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ASTRO: M97 with Skywatcher ED120
I got myself a Skywatcher ED120 as a wide field scope recently. This is
"second" light ("first light" was such an incredibly cold night that mount, scope and operator were not functioning correctly) in a very bright night with city lights, bright moon and a snow cover that reflected both. Sky background in a 10 minute exposure at f/7.5 was over 5000 counts though my Astronomik 13nm OIII filter. In a "normal" city night this would be below 1000. The ED120 gives good starshapes in Halpha, OIII and also broadband. This image is not sharpened in any way. Taken from the middle of Berlin with a Skywatcher ED120 at f/7.5 on a G11 mount, SXV-H9 camera, 14x10 minutes Halpha, 6x10 minutes OIII. The picture can also be found at http://ccd-astronomy.de/temp2/M97colourgut.jpg Stefan |
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ASTRO: M97 with Skywatcher ED120
Stefan Lilge wrote: I got myself a Skywatcher ED120 as a wide field scope recently. This is "second" light ("first light" was such an incredibly cold night that mount, scope and operator were not functioning correctly) in a very bright night with city lights, bright moon and a snow cover that reflected both. Sky background in a 10 minute exposure at f/7.5 was over 5000 counts though my Astronomik 13nm OIII filter. In a "normal" city night this would be below 1000. The ED120 gives good starshapes in Halpha, OIII and also broadband. This image is not sharpened in any way. Taken from the middle of Berlin with a Skywatcher ED120 at f/7.5 on a G11 mount, SXV-H9 camera, 14x10 minutes Halpha, 6x10 minutes OIII. The picture can also be found at http://ccd-astronomy.de/temp2/M97colourgut.jpg Stefan Looks like you have a winner with that combination! My sky is really bright of late here too but that's in LRGB. Still I normally run about 350 in 10 minutes lum binned 2x2 but am now running 1200 to 2000 with no moon, just scattering of starlight off a zillion ice crystals in the air. Most years it is rather dry so they tend to sublime. My counts can hit 600 to 800 but with high humidity this year that isn't happening. I am finding flats very sensitive to temperature at this background level. My focus changes with temp and that changes vignetting considerably so I have to take a zillion flats at all focus positions to find a set that matches. Then a new dust speck shows up and I do it all over again. Spending all day taking flats it seems. Does your ACF have that problem? I'm using a 3" Crayford with mirror locked. Move the mirror and the flats really change, more than just changing the Crayford's position. With the wide temp changes this winter, -35C one night and only -10C the next, I need new flats daily. Your smaller chip might not see that vignetting problem, I'm working right to the edge of the usable FOV where the internal baffle is doing the vignetting. Still a change in focus changes the size of the dust mots. So they don't flat out right. Rick -- Correct domain name is arvig and it is net not com. Prefix is correct. Third character is a zero rather than a capital "Oh". |
#3
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ASTRO: M97 with Skywatcher ED120
In article .com,
Rick Johnson wrote: Stefan Lilge wrote: I got myself a Skywatcher ED120 as a wide field scope recently. This is "second" light ("first light" was such an incredibly cold night that mount, scope and operator were not functioning correctly) in a very bright night with city lights, bright moon and a snow cover that reflected both. Sky background in a 10 minute exposure at f/7.5 was over 5000 counts though my Astronomik 13nm OIII filter. In a "normal" city night this would be below 1000. The ED120 gives good starshapes in Halpha, OIII and also broadband. This image is not sharpened in any way. Taken from the middle of Berlin with a Skywatcher ED120 at f/7.5 on a G11 mount, SXV-H9 camera, 14x10 minutes Halpha, 6x10 minutes OIII. The picture can also be found at http://ccd-astronomy.de/temp2/M97colourgut.jpg Stefan Looks like you have a winner with that combination! My sky is really bright of late here too but that's in LRGB. Still I normally run about 350 in 10 minutes lum binned 2x2 but am now running 1200 to 2000 with no moon, just scattering of starlight off a zillion ice crystals in the air. Most years it is rather dry so they tend to sublime. My counts can hit 600 to 800 but with high humidity this year that isn't happening. I am finding flats very sensitive to temperature at this background level. My focus changes with temp and that changes vignetting considerably so I have to take a zillion flats at all focus positions to find a set that matches. Then a new dust speck shows up and I do it all over again. Spending all day taking flats it seems. Does your ACF have that problem? I'm using a 3" Crayford with mirror locked. Move the mirror and the flats really change, more than just changing the Crayford's position. With the wide temp changes this winter, -35C one night and only -10C the next, I need new flats daily. Your smaller chip might not see that vignetting problem, I'm working right to the edge of the usable FOV where the internal baffle is doing the vignetting. Still a change in focus changes the size of the dust mots. So they don't flat out right. Rick Very Nice First Light Stefan. Geez guys, it must be nice to have such dark skies. I get 35,000 count background with a 7 minute exposure (same CCD as Stefan uses) for Luma with a C8 from Downtown Calgary on a dark moonless night. I can sympathize with Rick's temperatures too. Over christmas I was trying to shoot at -36°C and had solved most of my mechanical issues with the HEQ5 mount. However I had a heating pad I attached to the Laptop's screen and it could not keep it warm enough. After 10 minutes of exposure, the internal PRAM battery would freeze up, and the Laptop would shut down. Now we are at +11°C now and I have had to re-tune my RA gear tension because I have RA play due to the rise in temperature. TTYL.. Milton Aupperle http://www.outcastsoft.com/AstroImages/AstroIndex.html |
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ASTRO: M97 with Skywatcher ED120
Milton Aupperle wrote: In article .com, Rick Johnson wrote: Stefan Lilge wrote: I got myself a Skywatcher ED120 as a wide field scope recently. This is "second" light ("first light" was such an incredibly cold night that mount, scope and operator were not functioning correctly) in a very bright night with city lights, bright moon and a snow cover that reflected both. Sky background in a 10 minute exposure at f/7.5 was over 5000 counts though my Astronomik 13nm OIII filter. In a "normal" city night this would be below 1000. The ED120 gives good starshapes in Halpha, OIII and also broadband. This image is not sharpened in any way. Taken from the middle of Berlin with a Skywatcher ED120 at f/7.5 on a G11 mount, SXV-H9 camera, 14x10 minutes Halpha, 6x10 minutes OIII. The picture can also be found at http://ccd-astronomy.de/temp2/M97colourgut.jpg Stefan Looks like you have a winner with that combination! My sky is really bright of late here too but that's in LRGB. Still I normally run about 350 in 10 minutes lum binned 2x2 but am now running 1200 to 2000 with no moon, just scattering of starlight off a zillion ice crystals in the air. Most years it is rather dry so they tend to sublime. My counts can hit 600 to 800 but with high humidity this year that isn't happening. I am finding flats very sensitive to temperature at this background level. My focus changes with temp and that changes vignetting considerably so I have to take a zillion flats at all focus positions to find a set that matches. Then a new dust speck shows up and I do it all over again. Spending all day taking flats it seems. Does your ACF have that problem? I'm using a 3" Crayford with mirror locked. Move the mirror and the flats really change, more than just changing the Crayford's position. With the wide temp changes this winter, -35C one night and only -10C the next, I need new flats daily. Your smaller chip might not see that vignetting problem, I'm working right to the edge of the usable FOV where the internal baffle is doing the vignetting. Still a change in focus changes the size of the dust mots. So they don't flat out right. Rick Very Nice First Light Stefan. Geez guys, it must be nice to have such dark skies. I get 35,000 count background with a 7 minute exposure (same CCD as Stefan uses) for Luma with a C8 from Downtown Calgary on a dark moonless night. I can sympathize with Rick's temperatures too. Over christmas I was trying to shoot at -36°C and had solved most of my mechanical issues with the HEQ5 mount. However I had a heating pad I attached to the Laptop's screen and it could not keep it warm enough. After 10 minutes of exposure, the internal PRAM battery would freeze up, and the Laptop would shut down. Now we are at +11°C now and I have had to re-tune my RA gear tension because I have RA play due to the rise in temperature. TTYL.. Milton Aupperle http://www.outcastsoft.com/AstroImages/AstroIndex.html I would expect the same for Stefan as he's imaging from downtown Berlin. But he's talking narrow band filters rather than wide band. Mine are pure lum data so yes my skies are dark. I moved here for that! I used to live in a town of 250,000 and had to drive a minimum of 30 minutes to get to dark skies and I lived on the edge of town. Fortunately the Paramount works well in cold. My only concession to the cold with it is to slow the slew speed to 50% below 0C and to 30% below -20C. That puts less strain on the grease and less wear on the gear train. I also change the grease each spring just because it is easy to do. I have problems with blooming in the CCD below -30C ambient and with frost over the front window's telescope facing side when I cool more than 5C below ambient when it is below -30C or 10 below ambient when colder than -25C. This reduces the temperature regulation and my darks aren't as good as when there's more than a 10C difference between the imaging temperature and ambient. Electronics are only rated to -30C and I have some blooms when it gets much colder. I did further reduce a pot in the camera and that has pretty well eliminated it but I do see a slight loss in the quantum efficiency of the camera so I'll be moving it back each spring. My biggest hassle is with good flats with the wide temperature swings. I don't have a light box, they are hard to do for 14" scopes or expensive if you go the luminescent panel route. So I have to do those by day with T-shirt flats. Temp is always warmer then. I may have to bite the bullet and pay for a large panel but they don't like -30C either from what I've heard. I image from in the house (or even from bed) so keeping the computer warm isn't an issue. I've got the house wired for ethernet so where ever there's a jack I can work. What electronics are out there (USB to ethernet converters, serial to USB and a powered USB hub all seem to have no temperature issue and they aren't warmed in any way. I've found the ethernet converter buried under snow falling from the observatory roof and encased in an inch of ice. It never seemed to notice. Ice likely kept it "warm". Rick -- Correct domain name is arvig and it is net not com. Prefix is correct. Third character is a zero rather than a capital "Oh". |
#5
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ASTRO: M97 with Skywatcher ED120
Rick,
I usually take flats for every night of imaging. Still I sometimes have problems with flats that either over or undercorrect the dust donuts, don't know why. On other occasions I find that I can use flats from two weeks ago if I have not changed the setup. I don't have problems with vignetting with my small chip, though this might change once I get the QHY8. I have not seen small changes in focus (e.g. when I have to refocus because of dropping temperatures) to affect the flats, at least I never made the connection. I usually do an artificial flat in addition to a "real" one as I almost always have some gradients left. They are small enough not to be a problem in b/w images, but they can get nasty in colour images, especially with larger objects where an artificial flat is more difficult. Stefan "Rick Johnson" schrieb im Newsbeitrag ster.com... Stefan Lilge wrote: I got myself a Skywatcher ED120 as a wide field scope recently. This is "second" light ("first light" was such an incredibly cold night that mount, scope and operator were not functioning correctly) in a very bright night with city lights, bright moon and a snow cover that reflected both. Sky background in a 10 minute exposure at f/7.5 was over 5000 counts though my Astronomik 13nm OIII filter. In a "normal" city night this would be below 1000. The ED120 gives good starshapes in Halpha, OIII and also broadband. This image is not sharpened in any way. Taken from the middle of Berlin with a Skywatcher ED120 at f/7.5 on a G11 mount, SXV-H9 camera, 14x10 minutes Halpha, 6x10 minutes OIII. The picture can also be found at http://ccd-astronomy.de/temp2/M97colourgut.jpg Stefan Looks like you have a winner with that combination! My sky is really bright of late here too but that's in LRGB. Still I normally run about 350 in 10 minutes lum binned 2x2 but am now running 1200 to 2000 with no moon, just scattering of starlight off a zillion ice crystals in the air. Most years it is rather dry so they tend to sublime. My counts can hit 600 to 800 but with high humidity this year that isn't happening. I am finding flats very sensitive to temperature at this background level. My focus changes with temp and that changes vignetting considerably so I have to take a zillion flats at all focus positions to find a set that matches. Then a new dust speck shows up and I do it all over again. Spending all day taking flats it seems. Does your ACF have that problem? I'm using a 3" Crayford with mirror locked. Move the mirror and the flats really change, more than just changing the Crayford's position. With the wide temp changes this winter, -35C one night and only -10C the next, I need new flats daily. Your smaller chip might not see that vignetting problem, I'm working right to the edge of the usable FOV where the internal baffle is doing the vignetting. Still a change in focus changes the size of the dust mots. So they don't flat out right. Rick -- Correct domain name is arvig and it is net not com. Prefix is correct. Third character is a zero rather than a capital "Oh". |
#6
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ASTRO: M97 with Skywatcher ED120
Since I'm in an observatory I rarely remove the camera. Flats should
remain usable until dust mots change. And for much of the year that's the case. But winter seems to make that impossible. With my large chip a single image is as much as 22 meg in size. I usually use 12 flats for lum and each color, 48 in all, 60 if using Halpha as well. Even binning color the amount of disk space that eats up and the time needed gets to be rather nasty. So I try and do it as little as possible. Once a month usually suffices except in winter. Without a flat box I have to wait until day to take them (filtered T-shirt) and by then the temperature could have changed things drastically with a 20C change common. I should see about an illuminated flat screen in the observatory. One more thing for the todo list. Rick Stefan Lilge wrote: Rick, I usually take flats for every night of imaging. Still I sometimes have problems with flats that either over or undercorrect the dust donuts, don't know why. On other occasions I find that I can use flats from two weeks ago if I have not changed the setup. I don't have problems with vignetting with my small chip, though this might change once I get the QHY8. I have not seen small changes in focus (e.g. when I have to refocus because of dropping temperatures) to affect the flats, at least I never made the connection. I usually do an artificial flat in addition to a "real" one as I almost always have some gradients left. They are small enough not to be a problem in b/w images, but they can get nasty in colour images, especially with larger objects where an artificial flat is more difficult. Stefan "Rick Johnson" schrieb im Newsbeitrag ster.com... Stefan Lilge wrote: I got myself a Skywatcher ED120 as a wide field scope recently. This is "second" light ("first light" was such an incredibly cold night that mount, scope and operator were not functioning correctly) in a very bright night with city lights, bright moon and a snow cover that reflected both. Sky background in a 10 minute exposure at f/7.5 was over 5000 counts though my Astronomik 13nm OIII filter. In a "normal" city night this would be below 1000. The ED120 gives good starshapes in Halpha, OIII and also broadband. This image is not sharpened in any way. Taken from the middle of Berlin with a Skywatcher ED120 at f/7.5 on a G11 mount, SXV-H9 camera, 14x10 minutes Halpha, 6x10 minutes OIII. The picture can also be found at http://ccd-astronomy.de/temp2/M97colourgut.jpg Stefan Looks like you have a winner with that combination! My sky is really bright of late here too but that's in LRGB. Still I normally run about 350 in 10 minutes lum binned 2x2 but am now running 1200 to 2000 with no moon, just scattering of starlight off a zillion ice crystals in the air. Most years it is rather dry so they tend to sublime. My counts can hit 600 to 800 but with high humidity this year that isn't happening. I am finding flats very sensitive to temperature at this background level. My focus changes with temp and that changes vignetting considerably so I have to take a zillion flats at all focus positions to find a set that matches. Then a new dust speck shows up and I do it all over again. Spending all day taking flats it seems. Does your ACF have that problem? I'm using a 3" Crayford with mirror locked. Move the mirror and the flats really change, more than just changing the Crayford's position. With the wide temp changes this winter, -35C one night and only -10C the next, I need new flats daily. Your smaller chip might not see that vignetting problem, I'm working right to the edge of the usable FOV where the internal baffle is doing the vignetting. Still a change in focus changes the size of the dust mots. So they don't flat out right. Rick -- Correct domain name is arvig and it is net not com. Prefix is correct. Third character is a zero rather than a capital "Oh". |
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