Q for the Astrophoto types

Ok, so shoot me if I've missed the "Duh" factor on this one - but for
something simple, like moon-shots....could I just jam the lens of my little
point n shoot digital in the focuser tube, INSTEAD of an E.P.? Or am I
missing something really obvious?

Just wondering - and thought I'd ask before I tried a little unconventional
engineering to make it fit.

-Kevin
--
Remove "nospam" from domain part of address

Kevin M. Vernon wrote:
Ok, so shoot me if I've missed the "Duh" factor on this one - but for
something simple, like moon-shots....could I just jam the lens of my
little point n shoot digital in the focuser tube, INSTEAD of an E.P.?
Or am I missing something really obvious?

Just wondering - and thought I'd ask before I tried a little
unconventional engineering to make it fit.

-Kevin

Hi Kevin,

You can always try it without an eyepiece, but I think you're unlikely
to be able to reach focus.

If you do try shooting through an eyepiece, be careful the cameras lens
assembly doesn't scratch the eyepiece's lens! For very quick-and-dirty
shots it may help to leave the rubber eye cup in place, if there is one.
If you're planning on making some kind of adapter, it's probably easier
without the eye cup.

I made a very simple adapter out of an old photographic film canister
and it's proved stable enough to make some pretty nice shots of the moon
and a couple of bright DSOs. Details are on my site (see sig) if you're
interested.

Best of luck,

Steve

--
Steve Maddison
Den Haag, The Netherlands
http://www.cosam.org/

Kevin M. Vernon wrote:
Ok, so shoot me if I've missed the "Duh" factor on this one - but for
something simple, like moon-shots....could I just jam the lens of my little
point n shoot digital in the focuser tube, INSTEAD of an E.P.? Or am I
missing something really obvious?

No (to both questions). Your camera's lens won't have nearly enough
focusing range for this to work. But this idea occurs to lots of people;
the reason it works isn't obvious without knowing a little about optics.

The focal length of the camera's lens is approximately equal to the
distance from it to the focal plane where the CCD is (the "film" of the
digital camera). That's so that when parallel light rays from an object
at infinity enter the lens, the lens causes them to converge at a distance
equal to the focal length, where the CCD is (rather conveniently!).

For better or worse, not all objects are at infinity! Light rays from
objects not at infinity are diverging somewhat when they enter the lens--
the closer they are, the more they're diverging. And the more they are
diverging, the more gently they're converging when they exit the lens,
and the further out in front your lens must be, in order to get the light
rays to converge properly on the CCD. You can't take an image of a very
nearby object because the camera's lens won't go out far enough for light
from that object to converge properly on the CCD.

The real image formed by a telescope is typically very close to the
opening of the focuser tube; in fact, when you focus the telescope, what
you are doing is moving the real image backward and forth, in and out of
the focuser tube. The eyepiece is there to magnify that real image, just
as a magnifying glass is ordinarily used to magnify actual objects. (It
can be used to magnify a real image, too.)

If you put the digital camera right against the focuser tube, it is
looking at that real image as though it were an actual object very close
to the lens--probably no further away than an inch or so. So unless your
camera can take images of objects about an inch away (which I'm quite
sure it can't), it will take pictures that will be totally out of focus
and unrecognizable.

There's no real reason to do this, however. Just take afocal shots, with
all the lenses in place: eyepiece and camera. Light rays come out of the
telescope parallel--as though they came from an object at infinity. (And
after a fashion, they basically do!) Your camera therefore has no trouble
at all focusing them to the CCD. I've taken decent moon shots that way,
and I'm a horrible imager.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

I (Brian Tung) wrote:
No (to both questions). Your camera's lens won't have nearly enough
focusing range for this to work. But this idea occurs to lots of people;
the reason it works isn't obvious without knowing a little about optics.

Ahem. I mean, "the reason it *doesn't* work." Sorry about that.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Brian Tung wrote:

I (Brian Tung) wrote:
No (to both questions). Your camera's lens won't have nearly enough
focusing range for this to work. But this idea occurs to lots of people;
the reason it works isn't obvious without knowing a little about optics.

Ahem. I mean, "the reason it *doesn't* work." Sorry about that.

Even so, it was a very good explanation. Something a beginner can
visualize.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

--
Remove "nospam" from domain part of address
"starman" wrote in message
...
Brian Tung wrote:

I (Brian Tung) wrote:
No (to both questions). Your camera's lens won't have nearly enough
focusing range for this to work. But this idea occurs to lots of
people;
the reason it works isn't obvious without knowing a little about
optics.

Ahem. I mean, "the reason it *doesn't* work." Sorry about that.

Even so, it was a very good explanation. Something a beginner can
visualize.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000
Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

As I said - I missed the "Duh" factor. I'm a camera geek - I SHOULD have
known that. *grrr -slaps self on forehead*

Yeah, unless the thing can focus down to an inch...*yikes* I was simply
thinking of using the camea's lens to focus on the ccd, as the eyepiece
focuses the image - forgetting that the eyepiece is shooting the light to
yet ANOTHER lens - the one in my eye. *My brain hurts - it will have to
come out* The camera lens goes in the chain where my EYE does, not where
the eyepiece does. Why that didn't occur to me straight away is a mystery
lost to the depths of time.

-Kevin

"Kevin M. Vernon" wrote in message news:1102026686.xh6LVPvU0D3Tqp5/aDAjPA@teranews...
Ok, so shoot me if I've missed the "Duh" factor on this one - but for
something simple, like moon-shots....could I just jam the lens of my little
point n shoot digital in the focuser tube, INSTEAD of an E.P.? Or am I
missing something really obvious?

Just wondering - and thought I'd ask before I tried a little unconventional
engineering to make it fit.

You could point the camera in an eyepiece and take
pictures anyway. It's called afocal photography,
and is well understood. It's quite common to put
the camera on a separate tripod so it doesn't
collide with or shake the telescope.

You can take neat pictures of the moon, but all
bets are off for other objects. Of course, the
best way is to get out one night and try it and
see. Once I even tried holding my Pentax 67 up
to an eyepiece to see what I got. This requires
some muscle... :-)

Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte

--
Remove "nospam" from domain part of address
"Laura Halliday" wrote in message
om...
"Kevin M. Vernon" wrote in message
news:1102026686.xh6LVPvU0D3Tqp5/aDAjPA@teranews...
Ok, so shoot me if I've missed the "Duh" factor on this one - but for
something simple, like moon-shots....could I just jam the lens of my
little
point n shoot digital in the focuser tube, INSTEAD of an E.P.? Or am I
missing something really obvious?

Just wondering - and thought I'd ask before I tried a little
unconventional
engineering to make it fit.

You could point the camera in an eyepiece and take
pictures anyway. It's called afocal photography,
and is well understood. It's quite common to put
the camera on a separate tripod so it doesn't
collide with or shake the telescope.

You can take neat pictures of the moon, but all
bets are off for other objects. Of course, the
best way is to get out one night and try it and
see. Once I even tried holding my Pentax 67 up
to an eyepiece to see what I got. This requires
some muscle... :-)

Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte

A pentax 6x7? Muscle? Yeah, I'd imagine. *wink* I think I'll try that
with my Kiev 88 real soom. *grin*

Hey - while I'm on the subject - Anybody know if there is even made such a
thing as a T-ring for a Kiev 88?
That big box beast is definitely going to want to be solidly mounted in the
focuser.

-Kevin