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View Full Version : adding a mm focus scale (for dof calc.) to a field monorail



John Schneider
28-Dec-2008, 22:42
To lighten my load on long hikes, I picked up a 4x5 Galvin. I added some modern niceties like an adapter board to Linhof TK boards and levels on both standards. The other thing I'd like would be a focus scale marked in mm like I have on my Technikardan. When I had a Gowland Pocket View I milled a flat on the solid rail and glued in a strip from a ruler. All the rail on the Galvin is hollow so that's not an option.

Does someone have a suggestion? Also, as I recall some Sinars had a knob that gave the mm's or dof information (never owned a Sinar so my memory may be faulty). Something like that would be an option also. Any ideas are welcome. I have access to a machine shop so machining and fabrication are no problem. Thanks.

Dave Jeffery
29-Dec-2008, 02:03
The information about making the focusing knob is below but Iíll add the simple set up for a ruler on the bed as well.

I wanted a ruler on my rail to measure focus spread and since I wasn't exactly sure how and where it should ideally be placed so I just bought a small stainless steel ruler (in mm) in a plastic sheath ($5). Velcro was attached to the rail and the plastic sheath in a couple of spots to secure it to the bed. The ruler also slid a little too easily in the sheath so I cut long strips of an index card and pushed that into the sheath until the ruler would no longer move without me pulling or pushing it. The end of the sheath is even with the frame on the front of the camera when collapsed and the ruler is just pulled forward out of the sheath. The front edge of the lens support frame was used as my zero position.
To measure the focus spread I would focus on a distant point and set the ruler to say 20mm and when I focused on a near object I could just look at the focus spread in mm and select the optimal aperture from the chart on this page.

http://www.largeformatphotography.info/fstop.html

I eventually extended that chart to this

D mm---- F-stop
.17-------- F8
.13---------F 11
.7----------F 16
1-----------F 16.6
1.3---------F 22
2-----------F22.6
2.7---------F 32
3-----------F 32.2
4-----------F 32.6
5-----------F 45
6-----------F 45.2
7-----------F 45.4
8---------- F 45.6
9-----------F 45.8
10----------F 64
11----------F 64

I used the ruler in the sheath method for a while and then decided to make a focusing knob like the one you are asking about which is here

http://www.largeformatphotography.info/dofknob/

I eventually made a focusing knob out of PVC plumbing parts (a 1Ē coupler that is tightened by hand and some other pipe plugs) using a Dremel tool with a carbide cutting bit, and it was well worth the effort. All you need is a flat outer ring that a scale can be attached to that slides over an inner knob and since you have access to machining tools it will be easy.

I had trouble getting the scale that is provided on this site to adjust and resize properly for the settings for my camera so I just used the mm ruler mentioned above and made accurate marks on a piece of paper on the DOF knob.
To mark the focusing knob make sure and just turn the knob in one direction only. Using the mm ruler on the bed just turn the focusing knob and convert the mm measurements from the ruler on the bed, to the F- (aperture) marks on focusing knob. EG. so where the zeromark that you have chosen on the camera moves over the ruler (on the rail) at 2.7 mm put a mark for F32 on the focusing knob at the zero mark. I used small strips of paper and when a good scale was finally made I copied the marks to a backup piece of paper so another scale could easily be made, and then I Scotch taped the paper to the knob and tried to make it as waterproof as possible. You will have the luxury of machining a nice scale but you may want to make the marks on a piece of paper initally as well since I had some trouble getting the marks set accurately at first.
I never use the ruler anymore and oddly enough it has never moved or fallen off and if I ever lose the knob the ruler is there as a back up. Iím sure there are better ways but this was quick, cheap and easy for me.

Have Fun!

David Karp
29-Dec-2008, 07:47
I don't know if you have a spot on the rail that will work this way, but it is worth mentioning.

I added mm scales to my Crown Graphic and Walker Titan by printing out a mm ruler that I found by Googling "mm scale" or something like that. I printed it out on a laser printer, put Avery laminating material on one side, and two sided tape on the other, and stuck the thing to the cameras. Works well.

It just depends on whether you have a place on the rail where you could attach something like this without them interfering or being rubbed off as the camera travels on the rail.

Brian Ellis
29-Dec-2008, 17:58
I've put mm rulers on just about every large format camera I've owned - Tachiharas, Ebonys, Deardorffs, Agfa Ansco, Linhof Technikas, etc. I cut a strip of a standard tape measure that has inches on one side and mms on the other. Then I Scotch tape it, mm side up, somewhere along the bed or rail at a place where I can see the position of the front standard relative to the tape as the standard moves back and forth. Then I cut out a little piece of paper shaped like a small arrow and tape it somewhere on the front standard more or less abutting the tape so it's easy to read the difference in mms between the near and far focus points. No need to machine anything. : - )

Dave Jeffery
30-Dec-2008, 03:41
A dremel tool cuts PVC like butter. All a focusing knob needs to be is a pipe with a slit cut in it, which rotates over a slightly smaller piece of pipe that has a ID that will allow it to press fit over the focusing knob. Simple.
What turned out to be a big waste of time for me was trying to get the scale that is provided on this site to adjust to my camera dimensions. It was a lot easier to mark a piece of paper as mentioned above.
Due to the nature of my schedule on virtually all of my trips by the time I am setting up to shoot the sunrise I have been awake and on the go for over 24 hours at least. When the mm readings on the ruler get transferred to the large outer circumfrence of the focusing knob, the lines are further apart and easier for me to see than the smaller mm lines on the ruler. I am also reading the F-stop that is needed not a number that needs to be converted in the wee hours of the morning so for a newbie like me it's easier.

That being said when I eventually fantasize that I know 1/20th of what Brian does it will be cause for celebration. Out of necessity I have had to build a lot of underwater light heads using a dremel tool so the work is fast and easy for me.

You may want to see if the mm ruler is easier for you. I will always make focusing knobs using off the shelf cheap PVC parts.

Robert A. Zeichner
30-Dec-2008, 04:16
I might suggest the Cobalt Precision rule from Grayson Precision Technologies of Edison NJ. This is a laser deposited .007" polyester rule that can be easily cut with an Xacto or even in your cutting board. I glued strips on an old Wisner and later on my Deardorff with some very tiny dabs of Silicone adhesive (clear) applied with the end of an unbent paper clip. I then made several witness marks on the moving part of the focusing rail with a fine brush and 3 different colors of plastic model enamel. This allows me to use different parts of the scale (at different bellows extensions) without getting confused. It works great! That rule is a work of art. I've never seen a more accurate or easier to read scale. Good luck.

Dave Jeffery
30-Dec-2008, 05:00
Great input!

I notice the emphasis on the ease of reading the scales and one mention of avoiding confusion.

It's a wake up call for me that a larger scale is easier to read, especially in low light and obviously the larger the outer circumfrence of the focusing knob is, the larger the scale can be with easy to read F-stops. I love tinkering so now I'll make a larger diameter DOF knob that will accomodate a larger and far easier to read scale. I'll also look into a very tiny LED to mount onto my aluminum zero marker to illuminate it so I don't need to have the headlamp on. Very nice!

Have Fun!

Dave Jeffery
30-Dec-2008, 05:18
Switching from PVC to a 3/4" foam core epoxy fiberglass casting. I love to tinker and all I need is the foam : )

lloyd
30-Dec-2008, 07:00
"I glued strips on an old Wisner and later on my Deardorff with some very tiny dabs of Silicone adhesive (clear) applied with the end of an unbent paper clip. I then made several witness marks on the moving part of the focusing rail with a fine brush and 3 different colors of plastic model enamel."

The witness marks, yes, that's what I've done, works great. But for the rule I now use a self adhesive mm rule cut to size. Available somewhere online at sewing supply spots. Very thin w/good adhesive, easily cut to length.

Dave Jeffery
30-Dec-2008, 10:45
A feature that the focusing knobs haven't had is a small tab or lever to set them to zero which would mean that one doesn't have to come out from under the dark cloth to read or set the first mark. Focus on the far, slightly tighten the focusing knob, push the tab to set the zero mark, focus on the near, come out from under the dark cloth, split the difference from zero and that's your F-stop.
The lever or tab would have to be hinged to move away from the zero marker.

Leonard Evens
31-Dec-2008, 14:47
The information about making the focusing knob is below but Iíll add the simple set up for a ruler on the bed as well.

http://www.largeformatphotography.info/dofknob/


Have Fun!

I find it preferable to put a distance scale on the focusing knob. Typically you can determine the focus spread to with 0.2 mm, which is much better than you can do with a scale along the rail. Dave's depth of field method is essentially equivalent to a distance scale where the distances are measured in f-stops rather than mm. But, it assumes some specific choice of coc.

I described how I did this in

www.math.northwestern.edu/~len/photos/pages/dof_essay.pdf

Using a coc of 0.1 mm, you can calculate the f-number from the focus spread in your head. Multiply the focus spread in mm by 10 and then divide by 2. For example, if the focus spread is 4 mm, the f-number is 4 x 10/2 - 40/2 = 22. You would then use f/22.

Dave Jeffery
1-Jan-2009, 01:45
I'm excited by the push button design. It will be nice to be able to set the focus to one extreme and then just push a tab to set the scale without having to come out from under the dark cloth. Again, just set the focus on one extreme, then push a tab to set the zero mark while still remaining under the darkcloth, focus to the other extreme and then come out and simply split the difference, and the F-stop (or mm spread) is on a large scale and easy to see. It seems to me that this must be faster than having to come out from under the darkcloth and look at the reading on the scale on the bed, go back under the dark cloth, set the other focus, come back out and read the scale, and then do the math?

I also like the idea that with a push tab design it will be easier to apply a little more force to the ring with the scale on it, so the tension on the ring can be increased which will prevent it from moving off the mark easily. I have a small piece of aluminum angle mounted to my camera as my zero reference line and it's solid enough and straight enough to be continually hit by whatever is designed to stop the ring at the zero mark.

Whatever is designed to hit the aluminum edge and stop the ring at zero must be retractable so the knob can still turn either way and I haven't finalized that design yet. I will make the knob larger so the scale is larger as well.

Thanks Leonard for the heads up on the simple math and I may change the scale to mm in the future.

Happy New Year!

Leonard Evens
2-Jan-2009, 08:40
Thanks Leonard for the heads up on the simple math and I may change the scale to mm in the future.

Happy New Year!

That might be helpful to some people.

It might also be added that one should divide the f-number by the ratio of the bellows extension to the focal length, i.e, by 1 + M where M is the magnification. For distant objects, that ratio is so close to one that it doesn't matter, but for close-ups, it can make a significant difference.. Of course, if you don't bother doing that division, you will just stop down too far, which increases depth of field more than absolutely necessary. In most cases that is innocuous. Finally, all this ignores diffraction.