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
Slightly OT: Comet Lulin and Kalman Filtering and signal averaging
Started by ●February 25, 2009
Reply by ●February 26, 20092009-02-26
Reply by ●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.jpg http://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, 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
