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Thread: sensor displacement in casing

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    Senior Member danlindberg's Avatar
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    sensor displacement in casing

    I want to calibrate my Leica distometre for accurate readings and when I 'hook' the D5 onto the back of the Alpa MAX, I am not exactly at the sensor level.

    Looking at the back, there are a couple of mm distance before the protective glas, and then tilting it back and forth to see the underlaying sensor I estimate another 3-4mm to the actual sensor.

    Since I cannot measure that distance myself, maybe this is known somewhere and can post a precise number?

    Thanks!

    Oh, it is ofcourse my Aptus II 5 I'm talking about....
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    Re: sensor displacement in casing

    For which mount? You should be to get the flange distance for the back for the specific mount.

    But unless you are doing macrophotography using the D5 to measure, do you really need to be that precise?

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    Senior Member danlindberg's Avatar
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    Re: sensor displacement in casing

    Mamiya mount.

    It seems to matter just around minimum focusing distance. Especially with the SK 120.
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    Re: sensor displacement in casing

    At that level of macro it might be better to use live view than direct measurement. Can your application/workflow sustain a laptop or your budget an upgrade to a Credo?
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    Senior Member danlindberg's Avatar
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    Re: sensor displacement in casing

    I suppose you are right In my case a laptop would be the solution for those images.

    But anyway, you wouldn't happen to know how many mm the sensor sits behind the protective glas?
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    Re: sensor displacement in casing

    Focus your lens to a known distance and then use the D5 to figure out what position it needs to be in order to read that distance. You don't need the flange distance.

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    Senior Member danlindberg's Avatar
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    Re: sensor displacement in casing

    Yes, what I'll do tomorrow is focus with live view into a wall and then measure with the D5. The difference between D5 reading and what the lens says is the distance I am looking for.
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    Re: sensor displacement in casing

    Dan, do you measure distance with the Disto on every shot you take?

    I was thinking of getting a D5 for use with my new camera but have been thinking guesstimation and hyperfocal was a better method. Do you find you need more accuracy than hyperfocal?

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    Senior Member danlindberg's Avatar
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    Re: sensor displacement in casing

    Gazwas, I use both guesstimation, hyper and D5. Method depends on which lens I use, at what distance, what f-stop and how the scene looks. Open landscapes with the 35 XL the D5 never leaves the bag, but on the other hand if I'm in the woods and setup the Max, lets say, around 2 metres distance from a trunk. Then I really benefit from knowing if it is 1.91 or 2.32 to that trunk. At that distance it makes a difference to be correct even with the 35 XL.
    With longer lenses this is further enhanced, but having said that, I am surprised at how well hyperfocal and guesstimation actually works in many situations.

    Another example. My latest interior shots have been made exclusively with the SK 28 XL, most of them with f8 and most of them with the focusingring between 1.5-4 metres. If I go in 100% I can quite easily see where the focus is set. This means I would not dream of not using the D5 so that I can really pinpoint focus on 'the vase on the table' or 'the sculpture to the right'.....

    I for one would feel very limited and not satisfied without the D5, especially on assignments. But a 35 XL and an Alpa TC over my shoulder taking a walk along the beach, then guesstimation will do nicely.
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    Senior Member dchew's Avatar
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    Re: sensor displacement in casing

    Dan,
    I will be curious what you get. I tried various ways to measure the distance from the back edge of the STC body to the sensor surface, since I flip the D5 foot down and hold it up against the camera on either the top or port side. The offset I have programmed into my D5 is 0.02 ft, or 6 mm. I actually think it is somewhere between 6-9 mm, or 0.02-0.03 ft.

    But I have an IQ sensor.

    Dave

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    Re: sensor displacement in casing

    From reading many posts about tech cameras, the getdpi laser measure of choice appears to be the Leica Disto D5.

    Can someone please explain what does the D5 do over the entry level D210 as the specs say they measure to the same accuracy. The only obvious feature I could see different was the video pointer which seems useful outside when measuring objects at distance but of little real world use as at greater distance hyper focal focus removes the need for "to the centimetre" readings doesn't it?

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    Senior Member dchew's Avatar
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    Re: sensor displacement in casing

    Gareth,
    It is indeed the video that makes it the preferred model. In my head getting an accurate measurement matters up to about 50 ft, although I admit I haven't run the distance vs. "my" hyper focal settings through the appropriate calculations. There have been times when I could not see the laser in the 20-50 ft range due to light conditions or whatever.

    The distance estimates in my head are pretty shaky in that 20-50 foot range, so for me it really helps. The way it works you turn on the unit and the video is not turned on. You have to purposefully turn it on by pushing a button. So I usually try it without the video first. Point of that being I have a pretty good idea of how often I need that feature to get a good reading. About 20-30% of the time I need to turn on the video because I cannot see the red dot.

    I used to carry an off-brand distance meter. Frustrated the heck out of me and I gave it to a friend for non-photography applications.

    Dave
    Last edited by dchew; 6th May 2012 at 03:17. Reason: clear up some confusion
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    Re: sensor displacement in casing

    Quote Originally Posted by dchew View Post
    The way it works you turn on the unit and the video is not turned on. You have to purposefully turn it on by pushing a button. So I usually try it without the video first. Point of that being I have a pretty good idea of how often I need that feature to get a good reading. About 20-30% of the time I need to turn on the video to get the reading.
    What is it that stops you getting the reading with just the laser pointer, ambient light and not seeing the red dot or does the video pointer measure differently?

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    Senior Member danlindberg's Avatar
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    Re: sensor displacement in casing

    Quote Originally Posted by dchew View Post
    Dan,
    I will be curious what you get. I tried various ways to measure the distance from the back edge of the STC body to the sensor surface...

    Dave
    It was tougher than I thought. I have tried many times now and it seems to be very accurate if I add 5mm to the D5.

    Quote Originally Posted by gazwas View Post
    What is it that stops you getting the reading with just the laser pointer, ambient light and not seeing the red dot or does the video pointer measure differently?
    You simply cannot see the red dot many times! With the video it is game on...
    Last edited by danlindberg; 5th May 2012 at 14:23. Reason: wrong wording!
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    Senior Member dchew's Avatar
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    Re: sensor displacement in casing

    Quote Originally Posted by danlindberg View Post
    You simply cannot see the red dot many times! With the video it is game on...
    Yup that is it. Sorry Gareth I re-read my post and realized my description was not very clear.

    Dave
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    Senior Member danlindberg's Avatar
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    Re: sensor displacement in casing

    On a direct question to Alpa, I received this drawing within 4 hours. Thank you Alpa! Amazing service

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    Senior Member dchew's Avatar
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    Re: sensor displacement in casing

    That's awesome Dan, thank you! Plus, I feel so smart with my 6-9mm measurement. No I mean estimate.

    Dave

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    Re: sensor displacement in casing

    I've gone back and forth on the D5 now on keep it or take it out and I always seem to come back to focus mask than 100 percent viewing with a 3x Hoodman lupe. Worst case I'll use live view but I just don't use the D5 anymore. I guess here is where a IQ makes the difference since I'm pretty confident I nailed it with those techniques. But sometimes I admit it's nice to know a starting point instead of hmmm looks like 15ft
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    Re: sensor displacement in casing

    When this kind of level of focusing accuracy is required, what are people's workflows when it comes to measuring distance to an object that is off-axis?

    i.e. if the object you want to focus on is not dead-center in your composed FoV, you can't simply measure the distance with a laser and then dial that in on the lens. So what do you do?

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    Senior Member danlindberg's Avatar
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    Re: sensor displacement in casing

    Quote Originally Posted by Guy Mancuso View Post
    I've gone back and forth on the D5 now on keep it or take it out and I always seem to come back to focus mask than 100 percent viewing with a 3x Hoodman lupe. Worst case I'll use live view but I just don't use the D5 anymore. I guess here is where a IQ makes the difference since I'm pretty confident I nailed it with those techniques. But sometimes I admit it's nice to know a starting point instead of hmmm looks like 15ft
    With an IQ or Credo, I would most probably think the same. But with the Aptus, I could not live without it.

    Quote Originally Posted by gerald.d View Post
    When this kind of level of focusing accuracy is required, what are people's workflows when it comes to measuring distance to an object that is off-axis?

    i.e. if the object you want to focus on is not dead-center in your composed FoV, you can't simply measure the distance with a laser and then dial that in on the lens. So what do you do?
    I see what you are saying here, and in most cases the 7mm extra from the D5 readout is ofcourse just a non-issue. Don't get me wrong here, I am not at all after a few mm precision for readings of 5-10-40 metres, or off-axis readings either. It is in the very close range of the lenses it matters.

    I can illustrate it with this snapshot of the HPF ring. Setting up the camera at these short distances and shooting a completely flat surface - then those 7mm "does matter". Check how close the different distence settings are....

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    Re: sensor displacement in casing

    Hi Dan -

    Thanks for that shot. Always love to see things like that

    Perhaps the question wasn't so relevant to this thread as your subject matter is very close and on the focal plane - and I can see why the distance to the sensor plane needs to be known to such a level of accuracy.

    Kind regards,


    Gerald.

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    Re: sensor displacement in casing

    At such close distances would it be scoffed at to just use a good old fashioned tape measure or ruler?

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    Senior Member danlindberg's Avatar
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    Re: sensor displacement in casing

    Quote Originally Posted by gazwas View Post
    At such close distances would it be scoffed at to just use a good old fashioned tape measure or ruler?
    Still needed to know about the 7mm to know where to take the reading
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    Re: sensor displacement in casing

    Quote Originally Posted by danlindberg View Post
    Still needed to know about the 7mm to know where to take the reading
    Very true and good work Alpa for such a quick response to your tech question.

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    Senior Member dchew's Avatar
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    Re: sensor displacement in casing

    Quote Originally Posted by Guy Mancuso View Post
    I've gone back and forth on the D5 now on keep it or take it out and I always seem to come back to focus mask than 100 percent viewing with a 3x Hoodman lupe. Worst case I'll use live view but I just don't use the D5 anymore. I guess here is where a IQ makes the difference since I'm pretty confident I nailed it with those techniques. But sometimes I admit it's nice to know a starting point instead of hmmm looks like 15ft
    Guy,
    I'd basically agree. I tend to use all the tools though, focus mask, zoom and the D5. Focus mask is my ultimate judge. I have the focus mask set very tight (maybe too tight?); there are times when there is not enough contrast in the subject for focus mask to work. Then I rely on the D5 and zoom.

    Dave

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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: sensor displacement in casing

    So Dave, do you ever use the 'live view' of the IQ as well?

    I confess that it's probably the least used part of my IQ160 ... as in almost all situations I go through the similar set of tools as you, supplemented by my rangefinder more often than the D5.
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    Senior Member dchew's Avatar
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    Re: sensor displacement in casing

    Graham,
    Yeah I do once in a while, but the fact that I forgot to mention it...
    I moved up from a Canon 5DII, which has the best damn live view ever. When the focus is dialed in on that camera it is like you see moire. So that is what I was used to, and I struggle with minor adjustments using the IQ live view. I use it as "another source of information" sometimes but do not rely on it.

    I admit I haven't given it a robust try. There may be a learning curve I haven't jumped over.

    Dave

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    Re: sensor displacement in casing

    The fact that many don't use the live view feature on the IQ backs makes me feel a little better being a P65+ user. For me it was upgrade to an IQ back and stick with the ML2 or stick with the P65+ and get an Rm3di for exterior shoots. My Rm3di arrived at the weekend and having previously always shot tethered with my ML2 I've not had much experience shooting without a computer in tow. Will take some getting used to but just using a () tape measure the focusing seems so accurate and I'm amazed at how easy it is to get very sharp results.

    I'm not a big fan of the focus mask in C1 and just don't trust it so as a P back user the D5 seems like the way to go....

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    Re: sensor displacement in casing

    I kind of waited to buy the tech cam until I got the IQ with the focus mask. In the field on the back itself it certainly is a better tool. For me also live view is a last ditch effort. I also shoot zero latency so I watch for heat and battery drain which live is the worst at. Battery drain I really don't care as much but heat I keep a close handle on that one.
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    Re: sensor displacement in casing

    Quote Originally Posted by Guy Mancuso View Post
    I kind of waited to buy the tech cam until I got the IQ with the focus mask.
    Yes, I thought the same. Tech cameras need IQ backs but while I agree the added features of focus mask and amazing 100% screen are excellent shooting accessories to have in the field, following my initial tests with my Rm3di and a tape measure, the focusing of the Arca is amazingly accurate and nothing else is really required to get very sharp focus.

    IMO any additional feature in a digital back above that in the P backs is a massive bonus but not a necessity any longer. With the possible addition of a Disto to remove the physical measuring problems in combination with hyperfocal focus I don't feel inadequate for not sporting an IQ or new Credo any longer.

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    Administrator, Instructor Guy Mancuso's Avatar
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    Re: sensor displacement in casing

    Gareth a Disto 5 might be of great help here for you or some folks use a Leopold range finder as well. One used for hunting
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    Re: sensor displacement in casing

    Just wondering if the distance of 22.2mm quoted by Alpa would hold true for DBs besides the Credo and Aptus ? i.e. the distance of 7.2mm in the drawing is maintained for all DBs by varying the depth of the adapter (2) in order to account for differing sensor depths used by different manufacturers (unless they all use the same sensor depth, which would seem the sensible thing to do).


    Quote Originally Posted by danlindberg View Post
    On a direct question to Alpa, I received this drawing within 4 hours. Thank you Alpa! Amazing service


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    Re: sensor displacement in casing

    The curious thing about that drawing is that it says the distance from the mounting plane on the front of the camera body, to the mounting plane on the rear, is 22.2 - 7.2 = 15mm.

    Well, having just taken a set of callipers to my STC, I can tell you it's 11mm exactly.

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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: sensor displacement in casing

    Actually it is showing 7.2mm from the rear lip of the body vs rear face of the sensor adapter mount. Maybe there's your 4mm.

    Regarding the sensor distance - it should be the same for all makes of backs. The back adapter is sized (with shims if necessary) to ensure that distance is as exact as possible regardless of make or even instance of backs.

    The lens helicoid is the same (only one) for each lens for any back otherwise you'd have different adjustment there for each back if the 22.2mm wasn't common.
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    Re: sensor displacement in casing

    Let's get callipers out again ... yup there's the missing 4mm ... thanks Graham.

    Personally, even though it's a (very useful) sketch, I think it would have been better to indicate the measurement from the plane where (1) and (2) meet, which is consistent throughout all Alpa models of camera, rather than a point on the body of the camera.

    So that distance would be, um, 7.2 + 4 = 11.2mm.

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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: sensor displacement in casing

    I would agree in principle, but if you want to determine the sensor position relative to the body as seen from the outside then only the external face of the body would be visible when the back is on it. The internal face is, err, internal
    Remember: adventure before dementia!

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    Re: sensor displacement in casing

    I find this inaccuracy confounding.
    Unless the D5 is set to measure exactly from the dead centre of the sensor, there is bound to be an error which depends on the radius of the arc that the disto has to travel from the sensor's centre to it's hooked position. That is unless the object plane is exactly parallel to the sensor plane.
    Here, the arc of error would be x + Delta.

    Now normally, I would think it doesn't matter, the error being = delta, for larger distances to objects, but for close distances, it would have to be taken into account ?

    [IMG][/IMG]

    Quote Originally Posted by danlindberg View Post


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    Re: sensor displacement in casing

    Really, is this a problem? If the Disto is offset by 3 inches, at the minimum focus distance of a typical MF lens, focus at the center point of the view would be off by about .15 inches. If that is too imprecise for you, I guess you could develop a program to correct for the offset.

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    Re: sensor displacement in casing

    Actually, I'm not even sure if this is a problem. But if we are using HPF rings and shimming to the level of micrometers, then yes, an offset of 0.15 inches does matter. Otherwise all the hoopla about precision and tolerances goes out the window. Or so I think. Really, the only way ahead then would be to develop phase-detect autofocus for Alpagon lenses
    But hey, disclaimer: my MF kit and back is still 4 weeks away.

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    Re: sensor displacement in casing

    I think the Disto can also measure inclinations. So in principle, it's possible, knowing the inclination angle between of the Disto and the optical axis (read from the Disto) and x + \Delta (the distance measured with the disto) to calculate x. I think Jae_Moon's software for tech cam focusing does just that (and many other things):
    http://www.getdpi.com/forum/medium-f...cameras-2.html

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    Re: sensor displacement in casing

    Certainly with the D8 you can measure the angle and distance and it'll calculate the base distance for you. I believe the D5 will do that too.
    Remember: adventure before dementia!

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    Senior Member dchew's Avatar
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    Re: sensor displacement in casing

    Quote Originally Posted by GrahamWelland View Post
    Certainly with the D8 you can measure the angle and distance and it'll calculate the base distance for you. I believe the D5 will do that too.
    Yeah the D5 has a trig mode that can directly read out the horizontal distance based on the angle of inclination. Again, all this seems crazy detail for normal situations, but in the context of Dan's original application (very close work), it can help.

    My disto is on the fritz. It works 20% of the time, but I can't keep batteries in it because it gets a mind of its own, turning on by itself, then totally freezing up stuck on with the laser engaged. Very annoying! I sent it to Leica in Atlanta, but of course they got it during the 20% of the time it worked, so they returned it saying nothing was wrong. Ugh. The good news is I'm getting better at my distance estimates!

    Dave
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    Senior Member ondebanks's Avatar
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    Re: sensor displacement in casing

    Quote Originally Posted by danlindberg View Post
    Looking at the back, there are a couple of mm distance before the protective glas, and then tilting it back and forth to see the underlaying sensor I estimate another 3-4mm to the actual sensor.
    Dan, it's good that Alpa got back to you quickly with the proper overall distance.

    Even if someone had correctly answered your question, as posed, that would not have solved your problem.

    For your application, it would not be enough to add together the physical distances between the various components. One must know the optical path length. That requires taking into account the thicknesses and refractive indices of the IR-block filter and sensor cover glass. These values are not published by any DB manufacturer; so their combined effect would have to be found by experiment. Live View is the easiest way to conduct that experiment . But anyway, Alpa have bypassed the need for that experiment by giving you their diagram.

    Ray

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