How can I stitch photos in Hugin if the lens focal length is unknown?
Asked 3/19/2016
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I’m trying to stitch some Apollo 16 images into a panorama in Hugin, but I don’t know the lens focal length. Can Hugin work without that information, or do I need to enter a field of view or lens details manually? If so, what values should I use for Apollo mission still photos?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
7
No, you need to enter either the field of view (FOV), or the lens and crop factor information.
Luckily for you, for the Apollo mission images, the camera and lens information is well documented. The still photos taken by the lunar module team were taken exclusively by Hasselblad cameras modified to accept 70 mm film backs (56mm frame size, 1:1 image ratio), with 60mm Zeiss Metric lenses.
Calculating the angle of view, we get 50° horizontal angle of view:
$$ 2\arctan\frac{\omega}{2f} = 2\arctan\frac{56}{2\times60} = 50º $$
Alternately, you can just enter the focal length of the lens (60 mm) and the crop factor of the 70 mm Hasselblad. The crop factor is with respect to the diagonal distance of 35 mm film camera, which is 43.3 mm. The diagonal distance of 1:1 ratio 70 mm film is just 1.414 * 56 = 79 mm. So the crop factor is 43.3 / 99 = 0.547.
Taking a few of the Apollo 16 images you linked to on Flickr, and plugging in the 60mm lens, 0.437 crop factor into Hugin1, here is the stitched image I created (without any other editing or adjustments):
Note 1: The original version of this answer used a frame width of 70mm for 70mm film. This was wrong. 70mm film used in Hasselblads had a 56mm image height. The "6x6" format (1:1 aspect ratio) is therefore 56mm x 56mm. As edited, the crop factor for 70mm 6x6 should be 0.547. However, when originally creating the Hugin image in this answer, I used 0.437 (as I had wrongly calculated at the time).
Originally by user11924. Source · Licensed CC BY-SA 4.0
user11924
10y ago
0
Generated from our catalog & community — verify before relying on it.
Hugin needs lens information to start correctly: either the field of view, or the focal length plus crop factor/sensor size. So you can’t fully avoid supplying that data.
For Apollo mission still images, the good news is that the camera setup is documented. The lunar module still photos were taken with modified Hasselblad cameras using 70 mm film backs (about 56 mm image width, square format) and 60 mm Zeiss lenses.
That means you can enter either:
- focal length: 60 mm
- film/image width: 56 mm (square frame)
Or use the horizontal angle of view directly, which is about 50°:
2 × arctan(56 / (2 × 60)) ≈ 50°
So in Hugin, use the known 60 mm lens and the correct film/sensor dimensions, or enter roughly 50° horizontal FOV. That should give Hugin the information it needs to stitch the panorama properly.
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