A simple test is to put the modifier lens over the finder
lens, focus it and move it to see if the focus changes.
I think these are simple convex or concave lenses so the
exiting beam will be either converging or diverging. It is
possible to make a lens what is telecentric, that is that the
pupils are at infinity and rays parallel but it would not be a
simple lens. Telecentric lenses are found in applications like
gun sights.
On 12/8/2021 2:45 AM, John Wild wrote:
Wayne,
>From my memory of school physics, probably not really applicable in this instance, but if a lens is positioned from a subject at its focal length, the rays coming from the rear are parallel, thus simulating infinity.
In your case, using this basic principle, it does not matter how far from the image or viewfinder lens it is, the Rolleinar will emit parallel rays to the camera's lenses which can be set at infinity. The calculations for the angle of rays for subjects not at the Rolleinar's focal length is beyond my knowledge but within certain parameters, it should not make any material difference. I stand to be corrected on this point.
The principle of this can be used to check the accurate focus of a camera lens at its infinity setting...
A camera with known accurate infinity setting is set up with a ground glass (or similar) screen marked with a fine pattern/crossing lines, its back and shutter open with a light behind it. The camera to be checked is set up looking directly at the first camera. Depending on whether it is a viewfinder or SLR, with its shutter open or not as the case may be. If the infinity setting on the camera to be checked is accurate, the image of the fine marking should be sharp. If not, the lens to focal plane distance should be adjusted.
The distance between the cameras is not important because the rays coming from the projecting camera are parallel, hence perceived as coming from an infinite distance.
John
-----------------------------------------------------------------
*From:* rollei_list-bounce@xxxxxxxxxxxxx <rollei_list-bounce@xxxxxxxxxxxxx> on behalf of wayne pinney <tennjed@xxxxxxxxxxx>
*Sent:* 07 December 2021 22:36
*To:* rollei_list@xxxxxxxxxxxxx <rollei_list@xxxxxxxxxxxxx>
*Subject:* [rollei_list] Rolleiflex Old Standard/Rolleinar
I have noticed, on just about every Old Standard I have had a chance to look at, and even on my own two cameras, that the ring surrounding the taking lens and/or the viewing lens does not protrude from the front plate far enough to allow pushing the Rolleinar lenses fully onto the ring surrounding the lens. I assume that if the Rolleinar lenses do not bottom out on the edge of the lens ring, focus will be incorrect. Am I correct in this assumption?
Both of my cameras do focus correctly, without the Rolleinars. So I assume the taking and viewing lenses are properly adjusted.
Best,
Wayne---
Rollei List
- Post to rollei_list@xxxxxxxxxxxxx
- Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe'
in the subject field OR by logging into www.freelists.org <//www.freelists.org>
- Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with
'unsubscribe' in the subject field OR by logging into www.freelists.org <//www.freelists.org>
- Online, searchable archives are available at
//www.freelists.org/archives/rollei_list
