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ASTRO: NGC 2175 with (faulty?) new 6" achromat
On December 24 I got my new 152/900 mm achromatic refractor, which I bought
as a "light bucket" for narrow band images with short focal length (with the option to get f/3.9 with a focal reducer). Unfortunately the star test looks quite strange, see the image at http://ccd-astronomy.de/temp2/FokusIRSperr.jpg If anyone knows what is ailing this scope please let me know (looks like undercorrection?) Anyway, in Halpha the scope delivers sharp pictures, but brighter stars have "dents" as if there was something in the path of light, which definately was not the case. I'll post two pictures, first is Halpha only, the second Ha:OIII:OIII Taken from the middle of Berlin with a 152/900mm achromat, G11 mount, SXV-H9 camera, 7x10 minutes through Astronomik Halpha 13nm, 4x10 minutes through Astronomik OIII. Pictures can also be found at http://ccd-astronomy.de/temp2/2175-600sHa7x10gut.jpg http://ccd-astronomy.de/temp2/2175colourgut.jpg Stefan |
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ASTRO: NGC 2175 with (faulty?) new 6" achromat
Forgot to mention that the faint trail in the lower part of the image is
minor planet 3823 Yorii (mag 15.4). Stefan |
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ASTRO: NGC 2175 with (faulty?) new 6" achromat
Great picture Rick. I have never imaged that one, not sure if I have seen
pictures of it before. The other "big" galaxy is quite large for being 900 million lightyears away. Stefan "Stefan Lilge" schrieb im Newsbeitrag ... On December 24 I got my new 152/900 mm achromatic refractor, which I bought as a "light bucket" for narrow band images with short focal length (with the option to get f/3.9 with a focal reducer). Unfortunately the star test looks quite strange, see the image at http://ccd-astronomy.de/temp2/FokusIRSperr.jpg If anyone knows what is ailing this scope please let me know (looks like undercorrection?) Anyway, in Halpha the scope delivers sharp pictures, but brighter stars have "dents" as if there was something in the path of light, which definately was not the case. I'll post two pictures, first is Halpha only, the second Ha:OIII:OIII Taken from the middle of Berlin with a 152/900mm achromat, G11 mount, SXV-H9 camera, 7x10 minutes through Astronomik Halpha 13nm, 4x10 minutes through Astronomik OIII. Pictures can also be found at http://ccd-astronomy.de/temp2/2175-600sHa7x10gut.jpg http://ccd-astronomy.de/temp2/2175colourgut.jpg Stefan |
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ASTRO: NGC 2175 with (faulty?) new 6" achromat
I think the star images if from inside to outside of focus, left to
right, are an indication of severe over correction. Sutter has an example in his book of 1.7 wave over correction that looks something like your series. Does the lens use tiny spacers between the elements. I have a 60mm refractor with lead foil tabs arranged at 120 degrees. They make such notches in the inside focus image and bright star points outside. Don't seem to harm the image itself however. Stars look good in your images however. Not sure if the slight softness is due to the seeing or objective. I'd think a 1.7 wave over correction wouldn't make such tight star images. I'd imagine you have to refocus between OIII and Ha with an achromat. Scope and camera are a good match for the monkey head. About the same as I get with the ST-11K and 14" LX-200R. Rick Stefan Lilge wrote: On December 24 I got my new 152/900 mm achromatic refractor, which I bought as a "light bucket" for narrow band images with short focal length (with the option to get f/3.9 with a focal reducer). Unfortunately the star test looks quite strange, see the image at http://ccd-astronomy.de/temp2/FokusIRSperr.jpg If anyone knows what is ailing this scope please let me know (looks like undercorrection?) Anyway, in Halpha the scope delivers sharp pictures, but brighter stars have "dents" as if there was something in the path of light, which definately was not the case. I'll post two pictures, first is Halpha only, the second Ha:OIII:OIII Taken from the middle of Berlin with a 152/900mm achromat, G11 mount, SXV-H9 camera, 7x10 minutes through Astronomik Halpha 13nm, 4x10 minutes through Astronomik OIII. Pictures can also be found at http://ccd-astronomy.de/temp2/2175-600sHa7x10gut.jpg http://ccd-astronomy.de/temp2/2175colourgut.jpg Stefan -- 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: NGC 2175 with (faulty?) new 6" achromat
On Wed, 31 Dec 2008 14:01:46 -0600, Rick Johnson
wrote: I think the star images if from inside to outside of focus, left to right, are an indication of severe over correction. Sutter has an example in his book of 1.7 wave over correction that looks something like your series. It is hard to interpret the star test on an achromat unless you use filters. Our correspondent didn't say whether he imaged through filters. Bud |
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