Posts Made By: Ron Harper

Bruce,
Install one spacer with sticky side down, two with sticky side up. And hooray for correctly fitting cells, they aren't made for you, they are made for "them".
Ron

Kim,
That's as far-out an observing report as I have ever seen. My congratulations to you and your buddy for your success this high level.

With my 20" I have seen the galaxy near the Ring, but it was a real grunt, I have tried and failed to see Pease 1, and I never even HEARD of the Guitar Nebula--probably just as well! Of course, I only have old-fashioned Naglers, what do you expect?
Ron

George,
A great report, and an enviable night! The double in Stephan's can be tricky. It's not a detailed view, but if the sky is good, I like to back off to around 40x and see 7331 and the quintet in the same field--talk about perspective!

One of my greatest little moments was looking for companions to 7331. I forget how many I saw, but despite my best effort I was unable to find one listed in the guide I was using. Further research revealed that that one was "facetious" or bogus, in the first place! Better to be slightly blind, than to see stuff that isn't there, I always say!

13 inches, f/4.5, is that one of those old Coulters? I hope somebody is still using these things. They were not very sophisticated compared to modern scopes, but started the Dob ball rolling, and definitely suck in a lot of light.
Ron
Ron

Guy,
For me, the critical thing is the width of the 75% illuminated field. Anything less than 75% bothers me, and there are cases where even 75% bothers me, but it's liveable. With the 3.1" mirror, the 75% illuminated field is exactly the diameter of the maximum field stop in a 2" eyepiece. So, I'd definitely go with the 3.1", if I wanted to use such an eyepiece. That's already cutting it close. This scope is going to be seeing limited anyhow, it's so big, so don't worry about it. 3.5" would give visually perfect widest field views.
Ron

Alex,
I have seen something like this, but only after drug-induced eye dilation. Right, for an eye exam. Everything looked lousy 12 ways, but one of them was, on this bright winter day, edges of snow were lined with violet haze. I suppose you might have some intermittent eye condition that is similar to what the eyedrops did to me.
Ron

Larry,
I too have a 7x50 and love it. But my 10x50 goes considerably deeper. With a 10x50, you will be increasing the effective aperture to a true 50mm (assuming your eyes, like mine, don't actually open up to 7.1mm), so stars will be brighter. The extra magnification alone will increase the visibility of objects significantly, separate tightly packed stars in clusters, and split closer double stars. And, as you understand, you will be seeing all this against a darker sky background, and with improved sharpness, since the smaller pupil will not aggravate your astigmatism as much.

My greatest objection to the 10x50 is that 10x is too hard to hold steady unsupported and really get much out of the view. But you already get the idea, and mount your 7x50.

I'm not sure how much you want to spend. Over on the Cloudy Nights Bino forum, the most popular $150-ish 10x50s are the Pentax (narrow field, but sharp to the edge), and Nikon Action Extreme (wide field, but soft edges). Both are said to be good quality optically and mechanically.
Ron

Itz,
Yes, that does make sense to me. But in my opinion, both powers are rather high. Dim secondaries are best viewed at the lowest power that allows separation, to minimize the washout effect.

I think excessive magnification is the bane of double observing, but I'm sort of weird that way. Even for equal pairs at Dawes' Limit and closer, 42x per inch is the most I ever use, yet can see elongations at half Dawes. My visual acuity is only average/good, nothing special. I guess it's just practice at low powers, doubly inspired by having to hand track, and the eye relief of short orthos!

Unequal doubles are just about my favorite observing subjects. With my 5-inch achromat, I like to look for E and F. I usually see E, but F requires very good seeing. If I am going to see them, I will see them at 85x. Higher power never helps.

There is one caveat to my low power rant. If your sky is monstrously light polluted, the sky-darkening effect of the higher power's smaller exit pupil might let you use slightly higher powers to advantage where the secondary is very dim.

Happy E and F-ing!
Ron

My new style 16x70 works like a charm, but, annoyingly, appears to have uncoated prisms. My old style 7x50 is one rear end kicker of a good optic, the best view I have ever seen. Just hang on, one will come up in the US.
Ron

Brad,
The first thing is to understand how CA in an achromat depends on lens aperture and focal ratio, if it's well made. A common rule of thumb is that CA will not be too obtrusive if the focal ratio is 3x the aperture in inches. If you mix in poor quality as a variable, all bets are off. CA is indeed related to other aberrations, but if well made and of proper design, CA can be minimized to the above extent, and spherical aberration and coma eliminated as well.

By this rule the Hardin should be a quite good lens if well made, which apparently it is not. You don't state the focal ratio of the Jason, but I imagine it is f/15, so it should be virtually color free and perform well up to about 100x, if well made, which apparently it is. By all accounts, Vixen spec lenses are very well made, but will show some CA in difficult circumstances, like any achromat.

Of course, there are telescope enthusiasts who are extremely sensitive to CA that might strike others as inconsequential, and insist on a higher level of color correction than possible in a normal achromat, and more power to them. Sirius or Venus are popular CA-revealers. If CA is visible under any test, however harsh, they argue, views under normal use will be somewhat compromised as well. I'm not very picky I guess, and am happy with my 5-inch, f/12 achromat, ( allegedly of decent quality, made by D&G) which only rarely (Sirius and Venus) shows "obvious" CA, to my eye.
Ron

Markus,
I would be very interested in such a scope, a 7" f/12, for permanent mounting, obviously. You welcomed comments, I hope negative and not very well informed comments are okay too!

I am dubious about a doublet that big from this glass. I fear that the elements would be so thick and strongly curved that the lens would be hard to make, hard to center in the mounting, heavy, and hard to cool. Combined with spherochromatic effects and other aberrations resulting from strong curvature, the expense of such a lens might not be justified compared to an achromat, for visual use. Secondary spectrum isn't everything.

So, yes, with those reservations.
Thanks,
Ron