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ASTRO: NGC 2175 with (faulty?) new 6" achromat



 
 
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  #1  
Old December 27th 08, 01:40 PM posted to alt.binaries.pictures.astro
Stefan Lilge
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Posts: 2,269
Default 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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  #2  
Old December 27th 08, 01:58 PM posted to alt.binaries.pictures.astro
Stefan Lilge
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Posts: 2,269
Default 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


  #3  
Old December 27th 08, 02:03 PM posted to alt.binaries.pictures.astro
Stefan Lilge
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Posts: 2,269
Default 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




  #4  
Old December 31st 08, 09:01 PM posted to alt.binaries.pictures.astro
Rick Johnson[_2_]
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Posts: 3,085
Default 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  
Old December 31st 08, 09:50 PM posted to alt.binaries.pictures.astro
William Hamblen[_2_]
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Posts: 236
Default 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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