Comparing Telescopes of Different Apertures

In his book "A Portfolio of Lunar Drawings," Harold Hill makes a comment I find interesting. He originally used a 6.5" reflector, then moved up to a 12", and finally observed with a 10". At one point, he had an opportunity to once again observe with his old 6.5", which was freshly recoated.

He writes that he felt "positively handicapped by the apparent dimness of the image in the smaller instrument although using magnifications strictly proportionate to those in my present telescope." He continues that he could simply not see the amount of detail in the 6.5" that he had seen when he had used it as his regular scope.

Mr. Hill opined that his older age might account for some of the difference, but wondered if time is simply required to get used to the brightness delivered by a particular aperture.

If this is the case, a person who regularly uses a particular aperture may not be the best judge of the performance of some other aperture, and only the investment of time would overcome this handicap.

Just something to think about and consider when you are reading about or doing scope comparisons. If you want to read Hill's comments in full they are on page xx.

Clear skies, Alan

Alan,

That is very interesting. I regularly observe with a 16" Starmaster and an FS128. My sense is that the more I use my 16", the more I enjoy my FS128. I cannot fully explain it, but I think it has to do with being more familiar with what I am looking at by having had time studying various objects with the larger diameter.

That said, I wonder if I would be a better observer over time, if I used the 5" exclusively. Your wife is noted for coaxing a lot of detail out of small instruments as is Stephen O'Meara. I've read where O'Meara regularly uses instruments of larger aperture than the 4" Televues he popularized with his books. Could you share whether or not Sue French uses telescopes of much larger apertures on a regular basis?

Randy

Most interesting, Alan!

And thank you for mentioning the book which I haven't known about. I know I can always count on learning new things from your post. I just went to Amazon and they have it listed plus ability to preview some pages of the book; look like a must have for a lunartic like me ;-).

Thanks,
Ron B[ee]

If this is the case, a person who regularly uses a particular aperture may not be the best judge of the performance of some other aperture, and only the investment of time would overcome this handicap.
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I am not quite sure how this relates to judging scopes, but it does touch another area. I think that using a small scope and pushing it to it's limits develops ones observing skills. Viewing from my light polluted backyard does not offer so many targets but taking say a 4 inch scope and viewing those that are relatively easy in a 10 inch does seem to help. When I switch back to a large scope, the views seem much brighter and detailed..

Jon