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I have pentax scope that takes 1.25" lens.

HOwever i saw this adapter:

Blue Firebal 1.25"-to-2" Eyepiece Adapter for Telescope on eBay (end time 11-Mar-10 20:17:44 GMT)

What difernce woudl it make using 2" lens in the pentax, would the image be brighter or wider? or is there still a 1.25 bottle neck ?

IN general what are the advantages of 2" lens over 1.25

tnx

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The advantage of the 2" eyepiece would be that it could have a wider field of view than a 1.25". That adaptor would remove that advantage though so you might as well stick with 1.25" eyepieces.

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`it could have a wider field of view than a 1.25"`

am not sure what you mean, are you refering to afov ? ive seen no 2" lens that have higher numbers than their 1.25" version. eg meade 5000 ultra wide is stated at 82deg for both 2" and 1.25

AM guessing a 2" lens lets more light through??

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Better spelling in the future plz

I grade this paper: C+

/chuckle

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2" really give an advantage when it comes to imaging. The focal plane image produced by the telescope is really quite wide and when imaging with a 1.25" hole the corners of the image will be vignetted by the restricted aperture.

For visual use the vignetting is still there, but visually it will not really be apparent because most of the time you are looking at the centre of the field.

There is no advantage to using 2" eyepieces in a 1.25" focus barrel, and also because of the extra glass involved the 2" eyepiece will be more expensive than the equivalent 1.25". It will also be heavier so could potentially cause lateral movement in a focusser that is not very robust, then you'll get additional aberations.

;)

Chris

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Better spelling in the future plz

I grade this paper: C+

/chuckle

Pedant ;):D

Andy.

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`it could have a wider field of view than a 1.25"`

am not sure what you mean, are you refering to afov ? ive seen no 2" lens that have higher numbers than their 1.25" version. eg meade 5000 ultra wide is stated at 82deg for both 2" and 1.25

AM guessing a 2" lens lets more light through??

A 2" eyepiece wiil give a wider TFOV(true field of view. divide eyepiece AFOV by FL of scope and multiply by FL of eyepiece)on lower power 'pieces.

82 degree AFOV eyepieces can only be fitted into 1.25" barrels up to 18mmFL or so. 70 degree ones, up to 24mmFL.

Cheers,

Andy

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