Large format lens, why are they so Convex?

[Shaggysk8]

This is probably stupid question. But large format lenses look more Convex then medium format and 35mm, I might be wrong in this, but if so why?

Paul

[Ian Grant]

They cover far larger image circles to allow for movements so need to be wider particularly the front & rear sets of elements.

Ian

[Dan Fromm]

Um, er, ah, Ian, within a prescription every dimension -- radii, elements' thickness, spacing between elements -- scales with focal length. So, for example, the front surface of a 150/6.3 Tessar is relatively flatter than than the front surface of an 85/6.3 Tessar.

Paul, be more specific. Which lenses are you comparing? There are many many lenses for every format and some are quite, um, bulbous. Others with the the same or greater coverage aren't.

For example, Ian, I have an extremely bulbous 260/10 Nikkor-Q -- this lens, in fact: http://homepage2.nifty.com/akiyanroo...po/pro260.html ; Akiyan's image circles are at 1:1 -- that covers 75 degrees at infinity. I also have a 38/4.5 Biogon that covers 90 degrees. Its front surface is relatively flat.

[Shaggysk8]

It was more just a general question really, I can't be more specific as I only have 3 lenses and have only ever seen those 3 lenses. I would like to understand more about lens design, but not sure my brain could handle it.

[John Kasaian]

It was more just a general question really, I can't be more specific as I only have 3 lenses and have only ever seen those 3 lenses. I would like to understand more about lens design, but not sure my brain could handle it.

If they cover your format then whats the diff?
Now git out there and shoot up some film!

[Shaggysk8]

Haha it's dark!

[Ian Grant]

I think the answer needed to be a bit sweeping Dan

Ian

Um, er, ah, Ian, within a prescription every dimension -- radii, elements' thickness, spacing between elements -- scales with focal length. So, for example, the front surface of a 150/6.3 Tessar is relatively flatter than than the front surface of an 85/6.3 Tessar.

Paul, be more specific. Which lenses are you comparing? There are many many lenses for every format and some are quite, um, bulbous. Others with the the same or greater coverage aren't.

For example, Ian, I have an extremely bulbous 260/10 Nikkor-Q -- this lens, in fact: http://homepage2.nifty.com/akiyanroo...po/pro260.html ; Akiyan's image circles are at 1:1 -- that covers 75 degrees at infinity. I also have a 38/4.5 Biogon that covers 90 degrees. Its front surface is relatively flat.

[doughowk]

I also like to understand what I'm using. So I bought a couple of Rudolf Kingslake books on lenses. They haven't improved my photography, but they help me with gear-talk ;-)

[Christopher Walrath]

I have his book on the shelf.

But I wanna know, do you like your new toy, Shags?

[Shaggysk8]

I am in love with my new toy!!! it sleeps with me at the moment. Although I will get closer to it at the weekend when we can really get to business