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Old 25-11-2010, 10:10 AM
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multiweb (Marc)
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Pentax Lens and Focusing

Hi guys, inspired but Ross G.'s great barnard loop I was hoping to give it a shot tonight in Ha with a 65mm Pentax lens. I have a small bathinov mask for focusing that hopefully will work.

I'm a total noob at this lens business so I'm asking: do you need to refocus often with a lens like this or is it fairly stable? Also I plan to come around now and then with a hairdryer as I don't have dew straps. Do you reckon that'll do the job?

Thanks for any tips.
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Old 25-11-2010, 10:58 AM
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dugnsuz (Doug)
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Shouldn't need to refocus that often in a session - but best to check the subs every so often if there's a significant drop in temperature over the imaging run.

Consensus is that hairdryers are not the best option as you might be blowing dust onto the lens surface at speed and heated!!!
That said, I've never done any damage to my lenses with the hairdryer method - but got dew straps now just in case.

Do you have a link to the Barnard's Loop pic you mentioned?

Doug
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Old 25-11-2010, 11:16 AM
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Octane (Humayun)
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Marc,

Once you've reached focus, might be an idea to use some good masking tape to lock the lens in place. Reason being that some lenses shift focus under gravity -- as Orion rises, it may cause the lens to sag a touch. And, as you know, the slightest shift in focus for us means the difference between riches and ruins.

H
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Old 25-11-2010, 11:47 AM
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multiweb (Marc)
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Quote:
Originally Posted by dugnsuz View Post
Shouldn't need to refocus that often in a session - but best to check the subs every so often if there's a significant drop in temperature over the imaging run.

Consensus is that hairdryers are not the best option as you might be blowing dust onto the lens surface at speed and heated!!!
That said, I've never done any damage to my lenses with the hairdryer method - but got dew straps now just in case.

Do you have a link to the Barnard's Loop pic you mentioned?

Doug
Thanks Doug. I'll keep all this in mind when I get set-up properly in the future. No I don't have a link. Ross hasn't posted any. We're both just playing with this idea of doing super widefield Ha stuff lately.

Quote:
Originally Posted by Octane View Post
Once you've reached focus, might be an idea to use some good masking tape to lock the lens in place.
Good thinking. I'll stick a small strip of electrical tape across.
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