Image of the day

Captured by
Daniel Carter

Dolphin Head Nebula Sh2-308

My Account

New to Astromart?

Register an account...

Need Help?

Refractor Rationale

Started by tbennett, 07/08/2003 03:55PM
Posted 07/08/2003 03:55PM Opening Post
Hi All,

After getting up very early this morning and setting up my 10" F6.5 Newt to take a peek at Mars, I noticed that the seeing was typical for this area (central coast of California). In focus, Mars looked like a fuzzy edged red blob with barely visible white polar cap and black features on its surface. Out of focus, it looked like a bigger red blob at the bottom of a rushing stream of water. Ground level winds were fairly calm but upper air winds were really blowing and fuzzing out the image. My TV85 show a more stable view but no more detail due to small aperture. Would a larger refractor help me get better planetary views in this environment? My 10" does great further inland so I will keep it but this coastal wind really reek havoc on seeing most of the time. Would a 5-6" refractor (whatever I could mount on my GM8) improve this situation much?

Thanks, Tom
Posted 07/08/2003 04:13PM #1
Hello there Tom,

I wouldn't be so hasty unless you have cash burning in your pocket ;-). Can you tell us which eyepiece and/or magnification you used? Since you mentioned the upper air winds, how did the stars look?
The rushing stream of water sounds really like bad seeing :-(. Did you try a red or orange filter? This helps somewhat with the seeing.

Just to let you know, I was able to resolve the fork in Sinus Meridiani last month through my new 8" Discovery PDHQ Dob ;-), a feat I've yet to accomplish with my 4" TV-102 Light Cup :-(. So try again in better seeing.

Ron B[ee]
Posted 07/08/2003 04:32PM #2
Hi Bill,

I know what you mean about the Chinese Achros. I briefly had a 5" F8 that was grossly under-corrected (~2/3 wave) and the color was just awful - it was sent back to the dealer. My TV85 has spoiled me on color correction in refractors :-). - Tom
Posted 07/09/2003 12:27AM #3
Make an aperture mask for your 10", such that it's clear (i.e. just misses the vanes and the secondary). It should work out at just over 4". Then check out Mars, and see if it shows more detail than your TV85. This should give you an idea of whether a bigger refractor would help - though it mightn't - I find the viewing worst in summer and winter, people's heaters and air conditioners tend to muck up the views.
Posted 07/09/2003 09:39AM #4
Hi Tom:

I used to live in a coastal area in Alaska that had similar seeing problems to yours. I was pleasantly surprised when I acquired an old Vixen 80mm F15 refractor on Ebay. The tube is scratched up and ugly and the focuser isn't the best I've ever used but the depth of focus resulting from the long focal length solved most of my seeing problems.

Nights that the Gas Giants were boiling in my C-9.25 were no problem with the old refractor. Image scale is much smaller and images are somewhat dark but the sharpness, contrast, and detail are there. The mountains of the Moon really stand out in near-3-D even w/o a binoviewer. Hmmm, maybe Fraunhoeffer had something there...

Now I live in the mountains of SE Idaho where the air is clear and usually quite steady. Moving is a lot more expensive than a new scope so now you have justification! A 3" or 4" F15 would be no problem for your GM-8.

Clear skies!

Mike McIsaac
Inkom, ID