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[OM] Re: Small Format Aerial Photography

Subject: [OM] Re: Small Format Aerial Photography
From: Petri Nygren <petri.nygren@xxxxxxxxxxxxx>
Date: Thu, 19 Aug 1999 09:26:51 +0300

Jerry,

Aerial photographic survey of landforms - sounds like you are aiming to
vertical photography. You should be anyway because you won´t achieve much
just shooting through open window. You´d better build a mount for your
camera which is adjustable in tip, tilt and drift. Fix the mount just
outside the door or through the floor in co-pilots feet so that you can
adjust it. Simple bubble level is sufficent for tip and tilt adjustment.
Align the camera so that the long side of the frame is in flying direction.

To decide the lens/film combination go and take a few photos using your
50mm lens from 500ft(over inhabitated area!), 1000ft, 1500ft and 2000ft AGL
and so on in 500ft steps as high as you comfortably get with your aircraft.
Use 1/250 or faster and make sure the vibration doesn´t turn the focus ring
off the infinity (tape is often used for this).

You´ll be flying low and slow so I wouldn´t choose slower film than ISO
100. I am not familiar with Ektachrome IR but at least Kodak Aerochrome
Infrared 2443 is difficult to expose and filtrate for consistent results.
Very often the IR sensitivity is too high for low altitude work (it was
designed for U-2:s) requiring both yellow(etc.) and IR attenuating filter.
Results are red alright but you often loose the nyances from dark red to
pink which are especially useful for differentiating deciduous trees. 

Now the decision of the lens/film/height(=scale) really is dependent of the
objectives; what do you want to see from the images? Choose the highest
altitude you get acceptable resolution from. This way you minimize the
number of pictures, which makes comparisons easier.

I am sure you have a GPS in Tootie Mae. Use it to get your photos every
time from the same spot. It is surprising but navigation is the single
biggest problem in vertical photography after atmospheric haze. With little
creativity in electronics you can combine the GPS with camera so that you
get GPS to release camera automatically -flash port can be used for this.
If you are able to position your photos accurately enough, you can plan for
creating a sequence of 800verlapping frames for stereoscopic interpretation.

Do your flight planning based on a map; what kind of area you need to
cover, what is you photo scale(=flying height) and what is the field of
view of your lens perpendicular to the flying direction. 
Measure the coordinates for the photos, type them to GPS and go flying.

And oh yes I do recommend a navigator/camera operator if you want to fly
the plane. There´s _a lot_ happening in short period of time. Do not
program GPS if you fly!


Good luck,

Petri Nygren





>
>"W. J. Liles" wrote:
>> 
>> <snip>
>I want to
>use Tootie Mae for aerial photographic survey of landforms.  In
>Louisiana that means old stream courses, rivers, bayous, lakes, swamps
>and forests.  Many of these features are quite subtle.  Most of the work
>will be with the Geology and Biology departments of the local
>university.  I would appreciate any advice on films, lenses, techniques,
>etc.  I have an OM-1n and 2s with lenses from 24mm to 135mm.
>
>The airplane can fly low and slow (stall at 30mph) with the doors off
>but is rather cozy with two.
>





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