Getting there (Jupiter)

[Kaptain Klevtsov]

Managed this after learning today that smaller 'scopes suffer less from seeing.

Captain Chaos

[geppetto]

learning today that smaller 'scopes suffer less from seeing.

Thats interesting CC

How did that come about

[moondog]

Good image CC, you're starting to nail 'the striped one' !

Yes, I've read in several articles that the larger aperture scopes are more prone to bad seeing than smaller ones.

Violent movement of air molecules cause more disruption - apparently. I would have thought that this would apply more to open scopes than closed, but apparently it's all types. I'm sure someone will post an explanation of the science behind this phenomena.

You should get great shots when the seeing improves!

MD

[Kaptain Klevtsov]

learning today that smaller 'scopes suffer less from seeing.

Thats interesting CC

How did that come about

James told me - see Jupiter again in planetary. And it seems to work, now I need to get myself a 20mm f/100 APO and Bingo!

Captain Chaos

[MartinB]

Nice work CC.

Poor seeing is bound to nullify the benefits of a higher resolution scope. Can't see why a smaller aperture should actually be better though. Does anyone know about this?

[GordonCopestake]

The air currents come in "cells" that vary in size from about 5 cm to 30 cm across. A smaller scope only "see's" through one air cell, whereas a larger scope has to see through 2 air cells of different movement/structure/temperature. This difference gives a worse image.

If you look at a saucepan of boiling water you can see the same effect. Hexagonal convection cells appear and are about 2cm across in a pan.

[MartinB]

:? So a small scope has big wobbles the size of the field of view whereas a bigger scope has more wobbles going on at the same time. Not sure of the significance of that, not for stacked images anyway.

[Rob]

Big old argument zone, this one!. Bigger scopes can suffer from poor seeing... not all the time, but they do. This means a long standing quote from many an astro book claim a 6" scope is the best apature for urban viewing!!... Of course if you own a 150 APO your sorted!

Rob

[MartinB]

Or you've wasted a lot of money

[CELESCOPE]

Runs and grabs my ED 80 then throws away the gps 8 ehehehhehehe . ok i say nothing till i tried this, Hmmm maybe there is something in this , we will try,

Rog

[MartinB]

Don't believe it Rog. It's the frac brotherhood at work

[Jamie]

Don't believe it Rog. It's the frac brotherhood at work

Resistance is futile. 8)

[GazOC]

Big old argument zone, this one!.

Indeed!! I've never been in favour of the argument myself.

I've also heard that compound scopes are more sensitive to seeing than Newts and refractors. I din't know how true that is either......

[OXO]

Simple the more Aperture the more effect from seeing condtions hence magnified boil in the Bag seeing After so many years experiance of this it is a fact or at least in SCT'S FRAC'S and Reflectors oh and Maks :)

[GazOC]

I've never noticed in my scopes, a bad seeing is just as bad in a 80mm scope as in a 8" scope. maybe you just expect more out of the bigger scopes?

[Kaptain Klevtsov]

Big old argument zone, this one!.

Indeed!! I've never been in favour of the argument myself.

I've also heard that compound scopes are more sensitive to seeing than Newts and refractors. I din't know how true that is either......

I had wondered why the Mak. at 140mm diameter was worse than the 120mm Frac. Must say though that I can't try them side by side as I have only one mount.

Captain Chaos

[GordonCopestake]

From http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/forum/Depth-of-Focus_html-docs/depthoffocus.html

"When one is using a telescope with an aperture smaller than the air cells, the tendency will be for the definition to be good. When the air cells are smaller than the aperture of the telescope, and especially if those cells are moving fast, definition will be poorer. Air cells will have a slight difference of refractive index, and as they pass across the aperture, a displacement to the wavefront occurs. When no displacement is perceived seeing is said to be perfect. The probability of there being air cells larger than an aperture greater than 12-inches is vanishingly small. Couple this with the tendency of large Newtonians to have fast f/ratios, and you combine the worst of both scenarios."

It also mentions stopping down your aperture in poor seeing can improve resolution...

[Astroman]

The last post by Gordon nails it, but Gaz' post is also very true. If the seeing's bad, it's gonna be bad. The perception of bad seeing increases with aperture though, according to the post from Braybrooke Obs.