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Re: [ATM] barlow focal length
Hi Saqib,
>> negitive lens so is barlow bi-concave or plano-concave
Nearly any negative lens should work to some extent, if the virtual f.l. is reasonable. You could experiment with lenses from eyeglasses, for example. The nice thing about buying a Barlow is that you should get an achromat, a two element lens that reduces color aberrations. Mine appear to be plano-concave.
>> 2nd question is what is the focal length of
>> 2x,3x,4x... or even 8x barlow lens.
The power of a Barlow lens lies in the distance from the Barlow to the eyepiece, as well as the f.l. of the lens. So a Barlow with a given f.l. can be used at a variety of magnifications. Just move the eyepiece father or closer to the Barlow and re-focus to get the power you need.
John
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