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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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I was observing for 1 1/2 hours today and I am noticing that my eye is tired. When this happened to me 20 years ago as I started astronomy a friend who was an optometrist taught me to go from outside of focus to inside. This has worked for me in astronomy and in microscopy very well.
Tonight it crosses my mind that I have no idea what way to turn the screw to be either inside or outside of focus on my PST. Can anyone tell me or give me an idea how to find out. I guess a star test is out... 
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Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1990
Loc: Hockessin, De
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Focusing is done by moving a penta prism that is on a threaded rod. Hopefully I won't get this backwards. Turning the knob clockwise moves the prism toward the back of the scope which would move the focal plane lower in the eyepiece tube, hence your inside of focus. Turning the knob in the other direction moves the prism toward the objective and moves the focal plane higher in the eyepiece tube, hence outside of focus.
An easy test is to pull the eyepiece half way out of the eyepiece tube and then focus the image until it's sharp. Now turn the knob a turn or so and then move the eyepiece either up or down to refocus the image. If you had to move the eyepiece up, that direction of turning the knob moves the image to the outside of focus, if you have to push the eyepiece in that direction of turning the knob moves the image inside of the focus.
- Dave
(image removed for moderator review - Erix)
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
Edited by Erix (02/16/08 11:58 PM)
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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Hi Dave,
That works! Why did I not think of moving the eyepiece? 
Do you have a picture of the etalon and tilt mechanism?
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Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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Erix
Toad Lily
Reged: 12/25/04
Posts: 22358
Loc: Ohio, USA
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Colin, I'm sorry, but we don't allow images of taken apart PST's to be posted here because of the risk of danger if it's not put back together properly or parts become loose, etc. It falls under our PST modification rules here on CN, even though the photos you are asking for isn't intended for modifications.
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Erika
Automatic doors make me feel like a Jedi. 
Zhumell 16", 10" LX200 Classic,Orion ED80, ETX70-AT, DS Maxscope 60mm
My CN Gallery * 2007 July - tracking NOAA10963
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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Thank you Erika!
--------------------
Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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OK, I tried this out today. I slid the EP out a couple of mm then brought the PST to focus. Then I slid it in and had to turn the focus knob counter clockwise to bring it to focus.
So, my focus routine is run the knob clockwise, then slowly turn the knob counter clockwise till i am just in focus. And unless I got mixed up that makes my eye corrected to infinity and relaxed in the EP.
Thank you David.
--------------------
Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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