Needed: Info on LF close-up photography

[mikewhi]

Hi:

I haven't done this in years and I need to refresh my memory on the calculations involved in close-up LF photography.

I want to do close-up and get 1:1 and bigger (is twice as large expressed as 1:2 or 2:1?).

I would need to know the relationship between lens focal length, subject-to-lens distance, lens to film-plane distance, reciprocity effects. What else do I need to know?

For example, If I'm taking a picture of something 4-inches tall and I want it to be in focus and take up the full height of an 8x10 negative (basically reproduced twice as big as the actual size) what are the calculations as far as lens, bellow draw required, etc?

I am not asking anyone to do the research for me (but I'm sure there are people who can do this off the top of their head), but I'd appreciate it if someone could point me to a book or web-site that has this technical info on it so I can study up.

Is it even possible to photograph a 6-inch tall flower and make it fill up the full negative of, say, a 16x20 camera? I would think it is possible, but I have no idea of how to calculate it.

Hope I'm making this clear.

BTW, I just checked out the link to mamutphoto (the ULF link) here on APUG. It's pretty nice and we can even see pictures of some of the users here (like Sandy King - lookin' slim there, Sandy(!) and Emile de Leon who is buying Amidol with me).

Thanks in advance.

-Mike

 

[Mongo]

For a lot of tips on calculating bellows extension compensation, see http://www.largeformatphotography.info/bellows-factor.html

Since you're working with a ground glass, figuring out your magnification is easy. Measure the real object, and then measure it on the ground glass. The 2nd divided by the first is your magnification (i.e., a 4" flower that's 8" on the GG is a magnification of 8/4 = 2).

In answer to your query regarding having a 6" flower fill a 16x20 frame: Yes, you can do it. But there are some things to keep in mind. You'll need a lot of light to focus acurately (as the loss of light due to bellows extension will be large), your depth of field will be very, very small, and you will have to assure everything is perfectly motionless as the magnification of an object also magnifies the movement of the object and of the camera. (I've taken to turning my furnace off when I shoot macro stuff in the winter, as the moving air will ruin my chances for getting a good shot.)

 

[David]

More than one way to skin a cat. Get the image on your ground glass as you want it. Then measure the bellows length basically from the lens panel to the film plane. Take the focal length of your lens, lets say it's a 100mm for easy math. If your bellows is stretched to 125mm (1:1/4) you add 1/2 stop. At 150mm (1:1/2) you add one stop, 175mm (1:3/4)and at 200: (1:1) you add 2 stops. Compose, measure do some simple math. If the bellowsis somewhere in-between adjust accordingly. In other words each 25% of extension past the focal length of the lens is plus 1/2 stop.

 

[BarrieB]

There is this site on the Web that allows you to download plans for this 'Disk thing" you just place the circular disc next to the object and with the image on the ground glass measured you can just read off the Extra Exposure needed. Someone will put up the URL I am sure!! I am unable to locate mine at present.

 

[BradS]

Hoo-boy, here are a few ideas to work over....

(1/focal length) = (1/object distance) + (1/image distance)

object distance is the distance from the rear nodal plane of the lens to the subject. In practice the rear nodal plane is approximately at the lens board for lenses of conventional design.

image distance is the distance from the rear nodal plane of the lens to the plane of focus (the film plane in practice).

scale of reproduction = (image size) / (object size)
= (image distance) / (object distance)
----------------------------------------------------------------------
bellows factor = (image distance / focal length) ^2

apply the bellows factor like you would a filter factor. That is, multiple the factor by the metered shutter speed.

----------------------------------------------------------------------
an exposure factor (either bellows factor or filter factor) can be converted to stops by...

log(factor) / log(2)

----------------------------------------------------------------------

try some examples....

Let's say you have an eight inch lens and you want the image on film to be the same size as the actual object (i.e. sacle of reproduction equal to 1.0). This is also known as 1:1

(image size) / (object size) = (image distance) / (object distance) = 1.0
so, let...
d = image distance = object distance.

lens focal length: 8 inches

(1/focal length) = (1/object distance) + (1/image distance)
(1/8) = (1/d) + (1/d) = 2/d
multiply both sides by d and
d / 8 = 2
or,
d = 8 * 2 = 16 inches

so, to get 1:1 reproduction the image distance (i.e. bellow draw) has to be twice the focal length of the lens and the object that you are focussing on must be this same distance in front of the lens (actually in front of the lens board). This is always the case, no matter the focal length of the lens - as long as the lens is of conventional design.

Now, with this much bellows, you have much less light, so calculate your bellows factor as follows...

factor = (image distance / focal length) ^2
= (16 inches /8 inches) ^2
= (2)^2 = 2*2
= 4
and, log(4) / log(2) = 2 stops
so, if your meter reading suggests f/8 for 1/500 second you can either
open up two stops or, multiply 1/500 by four and get
4/500 = 1/125


another example:

Is it even possible to photograph a 6-inch tall flower and make it fill up the full negative of, say, a 16x20 camera? I would think it is possible, but I have no idea of how to calculate it.

six inch object, 16 inch image

image size / object size = 16 / 6

and we know that
(image size) / (object size) = (image distance) / (object distance) = 16/6

divide both sides by the image distance to find that...
(1/object distance) = (16/6)* (1/image distance)

again, suppose that we have an eight inch lens then,

(1/focal length) = (1/image distance) + (1/object distance)
combining these two relationships,
(1/focal length) = ( 1/image distance) + (16/6)* (1/image distance)

solve for the image distance...

multiple both sides by (6*image distance)...

(6 * image distance) /8 = 6 + 16 = 22

image distance = 22 * 8 / 6 = 29 1/3

and,
object distance = 6 * image distance / 16 = 11 inches

so, with you eight inch lens mounted, extend the bellows so that your lensboard is 29.3333 inches away from the film plane and see if the six inch flower that you are focused on eleven inches in front of the lens board fills the 16inch dimension of your ground glass.

Bellows factor for this case is...

factor = (29.33333333/ 8.0) ^2 = 13.4444

or, log(13.4444) / log(2) = 3.75 stops

whew!
I'm tired.



This is all explained in depth in:
Leslie Stroebel, View Camera Technique
Aaron Sussman, The Amateur Photographer's Handbook

and, I believe it is also covered to some extent in:
Barbara London and John Upton, Photography

 

[doughowk]

Too much math in calculating bellows factor. I just use Calumets Exposure Calculator. Place the target in the scene, then use their measure for ground glass size of target to determine f stop increase.

 

[mikewhi]

Brad is a big help. I needed more than just an exposure factor. I wanted to know how to determine the bellows draw and subject-to-lens distance for a given focal length lens in order to get a certain reproduction ratio. I believe he gave it to me, but I'll have to read it a few times and practice. I did notice that while taking polaroids to get 1:1 his calculations for bellows draw and subject-to-lens distances seem right on. So, I do think this is the 'right stuff' for me. I will also refer to his biblio as I believe I have all those books somewhere around here.

Thanks!

-Mike

 

[Donald Qualls]

Bellows draw and subject-to-lens come from the lens formula. The degenerate forms are: subject at infinity (more than about 500 times focal length), bellows draw is equal to focal length and subject size is determined solely by distance (angle subtended is arc-cosine of subject size divided by distance), and: 1:1, bellows draw and subject to lens both equal 2x focal length, image size is same as subject size.

In between, the formula you want is calculated Dead Link Removed -- this Javascript applet will calculate any of lens focal length (for infinity), distance to lens, object size, or image size, given the other three -- that doesn't get you bellows draw directly, but it can be obtained by reversing the object and image sizes with focal length held constant.

The actual formula used, in case you want to (say) program your calculator or PDA to do this for you, is here.

 

[mark]

free Exposure calculator:This works just fine for any lens length and goes to 2:1
http://www.southbristolviews.com/pics/Graphic/SBVCALC.pdf

Really indepth explanation of the math invloved
http://www.southbristolviews.com/pics/Graphic/CloseUpCalc.html

 

[jp80874]

Mike,

My interest is 8x10 contact printing so all the magnification has to be in the camera rather than an enlarger. One approach is looking at this from a specific hardware
point of view. I bought a Schneider 305 G Claron f9 lens. This is supposed to give
up to 1:5 magnification with a whole lot of bellows.

The camera so far is a Sinar P 8x10 with four standards and three bellows working
my way out to 60 inches. You can keep adding bellows and standards until you
need to be next to the sun for light.

The camera is mounted on a camera stand instead of a tripod. I have added lead
shot to stabilize the hollow legs. Because the rig is so heavy movement is still a problem. One possible improvement is to wedge a 5 or 6 inch steel pipe and a
house jack between the concrete floor and the rafters. Then mount the gear to
the pipe instead of the camera stand. At this point you move the set for
adjustments rather than the camera. Turning off the furnace sounds like a
great suggestion both from the breeze but also the vibration end.

Another problem I’m working on is that with all these pieces parts you have
many connections. Each one adds a bit of flex to the problem. This is a work
in progress. Good luck with your plans. Please tell us about it as you go.
We all learn from the conversations. You don't have to be crazy to play this
game, but being so is cheaper than the drugs needed for a sane person to play.

John Powers

 

[roteague]

I cheat. I have a meter with an attachment that allows me to take readings off the ground glass.

 

[BradS]

Brad is a big help. I needed more than just an exposure factor. I wanted to know how to determine the bellows draw and subject-to-lens distance for a given focal length lens in order to get a certain reproduction ratio. I believe he gave it to me, but I'll have to read it a few times and practice. I did notice that while taking polaroids to get 1:1 his calculations for bellows draw and subject-to-lens distances seem right on. So, I do think this is the 'right stuff' for me. I will also refer to his biblio as I believe I have all those books somewhere around here.

Thanks!

-Mike

Mike, Thanks. I'm very happy it was helpful. I enjoy math so this is all very beautiful to me. If you have any other questions, please don't hesitate to ask.

Brad.