Gaoersi 4x5 (and problem with calibrating lens mount)

[Jon W]

Hi all,

I have a problem with a recently-acquired Gaoersi 4x5, but since I’m fairly new to the forum and I don’t want my first substantive post to be a request, I’ll make some general remarks about why I thought it might be a good option.

I’ve used a Tachihara folding field camera before, for several years, before I had to sell it in 2014 at a moment when I was really short of money. I mainly used it for city scenes at night, and I found that:

I almost always used a 90mm lens.
I never ever used tilt and swing, but I used front rise almost ubiquitously.
Composing on a gg screen at night was pretty difficult (I used to place a torch on the ground in front of the camera and move it around to indicate where the bottom of the frame was, or use the light as a point for focussing on).
Opening and folding the camera was a pain, especially when I used the same lens 95% of the time.

Looking into how much it would cost to re-equip recently, I happened to come across a Gaoersi 4x5 going pretty cheap on ebay, which came with a 90mm lens cone and a viewfinder included. I’d never seen a design of this type, but it seemed to address most of my concerns, namely:

Eliminating movements I never use, retaining the one I use all the time.
Adding a viewfinder to simplify composition, and a lens mount with pre-marked distances to simplify focussing at night.
I could keep the camera ready to go, or even carry it round by the handle.

But mainly it was cheap (about $350) so it seemed worth a go.

The camera looks fit for purpose, and the front rise works fine, but of course there was a catch, which I’ll explain in a separate post.

[Jon W]

I've done a forum search, but couldn't find anything on this issue.

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It’s part of the normal set-up that the lens mount needs to be calibrated for the particular lens mounted on it. I have a Fuji SW 90/8. As it currently sits in the lens mount, with no adjustments, it’s too far forward. When the lens mount points to infinity, it’s actually focussed at about 2.5m. This sounds like a major discrepancy, but using the rough formula 1 / focal length = 1 / subject distance + 1 / image distance suggests that the lens is only about 93.4mm away from the focal plane when the subject distance is 2500mm, so the total adjustment shouldn’t be greater than 5-6mm (assuming I have applied the equation correctly, and allowing some variation for FFD variation on the Fuji, which I don’t know).

The only information I could find on adjusting the mount for lens calibration is here: http://www.bhcamera.us/install-lens.php.

It suggests that there should be two screws on the ‘lens ring’, which one loosens to adjust the ring. My mount has no screws, and the technician I showed it to at Aperture in London was adamant that the ‘lens ring’ on my mount is actually a fixed part of the mount and can’t be ‘loosened’ by any means. (But then again, he was also adamant that it was really a mount for a 120mm or 150mm lens, i.e. that it was 30mm+ out, rather than 5mm as I calculate.)

I could ask the Aperture folks if they can cut 5mm off the circular part of the mount and then reattach it, but a) I don’t if that’s possible; and b) it seems a pretty drastic and dodgy solution.

I could buy another 90mm mount, but a new one by itself is more than the entire camera cost me, and it would probably just have the same problem anyway.

I don’t need the focussing to match the indicated scale precisely: I can mark distances myself on the mount, and I only really need to be able to focus the 90mm lens between about 3m and 10m for my purposes. But a maximum distance of 2.5m is clearly unuseable.

Does anyone have any experience of resolving a similar problem, or can they recommend a London repairer where I can get a second opinion (ideally one that might have some experience of working with Chinese LF cameras)?

Thanks for your help.

[richardman]

The 90mm lenscone has a 10mmm rise possible. If it's the 120/150mm, I don't think you can make it work. I had one of these and they are fun to use. If you find the right lenscone, you can adjust the infinity focus. You can loosen the parts.

You will definitely need a adjustable lenswrench from ebay.

[Jon W]

Nice portfolio Richard!

It's definitely the 90mm cone, and it only needs about 5mm of adjustment, but the problem is that there's no obvious way to loosen the lens ring.

[richardman]

Nice portfolio Richard!

It's definitely the 90mm cone, and it only needs about 5mm of adjustment, but the problem is that there's no obvious way to loosen the lens ring.

I forgot exactly how it is done, but it can be done. You turn and prop and all of the sudden it comes loose :-) Just look at this page a lot: http://www.bhcamera.us/install-lens.php

and eventually somehow it works.

[Jon W]

I can't figure out how to do it myself without being able to loosen the lens ring, but I definitely want to get it checked by a second, knowledgeable technician before I resort to sawing 5mm off the whole mount. So if anyone can recommend a London LF technician I'd be grateful.