On Feb 25, 3:26�pm, Jerry Avins <j...@ieee.org> wrote:> c...@claysturner.com wrote: > > Hello All, > > > In the world of astronomy we currently have comet Lulin which will be > > observable in binoculars and telescopes for another couple of months. > > So I set up my scope to take a picture of it. So the DSP part comes in > > two ways. > > > First since the Earth rotates you need to have your scope track the > > stars to counter the rotation. Even with a moderate quality "clock > > drive" on a scope, the tracking is not generally great and when you > > try to track for a minute or more errors (periodic and misalignment) > > in the clock drive will show up. So the fix these days is to piggyback > > a smaller scope onto the main scope and put a ccd camera on the "guide > > scope." The ccd camera is connected to a laptop via usb and the camera > > is read into the computer every few seconds. You select a star that > > the camera sees to use as a guide star and the computer tracks the > > errors in the measured star position when compared to the ideal and > > these errors are then Kalman filtered and the corrections are sent to > > the telescope's mount to keep the guide star centered up. > > > Another DSP aspect (a pretty simple one yet effective) is taking > > multiple short exposures (1 to 10 minutes each) and stacking them > > together to average out the noise. You may also shoot a dark frame and > > use that to flatten out thermal noise in the sensor. This often shows > > up lighter portions along the edge or corner of the sensor. > > > Here is a result: �Comments welcome. > > >http://www.claysturner.com/CometLulin.jpg > > > I hope you all enjoyed. > > Clay, > > You might want to see what Keith Larson is up to these days.http://home.comcast.net/~klarsondsp/ > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������- Hide quoted text - > > - Show quoted text -Thanks for the link - he has good stuff there. Clay
Slightly OT: Comet Lulin and Kalman Filtering and signal averaging
Started by ●February 25, 2009
Reply by ●February 25, 20092009-02-25
Reply by ●February 25, 20092009-02-25
On Feb 25, 2:01�pm, "bungalow_st...@yahoo.com" <bungalow_st...@yahoo.com> wrote:> On Feb 25, 12:21�pm, c...@claysturner.com wrote: > > > > > > > On Feb 25, 12:05�pm, "bungalow_st...@yahoo.com" > > > <bungalow_st...@yahoo.com> wrote: > > > On Feb 25, 10:54�am, c...@claysturner.com wrote: > > > > > Hello All, > > > > > In the world of astronomy we currently have comet Lulin which will be > > > > observable in binoculars and telescopes for another couple of months. > > > > So I set up my scope to take a picture of it. So the DSP part comes in > > > > two ways. > > > > > First since the Earth rotates you need to have your scope track the > > > > stars to counter the rotation. Even with a moderate quality "clock > > > > drive" on a scope, the tracking is not generally great and when you > > > > try to track for a minute or more errors (periodic and misalignment) > > > > in the clock drive will show up. So the fix these days is to piggyback > > > > a smaller scope onto the main scope and put a ccd camera on the "guide > > > > scope." The ccd camera is connected to a laptop via usb and the camera > > > > is read into the computer every few seconds. You select a star that > > > > the camera sees to use as a guide star and the computer tracks the > > > > errors in the measured star position when compared to the ideal and > > > > these errors are then Kalman filtered and the corrections are sent to > > > > the telescope's mount to keep the guide star centered up. > > > > > Another DSP aspect (a pretty simple one yet effective) is taking > > > > multiple short exposures (1 to 10 minutes each) and stacking them > > > > together to average out the noise. > > > > do you cross correlate each exposure to line it up before stacking?- Hide quoted text - > > > > - Show quoted text - > > > I did this one manually, but I do have a program for aligning and > > rotating each image. It needs some improvement. Rotation of each image > > is needed if your telescope does not use a polar (equitorial mount). I > > do have such a mount so translation will suffice for me. For people > > using alt-azimuth mounts even if they keep a star in the field > > perfectly aligned from image to image, the field will rotate about > > that star. If you combined exposures add up to minutes or more this > > will become apparent. > > > I'm working on an auto align program to speed up this process. It is > > not unusual for one to combine a hundred images! I'm still new at this > > so I haven't done one with more than 10 images yet. > > > Clay- Hide quoted text - > > > - Show quoted text - > > I see, i don't work with CCD cameras, but a friend of mine works here > > http://www.flicamera.com/ > > �fun stuff!- Hide quoted text - > > - Show quoted text -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. Clay Clay
Reply by ●February 25, 20092009-02-25
clay@claysturner.com wrote: (snip)> 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.I didn't know about that one. Since the silicon bandgap is in the near-IR, it should be sensitive somewhat into the IR. I know some video cameras advertise IR sensitivity as a feature, that you can record in the dark with IR illumination. I do know that DSLRs have a low pass spatial filter to avoid aliasing. (Though I don't know how the filter actually works.) As usually, I have a skylight filter (mostly UV) for lens protection and I suppose also to keep UV out of the image. -- glen
Reply by ●February 25, 20092009-02-25
clay@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. �����������������������������������������������������������������������
Reply by ●February 25, 20092009-02-25
clay@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. >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, together with clearly highly expert discussions on kit, etc. I am sure they would be both pleased to see your results, and interested to discuss all scope+imaging matters. There is a little spam from time to time, but it is overall a very low-noise list, with three or four prolific regulars. Some images have been so amazing I have used them to make the odd birthday card. Comet Lulin has been posted very recently, unsurprisingly. It's really nice to access the list at the start of the day and see another "wow" picture. Posts get dropped from the news server I use rather frequently (I suppose because of the sometimes large image attachments), so checking it regularly is worth doing to be sure one has not missed something special. Richard Dobson
Reply by ●February 26, 20092009-02-26
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
Reply by ●February 26, 20092009-02-26
On Feb 25, 4:55�pm, Glen Herrmannsfeldt <g...@ugcs.caltech.edu> wrote:> c...@claysturner.com wrote: > > (snip) > > > 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. > > I didn't know about that one. �Since the silicon bandgap is > in the near-IR, it should be sensitive somewhat into the IR. > > I know some video cameras advertise IR sensitivity as a feature, > that you can record in the dark with IR illumination. > > I do know that DSLRs have a low pass spatial filter to avoid > aliasing. �(Though I don't know how the filter actually works.) > As usually, I have a skylight filter (mostly UV) for lens protection > and I suppose also to keep UV out of the image. > > -- glenThe big problem with DSLRs and red sensitivity stemmed from the sicon bandgap making the sensor highly responsive to infared. Unfortunately this created color balance issues based upon the amount of ambient infrared whether shooting in sunlinght or under xenon strobes or photolamps. Each new generation of DSLR has improved their color fidelity (compared to human response) by cutting into the deep red more and more. I remember when serious pro photogs were experimenting with "hot mirrors" on their lenses to keep the infrared from entering the camera. Clay
Reply by ●February 26, 20092009-02-26
On Feb 25, 6:37�pm, Richard Dobson <richarddob...@blueyonder.co.uk> 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. > > 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, together with clearly > highly expert discussions on kit, etc. �I am sure they would be both > pleased to see your results, and interested to discuss all > scope+imaging matters. There is a little spam from time to time, but it > is overall a very low-noise list, with �three or four prolific regulars. > Some images have been so amazing I have used them to make the odd > birthday card. �Comet Lulin has been posted very recently, > unsurprisingly. It's really nice to access the list at the start of the > day and see another "wow" picture. Posts get dropped from the news > server I use rather frequently (I suppose because of the sometimes large > image attachments), so checking it regularly is worth doing to be sure > one has not missed something special. > > Richard DobsonThanks for the heads up - I'll go and check it out. Clay
Reply by ●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. �����������������������������������������������������������������������
Reply by ●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. �����������������������������������������������������������������������
