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Thread: High mag viewing and DSOs

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    Default High mag viewing and DSOs



    Ok, since one look at the calendar reveals to my powerful intellect that is still not June 5th yet (the day my new scope ships) I find myself left with the only alternative to direct testing to ask questions on others experience ....

    Here's the question: if we assume that a 2mm exit pupil is the sweet spot for viewing DSOs, for my scope this translates to 183x. So how much time do you all spend viewing DSOs at mags above this? Obviously where you observe has a major affect on this but I curious as to how useful in real practice short FL EPs really are except for lunar & planetary ...
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    Default Re: High mag viewing and DSOs

    I don't use higher magnification EPs at all on DSOs. I start with a wide angle EP (a 27mm, for my f/4 scope), and usually stick with it. I want maximum brightness. If I'm going for details, I might try a moderate EP, like a 15mm. But by the time I get to a 10mm, most fuzzy DSOs have disappeared. It might be worthwhile for open clusters.
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    Default Re: High mag viewing and DSOs

    I will occasionally get down to a 13mm eyepiece for a DSO, but not too often. My eyepieces of choice for them are 30mm, 24mm, and 18mm.
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    Default Re: High mag viewing and DSOs

    I'm trying to convince myself that a wide field short FL EP is not very useful. I like the 20mm ER of the Delites vice orthos which are in the 4-5mm range so I'm thinking that 62 deg AFOV is plenty over the 42 deg orthos in something around 5mm FL vice a Delos for planetary & lunar ...
    Last edited by Nimitz; 05-17-2018 at 04:48 PM.
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    Default Re: High mag viewing and DSOs

    Skybird: you didn't say for which scope but for the Obsession it works out to mags of 63/79/105x & for the Xt10 it's 40/50/66x
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    Default Re: High mag viewing and DSOs

    I wouldn't worry much about the magnification factor. Let exit pupil be your guide.

    I do a LOT of galaxy hunting (skies permitting) with my 12". I typically hover between a 4mm and 2mm exit pupils for this endeavor. Occasionally, I dip down to a 1.5mm exit pupil on the small very faint ones.

    Short focal length wide fields? They are useful, at least in my case, with galaxy hunting. Sometimes these things are so faint that only averted vision is useful, and often enough the wider AFOV is helpful with inducing movement to shake these guys loose with a little scope tapping.

    I also have a 10mm Baader Classic Ortho I bought to employ in this endeavor, but unless I've specifically honed in on the target's location already, I find the narrower AFOV of that eyepiece to be a bit constrictive with my "shaking loose" methodology.

    That's just my experience and how I have evolved as a galaxy hunter. Others use their own methods for success of course.
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    Default Re: High mag viewing and DSOs

    There is a contrary POV to the wide field consensus that JG can elaborate upon as well. Whether one needs to go higher in magnification to maximize the contrast on a DSO depends on the object! One size (focal length) definitely does not fit all. There is a book by Roger N Clark that discusses optimum magnification based on the physiology of the eye combined with the optics of telescopes. Many of the resources of that book are located here:

    Visual Astronomy of the Night Sky, Clarkvision.com

    I think that the popular view that low magnification is always better is not supported by science. In particular small targets like galaxies benefit from greater magnification.

    I previously used a different, more cumbersome method to determine optimum magnification. Clark's method is well motivated in physics and physiology. I personally prefer to be a little less aggressive in magnification than Clark but still that puts Clark and I at much more aggressive than most DSO observers. Since I was put on to Clark JG might well agree but I won't put words in his mouth.
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    Default Re: High mag viewing and DSOs

    My take is use the conventional wisdom as a guide but never be afraid to try higher power on an object, every object (and conditions) respond to magnification differently. Sometimes I'm pleasantly surprised when going higher magnifications, it may not work at all but I may get a view that shows different details than the lower power views. It only take a few minutes to switch eyepieces and check out the view and you may get a very nice reward.
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    Default Re: High mag viewing and DSOs

    Quote Originally Posted by Nimitz View Post
    I'm trying to convince myself that a wide field short FL EP is not very useful. I like the 20mm ER of the Delites vice orthos which are in the 4-5mm range so I'm thinking that 62 deg AFOV is plenty over the 42 deg orthos in something around 5mm FL vice a Delos for planetary & lunar ...

    If you're getting the goto then why bother with a wide field? If you are guiding by hand then a wide field might be essential.

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    Default Re: High mag viewing and DSOs

    I really like the lower power eyepieces when searching and observing DSOs. A few nights ago I was amazed at how many galaxies I could see in the FOV of my 24mm Pan using the XX14g. But, sometimes you can’t pull them out of the dark without some magnification. The 14mm ES at 118x is a great DSO eyepiece and terrific at resolving stars in globs. I occasionally use my 9mm Meade at 183x for really faint objects but usually I use it on the planets mostly Jupiter and Saturn.
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