Focusing The View Camera

[Scott Fleming]

Well I'm about to get my feet wet again. I have my new to me camera, my first lenses are due today. I just cobbled together a gg loupe from a broken Canon 50mm f/1.4 lens that to my eye is as sharp as my Zeiss 3x 6x6 film loupe and in a couple days I'll have my roll film holder.

I would like opinions on why focusing with a loupe is any better than trial and error reiterations with the fine focus knob. I seldom use any movements other than small front tilt and or front rise. Normally I focus with highpower reading glasses by normal methods. Once everyting looks equally sharp I use the fine focus knob to go back and forth till I find the middle ... or the sharpest focus that 'I' can see.

I have to do the same thing if I use a loupe. What I see with my eyes is never 'tack' sharp as with my old and astigmatically challenged eyes nothing is ever perfectly sharp unless I have my 'real' glasses that are not as powerful as the 3x five and dime reading glasses I use. I can't stand looking through a loupe with any glasses on. I have focused my loupe so that it is sharp for me except for the astigmatism.

This is probably not comming through clearly. I should probably get special glasses made only for view camera focusing. So apart from the glasses thing .... why is a loupe better than the other focusing I described?

Thanks.

[MIke Sherck]

Keep in mind that lenses for LF are typically on the long side with respect to experiance you may have had with smaller formats, and that along with longer focal lengths comes shallower depth of field. Focusing errors with short focal length lenses can, of course, be masked by depth of field; you have less of a safety margin with longer lenses. You can't always correct for depth of field problems by using smaller f/stops, either: that often drives exposures into inconveniently long times. So, what a loupe does for you is to magnify the image on the ground class, so you can be sure of more precise focus all over your image, not just in the center. If your eyes are sharp enough perhaps you don't need the loupe; personally, I find mine to be invaluable. It can be something of a three-hand circus at times, managing the loupe, movements, and focus all at the same time, but it isn't all that difficult with practice (at least, not difficult with my lightweight loupe.)

[John Layton]

Scott - I find that the combination of a decently bright and sharp focussing screen (such as a Maxwell) and a pair of reading glasses allows me to leave my loupe at home. Particularly nice about the glasses is that they allow me to judge focus as an aspect of the overall composition, and this, with the further aspect of being able to use both eyes at once, increases the "zen factor" of the experience. When I began to use reading glasses to focus, I'd usually bring a loupe along as I doubted my abilities to focus without it - but cross checking my accuracy with a loupe proved, time and time again, that the glasses were plenty accurate.

[Louis Joyner]

Scott:

If you wear glasses as I do, you might want to try a pair of inexpensive clip-on, flip-up magnifiers designed for fly fishermen. (They look like clip-on sunglasses, but with clear lenses instead of tinted.) They are available in +1.50, +2.00, +2.50, and +3.00 diopters. You can find them at fly fishing stores or on line at www.flyfishusa.com; cost is about $12.00 a pair. A similar product is also available that pins onto the underside of a ball cap bill.

The +3.00 magnifiers that I use allow a full view of a 4x5 groundglass at a distance of about 6 inches. They are also a big help when adjusting/setting the shutter.

Only problem is the small protective rubber tips on the clamps kept falling off; I finally glued them in place.

As good as the magnifiers are, I still use a lupe to check final focus.

[Alan Davenport]

The groundglass is subject to the same principles as viewing a print -- at a given viewing distance, there will be a circle of confusion that you will perceive as a point. As long as the CoC of a point (in the object space) is rendered on the groundglass at or below that size, you will perceive it as being perfectly focused.

Enter magnified viewing. Your dimestore reading glasses magnify the image on the GG so that you can perceive a smaller circle of confusion, thus you are able to focus better than with your naked eyes.

Take another step up in magnification with a loupe, and you should be able to control (and "control" is the operative word) the plane of focus even better. In theory, the more you increase the magnification, the better you can focus; in practice you'll reach a point where you're seeing the grain of the GG and not really getting any advantage. That seems to happen for most people at around 5x -- 6X, but of course varies with the groundglass and the person looking at it.

[Scott Fleming]

Thanks guys. John, that's what I thought. I've had pretty much the same experience but was just not sure due to lack of practice that I was truly seeing what it seemed I was seeing. Thanks.

[Scott Fleming]

Louis,

I've been through 3 pairs of those things. I keep breaking them. But I was using them for fishing not photography ;)). I think you have an excellent idea. I'll get a pair of those puppies at 3x and force myself to put them into a hard case when not in use instead of in my shirt pocket which is how I killed the others. Thanks.

[Brian Ellis]

I use reading glasses bought in a drugstore to compose and general focus. Then I use a loupe to fine focus. Maybe it's my eyes but even with the reading glasses I usually find that I can improve the focus with the loupe, i.e. reading glasses alongedon't provide optimum focus. That's true with the Maxwell screen I recently added and has been true with all previous screens.

[Jim Rice]

I have plenty of reading glasses, and can not imagine taking a photograph without a loupe. I also can't imagine why one would want to try to.

[Scott Fleming]

Jim,

Because it's a giant pain in the butt cluster ____. If I could get away with just strong reading glasses I would do it in a heartbeat. I've never tried a magnifying binocular reflex viewer but if one worked i'd never take it off my camera.

[Scott Fleming]

I especially like using a loupe when I need one degree of tilt out of the detent on a camera without geared tilt. That's REALLY fun.

[Jim Rice]

A loupe is a reasonably sized pain in the butt. It is still neccessary to achieve reasonable focus. I hate it, but it is.

[Emmanuel BIGLER]

I perfectly understand the delicate point raised by Scott F., being myself short-sighted and affected by astigmatism to a point where it is out of question for me to to look through any optical instrument or focusing any GG image without my ophtalmic glasses on.
For looking through the eyepieces of a telescope or binoculars, I cannot use anything but modern high eyepoint eyepieces (or long eye relief ? not sure of the right English terminology), similar to B-type for binoculars.
As far as GG focusing is concerned. The main point is that you should use a loupe with a large exit lens element or a well-designed loupe with a long eye relief like B binoculars, or a pair of clip-on or additional binocular "loupes" as mentioned by Brian E..
I'm using a 6x9 camera so the GG surface it is actually too small to properly focus all the image including fine tuning of camera movements without a loupe or a viewfinder. This might be considered as a severe limitation of 6x9-only view cameras, and yes, a binocular viewer with reflex mirror and 2x loupes is superb (but bulky) ; this is another story ;-)
For a 8x10" camera on the other hand with a pair of reading glasses or clip-on watchmaker's binocular loupes you can easily switch from a global view (without loupes) to precise focusing (with a monocular or binocular loupe system).
In size, 4x5" apperers to be in between 6x9 (where a loupe is mandatory) and 8x10" where photographers gifted with an excellent vision and not affected by presbytia can even do the job without any loupe.

There is an interesting physiological point explained to me by Philippe Vogt (the boss of Arca Swiss, who is also a passionate photographer).
Philippe Vogt's point is that you should be able to focus as fast as possible and, if possible, avoid to rack the GG back and forth forever. Beyong a certain amount of time spent trying to find the best focus, your eyes get strained and things become worse.
I'm not sure that I fully get the point but my understanding is that you should be as comfortable as possible and you should try to avoid any strain as much as possible. The problem is that one might not be immediately aware of eye strain. This is a well-known problem for people looking at an aerial/virtual image through a pair of binoculars when the instrument totally offset w/respect to the best possible left+right focus setting ; in principe looking at a GG is less a problem since the eyes actually know where to focus, the image is real and "materialised" by the GG ; you can almost touch it with your hands ;-).

Another interesting point explained to me by Henri Gaud, a French professional LF photographer specialist of monastic architecture deals with proper focusing in low ligh levels.
When he has to focus a LF camera in very dim light, he does not try to find the best focus. On the contrary he tries to find as quickly as possible on both sides of the expected best focus two similar points where blur is roughly identical in the sense of : identically un-acceptable. Then he sets the best focusing point just in between.
This practical rule supported by years of professional practice is also perfectly supported by the simple model of what happens in a de-focused camera even when the back is tilted : the two limit planes of (un-)acceptable sharpness are parallel and placed at an equal distance on both sides with respect to the ideal best focus plane. So try and find those two equally unacceptable positions, and set the focus in the middle. Well this does not help one to precisely set the best tilt angle, but is saves a lot of eye strain finding the best position for the longitudinal focusing rack & pinion movement.

[Leonard Evens]

Emmanuel,

I may have misunderstood what you said. When you tilt, the two limit planes of acceptable sharpness are not parallel. They intersect in the hinge line which is (usually) vertically below the lens when the back is vertical. As the tilt decreases, the distance of the hinge line below the lens increases, approaching infinity as the tilt approaches zero. At that point, the lens plane is parallel to the back, and so are the limit planes and the best focus plane.
Also, the ideal focus plane splits the two limit planes in the following sense. Again, with the back vertical, if you draw any vertical plane parallel to the back, the section of that plane between the limit planes is bisected by the best focus plane.

[Scott Fleming]

Good post Emmanuel. Very interesting.

I believe it is correct that past a certain point ... focusing just gets more problematical. I had never been certain about it but HAVE noticed that racking back and forth while using a loup definitely loses 'certainty' so to speak, after a bit.

[Emmanuel BIGLER]

I may have misunderstood what you said
I was speaking of course about image space near the slanted 'focus' plane, not object space where slanted planes intersect at the pivot point.
Sorry for misunderstanding, I was speaking about parallel planes near the best possible position for film. Whether you move the front of the rear standard for focusing, this does not change the situation but it is simpler to imagine focusing by translation at rear.
For readers not familiar with Leonard's paper, the reference is here :
Leonard Evens, "Some Thoughts on View Camera Calculations",
www.math.northwestern.edu/~len/photos/pages/dof_essay.pdf (http://www.math.northwestern.edu/~len/photos/pages/dof_essay.pdf)
5.2 Getting adequate depth of field when lens is tilted
The key figure is Figure 7: Depth of field wedge for tilted lens...
...shows the usual fan-shaped rays in the objet space and plane and parallel plane in the image space.



From this excellent source I realized some time ago that I was mistaken, so I have redrawn figs 6, 7, 8, 9 and 10 in an updated version of
www.galerie-photo.com/profondeur-de-champ-et-scheimpflug.html (http://www.galerie-photo.com/profondeur-de-champ-et-scheimpflug.html)
and, shame on me ! I did not take time to upgrade the English version....
Now I know I have to do it quickly...