Wide F.O.V. EP

[Spec-Chum]

I always thought eyepieces were for looking through and enjoying the views, not analysing on a computer

If I enjoy the view I don't really care if it's got a true parabolic curve through the differential of the visible spectrum from the Oxygen III range.

Or something...

[Moonshane]

the chances are that there is more astigmatism in the average person's eye than in any decent eyepiece.

[michael.h.f.wilkinson]

I have spotted field curvature visually in my SCT with the Paragon 40. The edges required slight refocusing to get them sharp, leading to a slightly fuzzy image in the centre. Not a big problem, but definitely visible. Maybe you tend to refocus less with a 68 deg AFOV, than with the 82 deg AFOV of the Nagler 31.

[Ajohn]

Personally I suspect that the coma corrector is where peoples money should go on newtonians of any type. I've not been there so don't know. I have used 8in F6, 10in F6.2 and 11in F4.2 but not that much in the latter case. I see what these graphs show.

As far as apo's go I was rather lucky. I bought a meade 5in F9 when nobody wanted them used and that variant happens to be a good scope. I have had an 8in sct as well and the effects of the central obstruction can be seen. Can't compare this and the 8in newtonian side by side which is why I used the expression "I would say". I'm sure it would be a very close call at least. The 4in 6in comparison is mentioned in many old "boys own" type books on astronomy. Even one by Patrick Moore if I remember correctly. I probably have it around somewhere.

As toTexereau looking through telescopes he did a little more than that as anyone who read the book would see.

What it all boils down to is that there isn't such a thing as a perfect telescope really. All have one problem or another including cost and feasibility.

My interest in this sort of area came from the search for the biggest most perfect telescope I could possibly have in the garden. It took many many years to realise that it's more complicated than that. Texereau's book and later what I have seen with my own eyes helped a lot with that. It also helped me choose my 1st eyepiece purchases.

One of the reasons I posted this lot was a discussion elsewhere on here about the field of view of newtonians as against SCT's. Unfortunately it's not as simple as just the size of the hole for the eyepieces.

John

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[Moonshane]

Don't get me wrong John, when I have time I'll be doing the same as you - trying to understand more about optics generally and how and why they work - although I'm not sure I should now as it may lead to disappointment and everlasting pursuit of something unobtainable - hang on, I do that already

my comments as always should be taken to mean I do them with a smile on my face and am in no way 'having a go' as there's room for us all in astronomy, no matter what our observing and optical preferences are.

[Ajohn]

You may have got me wrong moonshane. Never meant to imply that I may have thought that.

Regards

John

[whitekiteuk]

This has all got very deep and I am lost. I have not as yet had chance to try my moonfish due to those fluffy grey things but as soon as I do, I shall let you know my experience and thoughts.

Baz

Hi Baz - I have exactly the same question as your original post. Santa treated me to a Skywatcher Flextube 300P synscan and the planetary views are fantastic, as is Orion Neb but I'm finding the open clusters filling the whole FoV and I feel like I'm missing something. Mrs Santa already thinks I pushed the budget a little bit with what I already have so the fact that I now 'need' another eyepiece is being met with a raised eyebrow and an 'oh, really' smile.

This has been a very timely and educational thread. I'm really looking foward to hearing what happens when you next get some some clear skies over Burnley...

Cheers,

Adrian

[bomberbaz]

Mrs Santa already thinks I pushed the budget a little bit with what I already have so the fact that I now 'need' another eyepiece is being met with a raised eyebrow and an 'oh, really' smile.

I know the look very well indeed Adrian, I shall report back to you once i get a try out

[bomberbaz]

Hello all, I prmosed to give my findings so here goes. I tried it out properly tonight and I was quite impressed with the results. Yes its not sharp accross 100% of the FOV but tbh, I didnt expect it.

What I did get was a very clear and sharp picture with no noticeable distortion of any sort accross 85% or so of the FOV. (although I am not that experienced but thats what my thoughts are)

Looking at pleiades through it was a joy, I absolutly loved it and spent an age peering at it through the EP. Just to clarify, its the Moonfish, 30mm, 80 degree FOV 2" EP. I picked it up for about £59.

I wouldnt mind comparing it to a more expensive 2" EP of a similar power etc, maybe shane has something we can compare next time I pay him a visit.

My overall opinion is its well worth what I paid for it and gives me all I expect and at this moment, want from my wide FOV, low power EP.

Baz

[Moonshane]

sounds like a great buy Baz! I have a 26mm 82 degree eyepiece so the results should be similar. in my big dob the figures would be as follows:

Moonfish 61x field 1.3 degrees exit pupil 6.7mm

Nagler 71x field 1.15 degrees exit pupil 5.8mm

[michael.h.f.wilkinson]

Sounds like a good deal you got there Baz.

Clear skies!

[Spec-Chum]

Nice one mate.

I knew you wouldn't be disappointed. It really is a remarkable ep for the price.

Welcome to the moonfish club haha

[Ajohn]

I've been in the moonfish club from shortly after they bought it out. They seem to try hard on what the sell.

Some one mentioned how effective coma correctors are. I believe they tend to be aimed at F4.5 but can be used at other ratios and will usually improve things. The need depends on the field of view that is used really, There was some one in Oz some years ago on the web who's main interest was photography. Last time I heard from him he was using one with a scope of about F3.5 and was so pleased with the photo's he was going to go even shorter.

The book I posted a link to has a table of fields of view against size and F ratio of scope in the section on 2ndry mirrors which should give people some idea of when they may be needed.

John

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[bomberbaz]

Tried it again last night but on a much larger scope. The mag went up to about 140. A bit of star spiking at this mag although in all fainess the scope wasnt cooled fully and it settled down in other ep's later that also had spiking, so it appeared it was more the scope than the ep. However the great nebula looked amazing though it, the setail was ssuperb and tbh, unless you have a 16" sct or better, you are not going to notice the spiking even when uncooled.