Lens problem or operator problem?

Chris Jameson · Post by **Chris Jameson** » Tue Apr 29, 2008 8:39 am Etc/GMT-1+01:00

I've been having a consistent problem with my 90mm lens, a Rodenstock Grandagon N F6.8, being used on a 5x4.
All the shots I've taken (which isn't many sadly) are soft in the corners.
There aren't any excessive movements applied, a small amount of front tilt (maybe 1 - 1.5°) and the whole camera angled up in some shots, angled down in others.
All shots were taken at F22 and all show this softness in the corners.
I'll post an example when I can (limited internet access) to show this.

Is this potentially a problem with the lens or is it just me doing something wrong?

Any help will be appreciated.

Thanks,

Chris.

Post by **masch** » Tue Apr 29, 2008 9:20 am Etc/GMT-1+01:00

Chris,

Pictures would be helpful indeed...
Do you have softness in all corners at the same time or just some of them?

Marc

Chris Jameson · Post by **Chris Jameson** » Tue Apr 29, 2008 9:48 am Etc/GMT-1+01:00

I'm getting softness in all 4 corners.
Centre of image and the centre at the sides and top/bottom is sharp.

I should be able to get a photo up tomorrow morning.

IanG · Post by **IanG** » Tue Apr 29, 2008 11:17 am Etc/GMT-1+01:00

I've been using an f6.8 90mmGrandagon N for over 20 years and get superb sharpness right across the image circle. So I've never had a problem with corner sharpness.

Grandagon's have an extremely good reputation so there may be a problem, some LF lenses have shims to space the lens elements, these are washers that fit between the lens cells and the shutter. It is possible that one has been lost if the lens has been changed from one lens board to another

Alternately and far more likely 90mm's are a little more difficult to focus, and particularly to set the movements, compared to a 150mm f5.6 so I would do some further tests. It is possible that even at f22 you're not accurate enough for the DOF to bring the edges into sharpness.

Ian

Chris Jameson · Post by **Chris Jameson** » Tue Apr 29, 2008 12:19 pm Etc/GMT-1+01:00

Ian,

The lens was changed to a different lens board when I got the lens. There were no washers at all, either loose in the box or on the lens.

I've taken a couple of test shots which I should get back tomorrow night.
Set the camera up to take a shot of a brick wall (plenty of texture to check sharpness on the film) and used a good spirit level to get the lens and GG parallel to the wall.

This couldn't come at a worse time.
While I've had the lens since December I've hardly had chance to use it due to other commitments. I've just started using it now and found this problem. There's about 1 week left on the warranty. And I'm due to go on holiday to Oban next week and go on the Richard Childs & David Ward LF workshop day. So I may be without a lens, d'oh!

Cheers,

Chris.

IanG · Post by **IanG** » Tue Apr 29, 2008 12:58 pm Etc/GMT-1+01:00

Chris

Hopefully your lens will be OK, if not good luck getting it changed under warranty.

Ian

Chris Jameson · Post by **Chris Jameson** » Wed Aug 20, 2008 4:31 pm Etc/GMT-1+01:00

Well the problem has finally been resolved, by me getting a refund on the lens.
The shop I bought the lens from received it back at the end of April, did whatever it was that they thought was necessary, then sent it back to me.
The details on the warranty / repair card stated that the repairs had not been tested as they didn't have a suitable camera on which to test.
This was annoying enough, any repairs should be quantifiable and tested.
Regardless I ran off a couple of test shots and there was no change so the lens went back.
It's been with them ever since, and they didn't seem to know what was happening with it.
I called yesterday for a refund as I'm sick of waiting around for them.
There was no problem getting the refund, they appologised for the time it's taken, and said that they had been waiting for a part to arrive from Rodenstock to repair the lens.
But a few minutes later I got another call back to say that there had been some confusion with their repair agents and they'd been talking about a different lens.
Apparently the cause of the image distortion is due entirely to the recessed panel the lens was fitted to.
When they fitted it to a flat panel the problem apparently disappeared.
They say my lens panel is "squint" at the back and should be checked out.
However they were still happy to refund.

Is it just me, or does that not ring true?
The way a lens, any lens, attaches to a panel should have no impact on the optical performance.
Am I missing something here?

Whatever the situation the lens is already back for sale.
I'm not going to name the shop, but anyone considering a 90mm Rodenstock Grandagon N F6.8 for sale at £449 with "slight signs of use" might want to exercise some caution.

Anyone got a 90mm for sale....?

timparkin · Post by **timparkin** » Wed Aug 20, 2008 10:34 pm Etc/GMT-1+01:00

Any problem with the lens board should really be resolvable by tilting/swinging as the plane of focus should always be a 'plane'. Soft in the corners suggests a problem with the lens itself, i.e. possibly the rear element wasn't screwing completely shut? (that is the only thing that the lens board could contribute to the issue I think).

Tim

buze · Post by **buze** » Wed Aug 20, 2008 11:00 pm Etc/GMT-1+01:00

it's possible that the lens board itself could interfere with the back group: ie prevent it being screwed/mounted properly.

However it doesn't explain uniform softness in corners, regardless of the lens position. Are you sure your film holders keep the film flat ? The sheet are not sliding in the wrong groove either ?

Apple · Post by **Apple** » Wed Aug 20, 2008 11:54 pm Etc/GMT-1+01:00

unless it's as buze says and the lens doesn't fit together properly due to the lens panel stopping something seating (you could check this with another lens if you've got one by unscrewing the rear element group by a turn or two and looking to see the effect on the ground glass), I think that having a recessed lensboard shouldn't make a difference - if it's a 10mm recessed panel then you have to move the standards apart by 10mm to achieve the same focus on the g/glass - this doesn't give you soft corners per se...

Presumably the lens had the correct set of rear lenses to match the front set and they hadn't been swapped by someone who didn't know/care?

Anyway, at least you got your refund.

IanG · Post by **IanG** » Thu Aug 21, 2008 6:29 am Etc/GMT-1+01:00

Sounds like they don't have a clue what the problem is. Even if your lens board was squint the lens should be sharp on at least one corner. Anyway f22 should be enough to cover ant issue like that.

So you did well to get a refund. Only the previous owner knows the true story/history of the lens.

I assume you have no problems at all with your standard lens, ruling out other possible issues. Sometimes Fresnel screens are fitted, or even removed altering the correct position of the ground glass. this can be enough to shift focus.

Anyway better luck next time.

Ian

Chris Jameson · Post by **Chris Jameson** » Thu Aug 21, 2008 12:17 pm Etc/GMT-1+01:00

Thanks for the replies guys, glad to hear that I'm not going nuts!

To briefly reply to some of your suggestions:

The seating of the front and rear halves of the lens has been checked, everything was ok and as it should be.

The lens panel, at its closest, is at least 5mm away from the rear half of the lens so couldn't actually physically intefere with it at all.

The film holder used for the test shots was a DDS, and shots taken with other lens on the same holder were pin sharp.

As to whether the lens had the incorrect rear half, I honestly couldn't say.

It's all in the past now anyway, I won't be using that shop again, I just need to start the shopping process again...

Thanks,

Chris.