Unsure which eyepiece to get

[Dreckly]

Hi all. I have a Dobsonian skywatcher 150p. I'm now looking to add a new eyepiece or two to my collection but I'm unsure what to get. I would like something with a little more magnification but I willing to put myself in all of your hands :-). 

[MarkVIIIMarc]

I saw an online listing for your scope with a list of 4 magnifications out of the box. Do you have four lenses or two lenses and a barlow?

[Dreckly]

Just the two lenses but no Barlow. The lenses which came with it are a 10mm and 25mm.

[Mak the Night]

What's the focal length and focal ratio of your scope?

[Dreckly]

I hope this is enough information,  I copied it straight from flo 

• Highest Practical Power (Potential): x306
• Diameter of Primary Mirror: 153mm
• Telescope Focal Length: 1200mm (f/7.84)
• 2" R&P focuser with 1.25" adapter
• Eyepieces Supplied (1.25"): 10mm & 25mm
• Parabolic Primary Mirror with Protective Silicon-Dioxide Overcoat
• Diffraction Limited Optics

[MarkVIIIMarc]

Is this what you own? http://www.firstlightoptics.com/beginner-telescopes/skywatcher-skyliner-150p-dobsonian.html

Think it said 1200mm focal so...

1200/6=200. So a 6mm seems safe. 5mm might be pushing it but I'd be tempted. 1200/5=250

A 2x barlow with what you own would give 96x and 240x views with no additional eyepieces.

Thats the limit of my knowledge.

[Dreckly]

Yep, that's the one I have.

Thanks mate, your a star :-) 

[Mak the Night]

http://www.firstlightoptics.com/celestron-eyepieces/celestron-2x-universal-125-barlow.html

[Dave In Vermont]

I should like to point out that a telescope's best attribute isn't the magnification it can provide, it's how much light it can gather. And this is dependent on it's aperture. In your scope, Dreckly, this is 150mm - or 5.9 inches. So it can capture quite a lot of light from dim objects that can never be seen with only one's eyeballs. This includes galaxies, nebulae, ring nebulae, and all sorts of deep-sky objects (DSO's). And it can, with it's large focal-ratio of F/7.84, easily give you 250X. But this would only on nights of nearly perfect 'seeing.' Which means a stable atmosphere without much high-altitude (and low) turbulence, particulates, and humidity. And these night are, from everyone I've spoken to and read accounts from, quite rare there in the UK. Most seem to believe even then, about 200X is the limit.

That is a very nice telescope. As Skywatcher tends to have very good equipment indeed! With simple care, it can last a lifetime.

Enjoy!

Dave

[Joe12345]

How do you find your current EPs? What's your budget? There are lots of different types of eyepiece, ranging from £5 to £650, so when asking for advice about eyepieces it's quite important to give your budget, either in total or per piece.

[dick_dangerous]

I bought BST eyepieces for my 150P - 25mm, 15mm, 8mm and 5mm. I don't use the 5mm as often though as at high magnification the image often becomes fuzzy, something true of all telescopes. At x240 the 5mm is on the cusp of being useful.

Paul

[Joe12345]

18 minutes ago, dick_dangerous said:

I bought BST eyepieces for my 150P - 25mm, 15mm, 8mm and 5mm. I don't use the 5mm as often though as at high magnification the image often becomes fuzzy, something true of all telescopes. At x240 the 5mm is on the cusp of being useful.

Paul

I agree, even in my 8" dob (same FL) an 8mm EP gives a much more pleasing view than a 5mm almost all the time

[Dreckly]

Thanks for your help guys. I have decided to go for a 8mm. My price range is about £50 maximum. There are so many lenses out there I never know what one to get, I'm guessing it's kind of a personal preference? 

[Mak the Night]

I think the maximum magnification you can achieve depends as much on the target and conditions as anything else. According to TeleVue anything more than 350x isn't really possible with the confines of the Earth's atmosphere. Anything over 350x won't show any more detail although it may be a larger image. I'd argue that 200x was the absolute limit in the UK though. In 243,610 square kilometres there has to be places where there is better seeing. I live on the edge of the greenbelt at a fairly high altitude and on a good night can easily get 300x plus on a 130mm Newtonian, admittedly principally with lunar viewing. I have even pushed a 102mm Mak to 260x viewing Saturn, which is a tad above its exit pupil limit of 208x (0.5mm) lol. The image was darker and a bit grainy, but quite impressive none the less.

Aperture size and focal ratio essentially govern any magnification limitation and once you are at or above a 150mm aperture the resolution constrictions of smaller apertures are not so much of a concern. I have recently acquired a 90mm Mak, f/11.3. Technically, its highest magnification to give me a 0.5mm exit pupil is around 180x (I can get 182x with an 11mm Plossl combined with a 2x Barlow). Although, with recent atmospheric conditions and viewing the Moon rising early I've found anything between around 55x and 140x suffices. Which is still pretty good for a three and a half inch scope. I think when calculating magnifications for scopes under 150mm it is best to range from the highest magnification obtainable with a 0.5mm exit pupil to the lowest useful magnification for the scope in question. For scopes 150mm or above, I would at least have an eyepiece range giving magnifications from about 300x at the highest, to around 250x, then possibly around 150x. Around 150x being a general lower limit to be able to discern much planetary detail. Although anywhere around 100x can still produce images where much detail can be seen.

Combined with a 2x Barlow, it should be possible to calculate eyepiece magnifications so that an eyepiece that gives you around 150x can be also used to produce around 300x with the 2x Barlow. Then all you need is an eyepiece to give around 250x. Then you have a spread of 150x - 250x - 300x.

[Ricochet]

At the £50 price point a BST Explorer/Starguider is a good option. 

[Mak the Night]

1 hour ago, Ricochet said:

At the £50 price point a BST Explorer/Starguider is a good option. 

They look good: http://www.365astronomy.com/8mm-BST-Explorer-ED-Eyepiece.html

I think they are GSO.

[John]

27 minutes ago, Mak the Night said:

They look good: http://www.365astronomy.com/8mm-BST-Explorer-ED-Eyepiece.html

I think they are GSO.

I believe they are made by Barsta:

http://www.barsta.com/show_hdr.php?xname=MDA8V11&dname=OPFOR71&xpos=13

They are sold with many different brand names on them and at quite a variety of prices !. The BST Starguider or Explorer branding seems to be the lowest cost.

For a little under £50 a throw these are good eyepieces. I have a couple for star party use (the 18mm and 8mm) but I've been quite impressed with them for my own use. My usual eyepieces are Tele Vue Ethos and Pentax XW so the BST's are doing rather well to hold their heads up in that company !

Another very good low cost wide field eyepiece is the Maxvision brand which come in 68 degree and 82 degree versions. Much better performers than their price tags suggest.

It's hard to recommend standard plossls when the BST's and Maxvision's are available for relatively low prices.

 

 

[Mak the Night]

2 hours ago, John said:

I believe they are made by Barsta:

http://www.barsta.com/show_hdr.php?xname=MDA8V11&dname=OPFOR71&xpos=13

They are sold with many different brand names on them and at quite a variety of prices !. The BST Starguider or Explorer branding seems to be the lowest cost.

For a little under £50 a throw these are good eyepieces. I have a couple for star party use (the 18mm and 8mm) but I've been quite impressed with them for my own use. My usual eyepieces are Tele Vue Ethos and Pentax XW so the BST's are doing rather well to hold their heads up in that company !

Another very good low cost wide field eyepiece is the Maxvision brand which come in 68 degree and 82 degree versions. Much better performers than their price tags suggest.

It's hard to recommend standard plossls when the BST's and Maxvision's are available for relatively low prices.

 

 

Thanks John, I have seen their website page before but couldn't for the life of me remember the name. They do look very nice.

[Dave In Vermont]

With just the Barlow-len cell from a Barlow, which is a 2X model, you'd get between 1.5X and 1.6X. Couple that to an 8mm eyepiece, and you'd have close to 250X from the 8mm.

Dave