Will a .5 focal reducer halve the power of a barlow?

[Marko of Oz]

I can't test this myself at the moment so I thought I'd ask.

For example, if I put a .5 focal reducer before my 5x powermate will that effectively make the powermate a 2.5x ?

cheers

[raymo]

Yes
raymo

[Marko of Oz]

Sweet, can't wait to try it. More economical than forking out another $250 on a 2.5x powermate.

You read here and there about buying a barlow to double your eyepiece collection but no one ever says buy a focal reducer to double your number of eyepieces. Until now. :P

[mental4astro]

No, it's not that easy folks.

Barlows and focal reducers are not simple multipliers or dividers. They each work differently depending on the telescope - optical system- being used, and the design of the 'Barlow'. As a result, they add their own set of aberrations. Combine the two, and thing go to hell in a handbasket.

There is more than just one design of 'Barlow' multiplier or 'reducer'. Glass types and lens designs vary greatly for both. Many are scope design specific, others only work with a very specific instrument.

Depending on the telescope system, barlow will either work well across the whole field of view, or ONLY the inner area. Same for focal reducers. Couple them and the result is even more dodgy. There will be some combinations of Barlows and reducers that will work with a particular telescope system, but that depends on the type Barlow, the type of reducer AND the telescope system - chances are very slim to get a trifecta.

If you have Powermate and a reducer, then try it out. Only then will you see if the combination works with you scope/scopes. There's no free lunch here either... :thumbsup:

[astro744]

I concur with mental4astro. Note also the 5x powermate magnifies up to 7.7x as the increase from the top surface increases. See http://www.televue.com/engine/TV3b_page.asp?id=123&Tab=_app#.U4gMOHKSy5I

If you have the 0.5x reducer and 5x Powermate try it and let us know, but I wouldn't buy a reducer expecting it to work. The 2.5x Powermate certainly will work. However note from the same chart above that the 2.5x Powermate magnifies less at an increasing distance from the top surface almost matching the 2x Powermate.

[Amaranthus]

I use a f/6.3 focal reducer/flattener and a PowerMate 2.5 in combination in my C8 and it works fine. I typically do this when I using the FR for a wider visual field, and then want to increase the magnification on a particular object without taking the FR out.

[cometcatcher]

I'm not a big fan of stacking elements to achieve the same result that can be achieved with fewer. One might get away with it for visual, but photography brings out the defects. Sometimes less is more.

[Amaranthus]

It works okay for visual and planetary cams, I would not do it for DSLR/CCD imaging!