Jump to content

sgl_imaging_challenge_6_banner_jupiter_2021.jpg.eacb9f0c2f90fdaafda890646b3fc199.jpg

 

 

Getting there (Jupiter)


Recommended Posts

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

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

:? 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.

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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......

Link to comment
Share on other sites

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 :) :)

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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...

Link to comment
Share on other sites

  • 2 weeks later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.