Wider absolute field in a 11 SCT

[kirkster501]

Hi guys,

I know SCT are not known for wide field and I bought it fully knowing that (and i love the scope by the way ). In a few months i will buy a wide field refractor too.

However, until that point would be interested what EP would give me the maximum absolute field in the 11 incher? 41mm Pan maybe? Anything wider than that?

Cheers, Steve

[John]

The 42mm Vixen NLVW has the largest field stop of any 2" eyepiece I believe. The AFoV is specced at 72 degrees. I think you need to move to a 3" eyepiece to get wider than that !

[cs1cjc]

But there are other less expensive wide angle eyepieces around 40mm focal length including the Aero.

[faulksy]

the williams optics swan is 72 degrees and a good price from flow

[kirkster501]

the williams optics swan is 72 degrees and a good price from flow

Will check into it. Thanks.

Steve

[John]

the williams optics swan is 72 degrees and a good price from flow

The 40mm SWAN is specced as a 70 degree eyepiece. It's only 2 degrees but the OP did ask "....what EP would give me the maximum absolute field..."

There are many lower cost options than the Vixen NLVW though. I didn't realise that cost was also a criteria - the OP did mention the 41mm Panoptic in his original post which is not exactly a low cost option

[kirkster501]

Not concerned about the cost. If its a nice piece of kit and I'll use it I'd buy it.

I want the maximum absolute field so, for instance, try and get the whole Pleidaes in the view (OK that might be pushing it but you get my meaning )

The PAN 35 fits the whole moon. So could I get ay wider?

Thanks, Steve

[Paul-F]

FWIW I have shortlisted the 42mm Vixen NLVW as I want the widest fov in mine at an acceptable cost (that's a list of 1!) ..... I currently have a 38mm 70deg afov 2" ep but it is a bit bright I feel unless its really dark so good contrast is on my list of 'features' and it shows me comets towards the edge of the view. The ethos, which I recently bought has spoilt me as the view in that has surpassed all that I have seen previously in my scope which I put down to afov & contrast.

[Plantins]

You have the 35mm Pan so know what a great eyepiece it is. The 41mm Pan will give you abit extra fov and again is a great eyepiece.

In a large SCT I haven't personally found a low power eyepiece that I prefer over the 41mm & 35mm Pans.

[Mr Spock]

I have the 42mm LVW and a C9.25. The Pleiades just fits in the field of view, so you will be a lot tighter with a C11.

The 42mm LVW is an incredible easy eyepiece to use. Really comfortable, sharp, and just like looking through an open window.

[cs1cjc]

Some field stops - the NLVW wins by a nose:

35mm Panoptic 38.7mm (Tele Vue)

31mm Nagler 42.0mm (Tele Vue)

36mm Hyperion 44.0mm (David Knisely)

38mm Adler Skarp 45.2mm (my direct measurement)

40mm Aero 45.7mm (TMB Paragon figure)

41mm Panoptic 46.0mm (Tele Vue)

40mm Pentax XW 46.5mm (Pentax)

42mm Vixen NLVW 47mm (from njopsahl.no - Vixen LVW 42mm 2")

[Don Pensack]

The widest possible field of view can be calculated from the following formula:

TF=(FS/TFL) * 57.3

TF=true field

FS=field stop in eyepiece

TFL=telescope focal length.

So, the largest field stop in a 2" eyepiece is approximately 46mm.

The focal length of an 11" Celestron is 2794mm.

Ergo, the widest possible field of view is 0.94 degrees.

That's it.

Now, the question is how well the edge of that field will be illuminated.

The standard visual back piece on the C11 has a 3.25" thread and reduces that thread to a 2" O.D. "SCT" threaded external thread which has a 1.6" I.D.

That reduces the illumination at the edge of the field significantly.

You can convert the rear 3.25" adapter to a Baader Click-lock 2" or use an AstroPhysics 3.25" SCT back that instead reduce to a 2" hole instead of a 2" thread.

On either of those two rear adapters, you can use a 2" diagonal by directly inserting the diagonal in the back of the scope.

then, it's a matter of using a 2" diagonal that has a large clear aperture and uses no internal stops to reduce the clear diameter through the diagonal.

I believe that most of the brands that machine the entire diagonal out of one piece have the largest clear apertures all the way through.

But, though that will increase the amount of illumination at the edge of the field, that will not increase the maximum field size over the just under one degree field the instrument is capable of.