ENG 2/3 b4 zoom lens for t3i
 

Hello,
Not sure this is the right forum for this, but I bought a Canon J15x9.5B4 KRS TV Camera Zoom Lens 9.5-143mm 1:1.8 off of ebay to adapt to my t3i. I got the adapter and the battery power but I'm not able to get it in focus when at the wide-angle end. I've tried adjusting back focus but it doesn't get anywhere near focused. This was bought from a top seller and they said it was used but in working condition. I doubt they tried it on a camera though. It will focus at the 143mm setting, so I have a pretty inexpensive 143mm lens (I only paid $99 for it). But I wanted to use it for it's ability to keep focus from telephoto to wide angle. I think the problem is with the back focus ring because I can feel it slipping, but I don't have a lot of experience with this. Is there an easy fix to this, should I send it somewhere to get it fixed, or do more research and buy something else?

Thanks in advance for any help.

Re: ENG 2/3 b4 zoom lens for t3i
 

This lens is not going to cover the full sensor of the T3i, since it's a lot bigger than 2/3". But you can use it for longer shots, probably. At wider angles you'll have some corner vignetting.

The way to adjust back focus on the lens is to find an object around 10-12 feet away that has some strong vertical or horizontal lines that are easy to focus. If you have a focusing chart, even better. Open up the lens to a wide aperture and zoom back all the way to the widest angle. Focus the lens as closely as possible. Then loosen the back focus ring and adjust it back and forth until the image is sharp, then tighten it down. You might have to go through the procedure a couple of times. Even so, the lens is probably not going to be as sharp as your regular lenses.

Re: ENG 2/3 b4 zoom lens for t3i
 

Hi Bill and thanks for replying. I'm using the 3x digital zoom to help cover the sensor and at f2.8 it looks pretty good at the telephoto end.

I've tried adjusting the back focus several times and several ways. I have macro off. I can only get it in focus at the wide-angle end if the aperture is almost closed and the iso is at 6400.

Re: ENG 2/3 b4 zoom lens for t3i
 

Which B4 adapter did you get? I'm guessing that it's too thick, which is causing your focus issues.

Re: ENG 2/3 b4 zoom lens for t3i
 

Hi Kin, I got the B4 2/3" ENG FUJINON Canon lens to EOS 550D 7D 60D T2i 600D T3i adapter from cieco7 on ebay. He said it has guaranteed focus to infinity. I wasn't able to get the lens ring off. I stripped one of the screws. But I was able to get three of them out and attach the adapter to the lens ring. The ring is only about 1/32" thick, so I don't think that would cause the focus to be off as much as it is.

Re: ENG 2/3 b4 zoom lens for t3i
 

Unfortunately 1/32" will indeed make that much of a difference at the wide end.

Re: ENG 2/3 b4 zoom lens for t3i
 

Well Kin, you were absolutely right. Now that I've done a lot of reading on back focus and flange focal distance I see how hilarious my last post was. Now that the last screw is "out of the way". I finally got the adapter on and the lens works perfectly. Thank you for saving me the trouble of sending the lens in only to have to wait 6 - 8 weeks, and who knows how much money, to find out there was nothing wrong with it.

Re: ENG 2/3 b4 zoom lens for t3i
 

Can you post pictures of the adaptor and configuration.

Re: ENG 2/3 b4 zoom lens for t3i
 

Hi Jose, here you go. I'm waiting for another tripod adapter plate for better focusing but this works for now.