Re: I need help focussing at macro distances
Chris, please tell us more about what you're doing. You shouldn't be having such horrible problems.
FWIW, I shoot closeup -- up to around 2:1 -- on 2x3. I normally set magnification first by setting film-plane to lens diaphragm distance with a tape measure. The distance = f*(1 + m). f is the lens' focal length, m is desired magnification. And then diaphragm to subject distance is approximately f*(1 + m)/m. Understand that these distances are very approximate, the lens' nodes probably aren't at the diaphragm and its hard to locate the film plane precisely with a tape measure. But they're good enough for initial set up.
And then I fine tune focus with a focusing rail and, sometimes, moving the front standard a tiny tiny bit. Focusing rail is better.
If the subject isn't immobilized, things get very dodgy. That's why I still shoot closeup with a Nikon and KM (deepfreeze isn't empty yet) and flash illumination.
Re: I need help focussing at macro distances
"One third/two thirds rule".
This rule only applies if you are focused precisely at one third the hyperfocal distance for the focal length of the lens and the f/stop. It most certainly doesn't apply when you are in the close-up range. In that range, DOF in front and in back of the exact focus position are pretty close to one another.
Re: I need help focussing at macro distances
You may have more than one problem. If so, the answers are probably amongst the suggestions you have received.
Andy Eads points out a common problem. When at or near 1:1 subject/image size, moving the lens just changes the size ratio, not the focus. As he recommends, to adjust the focus, you have to move either the entire camera or the subject.
You need two focal lengths extension to get 1:1. The distance from the lens to the subject will be the same. Each additional focal length extension gives one whole unit of magnification. For example,you need five focal lengths of bellows in order to get a magnification of four. This works in reverse, too. If your subject is three focal llengths from the lens, you are reducing by two.
Re: I need help focussing at macro distances
Fooled around some more this evening, tried moving the whole camera instead focussing with the front, and found it WAY easier and more definitive. It's a little awkward with an 8x10; I almost wished I had wheels on the bottom of the tripod.
Thanks everybody for the good advice.
Re: I need help focussing at macro distances
Quote:
Originally Posted by 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!
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
Re: I need help focussing at macro distances
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.
Re: I need help focussing at macro distances
Christopher - if you're going to be doing a lot of macro work, you may find it convenient to use some sort of focusing rail that sits between the camera and the tripod head. That makes it easy to make minor adjustments (a few inches) in the camera position without moving the tripod. Commercially made rails are easy to find for 35mm, but most are too light-duty for use with an 8x10. One for a heavy MF camera might be better. The ideal would be a heavy-duty unit that had bi-directional positioning, but I haven't seen one commercially available.
Re: I need help focussing at macro distances
"Is there a workable method to focus via measurement?"
Sounds like a job for BTZS man! Buy the Palm Pilot loaded with Phil Davis' expo/dev program (or whatever it's called now) from The View Camera Store. It's been a long time since I've used that program but I remember that if you punched in the lens-to-subject disatance and maybe a couple other things like front-to-back distance of the object you're photographing it would give you the required fstop needed to keep everything from front to back sharp (plus the shutter speed for the correct exposure at that f stop). Or you could punch in the f stop you wanted to use and it would give you the depth of field at that aperture. I think you could also tell it what circle of confusion size you wanted but I'm not sure of that. Of course the program will do many many other useful things, the feature I've described is just one small part of it. And of course a Palm Pilot loaded with this program isn't cheap but what's another few hundred dollars more for the LF photographer who wants to give the appearance of being so secure (psychologically speaking) that he's comfortable using an ancient film-based camera while also being hip enough to use a Palm Pilot with it?
Re: I need help focussing at macro distances
Linhof used to make a focusing rail that was pretty sturdy. There are "slides" made as machine components that could be adapted. Most of these are stout enough for MLF (Mega Large Format).
Re: I need help focussing at macro distances
Since Ernest mentioned it ... several of the monorail systems have such gizmos available. Horseman, for example, produces a bellows connector when you need to use more than one bellows, not infrequent for large magnifications. The bellows connector comes with an additional geared block that (I believe) has some reduction in it permitting even finer focusing than with the standard rail. I wish I could be more precise but I seldom use it.