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Focusing on a distant object

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#1 Dennis_S253

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Posted 02 February 2013 - 09:58 AM

This has always puzzled me. When focusing on a distant object, say a Galaxy. Would you focus the stars in the FOV as pin points? Or would they seem to be out of focus? Any thoughts...

#2 GlennLeDrew

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Posted 02 February 2013 - 11:22 AM

At such large distances, that being optical infinity, all objects from a satellite in low Earth orbit to distant quasars will simultaneously be in focus. (Now, with a MULTI-meter aperture, that low satellite may not *quite* be in focus along with the stars.)

#3 Carol L

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Posted 02 February 2013 - 12:08 PM

I tweak the focus while using averted vision on the actual object - seems to work well.

#4 Special Ed

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Posted 02 February 2013 - 12:59 PM

When viewing a diffuse object like comets or DSO's I focus on a star. I need a fairly bright star so I sometimes must sweep around until I find a nearby star that's bright enough, put it in focus, and then return to the object.

When I am observing Jupiter, I focus on the Galilean moons first and then tweak the focus as needed. For Saturn I focus on the rings.

#5 Dennis_S253

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Posted 02 February 2013 - 01:14 PM

Thx all, I figured that the case. Just wanted to make sure I wasn't missing something. Carol, that's interesting what you say. I tried that last night on M46 and it seemed to work.

#6 Carol L

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Posted 03 February 2013 - 02:21 AM

Carol, that's interesting what you say. I tried that last night on M46 and it seemed to work.


Glad it helped you out, Dennis. :)

#7 Cames

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Posted 04 February 2013 - 04:17 PM

Thanks for confirming that phenomenon for me, too, Carol.
I'm not sure why but it seems to work pretty consistently.

Someone recently posted that the eyes can pick up a detail better when it's in motion. Perhaps a few more photoreceptors are involved as micromovement that accompanies the the focusing takes place.

Another puzzle for me is when I focus on environment of Jupiter. It seems that when I focus to create the tightest pattern on the moons of Jupiter, I don't see crispest details on the planet itself. Then I try for the best focus on Jupiter's surface details and the moons appear a little bloated. Is it just me seeing this effect?

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#8 Carol L

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Posted 05 February 2013 - 02:33 PM

Thanks for confirming that phenomenon for me, too, Carol.
I'm not sure why but it seems to work pretty consistently.

Someone recently posted that the eyes can pick up a detail better when it's in motion. Perhaps a few more photoreceptors are involved as micromovement that accompanies the the focusing takes place.

Another puzzle for me is when I focus on environment of Jupiter. It seems that when I focus to create the tightest pattern on the moons of Jupiter, I don't see crispest details on the planet itself. Then I try for the best focus on Jupiter's surface details and the moons appear a little bloated. Is it just me seeing this effect?

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C


You're welcome, C! :) Averted vision is the best way to observe DSOs, so it's always seemed logical for me to use AV while getting a good focus on the DSOs. Aside from that, the stars are in our own galaxy - focusing on them to see a distant DSO would be like focusing on a nearby tree branch to see an Eagle's nest a few miles away.

Regarding focusing on Jupiter and its moons - the same thing happens to me as it does you. I've always thought that it was caused by the slight difference in distance between us and Jupiter, and us and Jupiter's moons. Might not be, but it makes sense.

"Someone recently posted that the eyes can pick up a detail better when it's in motion." I can sometimes 'detect' a dim object better when it's in motion (OTA tapping etc), but have always been able to pick up more detail when it's stationary than when it's moving.

#9 Crazyhorse1876

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Posted 05 February 2013 - 05:39 PM

When I release the focuser knob on my newtonian from final adjustment the image is in a sharper focus until the OTA settles down from shaking and then is in a bit more of a soft focus. I have added weight to my telescope mount/tripod and it seems to give it more stablitization and I have also ordered an Auto-Focuser to see if that will be of some help. :cool:






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