5x7 B&J no longer focusing correctly - why?

[paulbarden]

I have a rather beat-up Burke & James Watson 5x7 that I've been using for several years now, and it worked well, for the most part. However, in the past year I have had problems with the focus not being correct on film. I have done tests in the past few days, taking great care to lock down the camera tightly and focus with the greatest care, and I even tested different lenses. And yet, correct focus on the ground glass results in film that has a focus shifted a bit further back in the scene. Here's a good example - this photo was made 2 days ago, and I carefully focused on the front rungs of the ladder, but you can clearly see that focus ended up about a foot further back:

https://live.staticflickr.com/65535/51303545071_00c808a835_k.jpg

Any suggestions as to how I might remedy this problem? This is the first time I've encountered this on one of my cameras. As far as I know, nothing has changed in how the camera is set up, or how I use it. It seems to be a problem that has crept in gradually over about a year.

Thanks.

[maltfalc]

so your gg is slightly too far back then. are you sure it didn't get flipped around at some point?

[paulbarden]

so your gg is slightly too far back then. are you sure it didn't get flipped around at some point?

Quite sure. I’ve never removed the ground glass, and the back only fits one way.

[Jim Noel]

As an aside, what lens is this?

[Dugan]

Did you stop down after focusing wide open?
Some lenses shift focus.

[Jeff Keller]

It somewhat looks like the right side is focused further back than the left side. Could there be something preventing your film holder from seating flush to the back on one end?

[Jason Greenberg Motamedi]

Did you change holders at any point? I have a few plate holders that have non-standard film to glass depths.

[Tracy Storer]

Check to make sure the ground glass frame (which moves out of the way when you insert the film holder) is seating all the way forward when you're focusing. There could be some obstruction, spring rubbing the edge or something preventing it going "home". The effects of this would be the same as what you're experiencing.

[paulbarden]

As an aside, what lens is this?

Voigtlander Petzval, approx f3.5
I don't know its focal length - never bothered to measure. As you can see, it doesn't cover 5x7.

[paulbarden]

Did you stop down after focusing wide open?
Some lenses shift focus.

There is no stopping down with this lens - its used wide open.
I've tested other lenses and found the same thing occurs with them all, and stopping down doesn't entirely fix the problem.

[paulbarden]

It somewhat looks like the right side is focused further back than the left side. Could there be something preventing your film holder from seating flush to the back on one end?

I've inspected closely and I don't see anything that would act as an obstruction.

[paulbarden]

Did you change holders at any point? I have a few plate holders that have non-standard film to glass depths.

I have only one 5x7 plate holder (Chamonix), so its the same one I've been using all along.

[paulbarden]

Check to make sure the ground glass frame (which moves out of the way when you insert the film holder) is seating all the way forward when you're focusing. There could be some obstruction, spring rubbing the edge or something preventing it going "home". The effects of this would be the same as what you're experiencing.

I've inspected the back, and I discovered that one of the screws that the pressure springs attach to at the insert end was quite bent, and no longer holding that spring in tension at the "parked" position. It was allowing maybe 1/2mm gap at the insert end. So, I have removed it, straightened that screw and swapped it for one from the opposite corner, and am about to test it to see if that accounts for the focus shift. Thanks for that suggestion!

[Tracy Storer]

Fingers crossed for you.

I've inspected the back, and I discovered that one of the screws that the pressure springs attach to at the insert end was quite bent, and no longer holding that spring in tension at the "parked" position. It was allowing maybe 1/2mm gap at the insert end. So, I have removed it, straightened that screw and swapped it for one from the opposite corner, and am about to test it to see if that accounts for the focus shift. Thanks for that suggestion!

[paulbarden]

Fingers crossed for you.

It appears you were right, and the bent screw on the springs mechanism was contributing just enough slop on one corner to throw off the focus. I have some test film I'm about to scan to verify the fix, but Mr. Loupe has already pretty much verified it. Thanks, Tracy!

[Dugan]

Yay!
I love happy endings! :)

[MIke Sherck]

My B&J 5x7 tailboard camera has two levers below the rear standard to lock it into place after focusing but sometimes when I flip them down to lock the standard I can see the rear standard move backward a little bit. Well, it's an old camera. I've learned to watch for it and fiddle with the locks.

Mike

[paulbarden]

My B&J 5x7 tailboard camera has two levers below the rear standard to lock it into place after focusing but sometimes when I flip them down to lock the standard I can see the rear standard move backward a little bit. Well, it's an old camera. I've learned to watch for it and fiddle with the locks.

Mike

Mike, mine has the same hardware configuration, and I’ve become very careful in making sure those levers are snug after I’ve changed the back orientation. It’s an issue with this design.