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bob carnie
5-Jun-2012, 05:05
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
5-Jun-2012, 05:09
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
5-Jun-2012, 05:20
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
5-Jun-2012, 05:38
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
5-Jun-2012, 05:56
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
5-Jun-2012, 06:13
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
5-Jun-2012, 06:25
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. :D

- Leigh

jp
5-Jun-2012, 06:28
Perhaps using a reversed lens would be worth trying.

Larry Gebhardt
5-Jun-2012, 06:35
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
5-Jun-2012, 06:44
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.

Tracy Storer
5-Jun-2012, 08:43
Given the same bellows extension, a shorter lens will provide a larger image.
For example: At 480mm of extension, a 480 lens will provide infinity focus, and a 240 lens will provide 1:1.

To get your 4:1 you will probably need to go even shorter than 240, given that you said you were getting 1:1 with the 480 at full extension, that's 36". Try a 180mm, or shorter.

To answer your original question, if you have a lensboard with a hole smaller than needed, any machine shop should be able to put the board in a 4-jaw chuck and bore it to the new size very easily.

bob carnie
5-Jun-2012, 08:58
I got PM'd by a local photographer who is going to help me out with the mounting of the lenses.
I appreciate all the responses.

I will digest and ask a few more very stupid questions shortly.

Mark Sawyer
5-Jun-2012, 14:35
I think Dan gave you the information you need. But more questions will arise, I'm sure!

But my stupid questions for Dan: In a symmetrical design, adjustments for optimum focussing distance is generally done by spacing (sometimes shims, sometimes designed into the mount). Sooo...

If a symmetrical lens is designed for 1:1, should the spacing be symmetrical?

If a lens (say an Apo-Ronar) is optimized for infinity by shimming the elements for a different spacing (as I've heard was sometimes done by Rodenstock), if you reverse the lens, would it be better optimized for extreme magnification (like 4:1) than an Apo-Ronar optimized for 1:1?

My reasoning says yes to both, but I know better than to trust my own reasoning! :)

Dan Fromm
5-Jun-2012, 14:39
Mark, symmetrical means symmetrical, not sort of symmetrical. Yes, if a symmetrical lens is optimized for 1:1 it should be symmetrical.

Apo-Ronars optimized for use a distance are a special case, are said to be a little asymmetrical. As I understand it, one cell isn't the usual distance from the diaphragm. One of these should be reversed for use above 1:1.

ic-racer
5-Jun-2012, 17:56
The rule of thumb is to use a lens with focal length similar to the size of the object. So one inch is about 25mm. You could probably use like a 50mm to 25mm lens for a 35mm camera. If you have enough bellows draw you can go to a longer lens (large format lens with shutter 65mm to 150mm or so)

Just for fun I mounted up my 65mm Horseman lens in Copal 0 on my 8x10 camera and was getting bellows draw around 300 to 400mm depending on exactly how big you wanted the one-inch object magnified on the ground glass. Composing on the ground glass wide-open I did not see any difference with the lens reversed (but I was not projecting a flat object, I was only using the middle of the image circle).

Jim Jones
5-Jun-2012, 20:00
Reverse mounted enlarging lenses are fine for images of flat subjects larger than unity magnification. Most enlarging lenses can't be stopped down beyond the aperture where diffraction becomes conspicuous, which limits their usefullness on three-diminsion objects. Some macro, micro, and process lenses can be stopped down more. Perhaps most of these will also work best when reverse mounted. On my 8x10 Kodak, the longest lens that can make a 4" image of a 1" subject might be under 6" if my rusty math still works.