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Main
Date: 02 Aug 2007 14:45:52
From: Trev Boyd
Subject: Astrophotgraphy with Canon 350D (Rebel XT)
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Hi all,
Apologies if this is the wrong group - if so, can you point me in the
direction of a more appropriate one?
I have recently become interested in astronomy and (simple)
astrophotography. I have been using a pair of 10x50 binoculars to explore
the sky, spotting Alcor/Mizar and M31 so far from my moderately
light-polluted back garden in the SE of England.
I have seen some very nice photos of M31 on the web taken with a consumer
DSLRs and medium telephoto lenses. I have a Canon 350D (Rebel XT) with
Canon 28mm f1.8 and Canon 200mm f/2.8L lenses. I tried to image M31 last
night with the 200mm lens, but I discovered that exposures over 5s produce
trailing in the stars. I took a series of 4s exposures at a variety of ISO
and f-stop settings. Most are quite dark, but there is a very faint fuzzy
object visible in them. I tried to stack some of these exposures in
Registax4, and after some levels and curves adjustment in Photoshop, I have
an image of a very fuzzy white object.
I am guessing that the (much better) images I have seen online are taken
with longer exposures on an equatorial mount? Is this necessary, or can I
duplicate the effect with many more exposures of shorter length?
I also found it difficult to achieve perfect focus - the camera's autofocus
wouldn't work with any of the stars in my field of view. I ended up taking
shots, copying them to my computer and zooming in to check the focus. Does
anyone have any suggestions on how to do this better/quicker?
I am also interested in imaging some of the constellations, which should be
easier than DSOs. However, the light pollution tends to produce very
washed-out looking images. What combination of ISO, aperture and exposure
length would produce the best results? And is it possible to produce better
images using stacking in this case? If so, is it better to start with
original images that are brighter or darker?
I realise that's a lot of questions - sorry! I'd appreciate any input on
any of my questions from anyone.
Thanks in advance
Trev
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Date: 02 Aug 2007 17:47:30
From: Craig
Subject: Re: Astrophotgraphy with Canon 350D (Rebel XT)
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Trev,
Welcome to the wonderful world of DSLR astrophotography. All of teh
isses you raise affect all of us attempting teh same thing. I use a 20d
and have had some small successes, but more failures. But yet like a
masochist I keep trying.
As for taking astroimages with a DSLR, you will need an equitorial
mount. Anything over a few seconds (depending on teh focal length of
the lens) will produce trailing. the wider the field the longer the
exposure can be (up to about 30 secs).
Taking multiple short exposures and stacking is a possibility, but you
really want to use lots (100s) of exposures as a base for stacking.
Most people use a DSLR hooked up to a telescope to get some
magnification on an object. Of course this requires an EQ mount or a
scope on a wedge.
For focus I recommend the following, get a magnifing right angle finder
(Canon Angle Finder C) and use a software program like DSLRFocus or
DSLRStar that will take short exposured and download them to a PC
automatically and you will be able to tweak focus that way.
Balancing ISO and exp time vs light pollution is tough and will require
some post processing in Photoshop. I tend to use ISO 400-800 most of
the time and since I'm hooked up to a scope that tracks up to 1 min.
Exposures (although as I refine my polar alignment I'll get longer
exp.) Also a lot of folks use another camera as an autoguider to make
minor corrections to the mount's tracking.
Onle last thing Shoot RAW not JPG. this gives you more latitude in
adjust things in Post processing.
Hope this helps.
Craig
--
Remove My_Skin to E-mail me.
Trev Boyd wrote:
> Hi all,
>
> Apologies if this is the wrong group - if so, can you point me in the
> direction of a more appropriate one?
>
> I have recently become interested in astronomy and (simple)
> astrophotography. I have been using a pair of 10x50 binoculars to
> explore the sky, spotting Alcor/Mizar and M31 so far from my
> moderately light-polluted back garden in the SE of England.
>
> I have seen some very nice photos of M31 on the web taken with a
> consumer DSLRs and medium telephoto lenses. I have a Canon 350D
> (Rebel XT) with Canon 28mm f1.8 and Canon 200mm f/2.8L lenses. I
> tried to image M31 last night with the 200mm lens, but I discovered
> that exposures over 5s produce trailing in the stars. I took a
> series of 4s exposures at a variety of ISO and f-stop settings. Most
> are quite dark, but there is a very faint fuzzy object visible in
> them. I tried to stack some of these exposures in Registax4, and
> after some levels and curves adjustment in Photoshop, I have an image
> of a very fuzzy white object.
>
> I am guessing that the (much better) images I have seen online are
> taken with longer exposures on an equatorial mount? Is this
> necessary, or can I duplicate the effect with many more exposures of
> shorter length?
>
> I also found it difficult to achieve perfect focus - the camera's
> autofocus wouldn't work with any of the stars in my field of view. I
> ended up taking shots, copying them to my computer and zooming in to
> check the focus. Does anyone have any suggestions on how to do this
> better/quicker?
>
> I am also interested in imaging some of the constellations, which
> should be easier than DSOs. However, the light pollution tends to
> produce very washed-out looking images. What combination of ISO,
> aperture and exposure length would produce the best results? And is
> it possible to produce better images using stacking in this case? If
> so, is it better to start with original images that are brighter or
> darker?
>
> I realise that's a lot of questions - sorry! I'd appreciate any
> input on any of my questions from anyone.
>
> Thanks in advance
>
> Trev
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Date: 03 Aug 2007 13:42:32
From: Trev Boyd
Subject: Re: Astrophotography with Canon 350D (Rebel XT)
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Craig
Thanks for your quick reply!
I hope to buy a telescope sometime in the near future, so I guess I'll make
sure I get one on an EQ mount and with a motor drive. As I understand, the
accuracy of tracking an object with a motor drive is heavily dependent on
how accurately it is aligned with the pole? I assume that the quality of
the motor, etc also has an effect? I'll probably use the telescope both to
piggy-back my DSLR and for prime-focus photography through it.
I was out last night to shoot 100 or so images of a variety of things, and
this time, my focus was much better, from a combination of auto-focusing on
Jupiter and then zooming in on the image on the camera's screen to make
adjustments. Of course, now my stars appear as very sharp pick-pricks of
light, which is nicer than fuzzy blobs, but the images look less impressive
with a lot more empty space. I guess I need longer exposures or larger
apertures to capture more stars to fill in the blanks, but need to avoid too
much light pollution.
I did manage a set of shots of Jupiter and 3 of its moons, which when
stacked look quite good, so at least the effort was worth while! The other
images of Cassiopeia and Ursa Major are less inspiring! I can see myself
having a lot more failures than successes in this.....
Can you (or anyone else) suggest some possible targets for images that would
work well with my limited equipment and poor light pollution?
Thanks again
Trev
------------
(re-order domain name to be my name to reply)
"Craig" <CBobchin@My_Skinsbcglobal.net > wrote in message
news:xn0f9gy5r4hfn63007@news.la.sbcglobal.net...
> Trev,
>
> Welcome to the wonderful world of DSLR astrophotography. All of teh
> isses you raise affect all of us attempting teh same thing. I use a 20d
> and have had some small successes, but more failures. But yet like a
> masochist I keep trying.
>
> As for taking astroimages with a DSLR, you will need an equitorial
> mount. Anything over a few seconds (depending on teh focal length of
> the lens) will produce trailing. the wider the field the longer the
> exposure can be (up to about 30 secs).
>
> Taking multiple short exposures and stacking is a possibility, but you
> really want to use lots (100s) of exposures as a base for stacking.
>
> Most people use a DSLR hooked up to a telescope to get some
> magnification on an object. Of course this requires an EQ mount or a
> scope on a wedge.
>
> For focus I recommend the following, get a magnifing right angle finder
> (Canon Angle Finder C) and use a software program like DSLRFocus or
> DSLRStar that will take short exposured and download them to a PC
> automatically and you will be able to tweak focus that way.
>
> Balancing ISO and exp time vs light pollution is tough and will require
> some post processing in Photoshop. I tend to use ISO 400-800 most of
> the time and since I'm hooked up to a scope that tracks up to 1 min.
> Exposures (although as I refine my polar alignment I'll get longer
> exp.) Also a lot of folks use another camera as an autoguider to make
> minor corrections to the mount's tracking.
>
> Onle last thing Shoot RAW not JPG. this gives you more latitude in
> adjust things in Post processing.
>
> Hope this helps.
>
> Craig
> --
> Remove My_Skin to E-mail me.
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