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Old 14-02-2012, 10:09 AM
Poita (Peter)
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Pentax Astrotracer - first play

The clouds finally cleared enough last night to get my first go at using the Pentax Astrotracer on the night sky.

Basically Pentax has a GPS add on for their newer DSLRs that purports to allow you to take long exposures of the night sky, just using a tripod.

No tracking mount, no barn doors, just calibrate the camera and shoot for up to five minutes and the camera will do the tracking by moving its sensor internally.

That is the theory anyway.

My setup was a manfrotto Jr tripod, a Pentax K-r DSLR and the OGPS-1 GPS module.

First, after not being able to find the menu items in the instructions, I realised had to apply a firmware update to the camera to get it to recognise the GPS module.
Once I had that sorted, I took it all outside.

It is pretty straightforward, you set the ISO you want to shoot at, select GPS from the menu and then calibrate, which requires you to turn the camera at least 180 degrees through each axis. I nearly dropped the damn thing twice, but it seemed to calibrate okay.

The you select Astrotrace, and the amount of minutes you wish to shoot for (note to Pentax, please backlight your buttons!!).
You then focus and press the shutter release and the camera does the rest.

I chose a 5 minute exposure, just using the 18-55 kit lens at 18mm and F4.0
The clouds had started to roll in, and the light pollution from my backyard isn't fantastic. I pointed the camera to the sky, took a guess as to the focus (backed off from infinity a smidgeon) and pulled the trigger.

I could hear the sensor moving inside the camera, and five minutes later, i heard the shutter close. What I didn't realise was that long-exposure-noise-reduction was turned on, so I had another five minutes to wait whilst it shot its dark frame.

Then the battery went flat in the GPS unit :roll eyes: it turns out the GPS doesn't turn off when the camera does, so I had it on all day.
But still, I did get a single image out of it. There is a bit of star trailing, but it does seem to work. Maybe more calibration would improve things a bit, I'm keen to give it another go.

If anyone wants to download the raw image to take a look it is on
http://www.mudgee.net/ot/kr.DNG

I've attached an extreme crop of the jpeg image, no processing other than setting the black level quickly.
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Old 15-02-2012, 10:48 PM
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Nico13 (Ken)
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Hi Peter,

As I'm a Pentax man this interested me so I downloaded the image and had a bit of a play with it in CS5 and also in Capture One which is my favourite raw converter, it was over exposed a lot but I guess that's not what the test was about.
Anyway what I did find interesting was that the star trails almost all pointed to the center of the image in a radial manner.
It was a lot less noticeable from the bottom middle up through the center but it was a bit unusual though. I've reprocessed it and included crops from all four corners and one from the center, I'm guessing this is what you also saw so it will be interesting to see further shots from this with as you say a better calibration first.

Ken.
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Old 17-02-2012, 09:20 AM
Poita (Peter)
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I wonder if the effect is just the cheap kit lens?
I havent a decent prime to try it out with, unless I can connect my Nikon 50mm 1.4 to it?

I meant to have another go last night, but ended up fighting with the DBK21 until 4am. If it is clear tonight I'll give it another shot.

BTW, is that the Horsehead peeking out in the shot? I didn't really look at the image other than a quick look at the trailing.
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Old 17-02-2012, 09:29 PM
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No, it's the flame.
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Old 18-02-2012, 03:28 PM
Poita (Peter)
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Ah yes, had my head on backwards.
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Old 11-03-2012, 10:16 PM
Poita (Peter)
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The night was clear, so I dodgied up a 600mm lens onto the pentax and gave the astro-trace function another go.

This is a centre crop, resized down to display here.

The astro-trace feature really does work, my lens mount needs some work though. Not bad for a long exposure from a static tripod!
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Old 11-03-2012, 10:28 PM
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What was the duration of the exposure Peter?
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Old 19-06-2012, 09:13 AM
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An update on how this has been performing, Peter? Thanks.
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Old 19-06-2012, 02:03 PM
Poita (Peter)
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I'm planning on taking some shots as soon as the cloud clears.

It has been performing well, but I haven't kept track of exposure times, lens used etc. so I don't want to post stuff based on memory.
As soon as I get a clear night I'll do an imaging run with a couple of different lenses and record all the details.

-Peter
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Old 19-06-2012, 02:04 PM
Poita (Peter)
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Quote:
Originally Posted by Nico13 View Post
What was the duration of the exposure Peter?
That one was 3 minutes.
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Old 20-06-2012, 12:39 PM
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erick (Eric)
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Thanks Peter - look forward
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