier, because a lot of old lenses without auto-focus are replaced by newer ones by the regular photographers
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