Re: 2" eyepiece FOV not up to specs! (LONG)

David, appreciate the detailed outline of the method to *measure* the
apparent fov rather than simply calculate it.

I did have a question, however... you wrote the following:

"The formula AFOV = TFOV x
Magnification is an approximation *only* (typically, it can be from 5%
to as much as 10% off reality, although it can get a bit worse depending
on the eyepiece and the quality of the data available for it). "

Was wondering what you meant by the "quality of the data available for
it" Do you mean the advertised specs? In which, that's my point
exactly. Did you mean the measured true field of view? The method was
the same for each of the eyepieces, so I presume the error bar is about
the same, too.

If the old formula of AFOV/Mag = TFOV yields results to within 5% to
10%, then a couple of these eyepieces' advertised specs are off.

As you wrote at the end, "What you get will be the apparent field of the
eyepiece and not just some figure supplied by the manufacturer which may
or may not be accurate." That's exactly where I was heading, namely
that "some figure supplied by the manufacturer" or stated in advertising
copy is more advertising hype than reality.

Thanks for your input. It'd be great if someone would do the bench
measurements on the 1rpd and the 26mm GSO.

This can
> very probably explain the results you are getting:
>
> 39mm Rini: -7.8% off
> 32mm Burgess: -9.7% off
> 30mm RPD: -12.5% off
> 26mm GTO/GSO: -17.1% off
>

Larry Stedman
Vestal
.