Warnings on high magnification

[great_bear]

Over the last few years, I've seen constant admonishment of beginners for attempting magnification that is "too high" for their telescope.

Refreshing then to read this article <click> by Chris Lord's friend Rodger W. Gordon, pointing out that much of this caution is unwarranted. Also within the article is a list of well-known observers and the (surprisingly) high magnifications they frequently employed.

An interesting read...

[michael.h.f.wilkinson]

I frequently use high power (up to 435x on Mars). I think the warning stems from these 60mm department-store telescopes with 340x magnification, which is ridiculous.

[LukeSkywatcher]

It's fair to say though that high magnifications also magnify the atmospherics etc when observing. So when conditions are not at their best (or even good),using high mags will give a worse image. To this end,sure its ok to use high mags, but really only when conditions allow. Thats why the useful magnification stated on telescope boxes is a load of tosh. The great British weather will rarely allow for such magnification.

[ronin]

About a year ago I was at a talk that also spoke of using high magnifications, it was not however something where you could look at an object and then move on. The principle being (as best I recall ) allowing the eye and brain to gather information and eventually things would become apparent.

Now this could work with a tracking scope but would not I presume work on a manual dobsonian where the image was unable to "linger" on the eye stationary, and the viewer had to distract themselves with the necessity of following the object.

One other aspect is that saying high magnifications are OK/possible also leaves many expecting both large magnifications and clear sharp images.

From sheer simple reading, we get more people questioning why they couldn't actually see any thing at some high magnifications then we have saying how good the viewing was. Will add the proviso here that it is often with a poor scope and equally questionable eyepiece and barlow.

Equipment is additionally a big factor, it is I suppose more realistic to expect a TV 5x powermate and a 5mm Nagler to work better then two of the supplied 2x barlows back to back and a cheap 4mm plossl. Both however make up a 1mm eyepiece.

Why do we (SGL) use NxDiameter immaterial of the scope? A 150 f/7.9 LZOS lens APM triplet I would expect to be able to deliver a higher magnification then a 150 f/5 Startravel Achro but I have yet to read that in anything. Everything said implies they should perform the same. I might half expect 300x out of the APM, I would equally think myself lucky if I got 150x from the Startravel.

[michael.h.f.wilkinson]

The usual rule of thumb assumes ideal optics. This assumption is often forgotten. Much depends on your visual acuity as well. Therefore it is a matter of trying what works best given the prevailing conditions. Sometimes I can use 290x on Saturn, sometimes 200x is the limit.

[Moonshane]

I agree with you and it's often possible to use very high magnifications which seem almost impossible.

http://stargazerslounge.com/topic/105707-double-stars-dont-be-afraid-to-use-ludicrous-magnification/

[acey]

Why do we (SGL) use NxDiameter immaterial of the scope?

Because the rule of thumb for the last two hundred years or so has been that exit pupil should not be less than about 1/50th of an inch, hence magnification should be no more than 50 times aperture in inches. This is a limit imposed by the human eye, not lens manufacture. The assumption is that the optics are perfect. But it's only a rule of thumb and many people happily go higher, while poor quality optics might make it necessary to go lower.

I agree with the general principle that you start low then go up until nothing more is to be gained. Many people think that DSO viewing should only be done at low power, but this only really applies to very low contrast objects - which at a light polluted site means virtually everything - or to those few very large objects where you might want to get the whole thing in the field of view.

[John]

I used to be much more cautious about using very high magnifications than I am now. My scopes are better quality than they used to be and I know more about keeping them in good collimation which helps deliver good high power views when the seeing conditions allow.

I guess the lesson is to question and experiment with these "guidelines" and see what works for you