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Author Topic: fixed focal length ?  (Read 12024 times)

jerry

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fixed focal length ?
« on: September 03, 2013, 01:52:57 PM »
Hi there,
i plan a little multicam rig for faceshots, my idea are 6 cannon eos600D but i ask me is it usefull to buy a objectiv with fixed focal length? if yes: 35mm or 50mm??  or should i use standard objectiv  18-55mm??

thanks for answer
J.

FoodMan

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Re: fixed focal length ?
« Reply #1 on: September 03, 2013, 02:20:34 PM »
well a fixed lens is by definition always better..

Lee from Infinite uses 50 mm lenses

f/

jerry

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Re: fixed focal length ?
« Reply #2 on: September 03, 2013, 02:43:49 PM »
cool thanks!

is breeze solutions usefull? http://www.breezesys.com/ to handle multible cameras? any experience??

J.

FoodMan

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Re: fixed focal length ?
« Reply #3 on: September 03, 2013, 03:17:08 PM »
well this might work.. but $129 per camera.. Ask Lee, I think he uses something different :P

Alexey Pasumansky

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Re: fixed focal length ?
« Reply #4 on: September 03, 2013, 03:21:18 PM »
Hello Jerry,

It's better to use fixed lens (or at least zoom-lens set to their min/max position) for the same camera type, since it allows PhotoScan to perform grouped calibration for such cameras. Otherwise, it's necessary to use split calibration mode in Camera Calibration dialog.
Best regards,
Alexey Pasumansky,
Agisoft LLC

Andrew

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Re: fixed focal length ?
« Reply #5 on: September 03, 2013, 11:07:35 PM »
Logic suggests its best to stick to fixed lens or min/max zoom, though I wonder: does splitting calibration settings for photos shot at different focal lengths result in noticeably worse reconstruction?

Real world example: when capturing a monument, I can shoot it from most directions from the same distance @18mm, but there's an obstacle from one side, preventing me from shooting up close - am I better off shooting still @18mm with monument being rather small in frame, or can I zoom in and not worry about different calibration params for that photo?

-Andrew

David Cockey

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Re: fixed focal length ?
« Reply #6 on: September 04, 2013, 02:11:06 AM »
I've had success using "blue tape" to hold a zoom lens in one position while taking a set of photos.

I also usually turn off auto-focus and tape the focus ring in one position for all photos taken at approximately the same distance from the subject..

Alexey Pasumansky

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Re: fixed focal length ?
« Reply #7 on: September 04, 2013, 11:27:36 AM »
Hello Andrew,

Minimal number of calibration groups produces more stable result. But in case of variable focal length across we recommend to split each group (up to single camera) for every intermediate value of the focal length of zoom lens.
Best regards,
Alexey Pasumansky,
Agisoft LLC

Claude

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Re: fixed focal length ?
« Reply #8 on: September 04, 2013, 12:29:59 PM »
I just wonder...

I have small rig of 12 cameras. If I setup all cameras to the same focus i will produce better result in mesh reconstruction than different focus on each camera.
I wonder if it benefit to setup all camera exactly the same?

Wishgranter

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Re: fixed focal length ?
« Reply #9 on: September 04, 2013, 01:07:32 PM »
Claude we use almost same focus and same lenses in our 111cam setup, its divided in 2 groups.....
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Claude

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Re: fixed focal length ?
« Reply #10 on: September 04, 2013, 04:04:16 PM »
Claude we use almost same focus and same lenses in our 111cam setup, its divided in 2 groups.....

So  you think it is worth try to set rig to have it exactly the same?
I could manually set all focus at eg. 1.5 meter and move camera with tripod to get good focus on model. It is a bit harder than just focus separate cameras on model. I wander if this rig setup give better mesh?

Wishgranter

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Re: fixed focal length ?
« Reply #11 on: September 04, 2013, 04:24:30 PM »
as i say. 111cams is divided to 2 groups, every group have same lens and we use prime lenses.....
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Claude

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Re: fixed focal length ?
« Reply #12 on: September 04, 2013, 04:49:32 PM »
as i say. 111cams is divided to 2 groups, every group have same lens and we use prime lenses.....
Thanks,

I will try to do it like that. I just wonder if fixed rig will work with different heads, but maybe sizes of heads are not so differ from each other.


jerry

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Re: fixed focal length ?
« Reply #13 on: September 05, 2013, 11:37:13 AM »
whats the software to sync my 6 cam rig and send the pictures to my workstation?
whats the best flashes i should use?

holy cow thanks for answer!!
J.

meshmaster

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Re: fixed focal length ?
« Reply #14 on: September 05, 2013, 02:04:43 PM »
whats the software to sync my 6 cam rig and send the pictures to my workstation?
whats the best flashes i should use?

holy cow thanks for answer!!
J.

Suggestion to the Agisoft team....  Since this question gets asked so often here on this forum, I think it might be a good idea to start an FAQ page where answers to the questions could be easily located and addressed.

Cheers,

Joe