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[Rollei] Do Rolleinars require exposure compensation?
- Subject: [Rollei] Do Rolleinars require exposure compensation?
- From: "Dan Kalish" <kaliushkin >
- Date: Wed, 27 Mar 2002 19:16:13 -0500
- References: <200203270801.AAA21198
Well put, Richard. Now if I may interpret what you've said:
> Date: Tue, 26 Mar 2002 15:29:29 -0800
> From: Richard Knoppow <dickburk >
> Subject: Re: [Rollei] RE: Do Rolleinars require exposure compensation?
> Message-ID: <22.214.171.124.20020326152929.009564a0 >
> At 10:23 AM 03/26/2002 -0500, you wrote:
> >I don't understand the difference between the use of bellows and the
> >rolleinars. I also use a Mamiya TLR, and you have to admit the inclusion
> >bellows into the design was great. The bellows do require exposure
> >compensation as stated previously, and the compensation factors are
> >indicated on the side of the camera as you extend the bellows.
> >I'll try another test roll of Provia tonight, and bracket the exposures.
> >For an indoor still life lit from above (no flash), using Rolleiflex with
> >rolleinar #2 about 12-18 inches from subject, would you do an incident
> >reading or reflected light reading and why?
> >Thanks again,
> Exposure compensation using bellows is due to the inverse sqare law
> applied as the lens is moved further away from the film.
In other words, as the lens is moved away from the film, the same amount of
light is projected onto a larger area, so the amount of light per unit area,
or per frame, is less.
> A supplementary lens changes the focal length of the lens.
A positive supplementary lens, as a Rolleinar is, reduces the focal length
of the combination. This focal length is less than the focal length of the
basic camera lens (say 80mm) If the lens combination were positioned at its
focal length from the film (less than 80mm), there would be an increase in
light per unit area, or per frame.
> If the lens is
> used at infinity focus its speed also changes along with the focal length,
> as one would expect, close-up attacments making the lens FL shorter and
> lens faster. However, when its used at a _fixed distance_ the increase in
> speed of the lens with a close up attachment exactly compensates the
> bellows factor, so no exposure adjustment is necessary.
This is only precisely true if the lens is at infinite focus position of the
camera lens. If the lens is further away, there would be a slight exposure
compensation, as for bellows use. See Richard's last paragraph.
> I hadn't thought of it before but the same effect should take place for
> front-element-focusing lenses, since they focus by changing focal length
> rather than lens position.
> In fact, a bellows factor exists for any distance less than infinty,
> however its negligible until you get close enough for about 1:5
> magnification ratio.
> Richard Knoppow
Dan Kalish <kaliushkin >
Flushing, NYC, USA