ORION OPTICS (UK) OMC200 - Eyepeices?

[Dogsjag]

I have recently acquired the above scope, does anyone have experience of what eyepieces suite its long focal length and narrow field of view?

[cdd2455]

Congratulations on your new scope - I'm sure it's a lovely piece of kit.

I have an OMC 140 and binoview with 32mm Tak Orthos or 40mm Vixen NLV's.

For interest, I ran the Tele Vue eyepiece calculator against your scope and a good contender might  be the Panoptic 41mm as I think your OMC 200 can take a 2inch diagonal and for the 41 Pan it will give x 97 magnification, 0.66 degrees true field and 2.1mm exit pupil.

I hope you have a very solid mount for your OMC200 as my OMC140 is undermounted, something I'll soon address.

Good luck and Best Regards

Carl

 

 

[alan potts]

I don't know if the inside diameters are the same on your new scope as on my 180mm SW Mak but the 41mm Panoptic which I have vignettes on the this scope when used with a diagonal.

However I found the Meade 40mm SWA from the series 5000 range did not. Persoanally I never use above the 35mm Panoptic which is my low power so to speak. I have Televue eyepieces for other reasons and really they are not necessary on an F20 scope, though they are nice to own, I would say ExSc ranges in either 68 or 82 degree would be perfectly good enough and perform to a standard either as good or very close.

[Ruud]

Hi Dogsjag,

wow, it's an f/20, a real planetary / lunar / double star specialist with a focal length of 4000mm! The description says there are two versions. Standard it comes with a 1.25" focuser, but a 2" version is also available.

Considering the exit pupil alone, you can choose eyepieces of 10mm focal length and up, giving exit pupils of 0.5mm and up, and magnifications of 400x and down.

To stay on the safe side (atmospheric seeing), I'd stick with eyepieces of 20mm and up, giving exit pupils of 1mm and up, and magnifications of 200x and down. For nights with a very stable atmosphere I'd use a good 2x Barlow.

If you have a 1.25" focuser you'll get the widest possible views from 52° 32mm, 68° 24mm or  82° 16mm eyepieces. All will give about the same true field of view. These are the longest focal length eyepieces for the various apparent field of views that will fit in a 1.25" focuser. The true field will be about 0.36°.

If you have a 2" focuser, the widest possible views come from 50° 55mm, 68° 41mm or 82° 31mm eyepieces. These will give a true field of around 0.66°.

Here are three useful formulas

                focal length telescope
Magnification = -----------------------
                focal length eyepiece

maximum is 400x for your telescope, the atmosphere usually allows up to 200x or less, alas

                   Aperture of telescope
Exit pupil (mm) = ----------------------  
                      Magnification

below 0.5mm you'll get 'empty' magnification (no more detail is revealed)

                     Apparent field of view of eyepiece
True field of view = ----------------------------------
                              Magnification

I'd really like to see Jupiter through your telescope on a good night!

[Dogsjag]

Hi Many thanks for the info and an explanation of the technicalities much appreciated! my particular scope is around 10 years old and was built by a group of enthusiasts called the Bolton group who also carried out a number of modifications over and above the Orion Optics uk standard kit.

Still getting to grips with it, and after my Celestron 8" cpc finding the narrow field of view and presently no tracking or goto a bit challenging.

Next operation is to find a suitable mount, looking at the SW az eq5 gt or 6 gt or even the new Ioptron az pro, as I'm not very technical and only need Alt az.

Have had some fantastic views of the moon so far using a Baader 8-24 zoom.

cheers and clear skies 

[Stu]

I used to own one of these. Good advice already. I would say don't fight the narrow field of view, just accept the scope for its strengths which are high power views for lunar and planetary work, plus small DSOs like globs.

I used a variety of eyepieces, including a 31mm Nagler which still have something like x129 with only a 0.6 ish degree field of view!

I ended up using a set of TV plossls, down to 11mm but mainly longer than this and they worked very well.