I need help focussing at macro distances

[CXC]

I am competent focussing all my lenses at normal distances (>10'), but when I get down in the macro range (<10'), I have a very hard time. To my eye there is a large range around the true focus point that all looks kind of the same.

Is there a workable method to focus via measurement? Say I'm using a G-Claron 240mm, can I measure the distance from my target focus point to the lens, and calculate the correct distance from lens to ground glass? Actually, even if this was only an approximation, it might help me as a starting point. Where on the lens do I measure to?

I have normal 54-year-old eyes, meaning I wear bifocals, but normally I take them off under the dark cloth, just using a loupe.

All advice and pontifications welcome.

[Sheldon N]

Perhaps its because the f/9 G-Claron has more DOF than a f/5.6 lens would when focusing?

One approach might be to move the focusing knob back and forth to get a sense of where the focal plane gets too far away on one end and gets too close on the other end. From there, you could turn the focus knob to the halfway point between the two positions. I find I have to do this occaisionally when I can't see the subject exactly "snap" into focus.

[Peter Collins]

I am awaiting, like you, replies of those who have the Secret.

[Leonard Evens]

What you describe is normal. Depth of focus, which measures the range along the rail where the subject at a specified fixed distance will appear in focus, increases as you get close to the subject. At typical macro distances, it is very large. (See below.) You should focus by moving the rear standard since in that case the lens to subject distance will stay fixed. Using a loupe will also help by in effect reducing the depth of focus.

What you suggest in terms of measuring distances is a bit more complicated than you might think. There are two points in a typical lens from which to measure. You use the front nodal point from which to measure subject distance and the rear nodal point to measure image distance. These won't usually be at the same location. For most general purpose lenses, the two points are fairly close together and both close to the lens board. According to one description of your lens at the LFphoto website, that seems to be the case for your G Claron 240. Perhaps some kind soul will do the work to find out exactly where the two points are located. The difference seems to be just a few mm.

Note. At 1:1 magnification, with an aperture of f/9, and using roughly 2 X magnification when looking at the gg, the depth of focus is about 3.6 mm. That means that within a range that large, you won't be able to tell whether any one position is any better than any other position, if you have normal vision. By using a 10 X loupe, you can reduce this by a factor of 5 to about 0.7 mm. But it should be noted that the large depth of focus is not so much the problem. It also means that focusing won't be as critical. Where it becomes a problem is where the ability to distinguish fine detail differs signficantly between viewing on the gg, which may be like looking at a 4 x 5 contact print, and viewing a final much enlarged print. To the extent that you can get the level of resolution similar in both, by use of a loupe, you can expect the print to show roughly what you saw on the gg.

[Leonard Evens]

Looking more closely at what you posted, I'm now not sure I understand your problem. At 10 feet, the magnification is still not very large, so the increase in depth of focus is still quite small. It is when you get much closer that it may start to be a problem. I don't see why you should notice a difference between say 10 feet and 20 feet. Could you go into greater detail?

[Ed K.]

Not sure if any of this helps, and the other explainations were great -

I use a little Arri 150 fresnel to illuminate during focus, and focus with the rear standard ( no geared rail clamp ) - then usually I use electronic flash and light modifiers for the shot. Also, a couple of small led flashlights can help doublecheck depth of field calculations when stopped down. The loupes designed to sit flat on, and focus on, the GG such as the Toyo loupe, work nicely, and a finely etched GG works better for me than a fresnel Beatie when it comes to macro work. A gridded ground glass helps too, because then I can make sure that my eye is focused at the GG level - that seems to make quite a difference. I find that I have to focus my eye on the grid lines, then back on the image a few times to keep my eye focused at the right level under a loupe. More light on the subject definitely helps.

The great part about the suggestion to move the whole camera back and forth is that the magnification / bellows compensation then remain the same, so you don't have to keep refiguring that.

A couple of other thoughts - if all seems good in camera, then your film is not quite right, consider whether your lens shifts focus when stopped down, whether your film plane and ground glass align properly at the same height, and finally, whether the camera back has shifted a bit when you put the film holder in. In addition, some cameras will "sit" with a bit of weight ( such as film holder ) in a different place than when you are focusing or be susceptible to a bit of pressure on the GG while focusing - could there be a small issue or two with your equipment?

[Ted Harris]

I do a reasonable of macro work and I'm not sure there is any magic bullet.' Some of the things that help a lot:

1) Use a lens and lighting combination for focusing that give the the absolute greatest illumination of the object. I wouldn't think of doing macro work with an f9 lens but if you have to you have to so add more light. Blast the objet with something over 2000W for focusing and you will see a marked improvement in your focusing ability. You can also use a high powered sall quartz halogen lamp strictly for focusing but simple clamp on reflectors with 500W bulbs that you can get at any hardware store for a few dollars will work fine.

2) Use a fine ground glass or aerial image focusing ... whatever works best for you that reduces the physical imededments to 'seeing' the best focus.

3) Ue a high powered loupe. When I am shooting macro I generally use a 6x loupe but I always leep a B&L 15x linen tester handy just in case.

4) you can use actual measurement but you will still wantt o fine tune for the exact spot you want in sharpest focus remembering that you have very very (red almost none) depth of field and one fo the best ways to do the final fine tuning is to be prepared to shoot some Polaroid and examine the results with a magnifying glass. My general choice these days is T55 or T72 for sharpest images. For color, if I also wantto check other aspects of the setup I wll use T79.

5) If you are serious about macrowork and mean true macro distances, e.g. 1:1 and larger then you might want to consider a dedicated macro lens which is specifically designed for macro shooting. You will see differences in sharpness, especially at the image edges and corners, betweent he macro lens and yoru G Claron at these distances. Yes, the G Claron is a process lens and is thus designed to work at fairly close distances but it is designed to do so with flat objects, not 3D objects. Not to imply that you won't get pleasing images with the lens, you will. However, if it is a money shot then a macro lens will do much much better.

[Andy Eads]

Set the camera for the magnification that you desire and move the camera and lens as a unit relative to the subject (this means it may be easier to move the subject than the camera.) Cameras with a geared tripod block like the Horseman L series make this a piece of cake. If you have to make many photos at the same magnification, this makes the process much easier. Good shooting!

[Paul Moshay]

Set the camera for the magnification that you desire and move the camera and lens as a unit relative to the subject (this means it may be easier to move the subject than the camera.) Cameras with a geared tripod block like the Horseman L series make this a piece of cake. If you have to make many photos at the same magnification, this makes the process much easier. Good shooting!

Andy has the right idea, set the magnifcation you want of the subject on the groundglass, ie: 1:1 = 240mm lens x 2= 480mm between film and lens and 480mm between lens and subject. Move the whole camera to and fro to get the subject in focus on the GG and the image will snap into focus easily, stop way down and make the shot, except it is a PITA to actually do unless you have a racking type of slide for the camera. Paul

[Leonard Evens]

Is it definitely true that moving the whole camera works better than just moving the rear standard and keeping the lens to subject distance fixed? Off hand, I don't see why that should be, but it is hard arguing with the facts.

Also, I didn't know this was 8 x 10. For that, the coc would be larger, and that would mean the depth of focus at 1:1 with an f/9 aperture would be about 7.2 mm. That would be without a loupe.