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PostPosted: Wed Dec 31, 2008 5:17 am 
Hello,

I am preparing for the upcoming Solar Eclipse. I now have the new canon 55-250 lens. However, I do not want to use it unless suggested.

Request for some advice for the following setups (which one is better)

1: I would remove the Canon 400D kit lens and attach it to my
6" Newtonian Telescope. I will use a Solar filter (may be an inch or or inch and half in dia) which will cover the front part of the telescope and the remaining part will be covered with Hard Cover to eliminate any sunrays entering the scope.

2: I would use the Canon 55-250mm lens instead of the telescope. However I dont have any solar filter in this combo. Is there any photographic filter that can be used with this combo to photograph sun directly?

-> Finally, is it ok to photograph the sun using any of the above filters and at the same time doing no damage to the Camera and its sensor and as well as to the new lens?

Did anyone already took a pic of a Solar Eclipse using a zoom lens, if yes can you plz post it?

Which is the best combo and any other suggestions are welcome


regards,


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PostPosted: Wed Dec 31, 2008 12:23 pm 
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I haven't tried myself, but my first thought is that at 250mm the lens would be a bit short for the sun. It will be a small part on the image. But I don't know how far "other stuff" might extend around the sun so maybe it's not so bad after all. Is the corona very visible in an annular eclipse?

Assuming you could modify or adapt the filter, that could also be used on the lens. Assuming the filter is of a suitable quality, then it should be ok to use. Do check it for any minor damage before using just in case.

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PostPosted: Thu Jan 01, 2009 2:53 am 
"...at 250mm the lens would be a bit short for the sun. It will be a small part on the image..."

Yes even I did have the same doubt. However, if there are other planets around it and if this lens can cover them in its field, then it might be good catch.

Yes I also recently purchased a sun filter which produces a natural yellow-orange color of the sun... Hoping for more posts around this topic from other ppl also with some previously taken pics...


regards,
Phani Kumar.


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PostPosted: Thu Jan 01, 2009 8:47 pm 
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Hi phani, is it a total or a partial eclipse?

If any part of the sun is visible, then you will need a filter at ALL times. So for a total eclipse, you need a filter right up to and immediately after totality. For a partial eclipse, or an annular eclipse, you will need the filter on at ALL times.

The definitive source of information on eclipses is Fred Espenak, who publishes some fantastic information including photography tips here:

http://eclipse.gsfc.nasa.gov/OH/OH2008.html

If it's the one on February 8th, then I'll be able to see it too in New Zealand - weather permitting! But it's not a total, so we'll need to use filters throughout.

Here's a guide I wrote a while back for total eclipses which might be useful. It includes details of filter material you can buy in the UK - see if there's a local supplier for you...

A total solar eclipse is one of nature’s most secular sights, and with the right technique it’s possible to come home with some truly memorable images.

If you’d like a photo where the Sun fills a large proportion of the frame, you’ll need a powerful telephoto lens. For typical DSLRs with APS-sized sensors, an 800mm lens will produce a solar disk measuring almost exactly half the height of the frame; this can easily be achieved using a 400mm lens and a 2x converter. This is perfect for capturing most phases of an eclipse including the coronal atmosphere. For extended atmosphere shots, 500 to 600mm focal lengths (such as a 400mm with a 1.4x converter) are more appropriate for DSLRs.

To protect your eyes and equipment from the Sun before and after totality you will need a suitable solar filter. Dedicated glass solar filters which screw onto the end of lenses and telescopes are available, but equally good results can be had by making your own using a special sheet of material.

Baader’s Astro Solar Filter Material reduces solar intensity by 99.999% and is ideal for the job – some companies sell pre-made filters using this or similar material - for example at http://www.telescopesplus.co.uk/viewsub ... Filters/21.

You should also use a tripod to aim the camera and keep it steady, although at long focal lengths you will actually see the Sun move steadily across the frame as the Earth rotates. The solution is of course to keep readjusting the tripod, but a smooth video head is essential to avoid jerking and losing the target altogether.

As for exposures, study the invaluable table under the photographic section of NASA’s eclipse web pages – see snippet. If you use a 400mm f5.6 lens with a 2x converter, it will have an effective aperture of f11. If your camera is set to 200 ISO you’ll then be looking at a shutter speed of around 1/500 for the whole disc or partial phases with the solar filter attached.

During totality you should remove the filter and use a range of exposures from 1/2000 to 1 second to capture varying degrees of the coronal atmosphere; one of the easiest approaches is to simply take one shot after another at steadily decreasing shutter speeds, repositioning the tripod every few seconds to keep the disc in the middle of the frame. Once totality is over, quickly replace the filter.

Ultimately though don’t become obsessed with your camera, and always leave time to view this magical sight with your own eyes.


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PostPosted: Fri Jan 02, 2009 5:35 am 
Thanks Gordon, for the valuable suggestions.. The NASA Link you provided is great!

As you told that a long telephoto lens should be used to capture large potion of the Sun, I decided to use my 6inch Newtonian Reflector which is 1000mm (F/6.5). My telescope will produce much bigger image of the sun and the resolution should be much better than a 55-250 mm lens. and as per your message I see that the 55-250 lens will not be sufficient even with a tele-adapter... But still I will shoot two or more with it to see how would come out... also, I am planning to use a 2.3 inch refractor connected to my webcam.

Yes it is an Annular Eclipse, so I have already ordered for a solar filter. Here is the filter that I am using:

http://cgi.ebay.com/Telescope-Sun-Solar ... 1|294%3A50

This eclipse is happening on January 26, 2008 in the morning as per India time.. which I checked on Starry Nights Software.

-> Any other suggestions on how to keep the Camera in top condition while shooting the eclipse as it is very hot at Hyderabad, India?


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PostPosted: Fri Jan 02, 2009 8:08 pm 
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Hi Phani, if you want the Sun to fill your frame, or fill a lot of it, then you will need a long focal length, BUT some of the nicest eclipse photos are those which include a building or a landscape, taken with a shorter lens. So your 55-250mm could be pretty good. Start checking out locations. Go out at the same time the eclipse will be (preferrably only a few days before), then look for a position where you can capture the sun and something else in the shot. That way you will be ready for the real thing!


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PostPosted: Sat Jan 03, 2009 2:40 am 
That idea is pretty Coool Gordon! I will surely check out some nice landmarks for it, starting tomorrow :)

I was doing some experiments earlier this morning with a different set-up. This is exactly how and what I saw. The sun's disc is very clear-orange (little more than what it is in the below pic) and the disc is sharp as a ring and the sky was some what darker.. Generally we dont see Sun like this every day from our place (Hyderabad) may be because we are much closer to the equator!


Image


Here is the setup that I have used. The spotting scope is very small having a dia of little over 1 inch and its focal length is around 200 mm.


Image


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PostPosted: Sat Jan 03, 2009 8:38 pm 
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Pretty cool shot Phani! That's what I'm talking about - wouldn't it be nice to have a photo of an eclipse with some background to it rather than just a plain shot of the Sun itself? Obviously you have to know where it will be in the sky at that time of day though, and if it's high, then your options are limited...

And while early morning / late evening sky in some regions can act as a solar filter of sorts, you will need a proper filter for clearer days or when the sun's higher. Be careful!


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PostPosted: Sun Jan 04, 2009 2:07 am 
hmm.. you liked it cool. Yep, the eclipse seems to be starting in the morning arund 7:00 AM so I can use some background, later i will have not that choice..

Thanks for your suggestions Gordon. Bye for now will catch you soon here with some more topics later..


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