Another Daft Question, 1.25" vs 2"

[TopHouse]

If you take say a 32mm 1.25 plossl eyepiece, and you take a 32mm 2" eyepiece, I realise the field of view would be wider, but, here's the stupid question, do you get a better quality of image with maybe more definition in the 2" because in effect it lets more light up it's hole that the 1.25 OR, is that extra bit of light it gets distributed across the wider field in effect making the quality of view the same but more of it?

[Merlin66]

If the eyepieces are the same design ie Plossls then the FOV will be the same...they are both about 50 degree AFOV.

Depending on the scope and the magnification there can be some benefits in using a very low power 2" eyepiece. But the exit pupil is still limited to 7mm by the eye. ( Exit pupil = telescope aperture/ magnification)

[marcdearn]

So, (sorry to hijack the thread)

I have a 135mm Newt

Rearranging the equation gives:

Exit pupil / aperture = max mag?

so a 6mm exit pupil (minimum recommended) / 135 = 22.5 times max mag?

Not going to see much detail am I????

[acey]

6mm (or more usually 7mm) exit pupil is *max* recommended, not min. You use that to find the *minimum* mag your scope (or rather eye) can handle, which for your 135mm scope is indeed about x20 (the rearranged equation being mag = aperture/exit-pupil).

[Capricorn]

6mm will be the recommended or optimum, not absolute minimum.

As the optimum performeance of the scope will be when mag=dia (mm) it would seem that they are aimed at the 1mm exit pupil.

It is all just a choice. If you do not want to go below a 6mm exit pupil then you will need a much bigger scope.

[marcdearn]

Ah...Got it

I dont want a exit pupil larger than 6mm (or so) because My pupil cannot get that big or bigger and it is wasting light?

a exit pupil smaller than 6mm is ok ?

*Light bulb flashes on*

Thanks

[TopHouse]

So, to bring this back on subject, what's the advantage of a 2" eyepiece over a 1.25" eyepiece of the same mag?

[TopHouse]

In fact, to give more info, what would be the advantage of the following, if i have this :-

Antares 32mm Plossl eyepiece

And i change to this :-

Adler Optik Adler Optik Skarp 32mm 2" fit 5 element SWA Eyepiece

What would be the advantage?

[John]

You will get a wider true field of view with the 2" eyepiece. It depends on the focal ratio of your scope whether the stars are nicely defined in the last 20% or so of that field - fast scopes challenge budget widefield eyepieces more !.

[TopHouse]

It's quite fast, explorer 200p F5

[GazOC]

I THINK I have that eyepeice under I different brand name and, while there are distortions at the edge at f5, it gives pretty good performance for the money (a lot better than the budget 30mm 80 deg eyepiece I also have) IMHO.

[pvaz]

The 2" it self doesn't give an advantage.

It only expands the width of the barrel allowing engineers to make EPs with wider AFOVs for the same EP focal lenght. For example (if memory doesn't fail) the widest AFOV possible on a 1.25" 30mm EP is around 50 degrees. While a 30mm 2" EP can go up to 82 degrees or so.

In other words: you can't buy an 82 degress, 30mm 1.25" EP, even if you have all the money in the world, cause it's physically impossible to build. You can however find them in 2".

[TopHouse]

Thanks for that PVAZ, So it only widens field really, I thought maybe because it had a bigger hole, more light could get in and the view may be improved, logical thinking really.

[John]

Thanks for that PVAZ, So it only widens field really, I thought maybe because it had a bigger hole, more light could get in and the view may be improved, logical thinking really.

I can understand that logic !.

It's aperture though that captures more light, resolution, contrast etc. The eyepiece just magnifies what has been collected by the primary mirror or lens.

[TopHouse]

The whole reason behind all this is that when i bought my scope i got an antares eyepiece kit, one of the eyepieces is a 32mm plossl and i have to say I really like it, my fave object at the mo is pleides, also i'm trying more with orion nebula, double cluster etc, and just really liking the view that 32 gives me. For planetary i bought a baader hyperion 8mm and the tuning rings which i love, was just trying to work out how best to improve my 32mm viewing.

[PhillyDee]

I use a 2" 30mm 80degree lens (no idea of brand!) and it gives stunning views of pleides. The lens itself is massive and much better than the 1.25" I got in my celestron set!