Nikon FE2 - all lenses indicate short focus

Leigh B said:

it must fit against the INNER film rails, which are a bit below the outer rails.

- Leigh

Click to expand...

Ok ... this little groundglass test wasn't quite as easy as expected. But, yes, I don't have an adequate instrument to measure the flange distance nor have I the experience.

Anyway, this is what I did:

1. Using the film plane indicator on the body, I measured and placed an illuminated LED panel six feet away as precisely as I could measure. The lit panel and its frame offer high contrast. The lit panel is bright, but it's uniformly diffuse. My intent was to focus on the border between lit panel and frame.

2. Camera shutter on B, groundglass against inner rails, turned lens until image appeared sharp in magnifier. Best sharpness was difficult to determine actually. It actually looked sharp at 5 feet (as marked on lens) through 6 feet. So, it seems to me the reading on the lens is reasonable as to what's in focus at the film plane.

3. Released shutter, looked through viewfinder, split-image circle was considerably off. When image in viewfinder seems to be in focus, image at film plane is not.

Someone mentioned the mirror - maybe angle or seating is off?

Theo Sulphate said:

2. Camera shutter on B, groundglass against inner rails, turned lens until image appeared sharp in magnifier. Best sharpness was difficult to determine actually. It actually looked sharp at 5 feet (as marked on lens) through 6 feet. So, it seems to me the reading on the lens is reasonable as to what's in focus at the film plane.
3. Released shutter, looked through viewfinder, split-image circle was considerably off. When image in viewfinder seems to be in focus, image at film plane is not.

Click to expand...

Hi Theo,

OK. The test method is reasonable.

You might get slightly better accuracy using a reflective target (white sheet of paper, half covered by black construction paper), but not a big deal. The active light source might give you too much contrast to accurately judge the edge.

The results indicate that the flange focal distance is correct, at least quite close to nominal.

That means your focusing screen is out of position. I don't know why. The shop should find it.
In fact, the shop should have found it when the camera was in previously.

I would call this a service warranty issue, and definitely not pay for a second visit to the shop.

Theo Sulphate said:

Someone mentioned the mirror - maybe angle or seating is off?

Click to expand...

Compare the center of your gg image at the film plane with the center of the image in the viewfinder.
If they're the same point, then the mirror is correct. If not, it needs to be adjusted.

For the test, you can scribe a pair of diagonals on the test gg, or scotch tape two threads intersecting at the center.

It's pretty unlikely that the mirror seating is off, since it's not removable, but its mount could be bent.

- Leigh

Point of information (only matters at short subject distances)...

The focal distance indicated on the lens is from the subject to the film plane.

The film plane is indicated by an icon on the top of the camera, a small circle with a lateral line through it.

The line indicates the actual focal plane, i.e. the front (emulsion) side of the film.

- Leigh

I just ran some quick calculations to quantify this error.

Given a 50mm lens (you didn't specify), an actual distance of 6' and indicated distance of 4'...

Using millimeters, Ds = 6' = 1829mm and 4' = 1219mm. f = 50mm (assumed).

The universal lens equation is: 1/f = 1/Ds + 1/Df where
Ds is the distance from lens front node to subject, and
Df is the distance from lens rear node to film*.

1/Df = 1/f - 1/Ds
The true Df should be 1 / ( 1 / 50 - 1 / 1829 ) = 1/(0.02 - 0.000547) = 1/0.019453 = 51.405mm.
Indicated Df would be 1 / ( 1 / 50 - 1 / 1219 ) = 1/(0.02 - 0.000820) = 1/0.019180 = 52.139mm.

The lens is off-position by 0.733mm = 0.029 inches.

For reference, the emulsion layer is about 0.0254mm (0.001 inch) thick.

- Leigh

*NB. For convenience when working with "normal" lenses we make the simplifying assumption that the front node and rear node are coincident, i.e. at the same location. For wide-angle they may be different.
For telephoto lenses, they're usually at very significantly different locations.

To make focus testing easier download and print lens test targets available for free on line. Two very good ones are Dead Link Removed and http://www.graphics.cornell.edu/~westin/misc/res-chart.html
You can make several copies or just one and attach it to a flat wall or board. I use artist canvas or foam core. Plain paper works fine, use the printers highest resolution.

The FE2 is now fixed.

The groundglass and mirror were checked by an experienced repairman at my favorite shop and realigned for accuracy.

Theo Sulphate said:

The FE2 is now fixed.

The groundglass and mirror were checked by an experienced repairman at my favorite shop and realigned for accuracy.

Click to expand...

Fantastic, but which one was out? The ground glass, or the mirror?

Mick.

Mick Fagan said:

Fantastic, but which one was out? The ground glass, or the mirror?

Mick.

Click to expand...

He said the mirror wasn't seated properly under one of the tabs.

I'm a bit surprised, as I was thinking the cage or holder for the groundglass was at fault. The holder doesn't inspire confidence in me, since I'm used to changing the groundglass from the top, à la Nikon F3/T or Hasselblads.

Ok - here is a photo of what the situation was.

In the first photo you'll see another FE2, black, with the mirror seated normally. Looking at each side edge near the bottom you'll see a small rectangular tab (gray and blurred) that goes over the mirror.



In this photo is my FE2 and the lower edge of the mirror is clearly up over the tab, not being held:



I'm embarrassed I didn't spot this (see post #10!). I was too focused (heh) on the groundglass.