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Big eye piece, big picture?

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I understand that the smaller in mm the eyepiece, the more power it has but I've noticed you can get (for example) a 4mm with a bit of glass you look at that looks 4mm in size however you can also get a 4mm which has a bit of glass that looks massive.

Does the size of the bit of glass you look at affect how big the image appears? Would Jupiter through a 4mm with a tiny bit of glass appear the same size as one of the really expensive pringles tube impersonator eyepieces?  Is it purely down to the quality of eyepieces?

Ill add that I'm assuming same power and field of view.

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If you've got two eyepieces with the same power and field of view, they'll produce the same size image in the same telescope. A better quality eyepiece may well give a clearer, more detailed image - depending on the seeing. Large pieces of glass at the front of the eyepiece can still give views that are like looking down a straw.

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Magnification will depend solely on focal length of eyepiece.

If you have eyepiece that looks like this:


has small eye lens and 6mm of focal length and you have something that looks like this:


6.5mm Morpheus with huge eye lens.

Both will provide the same magnification. Planet like Jupiter will be same / similar size in both.

Sharpness and definition of the view will not depend on how big eye lens is. Sometimes sharpest and best views come from those small eyepieces (monocentric, orthoscopic and so on).

What does change with large eye lens is observing comfort and apparent field of view. You simply need larger eye lens to get good eye relief and to have wider apparent field of view.

Rest of the eyepiece in most cases serves the same purpose. Eyepiece is large if it has more elements inside and larger elements inside. These usually serve to get wide apparent field of view and comfortable viewing. Simple eyepiece designs have 3-4 lenses in them, while complex can have up to 10 or more.

More is not always better and seasoned observers often value less glass rather than more.

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Lets makes this interest.

When you look at a small pizza (the size of the lens) the can see the pepperoni lets say 4mm is size. When you look at an extra large pizza (bigger lens) the pepperoni is the same size 4mm but you can now see a lot more pepperoni of over a larger area. 



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14 hours ago, Ratlet said:

a 4mm with a bit of glass you look at that looks 4mm in size however you can also get a 4mm which has a bit of glass that looks massive.

In my experience, the bigger glass makes viewing easier on the eye. The detailed explanation has been provided by vlaiv 🙂

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