I just got to my 180 f/2.8 while I'm cleaning my gear - i just opened up the 180 and I know I never use it much but isn't there supposed to be glass on the back element??

There's no glass :(

Any idea what might have happened?

I may sound a little dumb, but are you certain there's supposed to be? The more telephoto lenses get, typically the farther into the lens body the rear element can be.

Just found the lens block diagram:



courtesy :http://imaging.nikon.com/products/im...d_if/index.htm

Ummmmmmmm... are you sure the element isn't just recessed? My MF Nikkor 180/2.8 has the rear glass about 1/2" back from the mount, and it can move to about 1/5". So, does yours look anything like this?

I'm not 100% sure, so I'm asking :)
Not really a big deal if it's supposed to be there, it's too slow for me when focusing.
Makes me mad to wait for it.

I think I got a bad copy.

I'll post a picture of it tonight after work.

Here's the back of mine, it's the non D version of the AF, rear element is set way in. First shot with the 85mm 1.8, second with the 105mm 2.8 micro. My guess is that your lens is fine

I guess maybe, I'm leaving work early I'll check it out.
I do think it focus' VERY slow though - like painfully slow on the D200

Focus speed on macro (Nikon calls them "Micro") lenses is generally designed to be slow. This is for two reasons:

1) At macro distances, DOF is extremely shallow, making focus critical. Slower focus speed allows finer increments for accuracy.

2) Slower focus also makes for smoother braking. On a dSLR, the autofocus is actually a type of electronic rangefinder and as the lens approaches prime focus the focus motor has to cut off just before actual focus to avoid over-shooting the mark. Slower focus speeds mean less momentum and shorter movement after the cut-off, also increasing focus accuracy.

Edit: Oh crud, it's not a macro. Never mind what I just said. I amuse myself sometimes.

I just looked, I have no glass in the back.
It just goes down about halfway to where the little blade thing that opens up is.

That normal?

I just grabbed the lens again and a lens pen, dropped the lens pen in, then grabbed a tape measure to measure how far in the lens pen went, it goes down 2.25 inches inside before the end touches glass inside.

This version of the 180, at least.





Yeah, the AF is pokey on this, but it does nice enough shots





I was able to catch this squirrel from behind the porch door

Originally Posted by nightowlcat I just grabbed the lens again and a lens pen, dropped the lens pen in, then grabbed a tape measure to measure how far in the lens pen went, it goes down 2.25 inches inside before the end touches glass inside. This version of the 180, at least. Yeah, the AF is pokey on this, but it does nice enough shots I was able to catch this squirrel from behind the porch door

That's the same one I have. Pull out hood, screw in cap.
I can put a pen in mine and touch no glass, I touch the screw type thing that controls the light input I think.

that normal?

Originally Posted by The Mack That's the same one I have. Pull out hood, screw in cap. I can put a pen in mine and touch no glass, I touch the screw type thing that controls the light input I think. that normal?

Nope, mine stopped at the 2.25 inch mark with the lens pen. In the first batch of pics you can see the light reflecting back from the glass where it meets the side. Wonder what happened to yours, can you shoot a shot of it and post it?

Picture of the back




Picture from the 180 f/2.8

According to Ken Rockwell, and I promise not to quote him too often, "This lens has no glass behind the diaphragm ..."


http://www.kenrockwell.com/nikon/180af.htm

Ok.
Oh well. It works, just not as fast as I'd like it to focus.

Originally Posted by The Mack Ok. Oh well. It works, just not as fast as I'd like it to focus.

Do you make sure to disengage the manual focus when you want autofocus (like it says in the article)?

Originally Posted by ziggy53 Do you make sure to disengage the manual focus when you want autofocus (like it says in the article)?

I gotta be honest ziggy, I didn't.
Lemme go see if that works.

Yeah, the A was showing.

I put it on the D50 I have and it does focus faster than it does on the D1h. Btw, I did notice that the aperture blades are bare nekkid before the glass, as well so it's normal, it works, and it's a sharp piece of glass. Enjoy it!

D1H, 180mm, f4.5, 1/60