Saturday, June 25, 2011

Rangefinder calibrations on 110B- part5

Last step on paper work, then we can go on to practical procedure.

By measuring rangefinder character and lens focus moving range, now we are going to combine two focus system into one-- cam, this cam will be inter-interpreting two systems, to sync each other in one. But bear in mind, one cam is synchronized with one lens, not all lenses mounted on camera.

Let's see how to do it. if there is a 150mm lens we are going to use for range-coupled with rangefinder, then before a dedicated cam is made, we need to measure the rangefinder character (A) and lens focus moving range in advance (B).

Refer two relations between (A) and (B), we begin to draw dedicated cam's outer curve.
  1. Define radius center and zero point.
    cam rotate pole radius is 2.8mm, and the zero point is 6.36mm
    The light blue dash line represents 127mm cam that Polaroid originally installed.

  2. The mirror rotates or moves as cam outer curve changes, if the outer curve is aligned with orange dash line, which is a circle in fixed radius, then no matter how you rotate the cam, mirror will always stays at the same position.

    Mirror moves as cam outer curve keeps changing it's radius (black line), outer curve across orange curve at zero point, distance between two curves is 0 at it. Outer curve is more or less radius than orange curve at other rotating angles, and according to the lens/rangefinder relations, radius changes differently.
    Use orange line as reference, to point out all the radius changes.
  3. As we measured before, cam rotates within 39° range as rail moves within 20.5mm range, effective outer curve will extended 10° more on both side, for easier installation in future.

    Draw lines across the orange curve, all lines radiate from pole center, distributed every 10°, these are the reference points. 
  4. According to the lens/ rangefinder measuring data, we now locate each reference point. Let's say while we measure the rangefinder, and find out the data as follows
    infinity  0
    30m     0.04
    15m     0.07
    10m     0.1
    8m      0.12
    6m      0.16
    4.5m   0.22
    3.6m   0.28
    3m      0.35
    2.4m   0.44
    1.8m   0.52
    1.5m   0.6
    1.2m   0.73
    1.0m   0.88
    0.9m   1.01
    and the data was transfered into characteristic curve

    Another data comes from measuring lens focus moving range

    notice the y-axis in this chart, it transfer rail moving range(mm) into rotating degree, as rail moves within 20.5mm range and cam rotates within 39°, so even distributes two measurement, safely transfer two units.

    find the focus distance at 10°, 20°, 30°, 39°, in chart above we get 4.45m, 2.4m, 1.7m and 1.35m. Then we back to the rangefinder chart, to locate 4.45m, 2.4m, 1.7m and 1.35m. we find that radius should add 0.24mm, 0.43mm, 0.56mm, 0.68mm accordingly.
  5. Drag reference points on orange curve according data we just read out from charts, move them to proper distance to reflect the variations.

    Then draw a smooth curve across all reference points,
  6. Enclose the curve with cam outline, make it a dedicated Geronar 6.3/150mm lens cam for 110B.

    to compare new 150mm lens cam to original 127mm cam, you can tell the differences on outer curves. (orange curve: 127mm cam)
so this conclude cam design paper work, what left is to make this dedicated cam for your camera.

Thursday, June 23, 2011

Rangefinder calibrations on 110B- part4

First system to be measured is RF parts.
We need to draw a rangefinder characteristic curve, to represent it's focus range. so there is a chart, focus distance in x-axis, and y-axis is the mirror moving range.
As we all agree, that Polaroid mass produced 110B cameras, so rangefinder part should  represent same character in every camera body, but after measuring so many rangefinders, I found out that they all have their own characters. Maybe the camera was for 3x4 instant film, no image enlargement required, so it tolerates for range variety, but it is intolerable if we use this rangefinder on 5x4 camera.

Each rangefinder on Byron will be measure their characteristic curve individually, record and draw in chart, for further matching their prime lens.

To quick finish this tedious job, I managed to use a laser beam to do the focus, no need to peek all the time, thus won't hurt my eyes too much.

The measuring result will be something like this.

Lens measuring is simple and straightforward, you mount the lens on a 5x4 camera, set it focus at infinity, then define this location as zero point. As we already know that 110B rail has 20.5mm moving range, so we should find out the focus range this lens has in 20.5mm rail movement.

Stick a simple ruler at the side of the rail, and a pin as a pointer, now you can focus object at different distance and record the rail movement.
The result should be as early post I made "Lens Curves".

Monday, June 20, 2011

Rangefinder calibrations on 110B- part3

So actually there are two focus systems, one by focus through lens, and one by focus through RF mirror.
Lens mount on front standard, from infinity to someplace near, limited by the moving range of camera rail, 110B rail got maximum moving range 20.5mm, for 150mm lens, it's about to 1.5m; for 127mm lens, about 1.0m; for 90mm lens, about 0.6m.
Rangefinder rotates mirror to adjust focus, by measuring 127mm lens cam, I found out that RF mirror rotates only 1mm to accomplish focus range from infinity to 1m.

How to synchronize lens and RF? that's what cam stands for. different lens needs different cam, cam with different outer curve. Outer curve comes from lens focal length. for 90mm lens, it can be set focus range from infinity to 0.6m, much wider than 127mm lens (i~1.0m) or 150mm lens (i~1.5m), so 90mm lens cam outer curvature steeper, 150mm lens cam outer curvature flatter.
Later I will show you how to synchronize two systems.

Saturday, June 18, 2011

Rangefinder calibrations on 110B- part2

Here are three main factors that you should know before you made a cam to fit to a lens.
1. Lens: You should know the range that lens can move on the rail, it is fixed range on 110B. But most important factor is within the moving range, how will the lens focus change?
Take 150mm lens as example, within the 110B rail moving range, it can focus between infinity to about 1.5m; in the same moving range, a 90mm lens can focus as near as 0.6m.

2. cam: cam curve controls the rotating range of the mirror, but cam rotates itself as rail moves, you should find out the cam rotation related to rail moving range.

3. RF mirror: All RF parts are fixed except mirror, it moves to change the RF focal point, I have shown you that for a 127mm lens, all the mirror moving range needed is within 1mm, but how about 150mm lens? how about 90mm lens?
Rail moving range is fixed, thus made 150mm lens to 1.5m, 127mm lens to 1.05m, 90mm lens to 0.6m. So we know that 1mm moving range for 127mm lens, and that will cover 150mm lens as well, but not enough for 90mm lens, we should extend beyond 1mm to reach the 0.6m focal point, it needs extended measures.

Wednesday, June 15, 2011

Rangefinder calibrations on 110B- part1

There is a mirror on rotation, according to the cam curves, thus each cam for different lens, will have different curve, reflecting the focal length.

this is cam for 127mm lens,
Vertical line on cam surface indicates when lens is focus on infinity. and as rotating in hole center, each degree of outer curve on top is keeping changing the radius distance, causing mirror rotate.

But how long the radius range a cam causes?

I used a usb micro scope to take photo of cam, and enlarged it, then make some distance measures.

After carefully measuring, converting digits into a curve, we found that outer curve of 127mm cam actually causes mirror rotate within 1mm range.

That means a lot, range finder that 110B equipped, focus from infinity to near 3.5feet, all controlled within 1mm range.

Monday, June 13, 2011

Spot head for SL66

Just bought a new Kiev spot prism head from Ukraine, new. and bought an adapter board for it, to fit it on SL66, from German.
So, it looks good, I can read the measures directly through the lens, no matter what lens I am on!