How to calculate required bellows extension?

**Dan Fromm** · 30-Jul-2017, 06:14

Originally Posted by Leigh

Sorry, Dan, but I am not mistaken.

The OP said "a 450mm lens", not further identified.

- Leigh

Please see post #5 in this discussion.

**Pawlowski6132** · 30-Jul-2017, 16:06

Originally Posted by Ken Lee

You might find this article helpful: http://www.kennethleegallery.com/html/tech/bellows.php

Honestly, this is everything I needed. Thanx. Very well written and organized.

Who could have written such great material????

**Pere Casals** · 30-Jul-2017, 16:58

Originally Posted by Leigh

Sorry, Dan, but I am not mistaken.

My comments suffer from the same problem as all generalities.

The FFL for the Nikkor M 9/450 is 435.4mm.

The FFL for the Fujinon T 8/400 is 226.5mm, much shorter than the optical focal length.
The FFL for the Nikkor T 9/600 is 409.8mm, "
The FFL for the Fujinon T 12/600 is 383.9, "

As I said previously, it depends entirely on the lens design .
The OP said "a 450mm lens", not further identified.

- Leigh

The general case for LF lenses is that flange to film distance is very close to focal distance in the vast majority of the cases. Most popular lenses follow that, all Symmars, Sironars, Nikkor SW, W, M...

Main exception is telephoto designs that are suitable for field cameras with limited max bellows extension, at the cost of some handicaps like lower max aperture. A few extreme wide angles are retrofocus type, so also an exception.

Here http://www.largeformatphotography.in...l=1#post111996 there is an interesting notice about where pupils and nodal points are located.

For barrels, you have to take the barrel mid point, as the lens is placed in front of the plate, and then in most cases it will also match closely.

With convertible lenses it happens same effect than with barrels, when using a single cell you can consider the cell midpoint to know the required bellows. With my Symmar 360 convertible, when converted to 620mm I need more bellows than 620mm because the lens is at the rear of the lens board. Instead, if I use the front cell only, then required bellows draw is shorter.

**Drew Bedo** · 30-Jul-2017, 17:11

Did the OP get his question answered to his satisfaction?

**drew.saunders** · 31-Jul-2017, 08:54

Originally Posted by Leigh

The distance commonly quoted is the Flange Focal Length of the lens.
That's the distance from the film to the lensboard when focused at infinity, i.e. the bellows draw.
You'll find that on every lens datasheet.
it may be substantially different from the lens' focal length

- Leigh

Fortunately, the Ebony web site is still up, so this page is still available: http://www.ebonycamera.com/articles/lenses.html Hopefully it'll be available for a long time.
It has the flange focal distance for many modern lenses. It helped me decide between the Fuji 300/8.5 vs. the Nikon 300/9 back when both were available new, as I could benefit from that wee bit shorter FFD from the Fuji for the camera I was using at the time (a Tachihara).

**Leigh** · 31-Jul-2017, 12:39

Originally Posted by drew.saunders

Fortunately, the Ebony web site is still up, so this page is still available: http://www.ebonycamera.com/articles/lenses.html Hopefully it'll be available for a long time.
It has the flange focal distance for many modern lenses. It helped me decide between the Fuji 300/8.5 vs. the Nikon 300/9 back when both were available new, as I could benefit from that wee bit shorter FFD from the Fuji for the camera I was using at the time (a Tachihara).

The Flange Focal Length (FFL) aka Flange Focal Distance (FFD) is a critical parameter in determining whether a particular lens is suitable for a particular use on a particular camera.

Lots of particulars, but they are certainly relevant.

My lens database includes that and other information on most modern lenses (except Schneider, which I dislike).

- Leigh

**Pawlowski6132** · 1-Aug-2017, 13:00

Originally Posted by Drew Bedo

Did the OP get his question answered to his satisfaction?

He did. I finally rolled up my sleeves and got a calculator and worked through some equations.

In fact, I was able to put them into practice. I had a group shoot yesterday. Based on my new found knowledge I was able to set up camera, seating arrangements, etc. in advance. By the time the group sat down, all I had to do was fine focus.

than