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08-06-2020, 03:34 PM - 1 Like   #1
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K-5 and Astrotracer issues Part II

Hi Folks,

This time I am baffled as I seem to be unable to have a picture without trails using manual lens.

When taking picture with kit lens Astrotracer seem to work OK'ish so so. But when I took SMC Pentax-M 135/3.5 manual lens every single picture taken has trails. I've put correct focal length in the menu and I am shooting via Astrotracer menu which is unavailable if things are not set correctly. But even 30 sec exposures have trails. Is there any limitation to the lens you can use? Or my camera is packing up?

08-06-2020, 04:52 PM   #2
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30 seconds may be a touch long for 135mm.......try 20's been a good bit since i tried 135 or 200 but i did not get very long exposure time from what i remember
08-06-2020, 06:26 PM   #3
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QuoteOriginally posted by Pikor69 Quote
This time I am baffled as I seem to be unable to have a picture without trails using manual lens.
Normally the lens kit is the 18-55mm, the 135mm has a longer focal length and therefore the angle of view narrows.

Have you ever heard of the 350 rule (or also called the 500 or 600 rule)? It consists of this, the longest shutter speed you can use is 350 divided by the focal length of your lens.

That means you have the 135mm so 350/135= ~2.59 seconds, this is roughly the maximum exposure time to avoid the trails.

With 18-55 you could go ~6.36 sec at the 55mm focal length and ~19.44 sec at the 18mm focal length.

Of course the astrotracer has to be calibrated well in order to work, if it disengages you have to recalibrate it. But in perfect condition it should allow you to use a longer time.

Ciao Mario
08-07-2020, 12:22 AM - 2 Likes   #4

Join Date: Jan 2018
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There should not be a problem if the calibration is good.
I have found that nearby metallic structures, garden furniture or a car for instance, will affect calibration. I calibrate and set up at least 10ft/3m clear of any such adjacent item.
With the camera and O-GPS1 calibrated and mounted on a tripod, it is not (usually) necessary to re-calibrate when changing lenses. Just turn the camera power off, (not the O-GPS1), change the lens, switch the camera back on and wait for the little green 'satellite' symbol to appear and I'm good to go. The camera appears to remember the previously set calibration
With this in mind, try a few comparative tests. Any apparent trailing at 1 minute at 55mm should be similar to 30sec at 135mm. I'd expect to see no apparent trailing at these settings, from my experience. I regularly use 200mm at 30sec with no problem.
Good luck


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