Some sums please can someone check.

[Chatham]

I have been reading some of the excellent primers and just want to check that I have followed them ok

I have ordered a 1500mm fl 127mm MAK so doing the sum gives me f 11.8 ( no hardship there it says that in the spec)

It has a 10mm 25mm and x2 barlow I make that gives possible magnifications of 60, 120 150 and 300

My exit pupil size comes to about 0.42, 0.85, 1.05 and 2.1mm

Guessing that the AFOV is 50 degrees gives at the highest magnification a TFOV of 0.16 degrees .

So if I was looking at the moon at the highest magnification I would be seeing around a third of its diameter.

If I was looking at 120 Mag my TFOV would be .42 degrees so the moon would still be slightly larger than my TFOV.

Does all that seem about right or do I need to go back to school ?

[umadog]

Sounds right to me!

[AWR]

The only thing to add is that using the barlow with the 10mm eyepiece will be pushing it a bit. 300x is a bit too much to ask from the scope.

Andrew

PS - Great scope choice though!

[pvaz]

I did this sometime ago Eyepiece Calculator by pvaz.

You do need to register so it can keep your list (a fake email will do). The fill in your scope, eps and barlows and press results. Come back and add as you buy new stuff and have it updated.

[Bizibilder]

Don't be too concerned about magnification - it is the atmosphere that generally governs what you can see and do! Often the highest magnificaton that the atmosphere will "allow" is around x200 - it doesn't really matter what scope you are using (within reason!).

Your sums seem OK to me so just go out and enjoy the view - you'll soon get to know what "works" for you and your scope depending on the conditions.

[Chatham]

Thank you all for your replies just wanted to see I was still following the plot

Yes I kinda knew 200x would be about the limit. I am heading to the Scottish highlands in spring though.