FA focus problem

JRoosa · Aug 3, 2014

I think that my new FA is focusing too close. The focusing screen looks OK, and the back and pressure plate seem fine. The mirror also looks OK, and the focusing screen is where it should be with the spring engaging it. It seems that if this is happening, then the film is either sitting too far back (which would require the pressure plate to be loose or something), or the focusing screen is too far down, which doesn't seem to be the case either.

This is off the first roll. It's with a 50mm E-Series that never gave me problems before. It's wide open, so no focus shifts, and this lens doesn't have a reputation of doing that anyway. Several of the shots look like this, and I feel that even though I was mostly just playing around and all excited about my new toy, I can't imagine that I wasn't able to focus properly.

See how the grass at the bottom is clearer than anything else in the shot, and the dog is just a little out of focus?

I usually use the side of the dog's head to focus and then recompose.

There are a few shots like this, but many don't have stuff in the foreground to find areas of sharper focus. Unfortunately, this is grainy film, so even the ones that seem OK may still have some focus shift. It's hard to tell.

I have a few rolls of Tri-X that I haven't developed yet. I don't have my darkroom back together yet, so checking the focus on those will be a challenge without enlarging. Maybe I need to fire off a roll of color film shot at test patterns and take it to Walgreens or something with quick turnaround.

This just seems like a weird problem to have on a quality manual focus camera. Maybe it's just me. Any thoughts?

Thanks!

-Jason.

shutterfinger · Aug 3, 2014

Instruction manual http://www.cameramanuals.org/nikon_pdf/nikon_fa.pdf
My first guess is the focusing screen is incorrectly installed. pdf page 67.
Is there a diopter lens attached to the eyepiece? If so remove it as it is most likely incorrect for your eye.
Is the lens mount ring perfectly flat around the body opening?

trythis · Aug 3, 2014

My first nikon was an FE in which someone had accidentally installed the pressure plate backwards. It was pressing on a little film guide screw pushing it away from the film plane. The film had a mm or so of wiggle room and my focus was off irregularly for each shot. If yours are always out of focus the same way its either the focus screen, mirror or the lens mount off plane.

pentaxuser · Aug 3, 2014

Is it possible for the focus on the side of the dog's head not to hold when you recompose? My Pentax FA works the same way but only holds focus with the right pressure on the shutter button. I have recomposed and not held the button properly and let this focus slip.

You might try focusing on a specific point and taking the picture instantly. This might tell you if when you recompose, the focus slips.

As far as I know moving the dioptre setting might improve "your vision" through the viewfinder but doesn't affect the camera's FA which is independent of how well or badly you see.

pentaxuser

JRoosa · Aug 3, 2014

Lens mount looks good. The eyepiece is actually from my FM and is plain glass.

I'll check the pressure plate. There is film in there now, so I'll finish the roll first.

I took out the focus screen and it is installed properly. It has the notch like it should per the manual.

Slipping focus seems unlikely with the manual lens. It's actually a little stiff after years of storage.

The plot thickens...I took a close look, and at the infinity stop, I have to focus in just a mm or two to get the prism to line up perfectly on a power line pole about a mile away. On a 28mm lens it seems to do the same thing, but it's really hard to tell in the wide angle. It seems to be just about the same in my FM but not quite as far off in that camera.

It sounds like there is a roll of test patterns in my near future. Any suggestions for testing infinity focus? Distant power lines? How far away does something need to be in order to be equivalent with infinity in a 50mm lens?

-J.

fstop · Aug 3, 2014

pentaxuser said:
Is it possible for the focus on the side of the dog's head not to hold when you recompose? My Pentax FA works the same way but only holds focus with the right pressure on the shutter button. I have recomposed and not held the button properly and let this focus slip.

You might try focusing on a specific point and taking the picture instantly. This might tell you if when you recompose, the focus slips.

As far as I know moving the dioptre setting might improve "your vision" through the viewfinder but doesn't affect the camera's FA which is independent of how well or badly you see.

pentaxuser

He is referring to a NIKON FA manual focus 35mm film camera.

The 50mm wide open has a narrow depth of field, recomposing may be causing the focus issue.

JRoosa · Aug 3, 2014

The 50mm wide open has a narrow depth of field, recomposing may be causing the focus issue.

Could be. I assumed the field is relatively flat, but maybe it isn't.

It it occurs to me that I should pop the lens on my d40 and see how it performs. That would instantly rule out lens issues.

J.

elekm · Aug 3, 2014

One thing you must check is whether infinity focus at the film plane and in the viewfinder is correct. When it comes to cameras, a lens should achieve infinity at a particular point. A lens can focus past infinity, so it's crucial that 1) you first check infinity focus at the film plane, and 2) you check infinity focus in the viewfinder. The first one involves recollimating the lens. The second generally involves altering the angle of the mirror, provided that no changes have been made to the focusing/viewing screen.

JRoosa · Aug 3, 2014

The lens infinity stop is fine. I put it on a digital body and it is tack sharp at infinity.

Time to print up some test targets.

I'm I hoping this is just me being careless with focus.

-J.

shutterfinger · Aug 3, 2014

How far away does something need to be in order to be equivalent with infinity

Infinity test target: any camera, lens, or rangefinder: use a target at least 5000 feet away. The moon, the sun with correct filtering to protect your eyes, or any other celestial object bright enough to be screen on the camera/rangefinder viewing window can be used.

I was using the tree line on the coastal hills as an infinity target and celestial objects were slightly soft. I brought up google maps to my location, and found the tree line was only 3/4 miles away. 5280*.75=3960. I found a building with lots of sharp lines 1.25 miles away and use it as my infinity target.

Checking infinity: Open the camera back and measure the guide rail distance and frame length area of the camera as they will be larger than the film format image area. Be sure to measure the area where the film lies, not the guides on the outside edges of the film path. Cut a piece of glass or rigid clear plastic to match the measurements. Some use a CD case as the source for the plastic. Place Scotch Magic Transparent tape on one side of the glass/plastic with the strips next to each other but not overlapping.

Mount the camera on a tripod, lock the shutter open on B or open the shutter on T if available, open the camera back and place the test ground glass/view screen against the guide rails over the image opening, tape side toward the lens. With a loupe focus the lens on an infinity target. Check the viewfinder image. If the viewfinder image does not match the film plane the problem is the focus screen, lens mount, or pentaprism.

It is possible the focus screen was put in incorrectly, the retaining frame deformed when closed, then the focus screen corrected. Check that when the frame is locked there is no play in the focus screen. Check that the focus screen is a correct one for a FA. I think some other F model screens will fit but the focus may not be correct.

Many years ago I had a 75-300 zoom on a FA on a tripod on a slight slope next to a sidewalk. A small gust of wind caught the setup and the pentaprism housing hit the sidewalk. It left a small scratch on the housing but the camera lens mount bent 15° outward an the bottom. I had difficultly getting the lens off the body, replaced the lens mount ring, and went back to using the camera with no other problems.

trythis · Aug 3, 2014

Great writeup but ...Please don't use the sun unless you have a shade 14 or darker welding lens and still since it will be focussed onto your retina through a lens its probably a terrible idea.

shutterfinger · Aug 3, 2014

Welders glass does not protect against the harmful rays from the sun nor does ISO 100 film exposed to direct sunlight for 5 to 10 minutes then processed normally. They do darken the sun to a small circular image.
Use solar observing filters only when using the sun as an infinity target. http://oneminuteastronomer.com/999/choose-solar-filter/

JRoosa · Aug 4, 2014

I tried the moon tonight after work. Still a little off in the prism when at infinity. It looks sharp on the ground glass. There seems to be some variability in the split prism based on my eye position. Sometimes it seems lined up, sometimes the top is a little right of the lower half with no change is focus setting. It is worse with glasses, but still there with contacts.

Tomorrow I have a hike planned and time to finish this roll. I'll be able to do some formal testing with some color film I can get processed and scanned at the lab down the street.

Always looking for a reason to get some more gear, I'm wondering if the 55mm micro lens in the used case at the local shop would make testing a little more precise...

A new focusing screen or two may also be on the shopping list. I wonder if the one in there is an aftermarket part. It has some solvent marks around the periphery, so somebody tried to clean it at some point. It is the correct one for the FA with a notched tab per what the manual says.

J.

trythis · Aug 4, 2014

shutterfinger said:
Welders glass does not protect against the harmful rays from the sun ...

Shade 14 welding lenses are actually Ok. Typical shade 10...or those dark green glasses (shade 3 to 5)...not so much

From Nasa:

"One of the most widely available filters for safe solar viewing is shade number 14 welder's glass, which can be obtained from welding supply outlets."

http://eclipse.gsfc.nasa.gov/SEhelp/safety2.html

shutterfinger · Aug 4, 2014

I've never been a fan of a split prism focusing screen/viewfinder. I use the matte area adjecent to the split prism and ignore the split prism when I cannot change to a matte screen.

JRoosa · Aug 4, 2014

Update:

The pressure plate is installed correctly. The odd shifting of the split prism view seems to be something to do with my eye position. I'm being more consistent now I guess. Now the infinity stop is a lot closer to being in focus. It makes very little sense to me how it can shift like that.

I shot a roll at a focus test sheet with several lenses. I also checked it with some distant power lines. Off to the lab.

Thanks for all the suggestions and help!

I am hoping this is all operator error and the camera is in spec. Otherwise I have 5 rolls of B&W film that might have some really bad focus issues along with a pricey trip to the repairman.

-J.

camtec · Aug 4, 2014

Were you shooting with lens wide open? Depth of field with a normal lens is NOT flat. It is curved. The distance from the lens mount to the film plane is called flange focal distance. This would be the least suspect. Keep in mind that depth of field decreases the closer to the subject you get. No need to use the sun, moon or other celestial bodies to check infinity focus with a 50mm lens. 1/2 to 1/4 mile will suffice. No, the 55mm micro lens would not be any better than a regular 50mm.

JRoosa · Aug 5, 2014

Yes, I was shooting wide open to try to bring out any odd mechanical issues. I don't usually use the largest aperture.

I have some high tension lines about a mile from the house that I used to check infinity.

If there is anything screwy, I bet it is with the mirror or screen now that I've checked the pressure plate.

I will have the film back today or tomorrow.

Thanks again!

J.

JRoosa · Aug 9, 2014

Film is back.

Infinity is fine:

Here is a crop from a larger image. Power lines are sharp. When I back off the focus a little to make the split image line up, it's slightly less focused.

Focusing with the ground glass area seems fine. This is from a zoom lens without using the split prism:

Reproducing a similar distance for the first image I showed gives significant front focus. This is also a crop from a bigger image, but focus is actually off the paper right about at the close edge of the placemat:

Here's a shot using a TC-201 with the 50mm Series E, also cropped, focused with the split prism on the black bar, focus is about on the near 6:

Time to ship it back to B&H for a little tweaking I guess.

I'm glad it's not the loose nut behind the viewfinder. I was feeling like a dope who couldn't focus a manual camera anymore.

-J.

trythis · Aug 9, 2014

Maybe the lens mount needs shimming?

elekm · Aug 9, 2014

Again, the first step is to check collimation of the lens. If it focuses to infinity correctly, then you probably need to adjust the angle of the mirror so that the split image is correct at infinity.

There should be a way to adjust this, but you would need to find where the adjustment is made. Some German cameras have a small post on which the mirror sits, and the adjustment is made from the bottom of the camera. On some Japanese cameras, the adjustment is under the front panel (the rewind crank side).

Every camera is different, so it might take a bit of time to find it.

I've done this with a couple of cameras, the last being a Contax 139 Quartz. Total adjustment time - 15 seconds.

Time to figure out where the adjustment screw was located - three months.

JRoosa · Aug 9, 2014

It's still under the used warranty from B&H so I'm not inclined to mess with it myself. There seems to be a little post with cross-slots under the mirror in the lens box. I suspect this is eccentric and functions as the adjustment screw.

It could use some new foam in the back too, so I might get two problems fixed at once.

Now I'm tempted to check the focus in my FM that I've had forever.

Thanks!

-J.

JRoosa · Aug 9, 2014

I looked inside and the adjustment screw looks like somebody tinkered with it...it has the telltale scratches of the wrong size screwdriver.

I think we have our culprit.

-J.

FA focus problem

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