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Halcyonic

4 or 6 mm Eyepiece for Planets

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Hi All,

  I will shortly be taking delivery of a second hand GSO 250 10" f5 dob after setting myself up for a Skywatcher Skyliner 250PX. The deal was too good to miss though and as a beginner means im not laying out too much up front.

The scope comes with a 25mm eyepiece only and as such i wanted to get a couple more to allow for different magnifications.

Having looked through the very helpful "Eyepieces - the very least you need." sticky thread i decided on getting a 5 and a 15mm eyepience to compliment the 25mm one for the different magnifications they offer and i think im going to go for the Vixen NPL Eyepieces as they seem to be well recieved and reasonably priced, although i'd really like a Televue as these seem to be the No1 choice, far as i can tell, however there are none second hand i can find at the moment and the Vixens seem to be well respected and within what i want to spend anyway.

Regarding size, I think im happy with my choice of a 15mm one, but there is no 5mm one, only 4 and 6. 

A 4mm eyepiece would give me a 312x magnification but in the thread mentioned above it states:-

"At about 200x, it gets hard to follow things with a Dob."

So im thinking the 4mm might be too much for a beginner like me to manage with, i expect, Jupiter quickly tansiting my FOV whilst i fumble about trying to keep up.

The 6mm will give me about 206 x Magnification and im thinking this would be the one to go for but i figured i'd ask you all first.

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I would not consider a 4mm and the be honest in the NPL I would not go to 6mm either.

At those focal lengths you will be wearing the eyepiece like a contact lens.

If it is planets then the Celestron X-Cels are good as they have a number at the shorter focal lengthss - 5mm, 7mm, 9mm, 12mm. They are however £59 each.

The others talked of are the BST Starguiders, not quite the selection at the lower end, 5mm, 8mm 12mm they are £49 each. Performance between the BST's and the Celestrons seem to be as close to identical as you can get.

So both an increase over the NPL's in cost but relevant if eye relief is relevant.

TV do not make a 5mm plossl, they stop at 8mm, and I suspect there is a reason for this.

The tracking with a dobsonian is simply that the field of view is narrow and so the objects drifts across and out in a short time.

Is the 250 f/5 ??

Expected f/4.5 of thereabouts.

Edited by ronin
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Hi Ya Halcyonic and a very warm welcome to the SGL - Have to agree with Ronin - you will really have to get in close to the EP's you mention, you mention a 15mm EP - this would probably be ok Barlowed (not sure if you have one) - In my 11" Celestron which has a longer focal length than your scope, I tend to "hover" around the 12mm EP for close up work on Planets - this is probably the maximum I can get away with on most of my nights out observing, but the 15mm Barlowed will give you enough magnification, but with the added eye relief - meaning you would not have to get so close into the EP and not have to nudge the scope as much when tracking and object.

Paul.

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I can raely use my 6mm in my little 130mm f5 so expecting 300x is going to be rare as hens teeth with the regular seeing conditions from my little experience.

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6mm all the way! 4mm will get used about twice per year due to unstable seeing/atmosphere.

The suggested BSTs are good but the Vixen SLV are better.....

Paul

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Hi All, thanks for the welcome.

I don't have a barlow, the only thing that comes with the scope is a 25mm eyepiece which is why I'm looking into a couple of others.

Reading the above it seems the 4mm is not recommended, the 6mm is, just not by Vixen. So with that in mind, would a barlow like the Baader Classic Q 2.25x as an example with a 15mm BST be a better choice or a 15mm BST and 6mm BST?

If there is a better barlow out there (for the price) and you think that is a better choice feel free to let me know.

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Why not start with just getting the 15mm (or there abouts) and see how you go.

Edited by happy-kat
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Never tried the NLP, but the SLV is certainly recommended for a 10" f5 Dob. They are two different ranges of Vixen eyepieces.

They are double the price of the BST! But they are better. Not night & day better. I'd be happy paying 50% extra for the BSTs any day.

Good luck

Paul

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x312 is reserved for only those few nights of exceptional seeing and are often so far and few between that it is hard to warrant the cost on a single eyepiece. Not to mention that the nudging of the scope would soon become a chore in a 52° fov eyepiece at those kind of magnifications. You would be better off putting the money towards a good barlow like televue or vixen. I have the 250PX on an eq mount and rarely use anything shorter than 7mm on planets due to seeing conditions where I live. The moon can be good for x250 (5mm ep) on some nights but my planetary ortho eyepieces only have a 40° afov so not sure how much fun it would be if I didn't have a tracking mount.

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Do you have any light pollution? If so you will struggle to get clear views with those high power eyepieces.

I had the Celestron X-Cell LS range and couldn't use anything more powerful than the 7mm, and then only rarely. If I were you I would go for one good quality EP at 8 to 10 mm rather than buying two at this point. You can then go higher or lower at a later date once you see how often you can get a clear image with the first one.

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A 5mm eyepiece will be suited to your f/5 telescope giving 250x power and a 1mm exit pupil.

Its recommended that a 2mm exit pupil offers more visual acruity, so maybe use a 10mm eyepiece.

Now you'll need to choose an eyepiece on design merit, and cost.

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Well,

  I think im more confused now that i was at the start despite all the useful advice here, i've been recommended and dissuaded from eyepieces of various sizes and manufacturers. :grin:

Trying to get a consensus from all the views here and slightly struggling BUT it seems that i may be better going for a better eyepiece than the Vixen NPL, possibly the vixen SLV's at around 8mm rather than 4 or 6mm. Which as luck would have it Vixen don't do. (its 6 or 9).

So does that mean i'm better off getting an 8mm Televue for now and simply leave it at that for now?

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I would try the 11mm TeleVue first as the 8mm is shorter on eyerelief. Guaranteed to work down to f/4.

As an aside, my Revelation 9 & 12mm Plossl's give great views for their silly prices. The BSTs offer wider views.

Edited by Charic

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There is so much choice in eyepieces these days and personal preferences vary so the recomendations tend to vary as well.

The scope you are buying has a focal length of 1250mm and when I had a 10" scope of around that focal length I found eyepieces with focal lengths of 8mm, 6mm and 5mm gave a useful and regularly useable range of higher magnifications at 156x, 208x and 250x. You will also find something mid range, say around 80x or 15-16mm eyepiece focal length, very useful as well to add to the 50x the supplied 25mm will give you.

There is always the option of using a barlow lens to fill some of these gaps of course.

My approach would be ultimately to "cherry pick" the best eyepieces in your budget to fill these niches. My guess is that in due course you will want to replace the supplied 25mm and consider something in the 2" fitting to give you access to wider fields of view in the lower magnfications. That guess is based on how I've seen others ideas progress who own a similar scope.

The GSO / Revelation / Vixen NPL plossls are very decent eyepieces for their cost so could provide a way to create a good 1.25" set to get you up and running nicely for a lowish outlay. As your experience with the scope develops you can be reading more about other eyepiece options that could be of interest in the future. 

Choosing eyepieces is probably more complicated than choosing the scope !

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As has already been mentioned, you will find it hard to get decent views above x200-250. Not because your scope or epepiece aren't capable, but because seeing conditions won't allow it. The temptation for beginners to go for high mags is understandable and we have all been there and done it, and probably wasted a lot of money and time doing so. Buy quality now, and you won't have to later.

happy-kat and charic mention starting somewhere in the middle (the tele vue 11mm plossl is a superb ep, as are the vixen slv's). Buy one of these, the Tele Vues often come up for sale second hand - I got 4 within 2 months each for £60 or less, the Vixens slightly less common s/h but around £60 too (for a +£100 ep - excellent value).

Actually, if you buy second hand, say around the £60 mark, you will have to spend much much more to improve on the views obtained.

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Should have said and it may be in a post (too lazy to scan through them all) there is a William Optics 6mm planetary that has almost entirely good reports. Cannot recall a poor review of it, but hedging my bets by saying almost, just in case.

Isn't there a club around Falkirk ??

http://www.sandyloan.f2s.com/

http://www.stirlingastronomicalsociety.org.uk/

Edited by ronin

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+1  #16 & #18.....not tried the 6mm WO SPL on an f/5 system, but it cant be any worse than on my f/6.  Second hand its a great purchase.

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When I started out, I basically bought the 9, 12, 18 & 25 Celestron excels, brilliant EPs, probs around £60 a pop now. I probably use the 12mm the most. I do have a 7.5mm EP, but like has been stated, your basically wearing it with the eye relief and it is incredibly uncomfortable.

My opinion (for all that's worth) would be to get a lower powered EP, maybe around 8mm, then work up towards so you have a nice range towards 25 or 32. Lower EPs don't get used all too often because of seeing conditions and because of how fast things will move across the FOV, you'll be forever nudging. I'm not going to suggest a brand because all I have is the excels and I don't plan to buy anymore (because they wouldn't fit in my case!)

Matt.

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I generally rate the vixen npl range highly and I own nearly a full set but I have to agree with the others with the 4mm npl.

I bought one (very, very cheap second hand) and you basically have to wedge your eyeball into the eyepiece to get anything useful out of it especially when using it for planetry viewing. Even the 6mm can be a struggle and doesn't make for comfortable viewing.

Personally, I'd look elsewhere.

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Short focal length plossl and orthoscopic eyepieces always have short eye relief. Its a feature of the design. This will apply to all brands / manufacturers.

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My most powerful NPL is the 8mm. I wouldnt go below this personally. I dont know what possessed me, but a couple yrs ago i bought a 4mm Celestron Omni. Ive used it once while observing the Moon on a night that was just perfect. I paid way too much for that EP (new).

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+1 for the 6mm Vixen SLV. Not the cheapest, but lovely in my 250px.

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The thing i love about Vixen EP's is that you can buy the NPL's (the cheapest range) and the LVW's (the most expensive range) and to the untrained eye the quality control/build is the same and the views are up there with each other. I know it sounds stupid to pay more if you are essentially getting the same result. Thats not what i mean. Vixen put the same effort into construction of each of their EP's, no matter the cost. 

The result: even on the cheapest range (NPL's), the view is sharp almost right to the edge of view and the contrast between light and dark is brilliant. My 30mm NPL easily detects faint fuzzies (galaxies) while scanning the night sky and then i zoom in using my 15mm and then my 8mm.

I'd love a full set of NPL's, but i think i'll give the 4,6mm a miss. The eye relief on them is not great but i get along with it. 4-6mm might just be pushing it.

Edited by LukeSkywatcher

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