How Long Does A Telescope And Diagonal Need To Cool Down?

[refractordude]

Had my scope and diagonal out cooling down for a 2 1/2 hours. Could not bring the stars of Orion into sharp focus with a 10mm eyepiece. I could bring the stars into sharp focus with a 20mm eyepiece. I could also bring the stars into sharp focus within 80mm aperture mask. The skies seem calm. I am thinking it is the 2 inch diagonal that needs more cool down time. What might be the problem?

[Demonperformer]

Welcome to SGL.

What scope have you got?

Off the top of my head, I believe the rule is 5 mins for every inch of aperture. Whatever, 2.5hrs should be plenty, so I doubt it is to do with cooling.

The fact that you can bring the stars into focus when you use a mask (reducing your aperture) suggests to me that the problem is probably more to do with the correction of the objective (I'm guessing from your username it is a refractor). Once we know what the scope is, may be able to advise further.

 

[refractordude]

Must have been turbulence high in the atmosphere. Returned outside for another try. Was able to get crispy sharp views of Orion's trapezium stars with a 6mm eyepiece. Thank you for your help. 

[spaceboy]

As above.

+ It is also worth noting how much experience you have with telescopes?

You clearly understand the need to cool your optics but the longer a scope is out the more chance it will be susceptible to dew. It can be a balancing act some nights between cooling optics and avoiding dew with the only way around it being dew bands, then other nights you can be out all night and there is nothing. Again it all depends on the size and type of scope.

Seeing conditions also play their part to how much magnification can be used on a given night. Poor collimation again can have an effect. Even picking an object to observe can limit use able magnification with low objects suffering and higher zenith objects seemingly unaffected by seeing. Quality of the scope and eyepieces needless to say play a huge part.

[refractordude]

1 minute ago, spaceboy said:

As above.

+ It is also worth noting how much experience you have with telescopes?

You clearly understand the need to cool your optics but the longer a scope is out the more chance it will be susceptible to dew. It can be a balancing act some nights between cooling optics and avoiding dew with the only way around it being dew bands, then other nights you can be out all night and there is nothing. Again it all depends on the size and type of scope.

Seeing conditions also play their part to how much magnification can be used on a given night. Poor collimation again can have an effect. Even picking an object to observe can limit use able magnification with low objects suffering and higher zenith objects seemingly unaffected by seeing. Quality of the scope and eyepieces needless to say play a huge part.

I used a 6mm eyepiece. A 4mm eyepiece did not look all that bad. The skies are great this morning. I may stay up to see Jupiter.

[spaceboy]

I was a little slow with my post and you replied before I had a chance to finish.

Great to hear its all sorted and your having good results now. 

[John]

My refractors (with their diagonals) take from 10-15 minutes to 30-40 minutes to cool completely from the house to outside in the UK. They range from a 100mm doublet to a 130mm triplet.