Combined use of Focal Reducer and Barlow - Opinions !!

[Telescope40]

Hi. This question crossed my mind. Just looking to increase my options on different magnifications. I also have a binoviewer so pairs of matched eyepieces are not cheap !

I know the more glass added the less protons but putting that aside how would you calculate magnification ?

Multiply the Barlow 1st then divide by the Focal Reducer or vice versa ???

More than interested in opinions, most probably saying forget it

Thx John

[GazOC]

1000mm times by 2 times by 0.6 is the same as 1000mm times by 0.6 times by 2.....

[Telescope40]

Yep I'm with you on that, now i think about it some more.. Opinion on my other comment on whether it's an option. I'm thinking not He He

John

[GazOC]

I've done it a couple of times by mistake, left a reducer screwed into a webcam and tried to use a barlow to increase the image scale. I don't remember to being that bad but unless theres a very specific focal length/ ratio you need I can't really see much point to it either.

[brianb]

how would you calculate magnification ?

Multiply the Barlow 1st then divide by the Focal Reducer or vice versa ???

More complicated than that, the magnification you get from a barlow or focal reducer depends on where it is, if you change the projection length you change the magnification.

The best way of calculating the magnification given by a barlow or a field reducer (or a combination) is to time how long it takes for a star to drift across the middle of the field of view without it, then time the same star again with the extra glass inserted. If it takes say 40 secs without and 15 secs with, you're getting x(40/15) = x2.67 from the lenses. Use this multiplier on the raw magnification from each of your eyepieces e.g. x120 becomes x120x2.67 = x320.

Personally I think it's daft to use more glass than is absolutely essential, but whatever turns you on, so long as it doesn't harm me....