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Dyptorden

TV Powermate vs eyepiece angle

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Hi everybody,

Can anyone tell me whether a 4x 2" Powermate preserves an eyepieces angle or limits it to a specific value?

Thank you,

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I believe the Powermates preserve the full field of view of the eyepiece they are used with. The 2.5x and 2x Powermates certainly retain the 100 degree field of view of eyepieces.

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A 4x 2" Powermate should preserve the apparent FOV of an eyepiece but the actual FOV will be smaller due to the incresed magnification.   :smiley: 

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Even if it hadn`t enough clear aperture (which isn`t the problem for a 2" powermate) it would introduce vignetting rather then reducing your field of view.

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Al Nagler designed his Powermate`s to go one step beyond the negative element Barlow. When a standard Barlow is used with short/medium focal length eye pieces, there is little or no problem with the increased eyepiece eye-relief. However, with long focal length eye optics, the diverging rays, moves the exit pupil further out, to a point beyond that intended by the lens designer. This may consequently cause some vignetting, due to the altered ray path, the lens optics not being large enough to allow the rays through. To overcome this problem, Al designed a 4 element system using a negative doublet and a positive pupil correcting doublet, restoring the field rays back to their original direction,  giving the magnifying function of the Barlow without any of its limitations. So there you have it, the most popular optical system used by our imagers, the only limitation that I can see is the price, something just over £280 for 2" versions and if you want the dedicated camera adapter, then you can add on a further £40 or so :)

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 So there you have it, the most popular optical system used by our imagers, the only limitation that I can see is the price, something just over £280 for 2" versions and if you want the dedicated camera adapter, then you can add on a further £40 or so :)

I know it, I own the 4x 2" one and the camera adapter. But my eypieces are Rubbish, and I wanted to know if it's ok investing in a large FOV EP.

Thank you everyone for your answers

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These quality optics along with top quality Barlows, neither add to or detract from the field of view, no matter what eyepiece it is being used, however, if the eyepiece is not up to scratch, no pun intended, then you will only exacerbate the optical imperfections. Used with a good quality eyepiece, there should be no problem. I am not into imaging myself, but if there were problems in this respect, I am sure someone with more knowledge would soon be pointing it out :)

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