VIEWING IMAGES

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I prefer to use colour slides rather than colour prints. This is mainly due to the ability to view the 'positive' images directly on a lightbox. They can be easily projected onto large screens and can be digitally scanned to produce colour prints.

I have a Leitz Pradovit Colour 250. This is an old but high quality projector which has an excellent lens, the Colorplan 1:2.5/90mm, which produces sharp images.

I am fortunate to have a good stereo microscope to view slides on a lightbox. The microscope has variable magnification which enables areas of interest to be viewed in detail. It also provides a good stand-off from the slide, which you don't get with a single eye magnifier or lupe. The stereo microscope provides a fantastic view of the slides and you can almost imagine you are viewing the scenes directly through some incredible binoculars. On a cloudy wet night this approach allows you to view the scenes in comfort and with greater sense of realism than can be achieved with a colour print. A photo through the microscope eyepiece is shown opposite. Who needs a telescope!

A useful trick is to cover the lightbox with a piece of black card with a hole cut in it to take the slide. This removes stray light from entering the microscope and improves the viewing.

3. Slide Scanner

A slide scanner was the next 'must have' item after the lightbox and microscope. I bought an Acer Scanwit 2720S, which can scan at resolutions of 2700 dpi (dots per inch). This can achieve a very high level of detail in a scanned image and is more than adequate for A4 size colour printouts.

The software provided with the scanner is Miraphoto. I have also bought Vuescan software, which allows greater control of the scanning process.

The images below show the capability of a slide scanner. Image 1, is of Cassiopeia taken with a 200mmm f4 lens. The slide is scanned at 2700 dpi resolution. The small area which is boxed, is shown in image 2. This is further expanded in images 3, 4 and 5 to show the individual pixels.

 

1. Cassiopeia Image used for zooming in below

2. View of small box from above right

3. Zoomed in

4. ..and again

5. .. and again

 

A 200 mm lens has a field of view of 7.2 x 10.3 degrees. A 35mm slide measures 24 x 36 mm. With 2700 pixels per inch, this gives a resolution of approximately 10 arc seconds per pixel.

Image 5 shows the quality of both the tracking accuracy when the photo was taken and the scanning performance. This image was resampled in Photoshop to increase the image size from 19 x 19 pixels to 150 x 150 pixels. The result is show in image 6 below. The resampling does manage to improve the separation between the central trio of stars. The tracking accuracy is probably 10 arc seconds or better.

6. Image 5 above resized/resampled in Photoshop

 

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