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Exit Pupil - Am I Mad ??????


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Okay I wasn't sure where to post this but I am wondering if I have weird eyes. :p

I often like to look at the moon, jupiter and doubles with my nag zoom set at 2mm. For jupiter this does not show any more detail but the planet is still nice and bright, the same detail is present and it fills up a lot more of the FoV which I like as it drifts across very quickly at 450X (with my C100ED).

Anyway I am wondering if this is strange as alot of people on here don't seem to push that mag very often. I went on a website to see what the figures were for this and it states an exit pupil of 0.2mm. Now to me the view is still crystal clear and I cant see any floaters either. I have heard that 0.5mm is usually the limit so have I got bionic eyes, am I mad or is this normal? :) I live in manchester in a light polluted area but is it a coincedence that the few times I have done this since buying the eyepiece the seeing has been superb.

P.S. When the snow clears and I get a clear night I am going to experiment by powermating the nag zoom and seeing what happens between 450x and 900x. Also seeing was terrible last week when I first tried out my XO. When I get better conditions I will post a review.

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I don't necessarily agree with the minimum exit pupil idea. I've used exit pupils under 0.5mm and not had a problem. A scope like the 100ED shouldn't have any problems with a 0.4mm exit pupil (250x).

For the record, I've also used exit pupils up to 8.3mm for deepsky observing without blackout problems - lovely to see nebulosity in the Pleiades like this :)

Andrew

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I looked up your scope's focal length and found 900 mm. According to my arithmetic, that should produce a magnification of 450x and an exit pupil of .22 mm. That is a lot of magnification for your aperture, but if it works that's great. If you have floaters, I would expect them to be evident with that exit pupil unless the image is so dim that floaters are not illuminated.

Another thought is that your eyes may have nicely adaptable irises. That usually goes with age, but if your skies are steady enough to permit high power viewing and your eyes can handle the small exit pupil, that is terrific. I have worked with a .25mm exit pupil occasionally, but my skies rarely permit that high power. I am envious!

- Phyllis

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I should add - I do have a problem with maximum magnification though, though it's more related to seeing. Tonight, under quite poor seeing, I could see more detail at 180x than at 230x in my 12" dob. I used to regularly push my 8" newt to 333x on good nights, but more would never improve the view IMHO.

Andrew

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I can get 533x out of my 12" and 6" dobs (see signature) on the moon occasionally but not often. in the 6" this is an exit pupil of 0.27mm and in the 12" 0.57mm. floaters can be an issue and it's usually the seeing lets me down above about 250x on the moon and about 150x on Jupiter, Personally I prefer a smaller sharper disk but we are all different I suppose.

Like many 'rules' the min exit pupil one can also be bent / broken from time to time and depending on a lot of circumstances. Another option of course is that you have lucked out with 'spanking optics'?!

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I have problems with floaters at 9mm 1.9 and is pretty much all I can see at 4mm 0.8 Drives me up the wall as with a good bit of rubbing I can move them out the way briefly until I blink a couple of times. I went to the optician and he said the work involved to sort them out is to horrific to think of as they are inside the eye ball. Annoying thing is my right eye doesn't suffer with them but my left eye focuses best in the eyepiece.

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Thanks for the responses guys. Just for your information I'm 30 and don't wear glasses and I'm pretty sure my vision is pretty good. regarding the exit pupil it is 0.22mm (2mm / FL9) but the website I used only does 1 decimal point (hence why I said 0.2mm) Telescope Eyepiece Comparator

At this mag I wouldn't say the image was dim either. Seeing has been really poor recently which along with the weather has made me not want to go out and play. Regarding the optics maybe I got a really good one!

Sad to hear about your eye spaceboy. I'm right handed and I would of thought I would have preferred to observe with my right eye but I too prefer the left eye.

One thing I will not forget was when I was round at Shanes and I powermated the speers to 2.5mm on one of his scopes. I cant remember which one but oddly the dust was perfectly visible in the view against the moon. You could see the specks as clear as anything. It has never happened since though.

Last thing is regarding the floaters. I rarely see them when looking through eyepieces but for some reason I sometimes can see them in the daytime when just looking around as normal doing day to day things. If I spot them in my eye I usually then actually focus on them in my own eyeball and then play a stupid game with myself to try to keep them in view. I do this by moving my eye around to make them move where I want. Does anybody else get/do this? :)

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Jupiter is rather low contrast. On many nights I see more detail on the disc at 150 to 200x then I do at 250x or 300x. YMMV, but that's a reason why many stick to lower powers for some objects.

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I'm not really debating about the contrast. The best view I've had of Jupiter has been through my 8mm TV plossl. It was really sharp.

I just sometimes like to make the object massive to give me that feeling of immersion if that make sense as it speeds past the FoV.

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I would have thought right handed/left-eyed was the norm?

I only rarely try to go beyond 245x because things get bigger without getting clearer. In fact they usually get less clear for me. There are exceptional mornings - the seeing is best here in the wee hours - when I have gone up to 500x but it is rare.

One way to test yourself would be to draw detail on Jupiter, trying different magnifications to see which really yeilds most information.

Olly

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One thing I will not forget was when I was round at Shanes and I powermated the speers to 2.5mm on one of his scopes. I cant remember which one but oddly the dust was perfectly visible in the view against the moon. You could see the specks as clear as anything. It has never happened since though.

Last thing is regarding the floaters. I rarely see them when looking through eyepieces but for some reason I sometimes can see them in the daytime when just looking around as normal doing day to day things. If I spot them in my eye I usually then actually focus on them in my own eyeball and then play a stupid game with myself to try to keep them in view. I do this by moving my eye around to make them move where I want. Does anybody else get/do this? :)

hi mate

I recall this too, it was the 120mm Achro which this happened with. Presumably the poorer (than your ED) optics or lesser aperture created a smaller exit pupil and maybe this was breaking point for your floaters? (This sounds so wrong).

I play 'floater tennis' too while bored sometimes at work! kindred spirits!

I am right handed and right eyed by the way.

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If I spot them in my eye I usually then actually focus on them in my own eyeball and then play a stupid game with myself to try to keep them in view. I do this by moving my eye around to make them move where I want. Does anybody else get/do this? :)
Yep... Not exactly tennis, but try to keep one in the centre of view static and wobble it from side to side to see if I can change it's shape at all (Okay, I'll get my coat...) :p
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If I spot them in my eye I usually then actually focus on them in my own eyeball and then play a stupid game with myself to try to keep them in view. I do this by moving my eye around to make them move where I want. Does anybody else get/do this? :)

This is sad but I do it too. I find if you look directly at one it starts to move, then you have to move your eye again to follow it and it moves faster. Endless fun if you're bored.

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I usually stay below 300x, I find it a bit boring to constantly nudge the dob at higher power and seeing usually makes the image shimmer too much.

I'm right handed and usually observe with my right eye even though it haves a couple of floaters. My left eye doesn't have any floaters, but I find it harder to place it correctly and the view always seam to get my brain a bit confused. If I'm looking with the left, and the right gets any glimpse of external light, my brain overlaps the image making the external light the subject of focus. This is really annoying.

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