22mm Vixen LVW

[iceman (Mike)]

I finally picked up my Vixen LVW 22mm from Astro-Optical last week, after winning it at the SPSP in March/April.

It had first light on Saturday night at Kulnura, and I had the chance to do a short comparison to Rod's 22mm Panoptic.

It wasn't a full in-depth review, so please take these comments as initial impressions only. Next new moon i'll endeavour to do a full review. The tests were done in my 10" f/5 newt.

The eyepiece is solid and well built, has a 1.25" barrel. It came with simple plastic end caps and in a cardboard box.

The eyepiece is very comfortable to use, with 20mm eye relief. I did not experience any blackouts or kidney beaning and eye positioning was not an issue.

The apparent field of view is quoted at 65°, and the stars are sharp mostly right to the edge. Only a little astigmatism was observed.

Some field curvature was evident in the outer 10% of the FOV, but not enough to be overly distracting.

The stars in the centre were sharp and bright, and the field had good contrast with a fairly dark background given the wide view and low power. I used the eyepiece to look at many galaxies, including over 10 in the Virgo Cluster, NGC5128, NGC4945, M83 and others. I also looked at Eta Carinae, Omega Centauri and the jewelbox. All the views were pleasing, especially Eta Carinae.


When compared to the 22mm Panoptic, initial impressions, both felt equally as comfortable to view with, having a similar AFOV (panoptic quoted at 68°) and similar eye relief (panoptic 15mm).

I found a similar level of field curvature to be evident in the Panoptic as the Vixen, however I found much more astigmatism to be evident in the Panoptic than in the Vixen.

Contrast and brightness seemed similar.

From the quick side-by-side I did, I know why I sold the 22mm Pano I owned for a week. I was just too distracted by the seagulls.

The Vixen isn't a perfect eyepiece, with some field curvature and a little coma but I would rate it higher than the 22mm Panoptic.

I would rate the 24mm Panoptic higher than both of these, as I had the chance to test RB's 24mm Panoptic at SPSP. It was sharper to the edge and had (from memory) no field curvature.

If I was going to buy an eyepiece at this focal length, I'd spend the extra on the 24mm Panoptic if you're critical of edge performance like I am.

If you're after something cheaper that still performs quite well, the Vixen LVW 22mm is a good buy (about AU$100 cheaper than the 24mm Pano).

I'll endeavour to do a more thorough review next month and after I've had the chance to observe with the eyepiece some more.

[matt]

I can now stop bugging you for a report, eh Mike?

[janoskiss (Steve H)]

Mike, when comparing the 19mm Pano and the 22mm LVW, I had the same impression regarding coma as you, but I'm not convinced that this is correct. Eyepieces don't fix coma, do they?

Re field curvature: The parabolic mirror itself has FC and only an eyepiece with matching FC will present a perfectly flat field to the observer. Such an eyepiece would show FC in other types of scopes though. OTOH, a "perfect" eyepiece with a perfectly flat focal plane would show the FC of the mirror in a Newtonian.

[square_peg114GT]

Originally Posted by iceman

....I found a similar level of field curvature to be evident in the Panoptic as the Vixen, however I found much more coma to be evident in the Panoptic than in the Vixen.....

I'm confused.

I thought that coma was an aberration inherent in parabolic mirrors and not (usually) in eyepieces. Do you mean astigmatism?

[iceman (Mike)]

Yes, Pegster. I did mean astigmatism (seagulls!).

Will amend my first post.

[davidpretorius]

thanks mike, you are a great guinea pig!

[ving (David)]

strike that one off my list....

thanks for the writeup mike

[ausastronomer (John Bambury)]

Originally Posted by janoskiss

I had the same impression regarding coma as you, but I'm not convinced that this is correct. Eyepieces don't fix coma, do they?

Steve,

Eyepieces can actually correct for coma.

Generally this occurs specifically with a given eyepiece design, a given eyepiece focal length in a given telescope design of known aperture and focal length. It does not generally happen generically. In other words you can't conclude that because a 7mm T6 Nagler corrects Coma in a 10"/F5 newt, that a 13mm Nagler T6 will correct Coma in a 6"/F4.5 newt. There have been attempts at producing "coma correcting eyepieces". University optics came out with a "Pretoria Design" in the mid 80's that was a coma corrector. How will did it work? Dunno never tried it, but try buying one now

I think you guys meant to use the term astigmatism, as opposed to Coma? Coma generally is not a major issue with an F5 Newtonian and only manifests in scopes faster than F4.5.

CS-John B

[square_peg114GT]

Originally Posted by ausastronomer

Steve,

Eyepieces can actually correct for coma.

Generally this occurs specifically with a given eyepiece design, a given eyepiece focal length in a given telescope design of known aperture and focal length.

That's a key point. An eyepiece designed to correct for coma in a particular mirror would introduce new problems when used in a refractor or an SCT.