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Geoff Barnes

Different Eyes = Different Focus

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I've just had a very enjoyable couple of hours with the 12" Dob, on a perfectly clear, mild evening though a tad breezy at times.

I always find on windy nights that the turbulent air leads to some very variable seeing, though during calmer spells the seeing is superb.

Anyhow, using the Baader 8-24mm zoom had a good look at Jupiter, Saturn and Mars (good details on all three at 8mm, 185x). Also the Lyra constellation, did a star test on Vega and eventually got the scope collimated pretty well using Gary Seronik's technique. Good views of the Ring Nebula, the Double Double and Albireo all at 8mm (185x).

Went back to Saturn which is currently in Sagittarius and had beautiful views of the Butterfly, Ptolemy and Sagittarius clusters. Must get a filter to see the nebulae.

The breeze had died by this stage and the seeing of Saturn was superb, Cassini clearly there, the shadow cast on the rings by the planet also, and definite banding on the disc. Was so thrilled I called out to my wife to have a peek. With a strategically placed small stepladder (she is quite short) I guided her to the eyepiece and showed her where to focus in case it needed adjustment. After a few "oh wow's" and "oh yeah's" she returned indoors and I placed my eye back against the eyepiece. Crikey! Saturn was just a fuzzy blob! Now I wear quite strong glasses for daily use, but not for telescope viewing, I prefer to go without. Wifey doesn't wear specs at all and the difference in focus at the eyepiece was astounding!  I had thought there would be a slight difference but never dreamed it would be so vast.

It does make me wonder just how differently we all see things, be it colour, contrast, sharpness etc. No wonder we all choose such a variety of different eyepieces and scopes to suit our individual needs.

Nevertheless, a great evening's viewing at last! 😀

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Nice report.

Yes I have always found that different people often require slightly different focus points. I have always found that my mom doesn't need refocusing if I show her the eyepiece, but my dad on the other hand always finds he needs to refocus by just a couple millimeters.

If you wear strong glasses for daily use, that probably means that the focus point is going to be way off from a non-glasses wearer, which matches your experience.

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Good report Geoff :smiley:

When I've done outreach sessions the different focus points for folks really becomes apparent - the focus needs adjusting a little for practically every person who looks though the scope !

 

 

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I generally leave my glasses on if looking through other people's scopes to minimise refocusing.

Also I'm sure my left eye sees things with a warmer 'colour' temperature than my right eye.

These individual differences are often not appreciated but must have an impact on how different EPs suit different users. Recently I've read two people state they don't like 'wide angle' eyepieces, for example.

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Our eyes are designed for stereoscopic viewing, so the eyes are slightly different, both in colour spectrum and focal length. Try swapping from eye to eye you will see a distinct difference in contrasts and minor focusing changes.

If our eyes were identical we wouldn't get any true depth perception.

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If you're short-sighted you will have to rack in the focuser a bit....I believe you also get a little more magnification than the usual simple formula predicts (Fobj/Feyepiece) which assumes the eye is focussed at infinity.

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My left eye shows objects closer than my right, quite a bit seems like about 10x when looking through the eyepiece. The point of focus for each eye is also slightly different, I like to alternate an eyepatch while observing dso so this little bit of ajustment has always been annoying but I have no interest in a surgical solution when focus cannot be achieved it will be time to address it. Been this way for as long as I have been observing and without the hobby I would have never noticed a deficiency.

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Eyes can vary hugely, colour perception, focus, brightness, perceived resolution and far more I’m sure. Some people will benefit from better quality eyepieces, others simply wont be able to see any differences.

I sometimes have to insist that people at least try to refocus when viewing through my scope. If they have never viewed the object before they won’t know if it is as good as it can be or not, yet often they have a quick look and say ‘that’s nice’ and I ask if it is focussed and they say ‘oh yes, it’s perfect’, when I know full well that the chances of our eyes being identical is pretty slim!

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When the mob are out to play.... I catch a galaxy, shout Steve over then return to the ep and think it's clouded over 😉

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Way back when I first discovered my eyes had different focus points and objects appeared closer in my left eye I also noticed using my left eye, eye placement was farther out and I of course immediately checked my eyes the next morning on the patio winking left than right watching the scene proximity change more than just slightly thinking how did I ever not notice this before and how amazing it is when used together I see just fine. 

Edited by SIDO

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12 hours ago, Sachakins said:

Our eyes are designed for stereoscopic viewing, so the eyes are slightly different, both in colour spectrum and focal length. Try swapping from eye to eye you will see a distinct difference in contrasts and minor focusing changes.

If our eyes were identical we wouldn't get any true depth perception.

While I agree about the differences, I can't agree about the depth perception, that's fundamentally down to the eyes being spaced apart.

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