Einstein
Established
OK got a Voigtlander Perkeo 11, not going to waste time explaining reasons why here but she is out of focus not by a lot but blatantly obvious. Now I thought I had sorted this issue, just developed a test film and I am needing help……..
I remove a fresnel focus screen from a Hasselblad, open the back on the Perkeo and tape the screen in place over the back. Set shutter to B, open aperture all the way, fire the shutter keeping it open and on looking through the glass at infinity in bright sunshine, everything is in sharp focus.
Now the last time I thought I had done this properly, I fixed an item at 3 meters, focused until it was sharp then put the focus ring at that distance and screwed it in tight. I figured that if she was sharp at an item at 3 meters she would be sharp on everything including infinity !!!
Now the Hasselblad fresnel screen is about a 1/4 inch thick and stands off the film plane, COULD THAT BE AN ISSUE preventing accurate focus setting ??????
I wondered how the service blokes set the focus and thought this would be easy, apparently I was wrong.
I remove a fresnel focus screen from a Hasselblad, open the back on the Perkeo and tape the screen in place over the back. Set shutter to B, open aperture all the way, fire the shutter keeping it open and on looking through the glass at infinity in bright sunshine, everything is in sharp focus.
Now the last time I thought I had done this properly, I fixed an item at 3 meters, focused until it was sharp then put the focus ring at that distance and screwed it in tight. I figured that if she was sharp at an item at 3 meters she would be sharp on everything including infinity !!!
Now the Hasselblad fresnel screen is about a 1/4 inch thick and stands off the film plane, COULD THAT BE AN ISSUE preventing accurate focus setting ??????
I wondered how the service blokes set the focus and thought this would be easy, apparently I was wrong.
Godfrey
somewhat colored
Chris Sherlock (retinarescue.com) captured the overhaul of a Voigtländer Perkeo II and has the videos on YouTube at Voigtländer Perkeo II service. I am not sure he detailed the focus calibration work, but it can't hurt to see what he did. Chris is a master camera repair tech...!
G
G
largedrink
Down Under
You can collimate a lens to infinity using an SLR and telephoto, as described here:
http://elekm.net/zeiss-ikon/repair/collimate/
http://elekm.net/zeiss-ikon/repair/collimate/
Mos6502
Well-known
You need to use a plain ground glass if you want to check focus by ground glass.
Ko.Fe.
Lenses 35/21 Gears 46/20
Yep. Use only flat ground glass. I made my own from dollar store tiny picture frame. Milky part is facing the lens.
I used one meter on two Perkeo to make it easier and they were spot on through all range after it.
I used one meter on two Perkeo to make it easier and they were spot on through all range after it.
Einstein
Established
well I have just hit 65 last month and some of my intelligence must have disappeared because I, even after reading this three times still do not understand how this works.
I have a Canon F1N and a Canon zoom lens that falls into this, as well as plenty of tripods.
I will look and see if this chap did a YouTube clip, I must be missing something.
I always use the same focusing and depth of field principles my late Father taught me when setting the focus. If I am using F5.6 as an aperture, I turn the infinity over to the F5.6 mark. This gives me the maximum depth of field. The out of focus images on the test roll are ALL out of focus at infinity, so I am really puzzled by this. I NEVER TAKE OUT OF FOCUS IMAGES, NEVER EVER.
The camera had been serviced, there was a large long fiber inside the lens when it arrived back. It just seemed easier for me to remove it and then put everything back, than go through the whole shipping and returning again.
This is the SECOND TIME A FOLDER OF MINE HAD RETURNED WITH FIBERS INSIDE AFTER A SERVICE FROM A TEC !!!!
OlivierAOP
medium format
The method you describe is sound. Only thing I can think of is that the screen is flipped? Matte side should face the lens. Also I would highly recommend using a loupe when inspecting focus.
Duofold RF
Well-known
If you do lot have an autocollimator, use a ground glass focus something 3 miles away, turn the front element to adjust the infinity all other distance should be accurate
Godfrey
somewhat colored
To this issue, I've had three Kodak Retina IIc cameras serviced at Advance Camera in Portland, Oregon in the past year and some. They did a superb job, cameras returned clean and ready for use, and charged a very fair price. I'm delighted with their service efforts!
G
largedrink
Down Under
Your comment about test roll images being out of focus at infinity, are you saying that you set focus exactly to infinity for these shots? Or was focus set to less than infinity and you relied on depth of field (using your late Father's method)? Reason I ask is that your rangefinder may be inaccurate, rather than your lens.
largedrink
Down Under
Here's another description of the collimation process using an SLR:
http://feuerbacher.net/photo/repair/InfinityFocus/InfinityFocus.html
http://feuerbacher.net/photo/repair/InfinityFocus/InfinityFocus.html
Absolutely. In order to accurately calibrate the infinity focus at the film plane, the image you're referring to actually has to be at the film plane. Given the Hasselblad screen mounting frame is not conducive to setting the screen hard against the film rails, it is not a good choice for inspecting focus. You need to use a ground glass at the film plane resting on the film rails, or alternatively, a piece of developed, unexposed, clear base film taut across the gate. (The latter presents the conundrum of how to keep said film flat without the pressure plate behind it, given you cannot examine an image through the plate).
I'm generalising, here, but I'm not really a fan of using a zoom lens for inspecting a film plane. I am not saying it cannot be successful. Merely that you are relying on your particular example of that zoom to be truly parfocal and calibrated ideally for best possible focus at infinity (presumably zoomed to the long end).
Fixed focal length lenses can be out of calibration, too. Hence, using one for autocollimating a camera doesn't, in itself, guarantee an excellent workflow. But, if it is possible to exclude a potential complication altogether from a focus calibration, rather than dealing with it—it seems logical to remove it. Hence, I think using a *known good* well-adjusted SLR and fixed focal length lens is a better scheme, than assuming a particular zoom's infinity setting and flat field performance at the long end are ideal for what is an exacting task. That a "prime" lens might well be of larger maximum aperture, and admit more light for easier, brighter viewing, is to the good.
It's good policy to fit to the SLR a lens a minimum of twice the focal length of that on the camera being examined. It increases the magnification of the target image, for better precision. For the doubters, note that professional autocollimators are invariably fitted with a lens of long focal length.
You should use an SLR with a plain ground glass focusing screen for assessing the sharpness of the other camera. Split wedge rangefinders fitted to most quality camera focus screens are generally very trustworthy when used with the maker's lenses. But they are *not* designed to be employed for accurately focusing an image through two lenses simultaneously, and edge aberrations in either lens which may be completely inconsequential, in themselves, might (I said *might*, although, I have encountered it personally) combine to significantly throw off the accuracy of the beams deflected by the wedges. (Howard Keppler discussed the phenomenon of inaccurate split wedges, and why they can mislead, as far back as the 1960s—I have previously cited the relevant article at this website).
EDIT
You mentioned removing a screen from a Hasselblad. Assuming it's still well adjusted, you could do a lot worse than that for inspecting the Perkeo film plane. If you have one, a 150mm Sonnar f/4 will be suitable for magnifying the image of a target through the Perkeo lens. Now, I mostly check a ground glass directly with a high powered loupe. But in the past I have successfully used my own 500C/M as a substitute autocollimator. Unless you have a 35mm SLR with a faster, long lens, your Hasselblad is not a bad option. Given you are adjusting another 6x6 camera in this instance, its larger viewfinder will also make it easier to note any irregularities in the plane of best sharpness across the film gate.
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Einstein
Established
Well I used the Canon F1N set the zoom at 210. Got everything set up, used a hair as the target. Turned the light on and could see that the hair was slightly out of focus. So removed the front holder that has three screws to grip the lens element holder. Discovered that screwing in the lens element got her into correct focus.
All goes well until I replace the front steel ring with three screws. I can only get at two of the screws while everything is set at infinity, so tighten them enabling me to turn the whole assembly and get at the third screw. Once this is done, the lens will not go back to infinity. I am not over tightening and trying to get all three screws in equally could be the problem, ie unequally set. But I was surprised that the front elect is all the way screwed in to get focused, thought it would have some Lea way but no.
so I am now stumped, each time I set it after turning away from infinity she will not return there !!!
All goes well until I replace the front steel ring with three screws. I can only get at two of the screws while everything is set at infinity, so tighten them enabling me to turn the whole assembly and get at the third screw. Once this is done, the lens will not go back to infinity. I am not over tightening and trying to get all three screws in equally could be the problem, ie unequally set. But I was surprised that the front elect is all the way screwed in to get focused, thought it would have some Lea way but no.
so I am now stumped, each time I set it after turning away from infinity she will not return there !!!
Einstein
Established
Just thinking if I use a ground glass, at the film plane set an object at 1 meter away. Focus on that and re assemble. Then re check again using the Canon and the single hair and see where I am !!!!!
Einstein
Established
Well it is fixed. I did your method kind Sir of 1 meter and fixed everything in place, she was a little hard to turn so I backed each of the three screws out a half turn and she was smooth again all the way to infinity.
Then did the other suggested set up again with one of the few remaining hairs on my head and the Canon. Turned on the light and it was spot on in the splitter.
So I am elated and thank you all for your help and advice gentlemen, all ,ice appreciated.
I now am awaiting the return from Dan Daniels of my Kodak Medalist, being serviced and converted to 120 spool use……..happy days.
Muggins
Junk magnet
Perfect timing - I've just got a flm back from an Ikonta I repaired and the corners of all the shots are very soft, I reckon the focus is slightly off (especially as the pics I took with the film in it when I got it have sharp corners). I've not got a true waist-level finder (OK, I do, but it's on an Edixa Reflex and I don't have an M42 telephoto), but I reckon I can take the prism off my F3 and use that.
Muggins
Junk magnet
Well, as you may have seen elsewhere, it turns out that Captain Brainfart here had reversed his rear element! However, I used the SLR method to re-set the infinity focus and once I'd got my head round how it worked it went pretty well. While probably not as accurate as a ground glass proper you can make quite a decent focus "screen" from a piece of greaseproof baking paper held taut between two spools, though you'll need to make a mark of some kind on it to ensure you have found focus.
I checked two of the other cameras I'd set around the same time as the Ikonta and they were bang on, which I was very pleased with as I'd used a dark room (not a darkroom!) and a streetlight outside as a target. However, now I know this method works, I think it gets the vote.
I checked two of the other cameras I'd set around the same time as the Ikonta and they were bang on, which I was very pleased with as I'd used a dark room (not a darkroom!) and a streetlight outside as a target. However, now I know this method works, I think it gets the vote.
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largedrink
Down Under
I collimated a couple of Olympus Trip 35's recently and figured out some refinements to the SLR collimation method. They work for me in any case and may be helpful to others.
For a camera such as the Trip 35, there is no B setting to open the shutter for a long period to inspect the ground glass image for infinity focus through the SLR viewfinder.
To get around this I set my Nikon DSLR to Bulb. With the SLR pointing into the Trip 35 lens (as per the regular collimation method) and both set to infinity focus, I set the Trip 35 to manual f2.8, opened the DSLR shutter and then released the Trip 35 shutter.
This results in a digital image of the ground glass, taken through the Trip 35 lens. I made sure there was a good back light for the marked ground glass mounted in the Trip 35 film chamber.
With the DSLR it's then easy to zoom and magnify the image, to see with incredible detail how in focus the markings are on the ground glass. I was able to make minute front cell adjustments and repeat until I could achieve very precise focus, as well as compare two settings.
The photos below are not originals, just phone pics of the rear screen of my DSLR. But you get the idea.
I have seen people using a similar approach to test shutter speed accuracy, by taking one photo with the good SLR shutter (camera to be tested on Bulb) and one with the shutter to be tested (DSLR set to Bulb) and comparing the average light on the resulting images.
Anyway, feedback welcome. Maybe I made a mistake doing this so please point out any errors.
For a camera such as the Trip 35, there is no B setting to open the shutter for a long period to inspect the ground glass image for infinity focus through the SLR viewfinder.
To get around this I set my Nikon DSLR to Bulb. With the SLR pointing into the Trip 35 lens (as per the regular collimation method) and both set to infinity focus, I set the Trip 35 to manual f2.8, opened the DSLR shutter and then released the Trip 35 shutter.
This results in a digital image of the ground glass, taken through the Trip 35 lens. I made sure there was a good back light for the marked ground glass mounted in the Trip 35 film chamber.
With the DSLR it's then easy to zoom and magnify the image, to see with incredible detail how in focus the markings are on the ground glass. I was able to make minute front cell adjustments and repeat until I could achieve very precise focus, as well as compare two settings.
The photos below are not originals, just phone pics of the rear screen of my DSLR. But you get the idea.
I have seen people using a similar approach to test shutter speed accuracy, by taking one photo with the good SLR shutter (camera to be tested on Bulb) and one with the shutter to be tested (DSLR set to Bulb) and comparing the average light on the resulting images.
Anyway, feedback welcome. Maybe I made a mistake doing this so please point out any errors.
Seems basically sound, Hugh. I tend to use a ground glass and high powered loupe out of habit more than anything else, but I have used an SLR as a substitute autocollimator with mostly success (and one failure which proved a useful learning exercise when resolved). I have never used a digital SLR for this—eventually, I decided that of all the various cameras I have on hand, the large finder and excellent calibration of my 500C/M made it the best candidate for inspecting film planes. Anyway—I suppose the only thing I worry about when someone uses a DSLR and zoom lens, for example—is the accuracy of the DSLR lens/body infinity calibration.
It might—possibly—have been the late Ed Romney who first suggested using a SLR to inspect a camera's film plane focus at high magnification. If not; he certainly popularised it in his camera repair book. (He described it in his main repair book as "back sighting", from memory). It's a very clever technique for those of us who do not have an actual autocollimator. Of course, the principle is: when two lenses are focused directly into each other, to the same distance, the light rays will agree and a target will appear in focus. So far, so good. But here's the thing: by using this method, what you are really doing is matching the calibration of one camera, to another. Or, to put it another way—the accuracy of adjustments to your patient camera/lens focus, can never be any better than the quality of calibration of your examining camera/lens. Ie. everything hinges on the standard of the auto-collimating camera adjustment. The takeaway, is that, when you set whichever camera lens you are looking through to its infinity stop—it had better be spot on. Otherwise, all you'll be doing is adjusting your other camera to equal the same "error factor".
I don't pretend to know a huge amount about zoom lenses, frankly (I've never used very many, or very often). However I understand that in some cases they may be able to focus past infinity before hitting their stop for various reasons. (To be fair, some longer manual focus primes could, also, to accomodate Eg effects of temperature on material dimensions etc). Nevertheless—whichever lens one uses—zoom, or prime—really does need to be both: well calibrated to the lens register, or "back focus" of the body system employed, and; utterly trustworthy, in its focus at the infinity stop. Otherwise, the whole exercise will be compromised (to a greater or lesser extent, depending on any error).
Autocollimators are invariably fitted with a lens of long focal length. Those made specifically for calibrating photographic equipment, such as the various Gokosha models, for example: tend to have lenses of varying focal length, according to the camera format they're optimised to check. The reason for this is so that an appropriate amount of target magnification may be used to check cameras usually fitted with standard lenses for the format. Ie. Their instruments for medium format camera repair tend to have a lens of longer focal length, than those marketed primarily for 35mm camera inspection—because, of course, a medium format camera will have a longer standard lens. (Our own RFF member Hans Kerensky could speak with more insight on this point, owning—or at least having, at one time, owned, simultaneously—a couple of different Gokoshas, of different types).
I suppose I have veered off track somewhat, above—but this is the internet—veracity of peoples' opinions/accuracy of info conveyed can be, well. . . variable. Using a lens of appropriate focal length with which to examine a film plane of another camera matters. It affects the degree of magnification, and, hence, the accuracy, of one's adjustments. The preceding paragraph, whilst not, directly, relevant (hopefully) helps to demonstrate that using a decently long lens of at least 2 x the focal length of that you are examining—is very desirable. If it didn't matter, instrument manufacturers wouldn't bother specifying different focal lengths, for different format cameras. OK?
Having said all of that—assuming your DSLR and its lens are well matched and the lens is, ideally, at least 80-odd millimetres focal length (based, of course, on the Trip's Zuiko) what you've described, Hugh, is a clever way of sidestepping the absence of a Bulb setting, and ought to be fine.
Cheers,
Brett