Okay, so I've got myself a decent setup to start with I think. I'm working on all the software and I'm getting polar alignment down. So now I want to know just how far I can take things with the equipment I have, plus what the recommended approach is. I think the Eta Carinae nebula is a good practice target, since it's bright and easily photographed through the light pollution, everyone has shot it, and it has lots of nice little details in it.
and I've also included a close up of the finger of god below.
Setup is:
Skywatcher 8" f/5 reflector
AZ EQ6 mount
QHY5L-II mono on a Orion 50mm mini guidescope guided with PHD2
Canon 700D DSLR at prime focus
All controlled with EQMOD from a laptop
Settings for the photos were 12 x 5 minute exposures, stacked in deep sky stacker with some tweaks to colours and curves in photoshop. Polar alignment using PHD2 drift alignment tool.
Given my setup, how can I improve on the examples I've provided? How much better can it get given the equipment I have? Clearly lots of people on here have taken exquisitely detailed shots of this nebula, but with different setups and much more experience.
I want to get the most out of what I've got, but aren't sure which way to go. More exposures? Shorter exposures? Longer exposures? Better polar alignment? Coma corrector (one is on the way)? Light pollution filter (also on the way)? Better processing? Darker site? ....
Any suggestions or even examples of what others have achieved with similar equipment on NGC 3372 would be greatly appreciated.
That Astrobin shot in full size looks over-exposed to me, or could do with layering to bring the star brightness down. What ISO was used? Your stars look like they are tailing a little, unless I am seeing coma.
I am assuming this is a crop? it would be better if you put up the full frame.
a great start. I would pump the iso up to 1600 and shorten the exposure especially if you are shooting in Mitcham and if you haven't got the light pollution filter going yet. I found down in mt eliza I was maxing out with sky glow at 70 seconds on an f4 newt (iso 1600) - that's moved out to about 3 mins or so with a light pollution filter (iso 1600).
double check collimation, and make sure you recheck focus during the imaging sesh. I'm not sure how sturdy your focuser is .. more experience in processing.
Your image isn't perfect but i sill like it
looks clear and clean and not over processed something that i tend to do.
Though for such a bright target it is a little dark.
I'm sorry i cant help you with tips on using your DSLR as i have no experience at all in using them.(i went straight to ccd)
Your stars do seem to be trailing in one direction a little suggesting tracking errors perhaps.
Check ensure the scope is well balanced in Ra and Dec.
Check your cables for guide scope make sure there is no cabble tension pulling on your gear.
We don't know how good your polar alignment is would help if you took a screen shoot of your PHD graph.
Perhaps you could try a different approach to polar alignment i use alignmaster works perfect for me.
If your using a stock standard focuser you could possibly improve thing allot by forking out for something decent like a moonlight.
I like the colours in your image and you managed to capture some detail - so not a bad attempt at all!
As others have already said, there are most likely a few factors affecting quality, so gradually eliminating them will help you in composing great astro photos.
I have noticed that stars show increasingly more distortion towards the bottom of the image, so I would definitely check collimation and also perhaps for camera's tilt to optical axis.
Light pollution will most certainly limit the degree of faint stuff you can capture - that's why many astro-imagers use cooled mono camera's with narrowband filters. But that costs quite a bit, and I think after tweaking your rig and properly polar aligning you will be able to campture some amazing astro images.
The astrobin pic is a crop - I ran 3x drizzle in DSS, which limits you to only processing a small section of your image. It's also not from the center of the frame, so I think coma is most or all of the trailing/eggy stars effect. I have an MPCC on the way, so that should hopefully help.
As to polar alignment, my sky view is a bit limited so I found alignmaster to be difficult. I quite like the PHD approach, but I have found it can jump around a bit (seeing perhaps?) which makes adjustments a bit difficult. Also once you are less than about 1 arcmin of error on an axis, the guide circle on the image is really small, at least with my setup. I was wondering whether I could be chasing periodic error, so I was interested in programming the PPEC in my mount, but I'm not sure how. I did take a first series of shots in this session where PHD disengaged for some reason and there was some trailing, so the polar alignment clearly wasn't perfect.
Oh yes and I haven't taken any flats or darks. The noise on the camera seems okay, so there hasn't been much of an issue with hot pixels (unless I really stretch the data), but I do think I need to work out some flats.
I did check collimation just before this session and I think it was pretty close. I spent a fair bit of time setting the scope up when I got it and think it's okay, though having someone with experience look at it would help too. I used my old collimation kit from 15 years ago, so there are no lasers
I'll take everything you've all suggested on board and apply it the next time I get out to do some imaging. Was hoping it could be this weekend at the ASV dark sky site, but the weather isn't looking positive.
I think my ultimate destination will be narrowband, but I might have to pay the house off before I get that past the finance minister... I'd also like to do some more longer focal length stuff, but that's something to look forward to as well.
Hi Marty, At the beginning of this thread you asked for examples of what others have produced with similar gear. This posted crop of Eta was
taken with an 8" f/5 Newt on an HEQ5 mount, using an 1100D.
Unguided, 30 x 30secs, noise reduction enabled, no separate darks;
no flats or bias. Stacked and manipulated in DSS only, other than
resizing for posting on IIS.
raymo
Very nice raymo. Spent a lot of time in Margaret River as a kid. My grandparents lived in the now abandoned forestry settlement. Remember the milky way being absolutely amazing on a dark night
Marty. I take it the feedback you are seeking is about acquisition and not processing, because 5 minute subs could do with darks and flats to make post processing more effective.
Marty. I take it the feedback you are seeking is about acquisition and not processing, because 5 minute subs could do with darks and flats to make post processing more effective.
No I'm interested in the whole thing, since it's all important. I do need to do darks, I just always forget
Honestly IMHO you can do darks at almost anytime. For uncooled DSLRs, people will argue that they need to be done when your shooting your subs but I don't agree with that, the marginal gains you get from duplicating the exact conditions of the subs are not worth chasing in most fairly quiet DSLRs (yes you do need to use the same ISO and sub exposure length). Just setup your intervalmeter (of BYEOS if you use that) and let it go with the lense cap on. I just set my camera on the table in the observatory and let it run by itself.
Build up a dark library on your laptop/pc that holds the darks for the ISO and sub lengths that you normally shoot. Once you have master darks for those values it make the process easier (at least I find it so).
Of course if you can cool your DSLR then darks become less important (but I am building a library of darks shot at my cooled setpoint of -10C, -15C etc) , but bias/offsets should still be done. As bias/offsets are taken at the fastest possible shutter speed of your camera, they can be done and then kept in the library for use at stacking time as well.
PS: Camera batteries will produce some heat, to minimise heat build-up use a AC/DC or a DC/DC adaptor in the camera so that your power is coming from outside the camera.
Even doing darks when I'm out taking shots isn't a problem. I just need to set the camera to do its thing while I'm packing everything else up. But yeah, I'll do some later and apply those to the data I've got.
Flats seem a bit more complex, since I need a light box. The images definitely aren't "flat" though, since when heavily processing faint shots they come up darker around the edges. Could that be related to coma?
Even doing darks when I'm out taking shots isn't a problem. I just need to set the camera to do its thing while I'm packing everything else up. But yeah, I'll do some later and apply those to the data I've got.
Flats seem a bit more complex, since I need a light box. The images definitely aren't "flat" though, since when heavily processing faint shots they come up darker around the edges. Could that be related to coma?
flats really need to be done on the night unless you keep your camera attached to the scope when its not being used. you don't need a light box you can do 'twilight flats'. set up your scope at sunset, point the scope to a clear patch of sky and set your dslr to AV mode and snap away. simple - the hard part is getting setup in time for twilight at this part of the year!
Really need to see a non-drizzled/non-cropped version of the image to give much more advice to your capture.
Okay, I've put a non-cropped stacked version here: http://astrob.in/172984/0/
I can't seem to get the colours right. I need to spend a bit more time on that, but it should show the quality of the capture I hope. I stacked from the raw images in DSS with median.
When I zoom in on that image I can really see the coma problem on the edges and corners. It looks fine the middle and the colour is improved. Get that coma corrector on, which one were you getting? Some need to be setup with correct spacing but the Baader MPCC mk3 works with most dslrs right out of the box.
