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first impressions Orion Mini Giant 15x63

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#1 Mark9473

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Posted 04 September 2008 - 04:03 PM

Picked up a pair of the 15x63 today, and here are my first impressions, from 3 minutes looking through them outside the store (under heavily overcast skies) and as many minutes peering at a few stars literally through haze and clouds:

- tiny compared to what I expected, these look just like 10x50s;
- surprisingly light, at 1168g I wouldn't even want them to be any lighter;
- prism housing looks small;
- a small fraction of the exit pupils is cut off by the prisms;
- call me old-fashioned but no rubber-covered binocular has yet looked very good to me (with the exception of Leica and Swarovski bins...);
- objective caps fit well, eyepiece caps are too loose and fall off easily;
- holds and handles well, nicely balanced (just a touch front heavy perhaps);
- nothing too ugly happens when looking at a bright streetlight after dark; I expect these will do nicely on the Moon;
- at 3.7° TFOV (55° AFOV) specified, they are certainly not wide-angle (my 20x80 have a confirmed 3.5°);
- on the stars, center sharpness (hand-held) appears quite decent and holds up to about 80% to the edge;
- at the very edge no ugly seagulls but instead a gentle unsharpness that can virtually completely be focussed out (i.e. is due to field curvature);
- was pleased to spot M57 in such poor skies.

That's all for now; the viewing opportunity was just too short and poor to do more, and looking at the weather forecast it may be a while.

#2 EdZ

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Posted 04 September 2008 - 04:16 PM

- at the very edge no ugly seagulls but instead a gentle unsharpness that can virtually completely be focussed out (i.e. is due to field curvature);



yes, field curvature is the only aberration that can be focused out.

edz

#3 Mark9473

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Posted 05 September 2008 - 04:33 PM

A few more tidbits from 2nd light under better skies:

- FOV spans from Vega to delta-2 Lyrae (my CdC is down so can't tell you how far that is);
- collimation is pretty good; throwing the right barrel completely out of focus shows a bright star (seen through the left side) close to the center of the blob seen through the right side;
- center sharpness: brighter stars such as Deneb and Altair focus to tight specks; there's nothing there that I don't suspect comes from my eyes;
- edge sharpness is best at bottom and left side, followed by the top side; right side is least good;
- highest amount of unsharpness is not at the very edge but about half a degree inward;
- there is noticeable geometric distortion - looks as if in the outer 1/3rd or so of the FOV the magnification is lower.

So far these 15x63 live up to my expectations: performance close to higher magnification mounted binoculars in a package much like most hand-held binoculars. I'm actually surprised at how easy I find it to hold them steady (when seated) - though this is certainly a point where YMMV!

#4 Mark9473

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Posted 06 September 2008 - 06:35 AM

Some more:

- coatings are purple on the objective end, green on the eyepiece side. The green ones reflect more light than the purple ones;
- viewing a dark object against a bright sky, chromatic aberration appears well controlled;
- light transmission seems on par with my 8,5x44.

#5 Mark9473

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Posted 16 September 2008 - 03:38 PM

Had an opportunity to watch the Full Moon yesterday. This is IMHO the easiest test for field sharpness in a pair of binoculars:
focus on the Moon in the center of the FOV, then move it towards the edge and note when it becomes soft (as if out of focus).

In this way I determined that the sharp area of the FOV is the full FOV minus 3/4°. This test also quite easily confirmed the asymmetry in the location of the sharp zone as noted earlier.

The Full Moon also quite stunningly illustrates the geometric distortion present in this binocular: at the edge the Moon is very much flattened, by about 50%.

Finally, I noticed - like I had on the stars a few times - that when I check for edge sharpness (especially towards the bottom, edge) about half the time there doesn't seem to be any unsharpness at all. I take it that in those instances my eyes fully compensate the field curvature and that virtually no other aberrations are present.

This seems to be a binocular in which some rather peculiar design choices were made, but which overall seem to work out well for astronomy.

#6 EdZ

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Posted 16 September 2008 - 03:44 PM

Finally, I noticed - like I had on the stars a few times - that when I check for edge sharpness (especially towards the bottom, edge) about half the time there doesn't seem to be any unsharpness at all.



I've seen unsymetrical field sharpness in many binoculars. I suggest you mount these up-side-down and I suspect you will find that what previously appeared sharp all the way to the bottom will now show sharp all the way to the top. I doubt you will find that the unsymetry is due to eye compensation.

Unsymetrical field sharpness I've found is generally associated with unsymetrical beam transfer. Somewhere in the optical train elements are slightly tilted (possibly the objectives) and the tilt is compensated for somewhere else, (most likely at the prisms).

edz

#7 Mark9473

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Posted 16 September 2008 - 03:45 PM

That was not what I was saying, EdZ.






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