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Back focus problems! Help!

J

Jason Ing

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I read through the threads I could find on back focus and watched Doug's nikon back focus video.

But I can't get the back focus to work. I'm using Andy's canon dumb mount but I don't think it would be the mount.

I can't get it to focus at 3 feet a focus chart. I turn the red back focus but it stops right before it hits focus.

It's all the way to the end and I can't turn it anymore (turning it the other way makes it worse). If I then adjust the manual focus ring, it shows something between 3.5 feet to 4 feet when it focuses.

I tested my 28mm 70-200L and 24-70L. All the same.

And when I tried the zoom focus where I focus one end and then the other the focus worsens from one end to another.

What am I doing wrong?
 
Hi,

Sounds like the mount is too thick so your in "macro"

Stephen
 
I am assuming this is not the case, but you did remove the whole PL mount, right? There are two pieces to it.
 
Yes, I had to be careful about the iwire.

My current status is that when I turn the back focus ring all the way tight, I can get the entire focus range of all my canon lenses except the 24mm. But if I try the other methods of setting a specific distance, then it doesn't work. I've tried this with my 28, 24-70 and even my 70-200 for kicks.

So the trade off is:

I can't use a tape measure to focus by. No big deal, I wasn't planning to.

I can't zoom in, focus, and then zoom out and keep the perfect focus (it gets really blurry if I do this).

But, I can now focus on anything within the range of each lens. Good enough for now.
 
Jason Ing said:
Yes, I had to be careful about the iwire.

My current status is that when I turn the back focus ring all the way tight, I can get the entire focus range of all my canon lenses except the 24mm.
Click to expand...

If the RED adjustment is as close to the sensor as possible then it's back at Andy. He may have to rework his mount.

A lot of canon lenses have beyond infinity focusing which may be saving you. Put a 17-55mm or 11-16mm on there and you'll probably find you're really out of whack with those lenses.

To verify your zoom actually will hold focus put it on a SLR and take pictures at multiple focal lengths and check that they are all sharp enough. If not, then the problem may be the zoom.
 
Jason... when i fixed my mount right out of the box.. and did my collimation.. it didnt work out for me... I noticed that the andy mount itself was a tooth out. see first image attached on the left.

In order to fix that, you will have to remove the black dial "the collimator" .. just keep loosening up the two screws until they come out. The round metal then loosens up and you can open it up and start to take it off. YOU DONT NEED TO TAKE OFF THE EF ANDY MOUNT.

Now push the front part, the part that has the andy mount until it almost touches the rest of the RED body's mount. See second image.

now put the collimator dial back on and put the screws back in.. go collimate.. and you will get what you want.
 
Akube, Thanks for the diagnostics! very interesting, I've not had to do that
on my camera, it just worked. it's good to note that the mount should NOT
stick out beyond the front of the red backfocus ring. should be flush or a little recessed.
The tolerances that are inherit are very tight, that's why the
backfocus has to be turned all the way back. there just isn't much room. also
I think Jason's mount might be a bit out of spec. so I'm going to check it out
since 1/4 of a mm, is too much. keep the feedback coming. I'll keep on top of it.

-Andy
 
thanks akube. yes, that's what my mount used to look like. i then tightened everything to down as much as possible and now it's practically flush, but i wouldn't be able to get it to recess because the back focus ring is tightened completely.

hate to ask this, but does your workaround risk voiding warranty?
 
Nope you don't risk voiding your warranty. I sent my Red back for a sensor clean, I clearly told them I opened those parts and more, and they told me I did not void the warranty.
 
currently documenting the install process, going to put up a step-by-step picture page sometime tonight..

for the latest in install instructions visit here.. >> LINK <<

I'll update it with info learned from the forum, thanks all..


-Andy
 
Akube said:
Jason... when i fixed my mount right out of the box.. and did my collimation.. it didnt work out for me... I noticed that the andy mount itself was a tooth out. see first image attached on the left.

In order to fix that, you will have to remove the black dial "the collimator" .. just keep loosening up the two screws until they come out. The round metal then loosens up and you can open it up and start to take it off. YOU DONT NEED TO TAKE OFF THE EF ANDY MOUNT.

Now push the front part, the part that has the andy mount until it almost touches the rest of the RED body's mount. See second image.

now put the collimator dial back on and put the screws back in.. go collimate.. and you will get what you want.
Click to expand...

thanks akube.

how come you have to push it back and it's not just set that way originally by Red? is there a reason Red did it that way that we're now countering it? will it pose an issue for something else later?
 
I just did on my camera as Akube did, and I just gained about 1.5mm of back focus room! nice.
don't need all that but it's there.. I'm working on a detailed write up on what to do if you
encounter back focus issues.

looks like what causes the offset, is the i4/s data cable. it appears to coil up
in between the back part of the mount, and the moving front piece. and when
you move the backfocus all the way back the cable prevents the mount from
going all the way back. so possibly you could just pull out that length of the
cable before adjusting the back focus without removing the back focus ring collar.

thanks again Akube for the help!

-Andy
 
quick update, the front moving part of the mount doesn't look like it can
crush the data cable, it stops before and leaves a small gap. but if the cable
is coiled more than once in there it does take away a little room for backfocus.
still looking into it... pictures will be up tomorrow, as my memory card reader
just decided to quit on me.. grrr.

also I did swap back and forth to PL mount, and you do have to repeat the
loosen ring procedure otherwise the PL front becomes very tight to turn.
I will document all of this.


-Andy
 
alesniak said:
looks like what causes the offset, is the i4/s data cable. it appears to coil up
in between the back part of the mount, and the moving front piece...

-Andy
Click to expand...

Ahh.. you beat me to it.

Yes, and inorder to not get the data cable to coil up, just stuff it in the front mount's hole, I used the tip of my tiny screw driver (the one that I used to fix those small ef screws into the EF mount).

Make sure you don't sandwich the cable between the two mounts... You can't miss it...
 
a little tweezer work takes care of that extra coil. i saw it back there, (it's easy to see everyone) so I just grabbed some tweezers and pushed it back into its hole until all the extra slack was gone.

edit: haha. and akube beat me to that one.

thanks akube for this tip. i haven't tried the 24-70 but i'm sure this was the fix i needed.
 
Man, I tried em all yesterday. all the sigmas and bigmas. 24-70, 18-50, 70-200, 12-24. 20 f1.8. and canon's 50mm f1.8.
 
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