New Meade 12" ACF with LX200 unable to focus with 15mm, 10mm, etc

Hi Guys,

New to the forum and stargazing and had a quick question. Finally was able to take out the Meade 12" for some stargazing in a decently dark environment (30 min outside a main city) and was blown away by the views offered by the 20mm - 40mm eyepieces. But when I switched to anything with more magnification, like the 15mm or 10mm I can never seem to get the focus "just right" as the image gets that "bloom" no matter how fine I tune to focuser. Even when I focus just right, the image seems very dark. 

I hope this is a simple solution as I was very confused how it seemed that I got better and more clear resolution out of the 20mm+ than the higher magnifications. 

Viewing conditions on both nights were during a new moon phase, and on a very clear night. Thank you for any help!

Originally Posted by Art Monzon

Hi Guys,

New to the forum and stargazing and had a quick question. Finally was able to take out the Meade 12" for some stargazing in a decently dark environment (30 min outside a main city) and was blown away by the views offered by the 20mm - 40mm eyepieces. But when I switched to anything with more magnification, like the 15mm or 10mm I can never seem to get the focus "just right" as the image gets that "bloom" no matter how fine I tune to focuser. Even when I focus just right, the image seems very dark. 

I hope this is a simple solution as I was very confused how it seemed that I got better and more clear resolution out of the 20mm+ than the higher magnifications. 

Viewing conditions on both nights were during a new moon phase, and on a very clear night. Thank you for any help!

It sounds like the seeing during your observing session wasn't able to support the increase in magnification afforded by the use of your shorter focal length eyepieces in your long focal ratio scope. That's not uncommon at all. Seeing is essentially turbulence in the atmosphere that you don't see visually or with the use of longer focal length eyepieces such as those in the 20-40mm range but when you switch to something like a 10mm you inadvertently magnify the turbulence caused by poor seeing and the image of a star bloats in response to it. Make sure your scope is out for awhile before you observe so it adjusts to the ambient temperature, too. If you point the tube down first before starting an observing session and remove the eyepiece holder and diagonal, the warm air inside the tube will vent upward and prevent any currents within the tube from affecting your views, too. 
Finally, consult the clear sky chart for a prediction of conditions in your area:    https://www.cleardarksky.com/csk/
Review the above site so you know how to use it and it'll help you plan for an observing session especially if you want to use higher magnification with your scope.

Thank you for the response! I was actually using the cleardarksky website before going out and basically everything was good EXCEPT for the humidity. I had left the telescope outside to acclimate to the temperature for about 3 hours before observing. So humidity can really mess up high magnification like that? 

Originally Posted by Art Monzon

Thank you for the response! I was actually using the cleardarksky website before going out and basically everything was good EXCEPT for the humidity. I had left the telescope outside to acclimate to the temperature for about 3 hours before observing. So humidity can really mess up high magnification like that? 

No, humidity should not be the problem unless your corrector plate dewed-over. It still sounds like seeing is the culprit. Try observing over several nights and see if you're able to use your shorter focal length eyepieces. Bloating of star images are most likely the result of seeing conditions. Remember that any predictive site like the clear sky chart or atmospherics are merely forecasts and not guarantees of seeing or other conditions. Novice observers are too quick in blaming some other factor like their equipment when a problem like this is seen. Your 12" scope operates at an f ratio of f10 and that translates to a lot of magnification with an eyepiece within the 10-15mm range. It was most likely affected by the seeing and little else...

I'll add one other thing: try observing the moon tonight with the eyepieces in question. Although you may see the effects of poor seeing while doing so, you should still be able to get a reasonably focused image so you'll know that you can, in fact, focus with your 15mm and 10mm eyepieces...

Thank you, I'll check it out tonight