Huygens Eyepiece?

Hi all....

Reviewing "Telescope Optics-evaluation and design" the section on eyepieces
shows plots and of course the simple Huygens looks absolutely
horrendous.....BUT.....when used on a high F ratio (F15) telescope AND allowing
the focus/field to be curved you get some VERY nice plots (better than a Nagler
at F5) instead.....and the Ramsden shows the same behaviour....

The problem IS is that you can only have a curved field if the focal length of
the eyepiece is long enough that your eye can refocus enough to accomodate the
curved field....

The authors indicate that a Huygens eyepiece can be used to good advantage if
the focal length is roughly a 100 mm or more....

Ive always dreamed of owning a LARGE off axis telescope (and yes I am very
familiar with the many designs)....and those designs are typically in the F20
to F30 range if you want a large one without too many mirrors, lenses or
non-spherical surfaces....

But the concept of having a scope that was limited to rather high
magnifications always bothered me...but then it occured to me that I could use
quality commercial eyepieces for the higher powers and one or two homemade
Huygens for the low power views.....of course a 100mm Huygen would have a
diameter of 4 inches....a 150mm six inches...and a 200mm eight inches! (Al
Nagler eat your heart out

My question here is....has anyone used a big huygen on a high f ratio scope and
how good was/wasnt it?

take care

Blll

Curious what the AFOVs of the Huygens in question might be?

Jon

Curious what the AFOVs of the Huygens in question might be?

Jon

Curious what the AFOVs of the Huygens in question might be?

Jon

IFFF you allow a curved focal plane (hence the requirement for using only long
focal lengths.....) AND using them on F15 or longer scopes....the AFOV can be a
wide or perhaps even a bit wider than plossls.....so 50 to 60 degrees...

take care

Blll

Curious what the AFOVs of the Huygens in question might be?

Jon

IFFF you allow a curved focal plane (hence the requirement for using only long
focal lengths.....) AND using them on F15 or longer scopes....the AFOV can be a
wide or perhaps even a bit wider than plossls.....so 50 to 60 degrees...

take care

Blll

I did up a set of 5 for my 200" refractor in the 3" diameter size. Focal
lengths ranged from 8" to 1 2/3" and they seem to work well. I don't notice
any distortion in the images even though the FOV is only 2/3 of a degree.
The AFOV is fairly decent at some 30 degrees or so for the longer focal
length to 50 degrees for the smaller ones. The AFOV sort of determines how
much aberrations there will be in the EP and generally about 40 degrees or
so is as much as you should expect unless you specifically set things up for
a bit less.
The Ramsden design is a bit better than the Huygens design and will be a bit
less of a problem with the shorter FL scopes of about F15 or so. At F45,
the Huygens design works quite well.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

I did up a set of 5 for my 200" refractor in the 3" diameter size. Focal
lengths ranged from 8" to 1 2/3" and they seem to work well. I don't notice
any distortion in the images even though the FOV is only 2/3 of a degree.
The AFOV is fairly decent at some 30 degrees or so for the longer focal
length to 50 degrees for the smaller ones. The AFOV sort of determines how
much aberrations there will be in the EP and generally about 40 degrees or
so is as much as you should expect unless you specifically set things up for
a bit less.
The Ramsden design is a bit better than the Huygens design and will be a bit
less of a problem with the shorter FL scopes of about F15 or so. At F45,
the Huygens design works quite well.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

I did up a set of 5 for my 200" refractor in the 3" diameter size. Focal
lengths ranged from 8" to 1 2/3" and they seem to work well. I don't notice
any distortion in the images even though the FOV is only 2/3 of a degree.

Hi Bob...

So made one of those LONGGGG single lens refractors huh? Pretty cool...got any
online pics of it? Ive been saying to myself for nearly 20 years now that Im
gonna build one of those babies.....sure would be cool to have one set up at
the local mall for astronomy day....how well does it perform? at what
apertures/f ratios does the color error from the single element lens cease to
be bothersome?

The AFOV is fairly decent at some 30 degrees or so for the longer focal
length to 50 degrees for the smaller ones.

So I take it your 8 inch focal length lens did NOT have an 8 inch diameter
field lens?

take care

Blll

I did up a set of 5 for my 200" refractor in the 3" diameter size. Focal
lengths ranged from 8" to 1 2/3" and they seem to work well. I don't notice
any distortion in the images even though the FOV is only 2/3 of a degree.

Hi Bob...

So made one of those LONGGGG single lens refractors huh? Pretty cool...got any
online pics of it? Ive been saying to myself for nearly 20 years now that Im
gonna build one of those babies.....sure would be cool to have one set up at
the local mall for astronomy day....how well does it perform? at what
apertures/f ratios does the color error from the single element lens cease to
be bothersome?

The AFOV is fairly decent at some 30 degrees or so for the longer focal
length to 50 degrees for the smaller ones.

So I take it your 8 inch focal length lens did NOT have an 8 inch diameter
field lens?

take care

Blll