Re: Closeup lenses

[T3D john bercovitz <bercov@xxxxxxxxxxx>]

BobH writes:
> RE: Eric says they're great as you just measure the diopter distance
> (reciprocal meter = power), but John B. says "devil in details" where
> do you measure from?  He says he will look into calculating nodal
> point?

According to my measurements, the front focus just about lands on the
closeup lens.  The primary nodal point will be 50 mm back of that since
the combination focal length isn't affected by the closeup lens if the
closeup lens is located at the front focus.  So the primary nodal point
is going to fall at about the juncture of lens body and camera body.

Eric G writes:

> You know, I've always measured from the film plane. If this turns out to
> be incorrect, please don't tell me, as all of my close-focused chromes
> will immediately appear soft upon hearing the news...

I wouldn't dream of mentioning it.  That would be rude.  8-)

John B

PS: Don't forget that if you want to play with lens combinations, that
Excel spreadsheet (XLS file) and accompanying diagram (GIF file) are at
http://www.frii.com/~rkymtmem/tech3d/tech3d.html


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