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YAIFP - Yet Another Infinity Focus Problem FD 200mm f2.8
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PostPosted: Sun Mar 02, 2014 11:58 pm    Post subject: YAIFP - Yet Another Infinity Focus Problem FD 200mm f2.8 Reply with quote
Hi all, I've been visiting here on and off for years but finally decided to post a problem I've got.

I have a Canon 200mm f2.8 IF nFD lens that doesn't quite focus at infinity. I use the lens for astrophotography so if it can't do infinity it's not much good. Ideally I'd like to adjust it so it goes a little past infinity, so I can turn the focus ring to the infinity stop and then back it up a little for sharpest focus, that way I can compensate for differing temperatures. I installed a conversion kit to adapt the lens to my EOS 20Da so I'm familiar with how the back of the lens comes apart.

Can anyone tell me how to fine-tune the infinity stop?

Thanks...
Andrew


PostPosted: Mon Mar 03, 2014 5:25 am    Post subject: Reply with quote
Most of the FD Super Telephotos have the adjustment screws under the rubber grip.


PostPosted: Mon Mar 03, 2014 12:21 pm    Post subject: Reply with quote
calvin83 wrote:
Most of the FD Super Telephotos have the adjustment screws under the rubber grip.

Is the focus ring in 2 pieces, where 1 part hits the stop, and the other part controls the focus mechanism? I know that some cameras have three tiny screws in the focus ring. You can loosen those screws and while the 'stop' is engaged, independently move the actual focus of the lens. Then just tighten the screws. I know the focus scale is independently held by three screws and it can be positioned correctly, after getting the stop and the true focus set.

Anyone know if this how it works for the internal focus 200mm f2.8 FDn?

Thanks...


PostPosted: Tue Mar 04, 2014 9:54 pm    Post subject: Reply with quote
Anyone have any definite information? Any help at all?

Andrew


PostPosted: Wed Mar 05, 2014 5:13 am    Post subject: Reply with quote
Why don't you stripped off the rubber in on the focused ring, see what happened to inside the lens when focusing from infinity to minimum focus distance and vice versa? There is free of risk to do so. Posts here photos or videos and explain what you have observed.


PostPosted: Wed Mar 05, 2014 5:48 pm    Post subject: Reply with quote
calvin83 wrote:
Why don't you stripped off the rubber in on the focused ring, see what happened to inside the lens when focusing from infinity to minimum focus distance and vice versa? There is free of risk to do so. Posts here photos or videos and explain what you have observed.

I did what you said, and since I had already had the back of the lens apart I was already familiar with it. I decided to pull the back of the lens apart since I didn't want to risk tearing the rubber focus grip by stretching it over the rear of the lens. In retrospect it would have been okay. Anyway, after getting to it, it is an easy adjustment. I'll post pictures of the entire operation.

Andrew
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