Barnard Microsystems Limited

We are taking the opportunity on our travels to test the capabilities of various cameras, in this section the Nikon D40X, and high performance lenses, in applications in which the photographs are taken from a moving platform.

• The Nikon DSLR
• Camera calibration
• Camera and lens setup
• Photographs from a moving train
• Conclusions

We test a Nikon D40X body and a Nikon AF-S VR 70 - 300mm f/4.5-5.6G IF ED Zoom Nikkor lens, as shown below. The ISO value was set at the highest supported value of 1,600 and the shutter speed was set to the fastest we can using the " S" setting for shutter speed priority. The large area lens should be able to collect a decent amount of light. The camera has a Hoya UV filter in front of the zoom telephoto lens to reduce glare.

The Nikon D40X camera body plus zoom telephoto lens with a focal length from 70 mm to 300 mm.

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The front of the camera lens was measured to be 4.024 m from the tape measure shown above. The field of view at the tape measure is 314 mm. From this we calculate the viewing angle for the lens set at a maximum zoom of 300 mm to be 4.4686 degrees. We calculate the width of the CCD from the following expression:

The width of the CCD imager is calculated to be 23.4 mm, which is not far from the data sheet value of 23.6 mm.

For a Nikon D40X DSLR camera as shown above:

• in an aircraft travelling at 30,000 feet (= 9,144 m) above ground level

• having a CCD imager supporting 3,872 pixels in the direction of travel

• with a shutter speed of 1/1,000 second

• with a CCD imager that is 35.1 mm wide in the direction of travel

• with the zoom telephoto lens set at a maximum focal length of 300 mm

we calculate an aircraft speed that would cause the image to be blurred by one pixel to be 184.2 m/s = 663 kph.

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Setting the Vibration Reduction system

The Nikon second generation vibration reduction (VR-II) system allows the user to set the shutter speed 4 stops lower than would be the case were this capability not used. The shutter speeds supported by the D40X are as follows:

• 1 / 100 second
• 1 / 125 second
• 1 / 160 second
• 1 / 200 second
• 1 / 250 second
• 1 / 320 second
• 1 / 400 second
• 1 / 500 second
• 1 / 640 second
• 1 / 800 second
• 1 / 1,000 second
• 1 / 1,250 second
• 1 / 1,600 second
• 1 / 2,000 second
• 1 / 2,500 second
• 1 / 3,200 second
• 1 / 4,000 second

On the AF-S VR-II Zoom lens used, shown above, one needs to set the vibration reduction. This is performed by:

1. setting the VR switch shown above to the ON position
2. setting the model selector from NORMAL to ACTIVE if filming from a moving vehicle.

Remember to turn the VR switch to the OFF position before turning the camera OFF

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These photographs were taken from the 08:35 train from Waterloo Station in London to Weymouth on Wednesday 7th November, 2007, using the Nikon D40X digital SLR camera with the 70 - 300 mm zoom lens.

This is a much clearer picture than that achieved using the Canon Powershot G9

Magnification of part of the image of the aerials above the Secret Intelligence Service building at Vauxall Cross, followed by the use of Auto Levels and Auto Contrast in Adobe Photoshop

Magnification of some parts of the photograph, taken from the moving train, of the aerials and other items on the roof of the Secret Intelligence Service building at Vauxhall Cross in south London.

Reflections from windows are a problem. Apparently, the polarised reflections from diectric surfaces, such as galss surfaces, can be reduced through the use of a circular polarizer in front of the lens.

Struggling with the imaging of nearby objects...

The reflections from the car windows really are a problem...

Struggling to get a decent image as we race through Farnborough station.

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• Progress is being made. The Nikon D40X with the high performance AF-S 70 - 300 mm zoom lens, perhaps not surprisingly, is giving better images from a moving platform than were obtained through the use of the Canon PowerShot G9.
• The ISO setting needs to be at the maximum value of 1,600, rather than having it set at AUTO, as was for the above photographs. Thanks to Dominic Brady for pointing this out to us. This high ISO setting, rather than the ISO setting selected automatically by the camera, will enable us to use a faster shutter speed and hopefully enable us to reduce the blurring that is still quite evident in many of the photographs.
• We need to use a circular polariser in front of the lens to reduce the level of relections from windows.

The reduction in glare from a window that occurs when a circular polarizer is used in front of the lens.

Above and below from the Hoya web site catalog http://www.hoyafilter.com/pdf/HOYACatalog.pdf

Description of Hoya 72mm SHMC PRO-1 Circular Polarizer Filter

Hoya 72mm SHMC PRO-1 Filter offer revolutionary performance in light transmission and color balance. Hoya 72mm SHMC PRO-1 has 12 layers of Super Multicoating are applied to the surfaces of the Skylight 1B and UV(0) models, which produces SHMC PRO-1 Filter an average transmission of 99.7%. Coupled with maximum surface precision, this allows Hoya 72mm Circular Polarizer Filter increased resistance to flare and stunning images can be recorded at wide apertures without compromising the performance of your lenses. Hoya 72mm SHMC PRO-1 ultra thin Circular Polarising filters have seven layers of Multicoating applied to their rear surface to eliminate internal reflections and ghosting. Hoya 72mm has Advanced thin selective film is used to guarantee perfectly polarised light with neutral color balance. Hoya 72mm Filter slim profile of just 5 mm avoids any vignetting problems and makes them ideal for use with wide angle lenses. Hoya 72mm SHMC PRO-1 Filter is no front female thread, but they do accept our push-on lens caps. HOYA Super HMC filters will appeal to the most demanding of photographers who require the ultimate in performance.

CIRCULAR POLARISING

The light rays which are reflected by any surface become polarized and Hoya 72mm Filter are used to select which light rays enter your camera lens. PL (Linear Polarizing) and PL-CIR ( Circular Polarizing ) filters have the same effect, but it is important that you choose the correct version for your camera . Hoya 72mm Filter allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc. Hoya 72mm Circular Polarizer Filter also enable colors to become more saturated and appear clearer, with better contrast. This effect is often used to increase the contrast and saturation in blue skies and white clouds. HOYA's polarizing filters do not affect the overall color balance of a shot.

from the http://www.microglobe.co.uk web site

Above: Photographs of a folded plastic bag on top of a Photon thermal imaging camera advertisement. On the left we have the circular polariser at 90 degrees to the optimum angle. On the right we have rotated the polariser to its optimum angle.

• We need to bring a GPS unit with us to enable us to also record the train speed for each photograph.
• Use of a circular polarizer will also reduce the amount of light entering the camera. We may need to use a larger f/2.8 lens as shown next to pick up sufficient light from a dimly lit room in order to detect people in the room.

The above photograph and some of the following text from http://www.photozone.de/8Reviews/lenses/nikkor_70200_28vr/index.htm

One way to improve things further is to use a fast zoom lens with a low f number, such as the Nikon AF-S 70-200mm f/2.8G IF-ED VR zoom lens shown above. The AF-S 70-200mm VR is the first high-speed Nikkor tele-zoom with a VR (Vibration Reduction) mechanism with an efficiency equivalent to 3 f-stops. The lens offers two VR modes - a " normal" mode for most situations inc. static scenes, object tracking as well as monopod shots whereas the 2nd " active" mode to compensate more pronounced vibrations (e.g. when shooting from a moving vehicle). Thanks an AF-S drive (Silent Wave Motor) the AF operations are nearly silent and extremely fast. The main problem with this lens is the weight: 1.470 kg. Thanks to Dominic Brady for pointing out the advantages of using this high performance lens.

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