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Ladies and Gents,
Question, I notice that when I try to stitch images from my Mamiya 645ZD the software wants to use 0.66 scaling factor. Correct me if Im wrong, but but the sensor scaling in the 645ZD is actually 1.16 , this is info we have gleaned form mamiya themselves. What is the reason for the 0.66 scaling. I routinely go in and switch the scaling to "not found" and write in 1.16 myself and get better RMS values.Ive realized that the scaling factor set the image to a 35mm equivalent, Im not sure why you would want to with this camera.......
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The scaling factor is used to determine the 35 mm focal length equivalent of your picture.
AFAIK the 645ZD has a 36x48mm sensor size (this is 1.5x more than the 24x36mm equivalent); the 0.66 scale factor (= 1/1.5) seems correct to me.
More info here.
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I still dont understand why we have to try to equate a 6:4.5 sensor to a 2:3 sensor,....the scaling I was under the impression was to understand what the equivalent focal length was for that system due the the scaling of the sensor in that system, (i.e. Nikon D80 is 1.5 so a 50mm is a 75mm), So we could adjust the distortion of the image accordingly to allow for optimal overlap and stitching. On a Mamiya 654ZD an 80mm lens is not a 52.8 mm lens (80x.66) its a 92.8mm lens,..Adjusting the 645ZD sensor to a 35mm equivalent would then give you improper distortion relative to the system...no?
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The D80 has a 15.8 x 23.6mm sensor (0.66 of the 24x36 equivalent) so the scale factor for the D80 is 1.5 (= 1/0.66) the same rule shoud be applicable for the Mamiya with its 0.66 scale factor.
CCompton wrote:
On a Mamiya 654ZD an 80mm lens is not a 52.8 mm lens (80x.66) its a 92.8mm lens,..
Who says that ?
According to the specification it is a 50mm lens equivalent as expected !
Last edited by Flash (2009-05-22 20:46:14)
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Again,...the sensor factors in, only that it changes the effective focal length of the lens and therefore changes the distortion factor of the overlapping images.....so if you were to adjust the mamiya images so that they are a 35mm equivalent you are essentially trying to adjust an apple so that it compares to an orange....again ...On a Mamiya 654ZD an 80mm lens is not a 52.8 mm lens (80x.66) its a 92.8mm lens (80 x 1.16).
The scaling conversion stated by mamiya is that of 1.16 for lens equivalence in the medium format system, not 35mm. That's the whole problem, 0.66 is inherently wrong because its not a 2:3 aspect and its not a 35mm system. A .66 distortion dosent make a 645 image 24x36 it makes it 23.76 x 31.68 whsich is still a 6:4.5 aspect , the math doesnt make sense..........there is no fathomable need in my mind why we need a 35mm equivalent when all that is needed is to adjust the image distortion relative to the camera system being used.
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The aspect ratio is not important : you can have 4:3, 2:3 or 6:17, it is not important. What is important is the FOV : field of view, in degree ( radial one, horizontal one or vertical one, we don't care if the sensor database always use the same reference ).
So the sensor scale is what allow us to convert a focal length given in EXIF into a 35mm equivalent. I doesn't seem really useful but in fact, it is.
In EXIF metadata, you can always found the focal length and sometimes a secondary focal length in 35 mm ( canon recorded them ). With our sensor scale database, we are now able to have all cameras expressing their quality in the same reference, le 35mm reference. It simplify all the code behind and will allow to make comparison of lens distortion for example between two different camera / sensor scale.
One note about lens and sensor scale. If you have nikon D300, a standard 200mm put on it will be in fact a 300mm. Now, there are some lenses which focal length is already expressed with that sensor scale applied. Nikon don't do that, but perhaps Mamiya does. That's a real problem in fact, because if you say a 50mm for a 35mm cover that angle, how to find the same angle with a 6:4.5 sensor ? The best would have been to put the angle in degree on the lens, but that's not the case. Anyway.
So Mamiya case : the sensor scale should be 0.66 because the sensor is bigger than the 24x36 with 0.66 factor. Now is the 80mm really a 80mm in the 6:4.5 reference or was this focal length expressed already in 35mm equivalent. That is the real question. Second question : what focal length is recorded in the EXIF for such an image ?
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Due to cost I am using manual lenses on the ZD body, so there is no exif data. therefore I put in the focal length manually. In the case of the medium format system itself the sensor is smaller than the actual 2.25" film plane so the focal length of the lense changes by a factor of 1.16. So do you think that should be added in to the mix as the "conversion factor ". Or should i do that multiplier first ( if im using a 35mm x 1.16 lens then its 40.6) and then put that in as the focal length to be multiplied by 0.66....?
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There is some confusion I'm afraid...
From an optical point of vue a 80mm lens will be always a 80mm lens (and will be never a 92.8mm or a 50mm)
However its FOV will change depending on the film format or the sensor size used.
As an example: take one picture with your Mamiya 654ZD and a 80mm lens...
In order to be able to shoot the 'same' picture in terms of FOV with another film (sensor) format; you'll need a 80x1.16 = 92.8mm lens with a true 4.5x6 (41.5x56mm) format or a 80x0.66= 52.8mm lens with a 24x36mm format.
This is the 'scale factor' or 'crop factor'.
So a 80mm on the 654ZD, acts as a 92.8mm on a 654 or as a 52.8mm on a Full Frame.
That's how we are able to compare 'apples' and 'oranges' in terms of film (sensor) format.
As Autopano uses the 24x36mm equivalent format as 'reference', you shoud consider the scale factor of 0.66 for your lens to be compatible with this reference. (This is the same as considering/comparing temperatures in Fahrenheit to Celsius - nothing more, nothing less)
You can check the FOV angles for your lenses and films (sensors) formats with the Rui Salgueiro's field-of-view calculator.
Hope this helps.
Last edited by Flash (2009-05-23 00:05:16)
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