Saturday, January 4, 2014

Legacy Series, the Bellow Cam Mk 2 SC GT

Bellow-Cam Mk 2 GT

 Being used to GOTO-telescopes, I also liked my wide-angle camera to be equipped with this feature. OK, it is not a big deal at all to handle right ascension and declination setting circles, pointing the scope/camera by α and δ looked up from catalog or star chart data, but, goto is sooo convenient! After some looking around, I got myself a used MEADE DS-127 mount with an AutoStar #957 computer. Perfect!
Fitting Bellow-Cam Mk 2 to the mount is so simple that I would not like to waist words on this issue. It took a piece of hardwood, two bolts and two nuts to get it all sorted.

Bellow-Cam Mk 2 GT, the wide-angle camera setup on the “autostared” DS-mount, in operation.


It is quiet obvious that this is an azimuthal mount, resulting in field rotation. For real long exposures (i.e. minutes to hours) this is utterly devastating for every image taken.
Here the abilities and power of CCDs are coming into play. With exposure times of a couple of seconds, field rotation does not play any role for the single frame. As long as the CCD amplifier ensures that the charge in a single pixel is high enough to result in a signal greater than the detection threshold we can integrate over several different frames. IRIS offers a very good possibility to register and stack frames which are slightly rotated between one another.
A very very short introduction how an analysis like this could be looking like can be found here.


The image of M45 was taken 2005 January 9th. Again I was to lazy to subtract a dark frame. Note the image tilt, that's the sacrifice for compensating field-rotation when using an azimuthal mount. To be noted on the image is amplifier-glow on the upper left corner. The QuickCam appears not to be the best camera, even with the use of non-raw patch, ear-like artifacts still occur.
It is amazing, I think, that the nebulosity of M45 can be recorded using a f=50mm SLR lens and a webcam from a light polluted place like South Holland, on a night with light overcast and quiet poor transparency...

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