> On Feb 26, 6:40 pm, Richard Dobson <richarddob...@blueyonder.co.uk>
> wrote:
>> Jerry Avins wrote:
>>> Richard Dobson wrote:
>>> ...
>>>> Just a general thought: if you do not already know about it, the list
>>>> alt.binaries.pictures.astro receives a steady trickle (by no means a
>>>> high-volume list) of fab astronomical pictures, ...
>>> Errm, do you by chance have a Dobsonian telescope? :-)
>>> Jerry
>> No, sadly; it is a cool design though, albeit not the best for
>> photography (I have never seen a guided one). Not enough sky visible
>> here (and f-a back garden anyway), and our UK weather here really isn't
>> that astro-friendly most of the time. We do have a good telescope shop
>> here though which I pass by, wistfully, from time to time, so one day...
>> (or rather, night...)
>>
>> Richard
>
> Richard,
>
> Someone makes a motorized base that you put your Dobsonian on and it
> will track for a short period of time - maybe up to an hour. Although
> won't likely be any good for autoguiding.
There was a 36?" Dobsonian at an amateur observatory at Chaco Canyon.
When I saw it (much plywood and Teflon, still in the reception of the
visitor's building) there were means for attaching a computer-driven
clock-drive system. The one there now seems to be different
http://www.nps.gov/archive/chcu/nightskyprogram.htm and
http://www.astronomy.org/chaco/index.html The night sky there is the
blackest I've ever seen.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by ●February 27, 20092009-02-27
On Feb 26, 6:40�pm, Richard Dobson <richarddob...@blueyonder.co.uk>
wrote:
> Jerry Avins wrote:
> > Richard Dobson wrote:
>
> > � ...
>
> >> Just a general thought: if you do not already know about it, the list
> >> alt.binaries.pictures.astro receives a steady trickle (by no means a
> >> high-volume list) of fab astronomical pictures, ...
>
> > Errm, do you by chance have a Dobsonian telescope? :-)
>
> > Jerry
>
> No, sadly; it is a cool design though, albeit not the best for
> photography �(I have never seen a guided one). Not enough sky visible
> here (and f-a back garden anyway), and our UK weather here really isn't
> that astro-friendly most of the time. �We do have a good telescope shop
> here though which I pass by, wistfully, from time to time, so one day...
> (or rather, night...)
>
> Richard
Richard,
Someone makes a motorized base that you put your Dobsonian on and it
will track for a short period of time - maybe up to an hour. Although
won't likely be any good for autoguiding.
Clay
Reply by Richard Dobson●February 26, 20092009-02-26
Jerry Avins wrote:
> Richard Dobson wrote:
>
> ...
>
>> Just a general thought: if you do not already know about it, the list
>> alt.binaries.pictures.astro receives a steady trickle (by no means a
>> high-volume list) of fab astronomical pictures, ...
>
> Errm, do you by chance have a Dobsonian telescope? :-)
>
> Jerry
No, sadly; it is a cool design though, albeit not the best for
photography (I have never seen a guided one). Not enough sky visible
here (and f-a back garden anyway), and our UK weather here really isn't
that astro-friendly most of the time. We do have a good telescope shop
here though which I pass by, wistfully, from time to time, so one day...
(or rather, night...)
Richard
Reply by ●February 26, 20092009-02-26
>
> I think I know what you mean. I haven't yet figured out why it should
> work, but I'll go with it anyway. What do you suppose is a good ratio of
> hole size to aperture? I figure to put aluminum foil in an embroidery
> frame as a convenient way to hold the mask in place. I have some leather
> punches that might be large enough to make the holes.
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
> �����������������������������������������������������������������������
For my scope I'm envisioning a disc about 13 inches in diameter and
the three triangles will be something like 3 to 4 inches on a side.
The reason it works is the light from the three aperatures is
converging on the focal plane and when you are out of focus you are
either before or beyond the plane of focus, so you will see three
triangles. I like the idea of the embroidering rings - I'll have to
see if my wife can spare one ;-)
Clay
Reply by Jerry Avins●February 26, 20092009-02-26
clay@claysturner.com wrote:
...
> I like the woodpecker shot. Digiscoping is becoming common among
> birders. I know what you mean about the LCD being hard to see in the
> daylight. Looks like you made a slip collar for your lens - cool! If
> the lens has filter threads then you may be able to find a step up
> adaptor or combination to get to a T-thread. If your camera is held
> well enough to not tilt the image plane, you may be fine with what you
> have. The images look good!
As you can see in the first photo, the slip collar is threaded, and I
could mate it to a T-adapter. The camera's lens isn't removable, so that
wouldn't work optically. The exit pupil of the low-power Kelner falls
nearly on the camera's diaphragm, so the setup avoids vignetting. The
80mm, F/5 scope in the illustration, by the way, was about $100 on eBay
with a 1.25" focuser. I added the 2" focuser (with T-mount). It isn't
quality optics, but it shows what one can do with the right low-end
stuff. It works out to about 13 power in front of the camera's zoom.
Both birds are downy woodpeckers, one male, the other, female.
> I can actually see some nebulae, galaxies etcs through my DSLR when
> connected on the telescope. This is more useful for centering the
> image rather than checking actual focus. Although I can get close to
> correct focus by looking at the stars in the viewfinder. For
> finetuning the focusing I can shoot a series of digital pics until I
> find the one that is sharpest. And to help with this I use the numbers
> on the focuser's adjustment knobs.
Good thought! Maybe I can affix a scale and pointer to my SCT's focus knob.
> Going back to the best number from
> a previous viewing session starts me close. I have yet to try a
> focusing aid where you cut a circle of cardboard to fit over the front
> end of the telescope and the cardboard circle has three equilateral
> triangular cutouts spaced every 120 degrees. When focusing on stars,
> out of focus is shown as a tripling of each star. I'll may make one
> this weekend since we are supposed to be cloudy and rainy. I wonder
> how well such an aid works. People advertise these aids for quite a
> bit on the web and I have plenty of cardboard and a razor knife!
I think I know what you mean. I haven't yet figured out why it should
work, but I'll go with it anyway. What do you suppose is a good ratio of
hole size to aperture? I figure to put aluminum foil in an embroidery
frame as a convenient way to hold the mask in place. I have some leather
punches that might be large enough to make the holes.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by ●February 26, 20092009-02-26
On Feb 26, 12:45�pm, Jerry Avins <j...@ieee.org> wrote:
> c...@claysturner.com wrote:
> > On Feb 26, 11:12 am, Jerry Avins <j...@ieee.org> wrote:
> >> c...@claysturner.com wrote:
> >>> On Feb 25, 5:44 pm, Jerry Avins <j...@ieee.org> wrote:
> >>>> c...@claysturner.com wrote:
> >>>> � �...
> >>>>> I'm using a CCD camera on the guide scope and a CMOS based DSLR for my
> >>>>> main imaging. There are a lot of ways to go with this. The big problem
> >>>>> with using a DSLR is it blocks the hydrogen alpha wavelength (the red
> >>>>> associated with many emission nebulae). Some modify their DSLRs by
> >>>>> removing the deep red blocking filter.
> >>>> With its sensor at the prime focus if a mirror, doesn't the camera body
> >>>> block a lot of light?
> >>>> Jerry
> >>>> --
> >>>> Engineering is the art of making what you want from things you can get.
> >>>> �����������������������������������������������������������������������
> >>> Hello Jerry,
> >>> Prime focus doesn't mean the camera has to be inside of the
> >>> telescope's main tube. The camera (without a lens) mounts in place of
> >>> the eyepiece. So I use a Nikon bayonet mount to 2 inch eyepiece
> >>> adapter. More often one uses a T mount (which is a particular 37 mm
> >>> thread mount) consisting of two pieces. One is the camera bayonet to
> >>> female T thread and the other piece is a eyepiece barrel (either 1.25
> >>> or 2 inch) to male T thread. This way you can find the right adapter
> >>> for almost any SLR.
> >>> Two other ways of coupling the camera to the telescope involve using
> >>> an eyepiece. In one method the eyepiece projects into the camera body.
> >>> The other way the camera with its lens focused at infinity is place
> >>> right up against the eyepiece.
> >>> These last two methods allow for high magnification will all of the
> >>> attendant difficulties. One can magnify the prime focus method with a
> >>> barlow lens or its improved version called a powermate made by
> >>> televue.
> >> Clay,
>
> >> I'm still confused. In my Schmidt (in every SCT I know) the eyepiece is
> >> behind a secondary. Unless the secondary mirror is flat and the
> >> telescope oddly proportioned, the eyepiece is at the secondary focus.
>
> >> I use T-mounts both on my 5" Schmidt and on the 80 mm refractor pictured
> >> at the end ofhttp://users.rcn.com/jyavins/photoadapter.htm. The lens
> >> isn't removable on my little pocket camera. The article is about using
> >> it anyway.
>
> >> Jerry
> >> --
> >> Engineering is the art of making what you want from things you can get.
> >> �����������������������������������������������������������������������- Hide quoted text -
>
> >> - Show quoted text -
>
> > I think I see the problem - I'm using a Schmidt Newtonian and not a
> > Schmidt. So like the Newtonian it has a primary mirror followed with a
> > 45 degree diagonal to pass the light out of the side of the tube just
> > like a Newtonian. But unlike the Newtonian, the Schmidt-Newtonian uses
> > a spherical primary mirror and has a Schmidt corrector plate at the
> > front ent of the scope. This design has a lower cost (than a Newt's)
> > primary mirror and the cost due to the corrector is more than made up
> > in the savings on the primary. This design has reduced coma when
> > compared to Newtonians if you are working with low F ratios. Typically
> > Schmidt Newts are F/4 or F5.6. If a Newtonian is made that fast you
> > will have strong coma at the edge of the field. However, Televue makes
> > Paracor which goes into your focuser and then the eyepiece fits into
> > the Paracor. The Paracor is an adjustable coma corrector specifically
> > for Newtonians and the reports I've heard about it are quite positive.
>
> > My scope despite its having a 10 inch aperature was quite inexpensive.
> > Its focuser and spotting scope were both quite crappy - I picked it
> > for its main optics. I replaced the spotting scope with a Telrad (I
> > highly recommend one) and replaced the focuser with a high quality
> > Crayford focuser made by JMI. I rarely use the computer's goto feature
> > - I can use star charts more quickly to find my targets. Back in the
> > 80s, Celestron made a 5 inch Schmidt Newtonian called a Comet Catcher
> > (They were bootstrapping off of the interest in comet Halley's return
> > in 1986). Now Meade is the only mainstream manufacturer of Schmidt
> > Newts.
>
> > There is a company now offering Ritchy Cretians OTAs (optical tube
> > assemblies) for pretty chreap (compared to other suppliers of RC's).
> > These work very well as astrographs and they are completely coma free.
>
> Thanks. I'm no longer confused. :-)
>
> Did you look at the digiscope adapter inhttp://users.rcn.com/jyavins/photoadapter.htm? It lets me photograph
> through any scope that uses 1.25" eyepieces, but since the camera's
> optical viewfinder is then useless, focusing in daylight can require a
> dark cloth, like an old-fashioned view camera. Here are pictures taken
> with it:http://users.rcn.com/jyavins/downy_lady.jpghttp://users.rcn.com/jyavins/woodpecker1.jpg
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
> �����������������������������������������������������������������������- Hide quoted text -
>
> - Show quoted text -
I like the woodpecker shot. Digiscoping is becoming common among
birders. I know what you mean about the LCD being hard to see in the
daylight. Looks like you made a slip collar for your lens - cool! If
the lens has filter threads then you may be able to find a step up
adaptor or combination to get to a T-thread. If your camera is held
well enough to not tilt the image plane, you may be fine with what you
have. The images look good!
I can actually see some nebulae, galaxies etcs through my DSLR when
connected on the telescope. This is more useful for centering the
image rather than checking actual focus. Although I can get close to
correct focus by looking at the stars in the viewfinder. For
finetuning the focusing I can shoot a series of digital pics until I
find the one that is sharpest. And to help with this I use the numbers
on the focuser's adjustment knobs. Going back to the best number from
a previous viewing session starts me close. I have yet to try a
focusing aid where you cut a circle of cardboard to fit over the front
end of the telescope and the cardboard circle has three equilateral
triangular cutouts spaced every 120 degrees. When focusing on stars,
out of focus is shown as a tripling of each star. I'll may make one
this weekend since we are supposed to be cloudy and rainy. I wonder
how well such an aid works. People advertise these aids for quite a
bit on the web and I have plenty of cardboard and a razor knife!
Clay
Reply by Jerry Avins●February 26, 20092009-02-26
clay@claysturner.com wrote:
> On Feb 26, 11:12 am, Jerry Avins <j...@ieee.org> wrote:
>> c...@claysturner.com wrote:
>>> On Feb 25, 5:44 pm, Jerry Avins <j...@ieee.org> wrote:
>>>> c...@claysturner.com wrote:
>>>> ...
>>>>> I'm using a CCD camera on the guide scope and a CMOS based DSLR for my
>>>>> main imaging. There are a lot of ways to go with this. The big problem
>>>>> with using a DSLR is it blocks the hydrogen alpha wavelength (the red
>>>>> associated with many emission nebulae). Some modify their DSLRs by
>>>>> removing the deep red blocking filter.
>>>> With its sensor at the prime focus if a mirror, doesn't the camera body
>>>> block a lot of light?
>>>> Jerry
>>>> --
>>>> Engineering is the art of making what you want from things you can get.
>>>> �����������������������������������������������������������������������
>>> Hello Jerry,
>>> Prime focus doesn't mean the camera has to be inside of the
>>> telescope's main tube. The camera (without a lens) mounts in place of
>>> the eyepiece. So I use a Nikon bayonet mount to 2 inch eyepiece
>>> adapter. More often one uses a T mount (which is a particular 37 mm
>>> thread mount) consisting of two pieces. One is the camera bayonet to
>>> female T thread and the other piece is a eyepiece barrel (either 1.25
>>> or 2 inch) to male T thread. This way you can find the right adapter
>>> for almost any SLR.
>>> Two other ways of coupling the camera to the telescope involve using
>>> an eyepiece. In one method the eyepiece projects into the camera body.
>>> The other way the camera with its lens focused at infinity is place
>>> right up against the eyepiece.
>>> These last two methods allow for high magnification will all of the
>>> attendant difficulties. One can magnify the prime focus method with a
>>> barlow lens or its improved version called a powermate made by
>>> televue.
>> Clay,
>>
>> I'm still confused. In my Schmidt (in every SCT I know) the eyepiece is
>> behind a secondary. Unless the secondary mirror is flat and the
>> telescope oddly proportioned, the eyepiece is at the secondary focus.
>>
>> I use T-mounts both on my 5" Schmidt and on the 80 mm refractor pictured
>> at the end ofhttp://users.rcn.com/jyavins/photoadapter.htm. The lens
>> isn't removable on my little pocket camera. The article is about using
>> it anyway.
>>
>> Jerry
>> --
>> Engineering is the art of making what you want from things you can get.
>> �����������������������������������������������������������������������- Hide quoted text -
>>
>> - Show quoted text -
>
> I think I see the problem - I'm using a Schmidt Newtonian and not a
> Schmidt. So like the Newtonian it has a primary mirror followed with a
> 45 degree diagonal to pass the light out of the side of the tube just
> like a Newtonian. But unlike the Newtonian, the Schmidt-Newtonian uses
> a spherical primary mirror and has a Schmidt corrector plate at the
> front ent of the scope. This design has a lower cost (than a Newt's)
> primary mirror and the cost due to the corrector is more than made up
> in the savings on the primary. This design has reduced coma when
> compared to Newtonians if you are working with low F ratios. Typically
> Schmidt Newts are F/4 or F5.6. If a Newtonian is made that fast you
> will have strong coma at the edge of the field. However, Televue makes
> Paracor which goes into your focuser and then the eyepiece fits into
> the Paracor. The Paracor is an adjustable coma corrector specifically
> for Newtonians and the reports I've heard about it are quite positive.
>
> My scope despite its having a 10 inch aperature was quite inexpensive.
> Its focuser and spotting scope were both quite crappy - I picked it
> for its main optics. I replaced the spotting scope with a Telrad (I
> highly recommend one) and replaced the focuser with a high quality
> Crayford focuser made by JMI. I rarely use the computer's goto feature
> - I can use star charts more quickly to find my targets. Back in the
> 80s, Celestron made a 5 inch Schmidt Newtonian called a Comet Catcher
> (They were bootstrapping off of the interest in comet Halley's return
> in 1986). Now Meade is the only mainstream manufacturer of Schmidt
> Newts.
>
> There is a company now offering Ritchy Cretians OTAs (optical tube
> assemblies) for pretty chreap (compared to other suppliers of RC's).
> These work very well as astrographs and they are completely coma free.
Thanks. I'm no longer confused. :-)
Did you look at the digiscope adapter in
http://users.rcn.com/jyavins/photoadapter.htm ? It lets me photograph
through any scope that uses 1.25" eyepieces, but since the camera's
optical viewfinder is then useless, focusing in daylight can require a
dark cloth, like an old-fashioned view camera. Here are pictures taken
with it: http://users.rcn.com/jyavins/downy_lady.jpghttp://users.rcn.com/jyavins/woodpecker1.jpg
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by ●February 26, 20092009-02-26
On Feb 26, 11:12�am, Jerry Avins <j...@ieee.org> wrote:
> c...@claysturner.com wrote:
> > On Feb 25, 5:44 pm, Jerry Avins <j...@ieee.org> wrote:
> >> c...@claysturner.com wrote:
>
> >> � �...
>
> >>> I'm using a CCD camera on the guide scope and a CMOS based DSLR for my
> >>> main imaging. There are a lot of ways to go with this. The big problem
> >>> with using a DSLR is it blocks the hydrogen alpha wavelength (the red
> >>> associated with many emission nebulae). Some modify their DSLRs by
> >>> removing the deep red blocking filter.
> >> With its sensor at the prime focus if a mirror, doesn't the camera body
> >> block a lot of light?
>
> >> Jerry
> >> --
> >> Engineering is the art of making what you want from things you can get.
> >> �����������������������������������������������������������������������
>
> > Hello Jerry,
>
> > Prime focus doesn't mean the camera has to be inside of the
> > telescope's main tube. The camera (without a lens) mounts in place of
> > the eyepiece. So I use a Nikon bayonet mount to 2 inch eyepiece
> > adapter. More often one uses a T mount (which is a particular 37 mm
> > thread mount) consisting of two pieces. One is the camera bayonet to
> > female T thread and the other piece is a eyepiece barrel (either 1.25
> > or 2 inch) to male T thread. This way you can find the right adapter
> > for almost any SLR.
>
> > Two other ways of coupling the camera to the telescope involve using
> > an eyepiece. In one method the eyepiece projects into the camera body.
> > The other way the camera with its lens focused at infinity is place
> > right up against the eyepiece.
>
> > These last two methods allow for high magnification will all of the
> > attendant difficulties. One can magnify the prime focus method with a
> > barlow lens or its improved version called a powermate made by
> > televue.
>
> Clay,
>
> I'm still confused. In my Schmidt (in every SCT I know) the eyepiece is
> behind a secondary. Unless the secondary mirror is flat and the
> telescope oddly proportioned, the eyepiece is at the secondary focus.
>
> I use T-mounts both on my 5" Schmidt and on the 80 mm refractor pictured
> at the end ofhttp://users.rcn.com/jyavins/photoadapter.htm. The lens
> isn't removable on my little pocket camera. The article is about using
> it anyway.
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
> �����������������������������������������������������������������������- Hide quoted text -
>
> - Show quoted text -
I think I see the problem - I'm using a Schmidt Newtonian and not a
Schmidt. So like the Newtonian it has a primary mirror followed with a
45 degree diagonal to pass the light out of the side of the tube just
like a Newtonian. But unlike the Newtonian, the Schmidt-Newtonian uses
a spherical primary mirror and has a Schmidt corrector plate at the
front ent of the scope. This design has a lower cost (than a Newt's)
primary mirror and the cost due to the corrector is more than made up
in the savings on the primary. This design has reduced coma when
compared to Newtonians if you are working with low F ratios. Typically
Schmidt Newts are F/4 or F5.6. If a Newtonian is made that fast you
will have strong coma at the edge of the field. However, Televue makes
Paracor which goes into your focuser and then the eyepiece fits into
the Paracor. The Paracor is an adjustable coma corrector specifically
for Newtonians and the reports I've heard about it are quite positive.
My scope despite its having a 10 inch aperature was quite inexpensive.
Its focuser and spotting scope were both quite crappy - I picked it
for its main optics. I replaced the spotting scope with a Telrad (I
highly recommend one) and replaced the focuser with a high quality
Crayford focuser made by JMI. I rarely use the computer's goto feature
- I can use star charts more quickly to find my targets. Back in the
80s, Celestron made a 5 inch Schmidt Newtonian called a Comet Catcher
(They were bootstrapping off of the interest in comet Halley's return
in 1986). Now Meade is the only mainstream manufacturer of Schmidt
Newts.
There is a company now offering Ritchy Cretians OTAs (optical tube
assemblies) for pretty chreap (compared to other suppliers of RC's).
These work very well as astrographs and they are completely coma free.
Clay
Reply by Jerry Avins●February 26, 20092009-02-26
Richard Dobson wrote:
...
> Just a general thought: if you do not already know about it, the list
> alt.binaries.pictures.astro receives a steady trickle (by no means a
> high-volume list) of fab astronomical pictures, ...
Errm, do you by chance have a Dobsonian telescope? :-)
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Jerry Avins●February 26, 20092009-02-26
clay@claysturner.com wrote:
> On Feb 25, 5:44 pm, Jerry Avins <j...@ieee.org> wrote:
>> c...@claysturner.com wrote:
>>
>> ...
>>
>>> I'm using a CCD camera on the guide scope and a CMOS based DSLR for my
>>> main imaging. There are a lot of ways to go with this. The big problem
>>> with using a DSLR is it blocks the hydrogen alpha wavelength (the red
>>> associated with many emission nebulae). Some modify their DSLRs by
>>> removing the deep red blocking filter.
>> With its sensor at the prime focus if a mirror, doesn't the camera body
>> block a lot of light?
>>
>> Jerry
>> --
>> Engineering is the art of making what you want from things you can get.
>> �����������������������������������������������������������������������
>
> Hello Jerry,
>
> Prime focus doesn't mean the camera has to be inside of the
> telescope's main tube. The camera (without a lens) mounts in place of
> the eyepiece. So I use a Nikon bayonet mount to 2 inch eyepiece
> adapter. More often one uses a T mount (which is a particular 37 mm
> thread mount) consisting of two pieces. One is the camera bayonet to
> female T thread and the other piece is a eyepiece barrel (either 1.25
> or 2 inch) to male T thread. This way you can find the right adapter
> for almost any SLR.
>
> Two other ways of coupling the camera to the telescope involve using
> an eyepiece. In one method the eyepiece projects into the camera body.
> The other way the camera with its lens focused at infinity is place
> right up against the eyepiece.
>
> These last two methods allow for high magnification will all of the
> attendant difficulties. One can magnify the prime focus method with a
> barlow lens or its improved version called a powermate made by
> televue.
Clay,
I'm still confused. In my Schmidt (in every SCT I know) the eyepiece is
behind a secondary. Unless the secondary mirror is flat and the
telescope oddly proportioned, the eyepiece is at the secondary focus.
I use T-mounts both on my 5" Schmidt and on the 80 mm refractor pictured
at the end of http://users.rcn.com/jyavins/photoadapter.htm. The lens
isn't removable on my little pocket camera. The article is about using
it anyway.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������