Which EP to keep?

[Raph-in-the-sky]

Hello guys,

I just bought a second hand scope (Skywatcher 250 PX) which came with a lot of EPs. Since I already had a few, I now find myself with some redundancies and some EPs with very close focal lengths. Obsviously, I ll go out when I have a clear night and find out by myself but in the meanwhile I was curious to know what more expercienced people would keep and what they would sell. None of these EPs are premium and I don't plan on getting any for the time being, so don't tell me to get rid of it all and buy Naglers 😉

Here is the list of EPs as best as I can describe them (All in 1.25'):

-4mm Skywatcher UWA-58°

-5mm BST starguiders ED

-6mm Skywatcher UWA-58°

-8mm Omegon Cronus WA 60°

-9mm 66° UltraWide Long Eye Relief Multi Coated (No brand - with a gold ring)

-15mm 66° UltraWide Long Eye Relief Multi Coated (No brand - with a gold ring)

-15mm BST starguiders ED

-25mm Super Plossl multi-coated (No Brand)

-30mm Bresser PL 

-32mm GSO Super PLossl

Keep in mind that my new scope is f4.7 and that I have a very decent 2x barlow (Celestron Ultima Japan). Give me your thoughts!

Cheers,

Raph

 

 

[DirkSteele]

Ok, I won't tell you to buy Naglers.. Buy Ethos instead!! 😁

[alan potts]

With a Dob of any type the 100 degree type eyepieces will help a great deal keeping the subject in view longer. You don't have to buy TeleVue even though they are very good indeed, what you will find though is the wider the field of view of the eyepiece, and faster the scope, the greater the chance of coma being seen at the edges of field. I personally find this annoying and the faster the Dob the worse it will be, mine is F4.3 and I do use a Paracorr, this stops the problem. On the same Dob I don't see anywhere near as much with a 68 degree eyepiece . Fellow Mod John has a F5.3 scope and I don't believe he uses a a coma corrector or Paracorr, this is just TeleVues name for it.

Alan

[Ruud]

The Bresser 30mm Plössl is around €60, and the GSO 32mm €50. Could you compare them for us in your fast dob? Especially edge performance, general sharpness and scatter would be interesting to know about.

About your original question, test the eyepieces, keep the better ones for yourself and sell the rest. For people with only kit eyepieces, most of your collection would mean an improvement.

The  66° UltraWide Long Eye Relief ones, btw, are sold under many names.

[Raph-in-the-sky]

1 hour ago, Ruud said:

The Bresser 30mm Plössl is around €60, and the GSO 32mm €50. Could you compare them for us in your fast dob? Especially edge performance, general sharpness and scatter would be interesting to know about.

I m not sure I m the best person since I have very little experience but I ll try to report what I can see.

[Rob Sellent]

Great buy, Raph. 10" dobs are an extremely nice sweet spot; not to heavy to lug out, breeze to set up and offer up spectacular views.

For general  viewing in my 10" f5, I observe with widefield eyepieces offering around 60x, 90x, 125x and 180x. Coupled with a decent Barlow or Powermate, you could do all this with just two eyepieces which should suffice a lifetime for most clusters, galaxies, nebulae, and casual lunar and planetary work. If it took your fancy, 50x for white light solar viewing would also be useful and all you'll need is a solar filter made from Baader's Visual Solar Film.

If you decide to really get into planetary and lunar observations, you will probably find that it helps to have a nice run of higher power eyepieces. Depending on the evening's seeing conditions, even the difference of just 1mm in focal length - about 10% to 15% difference of magnification - can be surprising. The good news is the eyepieces themselves do not need to be widefields and there's no hurry to build the collection all at once. Again, by way of example, in my own case I use little Orthos.

There's certainly no need to go spending loads of money to get decent eyepieces and on this account your best bet is to keep an eye on the secondhand market. Nevertheless, extracting budget from the equation and purely looking at a few eyepiece options which get rave reviews year in year out, we're looking at: Tele Vue, Pentax XWs (perhaps less the 14mm), Explore Scientific ES68, 80 and 100, Meade 5000 UWA, William Optics UWANs, Vixen SLV, Skywatcher Nirvanas, and Orthoscopics like Baader's Genuine.

I have found from experience that in the long term it is cheaper for a poor man/woman to buy decent quality eyepieces knowing that these eyepieces will be 'lifers' and will fit a range of different telescopes and retain their market value better, rather than going for quick fix cheaper eyepieces that will eventually need upgrading and will inevitably lose more on the secondhand market.  I cannot comment on most of these eyepieces mentioned but at the end of the day, I feel it makes more sense to have two, perhaps three really cracking, quality glass eyepieces, coupled with a Barlow or Powermate rather than a whole load of secondrate eyepieces under performing in a fast f5.

Edited August 15, 2019 by Rob Sellent

[John]

Probably best if you keep them all for now, try them and over time decide which do the best job in your eyes.

Of the ones you list, the BST Starguiders and the Skywatcher UWA 58's are the ones that are best corrected for a fast scope such as your F/4.7 250PX.

 

 

[Louis D]

22 hours ago, Raph-in-the-sky said:

-4mm Skywatcher UWA-58°

-5mm BST starguiders ED

-6mm Skywatcher UWA-58°

-8mm Omegon Cronus WA 60°

-9mm 66° UltraWide Long Eye Relief Multi Coated (No brand - with a gold ring)

-15mm 66° UltraWide Long Eye Relief Multi Coated (No brand - with a gold ring)

-15mm BST starguiders ED

-25mm Super Plossl multi-coated (No Brand)

-30mm Bresser PL 

-32mm GSO Super PLossl

Nothing redundant until 15mm really.  You'll find you'll want to fine tune your power at higher powers because small changes in eyepiece focal length leads to large changes in magnification.  I'd keep all of the 9mm and below for now.  Be aware that the 9mm is known to have rather severe SAEP or kidney-beaning.  Some folks deal with it better than others, so YMMV.  Try keeping your head as still as possible when using it.

At 15mm, the 66° is reputedly a simple positive-only design similar to a Konig or Erfle whereas the BST Starguider is a negative-positive design better able to cope with the fast f-ratio of your scope.  Compare them in your scope and see if that is the case.

I would compare the 30mm and 32mm Plossls and see which performs best for you in your scope.  Neither is going to be a stellar (pardon the pun) performer at f4.7.

[Ricochet]

1 hour ago, Louis D said:

At 15mm, the 66° is reputedly a simple positive-only design

Having looked through one, I'd say it is a negative only design 😆. 

[Raph-in-the-sky]

20 hours ago, Louis D said:

Nothing redundant until 15mm really.  You'll find you'll want to fine tune your power at higher powers because small changes in eyepiece focal length leads to large changes in magnification.  I'd keep all of the 9mm and below for now.  Be aware that the 9mm is known to have rather severe SAEP or kidney-beaning.  Some folks deal with it better than others, so YMMV.  Try keeping your head as still as possible when using it.

At 15mm, the 66° is reputedly a simple positive-only design similar to a Konig or Erfle whereas the BST Starguider is a negative-positive design better able to cope with the fast f-ratio of your scope.  Compare them in your scope and see if that is the case.

I would compare the 30mm and 32mm Plossls and see which performs best for you in your scope.  Neither is going to be a stellar (pardon the pun) performer at f4.7.

Thanks so much for this reply. Could you please explain a few things?

What's SAEP/kindney beaning? how will I notice it?

What do you mean by simple positive/negative positive? And will it impact my views?

[Raph-in-the-sky]

And one more question: Am I right in assuming that any of these EPs will be better than my 8-24mm Celestron Zoom ?

[Louis D]

7 hours ago, Raph-in-the-sky said:

What's SAEP/kindney beaning? how will I notice it?

It's spherical aberration of the exit pupil.  Here's a nice animation from @Ruud showing what causes it:

Basically, light rays from the edge, middle, and center of the image don't all come to a focus at the same point behind the eyepiece.  If your eye bobs around or if your iris is too constricted as when looking at the moon, some of the middle rays will be cut-off leading to a kidney bean shaped shadow in the image as seen in the upper right sub-image below:

You'll find it quite annoying to avoid seeing it under certain conditions if an eyepiece has it.  If you are fully dark adapted and seated, SAEP isn't as big a problem as when standing or when you iris isn't fully dilated.

[John]

7 hours ago, Raph-in-the-sky said:

And one more question: Am I right in assuming that any of these EPs will be better than my 8-24mm Celestron Zoom ?

Not necessarily. The Celestron 8-24mm zoom will probably be as good or better than the "66" eyepieces and the PL's. Plus the variable focal length is very useful for finding the "goldilocks" magnification for the conditions and target. A very useful tool I reckon.

[Louis D]

7 hours ago, Raph-in-the-sky said:

What do you mean by simple positive/negative positive? And will it impact my views?

A positive eyepiece design simply funnels the light rays of the objective (entering from the left below) into an image visible to the human eye as shown for several classic eyepiece designs below:

A negative-positive design is a hybrid in that there is a negative lens group ahead of the traditional, positive image forming section as shown below:

By first diverging the light rays (entering from the right above), image aberrations can be better controlled than is possible in a positive-only design.  This is especially true for usage in "fast" scopes such as yours.  Notice how much tighter the Nagler design's spot diagrams are at f/5 than the positive only designs.  It also allows for much wider apparent fields of view to be implemented while maintaining good correction.

[pregulla]

21 hours ago, Raph-in-the-sky said:

And one more question: Am I right in assuming that any of these EPs will be better than my 8-24mm Celestron Zoom ?

I think that the Zoom will be at least comparable in quality, especially closer to 8mm. I personally would just use it and a barlow for anything under 15mm. Out of all the eyepieces I would just keep 32mm or 30mm plossl, 15mm Starguder, Celestron Zoom and the barlow.  The 25mm is too close to 32mm to be worth keeping IMO. 15mm Starguider will be wider than the zoom, but may be still close enough so you will keep using the zoom.

It's all a matter of personal preference. Some people don't like zooms and barlows and would prefer dedicated eyepieces for each focal length. In the end you'll have to try for yourself and find out what works for you.

[Raph-in-the-sky]

Thank you guys for all your answers!

The skies seem to be clear tonight so I ll bring out my new scope for the first time. I'll briefly let you know how it goes and how the EPs perform.

Cheers,

Raph

 

[Raph-in-the-sky]

On 15/08/2019 at 19:12, Ruud said:

The Bresser 30mm Plössl is around €60, and the GSO 32mm €50. Could you compare them for us in your fast dob? Especially edge performance, general sharpness and scatter would be interesting to know about.

So... I ll finally got to try the EPs. And to me the GSO 32mm is the clear winner over the 30mm Bresser. To me it seemed that the GSO was clearer and sharper overall. I tested them on Andromeda and the disc seemed fainter and smaller with the Bresser. 

For the other EPs the BSTs were great (but I already had/knew these EP). The 8mm Omegon Cronus gave me my best view of Jupiter to date. Later the 5mm BST gave me a good view of Saturn although I wasn't able to make out the Cassini division. The BST 15mm was great on M13. THe 6mm Planetary was good for the ring Nebula... From my experience during this night, I think the 30mm Bresser, both ultrawide 66 and the 25mm plossl will colect more dust than photons. The 4mm might be useful when seeing is better.

Obviously this is not the most professional EP review but I was like a child with my big new toy. I didn't want to intelectualize too much and just enjoy myself

[Ruud]

Excellent non-professional review!

[Louis D]

22 hours ago, Raph-in-the-sky said:

So... I ll finally got to try the EPs. And to me the GSO 32mm is the clear winner over the 30mm Bresser. To me it seemed that the GSO was clearer and sharper overall. I tested them on Andromeda and the disc seemed fainter and smaller with the Bresser. 

For the other EPs the BSTs were great (but I already had/knew these EP). The 8mm Omegon Cronus gave me my best view of Jupiter to date. Later the 5mm BST gave me a good view of Saturn although I wasn't able to make out the Cassini division. The BST 15mm was great on M13. THe 6mm Planetary was good for the ring Nebula... From my experience during this night, I think the 30mm Bresser, both ultrawide 66 and the 25mm plossl will colect more dust than photons. The 4mm might be useful when seeing is better.

Obviously this is not the most professional EP review but I was like a child with my big new toy. I didn't want to intelectualize too much and just enjoy myself

That's the best way to settle on an eyepiece collection.  Try out a bunch under the sky on your own scope looking through them with your own eyes.

Try to locate a local astro club and attend a non-public star party of theirs to try out some other members' eyepieces in your own scope.  You'll also pick up some useful tips and tricks of the trade along the way.  You just might make some new friends as well.

[Raph-in-the-sky]

38 minutes ago, Louis D said:

That's the best way to settle on an eyepiece collection.  Try out a bunch under the sky on your own scope looking through them with your own eyes.

Try to locate a local astro club and attend a non-public star party of theirs to try out some other members' eyepieces in your own scope.  You'll also pick up some useful tips and tricks of the trade along the way.  You just might make some new friends as well.

Planning on doing this. First meeting with the club on Saturday!