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




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Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".