Night sky 60 second exposures - page 2 - Creative Uses of CHDK - CHDK Forum

Night sky 60 second exposures

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Re: Night sky 60 second exposures
« Reply #10 on: 10 / April / 2008, 17:18:16 »
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« Last Edit: 22 / April / 2008, 17:07:47 by Barney Fife »
[acseven/admin commented out: please refrain from more direct offensive language to any user. FW complaints to me] I felt it imperative to withdraw my TOTAL participation. Nobody has my permission, nor the right, to reinstate MY posts. Make-do with my quoted text in others' replies only. Bye

Re: Night sky 60 second exposures
« Reply #11 on: 12 / April / 2008, 01:55:46 »
At wide aperture you are depending on the precision of the whole area of the lens. The larger the lens the more difficult it is to configure them to "diffraction limited" specifications. (This means that the lens cannot resolve any more detail than is possible by the physics of light itself.) So there's always a trade-off going on. Larger diameter lenses *can* resolve more detail but *only* if they are ground to absolute precision. This is why DSLR glass invariably produces softer images at wider apertures, just due to their size.

Now you have another thing at play. At wider apertures you have to focus much more precisely. Your DOF is not as forgiving at wider apertures. I suspect that your wide-aperture images might be suffering from mis-focus more than poorly ground lenses. At wide aperture you have to depend on precision focusing and precision ground optics. At smaller apertures you hit the other wall and you delve into the area of diffraction limitations. Wider aperture can provide sharper images if all things are going in your favor. There's always a sweet-spot somewhere in the middle of any lens design where aperture (for resolution and lens quality) benefits more than the diffraction limitations and deep DOF at smaller apertures.

The nice thing about the smaller P&S lenses is that it is much easier to grind them to precision curvatures. So that sweet-spot can span a wide(r) range of f/stops. Whereas in larger lenses for DSLRs there's usually only one f/stop where they get the best images.


Ok. So what you are saying, that the reason the photos at F2.8 were less focused, is because of the shorter DOF (which makes sense), so the camera has big problem to decide what to mis-focus (if some of the lights are near and some are far).
In my photo, i was photographing some street lights along with far city lights at infinity. It now seems, after considering DOF, that the camera had to "average" focus between them, so the far lights seems almost sharply focused, while the near street lights are soft and out of focus.
Now it all makes sense, thanks! :)

Where can i learn all about photographing and digital photographing in particular?
I'm reading some articles on Wikipedia, but i would like more material to study from.

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Offline jetzt

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Re: Night sky 60 second exposures
« Reply #12 on: 12 / April / 2008, 05:11:59 »
Quote
I'm reading some articles on Wikipedia, but i would like more material to study from.
I think after having read all the basic articles on wikipedia, (I think dof, white balance, aperture, shutter speed and iso are the most important,) taking your camera and shooting is the best way to practise. I mean nobody can remember all the theory without having tried it out at least one time.  :D
At least I wouldn't :(.

Edit:
Quote
then try to reason-out why they did or did not work for your intended purposes.
Of course it's useful to read something about a particular topic if you didn't get the results you expected or in my words:
If you couldn't figure out why it does this or that.
« Last Edit: 12 / April / 2008, 08:22:37 by jetzt »

Re: Night sky 60 second exposures
« Reply #13 on: 12 / April / 2008, 08:18:04 »
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« Last Edit: 22 / April / 2008, 17:08:09 by Barney Fife »
[acseven/admin commented out: please refrain from more direct offensive language to any user. FW complaints to me] I felt it imperative to withdraw my TOTAL participation. Nobody has my permission, nor the right, to reinstate MY posts. Make-do with my quoted text in others' replies only. Bye


Re: Night sky 60 second exposures
« Reply #14 on: 13 / May / 2008, 22:28:28 »
I had the opportunity to try out Albest'st long exposure feature on my S3 IS recently. It was at a site with very a dark sky and no moon. The camera was mounted on a Meade ETX-125EC telescope and roughly aligned so it would minimise the star trails. ...
I can't wait to try out my wifes A560 which is a much smaller and lighter camera now that there is firmware for it. Thanks to all who have been involved in developing the CHDK firmware, being one who tries to do "more with less", it has made all sorts of previously impossible or horrendously expensive ideas now achieveable.
How did the A560 work out? I'm just starting out with CHDK & would love to try it.
thanks for your answer &
ESPECIALLY THANKS FOR ALL THE DEVELOPERS & USERS THAT HAVE SHARED!!!!!!!!!!!!!!!

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Offline sumoetx

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Re: Night sky 60 second exposures
« Reply #15 on: 27 / May / 2008, 02:39:57 »
Posco, Awesome photos!!  :D

Astrophotography is exactly why I bought my A720is, with the longer exposures  possible with CHDK I want to do this type of wide field shots from my 10" SCT.  Did you happen to have a counter weight on your ETX? I know that when I do imaging through my smaller ETX 90 I absolutely have to have a counter weight on the front end of the scope. I use Scopetronix's counter weights. How did you mount the camera to the ETX?

Also for the very impressive shot of M-42 does the S3-IS have a 12x zoom? the scale of the image is nice, even if you had to crop it. My 720 only has a 6x zoom I think I'd need to use a 2x tele-negative to equal yours.

I'm so jealous you see the southern cross, I'm too far north. :(

Clear skies  :)

sumoetx

Re: Night sky 60 second exposures
« Reply #16 on: 28 / May / 2008, 12:14:20 »
Here's my attempt:

10x64secs lights, 2x64 secs darks, ISO100, CHDK-hacked Canon PowerShot A720IS, max zoom, piggybacked on 4.5" reflector on RA "economy-drive" equipped EQ1 mount. Captured in RAW format, dcraw converted to TIFF, stacked with DeepSkyStacker. Original size 3329 x 2509 pixels. The Field of view is 9.75 x 7.35 degrees. I can detect stars down to mag 11.4 in this shot



The Coma Berenices Star Cluster, Melotte 111, May 6th

To appreciate it in "real size", make a clenched fist and extend your arm fully, then move away until the fist just covers the width of the view.
« Last Edit: 29 / May / 2008, 11:24:24 by themos »
A720IS A710IS A540

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Offline Posco

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Re: Night sky 60 second exposures
« Reply #17 on: 29 / May / 2008, 18:08:57 »
Thanks for your very kind words. My apologies for not responding to some of you earlier. The photo's were a "very first attempt" amd I realised I have a lot to learn - how to get the best out of the CHDK settings, the camera ISO and aperture and the telescope alignment. The location they were taken from is in a very dark sky area but unfortunately, have not been able to visit it very frequently since.

To answer your questions about the telescope - Yes I did use a  custom made sliding counter weight that attaches to the tripod mounting holes under the ETX-125 tube. The camera was mounted on a saddle I constucted to hold the repositioned finderscope on the right hand side of the tube (originally it is mounted on the left) to clear a Meade DSI camera. The camera mount is in the middle of the saddle and forward of the telescope eye piece. I have fitted a Meade LNT module in a similar position to the finderscope on the left hand side. The S3 IS is really too heavy with it's own batteries installed but might be OK if it was run off an external power supply.

As mentioned in my earlier message, I want to try my wifes A560 and may get a chance this weekend, all being well.
And yes, the Orion nebula was cropped, if you are interested in the original photo's let me know and I can send them.


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Offline Joshatdot

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Re: Night sky 60 second exposures
« Reply #18 on: 10 / June / 2008, 04:47:24 »
How do you make such clean long exposure pics?  My A570 is showing lots of hot pixels.  The camera is not that old, I got it in Late January and only recently found out about CHDK.


Re: Night sky 60 second exposures
« Reply #19 on: 11 / June / 2008, 17:07:00 »
In my case, I combined many exposures with a program called DeepSkyStacker. I also shot dark frames (same settings but covered lens) and fed them to DSS. That takes care of hot pixels.
A720IS A710IS A540

 

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