PDA

View Full Version : Fixed focus 4x5 camera



Degroto
10-Aug-2017, 11:33
Hi,

Recently I picked up a sinar camera with a bunch of lenses. Including a sinaron F5,6 65mm lens. Now I want to try a simple fixed focus camera with this lens. My reasoning that the DoF will be big enough to do without a focusing system. Is my thinking correct?

Peter

Jac@stafford.net
10-Aug-2017, 11:39
Recently I picked up a sinar camera with a bunch of lenses. Including a sinaron F5,6 65mm lens. Now I want to try a simple fixed focus camera with this lens. My reasoning that the DoF will be big enough to do without a focusing system. Is my thinking correct?

It depends upon how critical you are. The rest is physics you can get from a DOF table - how close, what aperture, degree of enlargement.

Bob Salomon
10-Aug-2017, 13:26
Of course you can. The quality will depend on the depth of field that is acceptable to you and the distance that you shoot from. The 45 Linhof Aero Technica EL used lenses from 90mm up and the 90 was in a fixed focus mount. Of course, being an aerial camera,meant that the minimum legal altitude is 500'.

Dan Fromm
10-Aug-2017, 13:29
Physically possible? Of course. Wise? Doubtful unless, as Bob suggested you focus the camera for a distance -- aerial cameras are focused on infinity -- and then use it only at that distance.

Drew Bedo
10-Aug-2017, 13:47
Be on the look out for a TravelWide. It was originally designed as a fixed focus 65mm camera.

Jac@stafford.net
10-Aug-2017, 14:43
If the OP is interested I can post one of my 6x10cm cameras (Plaubel Veriwide) which zone focuses, but with an attached compact laser rangefinder it can knock-on focus. There is no reason it would not work with 4x5". I've made no pictures of it yet.

Aside, I'm upgrading my 4x5" cameras which have earlier 47mm Super-Angulons to 47mm Super-Angulon XL. Not finished. Here are the 'before' pictures. First the f/8, (http://www.digoliardi.net/super-wide-4x5-1.jpg) and another (f/5/6) (http://www.digoliardi.net/veriwide-4x5/1-front-on-1.jpg). (Yes, that's 4x5). Both are in focusing mounts.

Degroto
10-Aug-2017, 23:58
Hi Jac that would be awesome. The idea of fixed focus for me comes from street photography where you use aperture f/16 for example and focus the camera that everything is sharp between 1,5 meters to infinty. I want to use that principle for my camera. Also I use an old Eho boxcamera that is more or less sharp from 3 meters onward. I should be able to achieve something like that with my fixed focus camera. Maybe not but I wil have become a wiser man after that (haha).

From where do I measure de focal lenght of the lens? From the plate where the lens is attached?

Emmanuel BIGLER
11-Aug-2017, 06:35
From where do I measure de focal lenght of the lens? From the plate where the lens is attached?

Hello from France!

This is a frequently asked question ;)

What you want is to set the proper distance between the lens mount and the film.
Hence, to do this, the knowledge of the focal length is not really useful, as strange as it may seem!
What you need is a distance given by lens manufacturers, named "flange focal distance" or sometimes "Flange Focal Length" (e.g. in Fuji lenses documentation).
This is the distance between the back side of the shutter and the focal point. The focal point is where an image of a far-distant object is projected sharp.
Now in order to properly set your lens mount in front of your film holder, you have to take into account the film holder's depth, which is for modern film holders compliant with the ANSI standard
- 2" x 3" and 4" x 5" : 5.0 mm +- 180 microns (0.197" +-0.007")
- 5" x 7" : 5.8 +- 250 microns (0.228" + - 0.010")
- 8" x 10" : 6.6 mm +- 400 microns (0.260" + - 0.016")

If you already have a springback with ground glass, simply focus the image of a distant object, no computation is required.

And if you wish to fix-focus at the hyperfocal distance, instead of infinity, starting from the flange focal distance, you'll need to slightly increase the length between the lens and film by a small amount, to be easily computed according to your working f/number, focal length and sharpness criterion.

You can have a look at this article (in French) by Gilles Barbier who built a fix-focus camera for the 5x7" format.
http://www.galerie-photo.com/barbier-hybis-90.html
In this case, focal length was 90 mm, the sharpness criterion was 150 microns, the working aperture f/16, hence the offset required to focus at the hyperfocal distance instead of infinity was 3.3 mm.

Dan Fromm
11-Aug-2017, 08:05
Emmanuel, published flange-focal distances are nominal. So are the focal lengths engraved on lenses. A lens' design focal length -- the focal length if the lens matches its prescription -- can differ from the nominal. Example, the 260/10 Process Nikkor. Its design focal length is 267 mm. And actual focal length can differ from design. Example, the 38/4.5 Biogon. Design focal length 38.5 mm, actual focal length of the twenty (20) I've had as measured by the original customer ranged from 38.3 to 38.8 mm.

The OP is going to have to get his lens, decide the distance at which his fixed focus camera should be focused, measure his lens' flange-focal distance when focused at that distance and then build his camera.

Jac@stafford.net
11-Aug-2017, 09:57
Hi Jac that would be awesome. [...]

I do not have the digital camera today to offer a snapshot so let me just briefly describe the set-up.

The key part is a Bosch GLR225 laser distance meter that I used in construction work. It is small & handy. (Shop carefully. Prices are all over the map).

The meter has a 1/4" tripod socket. I have mine in an L-bracket that places it on the side of the camera (a Plaubel Veriwide). It has four different measurement reference points - #1 from its front, #2 from the tripod socket location, #3 from the bottom and #4 from a point a couple inches rear of the bottom. Forget about #4. Just mount the meter so that any from 1-3 locate at the film plane. It is easy with a bracket. I use #2 and it's about perfect.

I can trigger the laser from my left hand and see the laser dot in my viewfinder. It does not work trying to see the dot on a ground glass for good reasons (light frequency mainly & brightness). I use viewfinders on most of my cameras.

Good news - it is good to about 225' and is accurate. Bad news - it does not work well in bright sunlight without a special target placed at the subject. It is also not good for pointing at a subject's eye. Don't do that. :)

So, surf for Bosch GLR225 laser distance meter and instructions to get the whole idea. Hope this helps. Will get a snapshot soon.

EDIT - Dan Fromm's advice is right-on and suggests a more cost effective approach. One thing I did with a 4x5" box camera with a sprung rear door was to drill a hole in the middle of the back, then took a spare 4x5 holder, removed the two slides and drilled a hole in its center, then used a lope to aerial focus on various distances and jot down the distance shown on helical focus mount. With a wide lens you can probably note a few significant distances and use DOF to take care of the rest.

DrTang
11-Aug-2017, 10:35
figure out what distance want to shoot from... build the camera to that.. then use a finder from a Polaroid 'Big Shot' to get you to that distance

Degroto
11-Aug-2017, 13:19
I only have one big shot. So not gonna mess that one up. :-)

Pfsor
11-Aug-2017, 14:48
The OP is going to have to get his lens, decide the distance at which his fixed focus camera should be focused, measure his lens' flange-focal distance when focused at that distance and then build his camera.

That is a highly theoretical approach which shows you have not built a camera using this sequence, I'm afraid. The practical difficulties you find in doing so are rather great - the difficulty to exactly measure the lens FFD, (using gg focusing, just try it and you'll see how difficult it is to find the plane where you put your callipers) the difficulty to build a camera with this exact space between the gg and the lens flange (with many parts in between) and the difficulty to do so while maintaining the lens plane parallel to the gg plane (very important for a lens of such a short FL).
A much better approach and much more practical is to built the lens into the camera in a way that it can be slightly moved forward and backward - even just 5mm is enough. In this way you can measure the lens FFD and built the camera with less precision and find the precise infinity focus while moving the lens to its right position. It is much easier this way.
There is a way you can fine focus the lens (using 4 rods) and fasten it in the precise position and be done with it regardless of the precision of your measuring and manufacturing of the rest.
Been there, done that. I have built fix focus cameras with lenses ranging from 90mm to the long telephoto of 800mm. Knowing what you want to use it for is necessary - my 800 mm camera is always used at objects in the realm of practical infinity. The 90, 135, 150, 180, 300mm lens cameras are also usable at shorter distances with no surprises at all.

Jac@stafford.net
11-Aug-2017, 15:02
That is a highly theoretical approach which shows you have not built a camera using this sequence, I'm afraid.

That is a risky assertion when it concerns Mr. Fromm's work.

Building a box camera is simple enough if one has the fundamental measurements that Dan posted, AND a focus helical. Build the body as very close to the required metrics, which can be done with striking accuracy, and the focus helix can make up for the micro-millimeter difference.

When I built my first, all I used were Mitutoyo gauges and decent, not outrageous wood machnes. Sure, actual focal lengths vary. I have years of experience with military lenses in which every single one was marked with absolute focal length, and then shimmed to accommodate the camera. (For land-based photography their metrics were overkill, overly expensive.)

This one (http://www.digoliardi.net/super-wide-4x5-1.jpg)had the board very carefully micro-planed, then using a compliant (variable compression) gasket the back was settled into accurate infinity focus. Eighteen years later it is no longer in spec, but adjustments to the helix and retorquing the gasket makes new, accurate alignment trivial. Next week I am converting it from an early 47m Super-Angulon to a later 47mm XL thanks to help from one of our LF members.

Pfsor
11-Aug-2017, 15:13
Jac, the OP doesn't want to use helical, see the 1st thread. And believe me, I know what difficulties you would fall in if you just tried to put Dan's theory in practice. To "have the fundamental measurements" is not at all a given fact, see my reasoning.
OTOH a helical focusing ring would be surely very helpful too, no contradiction in it.

Emmanuel BIGLER
11-Aug-2017, 15:27
a highly theoretical approach

As the saying goes:

"When Real World differs from Dan Fromm's theoretical approach, for sure, Real World is plain wrong." ;)

Not kidding (I stand corrected)
- the knowledge of the focal length is useless, except if you want to re-compute your distance engravings on an helical;
- the knowledge of the nominal flange focal distance of your lens is much more useful!
- if you have a complete springback handy with a ground glass, this will definitely help;
- adding 2 or 3 nominal numbers together to compute a measurement does not seem highly theoretical to me, but instead, as practical as can be in a mechanics workshop!
- the depth of focus focus @f/16 with a sharpness criterion of 150 microns, is plus or minus 16x0.15 = plus or minus 2.4 mm; no need of a submicron caliper to properly set a working device, to re-use a well-know expression by physicist Charles H. Townes, one of the inventor of the laser: "Nothing stops naysayers like a working device" (C. Townes, 1999)

Well, theoretical mechanics also exists :)

Jac@stafford.net
11-Aug-2017, 15:30
Jac, the OP doesn't want to use helical, see the 1st thread. And believe me, I know what difficulties you would fall in if you just tried to put Dan's theory in practice. To "have the fundamental measurements" is not at all a given fact, see my reasoning.
OTOH a helical focusing ring would be surely very helpful too, no contradiction in it.

Okay, thank you for that. Now I see that I drifted to my own preference. I am sure if the OP builds a camera with enough of a 'ball park' measurement without a focus helical he will be happy. I may be too fussy and have gone overboard. Again! :)

Perhaps he could search the Web for HOBO 8X10 CAMERA


Emmanuel: "When Real World differs from Dan Fromm's theoretical approach, for sure, Real World is plain wrong."

We have very good humor here. Thanks for grounding our dialog in good spirit.

LabRat
11-Aug-2017, 15:46
Without a focusing helical, a good idea is while building is to build up the lensboard so that it is a little short of the "proper" focusing distance, but has allowance for different spacers to be added to shim in final focusing distances...

You can also test a mild close-up lens if you want to find another mildly closer setting if you are somewhere where you would be closer to your subject...

You can also check out PVC/ABS plumbing fittings to find something threaded where when screwed in, it would be your hyperfocal distance, but slightly unscrewed for closer focusing (like an interior or garden path, etc)...

A wire sportsfinder is good, but I like these kind of cameras to have a GG so I can confirm the focus setting, compose when the edges are important, and have the option to use a rollfilm back...

Good luck!!!

Steve K

Jac@stafford.net
11-Aug-2017, 15:47
Steve, finding shims has always been a problem for me.
Wire sports finders work! Good of you to mention!

I have poor eyesight which can no longer be corrected so I use viewfinders, and yes, wire finders. I wish to promote the idea.

Pfsor
11-Aug-2017, 16:06
a highly theoretical approach

As the saying goes:

"When Real World differs from Dan Fromm's theoretical approach, for sure, Real World is plain wrong." ;)

Not kidding (I stand corrected)
- the knowledge of the focal length is useless, except if you want to re-compute your distance engravings on an helical;
- the knowledge of the nominal flange focal distance of your lens is much more useful!
- if you have a complete springback handy with a ground glass, this will definitely help;
- adding 2 or 3 nominal numbers together to compute a measurement does not seem highly theoretical to me, but instead, as practical as can be in a mechanics workshop!
- the depth of focus focus @f/16 with a sharpness criterion of 150 microns, is plus or minus 16x0.15 = plus or minus 2.4 mm; no need of a submicron caliper to properly set a working device, to re-use a well-know expression by physicist Charles H. Townes, one of the inventor of the laser: "Nothing stops naysayers like a working device" (C. Townes, 1999)

Well, theoretical mechanics also exists :)

No, adding 2 or 3 measurements is not difficult, indeed. To take the 2 or 3 measurements is much more difficult, because of the practical difficulties you encounter. Where do you take the measure of the distance between the gg and the lens flange? Where do you put the callipers when the gg is inside the camera box and you calliper is outside of it? While measuring on the outside frame of the gg do you take into account the manufacturing imprecision you find on it? Before you add the 2 or 3 measurements you must find how precise you are when fiddling with your callipers on different parts of your "complete springback". Because the complete springback is not built to 0.01mm tolerance all over, you will soon discover.
And then - if you think your gg plane can go off one side with 2.4mm and be happy then build such a camera for 65mm lens and be happy... When you focus your 65mm lens, moving the gg 2.4mm gives you the same focus, under your focusing loupe, doesn't it? It's just adding 2 or 3 measurements together, isn't it? After all, a camera is just a light tight box between a lens and gg, isn't it?
I think, Dan is intelligent enough to know the difference between saying a theory and following it in the practical way.

Jac@stafford.net
11-Aug-2017, 16:10
No, adding 2 or 3 measurements is not difficult, indeed. To take the 2 or 3 measurements is much more difficult, because of the practical difficulties you encounter. Where do you take the measure of the distance between the gg and the lens flange? Where do you put the calliper when the gg is inside the camera box and you calliper is outside of it? While measuring on the outside frame of the gg do you take into account the manufacturing imprecision you find on it? Before you add the 2 or 3 measurements you must find how precise you are when fiddling with you callipers on different parts of your "complete springback". Because the complete springback is not built to 0.01mm tolerance all over, you will soon discover.
And then - if you think your gg plane can go off one side with 2.4mm and be happy then build such a camera for 65mm lens and be happy... When you focus your 65mm lens, moving the gg 2.4mm gives you the same focus, under your focusing loupe, doesn't it? It's just adding 2 or 3 measurements together, isn't it? After all, a camera is just a light tight box between a lens and gg, isn't it?
I think, Dan is intelligent enough to know the difference between saying a theory and following it in the practical way.

:) Do not worry so much for precision. You are on track. Make it the best you can and be happy. The pictures matter a whole lot more than technical minutiae.

Pfsor
11-Aug-2017, 16:15
Jac, don't worry, I will still sleep well. :)

LabRat
11-Aug-2017, 16:19
Steve, finding shims has always been a problem for me.


OR, make a proper square lensboard (wood, metal etc) that will fit on the front of your shortened camera, and allow space for a foam or other soft gasket to make a limited range collapsible "bellows", and have screws on the four corners that you can tweak to find your favorite focusing distance... You might even be able to add some on-the-fly focusing arrangement for at least some different focusing zones...

You could also come up with some way to mount different length lens cones for different FL's that can be screwed down at will...

Steve K

LabRat
11-Aug-2017, 16:33
Hmm. And the foam or other soft gasket will get pressed more and more in the time passing or will just keep the same dimension? Seems like a great idea to make your FFD differ while seasons flow.

Nah, the heads of the screws holding it down in the corners are the register points, the foam or rubber just fills the gap and create outward pressure...

Steve K

Dan Fromm
11-Aug-2017, 17:03
Where do you put the callipers when the gg is inside the camera box and you calliper is outside of it?

Funny that you should ask. What I've done has been to mount the lens in question on a Speed Graphic board, put it on (surprise!) a Speed Graphic, focus to the desired distance, take the lens off, a drilled board with no lens on the camera and measure the flange-to-film distance with a depth gauge. The OP may have to borrow a camera to do this. Speed Graphic not necessary, it was what I had at the time.

Its better than guessing, which is what using published flange-focal distances amounts to. Published flange-focal distances are great for finding out what can probably be done but that's not what the OP needs.

About the need for focusing. The shortest lens I've had -- still have it -- for 35 mm is a 24 mm. It has to be focused for best results. My 35 Apo-Grandagon has to be focused for best results.

Pfsor
11-Aug-2017, 17:25
Funny that you should ask. What I've done has been to mount the lens in question on a Speed Graphic board, put it on (surprise!) a Speed Graphic, focus to the desired distance, take the lens off, a drilled board with no lens on the camera and measure the flange-to-film distance with a depth gauge. The OP may have to borrow a camera to do this. Speed Graphic not necessary, it was what I had at the time.


And the second lens board must have the exact same thickness (best to 0.01mm) and geometry as the first one and the depth gauge must not be inclined on it in any direction so that the measure is not false and the standard may not move at all (to the precision of 0.01mm) and all added you're in the situation that taking the measure 5x you get 5x different results... Been there, done that.
How much easier to build a camera where fine focusing of the lens plate takes care of the excellent result without asking the depth gauge its opinion.
Or you can can just say - I have 2.4mm of free space, what do I care about precision, ain't any naysayer, don't need any atomic clock and am happy...
To each his own.

Pfsor
11-Aug-2017, 17:32
Nah, the heads of the screws holding it down in the corners are the register points, the foam or rubber just fills the gap and create outward pressure...

Steve K

Ok Steve, got that even before I deleted my post. No need to fill the gap and create outward pressure. You first build the box and fasten down the screws in their correct position - if you know how to - and then cover the box from one standard to the other with whatever suitable light tight material. My preference was black leather - lighter than anything else and interesting photo look is assured.

Dan Fromm
11-Aug-2017, 18:05
And the second lens board must have the exact same thickness (best to 0.01mm) and geometry as the first one and the depth gauge must not be inclined on it in any direction so that the measure is not false and the standard may not move at all (to the precision of 0.01mm) and all added you're in the situation that taking the measure 5x you get 5x different results... Been there, done that.
How much easier to build a camera where fine focusing of the lens plate takes care of the excellent result without asking the depth gauge its opinion.
Or you can can just say - I have 2.4mm of free space, what do I care about precision, ain't any naysayer, don't need any atomic clock and am happy...
To each his own.

Interesting. The OP has three posts in this discussion. In none of them does he mention making a camera with a ground glass. Your approach will certainly work with a camera in which focus can be seen and adjusted.

Oh, and by the way, the OP says he has a Sinar. He didn't say that his lens is on a Sinar board. If it isn't, he can get a board drilled to suit the lens, put the lens on the board, mount on the Sinar, focus ...

Pfsor
11-Aug-2017, 18:16
Interesting. The OP has three posts in this discussion. In none of them does he mention making a camera with a ground glass. Your approach will certainly work with a camera in which focus can be seen and adjusted.
.

Interesting. How would you control the focus if not on a gg? Trying the focus on film each time you want to adjust the FFD and see what it does? Would be a highly original approach, it seems. The OP wants to try a simple fixed focus camera. Must be simple to do that, I suppose. Just add his lens on a fixed focus box and voilą...

Dan Fromm
11-Aug-2017, 18:34
Interesting. How would you control the focus if not on a gg? Trying the focus on film each time you want to adjust the FFD and see what it does? Would be a highly original approach, it seems. The OP wants to try a simple fixed focus camera. Must be simple to do that, I suppose. Just add his lens on a fixed focus box and voilą...

As you said in post #26 above,


How much easier to build a camera where fine focusing of the lens plate takes care of the excellent result without asking the depth gauge its opinion.

Pfsor
11-Aug-2017, 18:44
Hello from France!


Now in order to properly set your lens mount in front of your film holder, you have to take into account the film holder's depth, which is for modern film holders compliant with the ANSI standard
- 2" x 3" and 4" x 5" : 5.0 mm +- 180 microns (0.197" +-0.007")
- 5" x 7" : 5.8 +- 250 microns (0.228" + - 0.010")
- 8" x 10" : 6.6 mm +- 400 microns (0.260" + - 0.016")





- the depth of focus focus @f/16 with a sharpness criterion of 150 microns, is plus or minus 16x0.15 = plus or minus 2.4 mm; no need of a submicron caliper to properly set a working device, to re-use a well-know expression by physicist Charles H. Townes, one of the inventor of the laser: "Nothing stops naysayers like a working device" (C. Townes, 1999)

Well, theoretical mechanics also exists :)

Interesting. I wonder why the OP needs to know the +- 180 microns tolerance on his film holder when the depth of focus for the film is plus or minus 2.4mm...

Emmanuel BIGLER
12-Aug-2017, 02:16
I wonder why the OP needs to know the +- 180 microns tolerance on his film holder when the depth of focus for the film is plus or minus 2.4mm...

Good question for which I have no clue!

The +- 180 microns tolerance = +- 0.007" (for 2x3, 3x4 and 4x5 holders) is reported here in this well-known document
http://home.earthlink.net/~eahoo/page8/filmhold.html
and data are supposed to come from an ANSI standard PIMA IT3.108:1998 that I have never read, like all other DIN or ISO standards actually, taking into account the high price you have to pay to get a copy of them ;)

And since I never read the ANSI standard for film holders, consequently I have absolutely no idea about the rationale behind depth tolerances in this standard!
Those tolerances do not seem to be correlated with the classical theoretical depth of focus model = plus or minus N c, where "N" is the f-number and "c" the diameter of circle of confusion chosen as a sharpness criterion. Plus or minus 180 microns @f/16 would correspond to an improbable sharpness criterion c=11 microns, i.e. smaller than a diffraction spot @f/16 ...

BTW there is an old discussion here in the archives related to tolerances on sizes for film holders: our readers like to be 100% sure of what they are using! (at least this was the case as of year 2001)
http://www.largeformatphotography.info/forum/showthread.php?4383-Measuring-Film-Holder-Accuracy

Degroto
12-Aug-2017, 02:48
Wow what a nice discussion. I will read everything later on and I do enjoy the enthusiasm from everybody. My plans are rather simple and consisting of the lens and lensboard it is on attached to a wooden box. On the other side or opposite side the filmholder at roughly the focal distance of the lens. Hoping the DoF of the lens will make up for a slightly out of ideal focus of the whole system :-)
If the results suck I can always rebuild :-D

The lens is on a Sinar lensboard. I do not want to use a groundglas. I plan on focusing with a piece of see thru paper and then fix everything. I then can see if I want the focus fixed on hyperfocal or normal infinity at a certain aperture that I think I will use most or is most convenient in most situations. A small list of DoF on various apertures should give me some guidance in what situation my image will be sharp using a certain aperture. Now I have to start building I am afraid :-) :-D

Drew Bedo
12-Aug-2017, 04:45
Degroto: I say go for it!

Plerase report back as your project comes together and post pictures.

Emmanuel BIGLER
12-Aug-2017, 07:14
A small list of DoF on various apertures should give me some guidance in what situation my image will be sharp using a certain aperture.

Simply provide us with a list of
- preferred focal lengths,
- preferred working f/#,
- and preferred film formats,
and downloadable free (although theoretical) DoF charts will appear here "magically" ;)

Jac@stafford.net
12-Aug-2017, 10:18
[...] I have absolutely no idea about the rationale behind depth tolerances in this standard! Those tolerances do not seem to be correlated with the classical theoretical depth of focus model [...]

Might the standards be guided by manufacturing precision requisites rather than optical necessity?

Emmanuel BIGLER
12-Aug-2017, 11:17
Might the standards be guided by manufacturing precision requisites rather than optical necessity?

Certainly.
With tolerances for film depth taken as a certain proportion of actual depth value? Still difficult to understand the choice of the proper figures. I can understand, however, that bigger film holders need to be thicker in order to stay as rigid as possible when size increases.

BTW I have found that the ANSI standard for film holders, together with many standards related to photography, film and slide projection, has been withdrawn in 2003!
I do not know the exact meaning of "withdrawn" for a standard, but the text is still not freely accessible!

Degroto
12-Aug-2017, 11:43
I will of course. My very crude first attempt to figure out how to measure the actual distance the lensboard has to be from the film plane is encouraging. But it is to dark now to focus on infinity. I'll keep you posted.

Jac@stafford.net
16-Aug-2017, 13:54
The suggestions to make some sort of pliable/compliant gasket under the lens board or on the back was excellent IF your camera is already dimensioned very close to one specific focal point, which is rather constricting and in this case unrealistic.

An alternative is to use 1/16" (1.6mm) plywood in as many layers as necessary under the lens board as shims. That is what I am using to make my new 4x5 camera correct at infinity. You can, of course, make the focal point any distance you choose. If you use little wing nuts you can carry several shims of different thicknesses to choose different points of focus in the field. A pocket on the side of the camera to hold the shims would be cool. (Don't carry them a back pocket. They might bend) :)

Measuring the flange focal distance is as simple as Dan Fromm mentioned. Just first insert a film holder with the film side slide removed. A finely marked steel ruler can help. And recall my earlier suggestion - you are going to use film holders, I presume. To visually identify focus you can put a 4x5" holder in the camera, then remove both the dark slides, and drill a 1/16" hole through the center of the back and through the film holder in one drilling. Finally, remove the film holder. Drill another hole in the back to fit your loupe. If you use a proper, affordable hole saw, the 1/16" hole already drilled will guide the saw to be concentric.

No ground glass necessary. Then we should describe aerial focusing. Quite easy.

Best of luck!

LabRat
17-Aug-2017, 05:16
Funny that you should ask. What I've done has been to mount the lens in question on a Speed Graphic board, put it on (surprise!) a Speed Graphic, focus to the desired distance, take the lens off, a drilled board with no lens on the camera and measure the flange-to-film distance with a depth gauge. The OP may have to borrow a camera to do this. Speed Graphic not necessary, it was what I had at the time.

Its better than guessing, which is what using published flange-focal distances amounts to. Published flange-focal distances are great for finding out what can probably be done but that's not what the OP needs.

About the need for focusing. The shortest lens I've had -- still have it -- for 35 mm is a 24 mm. It has to be focused for best results. My 35 Apo-Grandagon has to be focused for best results.

I'll back up this suggestion from Dan, but I'll add something about the depth gauge...

If your lensboard mounting hole is more than 1" dia, a good, cheap tool to measure would be an adjustable square from a hardware store... With a another test camera, focus the lens to subject at your desired distance, then remove lens (but not lensboard)... Then the ruler part is inserted through the lens hole (if it fits), have a film holder with a piece of scrap film loaded (with the dark slide removed), touch the end of the rule to the film,and slide the square until it touches flush with the area where the lens sits... Lock the rule to the square, remove, and read the distance... When setting up your new camera, Build/use the same distance you measured... Leaving it a little short of this distance and by leaving some room to adjust this distance will allow you to fine tune your final adjustment...

Don't feel that you have to use the lensboard you have already, as you can easily make a new, smaller board that will match up to your design better, and might make it easier to build in some adjustments to fine tune your fixed focus,or maybe add some simple focusing device you can rig up...

I might have missed it, but what lens FL/make were you thinking of using???

Have Fun!!!

Steve K