venus

[apaulo]

ive just been viewing venus, i am seeing a disc made up of 3 colours, red, yellow, and greeny blue. i am using a 200p on a homemade dob. eyepieces are vixen slv 25 and 12mm. also bst  8 and 5 barlowed. seeing the disc of venus in these colours, id like to ask have i got a collimation problem, or is it seeing conditions. or something else. or possably normal. any help and advice from you guys would be much appreciated. thanks in advance.  paul

[Dark Vader]

Probably atmospheric conditions with it being at a low altitude. Could also be exceeding useful magnification if you barlowed the 5mm BST. I can't see it being collimation but still worth a star test or pop in a Cheshire if you're in any doubt. 

Edited July 21, 2021 by Dark Vader

[Pete Presland]

As DV said, i would try it on a star much highie rin the sky before you adjust anything.

[Nik271]

Venus is only 10 degrees in altitude and what you are seeing are the effects of dispersion of light in the atmosphere. This is most noticeable in bright objects like Venus (or Antares low in the south) and the rainbow colours should be horizontally banded. Collimation will not produce chromatic dispersion, if it was collimation you will notice that the stars don't come into perfect focus. Don't test this on Venus but on ideally on Polaris, which does not move so much easier to use high magnifications. Try the 5mm EP and examine the star shape. It should have a symmetric circular shape of concentric rings with 4 spikes. Collimation is perfect if everything is perfectly circular.

(You should also be able to see the Polaris companion as well, a dim 9-th magnitude star 18'' away from the main star.)

[apaulo]

thank you everyone for the feed back.  its much appreciated. i never thought of the light dispersion and the low altitude. will do a star to check things anyway. clear skies to you all.