How big is the field stop in the eyepiece used for your testing?

----- Original Message -----
Sent: Saturday, February 24, 2001 9:24 AM
Subject: Re: [M]: New back plate for LX scopes


> I don't want to burst anyone's bubble, but before you run out and buy one
of
> these adapters, be aware of what you'll gain. I built myself the very
> adapter being sold by Petersen Engineering for my 10" LX200 f10. Mine has
> two brass thumb screw rather then three nylon, and was just about to put
it
> on the market, even had a web page set up. But before I announced it's
> availability, I felt I had better do some tests on what it could really do
> for you. I felt that the only quantitative measurement that I could do
was
> True Field of View. I mounted a standard 2" Meade diagonal, that screws
> onto the Schmidt thread and using a 40mm 70 degree AFOV eyepiece, I
measured
> the True field of view. I then put in the new 2" back plate and a TeleVue
> diagonal, and using the same eyepiece measured the field of view again. I
> ran the tests three times and came up with the same result, 1.7 minutes of
> arc difference. What this means is that the cone of light coming down
from
> the secondary mirror, is only being cutoff by tinniest of margins by the
> Schmidt adapter. To say the least I was depressed. I had high hopes of
> selling these adapters, but didn't think people would pay $60.00 (my
asking
> price) for such a marginal improvement, so I dropped my plans for
marketing
> this adapter. The other benefits that Petersen claims are real, it is
> stronger and is shorter then the Schmidt to 2" adapter. It does give you
a
> tiny bit more light, just don't expect breathtaking differences. Just
> thought you should know.
>
> Scott Baker
> San Diego Astronomy Association
>
>

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