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07-04-2016, 08:12 AM   #1
eccs19's Avatar

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Astrotracer question

I thought I had read that the Astrotracer would calculate your exposure time based on the FL of the lens. I put on my DA-70mm Ltd and would still let me set the time up to 5 minutes. Am I doing something wrong, or can I do 5 minutes with a 70mm lens? I'm hoping to go try a few exposures tonight just for fun, but want to make sure I at least have some basics sorted out.

07-04-2016, 10:57 AM - 1 Like   #2

Join Date: Apr 2007
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Five minutes is a very long time though, so even if it theoretically should work chances are that the result will be less then optimal due to the tiniest error in any of all the sensors involved will show up after such a long time. And if it does it means that you have just wasted 5 minutes of exposure time. So the preferred strategy is to divide the shot in to several shorter exposures and then stack them. So it's usually better to take for example five one minute exposures and stack them for a total of five minutes exposure time.

Or at least start with 15 sec, and if that looks good try 30sec and so on until you reach the real limit of that particular position, angle and calibration.
07-04-2016, 02:11 PM - 1 Like   #3
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5 minutes is the maximum you can shoot. The astrotracer may impose a lower maximum based on where you are and what lens you've mounted, but it will not choose the optimal shutter speed for you. You will need to experiment.

With a longer lens like the 70mm you'll probably be looking at somewhere around 60 seconds for a motion-free astrotracer shot. And remember to calibrate as often as needed!

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07-04-2016, 02:38 PM   #4
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Thanks Adam and Gimbal for the responses. Experiment it is. Figured a limit would be set based on FL, but beggars can't be choosers. Either way, it will be a fun experiment.

07-04-2016, 05:02 PM   #5
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I was about to ask a similar question.
I finally could try the astrotracer out last friday (third time we had clear sky since I bought the K-1. Don't know what's happened to the weather..) and found that with a 35mm lens mounted I got pretty long streaks on a 3min exposure but non at all on a 2min exposure. Couldn't quite make out what was causing it as it seemed to me as it the sensor was just moving too slow.?

Has anybody experienced similar?

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