300mm lens bellows extension

[Xuereb]

I have a Toyo half-plate field camera with a 4x5 reducing back. I haven't used it yet and still exploring which longer lenses to choose. The bellows fully extend to 360mm.

From what I have read on this forum, about 300mm of bellows extension will allow a 300mm lens (non-telephoto) to focus at infinity.

My question is whether, with bellows fully extended, a 300 mm lens will focus at closer distances: say for example, rocks or streams at distances of 5 to 10 metres or permit portrait head shots where the camera is 4 metres from the sitter.

Your experiences would be appreciated. If this lens won't work I will settle on a 240mm as my longest lens.

[Tracy Storer]

The ways of figuring this out have been posted often. (search bellows, extension, magnification, etc.)
With 360mm of bellows and a 300mm lens, you should be able to focus down to 1800mm or about 6' from the lens.
Enjoy.

[Heroique]

From Ansel Adams’ The Camera:

1/u + 1/v = 1/f

u = distance to subject
v = bellows extension
f = lens focal length

* Use the same units for each variable!

Pop Quiz! :( :
“I have a 300mm lens, and maximum bellows extension of 360mm. What’s the closest I can focus (i.e., at the max. 360mm extension)?”

Let’s use millimeters – and plug-in the numbers:

1/u + 1/360 = 1/300

Now let’s do the fun part, rounding numbers:

1/u = 1/300 – 1/360
1/u = .00334 – .00278
1/u = .00056
u = 1 / .00056
u = 1785.7 mm

The metric system is easy on the brain :p :

u = 1.7857 meters


:)

[Leigh]

From what I have read on this forum, about 300mm of bellows extension will allow a 300mm lens (non-telephoto) to focus at infinity.
Why are you restricting the lens design "(non-telephoto)"?

I've recently researched this subject, since my field camera also has 360mm of bellows draw.

The important parameter is the "Flange Focal Length" (FFL) or "Flange Focal Distance" (FFD) of the lens, which can be much shorter than the optical focal length. For example, the Nikkor-T 360mm/f8 lens has a flange focal distance of 261mm, and the Rodenstock Sironar-N 360mm/f6.8 has an FFL of 333mm.

Hope this helps.

- Leigh

[Jack Dahlgren]

I have a Toyo half-plate field camera with a 4x5 reducing back. I haven't used it yet and still exploring which longer lenses to choose. The bellows fully extend to 360mm.

From what I have read on this forum, about 300mm of bellows extension will allow a 300mm lens (non-telephoto) to focus at infinity.

My question is whether, with bellows fully extended, a 300 mm lens will focus at closer distances: say for example, rocks or streams at distances of 5 to 10 metres or permit portrait head shots where the camera is 4 metres from the sitter.

Your experiences would be appreciated. If this lens won't work I will settle on a 240mm as my longest lens.

I think most of the 300mm lenses have a flange distance of a bit less than 300mm (Nikkor 300m is 290mm and the Fuji 300 C is 285) so you may want to choose a lens carefully.

[Xuereb]

Thanks everyone. It is reassuring to know that I can go ahead and look for this size lens. Its really comforting to have a forum such as this to keep us newbies in line.