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So, for those who want to know they have a good telescope, I propose the following test which will assure that level of optical telescope quality. If the temperature outside is different then the room in which you keep your scope, bring your scope outside and let it adjust to the air temperature.A half hour should do, but maybe an hour will be needed.Some of us become interested in the optical quality of our telescopes.We want to know that the optics are well figured and polished.Differential refraction due to mixing of air 'air parcels' having differing temperature is what makes a nearby target desirable--even necessary.But depending on aperture and focal length, one must observe the minimum target distance to avoid imparted spherical aberration.Point your telescope at some bright object or surface; a tree, a broken limb, a fence, a lock on the shed; something fifty to a hundred feet away.Into your scope, place a good quality eyepiece which will magnify around 30X per inch of aperture.
The only caveat, this is true now; but in my case, I see how the years are beginning to affect this capability- whether the optometrist says my 'script' hasn't changed much the past 15 years! The only thing a higher power eyepeice does is expand the linear scale of the image. The bigger you make the image and the dimmer it gets, the more the eye looses contrast sensitivity. Even with an Achromat, the amount of spherical aberration can be accuratly determined using a 30% obstruction.
Some of us are satisfied if we know that the telescope is of a quality that it will provide everything the eye can see.
We want a scope which, when the sky is transparent and steady, will deliver every bit of visual information our given visual acuity can see. We want scopes with optical components, each of which has a quality of glass, polishing, figuring, finishing, and coatings which are an order of magnitude better than what our eyes will ever be able to see.
We want scopes which in laboratory test situations or by use of field tests, has a quality which surpasses what even the best eyes can see.
Many of us have heard of such laboratory and field tests. But most of us don’t know how to make use of them; nor have the material means to do so.
Increasing the magnification makes the object larger which generally makes details more easily seen but it also dims them substantially, this would seem to be something of an eye test.