Getting my head around interval timer for star trails

[martys13]

Hi all,

I am fairly new to photography but enjoy shooting pretty much everything. One thing I've really started to get into is astrophotography and have had pretty good results getting spot stars but one thing I'd like to try next is doing some star trails.

What I'm not too sure about though is how to set the interval timer on my D7100. If I'm doing say a 30sec exposure, do I set the interval over 1 minute? So the camera has time to do the noise reduction and write the file? Does that mean I would have large gaps in the trail? Or can I turn noise reduction off so that it instantly writes and take the next shot? Would I be unable to remove hot pixels in post that way?

Or is it better to do a single 2hr long exposure at a lower ISO?

I'm just keen to get a formula down for when there is a nice clear sky for me to give it a try. I'm also thinking about getting a laptop and tethering the camera so that I can do over 30 second exposure intervals more easily. Good idea?

Any help would be much appreciated.

Heres a couple of spot star shots I'm pretty happy with anyway. The second is of a memorial for a mate of mine that I'm helping build, I wish I got the stars more in focus but I'll go back at a later date and nail it. Any tips with those would be much appreciated too.


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[peterking]

For so many to have viewed and not posted I am disappointed.
First up I'm a Canon user so can't advise specifically to your D7100.
On the Canon the max exposure on camera is 30 seconds. Yes you need to do longer exposures if you want star trails and the best means I've found for this is a remote.
The particular one I have is a cheap (fleabay) model that I have since given one to a friend and we're all very happy with it.
For information have a look at this sites forums (http://www.ausphotography.net.au/forum/forumdisplay.php?77-Night-Astro). I've garnered a huge amount of information there including doing star trails.
Don't even attempt a 2hour exposure unless you have an independent power supply for your camera.

[hakka]

Don't bother with the built in one, its crap. Grab one of these:

http://www.ebay.com.au/itm/YongNuo-LCD-Timer-shutter-release-remote-Nikon-D600-D610-D5300-D7100-Ship-f-SA-/181425613047?pt=AU_Cameras_Photographic_Accessories&hash=item2a3dcf28f7&_uhb=1

[arthurking83]

I've found the built in timer/intervalometer to be pretty useful actually.

So much so that I'm now selling my Nikon MC-36 remote because I just haven't used it enough to justify it's existence in the bag!

If you want to do stacked images as you've described, turn off the LNR feature(Shooting Menu) in the camera .. it's not needed. So just shoot your images sequentially.

If you do want to go down the path of getting an interval timer for the camera, be aware that you can't use the Nikon MC-36 type(ie. 10 pin connector end), as the connection to the camera is not made for the D7100, so you need to get an aftermarket type.

Hakka is right in his implication that the built in intervalometer isn't as fully featured as a dedicated type, but from what I think you're trying to do(simply get automated sequential shooting), the built in timer is fine.

So with LNR switched off, you'll just get an uninterrupted series of continuous exposures.
With LNR set to on, you'll get the dark frame blank spots in between each shot.

Note tho, that depending on the environment you are shooting in, there is a chance that after a few continuous exposures at 30 secs, the sensor may heat up a bit(not overheat!!) and produce more, or different, noise in the later exposures.

[martys13]

Thanks for the help guys, I was thinking of maybe an intervalometer or just using a tethered laptop as I mentioned. It was mainly the noise reduction stuff I wasn't too sure on and the compensation in time for that. You mention the overheating and different noise arthurking83 and that is what I'm trying to avoid. Doesn't the LNR stop those hot pixels?

If noise reduction is off. How would you remove the noise in post? I mainly just use lightroom and photoshop.

[arthurking83]

LNR does reduce hot pixel noise in a long exposure(I think anything over 2sec, or something).

But if you're going to stack images the way you've implied you're going to do, then it's a similar concept.
The LNR frames become redundant in a workflow like that.
By not using LNR, you avoid the gaps between exposures, which is one of the things you seemed concerned about.

[martys13]

Thanks. I did a bit of testing and with noise reduction off I didn't really see excessive noise on a few 1 minute exposures. Plus it wrote instantly to the card so that is definitely the way to go. Thanks for the help! I'm going into the country over the weekend so hopefully I can give it a shot if the night is clear.

[Solstafir]

Be aware that with most Nikon's, the built in interferometer I think stop at a maximum of 200 shots or something like that. Using the external remote avoids this limitation...

[martys13]

Ah thanks for that bit of info. How long do people usually go for a decent star trail? Can a full standard battery manage?

[Solstafir]

Man that's a large range, some people go for only a few minutes. My longest sp far has been around 6hours, I'm sure Hakka and others have done ones a fair bit longer than I. One battery, depending on your camera and battery capacity, should last anywhere from 3-5hours(ish) also depending on the temperature etc.

[hakka]

Ah thanks for that bit of info. How long do people usually go for a decent star trail? Can a full standard battery manage?

I shoot right through the night, the longest was 12 hours. Battery life will depend on the ambient temp but you should get about 8 hours from a battery. Turn off the lcd screens, lens correction etc.

[martys13]

Thanks guys, I might start at 1 hr and see how I go. I can't really leave the camera alone where I am planning to shoot and can't camp near it this trip unfortunately so a longer time-laps will have to wait.

[arthurking83]

Be aware that with most Nikon's, the built in interferometer I think stop at a maximum of 200 shots or something like that. Using the external remote avoids this limitation...

I think some do 999 shots, and others can do over 8000 shots.

The specific camera will have a counter system of some type to help with that, some are simple digit counters, other cameras(ie. more modern types) have dual counter system, with a count setting PLUS a multiplier setting.
The first simple type usually allow for up to about 999 exposures. The more advanced multiplier setup allows up to 999 x 9(ie. 8991) exposures.

The only advantage I've noted between my two cameras with intervalometers and the intervalometer remote, is that the remote allows gaps between exposures.
That is, you can set up a time between each shot where the camera doesn't take a shot .. otherwise the timer system takes continuous exposures one immediately after the other.

[Solstafir]

Actually I think you are right. I'm thinking of when locking down the shutter in continuous mode, not the intervalometer. My bad! :)

[martys13]

Well I managed to give it a crack over the weekend. Unfortunately the moon cast an annoying lens flare but that is a good lesson for next time. I tried another one on saturday but I stuffed up the timer and it only took 8 shots :(, again another lesson. I am surprised how large the swirl was for just one hour!

Here it is anyway. (quite a bit of jpeg compression, this one didn't like being shrunk down) You get the idea.

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