Panasonic 7-14 - Usage tips for UWA neophyte

Started Apr 19, 2014 | Discussions thread
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Michael J Davis
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Re: Panasonic 7-14 - Usage tips for UWA neophyte
In reply to Anders W, Apr 23, 2014

Anders W wrote:

Thanks! I have tested though regrettably not in advance. Had do to some trial and error out there in the desert.

For the shot I posted (7 mm on MFT), the formulas would give us 600 / (7 x 2) = 43 s or 500 / (7 x 2) = 36 s, where the latter value comes pretty close to the 30-second rule of thumb I gave Florida.

Now let's look at the evidence produced by some of my trials, the first at 15 s, the second at 30 s, and the third at one minute. These images are downsampled to about 2.6 MP but still reasonably large.

One problem that you can readily see is that the UWA distortion makes things worse toward the edges than in the center. That distortion makes the stars a bit oblong even without any motion. At 15 s, I would say things still look pretty much OK unless you look to close and there are no problems at all in the center. At 30 s, we are at the border line, and at one minute we have clear signs of trails even in the center.

So by and large, the formula you provided seems to work pretty well. However, UWA stretching towards the edges complicates things a bit and may give us reason to be a bit more conservative.

For the record, (and understanding that the posted shots are < half size) I 'corrected' the star trails in the last shot using Focus Magic's remove motion blur. It worked well, and better if I divided the scene into two areas corresponding to different angles of 'movement'. FM will consolidate up to 20 pixels of blur in one application. In this case, the fact that the clouds are already blurred disguised any other artifacts that might be introduced.

Just a contribution to the minimising noise at lower ISOs thought.


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Mike Davis
Photographing the public for over 50 years

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