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Budget 15mm Shootout!
Submitted: Thursday, 15th September 2005 by Mike Salway

Introduction

When you buy a telescope in Australia, you'll usually get a couple of cheap throw-in eyepieces so you've got something to look through when you take it home. Some suppliers offer the GSO Plossl, while others offer the Series 500 Plossl.

There's been much debate on the IceInSpace Forums about the quality of the Series 500 plossls, and whether you're better off asking for an upgrade to the GSO Plossl, use the series 500's as doorstops or paperweights, or even take them out of the deal altogether and get something of a little more value (and hopefully, quality).

So this review is to hopefully conclude once and for all, what the quality of these eyepieces are like and what you can expect when using them. Many thanks to slice of heaven and Rodstar for the loan of the Series 500 and GSO SV (respectively) for the purpose of this review.

The Contenders

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From left to right: 15mm GSO Plossl, 15mm GSO SuperView, 15mm Series 500 Plossl

EyepieceCan be Bought FromPrice
15mm GSO Plossl Bintel, AOE or Andrews Approx AU$50
15mm GSO SuperView Bintel, AOE or Andrews Approx AU$59-$79
15mm Series 500 Plossl Andrews Approx AU$30

The GSO plossl and SuperView are sold widely around Australia and the world. In the US, they're sold by Hardin, DBA and others. The Series 500 is sold as a "GTO Plossl" in the US.

All of these eyepieces will be tested in my 10" f/5 GSO Dobsonian, FL 1250mm, giving a magnification of approx 89x. The scope was collimated prior to the review.

Vital Statistics

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Top view

EyepieceDesignElementsBarrelAFOVTFOVEye ReliefExit Pupil
GSO Plossl Plossl 4 1.25" 52 deg 0.624 deg 13mm 3mm 
GSO SuperView Plossl 5 1.25" 65 deg 0.78 deg 20mm 3mm 
Series 500 Plossl 4 1.25" 52 deg 0.624 deg 12mm  3mm 

All 3 eyepieces are of similar design, but the SuperView has 5 elements to give it the wider AFOV, quoted in various places as 65 to 68 degrees. The GSO Plossl and Series 500 are both stated to have 52 degrees AFOV, but the field stop in the Series 500 is much narrower, and the AFOV looks and feels more like ~40-45 degrees.

Drift testing proved that the FOV on the Series 500 is narrower. I used Altair as the star, and timed how long it took to drift from one edge of the FOV to the other. The GSO Plossl took 2m:33s, the GSO Superview took 3m:07s and the Series 500 took 1m:56s

The field stop on the Series 500 is sharp and very well defined, but on the GSO Plossl and SuperView there is no well defined edge and as such the edge performance is much worse. More on that later.

I don't wear glasses, and the eye relief of all 3 eyepieces was acceptable (from 12mm for the Series 500 to 20mm for the SuperView). They were all quite comfortable to use, and I didn't experience any blackouts or kidney beaning. Because of the FOV differences, you could see the whole FOV easily in the Series 500, whereas the SuperView had more of a porthole feeling, needing to look around in all directions to take in the entire FOV.

Look and Feel

EyepieceEye CupDust ProtectionSafety UndercutFilters
GSO Plossl Fold down rubber End caps Yes Threaded for filters
GSO SuperView Fold down rubber End caps Yes Threaded for filters 
Series 500 Hard rubber Bolt case No Threaded for filters

The build quality of all 3 eyepieces was quite good. The SuperView looks the most impressive with the bigger body and nicer finish. The Series 500 lacked a fold down eyecup, and instead had a harder rubber one that didn't fold down. This wasn't a major concern, but was a bit uncomfortable at times if you pushed your eye too close.

Both the GSO Plossl and SuperView had undercuts in the barrel to hold it in the focuser more safely, but the Series 500 lacked this. I didn't find this too much of a concern, as we should always be careful to make sure the eyepiece doesn't fall out onto the ground!

The Series 500 had a nice plastic bolt case, whereas the GSO Plossl and SuperView had the standard plastic end caps. The SuperView lens cap was quite loose and had a tendancy to fall off.

At the barrel end, all 3 eyepieces were threaded for filters and appeared to have been painted in flat black, however the finish of the GSO Plossl didn't appear quite as dark as the other 2. I didn't notice any impact of this during field testing.

Edge Performance

Well, the biggest test of any eyepiece is the edge performance in a fast scope like my f/5 10" dob. Unfortunately all 3 of these eyepieces failed in their edge performance.

In the GSO Plossl, approximately 20-25% of the FOV was soft and suffered astigmatism with the stars appearing out of focus and having tails like little comets. They couldn't be focused out. The GSO SuperView performed the worst in this area, with 30-35% of the field softer. The last 10-15% on the SuperView was downright horrible with bright stars sometimes extending 3 times their length outwards. The Series 500 performed best at the edge, with only 10-15% of the FOV softer, but this is also due to the narrower FOV and the field stop hiding the imperfections that are visible in the GSO Plossl and SuperView.

Some people can accept softer stars at the edge, so it's really personal preference when you compare cost vs quality. The SuperView has a wider FOV, but most of that extra FOV isn't sharp. So really, all 3 eyepieces had approximately the same sharp useable FOV.

When barlowed with my 2x GSO 1.25" barlow, it took away most of the edge softness, leaving 5-10% soft in the SuperView and GSO Plossl, and all but completely eliminated it in the Series 500.

Object Testing

I observed the following list using the 3 eyepieces, to test how well each performed on different types of objects. The tests were performed on the 24th August 2005 and the moon test was on the 15th September 2005. The seeing was 5-6/10 and the transparency 7/10.

ObjectTypeGSO PlosslGSO SuperViewSeries 500 Plossl
M22 Glob Middle well resolved, sharp to about 80% of the edge. Eye placement easy. Middle sharp to about 70%. FOV larger but less useable. Eye placement a little more important.  Middle sharp to about 90%. Contast mildly better due to smaller FOV.
Alpha Centauri Dbl Good contrast around the bright double. Starts to seagull after 70%, or if eye placement not on axis. On axis good to about 70%, but there is a glow around the bright stars - less contrast. Also some internal reflections. Sharp, nice diffraction spikes. Clean and sharp to about 80%. Mild lighter glow around the star with a little less contrast.
NGC104 Glob SuperView appeared to resolve a few more stars, but not much difference apart from the FOV.
h5003 Dbl  All sharp on axis in centre of field. All displayed softness at edge of field, SV the worst, s500 the best due to the smaller FOV.
NGC7089 Glob  All resolved the same amounts. FOV different, contrast roughly equal.
NGC7009 Pl. Neb  Series 500 the best on this faint planetary as the limited FOV improved the contrast.
M7 Open Cl. All performed horribly on such a wide open cluster. The SuperView was the best due to the large FOV.
M11 Open Cl. All performed quite well on such a tight open cluster in the centre of the FOV.
M17 Neb Looks quite good, contast equivalent  The best view out of the 3. The wider FOV made it easier to see the nebula. Similar results for M8 and M20.  Hardest to resolve out of the 3, due to the small FOV.
Venus Planet Some reflections off the field stop when near the edge of the FOV. Small internal reflections, like a little moth flying around inside. Bright internal reflections, a big halo around the planet.
Jupiter Planet All performed poorly when placed near the edge of the FOV with various levels of distortion.
9 day old Moon Moon No ghosting or internal reflections, had the most flaring when outside of the FOV. Slight ghosting and internal reflections, however performed quite well with the moon outside the FOV. No excessive glare and no flaring, however contrast reduced when the moon was out of the FOV.

Conclusions

It was quite an interesting review for me. After all the debate and bagging of the Series 500 range on the forums, I expected them to perform much worse than they did. For a AU$30 eyepiece, it performs reasonably well on some objects. It is let down on the brightest stars and planets, with a bright halo around the star and reduced contrast.

However when compared with the other budget eyepieces at that focal length, they all had their problems, especially when it came to edge performance. But really, we're only talking a difference of $30-$40 between the Series 500 and the SuperView. The 15mm SuperView is well known not to be anywhere near the quality of the 2" 30mm SuperView, and it may well be true that other focal lengths in the Series 500 range are worse than the 15mm I tried.

But when comparing these three in the 15mm range, there wasn't a lot to differentiate them. If you're on a really tight budget, for AU$30 you do get a reasonable quality eyepiece that will work ok on most objects. And let's not forget that these eyepieces are usually throw-in's when you buy a scope, so you're not really paying anything for them.

For me, it would probably be worth upgrading to the GSO Plossl if it only cost you an extra AU$10-$20, but I wouldn't pay full price for them if you already had the Series 500's. There's just not that much difference in them at this focal length. If you wanted a good plossl, I'd rather save up and spend AU$150 and get a Televue Plossl (you can find these cheaper if you buy 2nd hand).

The SuperView is not a bad eyepiece, but the extra FOV really suffers from astigmatism and if that sort of thing bothers you, this isn't the eyepiece for you. It does well on wide open clusters, but has internal reflections on bright stars and planets. I wouldn't buy this eyepiece if I was after a wider FOV at that focal length.

All in all, it's going to be up to the individual to draw from this review what they need. I hope i've provided enough commentary and information for you to be able to make your own mind up about the budget eyepieces at this focal length.

Review by Mike Salway (iceman). Discuss this review at the IceInSpace Forums.
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