Stuck again

[Robert Watson]

Hi all,

What's the dif between a 3 element and a 4 element eyepiece

Robert:icon_scratch:

[Doc]

One extra element

[ollypenrice]

The 'elements' are the individual lenses which are combined into a compound lens. They serve different purposes; one may provide the basic focus, another correct the errors of colour inherent in the first while a third might correct optical defects at the edge of the field and so on. In the case of EPs I believe nine is the record but I may be wrong.

In order to have the staggeringly wide field of view that they offer, modern high end EPs have many elements. However great this is for widefield, coma free perfect colour the fact remains that each element absorbs a little light so there is, as ever, no free lunch.

Refractors, too, usually have two, three or four element lenses. (Doublets, triplets, quadruplets.) The latter are only needed for photography where a very flat field is required.

Olly

[johninderby]

This is well worth a read as it should answer many questions you might have about the various types of eyepiece designs.

http://www.quadibloc.com/science/opt04.htm

John

[Doc]

This is well worth a read as it should answer many questions you might have about the various types of eyepiece designs.

http://www.quadibloc.com/science/opt04.htm

John

What a great read John.

[Robert Watson]

Hi John,

Yes a very helpful read many thank's

Robert