Filming stars

valy · 03-29-2014, 02:56 PM

Tried to film stars (with kIIs) and got dark imges. While setting foto mode (Av, M, etc), the live view shows overexposed stars but switching to movie, live view and the record is blank even if I set +2 exposure compensation. Am I missing something?
Thanks.

Last edited by valy; 03-29-2014 at 03:26 PM.

**TER-OR** · 03-29-2014, 03:43 PM

The videos you often see of stars are actually time lapses of separate images. Usually you can do a few seconds per shot, and then use a software program to build them all into one movie.

valy · 03-29-2014, 03:48 PM

No stills, no timelapse, just movie because I want 30fps.

Stone G. · 03-29-2014, 04:00 PM

Originally posted by valy

just movie because I want 30fps

Well, there's your problem: Each frame will only have a 1/30s exposure time - try that with stills, even at very high ISO, and you will see that only the very brightest stars will be captured.

Dr_who · 03-29-2014, 04:05 PM

Just take more images and you can have 30fps

valy · 03-29-2014, 04:09 PM

I want real 30fps, or 25, meaning I want to aquire 25-30 frames per second.

So there is no way to set iso 51.200? How live view does to get proper images of faint objects and the movie mode don't?

DeadJohn · 03-29-2014, 06:35 PM

You want to record 30fps and playback 30 fps? The stars are not very interesting in real time video. Most star videos are done as a timelapse.

Possible starting settings with the 18-55 kit lens: 18mm, manual mode, f4.0, 30 second shutter, ISO 1600, 2 megapixel JPG, set the intervalometer to take a photo every 32 seconds. Let that run for ~300 shots.

Then use your existing movie software or Startrails application to merge the JPGs into an AVI. 300 shots played at 30 fps will yield 10 seconds of video.

Startrails also has the option to stack all the JPGs into one image, like

valy · 03-30-2014, 05:43 AM

I want to record 30fps, don't care the playback, just to record some signal.

Steve.Ledger · 03-30-2014, 11:15 PM

valy.
Divide 1 second by 30 and your answer is 0.0333333333 which = 1/30 as mentioned by Stone G.

You're really not going to get enough light to register on the sensor in such a short time even with the fastest lens available.
Super high ISO will make more noise than stars

DeadJohn · 03-30-2014, 11:48 PM

@Valy, can you explain why you want a 30fps capture of stars? The night sky usually doesn't change so quickly to make an interesting real-time video. Are you trying for an eclipse or occultation?

valy · 03-31-2014, 02:07 AM

Actually I want to film the seeing variations (air turbulences) at high fps (25-30 is max for k5), I need a bigger sensor (more surface) than my astro CCD camera which has only 640x480px. Examining the movie I've noticed that is pure black, no noise, perhaps the camera didn't raise the iso. I don't mind having noise since there is also usefull signal into the movie.

With my astrocamera I've managed to have a lot of signal at 30fps (0.03 ms exposure) and gain ~800 (from 0-1000 range) and it has almost the same pixel size and sensibility as k5 sensor, this on faiter star. So I expect the k5 is capable to get some white pixel at least on Jupiter which is brigter. I feel there is a missing setting but there is no actual settings to do, all is automatic. I'll try the user mode trick to force it to raise iso and set exporure 1/30s.

On the other hand, on photo mode - live view there is my star visible, so the sensor is capable to catch the light very well, but not in movie mode.

Stone G. · 03-31-2014, 04:22 AM

Originally posted by valy

I need a bigger sensor (more surface) than my astro CCD camera which has only 640x480px.

If you want to film the seeing variations, the Moon is an excellent target. You can also make movies with your DSLR with Jupiter as a target. However, you should realize that even HD movies are quite highly compressed, so you will never utilize the full, spatial resolution of your sensor in movie making. I suggest you take a look at the thread in the Astrophotography Group here:

https://www.pentaxforums.com/forums/groups/135-astrophotography/1486-dslr-video-astrophotography.html

valy · 03-31-2014, 04:51 AM

Actually I want such of this: http://arxiv.org/pdf/astro-ph/0111022.pdf
A mask infront of the telescope, image a little bit defocused and take a movie.

DeadJohn · 03-31-2014, 05:03 PM

Originally posted by valy

Actually I want such of this: http://arxiv.org/pdf/astro-ph/0111022.pdf
A mask infront of the telescope, image a little bit defocused and take a movie.

Okay, now the 30 fps makes sense. It's for scientific purposes to measure atmospheric seeing rather than capturing a nice-looking image.

The mask cuts down the amount of light (by reducing the aperture) but it should still work depending on the size of the telescope. I built a homemade Hartmann mask for focusing (with 3 triangular holes) and I got enough light through it with an 8" Schmidt-Cassegrain. A similar design on a 3.5" refractor was too dark for my K-5.

valy · 04-03-2014, 01:27 PM

Science is more interesting than some nice-looking images

Finally I've decided to use the astrocamera for this, is more flexible/controlable.

03-29-2014, 02:56 PM	#1
valy Senior Member Join Date: Jun 2011 Location: Bucharest Posts: 120	Filming stars Tried to film stars (with kIIs) and got dark imges. While setting foto mode (Av, M, etc), the live view shows overexposed stars but switching to movie, live view and the record is blank even if I set +2 exposure compensation. Am I missing something? Thanks. Last edited by valy; 03-29-2014 at 03:26 PM.

03-29-2014, 04:09 PM	#6
valy Senior Member Join Date: Jun 2011 Location: Bucharest Posts: 120 Original Poster	I want real 30fps, or 25, meaning I want to aquire 25-30 frames per second. So there is no way to set iso 51.200? How live view does to get proper images of faint objects and the movie mode don't? Last edited by valy; 03-29-2014 at 04:45 PM.

03-31-2014, 02:07 AM	#11
valy Senior Member Join Date: Jun 2011 Location: Bucharest Posts: 120 Original Poster	Actually I want to film the seeing variations (air turbulences) at high fps (25-30 is max for k5), I need a bigger sensor (more surface) than my astro CCD camera which has only 640x480px. Examining the movie I've noticed that is pure black, no noise, perhaps the camera didn't raise the iso. I don't mind having noise since there is also usefull signal into the movie. With my astrocamera I've managed to have a lot of signal at 30fps (0.03 ms exposure) and gain ~800 (from 0-1000 range) and it has almost the same pixel size and sensibility as k5 sensor, this on faiter star. So I expect the k5 is capable to get some white pixel at least on Jupiter which is brigter. I feel there is a missing setting but there is no actual settings to do, all is automatic. I'll try the user mode trick to force it to raise iso and set exporure 1/30s. On the other hand, on photo mode - live view there is my star visible, so the sensor is capable to catch the light very well, but not in movie mode. Last edited by valy; 03-31-2014 at 02:20 AM.

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03-29-2014, 03:43 PM	#2
TER-OR Site Supporter Join Date: Apr 2009 Location: Dundee, IL Photos: Gallery \| Albums Posts: 6,699	The videos you often see of stars are actually time lapses of separate images. Usually you can do a few seconds per shot, and then use a software program to build them all into one movie.

03-29-2014, 03:48 PM	#3
valy Senior Member Join Date: Jun 2011 Location: Bucharest Posts: 120 Original Poster	No stills, no timelapse, just movie because I want 30fps.

03-29-2014, 04:00 PM	#4
Stone G. Pentaxian Join Date: Jun 2010 Location: North Zealand, Denmark Photos: Gallery \| Albums Posts: 1,516	Originally posted by valy just movie because I want 30fps Well, there's your problem: Each frame will only have a 1/30s exposure time - try that with stills, even at very high ISO, and you will see that only the very brightest stars will be captured.

03-29-2014, 04:05 PM	#5
Dr_who Veteran Member Join Date: Jun 2009 Location: Edmonton, Alberta, Canada Photos: Gallery \| Albums Posts: 777	Just take more images and you can have 30fps

03-29-2014, 06:35 PM	#7
DeadJohn Pentaxian Join Date: Jan 2011 Location: New York Posts: 4,833	You want to record 30fps and playback 30 fps? The stars are not very interesting in real time video. Most star videos are done as a timelapse. Possible starting settings with the 18-55 kit lens: 18mm, manual mode, f4.0, 30 second shutter, ISO 1600, 2 megapixel JPG, set the intervalometer to take a photo every 32 seconds. Let that run for ~300 shots. Then use your existing movie software or Startrails application to merge the JPGs into an AVI. 300 shots played at 30 fps will yield 10 seconds of video. Startrails also has the option to stack all the JPGs into one image, like

03-30-2014, 05:43 AM	#8
valy Senior Member Join Date: Jun 2011 Location: Bucharest Posts: 120 Original Poster	I want to record 30fps, don't care the playback, just to record some signal.

03-30-2014, 11:15 PM	#9
Steve.Ledger Veteran Member Join Date: Oct 2009 Location: Far North Qld Posts: 3,301	valy. Divide 1 second by 30 and your answer is 0.0333333333 which = 1/30 as mentioned by Stone G. You're really not going to get enough light to register on the sensor in such a short time even with the fastest lens available. Super high ISO will make more noise than stars

03-30-2014, 11:48 PM	#10
DeadJohn Pentaxian Join Date: Jan 2011 Location: New York Posts: 4,833	@Valy, can you explain why you want a 30fps capture of stars? The night sky usually doesn't change so quickly to make an interesting real-time video. Are you trying for an eclipse or occultation?

03-31-2014, 04:22 AM	#12
Stone G. Pentaxian Join Date: Jun 2010 Location: North Zealand, Denmark Photos: Gallery \| Albums Posts: 1,516	Originally posted by valy I need a bigger sensor *(more surface)* than my astro CCD camera which has only 640x480px. If you want to film the seeing variations, the Moon is an excellent target. You can also make movies with your DSLR with Jupiter as a target. However, you should realize that even *HD movies are quite highly compressed*, so you will never utilize the full, spatial resolution of your sensor in movie making. I suggest you take a look at the thread in the Astrophotography Group here: https://www.pentaxforums.com/forums/groups/135-astrophotography/1486-dslr-video-astrophotography.html

03-31-2014, 04:51 AM	#13
valy Senior Member Join Date: Jun 2011 Location: Bucharest Posts: 120 Original Poster	Actually I want such of this: http://arxiv.org/pdf/astro-ph/0111022.pdf A mask infront of the telescope, image a little bit defocused and take a movie.

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03-31-2014, 05:03 PM	#14
DeadJohn Pentaxian Join Date: Jan 2011 Location: New York Posts: 4,833	Originally posted by valy Actually I want such of this: http://arxiv.org/pdf/astro-ph/0111022.pdf A mask infront of the telescope, image a little bit defocused and take a movie. Okay, now the 30 fps makes sense. It's for scientific purposes to measure atmospheric seeing rather than capturing a nice-looking image. The mask cuts down the amount of light (by reducing the aperture) but it should still work depending on the size of the telescope. I built a homemade Hartmann mask for focusing (with 3 triangular holes) and I got enough light through it with an 8" Schmidt-Cassegrain. A similar design on a 3.5" refractor was too dark for my K-5.

04-03-2014, 01:27 PM	#15
valy Senior Member Join Date: Jun 2011 Location: Bucharest Posts: 120 Original Poster	Science is more interesting than some nice-looking images Finally I've decided to use the astrocamera for this, is more flexible/controlable.