Setting minimum bellows extension

[Carl Schofield]

I've been practicing setting up and taking down a new Tachihara 4x5 field camera and have some questions about setting the minimum bellows extension. The instructions say to unlock the infinity locks and then pull the front standard to the "appropriate" position, based on the lens focal length (135mm in my case), and finally re-lock the infinity locks at that position. How do I measure the "appropriate" position? Is it 135mm, measured from the face of the front standard to the back of the rear standard or some other reference points? I assume that once this meaurement has been obtained I should mark the rail for future reference so I don't have to re-measure every time the camera is set up, or is this not a particularly critical measurement?

[John Cook]

I believe every lens formula is just a tiny bit different. Nikon calls this the "flange focal distance" in their literature. Their Nikkor-W 135mm has a flange focal distance of 133.8mm.

This actual measurement becomes critical when using a press camera without focusing on the groundglass.

[Brian Ellis]

You certainly can mark it but you don't have to get the lens in the absolute perfect infinity position just to start with. You can set it somewhere in the general area and then refine through use of the focus knob. Much of the time you aren't going to make the photograph with the lens at infinity anyhow, so you'll be moving the lens from its original position eventually regardless of how perfectly you get the infinity position as an initial matter.

[Jon Shiu]

The easiest way is to observe your subject focus on the ground glass as you move the front standard backward. Best to move the front standard a bit more compressed than you need, and then focus with the focusing knob.

[Carl Schofield]

Thanks to all for your help and prompt replies. Sounds like this is not a very critical measurement and I'll use Jon's suggestion for visual calibration of the infinity point.