jean wrote:Eric,
what micrometer are you using? I'm currently looking for something, but am not sure yet what I need, I guess the 0.001 mm tolerance devices are required, and I wonder how a working setup should be..
My project is to bring the cameras and lenses I use to spec, so I can interchange them.
jean,
it is very difficult to interchange lenses with differant cameras bodies using the same mount adjustment that is on each particular lens UNLESS each and all of your cameras and their respective turrets are adjusted to c-mount factory specifications as it relates to the flange distance. however, if you so desire to spend the time to correctly adjust the turrets on each of your c-mount cameras so they are all the same, then you will be 10 steps ahead of the game as it relates to ease of use in the interchangable lens catagory.
in the following photos, you will see a depth micrometer. the cross surface is what is used on the outside surface of the turret, thus establishing a fixed place to start your measurements. this does NOt mean you the c-mount flange distance ends or starts at this point ... it may be that you have to do some deducting or addition based on the extra surface area that may be caused by the micrometer cross section and the surface on the turret. so, like all things of this nature, you must pull out the ol pen and paper and start taking notes/measurements, so you can establish a zero point with which you add or remove measurement/distance upon/after film testing. so for your initial measurement/test, you will tkae the micrometer and place it on the outside surface of the lens turret so it is flat/flush against the turret. take and them measure the distance to the film plane ... so make sure to place some film in between the pressure plate and the micrometer and close the pressure plate as if you were filming. write down that measurement. determine the distance between any excess surface area outside/above the actual c-mount threading area, and deduct that from the measurement. this should give you the flange distance. if you do not know how to get the masurement from the thousanths indicator on the micrometer, then use a seperate measurement ruler to measure the amount of probing rod that is protruding on the micrometer ... in most cases you will be around 15-19mm. with time and practical application, you will start refining your ability to measure, so you can indeed obtain a measurement reading like 17.52mm.
once your turret/c-mount threaded mount piece on the outside point to the actual film emulsion is 17.52mm, then your lens turret is to factory spec. repeat this process for 3 lens turrets. if you find or learn that your terret is warped or bent ,and one or the other two c-mounts are measuring differantly, then you will need to remove the turret, and with a vice and pressure or hammering tools, gently start bending back into place, and continue measuring each mount until they are all at 17.52mm. if you are not ble to get all of them to this measure for whatever reasons, then get them to a measurement that is the same for all three, and then focus on making the adjustments on the actual lens/lens mount. but for what you are posing, you will want all of your camera bodies to be the same factory measure, so spend the time and make it happen.
now then, we are dealing with the lens. the lens must be measured from the actual male threaded c-mount on the outside edge ... the distance of the back glass has nothing to do with the mounts being correctly measured, but the back glass DOES have everythin to do with the measure between itself and the lens' mount. understand? now what you will find, and this is where things really become a practice in documenting all the measurements, is that not all threads are created equal. you may have 3 c-mounts on your turret, and one of them may thread deeper then the other two, or some variation of the sort along these same lines. this may also be the case with the threads on the lens' mount. so this is where marking the lens and the mount in the same place that the lens stops threading plays a crucial role in having repeatable success with interchanging your lenses. for the sake of simplification, take and designate one of the three turrets for a specific lens, and adjust that lens for that one turret. so when you are changing lenses, you will always use your switar 10mm on lens mount number 2, on camera number 3, for example. unless you cna verify that all of the threads on each of the c-mounts on the turret are the exact same when that lens tightens down, you will need to employ this practice.
so after marking the points with each of your lenses on each of the mounts, take and roll film tests. take and film using various measurements and an object or chart out in front of the camera as these particular measurements ... which are the same measurements on your foccusing ring on the repsective lenses. what you will want to establish here is if the lens is indeed in focus at any one of it's particular distance measurements. so if your lens has a 10". 1', 3', 10'. etc. markings on it, you will want to place an object at those distances. however, you will also want to place an object at the distance, and then adjust the lens in both directions(closer or further focus). this way, when you see your film, and you compare the focus of the image on film to your notes, you can see if your lens if to far out or too far in to the film plane. for example, lets say you have an object at 5', and your lens is set at 5', and after viewing the film you notice it is out of focus. if you did not bother to adjust closer or further away, you will not know what adjustment on your lens actually does give you the correct focus at that lenght. you need to know this at all markings on your lens so you can adjust your lens correctly. now it may be that your lens needs to be collimated, in which case merely adjusting the mount on the lens will not bring your focal lenghts into correct measure. for example, your lens may be dead on at 1', but at 20' it is out of focus. but these are things you need to learn for yourself so you understand the relationships going on between the optics in the lens to the lens' mount, and the lens' mount to the film plane. you will figure it out IF you write everything down while conducting the tests and making sure to measure things correctly.
jean ... it is merely an excercise in establishing a fixed point/location, or a zero point/location, and then basing all of your measurements from these. this applies to the micrometer and the surfaces it is resting upon(where the road meets the rubber in other words). it applies to the focal lenghts and the distance of measure in from of the lens or the flange or the mount(again, you can use any of the three, just add or subtract and always stick to just that one you have selected).
people purchasing cameras on ebay would be doing themselves a favor to spend the extra money in purchasing a camera from a person who has been recently filming with it, wherein that seller cna indeed answer questions as it relates to the nuances of the camera, thus providing you with detailed information of how the camera functions and what measurements/indicators need to be repsected when filming, so the images are in focus. or, if you like to do these things(like i do, and like it seems you do as well), then learn how to do it now, so that for each lens and/or camera you purchase later, this process becomes routine. if you are planning on becoming a cameraman for a profession, knowing this information goes a LONG ways. the other things to know are your dof's, filters, and chemical processes while developing. in hollywierd, there really IS a shortage of well informed camera men ... so this knowledge becomes an asset if you can apply it correctly. this is why dop's who have shot a shit ton of music videos are so damn good with a camera ... they know the relationships between the lens the camera and the film ,and all the other things like lighting and filtering and so on. being well rounded in this regard can make or break a film.
right now in television production, wherin the director has 7 days to prepare and 7 days to shot, error MUST be kept to a minimum, so when these directors find good cameramen, or rather and more often then not, when the producer's of the show find good cameramen, they keep them, becuase it is one of the greatest worries of the production that can be put to rest because the dop can be counted upon to get the right image ... in focus.
if you have some extra money, purchase a single chip, inexpensive c-mount camera head and plug it into your computer for capture ... use this to learn to adjust your lenses to that camera body. it is an excercise that is of extreme value for anyone considering this as thier profession ... some would argue most tv series products would rather pay for an onstaff camera tech ... but some would argue otherwise
i think that the majority of the people on this site, myself included, end up getting frustrated and spendign less time filming as a result of these very types of issues. to get a camera in tune, exactly where it needs to be, is indeed a process and one that requires a great deal of attention. i look back at the first film i shot about 18 months ago, and then the film i shot 12 months ago, and then the film i shot 6 months ago, and the film i am shooting now, and the differance between them are great. and the number 1 contributing factor is the time i have spent learning how to correct tune and keep tuned my camera(s). if you rely solely on a camera tech to keep your camera tuned, then you fail to know what you should know about your camera, which is the very thing that will make or break the images you eventually film. and from first hand experience, the good techs available, and often mentioned on this site and other sites, have so much back load that they end up taking forever ,and sadly and in many cases their work is less then satisfying ... at least for my level of quality discernment. because most filmmakers are starving and struggling and can barley afford to purchase a roll of film, it makes sense to spend the time to figure these thigns out, because then you stand on your own two feet, and have the ability to correct any such problems that may occur durign filming, and if you are actively working on your own projects, one after the other, then you will also start working on other people's projects ... why? becuase your product looks good, and you have proven to those who have seen it that it looks good, and you are responsible for this fact. this means someone will use you becuase they cna depend on you.
i went about my own filmmaking aspirations the wrong way, saying this in hindsight, but also knowing there really could not have been any other way. if i had to do it all over again, i would have STARTED by writing a one page film. with an intro, and problem, and a solution. i would have then taken and purchased a couple rolls of film, found some people ot rehearse the one page screenplay, and then i would have shot it(i would have done the above mentioned camera adjustments and film test before hand). then, i would have edited it, added sound to it, and completed it, and posted in here on this site. and then, i would do it all over again, with 2 or 3 pages ,and a little deeper storyine, or perhaps an installment to the first short film i shot. and then i would have finished it. and kept going. instead, i started out by wanting to go into a bg full feature length production ... and had i been able to maintain control over everything, menaing having the knowledge and experience to do everything, then all would have bene well. but this is not realistic. the truth is, you will experience the same set of challanges on a 1 page screenplay as you will on a 120 page screenplay, so it is wise to start with the 1 pager.
so, in my own experiences, and with my other non film projects that were already in the works, i was NOT able to make my feature film as was planned. and good thing i suppose. so in a couple of months after i complete my construction projects, i will shoot my one page film, and do as i have mentioned above ... because right now i have more family films and film test footage then i would like, but i do not have a film, not even a short one page film
live and learn ... thus is life. i hope this information was of some use.
eric
