6x7 back on my 4x5, focal length question

[brian steinberger]

I think I just made a fairly obvious observation but I'd just like to run it by you all. I have a 6x7 roll film back for my Wista 4x5 and have always wondered what focal length equivilents (in 6x7 format) I am effectively using when using large format lenses. Let's say I'm using my 210/5.6 lens on my 4x5 with my roll film back. The focal length is still 210mm, just in a different format.. right?

So in effect you could carry a nice set of lenses with your 4x5 (90,135,210,300) and with a roll film back you could also have a nice medium format camera with a nice set of lenses (although longer in effective focal length) as long as you don't mind setting up a view camera for every shot.

Sorry if this was obvious to others.

[Dave Miller]

You got it in one.

[David A. Goldfarb]

Yup, that's how it works. Then if your longest lens isn't long enough for 4x5" and you don't want to crop from sheet film, you can switch to the rollfilm back. I've occasionally done a little bird photography with my 4x5" Technika, a rangefinder cammed 360mm lens, and a 6x7 rollfilm back.

[Pinholemaster]

You got it. That's the same concept that DSLR shooters faced when they switched from 35mm to digital.

Basically your 90mm wide angle becomes your "normal."

[brian steinberger]

Guys, that's what I thought. Thanks for your help! This will be nice to know this next I go to shoot.

[Andrew Moxom]

That's the same reason why I have 75, 90, 150, 210, 360 lenses, and 3 x 6x8 graflex backs with 1 x 100 iso film, 1 x 400 iso film, and 1 for E6. Plus I also carry roughly 10 x 4x5 double darkslides. So I am covered for most eventualities with my Canham DLC.

I tried bidding tonight on Fleabay for a 58mm XL lens, but was sniped at the last minute. That lens would have covered 4x5, but it would mainly be for a wide end on the 6x8 format. That is going to be my next purchase when I can find one used.

[m_liddell]

What is the factor to apply to the focal lengths going from 4x5 to 6x7?

[Roger Hicks]

What is the factor to apply to the focal lengths going from 4x5 to 6x7?

Diagonals are approximately 150mm and 90mm so 15/9 = 1.7x and 9/15 = 0.6x, i,e. 150mm on 6x7 has same diagonal coverage as 250mm on 4x5 inch; 90mm on 6x7 has same coverage as 150mm on 4x5 inch; 47mm on 6x7cm (the widest I've found that covers 4x5 inch) is like 78mm on 4x5 inch.

Cheers,

R.