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04-03-2013, 05:40 AM   #586
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QuoteOriginally posted by gbeaton Quote
What?! The GPS will track stars?! How does it do that? With the moveable sensor mount? I think I wasted $300 on a Vixen Polarie :-( I read the GPS can track for 5 mins. I seem to be only able to track for 2 mins with the polarie - with the basic setup.
Well, first of all I belive that the Vixen Polarie IS in fact a better and more consistantly reliable platform for exposures of longer (minutes-long) duration. But you will of course need an adequate polar alignment.

But then, I am very fond of Pentax' GPS/Astrotracer solution because it is so easy to carry and use everywhere. However, don't expect it to work with lenses in the 200-300mm range for more than about 30s in general or perhaps up to 1 minute on a good night with perfect calibration.

And yes, the Astrotracer function of the O-GPS1 works by moving the sensor in its "free-floating" sensor mount. You can find an interesting interview with the developers at PENTAX here:

http://dc.watch.impress.co.jp/docs/review/special/20110708_458911.html

Close to the "Astro" tracer Pentax - Digital Camera Watch

Google-translate is still rather primitive, but the interview does provide a good explanation together with some interesting illustrations. Pretty ingenious, isn't it?!?

04-05-2013, 05:52 PM   #587
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I got this a couple nights ago.



It was shot with a Pentax K-5 and Takumar 135mm f2.5 at 4 seconds, f/4, iso 3200. It is a stack of 40 light frames, 15 dark frames, and 15 bias frames. The horizon is on the right and it was quite a challenge to remove the gradient and glow from the light pollution.
04-07-2013, 08:28 AM   #588
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My first attempt at using Astrotracer O-GPS1, having a bit of fun.

Camping in a field near a lake in southern QLD over Easter weekend. Unfortunately almost a full moon, but at least it wasn't raining like the day before and the next day.
I pointed the camera in a generally in a sort of southerly direction hoping the motion of the stars would be less than pointing west away from the full moon which had just risen in the eastern sky.

I had no idea what I was pointing at. After 5minutes this comes out.





K-5IIs, FA43, f2.8, iso 200, single shot, 300sec (perhaps too long - there are some short trails)
No PP excepting to pull down the blacks to try to minimise the light from the full moon (from the lower left corner of the frame).
GPS reading 28deg 42.67' S, 152deg 00.01' E, heading 164deg


A bit of googling and looking at pictures
The pinkish/red cloud almost of in the middle of the frame is "NGC 3372 Carina Nebula".
the little cluster of many stars just to the left of it is "NGC3532 Wishing well cluster"
and the open cluster of 8 or so bright stars diagonally down to the right is "Southern Pleiades IC 2602"

Very interesting stuff
04-07-2013, 10:07 AM   #589
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Nice pictures!
I'm starting to use my O-GPS1 and a week ago I finally got some time to shoot. I got this picture of the Orion constellation and while at it, an airplane flew by. I also tried with different lens and got a little closer views to the M42 nebula. I got some really sharp pictures but some others had a little trailing. Overall I'm happy with the results and look forward for more practice with the gps.

K-5IIs, A 50mm f1.4 @f2.8, Iso 800, 120sec. One single exposure since I'm not sure how to do stacking, dark frames and all that stuff lol.



04-11-2013, 04:22 PM   #590
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Usually airplanes are kind of annoying, but you managed to capture a nice set of racing stripes with that one.
04-15-2013, 01:41 AM   #591
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Mucked about with the astrotracker tonight, first time in a while. Had a huge failure rate, but thisone worked out pretty well. The bright star on the bottom is Antares. Shot this one with the M-200mm stopped down one or to pegs to f/8 or f/11. Is that smudge to the right of Antares M80? Apparently its M4, M80 is up top. :-D



Last edited by Sagitta; 04-15-2013 at 01:47 AM.
04-20-2013, 01:36 PM   #592
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Pentax DA* 200mm f/2.8 and Astrotracer

I finally pulled myself together and got that lens, which I have been wanting for a long time. After a good week of anxious waiting under overcast skies, I finally got a chance to test it last night. The sky was by no means perfect, nor was the seeing and there were nasty guts of wind too. But good enough for a first test.

I used Jupiter as one of my test targets and here's a full frame, stacked in DSS and post-processed in PhotoImpact. 6 images taken with the lens stopped down to f/3.5, 15 seconds of exposure time at ISO 1600. Tracking the stars was achieved by the Pentax O-GPS1's Astrotracer function.


click on thumbnail to see larger version, 1280 pixels wide.

Now, my real errand wasn't to produce "nice pictures" but to see how the lens performed across the entire frame. So, here come two 100% non-resized crops of the original stack without post processing:


Crop near centre. (One is not in doubt that the DA*200 has 9 aperture blades?).

Innermost to Jupiter in the 11 o'clock direction you see from closest to furthest: Europa-Ganymede-Callisto. Io is even closer to Jupiter and hidden in the glare of the planet. Note that in spite of seeing and wind, the pair Europa-Ganymede, though the moons are touching each other, is clearly split. At the mean time, UT = 21:03, of taking the six images, the distance between the two moons was 21.2 arcseconds. A promising result, I think.

Next to test was the apperance of stars in the extreme cornes:


Upper left corner.

The other corners show identical behaviour. To my eyes, star images areessentially the same here as near the centre. Considering that many photographic lenses do show coma at the extreme corners, this was yet an encouring result for me.

So, now I am just waiting for some nice, dark skies. They'd better come soon, because we are already somewhat into the bright Scandinavian nights that won't be dark again until well into August..........

Last edited by Stone G.; 04-20-2013 at 01:41 PM.
04-20-2013, 05:35 PM   #593
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Stone, those are promising results from the lens. Thank you for sharing the corner images as well. How did you get focus? Did you find that focus moved over time? I would expect that you'd need to put some kind of tape or rubber band on it to hold focus position given the plastic construction.

Lastly, I see the reflection disk around Jupiter. Usually that's from ghosting from internal reflections and would explain the slight off-center position because the planet was off-center. I can see this on Sirius with some lenses. If the halo follows the planet, then it's probably due to unfocused light wavelengths.

04-20-2013, 08:27 PM   #594
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QuoteOriginally posted by steve1307 Quote
My first attempt at using Astrotracer O-GPS1, having a bit of fun.

Camping in a field near a lake in southern QLD over Easter weekend. Unfortunately almost a full moon, but at least it wasn't raining like the day before and the next day.
I pointed the camera in a generally in a sort of southerly direction hoping the motion of the stars would be less than pointing west away from the full moon which had just risen in the eastern sky.

I had no idea what I was pointing at. After 5minutes this comes out.





K-5IIs, FA43, f2.8, iso 200, single shot, 300sec (perhaps too long - there are some short trails)
No PP excepting to pull down the blacks to try to minimise the light from the full moon (from the lower left corner of the frame).
GPS reading 28deg 42.67' S, 152deg 00.01' E, heading 164deg


A bit of googling and looking at pictures
The pinkish/red cloud almost of in the middle of the frame is "NGC 3372 Carina Nebula".
the little cluster of many stars just to the left of it is "NGC3532 Wishing well cluster"
and the open cluster of 8 or so bright stars diagonally down to the right is "Southern Pleiades IC 2602"

Very interesting stuff
Look for the Astrometry (spelled that way) group on flickr and add the photo to it. Its bot will come along and tag everything taggable in that shot for you.
04-20-2013, 08:40 PM   #595
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QuoteOriginally posted by steve1307 Quote
My first attempt at using Astrotracer O-GPS1, having a bit of fun.
I had no idea what I was pointing at. After 5minutes this comes out.
The Southern Cross is in the bottom left hand corner too.
04-20-2013, 10:47 PM   #596
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QuoteOriginally posted by Sagitta Quote
Look for the Astrometry (spelled that way) group on flickr and add the photo to it. Its bot will come along and tag everything taggable in that shot for you.
Thanks, steve ("smigol") commented in my flickr about that too. I havent tried it out yet.


QuoteOriginally posted by pixelsaurus Quote
The Southern Cross is in the bottom left hand corner too.
Yep that's right, actually it's easier to pick the Southern Cross out when looking at the sky in real time than picking it out of the exposure.
.
.
I've since tried it at home in Sydney with a 100WR macro which needed a bit of CA correction in LR (i find that i get some CA/PF with the K-5IIs wide open but not with my K-7 )




I also tried the 35 macro, where a plane flew right through my shot and it was a little OOF anyway.
This is 31minutes with 35macro (sans Astrotracer). I'm glad that DFS in the K-5 can be switched off.


04-21-2013, 10:53 AM   #597
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I went hunting Lyrids last night. While I didn't manage to catch any, I did get a bunch of shots like this, so I'm happy all the same. The light from the clouds is actually the gibbous moon behind the camera. This would be looking north-ish around midnight-ish.


04-21-2013, 02:30 PM   #598
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smc Pentax DA* 200mm f/2.8 for astrophotography

QuoteOriginally posted by smigol Quote
Stone, those are promising results from the lens. Thank you for sharing the corner images as well. How did you get focus? Did you find that focus moved over time? I would expect that you'd need to put some kind of tape or rubber band on it to hold focus position given the plastic construction.

Lastly, I see the reflection disk around Jupiter. Usually that's from ghosting from internal reflections and would explain the slight off-center position because the planet was off-center. I can see this on Sirius with some lenses. If the halo follows the planet, then it's probably due to unfocused light wavelengths.
Thank you smigol. In response to your questions:

1. How to get focus?
Normally, with a lens without reliable infinity stop, I would use MF and liveview at some 6-8X. Always works, even with fainter stars. With the DA* 200 I can actually, believe it or not, use AF on even not too bright stars. After that, I switch to MF, as that is a requirement for Astrotracer to work. I may add, that this lens is so crisp, that MF is a joy even just using the viewfinder.

2. Did focus move over time?
Actually, in the the DA* 200 you will have to look hard to find plastics other than the hood and the AF/MF switch. The optics is a true copy of the FA* 200mm lf/2.8 lens. The housing is metal and the lens is built as an icebreaker. Very nice feel! Focus is IF and so far, I have observed absolutely no focus creep. As always, one should check for changes due to thermal effects, but so far (with my limited experiences with this lens) focus adjustments have not been required.



3. Internal reflections?
So far, I have found that internal reflections are very well controlled with this lens. The disk follows the object as can also be seen in the following images of Castro and Pollux in Gemini (with the glaring Moon uncomfortably close) taken some fifteen minutes before the Jupiter images:


Castor (right) and Pollux (left). Stack in DSS of five exposures of 15 seconds at f/3.5 and ISO 1600. Post-processed in PhotoImpact.


Castor: 100% unprocessed, non-resized crop of the original stack.


Pollux: 100% unprocessed, non-resized crop of the original stack.

I believe that the disks seen are scattered, (unfocussed?) light in the atmosphere. The air at my urban observing site is only free of smog and haze on the very rarest of occasions - for example when the skies clear just after a weather front has passed. And the assymetry would most likely be due to a slight flaw in the collimation of the lens. Something one would never observe with ordinary, terrestrial photos, but stars are quite merciless in revealing such issues.

I shall continue testing, but it doesn't really detract from my pleasure so far in working with this lens.

Last edited by Stone G.; 04-21-2013 at 02:38 PM.
04-21-2013, 02:31 PM   #599
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QuoteOriginally posted by Sagitta Quote
I went hunting Lyrids last night. While I didn't manage to catch any, I did get a bunch of shots like this, so I'm happy all the same. The light from the clouds is actually the gibbous moon behind the camera. This would be looking north-ish around midnight-ish.


Sunkhaze Meadows Under the Stars; Benton, Maine by Jody Roberts, on Flickr
Very nice mood you have captured here, Sagitta,
04-21-2013, 10:04 PM   #600
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Stone,

I think that your estimates are right on regarding the halos as being unfocused light, especially since they follow the object. If it were ghosting, there would be a bright blur appearing at an opposite side of the frame that gained distance as the bright source was moved from the center.

I recently struggled with handling unfocused IR light with some lenses and finally solved the problem for that project by switching to a narrow-ish band filter. By only allowing Ha to pass via a fairly wide 35nm filter it allowed much crisper star images. I was surprised how far off the focus point was from the visual infinity point! (I usually focus via a bahtinov mask and a laptop screen)

I believe that the ED elements in this lens should help keep the focus points for the wavelengths together. If you decide this continues to be a problem, the solution would be to eliminate the source by using a filter that cuts off the IR.
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