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12-03-2013, 03:03 PM - 1 Like   #1
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K-3 astrophotography

There are a couple of astro threads strung out here in the forums. Might as well make a K-3 generic one.

The weather has gone clear and cold now here in central BC so I got the gear together last night and stuck it outside for about an hour to acclimatize to the -13C temperatures. There were still some ice crystals in the air since we had had a couple of days of rain before the cold hit and it was being drawn out by the cold air.

To make it short and sweet, the K-3 didn't even blink an eye for its first 5 hour session at -13C. Worked like a charm. All power is supplied by two jump start batteries with appropriate cabling and voltage regulators as required. However, an astro session is a combination of equipment + observer and I failed big time. Even with my hands clenched around a couple of hand warmers tucked away in my parka sleeve ends and shooting with the IR remote out of the heavy cloth tube, I just could not stop my gloved fingers from freezing. The main effect is that I could not take the time needed to make sure the focus and tracking were spot on. So I ended up botching the shoot for most of the targets, including Comet Lovejoy at 5 am when it was a few degrees colder. Lovejoy is a stunner right now and much brighter than it was supposed to be at this point in its journey. Its tail is getting stronger and longer and my 300mm isn't getting the whole thing now.

The only semi-successful target was Etamin, Gamma Draconis. I got the astro bug in the summer when I was ten years old. The first complete constellation I traced out of the sky was Draco the Dragon and it is still my favourite. Although Etamin used to be the third brightest star in Draco, this orange K-class supergiant is now the brightest since the other two have faded with time.

I will be out there tomorrow morning after Lovejoy. And this time I will be better prepared even if it will be ten degrees colder.

Just a note about the faster processing of the K-3. Having the luxury of allowing in-camera lens corrections means that you need to do less fiddling in post. The RGB channels line up almost perfectly in DeepSkyStacker after registration and stacking.

Jack




12-03-2013, 03:35 PM   #2
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QuoteOriginally posted by jbinpg Quote
There are a couple of astro threads strung out here in the forums. Might as well make a K-3 generic one.

The weather has gone clear and cold now here in central BC so I got the gear together last night and stuck it outside for about an hour to acclimatize to the -13C temperatures. There were still some ice crystals in the air since we had had a couple of days of rain before the cold hit and it was being drawn out by the cold air.

To make it short and sweet, the K-3 didn't even blink an eye for its first 5 hour session at -13C. Worked like a charm. All power is supplied by two jump start batteries with appropriate cabling and voltage regulators as required. However, an astro session is a combination of equipment + observer and I failed big time. Even with my hands clenched around a couple of hand warmers tucked away in my parka sleeve ends and shooting with the IR remote out of the heavy cloth tube, I just could not stop my gloved fingers from freezing. The main effect is that I could not take the time needed to make sure the focus and tracking were spot on. So I ended up botching the shoot for most of the targets, including Comet Lovejoy at 5 am when it was a few degrees colder. Lovejoy is a stunner right now and much brighter than it was supposed to be at this point in its journey. Its tail is getting stronger and longer and my 300mm isn't getting the whole thing now.

The only semi-successful target was Etamin, Gamma Draconis. I got the astro bug in the summer when I was ten years old. The first complete constellation I traced out of the sky was Draco the Dragon and it is still my favourite. Although Etamin used to be the third brightest star in Draco, this orange K-class supergiant is now the brightest since the other two have faded with time.

I will be out there tomorrow morning after Lovejoy. And this time I will be better prepared even if it will be ten degrees colder.

Just a note about the faster processing of the K-3. Having the luxury of allowing in-camera lens corrections means that you need to do less fiddling in post. The RGB channels line up almost perfectly in DeepSkyStacker after registration and stacking.

Jack


Hi Jack, I'm new to my K3 and have never tried astrophotography but would like to learn. I'll be sure to go through the threads on the subject on this forum however... Since I only have the DA 16-50 I was wondering which Pentax lens you consider to be the best option for astrophotography so that I can put it on my wish list.
Thanks, Bob
12-03-2013, 03:58 PM   #3
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Hi, Bob. As with just about every other genre of photography, the equipment needed depends on which type of astro work you would like to do. Basically, the dimmer or smaller the target, the bigger the lens or scope will need to be. So if you want to do wide-field star-studded skies, a fast ultra wide angle lens will do nicely. You can even get good results with a kit lens these days. But dim and distant galaxies will require a big scope. It would probably be a good idea to get your feet wet with the wide-field shots first. Then when you get hooked (you will), you can branch out as desired.

Jack
12-03-2013, 04:14 PM   #4
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QuoteOriginally posted by jbinpg Quote
Hi, Bob. As with just about every other genre of photography, the equipment needed depends on which type of astro work you would like to do. Basically, the dimmer or smaller the target, the bigger the lens or scope will need to be. So if you want to do wide-field star-studded skies, a fast ultra wide angle lens will do nicely. You can even get good results with a kit lens these days. But dim and distant galaxies will require a big scope. It would probably be a good idea to get your feet wet with the wide-field shots first. Then when you get hooked (you will), you can branch out as desired.

Jack
Thanks Jack, I have the DA 15 and DA 300 lenses on wish list so maybe they'll give me the ranges of view I'll need.
Bob

12-03-2013, 07:55 PM   #5
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Could you talk more about "appropriate cabling and voltage regulators"?

Have you made yourself a DC adapter for the K-3?
12-03-2013, 08:12 PM   #6
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QuoteOriginally posted by mamethot Quote
Could you talk more about "appropriate cabling and voltage regulators"?

Have you made yourself a DC adapter for the K-3?
Hi mamathot,


If you're interested in making your own power adapter, I recommend visiting this thread.
A few persons (including me) have been listing what's needed.


If you need more info, let me know.


François
12-03-2013, 08:25 PM   #7
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The voltage regulator circuit diagram I used was one detailed here by Bob-o-rama a few years ago. I will see if I can find the link. Any of the big N. American electronics part houses will have the necessary parts.

Jack
12-03-2013, 08:45 PM   #8
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Thanks, I've ordered the connectors from digikey.ca!

12-04-2013, 08:01 PM - 1 Like   #9
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Last night was perfect for astrophotography - clear and cold with a New Moon. Seeing and transparency were about 8/10, the best I can expect with a location only 15 km east of an urban centre. So I headed out early into the -14 degC cold. The first session image recording began at 10:06 pm local and the last at 11:03 pm local. In that hour, I recorded three targets: M42, M35 and Jupiter. The K-3 excelled. Here are a few results of the first session. I have included the full frame and a crop of M35 to show the resolution of the K-3 sensor.














Then I went in to start the post-processing of the first session images. Rather than take the K-3 in with me, I elected to torture test it and leave it out in the cold until I returned for Comet Lovejoy in the hours before dawn. So I pulled all the power cords out so as not to waste the batteries and went inside. When I got back out for Lovejoy at 5 am the next morning, I found the camera completely frosted over as expected. Ambient temperature was now -18degC (0degF). Lovejoy was glowing brightly in a gap between the willow and the cottonwood so I swung the camera around to the target. I fired it up and attempted to take the first shot. The mirror locked up, shutter opened and closed. But then when it should have written the image to the SD card, it instead began "machine-gunning", the shutter firing as fast as it could. Actually, it may only have been the mirror flipping as fast as it could but I couldn't be sure. I tried a few more times with the same result. Hmmm, I thought, must be a power problem. Sure enough, when I checked the cable going into the external power connector on the camera, I found that the connector had torn apart in the cold, So much for my soldering job. Luckily, I had made the cables modular and I had another connector in the house so I ran in and got it hoping the comet wouldn't rotate out of the gap in the meantime. I slapped on the new connector and fired off the shot. Eureka! There it was in the frame. Well, I had proved that the K-3 can handle the cold as long as it has power which was good enough for me so I packed it up at that point. I have a soldering job ahead of me this evening. In hindsight, I had probably stressed the connector when I re-aimed for my last target of the previous session. From now on, I will be removing all cables before re-aiming then re-connecting once the target is established to prevent cable stress, always a bugbear in cold weather. Here is the single frame of Lovejoy. - Jack




Last edited by jbinpg; 12-04-2013 at 10:55 PM.
12-04-2013, 09:51 PM   #10
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QuoteOriginally posted by jbinpg Quote
Last night was perfect for astrophotography - clear and cold with a New Moon. Seeing and transparency were about 8/10, the best I can expect with a location only 15 km east of an urban centre. So I headed out early into the -14 degC cold. The first session image recording began at 10:06 pm local and the last at 11:03 pm local. In that hour, I recorded three targets: M42, M35 and Jupiter. The K-3 excelled. Here are a few results of the first session. I have included the full frame and a crop of M35 to show the resolution of the K-3 sensor.

Very nice! Lenses?


Steve
12-04-2013, 10:03 PM   #11
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Astounding!

"If we are alone in the Universe, it sure seems like an awful waste of space"
12-04-2013, 10:50 PM   #12
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Sorry, forgot the specs. All images taken with the DA*300, f/4.5, 10s at ISO1600, 3200 and 6400 then stacked in DeepSkyStacker. I try to take at least 10 frames at each ISO. The comet was a single shot of 10s at ISO3200.

Jack
12-05-2013, 12:39 AM   #13
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Good work! I went out yesterday to shoot some stars with my K-3 and Tokina 235/2.8 tried to take a shot of milkyway...first tries almost. I did get startrail even at 15 seconds exposure. Might be better if I shot few @ 5-7 sec. And stacked them? Sorry for noob question. also I'm thinking of better wide for astro. 'They(web)' say samyang 14 would be good. Any ideas on that? Thanks.

Oh, and I must try my A400/5.6 also for astro. So stacking sounds good for that too...
12-05-2013, 02:05 AM   #14
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What kind of guider do you use?
12-05-2013, 02:32 AM   #15
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QuoteOriginally posted by jbinpg Quote
Sorry, forgot the specs. All images taken with the DA*300, f/4.5, 10s at ISO1600, 3200 and 6400 then stacked in DeepSkyStacker. I try to take at least 10 frames at each ISO. The comet was a single shot of 10s at ISO3200.

Jack
Great images, jbinpg!
I would also like to ask you about the tracing. You said the comet was a single shot of 10s but why are there no traces in it?
Tell us also how you handle the ISO noise. Looks like you did a good job of eliminating almost all noise from the image! If you could give your thoughts on K-3 in comparison to K-5 IIs it would be great too! Some reviewers say that K-3 is not as good as K-5 IIs but usually they do not have as thorough knowledge of photo teqnique as you do. Your shots speak for themselves that's why it would be very useful to many of us to know your opinion.
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