[rollei_list] Re: Rolleinar Parallax Compensation
- From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Thu, 4 Aug 2011 00:06:08 -0300
Emmanuel:
I add to your explanation below that the Heidosmat
Rolleinar ( or the older Rolleipar+Rolleinar for the viewing
lens)produces an optical perspective modification or perspective
distortion itself, you can clearly see it watching directly without
camera a vertical object with the Heidosmat Rolleinar and the same
object from the same distance with the taking lens Rolleinar, the
first one increases the object image size but it also causes a
perspective distortion for the object, you see it in different
position regarding its original position; in the other hand, the
taking lens Rolleinar increases the object size too but there is no
perspective distortion, you see the object in the original position;
the Heidosmat Rolleinar first element is an inclined plane, the
inclination varies for Rolleinar 1,2 and 3 being the most acute angle
for the Heidosmat Rolleinar 3, I have the versions 1 and 3, this
perspective distortion for the viewing lens Rolleinar is very
significant to compensate the parallax.
Carlos
2011/7/23 Emmanuel Bigler <Emmanuel.Bigler@xxxxxxxx>:
> Le 23/07/2011 03:32, Don Williams a écrit :
>>
>> Does anyone know what distance the prism is supposed to correct the
>> framing precisely?
>
> Hi Don and Rollei friends !
>
> I do not know the precise answer to this question, since, as you say,
> it would require some precise optical and mechanical measurements to
> be sure.
>
> However this is my guess. Call it "a conjecture" to be verified or
> contradicted by the real thing.
>
> As you know, under the Rolleiflex TLR ground glass (GG) you have a
> built-in mechanical parallax compensator. A moving frame, or a set of
> blades, connected to the main focusing system. Actually the ground
> glass is bigger than the 56x56 mm = nominal "6x6 cm" image frame, the
> height of the GG is larger than 56. When the camera is focused to
> infinity, the frame is set in a certain position. From memory, the
> frame is at its "lowest" position in the lower part of the GG image
> when focused at infinity.
>
> When focusing to closer distance ranges, the frame moves "up". Now,
> keep the Rollei focused to infinity and add a #N Rolleinar: N = 1, 2
> or 3. Infinity will then be "converted" to 1/N metres (** see note 1),
> and the shortest focusing distance, instead of being 1 metre on a
> standard Rolleiflex with a 75 or a 80 mm lens, will become 1/(N+1)
> metre. In fact the shortest focusing distance is .9 metre or so, about
> 3 feet, measured from the object to the film plane, an old convention
> for distance engravings. A minimum focusing distance of .9 metre
> instead of one metre ensures a minimum of overlapping focusing ranges
> between different Rolleinars.
>
> Now my guess is the following: when fitted with a #N Rolleinar, the
> camera being set to infinity (minimum of extension of the lens TLR
> panel), the parallax compensator is by construction set to infinity.
> Hence the #N Rolleinar prism HAS to properly frame for the distance of
> 1/N metre.
>
> What I do not know is: does the moving frame continues to properly and
> precisely correct parallax effects when focusing to the closest
> distance with a Rolleinar #N in place? The only thing that we can say
> without calculation, is that the displacement of the frame is is the
> proper direction, and that actually some compensation takes place ...
>
> And as Carlos says: if you are not satisfied with your Rollei-TLR for
> close-up work, take your SL-66 ! ;-);-)
>
> --
> Emmanuel from France, who fell "in love" with Rollei TLRs 34 years
> ago but still resists the SL-66 .. for how long ? ;-);-)
>
> (** note 1) "metre" since my spell-checker uses the British dictionary ;-)
> ---
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