Rich Field Telescope.

[jetstream]

Lockwood advocate a 300mm mirror as a reasonable size for a RTF. Using this and with sec to focal plane distance of 190mm a 73mm secondary gives a great 24% central obstruction.

Or maybe one of these https://www.loptics.com/articles/okietex2009/okietex2009.html

One thing to note: being able to use Ethos class eyepiece at the "right" exit pupil really ups the views with a RFT...

M24, got to say again- this is a must see and study...

[vlaiv]

9 hours ago, Deadlake said:

A newt would work, question around size of central obstruction

good point.

[Deadlake]

8 hours ago, jetstream said:

Lockwood advocate a 300mm mirror as a reasonable size for a RTF. Using this and with sec to focal plane distance of 190mm a 73mm secondary gives a great 24% central obstruction.

Or maybe one of these https://www.loptics.com/articles/okietex2009/okietex2009.html

One thing to note: being able to use Ethos class eyepiece at the "right" exit pupil really ups the views with a RFT...

M24, got to say again- this is a must see and study...

What about diagonal and EP.

3” explorer scientific and 30 mm EP versus greater then 44 mm aperture 2” and 41 m panopticon or 40mm paragon. How would image size the scope could illuminate effect this?

[jetstream]

5 hours ago, Deadlake said:

What about diagonal and EP.

3” explorer scientific and 30 mm EP versus greater then 44 mm aperture 2” and 41 m panopticon or 40mm paragon. How would image size the scope could illuminate effect this?

Don't know what you mean

[Deadlake]

45 minutes ago, jetstream said:

Don't know what you mean

The true field of view that will be seen through a telescope depends on the focal length of the telescope and the aperture of the field stop in the eyepiece.  A 2-inch barrel size eyepiece can have a field stop diameter of up to ~45 mm.

The aperture of the field stop will need to be illuminated?

If so if the maximum Illumination is 44 mm not much point going for a diagonal larger then the illumination circle, or it does not work like that?

[jetstream]

1 minute ago, Deadlake said:

The true field of view that will be seen through a telescope depends on the focal length of the telescope and the aperture of the field stop in the eyepiece.  A 2-inch barrel size eyepiece can have a field stop diameter of up to ~45 mm.

The aperture of the field stop will need to be illuminated?

If so if the maximum Illumination is 44 mm not much point going for a diagonal larger then the illumination circle, or it does not work like that?

Ok I see- you are using a T2 diag? then yes if the dia is smaller than the FS things happen , vignetting reduced TFOV I think.

[Deadlake]

2 minutes ago, jetstream said:

Ok I see- you are using a T2 diag? then yes if the dia is smaller than the FS things happen , vignetting reduced TFOV I think.

43 mm aperture in 2” diagonal ( I do have a T2 but no use for an EP where field stop > 33 mm).

Question is no point in larger diagonal aperture if scope can only illuminate 44 mm?

[jetstream]

1 minute ago, Deadlake said:

43 mm aperture in 2” diagonal ( I do have a T2 but no use for an EP where field stop > 33 mm).

Question is no point in larger diagonal aperture if scope can only illuminate 44 mm?

Maybe @vlaiv or @Merlin66 can answer. Solar imagers are pros at figuring this kind of thing out.

[John]

Going a bit too far perhaps ?

The scope is 67mm Borg. The eyepiece and diagonal are 3 inch format:

[Deadlake]

1 hour ago, John said:

Going a bit too far perhaps ?

The scope is 67mm Borg. The eyepiece and diagonal are 3 inch format:

Maybe for some in really dark skies... 😀

[jetstream]

20 minutes ago, Deadlake said:

Maybe for some in really dark skies... 

Nah, just need the eyes...

[Merlin66]

Back to basics....

Amateur Telescope Making, Volume 2, p623-647

The definition of the RTF = Richest-Field Telescope (note - not just a rich field telescope)

to quote: "....every aperture could be made "a" RFT of that aperture, for a given observer and that there was one of all these which, in connection with the curve of star density against magnitude of stars, was uniquely "the" RFT for the observer, in respect to the maximum countable number of stars per apparent square degree"

Note there's no real mention of field of view, just the maximum stars per square degree.

Based on the subsequent tables (p624/5)

a "real" RTF of 10" aperture at x33.9 would give a FOV approx 1.5 degree and show 306,000 stars per square degree down to 14 mag.

These figures were based on the available eyepieces at the time, AFOV 40 degree, and a rich galactic star field being observed.

It is also based on a dark adapted eye accepting a maximum of 7.5mm exit pupil.

EDIT:

The Borg 67mm is close to 2.5" aperture....

The ATM table (p624) gives:

Limiting magnitude 11

Magnification x8.5

Total stars per sq. degree 25,400

 

 

Edited February 14, 2021 by Merlin66

[Merlin]

Years ago, I read somewhere ( possibly in the classic three volume, American, “Amateur Astronomical Telescope-Making”, that a short-focus 75mm aperture refractor captures more stars in its field than any other aperture. I can’t recall what the focal length should be.