NIFE 40cm rangefinder

[magneticanomaly]

I bought a supposed Swedish military optical rangefinder made by NIFE, model 40 cm or A-40

It appears in good condition, images are crisp and the focus and range adjustment controls move and work, BUT, the small image which needs to align with the larger one is UPSIDE-DOWN.

I do not know if I am simply doing something stupid, or if a reversing prism or mirror has fallen out of the optical path...I do not see how this could be and still have clear and approximately coincident images.... Allowing for the uncertainty of trying to line a right-side-up image with one upside-down, the actual ranges shown on the dial seem plausible.

I'm looking for a little guidance as to what to look for, before I begin to take the thing apart

Anyone know anything about these?
Thanks!

 

[LouBoyd]

I'm somewhat familiar with the unit. I'll describe how mine works. It's a coincidence rangefinder and designed to double as a field periscope. To use it, it should stand vertically. The eyepiece is near the bottom. The top objective lens provides the right hand half (your right looking though it)of the image which has two horizontal lines superimposed on it.. The Objective lens approximately in the middle of the unit provides the left half of the image. On the far left side of the field of view is a graduated scale to display the range. The little window just above the lower objective lens provides light for that scale. At One end of the travel of the range knob (to the right above the eyepiece the scale will display an infinity mark (sidways 8).

So if you stand it up and look though it you should see one coninuous non inverted and non reversed image in the eyepiece. if the range setting is not correct for the image (at the distance of an object which has a horzontal component in >both< sides of the image) that edge will appear to be offset. When the range knob is correctly adjusted the halves of image will be coincident. Of course other objects in the field at different distances will still appear to be split.

The range scale is marked from 10 to 150 with subdivisions. I believe those are decameters so the range of the unit is from 100 meters (in 10 meter increments at the low end with the last two markings before the infinity sign being 130 and 150 (for 1300 meters and 1500 meters with 100 meter hash marks. At 1000 meters one can interpolate the scale to maybe 5 meters.

Don't be too quick to take it apart. Some simple tests should demonstrate what's wrong, if anything.

I'll re-familiarize myself with the unit tomorrow and post some more info. Maybe I can take a photo of what should be seen through the eyepiece.

Here are some pictures of an A-40-p (not mine) so others here will know what we're talking about.
Beautiful Swedish military range finder,NIFE OPTICS,as

 

[magneticanomaly]

Thank you very much, Mr. Boyd!

I finally managed to attach a picture of my rangefinder.

Mine has two eyepieces, spaced appropriately for my eyes, which makes me think it is supposed to be used horizontal. The right eyepiece shows both the main and the inset images, that is, a full field of view with a small square window in the middle in which the image is upside-down. The left shows the distance, from 200 to 4000, then infinity. There is a separate window as you describe to illuminate the scale. The range is adjusted by a roller-type knob near the right objective. There is a knob you can twist near the left objective, I'm not sure of its function.

I did not get the lovely case or the stand with mine, but it appears otherwise like the one in your link.

 

[LouBoyd]

I finally managed to attach a picture of my rangefinder.

Mine has two eyepieces, spaced appropriately for my eyes, which makes me think it is supposed to be used horizontal. The right eyepiece shows both the main and the inset images, that is, a full field of view with a small square window in the middle in which the image is upside-down. The left shows the distance, from 200 to 4000, then infinity. There is a separate window as you describe to illuminate the scale. The range is adjusted by a roller-type knob near the right objective. There is a knob you can twist near the left objective, I'm not sure of its function.
link.

Your picture didn't come though on LRH but I think i found your photo on The Practical Machinist forum. For some reason I can't repost the image on LRH, but it can be viewed here:

http://www.practicalmachinist.com/v...ot-optical-rangefinder-rangefinder-8-3-12.jpg

Apparently a model AP-40 has some major differences compared to the AP-40-P. The markings on the photo show the magnification is 8X. Having the objectives at each end and two eyepieces would definitely indicate it's made to be used horizontally as you surmised. The erect and normal image is typical for horizontal rangefinders. This image shows how the images should relate when it's in use, though this image is from a different make and model rangefinder.

This would be measuring the distance to the church spire.

This diagram shows how the images move when you adjust the range measurement knob. This is not specifically for the A-40:

The second knob on my A-10-P moves the left image so a given object can be moved so it's abutted exactly adjacent to it's other half. Then the image (at that range) will appear complete as with a spotting scope. The second knob on your AP-40 probably moves the inverted image up and down so the selected portion of the two images can be easily compared, as with the spire in the photo above. Part of the art of using this type of rangefinder is picking objects which have clearly visible lines perpendicular to the direction the images move when the range knob is adjusted. Diagonal lines or random shapes are not reliable.

The other "user" adjustment is the eyepiece diopter knob. On the AP-10-P it has +/- 3 diopter range. Does the A-40 have individual adjustments for each eye? Those should just be set for comfortable clear images. They should not affect the range measurement.

200 to 4000 would no doubt be the direct reading range in meters. What is the next written number smaller than 4000 and how many divisions are between those numbers? That will give an indication of it's usable distance resolution at maximum range.

Take it out and try it on some objects at ranges from 200 to 4000 meters. From your description so far (and seeing your photo of the unit) I'd bet it's working normally. On the A-40-P the infinity setting is not a user adjustment. I suspect that's adjusted at a higher maintenance level, but the user can check it on a very distant object, like a bright star.

 

[magneticanomaly]

Thank you very much, Mr. Boyd! I believe you have solved my problem.

I took the scope out this afternoon, and bearing in mind the way you dscribed the working of the one you were familiar with, I studied my images again.

Apparently,it works exactly like yours, only instead of a fully split field with the lower half right-side-up and the upper upside-down, my upside-down upper "half" is just a little box.

But I had not paid attention to the fact that the lower edge of my small, upside-down image was actually at the horizontal center-liner of the entire field

After I realized this, it became relatively easy to choose a feature of the landscape and align its upside-down reflection with its rightside-up bottom half.

I still need to come up with some sort of solid mounting or it so that I can see if the vertical position of the inset (top, upside-down) image can be or needs to be tweaked, and then I should find some measured distances to test it on (I read objects today out to plausible ranges of 560 M), but , again, THANK YOU, I have an instrument I can use.

 

[magneticanomaly]

Sorry I forgot to answer your question.

The next smaller number before 4,000 is 3,000, and there are 4 divisions, so 250 yd is the graduated interval. I would feel confident interpolating 50 yd intervals on the scale, but there would be few landmarks that I could line up accurately enough to justify that. The old distinction between precision and accuracy,

 

[LouBoyd]

...I still need to come up with some sort of solid mounting or it so that I can see if the vertical position of the inset (top, upside-down) image can be or needs to be tweaked, and then I should find some measured distances to test it on (I read objects today out to plausible ranges of 560 M), but , again, THANK YOU, I have an instrument I can use.

An easy way to get "measured distances to test" better than one meter is with google earth and it's ruler function.