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Small exit pupil - what is your experience?


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I am interested in your experience in using certain high magnification eyepieces which result in an exit pupil of 0.5mm or less.

I appreciate that age will come into the discussion with the problems of floaters etc. However, when trying to split tight doubles it means using eyepieces that give high magnification which results in small exit pupils. I know when we discuss mags of 50x or 60x (or even more) per inch of aperture it will be said that the UK climate will rarely be able to go this far.

Notwithstanding age, climate, poor seeing conditions etc - what has your experience been? What mag have you gone to and what was the exit pupil?

Mark

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hi Mark, I routinely use very high powers on doubles and the (winter, higher elevated) moon in particular. using my 6" f11 I find that very small exit pupils produce lovely round stars with airy rings and more of a refractor-like view. my main double star eyepiece is my 6-3mm Nagler zoom and at f11 this provides exit pupils ranging from 0.54mm to 0.27mm and magnification of 267-533x. I use this whole range, albeit more often towards the lower end given seeing conditions. in good seeing, the smaller the exit pupil, the better the split (to a point) and the cleaner the image.

I really like high power views of doubles although I am glad of the equatorial platform when doing so.

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300-400x with a 102mm MAK, even near Frankfurt, Germany, to view Jupiter and the moon. But usually I stick to 2x aperture-in-mm.

I notice my floaters a lot during sunny days, but then I'm around 30...

Someone here posted a link to http://brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/forum/highmagnifications.html , but I forgot who it was. Set least an interesting article To read.

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Hardly a "scientific" problem, but more personal technique: I just find it hard to casually look into a small exit pupil. Sometimes I even blink and "lose" the thing completely - Particularly with a very large eye lens or long eye relief. Usually need to sit down or "wedge" (don't ask!) myself. A good eye / light guard seems help? Or simply I "get on better" with some eyepieces / scopes than with others. :p

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Someone here posted a link to http://brayebrookobs...ifications.html , but I forgot who it was.

That'd be me :)

At the end of the day it's all about targets isn't it?

- I mean 50xpi / 60xpi plus is going to be like a dirty fishtank on the moon, but on doubles you're not going to notice the floaters much, besides which - as I think Chris Lintot pointed out on Sky at Night before, a slightly blurry view can help you appreciate colourful doubles better sometimes.

Then you've got targets like Mars for which you really need to push the magnification in order to get a satisfying image size. The high magnification figures in the article referenced above were all in relation to Mars viewing.

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I find if the exit pupil drops much below 1mm I start to see floaters in my eye which can get annoying, so I try to have an eyepiece that will give me around 1mm for my high mag viewing. With my f6 newt I have a 6mm lens and for the f10 C11 I have a 9mm ortho and 11mm tv plossl. This gives me around 300X mag.

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It might be advancing years but "floaters in my vision kill it for me at very high mags.

I use Binoviewers to help (it does), but nowhere near 0.5 exit pupil. That would be hard work!

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I frequently use exit pupils down to 0.5mm. Whenever I'm observing planets with my refractors, the shortest f/l ep I normally use under good conditions is a 3.5mm type 6 Nagler. This gives around the highest useable power in each scope and an exit pupil pupil of around 0.5 or 0.6mm (x197 and 0.53 in the 106mm apo)

I do find floaters to be an issue, but enjoy the benefits of the higher power so find ways to look around them.

I guess increasing aperture is the only way to increase exit pupil size. A similar x200 with a 20mm Plossl in my Mak has a 1mm exit pupil and floaters are less of a problem. I too am experimenting with binoviewers to avoid floaters but have yet to get really sorted with them.

Stu

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I suspect it'll be hard work lining up two tiny exit pupils to two eyes in a binoviewer.

I used the binoviewers on the 180 Mak Cass using 12.5mm EPs last night which gave a mag of 216x (although with extra F. L. of binos it would have been greater) and the exit pupil is stated as .83. I should try the 9mm which has an exit pupil on the binos of .6mm.

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Following some good advice above plus the excellent article http://brayebrookobs...ifications.html - I made the decision to buy a high mag EP.

I felt a 2.5mm planetary EP of the TMB design would not cost too much and it would give the opportunity to experiment. Well I was lucky because Macavity was selling a 2.5 TS Planetary HR which I duly bought - thanks Chris.

The main purpose was to use it on my William Optics SD66 giving me a mag of 155x and an exit pupil of 0.43mm. Anyway last night I could not resist using this EP on my 4" APO which I know is a quality, well collimated frac. The EP provides a mag of 284x and an exit pupil of 0.36mm.

Well viewing the Moon I had many floaters - must be my age!! I then turned to Saturn which was sharp although maybe too much mag. However, on some doubles it was really good. I split the double double into 4 very sharp stars and then had good views of Izar and Pi Aquila.

So I have answered my own question. I was obtaining 70x per inch of aperture with an exit pupil well below 0.5mm

Mark

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I agree with all that re doubles etc.

Mark, I used to have a 2.5 type 6 Nagler as a high power in the 66 and 106, but found it was more often than not too much for the conditions or my floaters were too bad. I used it a few times on Mars with success, it didn't add much detail if any, but gave some nice additional image scale.

I've since backed off to a 3.5t6, plus the 3 to 6 nag zoom which covers most options. I think I use the 3.5 more often now as it is regularly the highest useable power in the 'fracs.

Stu

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