11x14 extension

[Julian_3496]

I'm talking to someone about building me a custom 11x14. I'm planning on using only 210 and 480 mm lenses with it for landscape and urban landscape. What is the minimum extension I could get away with?

[Sidney Cammeresi]

IIRC,

1/f = 1/s + 1/i (f = focal length, s = subject-to-lens distance, i = lens-to-film distance)

So, for example, with your 480 and 600mm of draw, you could focus down to 7.9 feet.

(Lens is, of course, the nodal point of the lens, which is usually the lens, unless you have a telephoto lens.)

[Julian_3496]

Sidney, thanks for the maths! I really need to learn some of the technicalities

[wfwhitaker]

Just a couple of thoughts on camera design....



Plans change. You may be thinking a 19" lens is the longest you want to use now. But once you get into the format (and from your question I'm assuming that you're not already using 11x14) you may find that you want to use a longer lens. If you only have a 24" bellows, a 24" lens (the next logical step up from a 19") can only be used at infinity focus.



Why would you ever want a lens longer than 19"? You may easily encounter a composition which needs to be "tighter" to exclude distracting foreground/side elements. Cropping is always an option when enlarging. But few people have access to an 11x14 enlarger, which leaves only contact printing. You can crop with a razor blade. But it only makes the image smaller.



On the other hand, a shorter bellows makes camera construction much easier and with fewer compromises. A 24" bellows on an 11x14 camera can easily be accommodated with a single extension. Simpler construction implies lighter weight and lower cost. But a short bellows camera probably also has less market value should you decide to try to sell it later.



Everything is a compromise. Only you know what you really need. But don't handicap yourself unnecessarily.



Regards,
Will

[Julian_3496]

Thanks Will, in my MF work I never use anything longer than a 80mm, in 35mm never more than 50, and in 5x4 never more than 150.BUT I'd like to focus down to 1m. All compromises isn't it?