View Full Version : lens focus distance

2-Dec-2006, 05:05

If I have a 4x5 camera that has only 190mm of bellows extension with lens boards upright (and they can't be tilted), which lens gives the narrowest field of view possible for a portrait? Is there a calculator for such things ? I have searched but I think my search terms are too generic. In scanning the pdf docs listing lenses for 4x5, my guess is the Xenar 150mm because it has a 60 degree angle of view. I wonder if I could get a head 'n' shoulders portrait with that lens in only 190mm ?

It would be good to know roughly what image size to expect from a lens before buying it !

Another option might be a extension back by Ebony (?) to take the film plane back a certain amount ... ? This would increase the effective extension of the lens ...

I am sure that as the lens moves from infinity focus, the extension amount is not linearly related to the focus distance from the camera ... but what is the relationship ?

Thanks in advance,

2-Dec-2006, 06:05
You might want to try using a tele lens. I had an old schneider 240mm telexenar (5.5) that required less than 7 inches of bellows draw if I remember correctly. There was one on the auction site recently...about $250.

Dan Fromm
2-Dec-2006, 07:29
250/5.6 TeleRaptar/TeleOptar would cost less, covers 4x5 too.

Alan Davenport
2-Dec-2006, 11:42
The relationship of the image distance and the object distance (from the lens) is given by the formula:

1/p + 1/p' = 1/f


p = the object distance
p' = the image distance
f = the focal length of the lens

(Note that the distances p and p' are given from their respective principal points in the lens, which are not usually at the same point, but this can be ignored for casual calculations.)

So for a 150mm lens that can be extended to a maximum of 190mm from the film, you get

1/150 - 1/190 = 712.5mm subject distance.

A 60 degree view at 712.5mm distance should cover about 411mm across, so I reckon a 150mm lens would allow you to cover head and shoulders.

OTOH, the suggestions for using a telephoto design are worth thinking over, since a slightly longer-than-normal lens will usually be preferred for portraiture. A telephoto in the 240 to 250 mm range would probably work well.

Ron Marshall
2-Dec-2006, 12:24
You can also use a top-hat lens board. I use a 6 inch extender board on my Toho.

2-Dec-2006, 17:40
Thanks guys,

And especially for the formula Alan. I've been drawing triangles and trying to imagine how it all works and getting lost with it.

I am committed to buying the camera with only 190mm extension and am also realizing that it may only be for the wide angle shots. Another body (probably a cheapie monorail) would do the job for any portraiture.

I'll look into the 'Raptars' - what a great name !


Colin Robertson
3-Dec-2006, 02:56
At least you are looking ahead. I have a Shen Hao- 300mm of bellows. That sounds fine to begin with. Using a 150mm lens you can go down to life size, 1:1, no problem. Then comes portraiture . . . If we want a flattering perspective we need to be a few feet away from the sitter. To get a head and shoulders shot, of course, that means a longer lens. Think 35mm- you'd maybe use 80-100mm. On 6x6, maybe a 135 or longer. Here comes the crunch. For 5x4 you might need a 300mm lens. That's 300mm of bellows just to hit infiniyt. For head and shoulders you need even more. I was saving for a 300mm f8 Fuji telephoto. Then I caught a cheap 360 Tele-Arton. One stop faster, and (almost) head and shoulders at full stretch. And what a stretch- 1kg of lens perched right out at max extension. Not very stable, but it just works.

3-Dec-2006, 16:18
Thanks Colin,

I am in the process of buying a Shen Hao also. But not the normal one ! I paid the guy in China for the TFC45-II which I wan tmainly for 6x17 here in wide Western Australia. It is being shipped today so I may just wait to actually measure the extension before using it.