Wide field dreaming

[Camelopardalis (Dunk)]

Folks, tis the season and all, and what better way to idle away my commute than to think of something a bit different from my usual...a wide field scope

There'll be no such thing coming down the chimney this year, and this is all hypothetical for me as I'm not in a position to be buying anything right now, but I was entertained to think of the possibilities, and appreciate any suggestions... the goal being a scope with a nice wide field of view, decent image quality, sufficient light grasp to show plenty of detail in the globs and nebulae we're blessed with, but without costing the Earth...

• 100 / 110 / 120mm ED doublet... start getting a little costly and interesting to mount in the longer focal lengths (Orion's new f/6 110 Eon looks interesting, at a price )
  
• 8" Dob... inexpensive but all the mainstream ones seem to be f/6 and I can get the reducer for my C8 and drop it down to around f/6.3, so not inspired by this option
  
• 8" newt... imaging newts are available in f/5 and even f/4 for a bit more than the Dob, but any disadvantages? I have a GEM that should carry one, but would prefer alt az

Anything else obvious I'm missing? Besides a bigger refractor or smaller newt/Dob just dreaming about options for a dedicated, limited use scope, for the really big objects and scooting along the Milky Way, not one scope to rule them all

[skysurfer]

You want to capture the (small) constellation Camelopardalis in one field ? As it is rather close to the South Celestial Pole no tracking needed anyway and visible anytime, anywhere in AU... LOL !

But serious:

Well, Short Dobsons / Newtons (f/5 or shorter) have a disadvantage of collimation duty, but with 200mm this is done within a minute. There are enough f/4 or f/5 Newton for under $800.
Unlike the ED/APOs of 100-120mm which sell for at least the double.

BUT: a refractor has usually better images and requires virtually no maintenance. And an f/6 120mm has a larger true field than a f/6 200mm.
And modern cameras have no problems with using high ASA values such as 1600 or more so aperture is for AP less an issue than visual.

And, what about a 2nd hand telephoto lens ? I frequently a Canon 1.8/85mm for AP with very nice results ! I pictured the entire Southern Cross more times in one field and stars till mag +12.

[Camelopardalis (Dunk)]

Thanks skysurfer... the maintenance thing can't be underrated, but I can't reconcile the probable light grasp difference between even a 120 and an 8" newt/Dob.

I'm going to try my ol' faithful C8 with a reducer next time I get out, but the focal length/true field is still much less than I want ideally whereas a 120 f/6 could give a nice big field, about 4x greater off the top of my head. Hmm.

[Wavytone]

Originally Posted by Camelopardalis

try my ol' faithful C8 with a reducer next time I get out

Dunk using a compressor on a C8 for visual use is a bit pointless... the central baffle and aperture in the back of the mirror cell restrict the maximum field of view to about 1.3 degrees. You might as well use a big eyepiece - an ultra-wide 40-50mm will show everything there is to be had in the vignetted field of view just as well as a tele compressor combined with a somewhat shorter eyepiece, and it will do it very well, whereas the compressor and a short eyepiece could easily end up being not so sharp.

To get MORE sky you need a shorter refractor like the ones you identified and it is for precisely the same reason I have a 102mm f/7 ED refractor, which fills a big 2" eyepiece giving a maximum field of view around 3.8 degrees which the C8 cannot come close to, no matter what you do to it.

I'll also add that with a similar setup (the refractor + my 180mm f/15 Maksutov) the refractor has become just a very big finderscope and to be honest i don't use it nearly as much as I expected; if there's a choice the Mak always goes on the mount but not always the refractor. FWIW you're welcome to try my refractor anytime...

However an 8" f/5 dob is a very different beastie and more likely to be useful especially if the optics are excellent. On and off over the past 2 years I have contemplated a larger dob, but refrained because I simply don't get out often enough to justify it.

[MortonH]

My Skywatcher Black Diamond 200mm f/5 Newt cost me $280 used. It's the one I take to Katoomba and is my largest scope. My mount is a DSV-3 alt-az and is more than adequate for the load.

[pmrid (Peter)]

A Celestron SCT with a Farstar (or whatever the Starizona equivalent is these days) fitted - gets you plenty of aperture and a F ration down near 2 somewhere. If that doesn't light your Christmas candles, nothing will.
Peter

[Camelopardalis (Dunk)]

Originally Posted by Wavytone

Dunk using a compressor on a C8 for visual use is a bit pointless... the central baffle and aperture in the back of the mirror cell restrict the maximum field of view to about 1.3 degrees. You might as well use a big eyepiece - an ultra-wide 40-50mm will show everything there is to be had in the vignetted field of view just as well as a tele compressor combined with a somewhat shorter eyepiece, and it will do it very well, whereas the compressor and a short eyepiece could easily end up being not so sharp.

To get MORE sky you need a shorter refractor like the ones you identified and it is for precisely the same reason I have a 102mm f/7 ED refractor, which fills a big 2" eyepiece giving a maximum field of view around 3.8 degrees which the C8 cannot come close to, no matter what you do to it.

I'll also add that with a similar setup (the refractor + my 180mm f/15 Maksutov) the refractor has become just a very big finderscope and to be honest i don't use it nearly as much as I expected; if there's a choice the Mak always goes on the mount but not always the refractor. FWIW you're welcome to try my refractor anytime...

However an 8" f/5 dob is a very different beastie and more likely to be useful especially if the optics are excellent. On and off over the past 2 years I have contemplated a larger dob, but refrained because I simply don't get out often enough to justify it.

Thanks, I'd love a peek I usually use my 40mm with the C8 and last time was getting kicks from using it with the C11 + reducer, still only about 1.3-1.4 degrees, but the views of the Orion Nebula didn't disappoint.

But thinking about it even 8" f/5 is still a lot of focal length...8" f/3 would be much more appealing I guess I was wondering if I was fundamentally missing something...just chasing that unicorn with the scope on it's back.

For those long winter nights, a bigger Dob has gone through my mind more than once...

[Camelopardalis (Dunk)]

Originally Posted by MortonH

My Skywatcher Black Diamond 200mm f/5 Newt cost me $280 used. It's the one I take to Katoomba and is my largest scope. My mount is a DSV-3 alt-az and is more than adequate for the load.

Thanks Morton, I've just looked up the mount and it looks interesting, they even claim it will hold 28lb of SCT, which coincidentally is the weight if the 11

[Camelopardalis (Dunk)]

Originally Posted by pmrid

A Celestron SCT with a Farstar (or whatever the Starizona equivalent is these days) fitted - gets you plenty of aperture and a F ration down near 2 somewhere. If that doesn't light your Christmas candles, nothing will.
Peter

Thanks Peter - I'm pretty intrigued by the possibilities of the Starizona kit with a small SCT, so it's on the cards! Just a matter of when Still in awe of all the shiny new visual objects I've gained this year!