100 degree "bargain" eyepieces

[WayBig]

I was fortunate to be given the opportunity recently to test drive 2, ahem, ’bargain’ 100 degree eyepieces, in 16mm and 9mm focal lengths, interested to see how the cheapest access to the 100 degree world perform. I believe these are produced by Astro Tech, a link is here 2" Eyepieces

And these ones marketed by Zhummell look remarkably similar

Zhumell Z100 16mm Eyepiece with 100 Degree Apparent Field of View - Telescope Eyepieces at Telescopes

To set expectations, I didn’t go into this expecting them to rival anything with green writing on, instead I think they are designed to offer the 100 degree experience to a new market. At this price point, I did not expect perfect edge correction in a fast scope, and I only own fast scopes; and as expected, the 16mm showed more off axis distortion than the equivalent field in my 14mm ES 82degree eyepiece. It also required about 1/8 turn on the focuser to get the very edge into best focus. Though to its credit, the huge field of view and large aperture to look through meant it wasn’t an unpleasant eyepiece to use, and I’d be interested to see how it performs in a scope of f6 or slower, because if, as would be expected, the view is better at the edge, then this could be a very good eyepiece

The 9mm, however, surprised and impressed with sharp edge to edge views across the huge field. Eye placement is critical with this eyepiece, as it easily blacks out if your eye moves off centre so it takes a bit of getting used to, but once you do it offers lovely views.

Whether they are “worth” the extra above the cost of popular 82 degree eyepieces is a decision only you can make, but for me, the 9mm is a strong contender, and dependent on your scope, 16mm could be too.

I am going to have difficulty handing the 9mm back and going back to ‘only’ 82 degrees. I had been warned that the 100 degree experience is addictive!

Unboxing

I was interested to see how they cram such a huge field into a relatively small price, where have the cutbacks and compromises been made? One area of is the packaging, it’s certainly functional, but in no way luxury. So you get a box, inside which is a plastic bag, then a lot of bubble wrap followed by a bolt case padded with foam, then another plastic bag and then the eyepiece. I don’t have a problem with this, I only open the box once and then the eyepiece is moved to my eyepiece case.

Ergonomics

The eye pieces again look functional. Both are light for 2 inch large field eyepieces, weighing in at 425g for the 9mm and 420g for the 16mm and did not cause any problems with balance in my dob. They have soft rubber grip and a semi-soft fold down rubber eye guard. They also have a screw off 1.25 / 2 inch adaptor so will fit both focusers. In practice the fold up eye guard is of little use. When it is unfolded it vignettes the view to an unacceptable extent, enabling only around a third of the field to be seen. With the eye guard folded down, the whole field can be seen with slight movement of the eye. The rubber is semi-soft, and there is a huge aperture to look through, similar to a Skywatcher Aero or TMB Paragon, that makes for very comfortable viewing.

Because of the 9mms tendency to blackout if your eye is not in the right place, I wouldn’t expect it to perform well in daylight (though I did not test it then), and that it would also be a drawback for shared viewing sessions if people were not used to the criticality of eye positioning.

The test conditions

I tried the eyepieces on one evening (there haven’t been that many clear “non-school” nights, and I do have to give them back at some point) in a Skywatcher Flextube Auto 250. Which, at F4.7, should provide a good test of how well corrected they are. I was interested to see how they compare to my Explore Scientific 82 degree nitrogen purged eyepieces, which I hold in slightly higher regard than Meade 5000 UWAs. I have the 14mm which would give a good comparison to the 14mm and 6.7mm which I’ll have to compare to the 9mm.

Performance in the field

I started on M71, a fairly faint globular cluster. The 16mm framed it beautifully in a field of stars, though the sharpness dropping off rapidly off axis. When increasing the magnification, I found my ES 6.7 showed a darker background and allowed more star s to be resolved than the 9mm 100, however this may have been due to the increased magnification

Up to the Dumbell Nebula, the 100s gave comparable contrast on this to my ESs. I found that when studying a single object, the additional field isn’t as important, but when locating an object it’s a bigger benefit.

On next to the Andromeda Galaxy, and more specifically M110, it’s fainter companion galaxy. I find that from my garden, this galaxy is on the edge of of direct vision so I was interested to see how they performed on this. Both the 100s did not disappoint, matching the contrast i get in my ESs giving hints of the elongated shape of the galaxy.

Finally I wanted to see how they performed splitting a double, so I headed for Achird in Cassiopeia. The 16mm was able to split it up to about 75% of the way out, after that it quite quickly merged into one. At the edge of the field even refocusing didn’t allow the two stars to be distinguished. The 9mm gave a nice clean split all the way to the edge of the field. In both the eyepieces, the primary was a nice yellow colour, and the secondary slightly less yellow.

Summary

To summarise a way too long report, I love the wide aperture to look through and the comfortable viewing of both of these eyepieces. On returning to my ESs I had the impression of looking through a small hole down a long tunnel...and that’s an 82 degree eyepiece!

Would I buy them?

For a fast scope I wouldn’t buy the 16mm, although it’s very nice to use, If I was to spend £199 on any eyepiece I’d want it sharper. But In a slower scope, I’d expect it to be very tempting.

The 9mm is worth considering. Once used to the eye position, it gave lovely sharp views across the field. Of course the main drawback with both of these is that it could trigger an upgrade to wide field throughout your whole eyepiece case, so addictive is the view!

I should point out that I know Alan, from Skies The Limit, from my local astro club. Though when he offered to lend me these I said I’d review them and he told me I could write what I wanted...which is what I have done! I don’t stand to gain, or lose, anything form this review.

[Andrew*]

Excellent, well-written review, and a most interesting conclusion. f/4.7 is indeed a tough test for these cheap 100* alternatives, and from the sound of it they are putting up a fight. Ease the pressure to f/6 or 7 or so and I could imagine the view is quite impressive...

Thanks for sharing your experiences

Andrew

[Ben Ritchie]

Interesting review, thanks.

I guess the one thing that I don't personally "get" is cost, at £200 they're under half the price of a new Ethos but still quite a lot of money. In particular it's getting on for 40-50 quid more than you'd pay for a used 9mm T6 Nagler, say, which is a fine performer and the gold standard for resale value. A used Ethos would be £100-150 more, but you'd again get it all back at resale. Ok, it's a bit unfair to compare new and secondhand prices, but, for me personally, the sums don't really add up.

The 9mm used at around £120-140 would be very tempting though, although I doubt it would last long on the For Sale board

[John]

Interesting review, thanks.

I guess the one thing that I don't personally "get" is cost, at £200 they're under half the price of a new Ethos but still quite a lot of money. In particular it's getting on for 40-50 quid more than you'd pay for a used 9mm T6 Nagler, say, which is a fine performer and the gold standard for resale value. A used Ethos would be £100-150 more, but you'd again get it all back at resale. Ok, it's a bit unfair to compare new and secondhand prices, but, for me personally, the sums don't really add up.

The 9mm used at around £120-140 would be very tempting though, although I doubt it would last long on the For Sale board

Good points Ben - they bother me a bit as well

For £200 you can have a used Pentax XW10 and know that you are looking though one of the very best eyepieces there is. Personally, even though I love ultra-wide fields, I think I'd take the Pentax option or a Nagler T6 at £50 less - still a brilliant eyepiece and sharp to the edge even at F/4.

I recall the Sky's the Limit imported a few of these last year but could not shift them - I recall them going around £120 in the end after being initially priced at £299

[Ben Ritchie]

By the way I fully accept the old argument that you don't need a Nagler (or other premium eyepiece ) in a SCT etc., and these eyepieces may well be flawless in slower 'scopes and give the Ethos experience at a significantly lower price - indeed, the 9mm sounds respectable in a fast one.

It's just that in the past "fine at f/10" ultrawides have been genuinely cheap and occupy a completely different segment of the market to the mid- to high-end brands, but these seem to sit at a price point where a lot of other high-quality options are available. Will be interesting to see how they do.

edit: just in case there's any misunderstanding, I should say that this is no way criticism of the review, which is well done and thought-provoking, just me pondering where these sit in the general scheme of things.

[John]

Ooops

I should have added the same to my post - a very interesting review and thought provoking. Thanks for posting it

....edit: just in case there's any misunderstanding, I should say that this is no way criticism of the review, which is well done and thought-provoking, just me pondering where these sit in the general scheme of things.

[WayBig]

It's a good point you all make regarding resale value, the true cost of ownership being the difference between new and resale values...though I don't think many ethos owners consider selling theirs!

[michael.h.f.wilkinson]

Nice report, and very interesting read. I do wonder if part of the problem with the 16mm as compared to the 9mm lies in coma of the scope. At the same true FOV but in a different EP, does coma show up?

[Macavity]

Without (generally) the resources to move from "Budget" to "Green", always interesting.

As a slight conundrum, I have bought budget "82 degree" eyepieces, and found them to deliver little more TRUE field of view than common 68/72 deg ones. Even the "theoretical calculations" are puzzling.

But before phoning "trading standards", I sense there MAY be aspects re. how manufacturers / types handle distortions? I sense Teleview, presume rightly, that few astronomers worry over certain (pincushion / barrel?) distortions. Though for wide-field sweepers, there is the alleged "sea-sickness" effect?

Aside: For the true "immersive" effect, it'd be difficult to fake 100 deg AFoV? - One day, maybe...

[WayBig]

Nice report, and very interesting read. I do wonder if part of the problem with the 16mm as compared to the 9mm lies in coma of the scope. At the same true FOV but in a different EP, does coma show up?

That's an interesting point, the nearest focal length EP I have is the 14mm ES 82degree, the edge of the ES showed less distortion than the (approx) 82 degree point of the 16mm, so although coma may be part of it, the eyepiece is contributing too.

[michael.h.f.wilkinson]

That's an interesting point, the nearest focal length EP I have is the 14mm ES 82degree, the edge of the ES showed less distortion than the (approx) 82 degree point of the 16mm, so although coma may be part of it, the eyepiece is contributing too.

Quite likely a combination. You could try to see what happens at the same actual angle in say a 35mm wide field, but then the magnification would be lower, and coma would not be as prominent, perhaps.

[Gmeth]

Hi I got the bargain 16mm eyepeice 100 deg and everything you sayed about it  in your write up is right on.  I got mine from Orion telescope here in the states and the price was $199.99. I also bought the Astro-tech CC and I must say that when used togeather with my 12 f/5 dob the field of view is sharp out to about 95 deg which is not bad ,with out the CC it is only sharp out to about 75 deg. I like this eyepeice but with the CC it makes the eyepeice about a 14mm which is ok with me. Also when this 16mm is used with my 2 inch 2x barlow it makes it about a 8mm 100 deg eyepeice that in my f/5 is sharp out to the edge of field of view, so its like getting two 100 deg for the price of one. So for me this bargain eyepeice really was a  bargain. Clear Sky.