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07-10-2016, 03:37 AM   #1
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Astrography on K30?

Hi all,

just doing sme practice shots before the trip to Iceland I'll have this summer, a Aurora Borealis hunting trip :-)

I take a few test night-shots of the sky from the hills above my house yesterday night with a K30, Sigma 10-20 F/3.5.
Now, I noticed that If I kept my ISO as low as 200 or 400 to avoid noise I'd have to switch to B mode to compensate for the exposure, but, as you know, if shutter time is above 15 to 20" you get star trails...

I bumped up the ISO to 1600 but the K30 doesn't have that much of a performace at high ISO as the picture attached shows...(this was taken at F/3.5, 20", ISO 1600)

Now, while I wait a bit to get a K1, what to do?

Thanx



07-10-2016, 04:51 AM   #2
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If you follow the 500 guideline strictly - You'll have to see for yourself if it really works - you should be able to use 30second exposures

At 20mm, it would be 500/20*1.5= 16 seconds

But at 10mm, it would be 500/10*1.5= 33 seconds

So... shoot wider? That's the only thing I can think of
How wide was the example shot above?

---------- Post added 07-10-16 at 07:53 AM ----------

Now that I said that's the only thing I can think of, I thought of something else

You could do multiple shorter exposures, and then do auto-align layers in photoshop - mask out the foreground in all but one picture - and then average them? That might work... but i've never tried it before
07-10-2016, 05:03 AM   #3
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Hi, thanx, this was shot at 10mm with a 20 seconds exposure, and still it looks pretty dark to me with lots of noise.
I may try to use a different lens like the 17-50 F/2.8, hopefully that will help in getting some more light.
How's the Astrotracer function in the K30 working? I'll have to turn that on for B mode shots.
07-10-2016, 05:21 AM   #4
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Good Morning, I have been shooting with a K5IIs - essentially the same sensor as in your K30. I have gotten good results at ISO 3200. I have been futzing around since Feb experimenting at 1600 at 10 seconds to keep from trailing the stars. I have found that 10 is really a bit too short, and 13 sec to 15 sec is good (13 being about about the optimum) when I am including landscape elements within the frame. This is based on the rule of 200 (200/focal length) - which minimizes the trailing of the stars - essentially tries to maintain stars in about a 4 pixel box. Here is a calculator that is a refinement of the 200 rule.Since Feb (the start of Milky Way season), a couple of months were lost to bad weather (rain, high wind and cloud cover even here in AZ). I had a couple of good shoots, followed by some crappy ones, when the state park I have been shooting from put up some new area flood lights, that just killed me.

The other thing that you can do is use a faster lens. F3.5 can be a bit limiting. Obviously f2.8 or f2 is much better. Since you are going to have to manual focus anyway, older manual lenses (M42, K, M and A) with a f2.8 aperture are available for reasonable prices. Something like a M 28/f2.8.

I'm using a Sigma 18-35/f1.8 at f1.8. I have pre-focused the lens with liveview during the day on a ridge a couple of miles away, then put it into manual focus and taped the focus ring down with gaffers tape, so that it will not move. This saves a lot of time at night trying to just focus it.

Last weekend, I went out - essentially settling on 3200, f1.8 at 13 seconds. I also abandoned the state park location and moved down the road to a darker area which helped out a lot. I also use the GPS unit (about half the time) and for that I limit the exposure to 60 seconds. Hope that helps....



07-10-2016, 01:51 PM   #5
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Your lens is fair. Need good fast lens between 1.2 to 2.8.

---------- Post added 07-10-16 at 02:06 PM ----------

Your lens is fair. Need good fast lens between 1.2 to 2.8.
07-10-2016, 06:15 PM   #6
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The lens you want is a Samyang 14mm f2.8. This is sharp wide open, no coma is one of the most important attributes of an astro lens and not the speed. Forget about lenses at 1.2, 1.4 etc. as they are not sharp wide open!!!

I use this with a K30. 30secs, ISO 1600 or 20sec ISO 3200. The K30 has a great low noise sensor, even in 2016!

Most of the skill is in the post processing.

Check out image stacking etc, dark frames, bias frames etc. etc.

I'm sure you know about dark skies and light pollution. Don't forget about the moon, you want a new 'no' moon.
07-11-2016, 03:11 AM   #7
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QuoteOriginally posted by nocturnal Quote
The lens you want is a Samyang 14mm f2.8
And its a FF lens!
07-11-2016, 03:50 AM   #8
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I was checking the Pentax O-GPS1 module, but it's a bit costly ena considering the fact that I want to upgrade to the K1 (whihc has built in GPS) that's probably not worth it.
I'll try again with a different lens, the Sigma 17-50 F2.8 at 17mm, and see what I come up with. I have seen some excellent astrography pics here on the forum taken with that and the K30...
Like this:

http://static.wixstatic.com/media/9ff59e_4947de87f1b148b394f8be28128cc9e5.jp...0_0.00_jpg_srb

...whose author posted hon the ain K30 pics theread here:

https://www.pentaxforums.com/forums/151-pentax-k-30-k-50/192015-post-your-k-3...-here-163.html

---------- Post added 07-11-16 at 12:51 PM ----------

QuoteOriginally posted by nocturnal Quote
The lens you want is a Samyang 14mm f2.8. This is sharp wide open, no coma is one of the most important attributes of an astro lens and not the speed. Forget about lenses at 1.2, 1.4 etc. as they are not sharp wide open!!!

I use this with a K30. 30secs, ISO 1600 or 20sec ISO 3200. The K30 has a great low noise sensor, even in 2016!

Most of the skill is in the post processing.

Check out image stacking etc, dark frames, bias frames etc. etc.

I'm sure you know about dark skies and light pollution. Don't forget about the moon, you want a new 'no' moon.

How do you set the internal noise reduction system on the K30?

Thanx


Last edited by gerax; 07-11-2016 at 04:00 AM.
07-11-2016, 06:22 PM   #9
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QuoteOriginally posted by gerax Quote
How do you set the internal noise reduction system on the K30?
In Rec Mode Menu #3 the second item is Slow Shutter Speed Noise Reduction. I usually set it on or off rather than "Auto". When "on" it will make a dark frame after each picture you take. A 20 s shot will result in a 20 s dark. The camera processes the two images into a single one. The o-gps1 will track the stars but then the foreground gets blurry. You have to take another shot with astrotracer off and blend the two in photoshop. As I'm lazy I like taking 60 s shots at 16 mm with astrotracer on. Stars are sharp and the foreground is not too blurry. Anyhow for northen lights if they are bright and active you will want to keep your exposures short, from 5 to 20 s because longer exposures will make the nice details blurry.

Have fun hunting
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