500mm f/8 RF Rokkor-X
The Minolta 500mm f/8 RF Rokkor-X. As you can see the lens design is much smaller than a traditional 500mm lens. It is much lighter also, at 635gm compared to 1.44kg for the traditional design 400mm f/5.6.

You've probably all been in that position....a great opportunity presents itself but your 200mm/300mm lens is too short to get the shot you really want. When using a teleconverter the image is not only too dark, the sharpness just isn't there. However, a Minolta manual focus telephoto lens in the range of 400mm - 600mm is not only rare, but frightfully expensive and heavy. Even non-Minolta lenses such as the Tokina, Sigma and Tamron 400mm f/5.6 lenses are heavy, and not inexpensive.

Well one alternative is the Minolta 500mm f/8 RF lens. The 500mm uses a catadioptric design to enable the 500mm focal length to be achieved in a smaller package. These lenses are often called 'mirror lenses' because they use mirrors as well as optical elements in their construction, as shown below:

A basic mirror lens design, showing the manner in which the optical path is bent.

Mirror lenses are very common on ebay, and can be quite inexpensive. Certainly there are Phoenix and Samyang brand lenses that can be had for the Minolta system for under $100 new. So why should you pay more for a second-hand Minolta lens? Well first of all, like with all things, you get what you pay for. Many of the mirror lenses available on the market and advertised as f/8 have a theoretical aperture of f/8, but a light transmission value that is actually lower than this figure. Additionally, they often exhibit light falloff towards the edges, and are generally less than satisfactory optically.

The Minolta lens is in a different class altogether. With a slightly larger design it is a true f/8 lens, with no light falloff and very good optical performance. The design was so successful it was continued into the AF era, and was the first mirror lens design to be offered by any manufacturer in autofocus. At a price of between $180 and $250 on ebay it is also quite affordable.

Minolta X-570 with 500mm f/8 RF Rokkor-X Werribee Open Range Zoo, Melbourne, Australia Film: Fuji NPH 400

While cheaper and lighter than a traditional design telephoto lens, the mirror design does have two disadvantages. Firstly, the aperture is fixed at f/8. Given that it cannot be changed, there is no capacity to stop down the lens for greater depth of field if desired (albeit the shooting of large telephotos at longer shutter speeds is problematic in any event). Secondly, the mirror lens design results in the centre of the lens being obscured by the second mirror (as can be seen in the lens design diagram). This can result in out of focus specular highlights forming distinct circles on the image (see the bottom left corner of the image above).

If you look at the photo above you can see the 500mm f/8 RF at its best. The location has been chosen to minimise the detail in the background, resulting in an image that is very similar to one achieved with a traditional design lens. The image is very sharp, and demonstrates the excellent contrast of the lens.

Minolta X-570 with 500mm f/8 RF Rokkor-X. Werribee Open Range Zoo, Melbourne, Australia Film: Fuji NPH 400

In this second image the drawback of the mirror lens is obvious. While the focused image shows excellent sharpness and contrast, the background of the image is quite distracting due to the patterns created by the 'donut' highlights of the catadioptric design. It should be noted however, that as more and more photographers look to digital means to scan and print their own photos, the disadvantage of this bokeh is rapidly becoming less of an issue. This is because this poor out-of-focus rendition can be readily corrected in Photoshop to create a smoother, more attractive background.

Accordingly, the 500mm, while exhibiting distracting bokeh with some backgrounds, makes up for it through its small size, light weight and excellent price. Additionally, with the scarcity of long, fast telephotos in the Minolta manual focus mount, a lens like this often comes in handy.

The lid of the lens case holds the filters included with the 500mm f/8 RF. Make sure that any lens you purchase includes these!

Illustrated above are the filters included with the 500mm RF. They comprise a yellow, orange and red filter for black and white photography, as well as a ND x4 for use in bright conditions. A filter key is also included to permit easy removal of the filters. The filters are mounted at the rear of the lens by removing the 'normal' filter that is placed there when the other filters are not in use. The rear filter actually forms a part of the optical design and accordingly the 'normal' filter should be left in if one of the filters above is not being used.

Additionally worth noting for those interested is that the Catadioptric lenses are actually designed to focus past infinity. This is because in changing temperatures the mirrors can actually fractionally contract or expand, which can minutely affect the focusing. By allowing the lens to focus past infinity, this can never cause a problem achieving infinity focus. The design also means that these lenses do not suffer from the chromatic abberation that often affects longer telephoto lenses.

Minolta XD11 with 500mm f/8 RF Rokkor-X. Mornington Race Course, Melbourne, Australia Film: Fuji Superia Reala 100

It is easy for some photographers to dismiss the mirror lenses manufactured by Minolta as unacceptable due to the bokeh issue discussed above. However this conclusion can be premature. The 500mm f/8 is capable of taking great photos, the photographer simply has to use it in circumstances where the disadvantages inherent in its space and weight saving design are minimised. For Minolta photographers who already have the 300mm and are seeking a little more reach at a good price, the 500mm f/8 RF lens is certainly worthy of consideration.

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