Polarizers/ND Filters & Automatic Light-based Speed Adjustment

I use filters to help reduce glare off water surfaces mapping along the coastline, so they slow the shutter speed down pretty significantly. I have manually flown quite a few missions in the DJI Go App, with great results.

I've started using Map Pilot to help ensure proper overlap and control image capture, but I've been getting serious slow down of my P3P by the app - sometime flying less than 1m/s, which just destroys battery life and gets next to nothing done. Even though maximum speed is set to near 10m/s.

Could the drastic speed adjustment by the app be being caused by the filters? What are the factors that can contribute to such steep intervention by the app?

Timothy Thwaites March 25, 2016 03:33

Official comment

We recommend the use of a circular polarizing filter but not and ND filters due to the issue you are describing. A polarizer will typically cut 15-20% of the available light which is a reasonable trade for not having the strong reflections but an ND filter will likely cut it universally and too much. Even the ND8 (3-stops) is going to increase your exposure time by a factor of 8.

The slow down of the aircraft is there to keep the images from becoming unusably smeared. Keep an eye on that Motion Blur number that gets color coded. We attempt to slow the aircraft down to the point that that value does stays white, not yellow or red which indicate too much smear.

If you don't want Map Pilot to make that call for you you can turn it off the "Slow Aircraft According to Light Conditions" setting.

Jay March 25, 2016 15:53

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2 comments

Thanks, that's kind of what I figured.

I understand the purpose, it just seemed excessive, even when ground smear estimates were down to even 0.5cm, the craft wouldn't crawl faster than about 2m/s.

I removed the ND and went to the straight circular polarizer, as you'd said, and had some better luck, but was still slow at times. Was fighting major headwind though, so have to test further in better conditions.

Thanks for pointing me to that setting, so I can have that choice!

Timothy Thwaites March 25, 2016 16:04 0 votes