Something at last

It’s been a while since my last post, nearly 4 weeks in fact – a combination of poor weather and other commitments including going away in the campervan to Cornwall when we had that glorious 4 day bank holiday weekend has kept me out of the observatory, I could hardly say to my better half, sorry dearest we’re not going away this bank holiday – the weather is just too good. Anyway I have finally done some imaging, addmitedly over a couple of nights and on a very dim target – PK219 + 31.1 or Abell 31 or Sharpless 290 – this is a very dim and ancient planetary nebula in the constellation of Cancer it is slightly larger than M27 the Dumbell nebula  ( mag 7.5 ), though much much dimmer at mag 12.2. The image below is the culmination of two nights imaging, totaling 5 hours exposure time ( 30 x 600 sec ) in Ha, to be honest I think that 2 or 3 times as long is needed, it is brighter in OIII but that will have to wait until there is no moon around.

pk219
PK219 +31.1 in Ha

I also took the opportunity to check if my collimation efforts were any good or not, I centered the telescope on Pollux, β Gemini the brightest star in that constelletion and took a 60 second exposure, thankfully the collimation I did on the 8 inch RC was nearly spot on with only very small adjustment required. the exposure showed that while the stars in the image are round in all four corners, the vignette or uneven illumination was slightly off centered to the left of the image and only very minor adjustments to the secondary mirror is needed, the two bright patches to the right edge of the image is Amp glow from the camera sensor this would normally be  removed with dark frame subtraction when processing.

Uncentered Vignette
Uncentered Vignette and of course microlens reflections

This Uncentered vignette is only a problem if a bright star is in the field of view ( otherwise it is removed by subtracting flat frames ) as there are none around PK219 I’ll leave the final adjustment to a later date, below is the same image with a gradient map applied to make it easier to see, lots of clear skies needed, fingers crossed.

Gradient mapped
Gradient mapped image

3 thoughts on “Something at last”

  1. That’s a nice image, especially considering it is a 12th magnitude object spread over a diameter of 16 arc mins. How do you find the Ha filter? Does it realistically provide you with opportunities to image deep sky on moonlit nights?

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    1. The Ha filter does work fine in near full moon conditions, so long as your object is not close to the moon. Obviously at less than full moon you can image a bit closer, the OIII on the other hand is a total wash out under anything more than a qaurter moon and then you have to be quite far away. I use Baader filters with an 8 nm band width, the more expensive Astrodon filters have a 5 nm and 3nm bandwidth and could probably perform better under full moon conditions.

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