Explorer 150P Eyepieces - what is "poor" about them?

[YabiYabi]

Hi all,

I recently bought the Skywatcher Explorer 150P which comes with 25mm and 10mm eyepieces.

I've read on this forum from others with the same scope that the 25mm is okay but the 10mm is poor. So I went to experiment (not very scientifically) by comparing the 10mm with the 25mm used with a 2x Barlow.

Long story short, looking at Jupiter and Alberio, other than the FOV I couldn't really see a difference in image quality. Might just be my untrained eye though.

So - to continue my education, can someone explain what it is that makes the 10mm "poor"? Also a general question, if (when!) I buy some new eps, what sort of difference might I expect to see.

Cheer all!

[newman]

I'm guessing you got these?

Sky Watcher Sky-Watcher Super-MA Series Eyepiece upgrade set

Super MA stands for Super Modified Achromat. It's a design essentially similar to Kellners in performance. This would put them a step below Plossls, but for that price their performance really isn't bad. I also got 25mm and 10mm ones with my scope and both worked ok, I'm guessing they wouldn't be so great in a fast scope though.

They're certainly not top of the line but I found both of them ok with my f8.3 refractor, with the 25mm being a bit better. I was still able to barlow the 10mm and got satisfactory results on Saturn (my Kasai Ortho still blows it out of the water, though). Maybe Skywatcher used to bundle their scopes with poorer eyepieces before so that's where the "10mm is bad" story originates from? Some scopes used to come with plastic lenses which really weren't any good, but these super MA's are definitely a step or two up from that.

[brantuk]

Hi Yabi - the 10mm can be very poor in slightly worse seeing than we've had recently, because it will magnify the imperfections in the atmosphere. Jupiter and Alberio are quite high objects currently so you've been looking through least atmosphere at well defined objects in good seeing.

However - you'll notice the difference when looking at nebulae lower down in poorer seeing, or trying to resolve globs in similar conditions. I'd suggest you pay a visit to your local astro soc or obs group and try a few loaner eyepeices. You'll soon get a feel of what's good and what's not - then you'll be in a better position to get technical.

[Capricorn]

Another point is the barlow tends to be considered poor, so you could be using a poor 10mm and a decent 25mm on a poor barlow.

Equally you could have a decent 25mm and a decent 10mm. Several paople must have managed to get a decent one of each in their package.

The other thing is have you compare the supplied 10mm to say a BST Explorer 11mm or a TMP planetary of 10mm. You may suddenly find that what you considered fine is actually not that great. I did.

As said point the scope at a globular cluster, how individual and sharp are the stars?

How well collimated is the 150P, it will need to be collimated to start doing comparisons like this.

[YabiYabi]

Thanks for the input guys. The eyepieces are indeed the Super MA ones - it's good to know they are at least not completely bottom of the line.

I did manage to get a look at M13 globular cluster and I was struggling to resolve any individual stars to be honest - more of a general patch of light. Having little experience I don't know if this is normal or a consequence of the eps or indeed local light pollution.

I haven't had the scope long so I have assumed collimation is okay but no harm in checking I suppose!

Once the clouds go away I'll have another go.

[russ.will]

I would. Out of the box, my SW 200P was so far out of collimation, I initially couldn't work out why the view through the Cheshire collimator looked nothing like the pictures on the interweb. I thought I must be doing something stupid. I wasn't - It's just that the web guides assume your scope is somewhere near the right ball-park to begin with.

Even so, in this parlous state of adjustment, I was able to see the rings of Saturn and a few fuzzies using the 25mm EP and that was in June with poor seeing. Through the 10mm, the collimation issues were more obvious as it was impossible to get stars to resolve to a point and Saturn looked bigger, but ill defined.

Collimating it, was an unbelievable difference and I find that I at least check it every couple of back garden sessions, plus every time I drive it somewhere.

I think it is this lower tolerance of poor seeing/setup that leads to the suggestion that the SW Super 10 isn't any good. It's no worse than the 25mm, but the narrower exit pupil and reduced eye relief make it a more difficult view. That was the single biggest upgrade my TMB 8mm made, although in fairly short order, you start to notice the wider, higher contrast view that's sharper at the edges. But in terms of the bigger of the two improvements, it was definitely collimation first, eyepiece second.

Russell

[michael.h.f.wilkinson]

The 10 and the 25 have the same design, but at the rather low magnification of the 25 you do not get huge errors or aberrations. These are magnified in the 10mm (and likewise in the barlowed 25mm. I am going to build a mini dob for the kids, and I am giving them a 28mm Kelner scrounged from some old binoculars. That should be fine for low magnification work, but for higher magnification, errors get blown up, so I will get them a different type of EP.

A simple test: compare two 10mm EPs of different design, and you are bound to see differences.