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About digital_davem

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    South east London

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  1. Re: True FOV v Apparent FOV again

    Hi digital_davem,

    Out here in the Arabian desert, one can feel a bit astronomically isolated! I was out camping in a beautiful area of rocky and sandy desert last weekend. Amazing because recent rain had led to a brief sprouting of grass and the Bedouin had brought their herds of camels into the area to graze. I set up my small refractor on top of the huge dune we were camping on only to see clouds beginning to obscure the view!! Out here, clear skies are the norm, (but you do have to be careful when the wind whips up the sand and dust). I did get some nice views of Jupiter at least. A (photographic) friend queried when I explained that I was changing to an eyepiece with wider AFOV. I trotted out the stock answer about the difference between TFOV and AFOV, but quickly ran into difficulty when he persisted in asking why!! French philosophers used to say if you keep asking why about six times (or ten... can't remember!) you always run into God!!!

    I loved your questioning thread on this topic a couple of years back... By the end, I think you were theorizing that a telescope objective optic (lens or mirror) may produce a maximum illuminated circle. That the real difference between EPs with different AFOVs was how much of this maximum illuminated circle they could usefully use? With better quality (more expensive) optics and size, their field stop could be set wider giving the wider fields of view? Did you ever get to the bottom of this? Could you summarise your current understanding of the 'real' difference between TFOV and AFOV for us relative newcomers who still struggle!

    Thanks again

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