Fixed eyepieces for Celestron Regal 65 ED (1 Viewer)

[PedroP]

Hello to birdforum spektiv experst,
I am new here and asking for suggestions for my new Celestron Regal 65 fixed eyepieces. I observing without glasses however I need about 1 dioptry for reading the text.

After Regal purchase, I changed included Celestron zoom by Baader Hyperion zoom and become happy with the results but still for some specific situations I want to complement this combo with fixed eyepieces (EP). The first need is to get something wider for low magnification to make easier searching for birds (but also stars in the night sky). After reading some discussion here I decided for wide Explore Scientific EP probably 16 mm 68 deg. (FOV 3.18 deg., ER 11.9mm, Mag. 24x) or some of Exp.Sci. 20 mm EP with 19.2x magnification. There are two versions: the first: 68 deg., 3.53 FOV, 15.3 mm ER or the second LER version: 62 deg., 3.22 FOV, 14.8 mm ER). For the 20mm versions I have little doubts considering vignetting because in some threats here is referred that Exp.Sci, 24 mm version has serious problems with vignetting on Regals. Any suggestion or experience with these eyepieces on Regals?

The second need is to improve picture clarity (contrast) and get more details for longer distances (waterfowl on lakes or planets at the nightsky) because Baader zoom becomes a little dim at highest magnifications 48x (FOV 1.41 deg.). Here I ended my search also at Explore Scientific wide-angle 82 deg. eyepieces 6.7 mm (FOV 1.43, magn. 57.5, ER 15.7) or 8.8 mm version (FOV 1.87, magn. 43.75, ER 15.6 ). The prices and weights of both pieces are comparable and also LER versions of both EP with ca 1 mm longer ER exist (other parameters very similar). What is your suggestion here?

Many thanks for any comments based on your experience.

Petr

 

[Tringa45]

Hi Petr,

First of all, welcome to Birdforum.
I have no experience of the Celestron Regal, but see that it is nitrogen-filled so it will have a sealing "window" in the body beneath the eyepiece.
You can measure it by progresively cutting down a strip of paper until it matches the diameter of the window. Eyepieces with field stop diameters (often quoted in the eyepiece specifications) larger than this would vignette.
The loss of brightness and contrast you experience at 48x is not the fault of the Baader zoom but is due to the small 1,35 mm exit pupil at this magnification. Brightness and contrast with shorter focal length eyepieces will suffer even more.

John

 

[PedroP]

Dear John,
thanks for the explanations and suggestions. I tried to measure the first accessible window of scope and get 28 mm however after that first window is an unaccessible smaller hole which diameter I assessed to ca 14 mm. According to the experience of Regal 65 users on Birdforum, there is no vignetting for eyepieces like Baader Hyperion 17 (68 deg) mm with field stop diameter 20.3 mm while testing of Pentax WX 20 with stop diameter 24 mm shows strong vignetting. Controversially another review of Regal 65 from Cloudynights refers to slight vignetting for 16 mm EP (68 deg) - (probably Exp. Scien. EP) with field stop diameter 18.2 mm.

These numbers are a little confusing for me and I started to think about 20 mm Expl.Scien. EP (62 deg) with field stop diameter 20.9 mm (only slightly over field stop from Hyperion17 which works well). I prefer that ES 20 mm over Hyperion 17 because of 7% wider FOV, the half weight of Baader EP, and the remarkably lower price. Any experience with these EP here?

Thanks for advice

Petr

 

[Tringa45]

Petr,

That 28 mm window is larger than on both of my birding scopes but perhaps there is some other obstruction in the optical path of the Regal 65.
There is a limit to the true FoV you can attain, so perhaps it would be best to try and attain the largest exit pupil with an acceptable AFoV.
From what you say the ES 20 might fit the bill and if it does vignette a little, it would probably not be very noticeable, but would it offer that much more than the 20 mm and 24 mm settings on the Baader zoom?

John

 

[PedroP]

Dear John,
you are right that FoV is limited probably somewhere below the first scope glass. Considering the 20 mm fix eyepiece enlargement of FoV is ca 7% larger than for 24 mm zoom and ca 17% than comparable 20 mm Baader zoom view. It is not so much but I also expect a little sharper and brighter picture compare to Baader zoom. I never use fixed EP on my Celestron but some users here reported much better results with fixed EP (easier optical composition than in zoom etc.). So maybe my expectation considering picture improvement is too high? I am also thinking that in worse observing conditions could fix EP improve bird recognition and identification?

What is your experience?

Petr

 

[Tringa45]

Petr,

Simple fixed focal length eyepieces with three or four elements (Orthos, Plössls, RKEs) allegedly show better contrast when viewing the Moon or Jupiter at high magnifications, but only with an excellent telescope under excellent seeing conditions.
With a birding scope at moderate magnifications I don't think you would detect any difference in central sharpness and contrast between eyepieces of similar focal length. The scope's objective is much more important.
For difficult identifications, magnification is the deciding factor up to a point. The limit might be reached where you experience heat haze or where the loss of brightness of the small exit pupil negates any advantages of higher magnification.

John