Average useful size for a high powered eyepiece

[bendiddley]

Hi all. Can anyone tell me what is a realistic, useful size of high powered eyepiece for an average night ie. the most used based on average seeing conditions? I live in berkshire in a small town with light pollution you would expect from that. The reason I'm asking is that I have just started getting into astronomy and have a lovely SW 200p dob that I'm playing with and I'm wanting to buy a high powered eyepiece for it so I can see the planets and the moon closer than the 10mm supplied, but I just can't decide how much mag to buy as I don't want to waste money buying something that is not going to be used because seeing conditions are rarely good enough for it, although saying that as an extra question if it really is worth having an EP for these rare occasions what would it be and is it worth it? Hope to hear from anyone.

[Pete Presland]

i use my Hyperion 3.5mm with my 200pds which gives a magnification x286 more than enough on most nights, i have used this on my mak180 which gives x771 , a lot of magnification but not much of an image x300 does seem to be about the max for most nights

[John]

Hi there,

I've found you need a range of high powers in your eyepiece case ideally so that you can find something that works well on a particular nights observing conditions.

With an 8" F/6 dobsonian I've found having 7mm (171x) 6mm (200x) and 5mm (240x) eyepieces provides usable options. If I had to pick just one I guess a 6mm would be it.

Sometimes conditions can change for the better or worse as a session progresses so it's good to have some variety if possible.

[glowjet]

First I am not a Dob user, but the basic fundamentals are the same, your scope is 1200 fl that means 10mm will give a mag of 120X you scope having some 200mm or so of aperture, at the maximum of 50X per inch will be in the region of 400X, but in reality with the British climate it will be nearer 30x or so, you are now limited to around 240X which would be achieved with a 5mm, or because your scope is quite fast, your 10mm using a 2x Barlow could be a better option. if you choose the single lens approach try and afford a good quality optic with as wide an FOV as possible, or a new good quality 10mm EP if you are only using the stock supplied one, and a quality 2X Barlow such as a TAL or if you can obtain one, the Celestron Ultima . but a lot of magnification does require good seeing, on those rare nights you could push your mag a fair bit higher, your own eye can only be the judge of that. most users in the UK work around the 200X mag as giving the best results

John.

[Moonshane]

if you have a restricted budget (and assuming that you don't wear glasses to observe) I'd recommend a 2x barlow and a 15mm Plossl. this will sit well in between your current eyepieces and with the barlow will provude a 7.5mm equivalent. I find this combo works really well on the school's 8" dob and provided really quite nice views of Jupiter last Autumn. if you eventually buy more then a 12.5mm plossl would also work well and provide a little more mag on best nights. if you buy used, you could get all this on astro buy and sell for maybe £45.

[Capricorn]

For over all use the majority of nights then an 8mm eyepiece, if your scope is 1200mm that will give 150x and the vast majority you will not need any more neither will you be able to use it that often.

Problem is you use 2 terms that do not necessarily go together: Useful and High Power.

So you will get answers for High Power and another set for Useful.

[pvaz]

It depends a lot on the place where you observe. Atmospheric conditions have the most influence. I for once use 5mm more often then not, but I get good conditions quite often.

For my 8" I find the most useful EPs are:

- the widest you can get for large (or smaller but faint) DSOs (a 32mm plossl or a widefield EP)

- Something around 15mm to 13mm for a closer look on average DSOs

- Something around 10mm to 8mm for planetary nebulas, globular clusters and planets on bad seeing conditions

- 6mm or 5mm for planets on good seeing conditions

[AlBoning]

Depending on average seeing for the location and how steady an image one finds pleasing, I'd say an eyepiece that produces 150X (give or take) in one's scope.

[paul schofield]

The highest power ep I use in my 200p is an 8mm this gives me 150 x which I find very usable. And on really clear nights I can comfortably use my x 2 Barlow and that works a treat too, but the seeing does have to be good.

[LukeSkywatcher]

Hi all. Can anyone tell me what is a realistic, useful size of high powered eyepiece for an average night ie. the most used based on average seeing conditions? I live in berkshire in a small town with light pollution you would expect from that. The reason I'm asking is that I have just started getting into astronomy and have a lovely SW 200p dob that I'm playing with and I'm wanting to buy a high powered eyepiece for it so I can see the planets and the moon closer than the 10mm supplied, but I just can't decide how much mag to buy as I don't want to waste money buying something that is not going to be used because seeing conditions are rarely good enough for it, although saying that as an extra question if it really is worth having an EP for these rare occasions what would it be and is it worth it? Hope to hear from anyone.

On most nights of the year (which are clear), i rarely go below 8mm with any of my scopes (70mm,90mm,130mm and 200mm) .However on those same nights, if i am observing the moon..............i kick up the magnification on my 200mm to a 6mm EP and get stunning views.

On the very rare occassion (and i do mean very rare), i have a 4mm Celestron Omni EP that i use to observe the moon.

Is it worth spending cash on a good EP that you may only use once or twice a year?

Not really. It all depends on the cost...........

My 4mm Omni cost 60 euros and has been used once.

A better choice would be a 6mm Vixen NPL COSTING £30:

http://www.firstligh...-eyepieces.html

With scopes (and with the UK weather), i think there is an unwritten rule that says that you really should not expect to push the magnification of your scope above the aperture size.

This means with a 200mm scope, the highest you should push the scope is 200x.

There are nights when you can and will be able to push the boat out a bit, but they are not that common.

[LukeSkywatcher]

The highest power ep I use in my 200p is an 8mm this gives me 150 x which I find very usable. And on really clear nights I can comfortably use my x 2 Barlow and that works a treat too, but the seeing does have to be good.

Totally agree.

[bendiddley]

that's great! thanks everyone for all your comments they have been very helpful

[umadog]

I find this table useful: http://www.cloudynights.com/item.php?item_id=547

As you say, seeing will dictate what you can actually use. However, the seeing limit isn't the same for every object. For example, the moon is higher contrast and brighter so it can take more power than dimmer, lower contrast objects, such as Jupiter. The brightness matters in this case, because the eye integrates information over a shorter time period when the image is brighter ("low light stops play", remember!). Similarly, double stars are high contrast and can take more power. It pays to have a range of eyepiece tiling the seeing limit if you're doing a a lot of planetary observing.

[pvaz]

Umadog makes some very good points.

Well if you can only buy the one for now, 8mm is a much safer choice, however it pays to have a 5mm on your box. It's much better to see the small planets at 240x. The moon will also show more detail.

If you don't mind the trade off in confort and field of view, then an orthoscopic EP will be a good choice. My baader genuine orthos provide panetary views as good or even slightly better then my Ethos 10mm and I got them for 50 each in the second hand market, while the Ethos cost about 8x more.

[bendiddley]

Umadog makes some very good points.

Well if you can only buy the one for now, 8mm is a much safer choice, however it pays to have a 5mm on your box. It's much better to see the small planets at 240x. The moon will also show more detail.

If you don't mind the trade off in confort and field of view, then an orthoscopic EP will be a good choice. My baader genuine orthos provide panetary views as good or even slightly better then my Ethos 10mm and I got them for 50 each in the second hand market, while the Ethos cost about 8x more.

thanks pvaz, i'd been wondering whether an 8mm would be a good choice as I quite like the look of the bst/exporers from skies the limit which come in 5, 8, 12 etc and had good reviews, I'd also wondered about the 5mm too.