RE: "John Henshall's Chip Shop" - Review der RD-175

#1 von fwiesenberg , 15.01.2011 15:34

Dieser Bericht von John Henshall zur MINOLTA RD-175 alias AGFA ACTION CAM erschien als Beitrag "John Henshall's Chip Shop" erstmals in der Mai 1996-Ausgabe des Magazins "The Photographer".

Ich finde ihn als zeit- und technikgeschichtliches Dokument so interessant, daß ich ihn folgend ausnahmsweise komplett zitiere:

Delightful to use and not too expensive.
by John Henshall


The Minolta RD-175 digital camera

Although the digital market is now being flooded with low resolution cameras, the number of medium and high resolution cameras being launched is still only a trickle. The Minolta RD-175, also known as the Agfa ActionCam, is therefore a welcome addition to this small stream. The only difference between the Minolta and Agfa versions is the name on the camera and the opening screen of the software.

Most medium resolution digital cameras avoid re-inventing the wheel by adapting existing SLR camera bodies, originally designed to use film. The trick is to pack state-of-the-art technology into and around such bodies, turning them digital while retaining their hand-held portability, independence and ease of operation. In effect, such devices are highly sophisticated portable computers with a lens. They use the very latest miniature technology - right at the frontier of possibility - so it's hardly surprising that high prices are involved. The RD-175/ActionCam uses the established Minolta Dynax 500Si body.

There is no doubt that high prices have been restricting general market acceptance, except for special applications. It is difficult to get prices down if the camera uses a proprietary CCD chip, for such chips cannot be used in other products, to recover development costs. They are produced in small quantities, which also keeps costs high.

Low resolution digital cameras, on the other hand, use video camcorder CCDs. These are already produced in large quantities and development costs have been recovered elsewhere. This reduces CCD prices to the point at which digital cameras can be made for a few hundred pounds.

Unfortunately, such inexpensive CCDs cannot produce even a 10 by 8 enlargement and many low resolution cameras make matters even worse by using excessive compression. Good 640x480 pixel images are suitable for reproduction up to about 5.5x4cm at 300 pixels per inch in a high quality journal (200 line screen). You might get away with a little larger but not much - unless, like Minolta, you have a real brain-wave backed up with real technological skills.

Instead of one CCD, Minolta use three in their new camera. Not red, green and blue, as in professional video cameras, but two green and one striped (with microscopic filter elements) red and blue. A dichroic prism block splits the image-making light into the required components for each sensor.

Why two green CCDs? The human eye's sensitivity and resolving power is greater in the green region of the spectrum than in the red and blue. Two green chips make the camera almost twice as sensitive, with an EI equivalent to film of ISO800. But the really clever part is that Minolta quadruple the CCDs basic resolution by offsetting the two green chips physically, by a distance equivalent to the size of half a pixel, in both the horizontal and vertical planes. The two slightly different green signals produced by this spatial offset are used to interpolate a green channel with a resolution four times that of an individual CCD. Importantly, this means that Minolta can use CCDs designed for video cameras - low cost, low resolution - to achieve much higher apparent resolution than they possess individually. Full marks to Minolta's Takatsuki Laboratory scientists for this imaginative solution.

A disadvantage of using video CCDs is their small physical size when compared with a frame of 35mm film. The half-inch video chips Minolta use have 768x494 pixels and an imaging area of 6.4x4.8mm - you could pack 25 of them into the area of a piece of 35mm film. Relay optics are used to 'shrink down' the image size produced by Minolta's normal 35mm SLR lenses to 16x12mm. This means that the focal length of lenses used on RD-175 are effectively doubled and the widest effective aperture reduced to f6.7. But the small size of the CCDs turns to an advantage when it comes to cramming a complete prism block and relay lens inside a SLR camera body.


The PC Card slots neatly into the base of the camera


Images are transferred in raw form to a PCMCIA (PC card) Hard Disc Drive inside the camera. This takes just over two seconds per image, during which time no further exposure can be made. A raw image is about 1.2MB, so a 131MB drive can hold 114 exposures. Basic exposure details (f-stop, shutter speed and date) are recorded with each image.

The camera is connected to a computer (Macintosh only at the moment) via a SCSI-2 interface which has yet another type of connector, so take good care of the supplied cable. Acquire software is supplied both as an Adobe Photoshop plug-in and as a stand-alone utility. Unfortunately, the software is very basic when compared with acquire modules from other manufacturers. The thumb-nail images cannot be increased in size; the image sharpening is fixed and it is only possible to download one image at a time. This is a major waste of your valuable time. It takes almost two hours of constant attention to acquire and save all 114 images from the camera's PC Card to a PowerMac (fifty seconds each on an 8100) or even longer on an older Mac. It took one minute forty eight seconds per image on a Quadra 950 - over four hours to acquire and save a full PC Card. The lengthy acquire times are because the images are interpolated, converted from the rectangular pixels of the NTSC chips to square pixels and have other image processing applied in your computer during acquisition. Finished images are 1528x1146 pixels - just over 5MB each. The camera is an eight-bit-per-channel device, though thanks to superb A-to-D conversion within the camera this is not evident in the images.

The basic nature of the software lets down a great hardware product. Fortunately, software upgrades are easy to distribute via the Internet. Minolta should get the Agfa software experts in Mortsel, Belgium, to re-write the acquire module for them as a matter of urgency.

When you first pick up the camera, impressions are very positive. The camera is well balanced with a low centre of gravity. Anyone who has had experience of handling digital SLRs would find this camera very compact and, at 900 grams without lens, light in weight.


The best way to describe picture quality is by showing it. All the accompanying pictures - except the product shots and masthead - were taken with the RD-175. (The product shots (of the RD-175 camera) were taken with a Kodak DCS200.)

One important criticism is the inability to alter the ISO equivalence from 800, except by using exposure compensation. A neutral density filter is some help, but it is annoying to have to work with the resultant dark viewfinder image. A variant with more buffer memory, to enable a burst of images to be taken, would be a big advantage. Without this, the camera is useless for photojournalism - one of the main potential uses of this kind of camera. You can't capture much of the "Action" with a "Cam"era which has a two second delay between shots.


Enlarged to three times the theoretical maximum, this section shows how well the RD-175/ActionCam handles specular highlights. The electronic edge around the badge is added during image acquisition from the camera. It would be nice if this feature could be turned off as sharpening for repro should be a once-only process.


The price has not been established by Minolta UK (contact Wayne Snell +44 (0)1908 200400). Agfa (contact Paresh Patel +44 (0)181 231 4141) have a list price of £8,500 but expect a street price of around £7,500 - or less. Bear in mind that this price is a "system" price which includes the 24-85mm AF zoom, 131MB PC Card, Lithium Ion battery (a standard camcorder battery - spares widely available), charger and the acquire software. Many of these items are extras from other manufacturers of products in this class, so compare prices very carefully.

If you want tomorrow's technology today, you have to pay for it. This Minolta/Agfa offering is a delight to use and considerably cheaper than the present competition. But the market will really open up only when someone produces a digital SLR which is much cheaper still. Sell 'em cheap and you'll sell 'em fast - to everyone.


This review first appeared as "John Henshall's Chip Shop" in "The Photographer" magazine, May 1996.
This document is Copyright © 1996 John Henshall. All rights reserved.[/quote]


Grüße aus dem Westen der Republik!


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