Nikon Lens

I have a 20mm 2.8D lens for a Nikon. Unfortunately the lens will not stop
down so I have to adjust my appeture or the speed in order to shoot a pic.
The lens is always set at 2.8. Does anybody know where I can find a manual
that shows how to tear down this lens and fix it so it will stop down
properly, or am I going to need to send it in to get it fixed at a shop?

bob

"rlking" wrote:
I have a 20mm 2.8D lens for a Nikon. Unfortunately the lens will not stop
down so I have to adjust my appeture or the speed in order to shoot a pic.
The lens is always set at 2.8. Does anybody know where I can find a manual
that shows how to tear down this lens and fix it so it will stop down
properly, or am I going to need to send it in to get it fixed at a shop?

If you did manage to take it apart, what will you do to fix
whatever is broken? For that matter, will you even be able to
tell what it is that's broken???

Regardless, I'd learn lense [de]construction using a less
expensive model... :-)

--
FloydL. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

"rlking" wrote in message
ink.net...
I have a 20mm 2.8D lens for a Nikon. Unfortunately the lens will not stop
down so I have to adjust my appeture or the speed in order to shoot a pic.
The lens is always set at 2.8. Does anybody know where I can find a manual
that shows how to tear down this lens and fix it so it will stop down
properly, or am I going to need to send it in to get it fixed at a shop?

bob
Your question contradicts itself. You say the lens is always at 2.8, but
you also say to get a proper exposure you have to adjust the aperture or the
speed. If the lens is stuck at 2.8 you can't adjust the aperture.

According to Floyd Davidson :
"rlking" wrote:
I have a 20mm 2.8D lens for a Nikon. Unfortunately the lens will not stop
down so I have to adjust my appeture or the speed in order to shoot a pic.
The lens is always set at 2.8. Does anybody know where I can find a manual
that shows how to tear down this lens and fix it so it will stop down
properly, or am I going to need to send it in to get it fixed at a shop?

If you did manage to take it apart, what will you do to fix
whatever is broken? For that matter, will you even be able to
tell what it is that's broken???

For that matter -- are you sure that it really *is* broken? A
bit more detail may help here. I don't have this lens, but I have some
experience with other 'D' lenses and similar.

1) Do you mean that you can't turn the aperture ring? The "D:
lenses tend to have a lock to keep the aperture ring set to
the smallest aperture -- which is necessary for the auto
aperture to work. For use on older cameras, you slide the lock
disengaged to allow the aperture ring to turn.

2) Do you mean that you *can* turn the aperture ring, but nothing
happens in the lens? Normally the lens will remain wide open
while it is on the camera body until the instant of exposure, or
unless the depth-of-field preview button is operated. (On a
D70, you have to press it a bit harder than you may feel is
normal -- at least such is the case on my D70. Also, when you
remove the lens from the camera body, the lens should stop down
to the aperture set on the aperture ring, as the camera body is
no longer holding the pin from the lens in the proper direction
to hold the lens wide open.

3) Do you mean that you can turn the aperture ring, and the lens
remains wide open, even when you depress the depth of field
preview lever or during the instant when you take a shot, or
when you remove the lens from the camera?

*This* last is an actual problem with the lens, and (depending
on the conditions under which the lens has been stored, I
consider two likely causes:

a) Oil on the aperture blades, which causes them to stick
together. This can happen when the camera is in too hot
an area for too long. An example would be shut up in a
car (the body or the trunk) during the heat of summer.
The lubes in the focusing mechanism (at least on manual
focus lenses) evaporates and condenses various places --
on internal lens elements causing the images to become
softer, and on the iris diaphragm blades, causing them
to stick -- usually wide open, but sometimes at other
settings. I'm not sure what lubricants are used in the
autofocus lenses. The manual ones use a rather thick
lube, more a grease than an oil, to give a smooth focus
adjustment which is unlikely to shift from vibration.

b) A broken spring -- the one which normally biases the
stop-down linkage towards the fully-stopped-down
position. (Or, if it had been subjected to severe shock
in just the right direction, it could decouple the
spring from its pins.)

Regardless, I'd learn lense [de]construction using a less
expensive model... :-)

I must agree. If the problem is a broken or disconnected
aperture return spring, you *might* get to it before you got too deep
into the lens to be able to recover.

Get a *good* jeweler's screwdriver set, work on a flat surface
with a raised border to keep small parts from rolling off, put out
several shallow dishes (Petri dishes are excellent, if you have them,
otherwise consider medium sized bottle lids (after cleaning off anything
which might harm the parts, such as salt from olive jar lids.

And get a stock of lint-free cloth for handling and setting down
the glass lens elements. (Note that some lenses -- notably Cannon --
use an exotic glass (Calcium Fluoride, IIRC), which can be attacked by
humidity in the air, if not sealed inside the assembled lens. For this
sort of thing, you will want a glove box with an inert gas (dry
nitrogen, argon, or something similar) introduced to displace the air.

However, if it is oil-covered diaphragm blades, you will need to
disassemble it rather thoroughly, clean the blades in the appropriate
solvent, (and probably clean the lens element surfaces as well), and
then figure out how to re-stack the blades. It is a very touchy task,
and if you don't have good fine motion skills, you may never get it
right again. (And -- you need special tools for the task, including
jeweler's tweezers for manipulating the diaphragm blades. It is a
similar task to deal with a between-the-lens shutter mechanism -- which
at least is unlikely to appear on any Nikon lens. But with that, it is
possible to send the shutter petals all flying by accidentally
triggering the shutter release as you are trying to position them
correctly.

I really think that you should experiment on cheaper lenses
first -- and work your way up to the Nikons as your skills improve.

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

I am not sure what your problem is. All of the newer Nikon bodies do
not allow you to adjust aperture using the aperture ring on a lens --
it has be locked at the smallest aperture. The lock button on your lens
is located just in front of the aperture ring and has two positions.
Orange dot is locked and white dot is unlocked. The lens must be set at
f/22 in order to lock it, unless you broke it trying to force it to do
something else. Aperture is adjusted by the camera, either
automatically or using one of the adjustment options. Most newer Nikon
lenses for this reason do not even have an aperture ring.

You can use the preview button on the front of the camera to force the
lens to stop down to the aperture selected by the camera; very useful
for checking depth of field.

OTOH, if your lens is really broken, you probably cannot fix it
yourself. Most likely the lens lock is physically broken, which will
render the lens useless on most modern bodies.