A different question about eyepieces

[Cazz]

I will measure the exit pupils when it's light and report back. I'm pleased you've enjoyed the puzzle.

This thread will also be a puzzle for anyone to follow it, lol.

[Tweedledee]

Hi Cazz,

If you have an exit pupil size then we can solve this puzzle in a jiffy . Or you can solve it using the following.

We now know the specifications of your scope...

Aperture = 60mm

Focal length = 900mm

Focal ratio = 15

Now you need the exit pupil.

Eyepiece focal length = exit pupil (mm) * Focal ratio

Therefore for your telescope: Eyepiece focal length = exit pupil (mm) * 15

Magnification = telescope focal length / eyepiece focal length

Therefore for your telescope: Magnification = 900 / eyepiece focal length

It should be noted that the same eyepiece, when used in a different specification telescope will provide a different size exit pupil and a different magnifiication. Still all in accordance with the above formulae.

Hope this helps.

[Cazz]

Thanks for the fab workings, it takes me back to GCSE maths, lol, I loved maths at school. I've taken notes in my new little note book.

Assuming I've measured it correctly, the exit pupil is 2mm at the 15X setting, and 1mm at the 45X setting.

[Tweedledee]

Hi Cazz,

It is difficult to measure such small exit pupils accurately. The 2mm lower power equates to about 30mm focal length.

2mm x 15 = 30mm

I reckon that if you were able to measure it more accurately, it would actually be about 1.6mm which would equate to a 24mm eyepiece.

1.6mm x 15 = 24mm

24mm is a standard maximum size for a zoom eyepiece.

If we assume this to be the case, then the higher power is one third this focal length ( you said it says 15x to 45x ) a factor of 3.

So to conclude, I think you have a zoom eyepiece of focal length 8mm to 24mm.

In your particular telescope, this will give magnifications from 37.4x to 112.5x respectively.

In my opinion, you should not consider getting any shorter focal length eyepiece ( higher power) than the 8mm 112x. They will not give a good view on a 60mm scope. There are many other eyepieces around with different characteristics that could give you a better view within the focal lengths mentioned ( which is a good range). Some wil give wide fields, some better definition on planets. Depends what you want. The main limitation for you is really that the scope is designed for use with 1" eyepieces which are now outdated. Larger 1.25" eyepieces will not perform best in this scope, but will fit with your adapter.

Best regards,

Pete.

[Cazz]

Cheers thank you for the advice, tips and pointers

8mm to 24mm was suspected in an earlier thread, it would be logically to assume it's a run of the mill spotter eye piece. My guesstimation of 7mm to 21mm wasn't far off, but I've no idea of how or why I thought of this figure, clearly my brain knowledge is ahead of my thought and thinking process, or I had read this combination somewhere and put two and two together.

At least getting my head around things is giving enjoyment from the hobby whilst it's so cloudy and wet, I've not done much else yet, lol.

[Tweedledee]

Cazz,

The 7mm to 21mm you mentioned is the next most popular zoom eyepiece size after 8 to 24. There are very few variations on these zooms. The 7 to 21 would produce slightly smaller exit pupils, so that is why I think yours is actually an 8 to 24.

I spend a lot of time messing with the numbers, especially during weather like we're having