My first photo - NGC 4755 Jewel Box Cluster

[Pierre_C]

Hi people.

Here is a photo from my very first session using a DSLR on a tracking mount last night – Jewel Box Cluster, NGC 4755.

I am pleased with the colours of the solitary red giant and scattered blue giants among the white stars.

There is a small amount of star trailing which I think is due to slight polar malignment.

I am looking forward to practicing on other objects.

Any thoughts on how to grow from here would be appreciated.

Thanks.

Equipment:

Celestron AZ102 refractor.
Sky-Watcher equivalent EQ3 mount with dual axis motors and steel tripod.
Nikon D7000 camera. 10s exposure. ISO 1600.
NX Studio processing.

[Nikolas]

If you take a series of photos then stack them together you will have a much more pleasing result. If you get your polar alignment perfect you will not get the star trails for 10 seconds. As for the violet fringing that can be minimised with decent processing. Welcome to the rabbit hole that is Astrophotography :)

[Leo.G]

Many photo based packages have an eye dropper which let you sample the fringing and remove it. An older version of PS and other software I use all have it.
Which mount are you using?


I have an Astro-trac I haven't had the opportunity to use yet. I nearly got it right one night but I confused myself trying to get decent alignment with the QHY Polemaster I fitted. I've read the manual now, I was also using a 25Kg capacity gear head I'd never used (I'd only just got it) and confused my RA and DEC axis, I should know better, I have a guided mount.


Many people use the 500 rule for timing their exposures without star trailing, I tend to use 400 for better clarity with my 14mm (I use 16 seconds so maybe not 400, I can't remember how I arrived at that figure) but it's 500 divided by the focal length of the lens. A 20mm lens you're good for 25 second exposures without drifting but there are variables.


Once you get your first image that shows the slightest detail you're hooked, good hunting and clear skies!

[Nikolas]

You are quoting me by mistake

[Leo.G]

No, just a mention of the eyedropper tool in several packages since you mentioned the processing to get rid of fringing.

[OzEclipse]

Hi Pierre,

Great start.
A few suggestions: -

Trailing
Your main trailing is in declination indicating polar alignment error. That much trailing in a 10s exposure is more than a minor polar alignment error. If you are using an optical polar finder, you need to learn the polar star patterns. Once you learn the patterns, they are much better for optical polar alignment than the North hemisphere "Pole Star."

Focus
Your image is badly focussed. Use live view If your camera's live view is not sensitive enough for the stars in a particular subject, no problem. Just slew across to much brighter stars. You can try buying a Bahtinov mask and use live view. However if live view sensitivity is limiting you, a Bahtinov mask will make that more difficult. Make a mask with a few criss crossed pieces of string. This will transmit most of the light and you will see the diffraction lines from the stings.

keep up the good work
Joe

[Pierre_C]

Thanks for all the advice and encouragement.

I will incorporate it into my work.

I am using an old Sky-Watcher-equivalent EQ3 mount with analogue dual axis motors and matching steel tripod. The ‘equivalent’ caveat is that it looks just like a Sky-Watcher mount, but it does not have a logo on it. I am not sure if this means it is a Sky-Watcher that lost its logo, or never had a logo, or whether it belongs to another brand. Either way, it looks so much the same that I suspect it came out of the same factory.

For an old mount, the RA motor seems quite reliable. I tried some drift alignment on Venus at the meridian during the day and there was definite declination drift, so my current challenge is in learning how to adjust the mount for precise north-south alignment. The mount altitude setting seems good for my location in Melbourne when checking with a smartphone inclinometer and planetarium app. I am still learning manual techniques using a compass, spirit level and drift alignment – early days.

[Leo.G]

I have the same mount with GOTO (A Skywatcher I got used only once for $300 from an AMAZING fellow with a big heart and if I spend the time to set it up accurately and balance everything out it's a decent mount for shorter exposures. I frequently used it in the past to hold my 14Kg skywatcher 152mm Achromat (with heavy W/O DDG focuser addition and larger finder plus other crap) and it was highly suitable for viewing but I didn't do imaging through it except for short exposure moon shots (with lots of purple fringing, not actually that bad visually for a blind old goose like myself). I'm contemplating doing a full strip down and may end up machining the RA axis to fit a real bearing. The mount is on long term loan to a friend but I don't think he uses it, I also loaned him a smaller, lighter EQ mount with a single axis motor drive (removed from my original Tasco timber tripod) and he likes it for the weight factor, he's 68. Even the single axis 220/240 volt clock motor on the other mount makes viewing pleasurable.

[ChrisV]

Nice, looks better than my first effort. Enjoy the journey!!