Zone focus for LF...

[rubbernglue]

Most cameras I use has a good focus scale so that I can appreciate good focus from a given aperture; and/or perhaps make sure infinity is out of focus, which is often what I want as I set infinity at f/11 while I shoot at f/8 for example.

But I find it hard to select my focusing zone when shooting large format and was wondering what is the best practice for this?

I tried to make my own simple zone-scale on carboard but it was not as simple as I thought as the distance between distance markings cannot be the same for all or something like that.. So imply that I have a 120/5.6 lens for which I want to make a scale, is there a easy way to achive this?

I understand of course that there are apps and various DOF websites for this but I REALLY dont want to fumble around with scaling on a cellphone! I really would like to find a website which can generate a scale in PDF or such for a given lens which I can print and use in the field... At least then I can appreciate distances more easily even if the zone scale is not coupled with the lens.

How do you guys do this and how did people do this before??

 

[AgX]

I could not find a download for a DOF-slideruler-scale print.
Disc-rulers are available though.

Though with a handle of rubber&glue you sure are able to fumble together two pieces of cardboard with a ruler and pen and with a plain DOF calculation:

I like this online calculator:
http://www.erik-krause.de/schaerfe.htm

You would need two scales per focal lenght. One at the front standard with focus mark and DOF-scales and a static one with the object distances at the baseboard.

-) fix a blank scale at the front standard, chose a point as focus mark
-) mark at the static scale the mark for the infinity extension (either found visuallly via the ground glass or metered via the back focal distance, given by some lens manufacturers)
-) chose object distances of your like (keep in mind the calculator understands object distances as metered from the center of lens)
-) calculate for these distances the respective extensions, add these to the static focus mark and mark them
-) calculate for one distances and one aperture the respective far- and near- point. Mark them provisionally at the static scale too. (You may calculate their respective extentions for more accurate location on the static scale)
-) set the standard mark at the chosen distance and transfer the respective two marks at the standard scale. If all is right the two marks are located symmetrically at both sides of the standard focusing mark.
-) indicate these two marks (by colour) for the resopective aoperture
-) repeat this marking at same object distance for a variety of apertures
-) you may add futher object disntance mark at the static scale to fill gaps

For other focal lenghts you would have to repeat that all. To avoid confusion, best use two sets of scale per focal lengt. Then of course you must make some arrests that enable to locate the scales repeatable.


The maximum circle of confusion (Zerstreuungskreis) for 8x10 is chosen by Rodenstock as 0.2mmm, though the above calculator advises a larger figure. (you may set a figure of your choice)


Due to the large extensions this all may become clumsy.
That may explain that there are only seperate disc-rulers, or that manufacturers have integrated the DOF scale into the focusing wheel.

 

[rubbernglue]

Hmm well, a bit of me thinks that this should be quite simple in the end, but since i'm really not that familiar with Circle of Confusion (which seems confusing!) and all possible math behind depth of field and so on..
I think I will have to dig a bit deeper in order to comprehend all variables in this subject.

Also I have very hard to understand why so many 6x6, 6x9 folders lack the dof-scale which is mostly found on voigtländers but not many brands thought that was needed (??) still kodak etc included them on lots of 135-cameras of the time... wierd.

 

[AgX]

As there is only one plane of sharpness the idea behind the circle of confusion is to set an maximum of un-sharpness at the negativ to accept. Which then again leads to just those two figures (near- and far-point) you want to establish for your depth-of-focus scale.

This acceptance then again is related to the degree of enlargement, which for a 24x36mm negative typically is greater than for a 8x10' one.

Thus the typically used COC for 24x36 is 0.03mm and for 8x10 is 0.2mm.

 

[jim10219]

If you have a good ground glass, good dark cloth, good loupe, and possibly a good fresnel, you should be able to stop down the lens and see what's in focus and what isn't. Often times the image will be too dark for me to get a feel for the entire composition at once, but I can magnify important areas to see what's happening there, and set up my composition with the lens wide open.

Those calculations will just slow you down for LF. Plus, if you add movements to your shot, your calculations change and become much more complex.

 

[henpe]

I have made a couple of DOF-dials that I use for my 4x5 large format field work. The dials are specifically made for my lens setup {90mm, 135mm, 210mm}, but I guess this is a quite standard setup and may hence be useful also for others? Each focal length have two scales and which one to use may depend on your current criterion for acceptable sharpness: one scale is for "normal sharpness" (0.085mm CoC) and one for "critical sharpness" (0.030mm CoC).

The dials are available for download, if anyone have use for them?
https://www.henpe.se/cms/misc/downloads/category/2-photography?download=5:lf-dof-f90
https://www.henpe.se/cms/misc/downloads/category/2-photography?download=6:lf-dof-f135-f210

You need to print the pdf's and laminate on clear film. Before you laminate you also need to cut a window on the front dial such that the distance scale on the back dial can be seen through the window. Hope this description makes sense?

Regards
Henrik

 

[AgX]

Here is one more:
http://www.dofmaster.com/custom.html

There are also readymate samples of DOF ruler-discs.

But I understood the OP actually did not want an external disc-ruler but a camera mounted, lens coupled slide-ruler, as I described above.

 

[rubbernglue]

Indeed does movements change the game, however it looks way more obvious in the finder when a movement is used.

 

[rubbernglue]

I have made a couple of DOF-dials that I use for my 4x5 large format field work. The dials are specifically made for my lens setup {90mm, 135mm, 210mm}...

Here is one more...

Very nice!! What I am interested in is mostly a better workflow and a way to think during composition and setting my chosen DOF. I thought mostly of some kind of slider, but disc works just as well!

 

[AgX]

If you have a good ground glass, good dark cloth, good loupe, and possibly a good fresnel, you should be able to stop down the lens and see what's in focus and what isn't. Often times the image will be too dark for me to get a feel for the entire composition at once, but I can magnify important areas to see what's happening there, and set up my composition with the lens wide open.

Those calculations will just slow you down for LF. Plus, if you add movements to your shot, your calculations change and become much more complex.

But the OP wanted zone-focusing and thus not to look at the groundglass. And with a mounted slider (if feasable) there would not be any calculation.

 

[rubbernglue]

I never really mentioned that it would be mounted, but I am pretty open minded regarding a best practise for this. I would really like to hear about how others do and if there is some sort of neat way for me to learn from.

EDIT: That disc which by using DOFMaster from the link above was quite nice in fact, and since I run Linux at home I guess ironically I am one of a few which can run that application today as modern windows will not allow it - but in linux I can make "wine" to run it.

 

[ic-racer]

These Horseman focus scales (for 4x5" cameras) work with any camera that has the indicated focal length lens. Having a focus scale is the first part of the problem.

 

[ic-racer]

For the scales above, you need a corresponding set of marks for the aperture. The aperture range marks are dependent on many factors, CoC size, Airy disk size or a combination of both.
Rather than doing the math you can use this table:
For example, for conventional DOF based on CoC, you would make hatch marks 2mm (4mm spread) on either side of your focus indicator mark and assign those marks to f22 (round up from f20).
BTW I personally use the MTF optimum scale because I enlarge my Large Format negatives (even 8x10).
Also, since the math is not shown, I'll make it clear, the table below does not change with focal length. So you only need to make one set of aperture range hatch marks on the focus track and it will work with all of the focal-length scales above.

 

[ic-racer]

This exercise brings home the message that 4x5 handheld zone focus is difficult without a flash unless you are using pretty short focal length lenses.
For example ISO 400 in sunlight, add the safety factor to get ISO 200 assuming if you don't have a rangefinder to focus you don't have the meter either. In the sun you might be at 1/125 at F22 giving you only 0.5mm movement error on the focus track either side of the exact focal point (MTF-Optimum scale above).

 

[AgX]

Linhof once even made a 8x10 handheld camera...

 

[ic-racer]

Linhof once even made a 8x10 handheld camera...

Inches?

 

[AgX]

Yes, inches. It was a kind of huge pentaeder. Fix-focus.