My 1st Astropicture

[bharat]

1st attempt at M7 cluster
Celestron Omni XLT 150 reflector (F/5); Nikon D5000; exp 10sec; ISO 800, Tungsten WB, JPEG image (single shot), unprocessed.

Hi guys! This is my very first attempt at any sort of prime focus astrophotography. Ideally, would have liked have an easier target to begin with. However, moon will be on leave for a few more days and I did not have the patience to wait until he makes reappearance, so I decided to take a crack at the M7 cluster on a relatively clear Saturday evening. (venue: MSCP top deck in of my block).

There’s obviously nothing great about the picture, but being my 1st attempt, I am thrilled at having at least captured a few dots in the picture frame! As a newbie, here are a few questions that came to my mind:

1) I did not have any camera control or image acquisition software. Focusing was quite a nightmare. The stars could not be spotted in liveview (even with zoom). The view finder was at an awkward position and I had a hard time getting my eye close to the finder without making contact with the telescope. Besides this, the stars appeared so tiny that it was impossible to know if they were really in focus. So, I just took my best guess and shot the picture (using the built in timer on the camera).

For more accurate focusing, do I need to get a camera control software and if I do so, will the live view displayed on the computer screen have sufficient clarity to judge if the focus is correct?

2) I have seen pictures of the same cluster with many more stars captured in the frame than what I managed. Is the exposure time of 10secs too small? I had also taken a picture with 20secs exposure but the background turned sort of bluish and the picture appeared overexposed.

3) I did try to make drift alignment before taking the picture, although I am not sure how good the result was. Does my picture show any evidence of star trail?

4) Good pictures usually have a pure dark background (unlike the bluish one which I have). How is that achieved. Will it help if I take pictures in RAW format (instead of JPEG) followed by post processing? Or do I need a different white balance setting?

Many thanks for your comments. Hopefully, I will have better pictures to post in the future!

[cloud_cover]

Very well done indeed! You were imaging at the relatively longer focal length (for a first pic) of 750mm and this is a single shot!
To answet our questions:
1. First, shoot in RAW mode. This makes white balance irrelevant and eliminates jpeg processing as a cause for lost stars.
2. Shoot multiple exposures. Stacking will reduce the noise as well as increase faint signal (it won't be lost in the noise) hence show more stars
3. The bluish tint is skyglow, or light pollution and its blue because of your white balance. There are a couple of ways of post-processing this out
4. There is negligible star trailing as far as I can see. The smeared out stars at the edges are due to field curvature and that's due to the fast optics you are using. Not an issue if you're shooting objects that fit within about 50% of your frame.
5. Focusing is always an issue. One suggestion is to use your liveview screen, zoom in to max (check your manual!), bump up the brightness (this makes moderate stars appear on liveview) and then focus to gett he smallest possible star. Another method is to focus on a nearby bright star (e.g. Antares in Scorpio or Nunki in Sagg.), lock the focus then slew around to your target. Take a trial shot or two to make sure its framed the way you want it

Its a really great first try, especially for a single shot. I suggest you take multiple exposures, maybe about 100 shots and stack them. If you care to go for an hour or two, shoot away and you'll see a drastic reduction in noise and more stars when you post-process

[rcj]

That is still a nice fine attempt from Singapore. Kevin has pretty much summed up the important areas where you could organize your shooting session and improve on the workflow. Here are some other areas that you could look into as well:

1) Might be a good idea (and convenient too) to get a micro-controller emitter cable for the D5000. As such you could use freeware DSLR Shutter software to execute timed exposures. Such cables could be purchased from Hap Griffin (NIRP, NIRS) for the Nikon, where it will use an emitter (to trigger the bulb exposures) with serial cable connected to laptop. You may however require a serial-to-USB converter for most modern laptops if you do not have a serial DE9 port.

2) Contrary to most astro-imagers think, any finished astro image should not have the background jet black. This is cutting out any precious faint stars or (worse) nebulosity that actually defines what astrophotography is all about (capturing faint stuff!). You can check this through software like Photoshop for the histogram - there should not be a tall spike at the extreme left. Learn how to intepret such histograms from the internet. For the camera itself, a good exposure is when you can see the histogram (from the camera) having a nice left-sided hill profile with a gradual drop-off as it runs to the right. Nothing should be chopped off, or ended with tall spikes on either extreme ends. What this translates to, would be take long enough exposures (assuming your mount can track well enough for this) to take the signal acceptably above the noise background (attributed to light pollution, etc) as far as possible. You should still be possible to take longer exposures. Nevermind if the sky background looks brighter as a result, as long as when you monitor the histogram and it does not show clipped extreme ends, you are good to go. Experiment.

3) Ensure that your mount tracks good enough for what you are embarking currently (from point 2). No need to straight away think about premium mounts. Go easy, start steady, and you will learn more.

4) If I am not wrong, the D5000 have a swivel screen that makes it convenient to view stars to check for focus (even at zenith position). As Kevin has pointed out, if you are taking an object like M7, you could pre check focus point at a bright star nearby like Antares, or even Shaula. But this is not deterministic. A good way to consistently get focus (without falling prey to poor astigmatic eyesight, etc), is to make a Bahtinov mask. Take a few shots of the bright star at various focus points with this mask in place on top of your optical instrument, and you will slowly notice that it is easier to see once the star is in proper focus (spikes start converging to a symmetric profile, search the internet for this info) at greatest magnification (accessed from the camera's zoom function), and then you lock this focus point. This can be done by marking out this focus point on your instrument's draw tube (paste thin sticker, masking tape, etc).

5) Download freeware like DeepSkyStacker to assist you in processing multiple stacks of images (of M7, etc). But do not forget to take dark frames of the equal exposure duration at same ISO setting. It will also be helpful to take flat frames to correct for uneven illumination due to your system.

Hope the above helps!

[bharat]

Remus and Cloudcover, thank you for your feedback. I will certainly work on your tips and advice.

[Gary]

Hi Bharat. Great First Attempt! Keep up the good work!

[bharat]

@Remus and others:
I understand that there are remote (wired) shutter release devices available that also have functions like exposure time (including in bulb mode), interval and number of exposures. Nikon does not produce such a device for D5000 (for this model, they just have a simple no frills remote shutter release), a 3rd party brand - Satechi does have one compatible with D5000/ D90.

Can this be an alternative to the micro-controller emitters that you mentioned or are there any know issues (negatives) with these devices? I believe this will eliminate the need to carry a lap top along. Based on a few reviews on internet, users, in general seem happy with Satechi's shutter release. Does anyone have experience of using this device?
Thanks

[rcj]

Hi bharat,

Yes the 3rd party devices should do fine. Not sure about Nikon ones, but those for Canons are quite popular. Like u said, if there are users already having the Satechi's shutter release is happy with that, perhaps it is worth a try. It is always good to do without the laptop too!

[cloud_cover]

I thought I replied a few days ago...... it didn't get posted!
Yes, there are wired and wireless remotes available.
Firstly, if you don't want to spend any additional money, I'd suggest simply using the manual mode as it allows up to 30s exposures. The downside of this is that you have to manually trigger each exposure so you can't just walk away and chat with your friends
The next is a simple shutter release. It allows you to do manually timed exposures or multiple exposures up to 30s each (which is the max settable duration on your D5000). The downside to manually timing each exposure is that you need to handle the remote to trigger and to end the shot, potentially introducing vibrations. I have one, I don't suggest it but if you wish, Phottix sells one for about $10. You can find them by googling red dot photo for find them at any Comex.
What I use now is a remote timer. I bought this from ebay, its a generic China made product that allows me to set timer delay, exposure length (up to 99 mins, I think), delay between exposures and total number of shots. It also has a backup manual mode like a manual shutter release cable if I want to ad-hoc it. Cost me less than $30, inclusive shipping.
This is a copy of the one I'm using (they are all copies, I think). I'm not recommending this seller in particular but just to show you what the itme is Generic Nikon D5000 timer remote Ebay

[bharat]

With many useful tips received from members last week, continued my astrophotography attempt last night...Here are a few pictures...


Celestron Omni XLT150 Newtonian (F/5), Nikon D5000, 1/400sec x 10exp (RAW), ISO640, stacked (using Registax).
Used 2 alignment points for stacking - 1st - the 3 adjacent craters (approx 1/3rd height from the top and 2nd - the small plataeu like feature at approx middle of the image). I tried a couple of additional alignment points but the final image appeared with a block sort of misaligned with the rest. Used the detault settings of Registax during stacking.



M7 cluster; 30sec x 20 exposures, ISO800, stacked using Deepskytracker. Used most of the detault settings for stacking. I just tweaked a bit, the histogram (R-B-G) and other parameters (mid tones, saturation etc). I think I managed to capture a few more stars compared to my 1st attempt. Used RAW instead of JPEG. Since I am not yet having a timer device to use the bulb mode I had to restrict the exposure time to 30sec, I wonder if I would have captured more stars with longer exposure and also with more number of exposures (50 or 60 recommended?). Should I try with a higher exposure? I have seen pictures of clusters taken by other members with 60sec exposure.



M6 cluster, 20sec x 20 exposures, iso 800 stacked using Deepskystacker.

Looking forward to your comments...

[rcj]

I like your M7. Stars look even tighter now, and there is more definition. If you can go even longer subs, by all means please do. Stacking more would help too, but the benefits will taper off. Aim for at least 12. There is a general bluish cast for the background, perhaps you can bring in a little bit of the warmer tones. Otherwise it is already quite a good attempt for nikon dslr in SG skies. keep it up!