40mm vs 32mm EP

[Maideneer]

I don't yet have a 40mm EP but do have a 32mm EP and wondering if there is a substantially large difference between them (yes I know, 8 mm ha ha ha).  Going to AstonomyTools site I can't notice that much of a change between them but would appreciate some insight from those who have used both.  I'm operating a little Travelscope 70 + AZ-GTi mount (for now).

[Starwatcher2001]

I'd say much of it depends on the scope and the eyepieces in question.

I've got a 40mm Celestron Plossl ep with AFOV of 40 degrees, and a 32mm Bresser Plossl with a 50 degree AFOV.  The 40 gives me 59x and the 32 gives me 73x, but the true field of view for both of them is identical at 0.68 degrees.

I don't find that much difference in the magnification at long focal lengths. 59x and 73x are not that far apart.

The 40mm came with a telescope and is slightly better quality, but I've had the 32mm for decades and am kinda attached to it.

[vlaiv]

You won't see any difference in the amount of sky you can see between two eyepieces provided that they are both 1.25" eyepieces.

32mm 50° AFOV EP  (regular plossl) will have field stop that is max field stop for 1.25" format. 40mm will show you same sky only smaller in AFOV - only about 43° if I'm not mistaken.

Only thing that will change apart from image size will be exit pupil. This is sometimes good if your scope is particularly slow (think F/12 and above) - otherwise, 32mm is simply more sensible option to use.

[Stu]

I don’t see too much benefit in getting the 40mm. It would give you an exit pupil of 7mm vs 5.6 for the 32mm, but to be honest the 32mm is probably all you need unless using narrowband filters like an OIII. Which other eyepieces do you have?

[Maideneer]

11 minutes ago, Stu said:

I don’t see too much benefit in getting the 40mm. It would give you an exit pupil of 7mm vs 5.6 for the 32mm, but to be honest the 32mm is probably all you need unless using narrowband filters like an OIII. Which other eyepieces do you have?

I've got my 32mm Omni Plossl, 8-24mm Zoom, 20mm stock Plossl, 10mm stock Plossl, a 3x Barlow, and 2.3 X-Cel for some newbie impulse reason smh

[Alexis]

No reason to buy the 40mm. If you had an SCT or Mak and wanted to confine yourself to 1.25" eyepieces, then it would make more sense to add one, but you're not in that target audience.

Edited June 3, 2021 by Alexis

[LukeSkywatcher]

I tried a 40mm Celestron E Lux (once), and quickly sold it on. It was like looking through a Smarties tube. I have a 32mm Celestron Plossel which came in an EP kit. I absolutely adore it. It's so emmersive. It's my workhorse for scanning the sky. 

I'm sure I used the 40mm in my Skywatcher Heritage 130P. They didn't get along.

Edited June 3, 2021 by LukeSkywatcher

[Tiny Clanger]

2 hours ago, Maideneer said:

I don't yet have a 40mm EP but do have a 32mm EP and wondering if there is a substantially large difference between them (yes I know, 8 mm ha ha ha).  Going to AstonomyTools site I can't notice that much of a change between them but would appreciate some insight from those who have used both.  I'm operating a little Travelscope 70 + AZ-GTi mount (for now).

I have both ... madness I know, but the 32mm plossl belongs in my main eyepiece case, and I wanted another to use as a 'finder' in my small and very portable 80mm frac which has its own small case of plossls . A second hand 40mm came up for sale at a good price, so I went for it.

The view is pretty much identical in my little refractor, 32mm to 40mm, the main difference is that the 40mm ( a Celestron plossl,) is markedly bigger and heavier than the 32mm (a skywatcher super plossl) which affects the balance of the light weight 'scope , and puts a bit of a strain on the quite  flimsy stock diagonal I use with it .

I'd say stick with the 32mm .

Heather

Edited June 3, 2021 by Tiny Clanger

[Louis D]

If using an image intensifier, the 40mm will allow for a larger field of view than will the 32mm if it has an angle of view of less than 43 degrees.  Obscure reason, but it might apply someday.

[Alan64]

Almost 20 years ago I got a Tele Vue 40mm Plossl, instead of their 32mm, and simply because I didn't know any better.  I still have it. 

A few years ago, I got a Vixen NPL 30mm, which is okay, and then later, most recently, a GSO 32mm Plossl...

I can't tell you how relieved I am in getting that much further away from the 40mm, and there you are with a 32mm, yet contemplating a 40mm.

You can go ahead and get a 40mm, and compare it to your 32mm.  It wouldn't break the bank...

https://agenaastro.com/gso-40mm-plossl-eyepiece.html

But there is one important difference: whilst the field-of-view of a 40mm is practically the same as that through a 32mm, the background sky will be darker, blacker, more contrasty, through the 32mm.  The object being observed, therefore, stands out better.  So there you are.  Leave the 40mm Plossls on the stores' shelves, gathering dust.

With all your telescopes and eyepieces, ideally, you want a background sky of jet-blackness, black as coal, all the way up to the edges of the planets, the stars, whatever.