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Thread: focusing techcamera with distometre

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    Senior Member danlindberg's Avatar
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    focusing techcamera with distometre

    I can imagine that in landscapes you get away with this method. But in architecture, how easy/accurate is this method? For instance, aiming straight at a facade that is paralell to the sensor, the accuracy must be greater and I am wondering if you can rely on an external distometre as your day to day working tool?
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    Re: focusing techcamera with distometre

    outside, the leica disto D5 is the way to go...

    but you must remember few things...

    the distance from the camera and the faηade even if it is // to the sensor, differ from the base to the top...

    some wide angle lenses shows field curvature

    for architecture, most of the time hyperfocal is the way to go, so no disto needed...

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    Re: focusing techcamera with distometre

    I've only been using a D5 for a couple months with the first real acid test this past trip to Bluff UT and Anasazi Cliff Dwellings. I also used it to shoot inside slot canyons later in the week. The D5 has options of where the measurement will be taken from; rear or front of the device. I choose the front element and make sure I have it close to where the lens is when taking the measurement. I've also found that for closer work such as the slot canyons where the closer focal point is less than 4' I switch to meters and while I photographed further objects like the cliff dwellings (20 feet) I switched to feet.

    While I like the D5 it nevertheless is just one tool which should not replace hyperfocus.


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    Re: focusing techcamera with distometre

    Quote Originally Posted by Don Libby View Post
    I choose the front element and make sure I have it close to where the lens is when taking the measurement.
    Don
    My understanding is that the film/sensor plane is where the measurement should be taken not the lens.

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    Re: focusing techcamera with distometre

    Quote Originally Posted by alan_w_george View Post
    My understanding is that the film/sensor plane is where the measurement should be taken not the lens.
    It definitely should be the sensor plane.
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    Re: focusing techcamera with distometre

    Yeah I screwed up there. Too early and distracted ...
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    Re: focusing techcamera with distometre

    there is a theoretical point within the lens from which distances should be measured.
    that point to the object = object distance, that point to the sensor = image distance. when the object distance approaches infinity, that image distance is defined as the focal length of the lens.

    I would think that the numbers engraved on the focus ring correspond to the object distance, not to the object distance plus the image distance.

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    Re: focusing techcamera with distometre

    If you are photographing buildings and interiors, I don't think it is going to make a difference whether you measure from the image plane or lens plane (unless you have really long lenses).

    Object distance is from the lens' front nodal point to the object.

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    Senior Member dchew's Avatar
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    Re: focusing techcamera with distometre

    Like Jack I am pretty sure the distance scale is for focal distance, which is subject to focal point (film plane).

    Dave

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    Re: focusing techcamera with distometre

    The D5 allows for 2-different point of measurements; front and rear of the device. I've found that I get a better focus by using the front portion - at least it makes me feel better using it.

    I might start a minor war here however I don't feel 2 inches either way amounts to a hill of beans when you're measuring beyond 10 feet. At least I don't see it in my images. If I'm shooting closer than 10 feel I'll still take the measurement however I add insurance by taking additional images on either side of that measurement and in the end normally use 2 to stack the focus.

    Again it all depends on what you're capturing and in most of my cases it's landscape - large panoramas to smaller single capture images but for the most part beyond 10 feet. The only recent thing I've captured was in the slot canyons where 10 feet was the norm for being max.

    Don

    In the end I thinks it's whatever works best for you and your shooting enviroment.
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    Senior Member danlindberg's Avatar
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    Re: focusing techcamera with distometre

    Lets say I use a HR-S100, shot wide open, and I want to pinpoint a vase on a table inside a large livingroom. Around 2 metres distance, nothing in front and nothing behind the vase on 'that big' diningtable. You can see in this case the importance of exact focusing. Would you achieve this on your first try with a D5?
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    Re: focusing techcamera with distometre

    i am of the opinion that prefocusing and expecting to get it is a pipe dream. even if you can measure to the nut, good luck setting the focus ring.

    peep the shot, and here is where the IQ phase will shine

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    Re: focusing techcamera with distometre

    Having nothing better to do I decided to see what I could do.

    I sat the moose up at a measured distance of 2 meters and shot it with a Schneider 72mm. The vase was then shot with a Schneider 120mm at a measure distance of 2.95 meters. I showing single image results with no focal stack; if I were doing this for real I would have measured the shot 3-images 2-slight off one-way or the other of the measure distance. I did peep as I took these and the screen shown reasonable sharp focus.

    I agree with jlm - no matter how precise a measurement you have you're still left with dealing with the focusing ring of your individual lens. Measure the shot to get a reasonable idea the peep the images as they're taken. And yes the IQ will shine at doing this. I had to do several things with my P65 to get to 100% - a far cry from a simple tap on the screen.









    The focus point on the moose was his nose while the main body of the vase was the focal point. I noticed the flowers are soft which is due to the focal point.

    Sorry about the crappy light however we're experiencing a thunder/electrical storm at the moment.


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    Re: focusing techcamera with distometre

    I screwed up. I'm so dang used to shooting landscape I completely forgot I had Sensor Plus. Chalk it up to a (very) senior moment...

    I hadn't moved anything when I went back into the kitchen and it was just as I was about to reformat the card I remembered the sensor plus. Having little to no use for it I haven't really tried it out until now. I added the moose and for a little added benefit I added my business card. The focal point was still on the main body of the vase which appeared sharp as I peeped it - so did the card. The first thing I did after opening in C1 was use the focus mask which showed the card to be in focus. It rally isn't as you can see. Anyway this is enough from me as we're loosing power every could minutes and I need to batten down the hatches.





    If nothing else I've come away with a much greater appreciation of sensor plus.
    Last edited by Don Libby; 9th July 2011 at 16:48.
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    Re: focusing techcamera with distometre

    I use the D5, which is a joy, with the high resolution focusing rings on the Alpa/Schneiders with very good results.

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    Re: focusing techcamera with distometre

    I hate doing anything half arsed; therefore I kept at it until just now.

    I re-measured the distance using the sensor as the point of focus and sat the camera exactly 10' (3 meters) from the moose, vase and card using the card as the focal point. Opening the image in C1 again showed it card in focus using the focus mask; peeping the screen after capture show it in focus as well.





    Cambo WRS1000, P65+ (sensor plus) Schneider 120mm lens
    The moose and vase remains in focus however the card is still soft. I believe the problems lies in the card material and the fact that it's on an angle.

    Enough from me; I'm sorry added the stupid card!


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    Senior Member danlindberg's Avatar
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    Re: focusing techcamera with distometre

    Thanks a lot for the tryout Don Very sweet moose

    I am going to try and find someone in Sweden that has this kind of setup and try it myself.
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    Senior Member malmac's Avatar
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    Re: focusing techcamera with distometre

    Hi Don

    What was the aperture setting for the moose, vase and card?
    Is the card soft because of a really narrow DOF at 3 metres?

    I am also shooting with a Cambo WDS, though only have one lens a SK 35mm lens at this stage.

    Cheers.


    Mal

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    Re: focusing techcamera with distometre

    Quote Originally Posted by Don Libby View Post
    And yes the IQ will shine at doing this. I had to do several things with my P65 to get to 100% - a far cry from a simple tap on the screen.
    Three button taps is hardly a major inconvenience Don.

    Quote Originally Posted by Don Libby View Post
    I hate doing anything half arsed; therefore I kept at it until just now.

    I re-measured the distance using the sensor as the point of focus and sat the camera exactly 10' (3 meters) from the moose, vase and card using the card as the focal point.
    Don, did you phisically measure the distance with a tape or did your used the D5. And are you saying the D5 is not accurate enough at this range. Sorry, confused by your findings.

    I shoot a lot of ceramics and sometimes the print/transferes used on them always looks OOF, even if it looks sharp by eye on the object. The bodies look pin sharp but the transferes are still fuzzy. Can't explain why but it happens a lot and is always a source of frustration to me and might be what the issue with your card is. Physics or Voodoo probably!

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    Re: focusing techcamera with distometre

    Looking at the images again I'd say overall I'm pleased with the moose and vase; not so with the card. If I had to do it all over I'd do it differently.

    First the 3-objects were all made of different materials, wood, ceramic and paper. The moose doesn't have any real sharp lines to begin with although I believe he is sharp. Likewise the vase appears to be sharp with the flowers slightly soft and this could be on account of the aperture (5.6) and possible need of better measurement. The moose and vase were all sitting straight up and down however the card was just propped up against the vase in a rush thus at an angle with the top portion angled backwards.

    danlindberg: You're welcome and thank you for the test.

    mal: You're on the way to a great setup with the 35mm.

    Gareth: Actually it's 4-button taps but compared to the screen tap light-years of difference.

    I'm still new to the D5 and need to work all the bugs out. And no, I didn't mean to infer that it was not accurate at the range; if anything I'd bet on operator error.

    I don't shoot product work and this was the first time shooting ceramic. Actually now I remember why I shoot landscape and nature.

    I like the Voodoo idea!

    The more I test the more I learn and the better I get. Thanks for the suggestion. Nothing like trying something in the middle of a thunder/electrical storm.


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    Re: focusing techcamera with distometre

    i briefly saw a few things today at lance's get together re focusing.

    1. the distometer D5: i ordered one after seeing Woody's. I had no idea it had a video screen with crosshairs where you are aiming the laser, and it zooms! this will get your distance number, eliminating one variable. may need a tripod adapter as it is tough to hold it still at long distance measuring
    2. the Arca fine focus ring and look-up table: looks like with #1, above, this will work very well
    3. the alpa HR lens rings: they read out directly in distance and closely enough marked to work very well also with #1
    4. focus mask on the IQ180; you snap a shot and peep it, it shows with a highlight exactly what is in focus. seems like a great feature, especially if using T/S

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    Re: focusing techcamera with distometre

    Quote Originally Posted by Jack View Post
    It definitely should be the sensor plane.
    Could you explain why the sensor plane instead of lens plane? I thought the equation was 1/A + 1/D = 1/F where A is lens to sensor distance, D is lens to PSF distance and F is the lens focal length.

    Thanks,

    Jae M

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    Re: focusing techcamera with distometre

    The markings on the lens are calibrated for the sensor plane.

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    Re: focusing techcamera with distometre

    I assume this is a convention accepted by camera/lens makers?

    probably only really matters for closer distances as the difference is a lens focal length, more or less

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    Re: focusing techcamera with distometre

    Marked lenses are for the sensor plane. Fixed lenses with no focus mounts like for LF shooting, use the focus formula 1/f = 1/i + 1/o where f is the lens focal length, i is lens to image distance (usually measured from the optical center which is generally assumed to be the lens flange), and o is lens to object distance. One needs to consider that as distance o increases distance i decreases, so there are two variables; then secondarily that the formula does not work for retro, tele internal focus lenses. Fixed-body cameras use the sensor plane convention for helical markings since it is the one constant in the fixed body camera -- which can at the same time be using conventional, retro, tele or internal focus lens designs.
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    Re: focusing techcamera with distometre

    Quote Originally Posted by Jack View Post
    Marked lenses are for the sensor plane. Fixed lenses with no focus mounts like for LF shooting, use the focus formula 1/f = 1/i + 1/o where f is the lens focal length, i is lens to image distance (usually measured from the optical center which is generally assumed to be the lens flange), and o is lens to object distance.
    Jack:

    How about RM3Di? How is its helical focus ring calibrated, ie., the subject distance from the lens plane or from the sensor plane?

    thanks,

    Jae M

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    Re: focusing techcamera with distometre

    Quote Originally Posted by Jae_Moon View Post
    Jack:

    How about RM3Di? How is its helical focus ring calibrated, ie., the subject distance from the lens plane or from the sensor plane?

    thanks,

    Jae M
    I honestly don't know because I've never measured that close, but I'd assume the sensor plane.
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    Re: focusing techcamera with distometre

    From analysis of Arca's calibrations for a few lenses, the Rm3di calibration seems to be based on distances measured from the front nodal point (i.e., the lens, not the sensor). However, the data on Arca's crib cards appear to be based on calculations for lenses with specific focal lengths -- not necessarily the nominal focal length for each lens. So you have to know the actual focal length of each lens.

    Dave.

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    Re: focusing techcamera with distometre

    Jack:

    Thank you for info. I just ordered my RM3Di and am trying to learn about it as much as possible while waiting.

    Jae

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