which eyepiece

[melt]

yep I know another ep one

been looking at the BST ep's and not sure which one to get first ,found Jupiter last night and could see its 4 moons(just) with my 15mm possel and x2 barlow and wanted to get closer tried my stock 10mm and it was shocking (not as clear as 15mm)

looking at the BST ( 60 degree field of view) 8mm and 5mm

on my scope 5mm is x130 and x260

and 8mm is x81 and x163

or a   Skywatcher UWA 6mm (58 degree field of view) which is x108 and x217

 

my 130p has a Highest Practical Power (Potential): x260

 

would love some advice , thanks again

[Bart]

The BSTs are good EPs. Don't know about your x260, might only get that high occasionally. But I'd probably like something around x200. 

BUT, the 8 and 5 would be an excellent start?

[Joe12345]

260* is far too much magnification, I would go for the 8mm. Jupiter will never be big enough to fill the whole eyepiece, and

What other EPs do you have? It might be a good idea to go for a wide field eyepiece for large DSOs first.

[Ricochet]

I've found that 200X is often too much and only really available on good nights so I would suggest keeping below that limit. It is also useful to have a close range of eyepiece focal lengths at the top end of magnification so that you can best choose an eyepiece to match the conditions on any particular night. With that in mind I would suggest that you get both the 8mm BST Starguider (81X/163X) that you are looking at and the similarly performing 7mm X-Cel LX (93X/186X).

[rwilkey]

i would agree with others, the BST StarGuider 8mm is the best one to get, will be more useful more often.

[LukeSkywatcher]

Cant go wrong with an 8mm on any scope really when observing planets. It will serve you well with the 130P. In this part of the world, i and many others find that if you take the diameter of the scope (in this case 130mm) that this is the maximum magnification you should be aiming for. You will always be able to push it a bit more so 163x (if using an 8mm) should be right on the button.

*edit*

A few yrs ago i bought a 4mm (maybe a 6mm) Celestron Omni EP to see if i could get better views of the inner planets. Since i bought it, i have used it exactly ONCE and that was only to observe the Moon. Worked out brilliantly for me and the views felt like i was orbiting the Moon a couple of miles above the surface. Thats 1 night in 8 yrs when the conditions were absolutely perfect. I was using the Omni EP with a Heritage 130P which has the same optics as the standard 130P. I basically never go below an 8mm to observe the planets........even now when my main scope is an 8" SCT. In fact i dont use anything below 8mm for observing ANYTHING.

[Bostonteax]

I've just literally got one yesterday and tried it last night on full moon and Jupiter .  Moon looked good even though full. Jupiter (fairly low in sky) was picking up some nasty Chromatic Aberration ( I didn't try any other lens last night as time was tight.) Tried x2 Barlow and image was so soft it couldn't be focused.  I have 4" 500mm refractor . Tempted to send the lens back. Very disappointing .

[Ricochet]

Have you tried other 8mm or shorter eyepieces with your scope to compare? I've got an 8mm Starguider and while it can show a bit of false colour at the edges of bright planets its still preferable to the field distortions seen with cheaper eyepieces. 

The other consideration is the scope itself which from your other posts looks to be a Startravel 102. The Startravel line are all short focal length achromats and as such will all exhibit chromatic abberation. I suspect that any 8mm eyepiece will show the same effect because it is an intrinsic property of the scope itself and you may find that it is worthwhile to invest in a semi-apo filter which will block the violet part of the visible spectrum. 

[rwilkey]

Your scope is f/5, a rich-field scope and not really best suited for planetary observation, but patience will win in the end.

[LukeSkywatcher]

I'm not one bit technically minded when it comes to the mechanics of EP's and scopes and what works with what. I think if the views are pleasing then that is all that matters. A great range of EP's that work really well for me across all of my scopes (F5,F10) are the Vixen NPL's. The short eye relief is an issue for many people but i dont find it a problem. The NPL's have a solid fan base here on SGL (as much as any other range of EP's). There are equally as good EP's available but they cost more (BST's). These do offer better eye relief..........so are more popular.

 

[Mak the Night]

A 130mm (5.1") should give you a maximum of around 300x with good optics (60x : 1"), although depending on focal ratio I suppose. At least 150x to 200x should be achievable easily with a 5" scope.

[LukeSkywatcher]

2 hours ago, Mak the Night said:

A 130mm (5.1") should give you a maximum of around 300x with good optics (60x : 1"), although depending on focal ratio I suppose. At least 150x to 200x should be achievable easily with a 5" scope.

With a 130mm scope.....somewhere between 130x and 160-180x should be possible. 200x seems a bit ambitious.

[Mak the Night]

Just now, LukeSkywatcher said:

With a 130mm scope.....somewhere between 130x and 160-180x should be possible. 200x seems a bit ambitious.

I could regularly achieve 300x with my Explorer 130M. I can easily get 208x (0.5mm exit pupil) with my 102mm Mak.

Before I swapped this Luminos for a Delos I could easily get 270x with it on the 130M combined with a 3x TeleVue Barlow. Viewing the Moon was superb. And the Celestron eyepiece was less than a 100 quid!

I could get 300x exactly with a 9mm and the Barlow. I used a TV 2x Barlow and a 10mm EP on my Mak for 260x with Saturn once. That was pushing the Mak's 241x limit though. The image was impressive but dark and grainy. It still looked pretty good though. Mind you, I do live in the greenbelt.

[John]

You can get all sorts of very high powers out of scopes by combining eyepieces and barlows. 300x, 400x whatever. The Moon can soak up a lot of power and it's fun to do this but are you really seeing any more details when you do this with a small aperture scope ?. I don't think so from my experience with my scopes from 4" to 12" in aperture.

The aperture of the scope provides the richness of information, for the want of a better term and the more aperture you have, the more information you have and the more magnification you can apply to it while it still retains sharpness and contrast. When certain limits are exceeded the additional magnification becomes what is often referred to as "empty magnification" in that the image scale expands but the actual detail and contrast visible starts to decline because the information that the primary has gathered is being stretched too thinly.

 

 

 

 

[Mak the Night]

Then there's the TV Eyepiece Calculator: http://www.televue.com/engine/TV3b_page.asp?id=212&plain=TRUE

[Bostonteax]

folks, I need you to reel in your enthusiasm. I have a humble Skywatcher 102 refractor , 500m f5. I am learning about chromatic Aberration and guess it's something I will have live with. Am I right in coming to the conclusion there is no perfect telescope and set up? There is a temptation to keep spending money in the pursuit of excellence which I'm not really sure exists.

[Mak the Night]

I may be wrong, but I think some contrast filters are designed to alleviate chromatic aberration on some fracs. I believe they act a bit like Wratten 12 longpass filters .

http://www.firstlightoptics.com/achromat-semi-apo-filters/baader-contrast-booster-filter.html

https://en.wikipedia.org/wiki/Wratten_number

 

[Dave In Vermont]

I have a number of different Semi-APO type filters in my collection. My only grudge with them is they all add a yellow-tinge to everything bright. Other than this, they all work for what they're made to do - take out most of the colouration from CA on bright objects. But I don't really mind a bit of purple around bright objects like the Moon and Venus.

Haven't tried the #12 Wratten yet for CA, but sounds like a worthy experiment to entertain a certified filter-nut such as myself!

Thanks, MTN -

Dave

[bomberbaz]

Back onto the OP's question to which eyepiece might be of use I would also go along with an 8mm BST this giving circa x80 and x160 with your barlow. This magnification will still give great views of Jupiter's moons, the equatorial belts, festoons, barges and the great red spot in the right conditions.

Depending on your budget the next question is how good is the barlow, do you need upgrade this to a better quality one. Remember your optical view is only a good as the weekest link in your optical train. If its a decent quality one then all's good.

Assuming you are also happy with the 15mm the next question is do you have a decent 25mm eyepiece? They usually come with a 25mm modified plossl type that is usually ok to get along with. If you have that then again you should be ok.

Maybe now simply replace the 10mm stock eyepiece with something better and you have a decent range to be getting along with (if my assumptions above are correct) and you will have a decent 25, 15, 10, 8 (x26, x43, x65, x81) barlowed you get 12.5, 7.5, 5, 4. (x52, x86, x130, x162). That is a pretty good range for your scope and should cover just about everything for now until you find your feet better. 

As for a 10mm eyepiece, you could simply get a better 10mm plossl such as the skywatcher omni, only £20 but tight on eye relief. Or either the baader hyperion or vixen slv 10mm and have very good eye relief. Both are the same price at £99 but the hyperion has the wider fov of 68 degrees rather than the 50 degrees of the Vixen. However the Hyp will be softer towrds the edges whereas the vixen should be pretty sharp right accross.

All can be found here http://www.firstlightoptics.com/eyepieces-barlows.html

hth

[Mak the Night]

8 hours ago, Dave In Vermont said:

I have a number of different Semi-APO type filters in my collection. My only grudge with them is they all add a yellow-tinge to everything bright. Other than this, they all work for what they're made to do - take out most of the colouration from CA on bright objects. But I don't really mind a bit of purple around bright objects like the Moon and Venus.

Haven't tried the #12 Wratten yet for CA, but sounds like a worthy experiment to entertain a certified filter-nut such as myself!

Thanks, MTN -

Dave

You're welcome Dave. From what I can gather #12 Wrattens and similar are used as high contrast filters in more fields of use than astronomy. I believe they are often employed in cinematography in the movie industry.

[Mak the Night]

Incidentally, I'm pretty sure the stock give-away EP's with SW scopes are Modified Achromats and not actually Plossls. I believe they are based on a Kellner or Erfle design.

http://www.scopesnskies.com/prod/skywatcher/eyepieces/super-maserieseyepieces.html

In regards to Jupiter in the OP's post, I should probably clarify what I meant by magnification. The Moon and Saturn can often be observed successfully with quite high magnifications, but Jupiter is a bit of an anomaly. It is easily one of the brightest objects in the night sky due to its very high intrinsic reflectivity (albedo). Paradoxically this can make it difficult to observe well at high magnifications, possibly due to constantly changing atmospherics. I've not really seen it with much clarity above 170x. Recently I've been experimenting observing it with binoviewers and I find that on a good night 144x to 166x with a neodymium filter and orthoscopic eyepieces produce the best results, although I often drop down to around 115x or even 72x.

[Bostonteax]

Really disappointed with the Starguider 8mm in conjunction with my refractor so it's gong back. I even tried it today in daylight and it was awful.  If CA is a problem with my Startravel 102 it might just mean I can't go under 10 mm?  Perhaps a 12 mm with 2x Barlow might remove the CA?  Sorry but I'm really out of my depth with all this. Just seems I stumble from one problem to another lol.  On the plus side I have a 32mm and 25mm which seem very good with no CA,

[John]

Modified achromats are a 3 element / 2 group design similar to the Kellner or Achromatic Ramsden. Skywatcher and Meade have supplied these as "stock" eyepieces with many of their scopes. Sometimes however they provide plossls or in Meade's case, a 26mm QX 2" wide field.

 

 

[John]

13 minutes ago, Bostonteax said:

Really disappointed with the Starguider 8mm in conjunction with my refractor so it's gong back. I even tried it today in daylight and it was awful.  If CA is a problem with my Startravel 102 it might just mean I can't go under 10 mm?  Perhaps a 12 mm with 2x Barlow might remove the CA?  Sorry but I'm really out of my depth with all this. Just seems I stumble from one problem to another lol.  On the plus side I have a 32mm and 25mm which seem very good with no CA,

Low powers show CA less than higher ones. Unfortunately there is no escaping CA with an F/5 achromat. Even the F/8 ones show a fair amount of it. It's the nature of the achromatic doublet design. If you get to around F/15 or slower the CA is much, much less but the scope has grown much much longer and can be a handful to mount steadily.

A barlow does not reduce CA because it's already in the optical system by the time the light reaches the barlow.

The filters mentioned earlier in this thread can reduce the visbility of CA by removing some of it but they often add a tint to the image of their own in return for this.

The F/5 acrhomats are best used in the role they were designed for which is as low to medium power widefield scopes.

 

[Bostonteax]

Thanks John, so I need another telescope for close up planetary stuff then ? Lol