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# Trying out eyepieces in Stellarium

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Posted (edited)

What I want to do is input the details of each eyepiece into Stellarium so I can see what view the give me before I spend any money on them.
I have entered quite a few already, but on some, they don't give the field stop. I wonder if anyone could help me fill in the blanks, is the 'field stop' actually needed?

If anyone already has these details, could you please post a message with the details of your eyepiece(s) below;
Name
aFOV
Focal Length
Field Stop

Many thanks
(I've included my current list of eyepieces)

Edited by pooky2483

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Another option is to use this field of view calculator.

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I am no expert, but having a look here might help ( I leave mine at zero also). Hope it helps.

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Posted (edited)

The purpose of the field stop in Stellarium is for the program to calculate a more precise true field of view.

If you don't know the field stop, just leave the box empty. The program will then assume zero angular magnification distortion (amd) and will calculate the field of view based on that.

Often angular magnification distortion differs from zero. It very commonly has a value of around 5%.

I made a spreadsheet that calculates true fields from either known field stops or from apparent field of view and magnification.

The formulas used are here: Scope Calculator Formulas.pdf

And the spreadsheet is here: ScopeCalculator-2019-06-16.xlsx

The "known field stops" in the spreadsheet are from the websites of the manufactures of the eyepieces.

If you cannot find the field stop diameter of an eyepiece you can use trial and error. Enter field stops until the spreadsheet calculates an amd of about 5%. Then you have most likely entered the correct field stop for the eyepiece involved.

"Better" eyepieces like Ethos, Delos and Morpheus have amd values close to zero, and the manufacturers of such eyepieces are generally proud to publish their field stop diameters.

Edited by Ruud

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There is extensive data here on eyepiece specifications compiled and updated each year by Don Pensack in the USA. Don knows a lot about eyepieces !:

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That's a useful link John. Some work has gone into compiling that table.

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