| article: Mounting an astronimcal CCD camera to various optics using SLR bayonet |
The T2 connection
It is standard to connect a camera and a telescope by means of a T-ring.
The T-screw is M42x0.75 mm.
The T-ring converts the specific connector of the camera manufacturer to the T-screw.
Other parts between the camera and the optics will also fit that T-screw.
You can assemble filter wheels, extension tubes to keep flange distance, coma correctors and so on.
So far - so good.
The problems
The scale of the different astronomical objects varies a lot.
From tiny objects like the planets ( 1 arcmin ) to large galaxies like M31 Andromeda ( more than one degree).
Therefore different optics with different focal lengths are needed to picture them correctly.
My typical setup is the main telescope in prime focus of 1200 mm for medium sized deep sky objects.
For the planets there is a projection system to enlarge the focal length by 3x to 4x.
For the larger deep sky objects I am using telephoto lenses, usually second hand M42x1 (Pentax) types or APO teles for Canon EOS.
In other words: the camera must be mounted and dismounted very often.
A screw system where I have to turn the camera to mount it to the optics (or the other way round) is very tedious.
I also found it cumbersome to refocus over a wide range after insertation of the projection system.
My solution
In former times I used cooled, monochrome astronomical CCDs together with a R G B filter wheel.
When the Canon EOS 300D turned out to be a reasonable colour camera for astronomy I bought one, along with a T-ring, Canon lenses and Kenko tele converters.
Meanwhile cooled 1-shot cameras for astronomy became available and I ordered one.
My camera, the Starlight XPress SXV-M8C came with a M42x1 connection.
Thinking about the necessary adapters to keep all the proper distances I found that I should keep the EOS bayonet as the main connector to all optics!
I found an adapter for the Meade Deep Sky Imager DSI to connect EOS lenses.
This adapter has just the length to allow for the proper 44 mm of flange-to-focal-plane-distance of the EOS system with Starlight Xpress CCDs.
Advantages of the EOS bayonet
- No endless screw turning needed for fast interchange
- Rigid connection, no movement or flexure
- Affordable SIGMA APO lenses can be used (the ones which are not 100% comaptible with the new digital cameras)
- KENKO or Canon tele extender can be used to increase focal length without changing the focus or screwing hazzle to mount it
- Affordable Zeiss and other M42x1 lenses can be used by using an adapter keeping the proper flange-to-focal-plane-distance
- A anti-sky-glow filter (or any other) can be mounted in front of the CCD inside the adapter for ALL optics above
- Fast change of EOS cameras to M8C camera and the focus will almost be perfect
More details and reviews about the equipment used above
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