Need recommendation for Lens Mount

[bob carnie]

I am currently working on a project using a Century 8x10 camera with a 480mm lens.. I want to get larger image magnification on the film of rather small objects and in another thread the suggestion was to try a 240 mm enlarging lens...
I have a spare 240mm lens and took it to a place here in Toronto where I have had this type of thing done in the past and to my surprise they are out of business..
Does anyone here know where I can get this lens mounted on a new board so it fits on my 8x10 camera?? preferably close to or in Toronto, but I am willing to ship to the right vendor.
any help would be appreciated.

[Leigh]

To get a larger image you need a focal length longer than your current 480mm. 240mm is going the wrong way.

For any lens, the distance from the lensboard to the film will be approximately twice the focal length,
so about 960mm for your 480mm lens. That's a lot of bellows.

- Leigh

[bob carnie]

Leigh I am talking about taking a one inch object and making it 4 inches on the film.. are you sure ? as that was not the drift of the thread .
My understanding is by using a shorter lens I can reduce my bellows.
With the 480 I am getting about a 1:1 mag on 4 inch objects with pretty much maximum bellows on this camera.

To get a larger image you need a focal length longer than your current 480mm. 240mm is going the wrong way.

For any lens, the distance from the lensboard to the film will be approximately twice the focal length,
so about 960mm for your 480mm lens. That's a lot of bellows.

- Leigh

[Leigh]

Hi Bob,

4:1 is some serious magnification. A shorter lens will reduce the bellows extension but also reduce the image size.

Short FL lenses are called "wide angle" lenses because they see a much larger area than long FL lenses,
but each particular feature of the subject is smaller on the film than with a longer lens.

The equation for bellows extension is X = (M+1)*FL,
where X is the distance from the film to the lensboard and M is the magnification.
At infinity, M is essentially 0, so X = FL as we would expect.
At 1:1 image ratio, X = 2 * FL, so the available bellows draw must be twice the lens FL.
At your 4:1 ratio, X = 5 * FL, so your bellows draw would be five times the lens focal length.

- Leigh

[Dan Fromm]

To get a larger image you need a focal length longer than your current 480mm. 240mm is going the wrong way.

4:1 is some serious magnification. A shorter lens will reduce the bellows extension but also reduce the image size.

Leigh, have you had your morning coffee yet?

The rule is: extension (in focal lengths) = magnification + 1

Equivalently, magnification = extension (in focal lengths) - 1

Extension is the distance from the lens' rear node to the film plane.

For a given extension (in focal lengths) all lenses give the same magnification. For a given extension (in measures of distance, e.g., light years, miles, chains, furlongs, meters, feet, ...) the shorter the focal length the greater the magnification.

This is why those of us who do photomacrography and can't obtain long extensions use short lenses to get the magnification.

Bob, if you need 4:1, extension will be 5 focal lengths. You can work from that. At the max extension you can get (I think you said 960 mm) you'll need a lens no longer than 192 mm. Y'r 240 is too long. Something like a 150 mm process lens will do what you need.

[bob carnie]

looks like I have opened a can of worms.. I appreciate both of your comments.

Ask me any question about printing and I am good to go, but taking photographs and lens optics are not a strong suit.
My Images are solarized and with printing I get the image,, so the taking is secondary. I hope to be in focus and exposed well, than everything else is done in the darkroom.

Dan if I mount a 150 enlarger lens on the board do you think this will work.. the objects are any where between 1 inch and 4 inches and I want to get as much magnification on the 8x10 film ? I do not need to fill the frame but want to use as much of the format as possible.
I am making mural silver gelatin prints and I really like working with this old camera... I thought 4x5 was fun but this really is a nice fit for me.

[Leigh]

For a given extension (in focal lengths) all lenses give the same magnification. For a given extension (in measures of distance, e.g., light years, miles, chains, furlongs, meters, feet, ...) the shorter the focal length the greater the magnification.

Yes, that's true. In fact I posted the same equations previously.

I'm afraid a bellows measured in light-years would be awfully expensive, and require really long arms to focus.

- Leigh

[jp]

Perhaps using a reversed lens would be worth trying.

[Larry Gebhardt]

I would look at reverse mounting an enlarging lens. You might get better quality with a shorter lens such as an 80mm for the smaller objects. The idea being that your subject is like the film and your film like the printing plane. This should keep the lenses used in the orientation they were designed for. So for the 4 inch object try a 150mm lens. I assume you know that your depth of field will be very shallow when you get to magnifications of this size.

[Dan Fromm]

Bob, yes, by all means try a 150 mm enlarging lens.

About reversing lenses. Most lenses are optimized for magnifications less than 1:1. That is, they're designed to image a large subject (in front of the lens) on a small piece of film (behind the lens). Above 1:1, we have a small subject in front of the lens and a large (relatively) piece of film behind it. This is why we reverse lenses when shooting above 1:1

Lenses made for shooting above 1:1 generally don't have to be reversed. And lenses that really are symmetrical, e.g., dialyte type Apo-Nikkors, don't have to be reversed.