An evenings stargazing

[Mr Darcy]

I have been experimenting with startrails using the stacking technique, but have been disappointed with the gaps it leaves when you use an intervalometer with the camera on "bulb". I am aware of the issues with doing a single really long exposure, so I tried a slightly different technique. I used the intervalometer set to 29seconds with a 1 second interval as normal, but I set the camera to 5 second exposures in rapid fire mode. The result of this was that the camera took a new shot every five seconds with a virtually indiscernable gap between exposures. The meteors were a bonus. As were the exceptionally clear skies. The downside was that the memory card filled up after only a couple of hours. 841 images in the stitch.

Click through to larger (7360x4912)

And a single image from the stitch:
I have pushed saturation and exposure in this one to bring out the Milky Way

I used a five second shutter speed as I read somewhere that this will give maximum exposure. Any longer than that and the light form a single star will have moved on to the next pixel. Actually since I was using the D800, I probably should have halved the exposure.
The downside is that the memory card fills up too quickly. I only got about 2 hours worth of exposures in this set. I tried again last night with 20 second exposures, but I suspect the sky was not as clear. I will process them today. It takes pretty much a full day to stack this many exposures

[the foto fanatic]

I love #2 Greg!

You have captured the beauty and remoteness of space and the Milky Way.

Being a vertigo sufferer, I'm not too keen on the first pic - it makes me feel like I'm going to fall over.

[Remorhaz]

I too like #2 Greg

I know #1 is more about testing the technique (which appears to have worked quite well - and you lucky sod getting such clear skies and so many stars ) but I agree - compositionally it's pointed to high with the UWA. Perhaps one which was higher so there were no trees at the bottom (for a falling frame of reference) or a more "normal" one pointed more down towards the horizon more.

Quite short exposures - what ISO were you shooting at?

[Mr Darcy]

Perhaps one which was higher so there were no trees at the bottom (for a falling frame of reference) or a more "normal" one pointed more down towards the horizon more.

I didn't intend to have any trees in the exposure. It was just too dark to see just where I was pointing the camera.

Last night I took out a stronger torch and used it to illuminate the trees so I could cut them out.That worked, but sadly it clouded over after an hour or so, so bombed again.
I did try a different technique with the good images though:

Basically, I took nine images that were OK, pushed contrast in LR, then opened them in layers in PS. Then I AutoAligned the layers and applied "ColorDodge" layer style to all but the last one. After flattening this is the result.
Yes the colours are probably a little too saturated, but that is often the case with commercial astrophotography too.
20" exposure this time.14mm@f/2.8 ISO1600

Quite short exposures - what ISO were you shooting at?

Last night were 5"@f/2.8 ISO800
If you stop to think about it, unless you are using a motorised equatorial mount (Yes I am thinking seriously about one), length of the exposure is meaningless beyond a few seconds. The exact timing will vary from camera to camera, but basically what is happening is that as the stars "move", they will track from one photo site to the next. Once they have left the first site, any further exposure is effectively a new one as the photons are falling on a different part of the sensor. If you can see visible trails in a single frame, no matter how short, then this is happening and you have exceeded the slowest effective shutter speed. The issue is complicated somewhat by the way a cluster of photo sites are used to capture colour information, and will be affected by the focal length of the lens and what part of the sky you are looking at, but at 14mm, I can see very slight trails near the zenith even at 5 seconds.

[Mj]

...the intervalometer set to 29seconds with a 1 second interval as normal, but I set the camera to 5 second exposures in rapid fire mode....

Help... feeling a little stewpod here... run that by me again? This is to say... set the remote timer to 29" exposures with 1" breaks but the camera is set to 5" exposure in high speed continuous shooting???

Maybe I should stick to models

[Mr Darcy]

Help... feeling a little stewpod here... run that by me again? This is to say... set the remote timer to 29" exposures with 1" breaks but the camera is set to 5" exposure in high speed continuous shooting???

I had to think about it for a while too.
If you use an intervalometer in bulb mode, you have to leave a 1 second gap between exposures. This translates to a gap in the star trails which is quite noticeable at high res.

My next step was to set the camera to 30 second exposures and lock the shutter down. That's when I discovered that Nikons set an internal limit on the number of exposures you can take in continuous mode. The maximum allowed is 100 exposures.

I did a lot of thinking and realised
1. that once an exposure is longer than about 3 seconds, the stars motion effectively shuts down one photo site and opens up the next, so that is the effective maximum exposure of a single star. The rest doesn't do anything to the exposure, it simply creates streaks. 5 second shutter opening allows for a pixel to be only partially exposed before it moves on to the next one and fully expose that one.
2. To get around the 100 exposure limit, I realised that if I reset the shutter at regular intervals, I could reset the internal counter. As I was doing 5 second exposures, A multiple of 5 seconds would work best. The intervalometer was already set to 30 seconds with a one second gap, so the simplest change was to set it to 29 seconds shutter. So I tried and it worked. I ran to 800+ exposures before the cards ran out The battery was dead in the morning, but the cards were full, so that was the limiting factor. It is interesting to note that the camera predicted 200 exposures per card (2x 16Gb cards) So clearly the compression works really well for night scenes.
3. High speed continuous will minimise the lag between exposures.

The next thing to find out is whether the shutter count will reset if the shutter is already open when the trigger is toggled. But that is an experiment for another day. It will take a while to work out the timing to test it.

My other test was to try and boost the image of a fixed part of the sky. That was the last photo posted. I discovered that I only need 10 or so images for that, so I will only do 5 second exposures in bursts of a dozen or so. I will go back to 30"exposures when my intent is star trails.

[biggerry]

I like the last image posted, whilst the colours are pushed a bit too much it does add some nice drama to the scene.

I reckon a trip out to flat rock would be the way too go, get rid of those annoying trees (except for those foreground interest items)