Help me photo Eta Carinae nebula

[bugeater]

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.

So a crop of my latest attempt is here:
http://astrob.in/172435/0/

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.

[glend]

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.

[bugeater]

ISO was 400. The trailing is probably coma, but perhaps there is some trailing - might not have gotten the polar alignment perfect.

[rustigsmed]

Nice one Marty,

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.

did you take flats?

Cheers

[Flugel88]

Your image isn't perfect but i sill like it :D
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.

[Slawomir]

Hi Marty,

I like the colours in your image and you managed to capture some detail - so not a bad attempt at all! :thumbsup:

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.

[LewisM]

I did a simple stretch, slight rebalance and a touch of curves to your original. More popped out :)

[bugeater]

Thanks guys.

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.

[multiweb]

I reckon it's very good. Not an easy feat at that FL.

IMHO don't worry about LP. You need to pay attention to guiding, collimation and focus. Just keep at it. Practice makes perfect.

You're going pretty good already. Keep doing what you're doing. :thumbsup:

[raymo]

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

[chuckywiz]

Geez thats a cracker of a shot Raymo.. jealous of those margeret river skies.

[raymo]

Thanks chuckywiz, but I don't want to hijack Marty's thread. Margaret River skies are nothing to get excited about, in fact, rubbish.
raymo

[bugeater]

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

[rcheshire]

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.

[bugeater]

No I'm interested in the whole thing, since it's all important. I do need to do darks, I just always forget :question:

[glend]

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.

[bugeater]

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?

[rustigsmed]

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. :thumbsup: 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.

[bugeater]

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.

[glend]

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.

[bugeater]

A MPCC mk3 is on the way. Seemed the best option. Hopefully it'll arrive tomorrow...

[rcheshire]

Marty. You may find colour calibration difficult without dark reduction.

[Mosc_007]

The way I get my Color correct is to look at the background color. The sky's background should be dark gray. The color balance is adjusted until their is no color in the background sky.

Charles

[rcheshire]

I mean lifting the data out of the noise other than getting it to look right.

[Mosc_007]

When I was using my 100d and modded 1100d I used the very powerful stretch tool in Nebulosity to bring out the detail. Then I used curves after that to fine-tune it.

If your camera is not modded you will be missing most of the Ha light.


Here are two examples of what I did with the 1100D. These were both Very early on doing Astrophotography.
Notice the short exposure times with the modded camera. Also I would have been using a CLS clip filter to reduce the skyglow.

First is with the 300mm Zoom lens. 10 x 30 Sec Subs
Second is with a meade SC8 prime focus 15 x 1 Min subs.


Charles

[bugeater]

Does anyone have any views on the relatively usefulness of the various specialist processing packages? Pixinsight seems to be the most comprehensive, but also the most expensive. The others seem cheaper (Nebulosity, Startools etc.), but I don't want to buy these and then end up purchasing Pixinsight anyway.

[rustigsmed]

Hi Marty,

how have you been processing yours so far?

I was planning on editing your full frame shot when I get a chance but
that won't be till sat/sun. there is plenty of data in there that can be teased out further.

I pretty much use photoshop only. It is a good way to learn, PixInsight gets good wraps but apparently is fairly complicated. I plan on buying it down the track.

[glend]

I use Photoshop simply because there is so much info, add-on tools, etc available. You can get Photoshop CS2 for free as it is no longer maintained but it has limitations.

[Mosc_007]

I am using a very old version of PSP8.

I have looked at Pixinsight but it is very expensive.

I did pay for Nebulosity just for the Canon camera control. The Image processing in it was a bonus.


Charles

[bugeater]

I've been using very basic features in an old version of photoshop. But pixinsight sounds like it has a lot of potential. As to camera control, there seem to be free options and so far I've just used Magic Lantern installed on my camera. I also tried the feature in the mount hand controller, which worked okay, but I've ditched the controller now. Wonder if anyone has managed to control that via the EQMOD cable?

Anyway, the MPCC and IDAS LPS filter have arrived. Hence I'm the reason for this thick cloud cover.

[rcheshire]

Not explaining myself well here - white balance.

[rustigsmed]

hi marty,
hope you dont mind but i did a quick play around with your image.
obviously it was just with the jpg, but you have a lot more data in the image you can pull out. your current processing is a bit heavy in the green but the red blue and green could all do with some boosting in curves.

russ

[bugeater]

Don't mind at all. It looks much better. I'll have to sit down and play a bit with it myself.

So you you apply separate curves to each of the colour channels separately? I've been trying to balance the colours at the start and then play with curves for all combined (i.e. RGB).

Crossing my fingers, but I might be able to get some fresh data tonight if the clouds stay away. With the new coma corrector and light pollution filter :D Would be nice to go to the ASV dark sky site, but I'm not sure how you drive out of that place at night without causing problems for those stay overnight.

[rustigsmed]

no worries, you can apply separate curves/levels to each channel, you go to the drop down box that says rgb and choose which channel. if you want to stretch all colours at once, first do 'auto colour' in photoshop but using each channel individually allows you to squeeze more out of the pic in my view. you should be able to dig more out. good luck tonight!

[bugeater]

Okay I managed to polar align and take some shots between the showers coming through. Would have liked more time, but oh well. This time 5 x 3 min exposures and I did a bunch of darks. Minimal processing so far:
http://astrob.in/173909/0/

Below is a crop. I'm actually surprised how much better it is with only 15 min of data. Light pollution filter and coma corrector really worked. Though there is still some coma :(

[rustigsmed]

Hi marty,

colour balance looks better :thumbsup: its still very dark you have a lot of information hidden in there, here's a quick tutorial on using curves and levels I think explains it simply and well.
http://myastroimages.com/Astro_Imaging_Tutorials/Learning_To_Use_PhotoShop_Curves/

Cheers

Russ

[guggle]

I don't see any coma - stars look pretty round to me. Good work!