<p>Hey Keir, </p>
<p>Just thought I'd chime in on the point about the focal length changing during focusing on. </p>
<p>That isn't a function of the lens being a cine lens but rather the lens design being poor. That effect is called breathing. </p>
<p>Good lenses, master primes etc., don't breath. </p>
<p>Cheers, </p>
<p>Andrew</p>
<div class="gmail_quote">On 2011-07-17 11:42 PM, "Keir Mierle" <<a href="mailto:mierle@gmail.com">mierle@gmail.com</a>> wrote:<br type="attribution">> On Sun, Jul 17, 2011 at 4:59 PM, mindrones <<a href="mailto:mindrones@gmail.com">mindrones@gmail.com</a>> wrote:<br>
> <br>>> Hi all,<br>>><br>>> a couple of weeks ago me and Corrado Zacchi have shot some footage with<br>>> a HD CCD camera, to see if we could help providing some imagery not<br>>> affected by rolling shutter.<br>
> <br>> <br>>> Enrico Gusso has been so kind to lend us a Panasonic AJ-HDX900P<br>>> (<a href="https://panasonic.ca/english/broadcast/broadcast/hd/aj_hdx900.asp">https://panasonic.ca/english/broadcast/broadcast/hd/aj_hdx900.asp</a>) and<br>
>> Gianni Centonze helped on the capture part :)<br>>><br>>> <a href="http://download.blender.org/ftp/incoming/libmv/mindrones/">http://download.blender.org/ftp/incoming/libmv/mindrones/</a><br>> <br>
> <br>> Very cool!<br>> <br>> <br>>> Feel free to use this footage to test libmv integration as you like, and<br>>> please report any problems related to this footage, so that next time we<br>>> can shoot some better test.<br>
>><br>>><br>>> We were a bit in a hurry that day so we've done mistakes for sure, but<br>>> this was a first test to hear from libmv devs. Hopefully we'll do more<br>>> later.<br>>><br>
>> Some examples of mistakes to learn from:<br>>><br>>> * make sure the calibration pattern is *really* flat, taping the grid is<br>>> never enough flat (we didn't have time nor a place where to glue the<br>
>> grid, sorry)<br>>><br>> <br>> It's probably fine.<br>> <br>> <br>>> * as I've learned today chatting with Matthias: let the paper grid fill<br>>> the frame:<br>>><br>>> <MatthiasF> also, next time you shoot calibration, don't hesitate to<br>
>> have the paper fill the frame<br>>> <mindrones> you mean also borders going out?<br>>> <MatthiasF> yes<br>>> <MatthiasF> we detect the inner corners of the checkerboard<br>>> <MatthiasF> so you can have those corners at the corners of your frame<br>
>> <mindrones> oh crap! didn't know that!<br>>><br>>> * increase the shutter speed to reduce the motion blur (not always<br>>> possible in a real situation this is let to the director of photography<br>
>> to decide this parameter)<br>>><br>> <br>> The shutter speed doesn't change the calibration, so it should be fine to<br>> set this temporarily. However, it also works to just hold the calibration<br>
> grid still momentarily when waving it in front of the camera in a few<br>> positions.<br>> <br>> <br>>> * remember to remove any gain to avoid noisy grain (same as above)<br>>><br>>> * (to self) remember to check the iris more often, damn! :)<br>
>><br>>> * also, as seen in the camera specs, the sensor effective pixels are<br>>> 1280x720 and instead we've shot at 1080/25P, which means that the camera<br>>> does some image manipulation to pump the image to 1440x1080: next time,<br>
>> best shooting also at native resolution to check if this helps the tracking<br>>><br>>><br>>> As an interesting test that we had no time to make, very often, even on<br>>> cine lenses, while focusing you also end up varying the field of view,<br>
>> hence zooming a bit because of lenses mechanical and optical<br>>> imperfections. For this reason we didn't focus during these shots and<br>>> hence we had to choose a fixed focus distance, but this forced us to<br>
>> have unfocused parts, which I'm sure won't help the tracking much.<br>>><br>>> What to do in real situations when you have to control the focus? Will<br>>> libmv take in account this factor one day?<br>
>><br>> <br>> This is interesting. I didn't realize cine lenses vary the focal length with<br>> focus, but it makes sense. I suspect the calibration would still be good<br>> enough to work in practical cases.<br>
> <br>> There is also my autocalibration code which I am still working on.<br>> <br>> This is great stuff! Thanks for making a contribution. When I get back to<br>> the states, I'll check it out.<br>> <br>
> Keir<br>> <br>> <br>>><br>>> (Not to mention real zoom of course)<br>>><br>>><br>>> Regards,<br>>> Luca<br>>><br>>> _____________________________<br>>><br>>> <a href="http://www.mindrones.com">http://www.mindrones.com</a><br>
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>><br></div>