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Meade 56mm
Michael,
On an f5 scope, using a 56mm eyepiece will result in an exit pupil of 11mm. Maximum pupil dilation in a teenager is 7mm, it goes downhill with age from there, see the age graph in my post above.
I don't know the age of the OP but even if Ryan is 18 yo and has a 7mm dilated pupil, using a 56mm eyepiece will result in the loss of about 60% of the telescope's light. If his eye is a 6mm dilation, the light loss increases to 70%
The specific light loss is dependent upon the maximum pupil dilation of the observer. In the attached table you can see that even if he has a full 7mm pupil dilation, he will reduce the light from his 300mm scope to that of a 190mm diameter scope. I had temporary custody of a Takahashi LE 50 some time ago and I confirmed this in my f5.5 scope. The image was very dim and unimpressive compared to my 31mm eyepiece.
Also, these eyepieces don't give you the widest possible field of view as you state. A 50mm class eyepiece will only have an apparent field of view between 40-52 degrees. The true field of view (TFOV) is at most, the same as or less than an 80 degree, 30mm class eyepiece. The TFOV with the Takahashi LE50 was roughly the same give or take 0.1 deg as my Nagler 31mm. 50mm eyepieces are usually basic plossls and are not well corrected for fast newts so you will lose the outer field.
These 50mm class eyepieces are used to gain a bigger exit pupil hence brighter image on long focal ratio telescopes, f9 and longer. SCT's, Mak's and Cassegrains are very forgiving of optical correction and these eyepieces work perfectly well.
In short, a long eyepiece is a waste of money on a short focal ratio instrument. If you're looking for something cheaper than a Nagler 31mm, the eyepieces John Bambury recommended are your best bets.
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