Excuse me, I'm using a translator. If words are not clear or are funny .... ...

I have almost finished reading and translating the 13 pages . Can someone answer me to one or more questions, please ? :

1) Anyone know how to calculate the magnification with a Plossl 55mm with an NVD on it? Is there a general formula for any eyepiece ?

2) And by directly placing the NVD in the focusing point ( and therefore without putting an eyepiece ) , what magnification compared to the focal length of the telescope, and the advantage of this assembly?

3) If we put a reducer x0,7 or x 0,5, on a dobson, is there a central black spot, because of the very very low magnification (plossl 55mm + reducer). Because having a very fast F / D is good for the arms of galaxies ...and also avoid buying a small telescope to have large fields , or increase the fully visible objects in the field

4) Finally a last opinion, also for connoisseurs / specialists, I read that it was necessary to put a ring Canon EBX 2120 (?) , Between the plossl and the paracorr 2, to have a better image, is this true?

Thank you very much for your knowledges.

alain .

1) As an approximation, divide the NV eyepiece focal length (27mm) by the afocal "host" eyepiece to get the reduction factor:

27/55 = .49x.

Magnification is then telescope focal length / NV eyepiece focal length * reduction.

Since that is an approximation, I just use 0.5x. Based on true field, it is observational very close, and very close to the result with an actual 0.5x reducer.

2) You are discussing prime focus in this question. Magnification is computed just like a conventional eyepiece. The advantage of the prime focus arrangement is physical handling compared to the afocal method. Less strain on the focusers, star diagonals, and focuser boards. Changing magnifications is generally somewhat easier by adding barlows or focal reducers as desired.

3) No practical exit pupil considerations with devices such as cameras or NV eyepieces. The NV eyepiece can "see" a very large exit pupil - 18mm or more depending upon model.

4) I'm not sure I understand this question. Perhaps you are referring to a field flattener? Certainly not a requirement observationally, I have been using my NV eyepiece on a variety of telescopes and telephoto lenses for three years. But it would be an interesting thing to try.