Are Poor seeing conditions why this is happening? Is there anything I can do?

Started May 15, 2020 | Discussions thread
OP Metastro Forum Member • Posts: 56
Re: Are Poor seeing conditions why this is happening? Is there anything I can do?

sharkmelley wrote:

The movement in the Bahtinov spikes will be a combination of the seeing and of tube currents within the optical tube. I encounter the same with my 11" SCT. An enclosed tube like a Maksutov or SCT needs plenty of cooling down time - I always give mine at least an hour. On a night when the temperature is continuously falling, tube currents can remain a problem for hours because it never reaches thermal equilibrium.

You will need to take the average position of the central spike rather than the instantaneous position because the instantaneous position will jump around unless the tube has reached thermal equilibrium and the night has good seeing.

Unfortunately London is always a bit too close to the jet stream so this is something you'll need to get used to.


Hi Mark

Thank you for your response.

In regards to taking the average position of the central spike, what might this entail in practice for me, when focusing using the Bat-mask? I trust there isn't an option to tell APTool to use an average instead of each continuous instance?

At this time, I can't entirely comprehend how anybody near London can ever achieve a nice result, but I will certainly try with the advise you've provided

Thanks again,


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