|Photographs from a moving train: Part 2||- Aerial Photo 2|
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.
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.
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:
we calculate an aircraft speed that would cause the image to be blurred by one pixel to be 184.2 m/s = 663 kph.
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:
On the AF-S VR-II Zoom lens used, shown above, one needs to set the vibration reduction. This is performed by:
Remember to turn the VR switch to the OFF position before turning the camera OFF
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.
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.
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.
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.