Lens coverage.

laz · Oct 25, 2005

I know where to find the image circle size for modern and many older LF lenses. But is there a way, knowing focal length to calculate, however roughly, the coverage for an unknown lens?

(I can't be asking Jim Galli about every lens I see all the time!)

Paul Sorensen · Oct 25, 2005

I think you would need focal length and angle of coverage. There are those who will know based on lens design, but that means that you need to be like Jim Galli and know just how all those old lenses are construted. We don't want that, do we?

laz · Oct 25, 2005

Paul Sorensen said:
but that means that you need to be like Jim Galli and know just how all those old lenses are construted. We don't want that, do we?

I live and breath to become more Galli-like every day!
(actually I just think it's tacky to ask Jim to provide info on lenses he'll likely be bidding against me for on ebay!)

Nick Zentena · Oct 25, 2005

How unknown?

If you know the lens design a little math will give you the possible coverage.

2 X the focal length X tan(angle of coverage/2)

Simple if you know the angle and have a calculator. OTOH it's only telling you what the design should do.

If you have the lens name and other info then google is your friend. If just a web search doesn't find it then click on groups. If neither of those finds it the lens likely doesn't exist-) Or you typed something wrong.

Dan Fromm · Oct 25, 2005

laz said:
I know where to find the image circle size for modern and many older LF lenses. But is there a way, knowing focal length to calculate, however roughly, the coverage for an unknown lens?

(I can't be asking Jim Galli about every lens I see all the time!)

No. Coverage depends on the lens' design and on what you mean by coverage. For examples of widely-differing views on what coverage means, look at eBay listings for LF lenses.

Sorry,

Dan

laz · Oct 25, 2005

Nick Zentena said:
If you know the lens design a little math will give you the possible coverage.
2 X the focal length X tan(angle of coverage/2)
Simple if you know tangle and have a calculator. OTOH it's only telling you what the design should do.

,
Nick, Okay. So take the Goerz Dagor 10 3/4 inch series III, f:6.8 listed for sale here on APUG. Googling around I find that the Dagors have a 47 degree angle of coverage. I know the best thing would be to find this specific lens, but I plug in the numbers, 47 degree angle of coverage, 270 mm focal length, and get:

540 x 0.4244748162096 = 230mm

Correct?

Tom Hoskinson · Oct 25, 2005

laz said:
,
Nick, Okay. So take the Goerz Dagor 10 3/4 inch series III, f:6.8 listed for sale here on APUG. Googling around I find that the Dagors have a 47 degree angle of coverage. I know the best thing would be to find this specific lens, but I plug in the numbers, 47 degree angle of coverage, 270 mm focal length, and get:

540 x 0.4244748162096 = 230mm

Correct?

Close, but 0.4244748162096 is = Tan(23). Tan(23.5) = .43481237...

Thus 234.7987mm

laz · Oct 25, 2005

Tom Hoskinson said:
Close, but 0.4244748162096 is = Tan(23). Tan(23.5) = .43481237...

Thus 234.7987mm

I should know better than to try my in the ballpark calculations here!

David A. Goldfarb · Oct 25, 2005

And just to make life more complicated, coverage for a Dagor increases significantly at small apertures. 10-3/4" should cover 8x10" plus a little more at f:22 and smaller.

jimgalli · Oct 25, 2005

Dagor's generally will cover about 80 degrees. Not sure where you got the 47 number. The older Series III were usually good for about 82-perhaps 85 at f64. Do the math over with those numbers and you'll find out it should cover a 7X17 & 11X14 OK and an 8X10 handsomely.

laz · Oct 25, 2005

David A. Goldfarb said:
And just to make life more complicated, coverage for a Dagor increases significantly at small apertures. 10-3/4" should cover 8x10" plus a little more at f:22 and smaller.

One of the things I'm just loving about LF are these sorts of details that as you say, make life more complicated!

I am especially intrigued by old lenses and what they can do. No offence intended to the 35mm crowd (of which I'm still a member) but 35mm seems so cookie cutter compared to LF where the almost endless variables ensure a unique photo every time (maybe a bad one, but it will be uniquely bad!)

I've sprung for a CD of The Lens Collectors Vade Mecum. I guess I'm a totally lost soul now!

-Bob

laz · Oct 25, 2005

jimgalli said:
Dagor's generally will cover about 80 degrees. Not sure where you got the 47 number. The older Series III were usually good for about 82-perhaps 85 at f64. Do the math over with those numbers and you'll find out it should cover a 7X17 & 11X14 OK and an 8X10 handsomely.

Oh boy, must be stupider than usual today! I lost track of where or what I was reading. It was Goertz Red Dot Artar that I had read had a 47 degree angle!

(My first attempt and I've embarrassed myself before the great Galli! )

Thanks Jim!

-Bob

Dan Fromm · Oct 25, 2005

laz said:
<snip>

(My first attempt and I've embarrassed myself before the great Galli! )

Thanks Jim!

-Bob

The Great Galli? Cousin of the Great Oz? Nicer guy, though, than Oz was before the great unmasking.

Tom Hoskinson · Oct 25, 2005

It's Curtains for you, Dan - focal plane, of course!

Lens coverage.

Moderator

Privacy & Transparency

Privacy & Transparency