Last night seeing that it was cold clear and great seeing, I thought I would tackle a faint and distant object, The Pencil Nebula, in Vela.
However I was a little disappointed with the result, and expect that it is either just to faint for a 4 inch refractor, or I have to go even longer with the subs.
I would be pleased with some advice on my efforts, please.
This image consisted of 17 exposures @ 6 minutes each at 500 ISO, giving a total of 102 minutes on the object, with the Tak on the G11, auto guided, and Canon 5D, with ICRN on, and Master flat applied.
Conditions were good, the guiding was pretty well spot on, but I expected more in the final image, Should i have gone longer with the subs, do you think.
Please could those more experienced people advise me on, either the processing, or the sub lengths, or both.
Anyway here are two images, one is a full frame wide field of the area and one is a half size crop, both processed in Image Plus and CS2.
And could some one please tell me what that red object is in the bottom left of the wide field.
Hi Leon,
Longer subs would be better if you could?
My attempt was with 6min subs at 800 iso @ f/5.6
I have noticed that you have lost a lot of the reds and thats the Ha from the pencil so you would need much longer subs with your unmodded camera.
That 20D would have been ideal for this..
I don`t know about the red bit in the full frame if its some emission neb or another part of the Vela supernova remnant.
I can post a pic of my attempt if you want a look!
cheers Gary
Good work trying a different target Leon. I think the red object to the lower left is GUM23, but this is from memory so could be wrong. Your data looks black clipped in all channels. In could be that it needs to be stretched some more or the calibration process has caused this. If you find that stretching it further introduces noise, then your subs aren't long enough - go with what Gary and other suggest. Also you'll notice an improvement in image quality when you start taking/apply flats. Keep it up!
You must have been cold last night . Nice widefield image. I agree with the other posters, more data never hurts.
I used to think flats were hard. I just took 3 in about 5 minutes. I stretch a grey tshirt over the lens and point the scope at the sky. Depending on the time of day I shoot for between .1 and 2 seconds; basically until the photo is half saturated. You know you have done it correctly when you see nice dust bunnies on the photo.
It helps to mark the camera orientation and leave the focusser at the last focus position.
Thanks Guys, your responses are very helpful, however you may have mis read the bit about the Flats, I do take them and apply them as well, this image had a fresh set, so to speak applied from that night of imaging.
Well I will just give it some more next time it is clear and see what happens.
Leon.
Ps, Gary I would be very interested in seeing your image please
Sorry Leon, my flats comment maybe unjustified. Its just that when I looked over your data I noticed what appeared to be a centered radial gradient. I've attached a diagonal line profile which shows the histogram increase. This could simply be wispy nebulosity, but I have not seen this before. If there is a calibration process that is going to cause you grief - it will be with your flats!
The FSQ-ED with its large flat wide field doesn't have a huge light drop off in the corners. Tests performed by Don Goldman with the KAF16803 (16mp) chip showed a very minor drop off of 2,500 ADU (22,000 ADU at center and 19,500 ADU in the corners) - impressive. Flats are still required though (for obvious reasons).
Its just that when I looked over your data I noticed what appeared to be a centered radial gradient. I've attached a diagonal line profile which shows the histogram increase. This could simply be wispy nebulosity, but I have not seen this before. If there is a calibration process that is going to cause you grief - it will be with your flats!
Jase, This central gradient you have pointed out has caused me grief from day one, it appears in all my images after i have processed then correctly with darks/flats etc.
I always have to work on the image by making it darker to get rid of it.
I know the procedure i follow is correct as i have had good advice from many members, as your self, but that central gradient is always there.
Leon the nebulae in this region are very faint and need a lot of exposure through narrow band filters to minimise noise and skyglow. I am surprised you did as well as you did.
Here is a very good image of this area by Rob Gendler.
Thanks Doug, and Matty as well, I think I expected to much from this image run, due to the fact that i exposed for 1 hour and 40 minutes, but it seems that i will have to give it a bit more time to get a better result.
Have to admit it is a tricky faint little bugger to capture.
Sorry for taking so long to get back to you Leon,
but here`s my pencil.
16 x 6 min at iso 800.
Might give you a idea of how faint that pencil is!
cheers Gary
Good one Leon
I also had a go at this item on 2nd May. Mine is a stack of 6 x 300secs through my VC200L wit ha unmodded 40D. Temp was about 2deg C. Who needs cooling.
It is still pretty dim.
