Hi,
Main thing will be cost $$$$$$$$$
Where I work we use two in house manufactured collimators and a Chrosziel for setting infinity on cine lenses.
Way more than required to set up a stills camera.
An autocollimator is used to measure angular displacement of a mirrored target. but could with a little modification be used to set infinity on a stills lens. Also $$$$$$ though.
Simply all you need is a long focal length (500mm +) lens with large aperture set at it's focal length from an illuminated target. Simply place your unknown lens in the collimated (parallel ) beam produced with some means of viewing its image and adjust lens mount / focus ring to read infinity.
I do this daily so if you need any more in depth info please ask.
Steve.
Hi,
Main thing will be cost $$$$$$$$$
Where I work we use two in house manufactured collimators and a Chrosziel for setting infinity on cine lenses.
Way more than required to set up a stills camera.
An autocollimator is used to measure angular displacement of a mirrored target. but could with a little modification be used to set infinity on a stills lens. Also $$$$$$ though.
Simply all you need is a long focal length (500mm +) lens with large aperture set at it's focal length from an illuminated target. Simply place your unknown lens in the collimated (parallel ) beam produced with some means of viewing its image and adjust lens mount / focus ring to read infinity.
I do this daily so if you need any more in depth info please ask.
Steve.
One way to autocollimate a camera is to use the lens itself to self-collimate. You need a focus screen, like a piece of glass with Scotch tape on it, a groundglass, or something that can take a mark, placed on the film rails, with an off-center mark on it like a pencil X. You then place the camera lens face down on a flat mirrror - any mirror will do, doesn't have to be first surface. Illuminate the X by shining a flashlight down on it. The reflection, traveling through the lens twice, will form an image at the focus screen. Adjust the lens until this image is in focus. Now the lens is focused at infinity.
There is another way to self-collimate, by omitting the groundglass. You place a transparent target (like a reticle) at the film rails, mirror in front of the lens, and then move your head side-to-side to judge the parallax between the target and the aerial image of the target. When you reduce the parallax to zero, the lens is focused at infinity. This is, however, hard to demonstrate in words only.
Both of these are cool ideas and I just tested the first out with my TLR. I have to admit I have a bit of trouble seeing the return image but it is definitely there and I can see how you would use it and the optical principle behind it makes sense. Do you have any suggestions for making it both easy to illuminate and also not washed out by the illumination? For the second method, I am having some trouble seeing the aerial image. Do you have any tips?
---------------------------Thank you Steve, this is very helpful! I was using the terminology I found here: https://learncamerarepair.com/downloads/pdf/NatCam-Auto-Collimators.pdf Are these really collimators and not autocollimators?
One question on this technique. How essential is the distance between focusing target and lens? I know marked focal lengths are mostly estimates - would I have to determine true focal length myself? If so, what's the best way to do that? Also, what would you suggest as the best way to avoid stray light and internal reflections? A 500mm long black PVC pipe?
Both of these are cool ideas and I just tested the first out with my TLR. I have to admit I have a bit of trouble seeing the return image but it is definitely there and I can see how you would use it and the optical principle behind it makes sense. Do you have any suggestions for making it both easy to illuminate and also not washed out by the illumination? For the second method, I am having some trouble seeing the aerial image. Do you have any tips?
---------------------------
Yes the text you mention does refer too using an autocollimator, which can be used and has some other uses as described in the text. But that is not what is 'required' to set or test the infinity setting of your camera/lens and cost is a factor as mentioned. If you note in the main body of the text when referring to the device they do call it a collimator.
The collimators we use at work have no covering or tube they are just open and obviously work very well. Illumination of the target graticule is with an ordinary frosted domestic led lamp. The focal length of ours are 720mm and 1124mm (I'm not at work at the moment so cant check but that is very close.) Imagine trying to buy an autocollimator of that size in a tube and a clear aperture of some 100mm.
Yes the lens does have to be accurately at its focal length from the target. As a guide I'm working on a project to use one collimator (the 700mm one) to mark all lens distances on new lens barrels. It's ongoing but as a guide 100m is with the collimating lens approx 5mm closer to the target than at infinity. This is partly why a long lens is used this position is less critical the longer the focal length of the collimating lens. I would suggest +-0.5mm would be a good start. Unfortunately if the focal length is unknown that does make matters tricky without other equipment. Focusing the sun with a suitably extreme ND filter of some kind and measuring the position of the focal plane is something I've done in the past with of course all the safety measures in place (Don't look through it - Obviously!) Just clouds can be used on bright day if inside a relatively dark room - basically your inside a camera focusing on something far away!
Hope some of this helps.
Steve.
I think a prime lens should be used on the DSLR to get anywhere near consistent results using this method. I assume by zoom you meant the screen display only. Most - if not all, still camera zoom lenses are nowhere near par-focal. This also means the cameras are going to have to be a long way apart as the close focus on a reasonably long lens with no digital intervention will not be great?Alright, I think I found a method that gives me most of what I want and avoids me having to buy a device that is no longer available for a reasonable price. My previous complaint with most of the methods on the web for setting infinity that uses two cameras is that it limits the maximum possible precision of the method to the calibration of another possibly-miscalibrated old film camera + lens combination with whatever loupe you have available. Also, most methods suggest using a ground glass that does not necessarily represent how film sits as it goes through the camera. I am not the complete originator of this method, and I've seen hints of it mentioned in a few old forum posts and archived geo-cities websites so I'm going to repeat it and add to it a bit here for completeness in case someone else runs across this thread. It requires a DSLR and the longest lens you have with a physical infinity stop.
You may want to prepare some special negatives for this method, but if you have any developed test rolls you don't care about lying around, they should be good as well. These instructions are for 120 cameras and folders in particular which are the most likely to need an infinity adjustment.
I am pretty confident this "computer assisted" zoom can equal an optical autocollimator, and using a real negative is better than a ground glass. The only downside to the technique is you are limited to the sensor size on your DSLR -- you cannot examine focus at the edges of the frame, so if the lens has field curvature, you will have a very sharp center but less sharp edges (compared to some tutorials I've seen that call for setting the focus half way between the middle and edge of the frame so you get a relatively large ring of good focus, but less well focused edge and center). But that's nit picking.
- Put the long lens on the DSLR, and take it outside. Open it to its widest aperture, set to infinity, take it outside, point it at something very far away and take a picture. On the DSLR, zoom in on the screen and verify that the object is perfectly in focus. If it is then you can be confident you will be setting your candidate camera to a good infinity.
- Closely examine the candidate camera for where film sits (in a channel usually) and where the pressure plate pushes on. There is often a lip for it, so that the film is sandwiched in, but not pushed on by the backing plate so that it will not scratch. Put an already developed negative in the candidate camera film gate. Ideally, it would be an uncut roll of 120 film, spooled into both sides and under the tension the camera would usually put it under. If you are persnickety, put a second piece of clear negative (make one of these by forgetting to take off your lens cap!) or similar acetate behind the negative to simulate the backing paper thickness, but I don't think this is necessary. Clear tape on the edges of the glass could work as well. On top of the negatives, put a piece of glass cut to the correct size of the backing plate so it sits on the same lip the pressure plate (Home Depot sells glass and glass cutters for cheap cheap, or a 6x6 ground glasses will work with most cameras).
- Put the two cameras on tripods and point them at each other. Illuminate the back of the candidate camera. Set the reference camera's lens to infinity. Open the shutter to "bulb" for your candidate camera, and turn your DSLR to live view mode. Zoom in as far as you can on the DSLR live view display, and then adjust the candidate camera's focus until the negative's grain is in sharp focus. Viola! You're all set! The longer the lens on the reference camera and the more accurate its infinity stop is, and the high resolution your DSLR is the better you can get!
I think a prime lens should be used on the DSLR to get anywhere near consistent results using this method. I assume by zoom you meant the screen display only. Most - if not all, still camera zoom lenses are nowhere near par-focal. This also means the cameras are going to have to be a long way apart as the close focus on a reasonably long lens with no digital intervention will not be great?
Still not sure how much an advantage it is to have infinity set perfect if all the other lens markings are just guides with no definite line markings and only mass produced original positioning to a standard design rather than actual position for an individual lens.
Sorry, yes, I should have been clear about that. I meant a long prime lens with a hard infinity stop that you know to be good (reason for testing it outside). And digitally zoom into the image taken by the DSLR. I agree on zoom lenses, I am not very trusting of them keeping their infinity throughout their range without it being just out of the factory.
I am not sure what you exactly mean about close focus. The lens on the DSLR is set at infinity, not a close focus, and since it is looking through the lens of the other camera to that film plane, it shouldn't be on a close focus
Setting the infinity point is important to me for two reasons:
1. On scale-focusing cameras, the scale is all I have to work with, so it had better be right. At the very least I want it to be correct at infinity! I tested my Perkeo II today with this method and found it is totally wrong. Which explains why the images I've been getting out of it a year or two ago were so bad! Eventually I'd like to service its shutter, which will require taking off the front cell which is on a helicoid. And then I'll have to put it back on and make the front cell focus correctly. A sub-usage of this case is that any lens repair that requires a helicoid removal should be checked for proper infinity focus at the end.
2. On SLR or TLR cameras, the focusing screen has to be in sync with the image projected on the film. As far as I know, the only way to do this is by making them line up at infinity. I guess you could do it at another focal length, but infinity is easy because you can use a collimator to do it and there's a hard stop for it.
I only did find this message today Sept. 26. I do own a National Camera autocollimator, made by Pearl Optical, In the Netherlands, it is set to 220 Volts AC, but it can easily be rewired for 110 volts. I used to work for Polaroid, and as such I acquired this autocollimator. I will offer it for a reasonable price, but shipping costs could be important, as this unit is rather large and weighs close to 15 kgs. I can send you some pictures if you still are searching such unit.I want to buy an autocollimator to calibrate infinity focus on some of my cameras. I would like more precision than is offered by the "line up two cameras" method, mostly because I don't know if any of my cameras are correctly calibrated to begin with. Does anyone know where I can get an autocollimator, have one for sale, or know of someone who has one for sale?
I only did find this message today Sept. 26. I do own a National Camera autocollimator, made by Pearl Optical, In the Netherlands, it is set to 220 Volts AC, but it can easily be rewired for 110 volts. I used to work for Polaroid, and as such I acquired this autocollimator. I will offer it for a reasonable price, but shipping costs could be important, as this unit is rather large and weighs close to 15 kgs. I can send you some pictures if you still are searching such unit.
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