Powermate AFOV

This might e a stupid question but I can't find any info on this and since I'm a newbie...

f I use a 2" x2 Powermate, for example on a 17mm Ethos, will I have the same AFOV (100º)? or will the AFOV be narrower? My doubt is because if there is a 8mm Ethos with 100º of AFOV then one could assume that a 8,5mm "virtual"EP generated from a 17mm Ethos + a 2x Powermate would also give a 100º AFOV.

Am I wrong about this?

Cheers

Paulo Mesquita said:

This might e a stupid question but I can't find any info on this and since I'm a newbie...

f I use a 2" x2 Powermate, for example on a 17mm Ethos, will I have the same AFOV (100º)? or will the AFOV be narrower? My doubt is because if there is a 8mm Ethos with 100º of AFOV then one could assume that a 8,5mm "virtual"EP generated from a 17mm Ethos + a 2x Powermate would also give a 100º AFOV.

Am I wrong about this?

Cheers

Paulo,

A barlow or powermate would keep the AFOV usually. So the answer is yes, the 17mm + powermate would be similar to an 8.5mm Ethos, but with more glass and weight. The performance may not be quite as good as an 8.5mm. And switching barlows is not as convenient. But a barlow or powermate is a good way to save some money.

There are some barlow/eyepiece combinations that don't work well. For example, the Televue plossls and the Televue 1.25" 2x barlow would cut off some of the AFOV, from 50 degrees to about 45 degrees.

I don't know if the Ethos will have a similar problem. You may need to ask someone who has tried it.

Hope that helps.

Mike

The Powermate will not change the AFOV of the eyepiece.

Clear skies, Alan

All AFOV's are inherent to the eyepiece, by definition. However actual FOV's will depend on telescope focal length, and other things.

Another question is whether you will get vignetting (darkness around the edges, relative brightness in the middle). I simply have no experience with the Ethos/Powermate to tell you.

And I also would not buy the idea that you can add a Powermate or Barlow and expect to get the performance of a native shorter focal length eyepiece--too much added glass.

Alex