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Making & Testing a Cam for SSG

 
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bartbob



Joined: 30 Oct 2010
Posts: 102

PostPosted: Tue Jul 26, 2011 2:54 pm    Post subject: Making & Testing a Cam for SSG Reply with quote

Used 45PSS's instructions to make a home-made P4 cam from a nail plate. Cutting and griding it for a 90mm Graflex Optar was a learning experience. Hardest part was getting the high/distant end fit all the way to the end. Filing and smoothing the high end tended to round it off too much. I finally put a scrap piece of nail plate next to and aligned with the high point to make the slope at the top fairly well correct. Next time, I may make the 7 degree angle at the high end only half way up then straight up so the curve goes past the infinity and .703" max height. Then make the curved cam surface easier to finish better to the peak. That part of the cam could stay further to the left side until the cam curve's finished to match rangefinder coincidence and lens focus. But it finished up darned close to perfect and final smoothing the cam slope made it as smooth as the Graflex P34 cam.

Two problems came up.

First, the nail plate was .035" to .036" thick in some areas and .040" or so in most others. I used the thinnest part of it for the cam. After dressing all edges smooth as well as the front and back sides, it often stuck in the cam tube when focussing. The Graflex P34 cam for the 135 Optar is about .031" thick and it slides easily and never sticks in position. I don't know what's causing the home made P4 cam stick unless it really needs to be thinner. Checking the edges where it rides in the SSG's cam tube and surfaces don't show any sharp or ragged edges that could catch on something.

Second, with the 90mm Optar lens wide open and sharply focused at f/6.8, focus shifts when stopped down to f/16 and smaller. Subjects at all distances with rangefinder coincidence but only when the aperture's stopped down to at least f/16. Both lens groups are tight in the shutter. Any ideas why this happens?


Last edited by bartbob on Tue Jul 26, 2011 6:32 pm; edited 1 time in total
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1banjo



Joined: 16 Nov 2008
Posts: 478
Location: kansas

PostPosted: Tue Jul 26, 2011 6:30 pm    Post subject: Reply with quote

will I use Brass Door kick plate & it is .030 to .032
AND not as hard to cut!!
AND as it is not like metals it will slided better!!

I came up with 17.81mm[.701"] //infinity and .703" max height.
and 10.9mm on the other end
BUT with most of your cams infinity and .703" max height
should be about the same But the other end should be bifferent
on each cam!
your 90,100,127,& 135 should have a curved to the ramp
but a 203 or 210 will be almost straight
what I come up with for my cams
about 17.81mm large end for infinity on all cams
10.9mm small end for 90mm
11.2mm small end for 100mm
11.73mm small end for 127mm
11.99mm small end for 135mm
15.42mm small end for 203mm
15.69mm small end for 210mm

now #2 yes there is a slite focus shift any time you stopped down
BUT as you are gaining DF it should get better

banjo
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bartbob



Joined: 30 Oct 2010
Posts: 102

PostPosted: Tue Jul 26, 2011 7:44 pm    Post subject: Reply with quote

1banjo wrote:
will I use Brass Door kick plate & it is .030 to .032
AND not as hard to cut!! AND as it is not like metals it will slided better!!

now #2 yes there is a slite focus shift any time you stopped down
BUT as you are gaining DF it should get better

banjo
Banjo, thanks for mentioning a brass door kick plate. I could also use 1/32" thick brass stock. I'll check Ace Hardware next time I'm there so see what brass stock they've got. I though brass might be too soft and wear away as the rangefinder's "knife edged" arm rides on it. If you brass cams work well, I may make another one out of brass just for grins. Then polish it to a glistening shine and tell folks it's solid gold........

Regarding my lens' focus shift when stopping down. Wide open, it's not focused at the same distance as when stopped down. At rangefinder coincidence at short, medium and far distant subjects, f/16 shows focus is good. Moving the lens position back and forth with the knob has sharpest focus equaling rangefinder coincidence. At 5 to 6 feet, f/16 and smaller has best focus at rangefinder coincidence. Wide opn at these short distances, wide open doesn't get best focus. Either my cam slope shape is not correct or this particular lens has an optical flaw 'cause I don't think a decent lens would shift focus that much stopped way down.
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45PSS



Joined: 28 Sep 2001
Posts: 3197
Location: Mid Peninsula, Ca.

PostPosted: Tue Jul 26, 2011 8:01 pm    Post subject: Reply with quote

Quote:
it often stuck in the cam tube when focusing

Lay the cam on a 10 to 12 inch mill bastard file, keep even pressure on the cam, and dress each side down .001 - .002 . If the nail plate is galvanized then file the galvanized coating off. Other file types can be used.
Option B: expand the cam gap slightly. The tube is brass and can be compressed slightly in the cam slot area when being removed/reinstalled in the camera body or when changing cams depending on the user.

Quote:
with the 90mm Optar lens wide open and sharply focused at f/6.8, focus shifts when stopped down to f/16 and smaller. Subjects at all distances with rangefinder coincidence but only when the aperture's stopped down to at least f/16. Both lens groups are tight in the shutter. Any ideas why this happens?


If the lens is shifting focus when stooped down, a characteristic of a Dagor, it is either due to the lens design or someone has had one or both groups apart and reassembled them incorrectly, most likely mis spaced.

If the cam is off until the lens is stooped down then file the cam with a needle file until it works correctly in the camera. The grinding stone used to form the slope can leave the edge slightly angled causing it to be higher on one side. The base edge of the cam may be uneven also causing it to sit higher than it should. Error is most likely .001 or less.
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bartbob



Joined: 30 Oct 2010
Posts: 102

PostPosted: Tue Jul 26, 2011 10:05 pm    Post subject: Reply with quote

45PSS wrote:
Quote:
it often stuck in the cam tube when focusing
Option B: expand the cam gap slightly. The tube is brass and can be compressed slightly in the cam slot area when being removed/reinstalled in the camera body or when changing cams depending on the user.
Thanks, 45PSS, I like this idea best. I'll expand the tube slightly and see if any improvement happens.
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45PSS



Joined: 28 Sep 2001
Posts: 3197
Location: Mid Peninsula, Ca.

PostPosted: Wed Jul 27, 2011 1:47 am    Post subject: Reply with quote

A local hardware store started carring .032 aluminum sheet at a reasonable price so I may remake my cams.
http://www.ksmetals.com/index.html
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bartbob



Joined: 30 Oct 2010
Posts: 102

PostPosted: Wed Jul 27, 2011 2:54 am    Post subject: Reply with quote

45PSS wrote:
If the lens is shifting focus when stooped down, a characteristic of a Dagor, it is either due to the lens design or someone has had one or both groups apart and reassembled them incorrectly, most likely mis spaced.
I think my Graflex 90mm f/6.8 Optar is a rebadged Wollensak Raptar with only the name plate info different. According to pages 52 and 53 in:

http://www.cameraeccentric.com/html/info/wollensak_14.html

it looks to me like it would be nye impossible to put the lens elements and spacers back together wrong. But I never put anything past a "make it fit at all costs" mechanic.

Using optial lens formulas to calculate how far they've got to move forward as subject distance shortens, this lens does not follow calculated answers. I used a focal length of 89.7mm which is what the Graflex P15 cam that came with it is cut for (Note: both the lens board and cam had a red dot on them; I assume they were meant for each other.) Each distance focused on requites a different amount of yoke movement forward than the optical formulas gave. So, maybe it's a design issue. But stopped down images it makes are very sharp; even good out to the edges of a 4x5 one.

If others having one of these lenses, your comments on focussing wide open and stopped down would be of interest.

Regarding:
Quote:
A local hardware store started carring .032 aluminum sheet at a reasonable price so I may remake my cams.
I'd use aluminum, too, if it was hard enough to prevent the knife edge in the arm riding on it from damaging it.

Last edited by bartbob on Wed Jul 27, 2011 11:38 am; edited 1 time in total
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45PSS



Joined: 28 Sep 2001
Posts: 3197
Location: Mid Peninsula, Ca.

PostPosted: Wed Jul 27, 2011 4:56 am    Post subject: Reply with quote

A P15 cam for a Pacemaker is 89.7mm while a P15 cam for a Super is 107mm so is it safe to assume it came with a Pacemaker cam?

Yes, lens made by Wollensak for Graflex are made the same as Wollensak lens the only difference between the two being the name plate, the same being true for Wollensak supplied shutters.

The lens diagram shown in the Wollensak catalog resembles a Double Gauss design. I know of no focus shift in this type of lens. the catalog does say the lens should be stooped down to f11 or more, probably for DOF not focus.

An earlier post suggest that the quality control for Wollensak lens was weak or there was a w i d e tolerance range.

With both lens groups disassembled would it be possible to transpose a rear cell element for a front cell element?
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bartbob



Joined: 30 Oct 2010
Posts: 102

PostPosted: Sun Aug 14, 2011 4:09 pm    Post subject: Reply with quote

Here's a 3 x 5 inch crop near the corner of a 20 x 30 inch landscape print used to see the lens' performance on Ilford FP4+ film enlarged 6X. The negagive was scanned at 750 ppi.



I think it looks pretty good. If a lens element or group was installed wrong, I don't think it would do this well. But I've nothing to compare it to, so I'm only guessing.
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