Mars 7th Feb partial success????

[tonyowen]

Attached are four images of Mars taken 7th Feb 2012 between 20:30 and 21:31 hrs GMT using a 75mm obj terrestrial refractor telescope, f16, hand guided with unmodified spc880nc webcam attached and no barlow.

The temp was +1C and thin cloud, and moon lit. I used SharpCap with zero gamma and maximum gain, 10 fps and exposures of 1/50th & 1/25th. The SharpCap histogram occupied circa 80% of the display (from left to right)

Mars01 is from 2 avis totalling 6780 frames, Mars02 is from two different avis totalling 4749 frames. Both of these images were produced via VirtualDub and Registax v5 on auto.

Mars03 is from a 2022 frame avi taken at the start of my session, Mars04 is a 4115 frame avi, the last one taken last night. Both of these were processed using Registax v5 on auto.

In all four cases RGB align did not seem to do anything.

The telescope was set to the 'extension' that previously gave reasonable images of Jupiter, but last night's efforts seem fuzzy!

Comments and help welcome

regards

Tony

[michael.h.f.wilkinson]

Mars requires very careful focus, due to its small size. Practice, practice, practice! Seeing also affects Mars a lot.

[tonyowen]

! Seeing also affects Mars a lot.

Your reference to 'seeing' made me think of the thermal contraction due to last night's relatively cold air temperature

My comment about using my setting dimensions for Jupiter DID NOT take into account the temperature difference between the air temperature when I was imaging Jupiter and last night's temperature of +1C.

My telescope is essentially a brass tube 1200mm long. Coefficient of linear expansion for brass is 0.000019/degree C.

Therefore , unless I've made a grave error, the relative change of the focal length of my telescope due to a temperature change of 10 degrees is 0.23mm!!

This is equivalent to a quarter turn of the focusing knob!!

I would be pleased to know whether or not this response is complete nonsense.

regards

Tony

[Clayton]

Only complete nonsense if you had adjusted the focus since you imaged Jupiter

More likely a tad out of focus as Mars is so small that it is difficult to focus on.

If you can up the scale a bit it might make it easier.

[michael.h.f.wilkinson]

Your reference to 'seeing' made me think of the thermal contraction due to last night's relatively cold air temperature

My comment about using my setting dimensions for Jupiter DID NOT take into account the temperature difference between the air temperature when I was imaging Jupiter and last night's temperature of +1C.

My telescope is essentially a brass tube 1200mm long. Coefficient of linear expansion for brass is 0.000019/degree C.

Therefore , unless I've made a grave error, the relative change of the focal length of my telescope due to a temperature change of 10 degrees is 0.23mm!!

This is equivalent to a quarter turn of the focusing knob!!

I would be pleased to know whether or not this response is complete nonsense.

regards

Tony

As I understand it, you focused based on an earlier setting on Jupiter. I never do that, because changes in temperature have a profound effect on focus. I always focus each time on the live image. Difficult, but it pays off. You can create a Bahtinov mask, and focus on a bright star before swinging to the planet.

astrojargon - Bahtinov Focusing Mask Generator: Overview