Products affected
Trimble® UX5 aerial imaging rover
Summary
How do I select ISO setting and shutter speed on a SONY A7R camera to obtain the best pictures?
Answer
ISO
● The ISO is set automatically: the camera decides which ISO value to choose, based on the incoming light from the scene.
● The base ISO is 100, the maximum ISO is 6400, using ⅓Ev increments. Note: The camera can theoretically go up to ISO 25600. The limit is set to 6400 to avoid noise and effects of noise reduction that lead to an unacceptable loss of image quality.
● You do not need to change the ISO range between different lenses.
Shutter Speed The shutter speed should be as slow as possible, to gather more light so that the ISO (and resulting noise) can be kept to a minimum.
Since shutter speed is the only means available to counteract (forward) motion blur, there is a practical lower limit to the shutter speed. The rule of thumb to prevent forward motion blur is that the forward motion of the camera over the ground during the exposure time should never exceed 0.75 * GSD.
Additionally, we use an absolute minimum shutter speed of 1/1000 regardless of GSD to minimize other kinds of motion blur, when forward motion blur is not a risk factor in case of coarse GSD.
Example 1
When using the 15 mm lens at 120 m AGL, meaning 3.8 cm GSD, we could in theory use 1/800 to prevent forward motion blur (the aircraft moves 2.9 cm over the ground during the exposure time of 1/800 of a second at the nominal cruise speed of 23 m/s, which is less than 0.75 * 3.8 cm), but we will resort to the minimum "safe" shutter speed of 1/1000 to minimize other forms of motion blur.
Example 2
When using the 15 mm lens at 75 m AGL, the forward motion during a millisecond long exposure time at the nominal cruise speed of 23 m/s is 2.3 cm, which is more than 0.75 * the GSD of 2.4 cm, so we need to choose a faster shutter speed. Following the 0.75 * GSD at 23 m/s, 1/1600 will do.
To simplify the decision, the software shows the minimum allowable shutter speed in the camera preparation screen of the preflight checklist, based on the above rules and the flight plan.
Note: The software always suggests the safest shutter speed. For example, it states 1/4000 as the minimum for the 35 mm lens at 75 m AGL while 1/3200 would suffice in calm and clear weather. You can always use a slightly different setting, taking into account weather and flight line orientation relative to the wind.
Related Information
For more information For more information visit http://trimble.com/knowledgecenter/ or contact your local Trimble Distribution Partner at http://dealerlocator.trimble.com/.
Source: http://mytrimbleprotected.com/knowledge/docushare/retrieve?handle=File-815694
