250 Dob. thoughts on my Planetry EP 'shortlist' please

[Eastridge]

I have c.£100 to spend upgrading EP for planetary viewing on Skyliner 250 (1200mm f/5) Dob. I have drawn up what I think is a reasonable shortlist based on hours scouring reviews threads etc. and would like thoughts on it before taking the plunge.

The scope is usually used in our back garden towards the edge of a small town in Devon (Bideford), which light map gives Bortle 5ish rating to but not far from Exmoor so intend to go there for any special viewing maybe 1 -4 times a year.

I wear glasses so understand that good eye relief is important & hence based on information on FLO website have discounted Vixen NPL’s.

The 10mm that came with the scope I know is poor and Jupiter’s bands (for me) were hard to see in any detail and the planet itself just that bit too small. However, I am aware of the 200-250 mag. limit for UK seeing.

I know lots of people rate 8mm for Dobs. esp. the 200P in most conditions but feel unsure that at x150 for me it has the magnification I want compared to the 10mm. Others seem happy with 6mm. presumably they only go out on nights with good seeing?

Anyway the shortlist and associated questions is:

Baader Hyperion 5mm – not sure what eye relief on this is like and is 5mm pushing it just too far with my scope for conditions?

Baader Hyperion 8mm + 14 & 28 fine tuning rings. Same question as above re eye relief , I am attracted to the range this gives but is the quality with the rings still good?

Celelstron X-Cel LX 5 OR 7mm – again is 5 pushing it? The 7 gives a bit more mag than an 8 but still have nagging doubt I want more magnification to be happy. Seems to have better edge correction than the Explorers which I understand is important for a fast scope like mine.

Williams Optics SPL 6mm – seems well liked and my gut feel is 6mm is the sort of mag. I want, but is one of the other options better.

BST Explorer / Starguider 5 AND 8mm – I know people really like the value for money & could get both for my budget to cover all bases but not sure about eye relief with glasses (it’s quoted at 13mm.) As this gives the same range a Hyperion 8 + 28 fine tuning ring which is better at 5mm: the individual Explorer lens or the better quality Baader with ring?

What do people think ?

Anyone who wears glasses with a 250 Dob who can comment based on their experience?

[Damo636]

The 8mm Hyperion with both fine tuning rings would give you a nice range of magnifications and enough eye relief to use with glasses. The fine tuning rings do not degrade the image as no extra glass is added into the optical train. The only thing is at f4.7 i think the Hyperion would show a fair amount of astigmatism in the outer fov.

I haven't used any of the others so cannot comment on them. I do feel though that the BST's 13mm eye of relief will be tight with glasses.

A used 6-8mm Televue Radian would fit the bill perfectly, pinpoint stars down as far as f4 and loads of eye relief. I had the 6mm and found it very sharp.

[Karen]

I have two hyperions and they are have very good eye relief and perform well with the fine tuning rings. I believe this is the case with all focal lengths.

I use a TMB 7mm a lot in the 250mm Dob and I feel it could easily go to 5mm a lot of the time. So I think that wil be my next size eyepiece but NOT a Hyperion because at £95 that would buy two TMBs or BST explorers which are very good eyepieces also. Having one or two Hyperions with their adaptability and 68 degree fov is useful though.

[Eastridge]

Thanks both. I can see some overlap here with similar thread on 10" Dob eyepieces but the key difference here may be that I am a glasses wearer and so need good eye relief.

Damo - i think you are right that the key downside is the astigmatism but if I have researched correctly that only effects the outside 15% or so? So it won't be where the planet is ? AT FOV 68% I think maths says that I still get almost the same sharp FOV as the XCel and more than the WO assuming they are both sharp to the edges?

Barring finding a Radian second hand The Xcel seems well liked by less eye relief ( 16 as opposed to 20) is a little bit of a factor.

[John]

I've tested a number of the Hyperions and they do suffer from astigmatism quite a bit in scopes faster than F/5 to the extent that I feel they are not good value buys for use in such a scope. 15% is being optomistic I feel - in my F/4.8 newtonian I was seeing astigmatism (rather than coma) in the last 30% approx of the FoV.

They are sharp in the central 50 degrees of the FoV but then so is a good plossl like the Tele Vue

[Bart]

My view on this is that if you are using it for planetary use, you probably wont be too worried whats going on in the outer edges of the FOV. If you are, then you're probably talking good money for the better EPs. I don't wear glasses Eastridge so maybe my views won't count for much in your particular case, but I can tell you the following. I bought the BST 5mm for my 250mm F5 and this gives me x250. I was reluctant to go to x250 but some members did say that you can go to that mag, just not that often. I thought, for <€50, I'd give it a go, what was there to lose? I am delighted I did chance it. I realise that's a lot of mag, but with this combo, I have seen the GRS transit Jupiter beautifully, and spotted Io transit as well, nice and clear.

Hope this helps.

Bart

[Eastridge]

Thanks Bart.

That's what I am wrestling with - is it better to get the Hyperion 'set' which gives me 5, 6, & 8mm + the photo adapter hubby wants but only sharp in central portion OR a sharp to the edge piece like others have suggested but then have to plump for a single magnification.

I am tending to the former but awaiting a reply from FLO to an enquiry. Also the 68' whilst distorted does help a little with finding and nudging.

[gooseholla]

A hyperion is better than two TMBs. Get 3 or 4 1.25" focal lengths from it and a 2" focal length.