Camera Specifications computing focal length and f/#

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Discussion Overview

The discussion revolves around calculating the focal length and f-number (f/#) of a narrow field of view camera based on its specifications, including IFOV, FOV, resolution, and sensor characteristics. Participants explore the relationships between these parameters and the implications for camera design, with a focus on theoretical calculations and assumptions.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculates a focal length of 6.167E5 mm and an f/# of 1.6E4 using the formulas f/# = Focal Length / Aperture and Focal Length = Aperture / (2 * tan(IFOV).
  • Another participant requests clarification on the units of the field of view (FOV) and additional details about the lens or product specifications.
  • A participant notes that the provided specifications only include IFOV, FOV, and resolution at 1 km, suggesting that the supplier is responsible for the design of the lens.
  • One participant mentions that the resolution specification involves a lens and indicates a focal length of 400 mm if the pixel size is 9 microns, while also highlighting the complications of atmospheric distortion when imaging over long distances.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the calculations and specifications, with differing interpretations of the information provided. There is no consensus on the correctness of the initial calculations or the implications of the specifications.

Contextual Notes

Participants note limitations in the provided specifications, including the lack of clarity on whether the FOV is in degrees or another unit, and the potential impact of atmospheric distortion on resolution at long distances.

thiirane
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So I have come across a specification of a narrow field of view camera. The specification states
IFOV=30 microrad
FOV=2x2
resolution=<.1m at 1 km

If I assume a 1K sensor at 9micron pitch and an aperture = 3.7cm

I have resolution at .013 m

Chip size = 9.2mm

Focal length is 6.167E5mm?? can this be right? Also f/#=1.6E4

Do I have the formulas correct

f/#=Focal Length/Aperture

Focal Length=Aperture/2*tan(IFOV)
 
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Can you provide additional information- for example, the field of view = 2x2 what- radians, degrees, other? Any specific information on the lens?

Alternatively, do you have a product ID/name?
 
Hi Andy,

Actually the only thing specified is the IFOV, FOV and resolution at 1Km I think it is up to the supplier to design the rest. FOV is degrees. I assumed a sensor 1K sensor at 9 microns.
 
It's still not entirely clear- are you specifying a sensor, a lens, or an integrated sensor+lens? The IFOV and FOV specs define the sensor array size (I also got a 1k x 1k array), but the resolution spec involves a lens (which will operate at f/15 at a magnification of 1*10^-6, according the spec and assuming you are using visible light), and combining everything indicates a 400mm focal length lens, if the pixel size is 9um.

Note- imaging over 1 km distance is complicated by atmospheric distortion, you are unlikely to meet your resolution spec unless your application is able to avoid this. Some friendly advice- providing the OP specs to a supplier will result in an irritated supplier.
 

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