Posts Made By: John Wilson

Hi Larry.

I'm mostly a Moon/planet/double star observer and I tend to use longer focus scopes of different designs in the f/8 to f/20 range. With any scope I use, I aim for exit pupils of about 2mm, 1.2, .83, and maybe .5 or so (the last maybe with a barlow). Then I try to have a longer focus eyepiece for object finding and wider fields (right now that's a 40mm VernonScope Erfle with a 45mm field stop diameter). So I guess "enough" for me would be those 5 eyepieces. (Not that it isn't fun to try others!!)

Cheers,
John

Ed,

Is there any possibility that you have uncorrected astigmatism that comes to the fore with the larger exit pupils a 40mm eyepiece gives you? I have no idea how common this is but I have astigmatism problems with eyepieces that give more than 3mm of exit pupil, even using my glasses (which include a correction for cylinder).

Just a thought...

John

This looks identical to the eyepiece I bought from Edmund in 1967 (and still have so I can compare your photo to the eyepiece). In the catalog, it was advertised as a 1 1/8" Kellner, though as you say it appears to have 4 elements rather than 3.

Cheers,
John

A fellow in our club mounted his FS-128 on a GM8, didn't like it (wobbly at high power), and replaced it with a G-11. He is happy with the G-11.

Cheers,
John

Hi Steve.

I own one of the older 8" f/20 scopes and have found it a gem for planets and double stars. Very sharp images. It's good for compact DSOs, too, but I get about .5 degrees of unvignetted view and sometimes that feels a little restrictive. The f/15.5 would offer a slightly wider TFOV, which would be nice.

I cool the scope for at least an hour (usually two) before observing and haven't had much problem with unsteady images.

I've never had to goose the collimation so whatever TEC is doing to keep the system stable seems to be working.

Hope this helps,
John

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Hello Peter.

I also have to observe with glasses at most magnifications and I've spent a fair bit of time looking around for suitable eyepieces. What I've come up with is to use a 30-32mm Plossl or similar design (I use a 30mm Celestron Ultima) and 25mm and 18mm orthos (I use UO volcano tops) with a variety of barlows (I use 2x, 2.4x, and 2.8x). In my experience, all 3 of these eyepieces have good enough eye relief to use with glasses. Different combinations of these eyepieces and barlows give a range of magnifications that would be useful in an f/10 scope. The field of view is narrower than on some other eyepieces but I find myself enjoying the view anyway.

Hope this is useful,
John

Please humor me as a guy who doesn't do a lot of handy-work... What do I look or ask for if I walk into a plumbing/hardware place? Is 1.25" a standard diameter for PVC pipe? Is the larger-diameter portion a joint with another piece of 1.25" pipe with a clamp to secure the other pipe? Thanks...

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Hi Wes.

For planetary observing, I like to use lower magnifications than a lot of folks do. That qualification stated, some guidelines might be:

20x per inch of aperture would require a 34.3mm eyepiece, 25x per inch a 27mm eyepiece, and 30x per inch a 22.5mm eyepiece. You might consider 20mm, 25mm, and 32mm TVO plossls or some combination of the 20 - 35mm Ultimas or Ultrascopics. I've found the 25mm and 18mm University orthos to be very good eyepieces, too.

The "ultimate" eyepieces in this focal length range might be 20, 25, and 30mm Clave' Plossls, 25mm and 34mm Zeiss orthos, and the Pentax SMC 25mm Kellner and 18mm ortho. I have more experience with these "older" brands than the newer ones folks have mentioned (TMB, Baader, Burgess, etc.) so I can't comment on the newer eyepieces. But the oldies are reliable performers when you can find them.

The same lines of eyepieces have excellent representatives in the 10-20mm focal length range (Clave' 10, 12, 16, and 20mm, Zeiss 10, 12.5, and 16mm, Pentax 12 and 18mm).

Good luck in your quest!

John