Tuesday, January 18, 2011

large field explained

I was wondering why the Field of View outline for the StellaCam3 in SkyTools seemed too small. The imagery that I obtained of M42 and M43 represented a larger field.

It was while all the occultation gear was out for audio and GPS testing, I noticed something on the front of the CCD camera: an Antares focal reducer! That explains it!

This is dropping the focal length anywhere from 0.5 to 0.23 times. The documentation says that "the reducer will provide a reduction of 0.5x when the center of its lens assembly is placed 47.5mm from the focal plane of the eyepiece or imaging device. Move the focal reducer closer to the eyepiece/camera and its reduction factor will increase. Move it away and the reduction provided will decrease."

There is a tube that the reducer is screwed into. It looks like it is doing the optimal spacing: I roughly estimate the centre of the lens to be 47mm away from the chip.

Thus, it is turning my f/10 'scope into an f/5.


Well, with respect to Denis's setup and SkyTools, the magic number is actually 0.6x. Used old Fireworks to confirm this.

That means the rectangular size covers about 18 by 13 arc-minutes of the sky. For comparison, the Meade 18mm eyepiece is 22, which just fits around this, and the Celestron 26mm is 41, totally encompassing the area.

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