Object name: VDB128
Designation(s): VDB128,
vdB 128 is a mostly reflection nebula around a pulsating variable star in Cygnus. I found little distance information but one source lists a very iffy estimate of about 3600 light-years (1100 parsecs). I found revised Hipparcos data saying 0.00057\" for the parallax of the illuminating star. If right that puts it some 5700 light-years away. The star is V1768 Cyg to variable star observers. SAO 69362 or HD 190603 are more general catalog entries for it. At magnitude 5.6 it was a major pain to deal with! Fortunately, my new filters eliminated most reflection issues.Objects in the vdB catalog, while classed as reflection nebula often have some or even a lot of H alpha emission as well. Note the red streaks of H alpha throughout this reflection nebula.This object is a good opportunity for me to again address what I call the f ratio myth. That is, that the faster the optics (lower the f ratio) the less exposure time you need for faint objects using a CCD. That is true of typical snapshots with an ordinary camera, digital or film. With such a camera taking an earthly picture at f/8 you do need 4 times the exposure compared to f/4. This isn\'t necessarily true when applied to CCD images of the night sky. Though many can\'t seem to shake this myth.A camera lens changes its aperture when \"stopping down\". Thus it gets less light and needs more exposure time. With a telescope, the focal length changes via extenders and compressor lenses. This doesn\'t change the amount of light being seen by the sensor for a given area say 0.5\" of arc. A zoom camera lens does the same adjusting its aperture internally as you zoom in and out. For some reason imagers use up to 10 to 1 zoom lenses without seeing a light loss but seem to think a focal length change of even 2:1 is fatal for deep sky imaging and get an f/3 to an f/5 system for imaging rather than an f/10 one then complain the image scale is too small. Edit: New CMOS cameras with very small pixels give these back the image scale they want.Choose a fast system for its wide field of view not because it will save you imaging time. Aperture is what will reduce or increase your imaging time, not f ratio at a given image scale.14\" LX200R @ f/10, L=4x10\' RGB=2x10\', STL-11000XM, Paramount ME
Permanent link: http://images.mantrapskies.com/catalog/vdB/VDB128/VDB128L4X10RGB2X10R2.JPG
Alternate Designation(s): VDB128,