Budget Device to measure flange distance

[stan_1]

Does anyone know of a good and budget friendly device to measure flange distance for adjustment (e.g. leica iii). What is commonly used. In the Leica repair manual they mention putting a mirror at the film plane and using a collimator but I imagine one could also use a depth gauge or similar?

 

[reddesert]

This kind of measurement (for setting infinity focus) is usually made with an autocollimator. That's a device that produces a parallel bundle of light rays. You can make an improvised one with another camera that is known to focus on infinity, for example an SLR with a telephoto lens and a focusing screen - you focus the SLR on an object at infinity, and then the lens + focusing screen is collimated (the actual location of the SLRs film plane doesn't matter since you're not using it). So if you shine light through from the eyepiece end to illuminate the screen, or have the light enter the lens, reflect and exit it, it's collimated. A search will turn up more detailed instructions.

The measurement needs to be more precise than one can improvise with a depth gauge.

 

[vandergus]

This is what I use to measure flange distance.



It's a depth gage with a gage block in the film plane. The two markers on the dial show the tolerance range for the K-Mount so the setup is precise enough to calibrate in this case. I think I got the gage for around $60 used and a small set of blocks for $30 or so (the blocks are also necessary to calibrate the depth gage with a 1" extension added).

But I'm not sure if this exact setup would work with a Leica iii, since you can't put a gage block in the film plane. You would have to put the depth gage against the pressure plate but also make sure that it isn't pushing the plate away. And you would need to correct for the difference in distance between the pressure plate surface and the film plane.

 

[stan_1]

This is what I use to measure flange distance.



It's a depth gage with a gage block in the film plane. The two markers on the dial show the tolerance range for the K-Mount so the setup is precise enough to calibrate in this case. I think I got the gage for around $60 used and a small set of blocks for $30 or so (the blocks are also necessary to calibrate the depth gage with a 1" extension added).

But I'm not sure if this exact setup would work with a Leica iii, since you can't put a gage block in the film plane. You would have to put the depth gage against the pressure plate but also make sure that it isn't pushing the plate away. And you would need to correct for the difference in distance between the pressure plate surface and the film plane.

Thanks! Do you know what an accepted tolerance range is for such a flange distance?
Which gauge blocks can I use? I find sets on Ebay which are frankly of an unknown origin but advertised as Grade 1 precision for around 60€. All sets from known companies seem much more expensive.

 

[vandergus]

Thanks! Do you know what an accepted tolerance range is for such a flange distance?
Which gauge blocks can I use? I find sets on Ebay which are frankly of an unknown origin but advertised as Grade 1 precision for around 60€. All sets from known companies seem much more expensive.

The spec for the K-Mount is 45.46 mm +/- 0.04 mm. I think the tolerance on the Leica thread mount is a little tighter, I'm guessing because the total distance is shorter.

I just bought some random used gage blocks. From what I could tell, the expensive ones are just rated to a higher precision. Necessary if you are doing GD&T work in manufacturing but kind of overkill for our application. Even workshop grade blocks, the lowest grade, have sub micron levels of precision.

 

[Dan Daniel]

FYI, the Rolleiflex spec for alignment of the lensboard, meaning variance from true parallel to film plane, is 0.05mm across the film plane. Which would be 0.025mm +/-, if I am thinking about this right. This seems to be in same area as the K-mount and similar to what I have seen for a variety of cases. Although this is not the same as flange distance, it gives an idea of basic slop factor for lens distance. Actual 'flange distance' on most TLRs is variable and used to set infinity focus.

A quick look at a repair manual for a Fuji GW690 says 0.02mm +/- across film plane. Again giving an idea of permissible limits.

 

[RalphLambrecht]

Does anyone know of a good and budget friendly device to measure flange distance for adjustment (e.g. leica iii). What is commonly used. In the Leica repair manual they mention putting a mirror at the film plane and using a collimator but I imagine one could also use a depth gauge or similar?

calipers will do the trick but most camera flange distances are known and can be looked up on the Internet or in books. For the Leica III I find a flange distance of 28.8 mm.

 

[Kino]

Issak S. Maizenberg's book on repairing Soviet Cameras mentions that he used a Indicator Dial Depth Gauge with the return spring removed. If you do not remove the spring, the pressure from the return spring will shift the pressure plate slightly, giving inaccurate readings.

Here's a link with an example of a depth gauge: https://www.qualitymag.com/articles/92583-depth-gage-basics

 

[_T_]

You can use this formula to calculate the tolerance that you’re willing to accept:
1/f - 1/ffd = 1/od


Where ffd is flange distance and od is object distance.

For simplicity’s sake you would assume the ffd is the same as the focal length of the lens, but you’d just have to subtract the focal length from the actual flange focal distance anyway so there’s no reason to take that extra step.

Anyway if you have a 50mm lens and you are off on your ffd by 0.05mm you can plug f=50mm and ffd=50.05mm into the formula and find that when set to infinity the plane of sharp focus would actually be only 50 meters away.

And if you’re only off by only 0.01mm the plane of sharp focus would be only 250 meters away when set at infinity.

Most of the time small errors will be taken care of by the depth of field but I think you can see that the precision required to set the ffd is very high.

 

[Dali]

For my FED 1 cameras, I used a depth gauge and a film.

I remove the lens (if necessary), I load the camera with the film, keep the shutter open (B), put the camera on the back and watch closely the light reflection on the film surface (facing the gauge). As soon as the reflection changes, it means that the tip of the gauge touches the film. With this method and a little habit, it is easy to check the flange distance, especially for cameras with wide manufacturing tolerances (like pre-war FED). I guess this method can be used with Leica II / III.

 

[stan_1]

Thanks again for your replies. And how do you actually to the adjustment on such a small scale on an old camera? you can get shims down to maybe 0.1mm or for that small screw size only 0.25mm. what are other options?

 

[RalphLambrecht]

Thanks again for your replies. And how do you actually to the adjustment on such a small scale on an old camera? you can get shims down to maybe 0.1mm or for that small screw size only 0.25mm. what are other options?

a sheet of paper has a thickness of 0.1 mm

 

[Dan Daniel]

Thanks again for your replies. And how do you actually to the adjustment on such a small scale on an old camera? you can get shims down to maybe 0.1mm or for that small screw size only 0.25mm. what are other options?

Look for brass shim stock. Available in .001" and up. Which is about .025mm. At this thickness, be sure to clean up edges after cutting to avoid burrs moving out of spec.

Shims can be simple rectangles next to a bolt. Does not need to be a washer.

K+S sells small assortments. I'm sure similar items are available in Germany. Amazon in the US, search for (this site doesn't allow amazon links, it seems)

K & S PRECISION METALS 258 BRS Shim Metal ASSTD​

 

[Dali]

Thanks again for your replies. And how do you actually to the adjustment on such a small scale on an old camera? you can get shims down to maybe 0.1mm or for that small screw size only 0.25mm. what are other options?

Paper of various thickness.

 

[stan_1]

Thanks a lot for the replies! So now I ordered a depth gauge (tolerance 0.01mm), a gauge block (grade 1), crafts tool to stamp out paper of 1.5mm (hole) and 3mm (shim) and thin paper about 40g/m2 (should be around 0,04mm) and am looking forward to when it arrieves. I‘ll give an update to how it works out.

 

[stan_1]

To give an update: measuring the distance with the above setup with a clock-like depth gauge seems to work quite well. Though I guess you should position the gauge plate with the polished side on the inner rails (the polished side is 9mm wide and 35mm tall I think as per ISO standards, mine was 20mm thick, Grade 1).
I used this on a Konica Hexar RF that was sold with defective rangefinder focusing that a specialized shop couldn't adjust. And sure enough I found a problem with the flange distance that I could adjust by moving the washers around that were already there. I tested it with a ground glass with split prism on the film plane, so hope that should solve it. BTW: I don't have experience with upper class rangefinders but it seems like a miracle to me that you can actually achieve a similar focusing accuracy with that small patch and the rangefinder coupling on e.g. a 90mm f2 lens as on an SLR with split prism focusing!

Second I tested my Leica IIIf that I had previously disassembled and replaced the shutter curtains. If I remember correctly it did not have any washers or spacers for flange adjustment. Here I had to take off the housing. It does not have any outer rails, so I just put the gauge plate on the back of the film window. Now that seems like an acutal miracle to me: all four distances were correct 28.8mm down to 0.02mm! Without any washers, just with the factory parts! A camera produced in 1951!!! Go Leica

 

[250swb]

I'm not sure you need a dedicated depth gauge, a normal set of vernier callipers can measure depth, knowing how to read the sliding scale to make a perfectly accurate measurement is the skill. On the other hand you could get a digital vernier gauge to do it for you.

 

[eli griggs]

calipers will do the trick but most camera flange distances are known and can be looked up on the Internet or in books. For the Leica III I find a flange distance of 28.8 mm.

Digital or analog calipers simple tools that only need to be in calibrated condition, often from the Point of Sale, say from example, Harbor Freight, Snap-on, NAPA, are simple, cheap to expensive, with accompanying "Gage block" or Third Party block bought for just this type of calibration are ample for this tasks, and, for example, readjusting FSU Fed Cameras to more accurately adjust the flange depth to the Leica m39 lense universe.

In fact, I'll recommend practicing and training for this very task, with a Fed LTM or other low cost alternative, by using the video examples on YouTube as your guide.

Good Luck,
Eli

 

[eli griggs]

a sheet of paper has a thickness of 0.1 mm

Or, in general .0008 inch (.232 mm) for notebook papers

This is where digital calipers shine, by auto converting from metric to SAE or Fractional.

Fractional is not needed to do this, as metric and SAE are good to go.

I use both a 1" and 2" gage blocks from my 1 and 2 inch micrometers to test calibration and, a Mitutoya and a Harbor Freight, digital calipers for depth measurements, which is easier to do with their push button conversions and displays.

Used quality Machinist tools can be a very good value, just as good or better than new, but know for yourself how to actually calibrate them and tests both before use and after, prior to storage, correcting as needed.

IMO,
Eli

 

[stan_1]

I see two problems with a caliper even if it‘s at 0.01mm precision (most are .1mm precision btw., which is 0.004inch or one sheet of office paper): 1) vertical placement (can you really place the depth rod perfectly vertical? The depth gauge has this wide and long flat feet on both sides that you can place on both sides of the bayonet ring. 2) precision of the surface of the depth rod tip. The precision depth gauge has a defined rounded tip of hardened steel to achieve the required precision, while most caliper I saw have a flat tip of the depth rod, making it difficult to perfectly align with the surface.

I think this hassle is less of a problem for SLRs since errors in flange distance do not affect focusing. However I think there is a reason for the small tolerances for rangefinders. Example: after a first rough adjustment I had only one (of 4) screws of the bayonet off by 0.10mm on the hexar RF (leica M mount). Using a split-prism focusing screen I adjusted the rangefinder for an object at 7meters (23feet) using a 90mm f2 lens (leica summicron), which is really close to infitiny on this lens. However the infinity was very visibly misaligned in the rangefinder. Correcting this one problem led to a good calibration of the rangefinder throught. So the effect of a single sheet of paper off (0.10mm), only in one corner!, was really visible in the center.

 

[ags2mikon]

I have used paper shims in the past. The paper instructions from some of the old filter data sheets from 1960's Japan and Bible pages were the thinnest I found. I don't recommend destroying sacred books just for camera repair.

 

[dirbel]

To give an update: measuring the distance with the above setup with a clock-like depth gauge seems to work quite well. Though I guess you should position the gauge plate with the polished side on the inner rails (the polished side is 9mm wide and 35mm tall I think as per ISO standards, mine was 20mm thick, Grade 1).

For some cameras (e.g. Nikon F80) the mount flange distance is measured between the mount and the outer rails. Best to check the repair manual first.

 

[eli griggs]

I see two problems with a caliper even if it‘s at 0.01mm precision (most are .1mm precision btw., which is 0.004inch or one sheet of office paper): 1) vertical placement (can you really place the depth rod perfectly vertical? The depth gauge has this wide and long flat feet on both sides that you can place on both sides of the bayonet ring. 2) precision of the surface of the depth rod tip. The precision depth gauge has a defined rounded tip of hardened steel to achieve the required precision, while most caliper I saw have a flat tip of the depth rod, making it difficult to perfectly align with the surface.

I think this hassle is less of a problem for SLRs since errors in flange distance do not affect focusing. However I think there is a reason for the small tolerances for rangefinders. Example: after a first rough adjustment I had only one (of 4) screws of the bayonet off by 0.10mm on the hexar RF (leica M mount). Using a split-prism focusing screen I adjusted the rangefinder for an object at 7meters (23feet) using a 90mm f2 lens (leica summicron), which is really close to infitiny on this lens. However the infinity was very visibly misaligned in the rangefinder. Correcting this one problem led to a good calibration of the rangefinder throught. So the effect of a single sheet of paper off (0.10mm), only in one corner!, was really visible in the center.

Using a digital caliper such as the Mitutoya, I suggest you take a rigid METAL short ballpoint pen ink cartridge, cleanly cut if needed and with the caliper's steel probe extended long enough and laying flat next to each other, use a couple of drops of gel super glue to affix the ink cartridge ball point about one inch beyond the flat of the caliper and let it cure, completely, before moving.


Digital calipers have reset or zeroing buttons so you can retract the probe into its body and the new stop, the squared ink cartridge, which you now zero to.

I should mention that a "squared" cartridge does not mean it must be inline precisely, but, in this case, that the back end of the cartridge is not in a diagonal or ragged condition that, when it stops at "Zero", there is collapsible or compressible material that moves or folds up, screwing with your measurements.

The length of the pen can be slightly at an angle, so long as ALL measurements have the same firm setting.

This gives you the single ball in the cartridge as your touch point, though you must be mindful of how it plays on the camera's lens opening, for a smooth operation measuring the distance needed.

After your job is finished, use Acetone or Finger Nail Polish Remover to free the ink stick and the supper glue, with the probe left absolutely clean.

Cheers.

 

[reddesert]

The required precision for setting the flange distance can be understood by considering the depth of focus at the film plane. A common value for acceptable circle-of-confusion for 35mm is 0.03mm, meaning a spot size of 0.03mm is considered "acceptable." Most depth-of-field marks on 35mm lenses correspond roughly to this choice. However, for critical focus/best results many people want to do a little better, and rate depth-of-field one or two stops more conservatively (a factor of 1.4-2x in spot size).

Let's say we are going to be about 1.5x more conservative, so our acceptable spot size is 0.02mm. Further let's say that we want to be able to achieve this with a f/2 lens. An f/2 beam emerging from the lens is a cone whose taper is: length is a factor of 2 times the base diameter. This means that the focus offset (length between the true plane of focus and the film) can be 2x the spot size, 2 x 0.02mm = 0.04mm. So the maximum error of the position of the film plane is +/- 0.04mm. That's really quite small - 40 microns, about half the diameter of a human hair. And, if one is 0.04mm off, one has used up all the conservative depth of focus in the film plane (depth of field in the subject plane) at f/2, which is not desirable. So when manufacturers specify the flange-film distance to 0.04mm or better, they aren't just being persnickety. It really does need to be that accurate.

As others have mentioned, you might get away with a small error with an SLR, as long as the focusing screen is off by the same amount (IOW, if you move the lens flange in or out, it should still focus ok, but the focusing scale may be off and you might not reach infinity). But for an interchangeable lens rangefinder it's got to be quite close.

I was negative early in the thread about improvising the measurement, because typical home tools like a caliper aren't precise or accurate enough. As others have said, a dial indicator, an accurate length standard (gauge block), and a very rigid fixture are needed. I'm glad to see that people have gotten it to work mechanically. If one isn't ready to buy that gear, I think optical alignment (autocollimation) is better than trying a vernier caliper.

 

[stan_1]

The required precision for setting the flange distance can be understood by considering the depth of focus at the film plane. A common value for acceptable circle-of-confusion for 35mm is 0.03mm, meaning a spot size of 0.03mm is considered "acceptable." Most depth-of-field marks on 35mm lenses correspond roughly to this choice. However, for critical focus/best results many people want to do a little better, and rate depth-of-field one or two stops more conservatively (a factor of 1.4-2x in spot size).

Let's say we are going to be about 1.5x more conservative, so our acceptable spot size is 0.02mm. Further let's say that we want to be able to achieve this with a f/2 lens. An f/2 beam emerging from the lens is a cone whose taper is: length is a factor of 2 times the base diameter. This means that the focus offset (length between the true plane of focus and the film) can be 2x the spot size, 2 x 0.02mm = 0.04mm. So the maximum error of the position of the film plane is +/- 0.04mm. That's really quite small - 40 microns, about half the diameter of a human hair. And, if one is 0.04mm off, one has used up all the conservative depth of focus in the film plane (depth of field in the subject plane) at f/2, which is not desirable. So when manufacturers specify the flange-film distance to 0.04mm or better, they aren't just being persnickety. It really does need to be that accurate.

As others have mentioned, you might get away with a small error with an SLR, as long as the focusing screen is off by the same amount (IOW, if you move the lens flange in or out, it should still focus ok, but the focusing scale may be off and you might not reach infinity). But for an interchangeable lens rangefinder it's got to be quite close.

I was negative early in the thread about improvising the measurement, because typical home tools like a caliper aren't precise or accurate enough. As others have said, a dial indicator, an accurate length standard (gauge block), and a very rigid fixture are needed. I'm glad to see that people have gotten it to work mechanically. If one isn't ready to buy that gear, I think optical alignment (autocollimation) is better than trying a vernier caliper.

That's some really cool knowledge. Where can I read stuff like that? What would also really interest me is optical design, like how does a Tessar or Planar design work
I can confirm that measuring with a 0.01-0.02mm precision works quite fine with a clock depth gauge with horizontal feet and a gage block on the other side. I bought mine used as new for like 60€ (by "Käfer", a german company).