Sun, 07/21/2013 - 05:15
Hello! I've been struggling with getting my focus down with my 8 inch LX200 classic and SBIG ST-402. Laast night, I switched froma Meade DC focuser to a Robofucs. The focus is much better during the evening's run.
Whe I checked my B and V images of R CEN, there is a distinct haziness about 1/2 arcminute south of R CEN. My previous images over the last two months were of variable quality, so I'm not sure what I'm seeing, but I can make myself imagine a haziness close to R CEN in those images, as well.
Could internal reflections create this? Could someone take a look and see what they think?
Thank you and best regards.
Michael A. Heald
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Hi Michael,
While your images show a blob near R Cen, remember that this is a Mira variable and so VERY red (it is currently 8th magnitude at V, but 4th magnitude at Ic). This looks like a residual image after an overexposure, especially since it is close to the variable. My guess is that your focusing routine is using the clear filter, overexposing the variable, and then you were taking science frames. The DSS image does not show any nebulosity near the variable. Unfortunately, the only images of R Cen that I have were taken with APASS, and the only one that is easily available is a 10-second exposure taken for the bright extension on 2013-03-10. I've attached the jpeg cutouts of the field, but no nebulosity is seen with about the same depth (but poorer pixelization) as your images. Note that there is a bright star (alpha Cen?) about a degree away.
Arne
I have had similar apparent nebulosity appear with my front illuminated camera. Try a couple of things. Arne taught me to Focus through the V filter or B filter if you have a sufficiently bright star. That almost always eliminates any residual (ghost) image problem. Then image R Cen again a few times and move the camera slightly between images. Even if there is some small residual image it won't follow R Cen as it moves around the FOV. If the bright spot follows R Cen. Then you may have something very interesting on your hands.
I checked the DSS image using Aladin and there were only the two dim background stars just below your hazy patch. I think I can make them out in your V image if I crank up the contrast sufficiently.
It would be interesting to read what you find out if you do this little test.
Brad Walter
Thank you! Getting the focusing down has been an issue. I thought these might be internal reflections of some sort. I'll change my approach to correct it. Best regards.
Mike