Focal reducer??

[jed]

As a newbie i was wondering what a focal reducer was,

is it like a Barlow??? :?

Jed

[Ambermile]

Hi Jed

It's like a barlow but does the opposite. A barlow magnifies (and so reduces light a little as it magnifies the image and therefore the light is spread out more) whereas a reducer reduces (and so increases light as it "bunches" it up)

Arthur

[Naz]

As Arthur says that is the simple and easiest explanation, mine is a bit more tecky.

A barlow gives the effect of increasing the focal length, if you had a 1000mm focal length f8 (125mm dia) scope, a 2X barlow would make your scope behave as if it were a focal length of 2000mm, but now the f ratio would go from f8 to f16, the dia is still 125mm. this would allow greater magnification. i.e. A 10mm ep would give you mag. of 100X without the barlow, and 200X with.

A focal reducer works in the opposite manner, same scope as before, a 2x reducer would now make the scope behave as if it were a focal lenght of 500mm at f4. Now the 10mm would give you a mag. of 50X

nabban

[jed]

oh I see,

so am i right in thinking that if I use a 10mm ep with the focal reducer

I will get 20mm magnifaction but with twice the light and so help with deep sky objects???

thanks

Jed

[Naz]

You wont get any more light, that is fixed by the diameter of your object glass, be it mirror or lens.

These devices only give the appearance of altering the focal lenght, hence magnification. It would be better if you could meet up with someone locally, such as a the local astro club, then you could have a demo.

It's difficult to grasp with diagrams / maths and demonstrations

nabban

[Ambermile]

You get more light at the EP - but that light is spread over a larger area/field. Hard to visualise ...

[jed]

ok thanks,

i've seen a local ac i think i shall go along and have a gander