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Astraforce Paul
Carpal Tunnel
Reged: 04/05/05
Posts: 1879
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Wasn't sure where to post this... but given all the photos I see in this forum, figured I'd put it here.
I've been seeing some detailed prominences the past several days through my PST and tried one afternoon taking some photos with a Canon Powershot A70 (a basic consumer digicam that's several years old). I varied the exposure times, zoom, and even the aperture, but the pictures were generally disappointing. I did use the shutter delay (2 seconds) to let the scope settle down (maybe I should have used 10 seconds). I also tried varying the focus-- macro, auto, and infinity. Exposure time seemed to matter the most. The best ones were around 1/125 of a second, but the prominences didn't seem as crisp as they did through the scope. (I've attached one of the "good" photos here.)
In any event, was wondering... What are the best settings for taking digicam photos of the Sun through a PST? Any particular tips on how to get a high quality shot?
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ragebot
Carpal Tunnel
Reged: 08/26/05
Posts: 1672
Loc: Tallahassee, FL, USA
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Quote:
SNIP Any particular tips on how to get a high quality shot?
I use to take pix using a PST and a Nikon CoolPix 4500, a digicam similar to your Canon.
The first thing I notice about your image, possibly because I captured so many with similar problems, is that there seems to be what I call a hot spot. The surface of the sun does not vary much in color, but your image goes from what looks like almost pink to an orange red to me. This looks like an exposure issue to me. But it is also possible that there are tuning issues as well.
Exposure is always a problem for me. Keep in mind that clouds, pollution, dust, and the like can change the "right" exposure from day to day; so it is not really possible to post "the digital camera" settings. It also seems to me that tuning can also change the settings.
First off I play around with some visual observing to make sure things are stable. Then I normally try and capture several test images to get the exposure for the day I am shooting; and the test images are darker than yours. Once I have a base line exposure I bump up the magnification (via the zoom feature of the digicam) and try and center the feature I want to capture an image of. The increased magnification will result in changing the exposure again, and after a few iterations I am usually able to get an image.
I would also note that not all days are equal in terms of imaging, or observing, and that there have been multiple threads about how while in general around 8-9 AM is usually the best time to observe on a clear cloudless day that at times 4-5PM with a very light cloud cover or dust particles in the air can provide great observing or imaging.
YMMV.
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Meade ETX 90, Meade AR5, Orion ED80, Atlas GT, 8 in Newt, Coronado DS SM40, Garrett 10.5X70, Sigma SD10, SD14, Canon 1D2, Xti, Nikon CP4500, C-14
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Astraforce Paul
Carpal Tunnel
Reged: 04/05/05
Posts: 1879
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Very helpful tips and information! I'll have to get the camera out and try this again, especially fiddling more with the exposure.
The pictures I took that are darker (without those hot spots you mentioned) didn't show the prominence! Interestingly, while one of them was 1/1000, another was 1/125--the same setting as the ones that showed the prominence!
I supposed conditions can change from minute to minute as well as day to day. I certainly noticed that visually. There were clouds in the sky and the prominences would come and go.
Does 1/125 sound reasonable? Much faster (1/320, 1/1000) seemed to miss the prominences. 1/200 did work.
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ragebot
Carpal Tunnel
Reged: 08/26/05
Posts: 1672
Loc: Tallahassee, FL, USA
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Quote:
SNIP
Does 1/125 sound reasonable? Much faster (1/320, 1/1000) seemed to miss the prominences. 1/200 did work.
The shutter speed is only half the exposure; without knowing the focal ratio, or what photographers call f-stop, you really can not determine the shutter speed.
That being said I would point out that what you see when you look at an image you have captured does not always display what was or was not missed.
Digicams are famous for non standard basic ISO settings, sensitivity of sensors, non standard focal lengths, shutter speeds, and focal ratios, and other variations. Not to mention different work flows for post processing.
I just noticed you did not mention the work flow you used to post process your images; or even if they were post processed. Here is a link to a guy who uses a digicam and an SM40 (very similar to a PST in many respects) and describes a very usable work flow. As with all digital photography, but especially astrophotography, the final image is usually the result of a standard work flow to post process at least one, and sometimes multiple images.
While the work flow, and settings, for your digital camera may not be identical here is a good starting place.
While this link is for Paint Shop Pro, most of the adjustments described can be done using a host of other software packages.
I usually spend more time post processing my images than capturing them.  
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Meade ETX 90, Meade AR5, Orion ED80, Atlas GT, 8 in Newt, Coronado DS SM40, Garrett 10.5X70, Sigma SD10, SD14, Canon 1D2, Xti, Nikon CP4500, C-14
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