(meteorobs) IR Camera is up. -Important notes....

Chris Peterson clp at alumni.caltech.edu
Thu Dec 11 10:29:40 EST 2008

Hi Larry-

You can trust your eyesight when focusing a video camera on a monitor. There 
is no ambiguity in the focus position resulting from your eye's own 
accommodation. Where you get into trouble using your eye is when using a 
telescope visually. In that case the correct focus (on your retina) is a 
combination of the telescope focus position and your eye's focus position. 
The two interact, which is why you often fiddle with focus when using a 
scope visually. I think that's the effect Doug is referring to.

As a rule, the best method of focusing a video camera used for meteor work 
is to use a local monitor (that is, close enough to the camera that you can 
focus without having to run back and forth between it and some other 
location) along with a distant, bright point source. I use Venus for my own 
camera, but for our cameras in less rural areas we normally use 
streetlights. Point sources work best for most people because there is less 
ambiguity in determining the point of best focus.

The other point is that with an autoiris lens, you need to make sure you 
focus at night. Otherwise, the lens stops down and you get a large depth of 
focus. What appears well focused in bright light usually isn't once it gets 
dark and the iris opens up.


Chris L Peterson
Cloudbait Observatory

----- Original Message ----- 
From: "stange" <stange34 at sbcglobal.net>
To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
Sent: Thursday, December 11, 2008 12:12 AM
Subject: Re: (meteorobs) IR Camera is up. -Important notes....

> Thanks Chris & Doug!
> I was not aware of my eyesight creating so much subtle error. This means
> then that I must focus by finished picture images rather than judge by
> Monitor or eyesight in any way.
> I wonder what other parts I have don't work well...........
> Larry

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