So, what about those add-on lens converters?  May 2001


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Introduction
This pic copyright some official Sony siteFurther to the article I had previously written in the DTV Forum, this page is here to show one or two things that might help people make up their minds about buying a wide-angle lens attachment.

Please review that article here before continuing.

What is an afocal lens attachment anyway?

A pair of binoculars or a telescope is an afocal attachment for your own eyes.  Look through the eyepiece and you'll see a magnified image, look through the other end and you'll see a reduced image but a wider angle of view to match. If you can imagine placing such a lens in front of your camera, then you've got the idea of a lens attachment.

The ideal way to alter focal length is to use a completely different lens, as photographers do with professional cameras.  The next best solution is to replace just half of the lens. This was popular with certain enthusiast cameras in the 50s and 60s by Kodak, Zeiss and Voigtlnder among others. The front of the lens would come off and another group of elements would replace it.  Beyond those two methods, the only thing left to do is to add extra elements to an existing lens to try and alter what it sees, and that is what we are talking about with these afocal attachments.

Place one on your lens and you instantly increase or decrease the field of view.  What could be better?

Well, there are drawbacks to these things. Most problems arise because the engineers are not able to design their attachments for a particular lens and instead have to make it work with a wide variety of focal lengths and lens diameters.  Another problem is that they have to be made to a price, and that usually means cheap glass and rotten build quality and precision.  Note that the shop price of these things bears no relationship at all to the actual cost of manufacture. The only rule of thumb is: The more expensive lens of any two from a particular manufacturer will probably be slightly better made.

Quality considerations

Of paramount importance in the case of photographic stills cameras are low distortion, high contrast, high resolution and good colour-rendition.  All of these things may be traded off to different degrees to cater for both  limitations in price and materials set by the manufacturer and also in favour of creating a lens of very high speed.  Speed is the maximum f-Stop and it refers to the amount of light that a lens will let through.  A fast lens is very large for its focal length and lets lots of light through whereas a slow lens is smaller, but also cheaper to make.

I'm getting off the point of this article though..... so, back into it:
As a rule, zoom lenses on video equipment generally have fairly high levels of distortion due to their extreme zoom ratios and relatively low cost and size.  As well, these flaws mostly go un-noticed to the viewer due to the fact the the image is usually constantly moving. 

Add-on-lens designers are therefore able to produce a very simple and cheap-to-make item that does a reasonable job and, in theory, at a reasonable price too.  The downside is that the already noticeable distortion is often increased to the point where it becomes quite significant, even more so if your camera is able to do stills and you actually use it for that purpose.

Afocal lens attachments have been around for decades.  Rollei Mutar 0.7x - Click for Torbjorn Aases Rollei page

The old Rolleiflex twin lens reflex from the Fifties had some high quality attachments of this sort (right)  .  Every Super-8 movie camera had one or two listed in their accessories catalogue and even a few compact cameras still have them available today. 

Certain pricey all-in-one cameras of the Olympus IS3000 variety also have them available to widen the range of focal lengths available to them.  The other day I noticed a very tacky-looking attachment for the Olympus in a shop and picked it up.  It was completely made of plastic and judging by the weight of it had plastic lens elements as well.  The price for this lens was $849.- New Zealand Dollars - which is around US$400.- !!!!!
 think that sort of price is disgraceful.  It really show that quite a bit of money can be made on these aftermarket accessories.  When someone has just spent $2000.- on a camera, the extra $300 for a lens seems quite reasonable... until one realizes the lens is all of $20.- worth of plastic. 

What I am getting at here is that there has to be some real added value in these "High Grade" Sony lens attachments to justify their high cost.

There are a few basic points to note about lens attachments:

  • They are in effect an extra lens element that alters the field of view before the camera lens sees it.
  • They alter the focal length of the main lens by an amount expressed as a factor, for example 2.0x which doubles the focal length or 0.5x which halves it.
  • They are called afocal, meaning they do not have their own focal length and cannot focus an image by themselves. They must be used in front of a real lens to produce an image.
  • They add additional distortion to lenses that are usually already distorting too much.
  • They do not affect the speed of a lens (a good point)
  • They are generally a very simple two-element optical design.
  • You can usually gauge the level and type of distortion created by an attachment by looking  at straight lines through it.

 

I have now tried out 4 different attachments on my PC110 and can show some results here.

First off is an off-brand 0.6x converter originally made for a Yashica 35mm auto-focus compact camera.  Being designed for a stills camera, this lens is marked "2m-infinity" implying that the quality is so bad at closer distances that its use is not recommended at less than 2 meters.  This and the next lens were both picked up for next to nothing in the junk bin at a local camera store.

The next one I found is a 0.7x Itorex Wide + Macro attachment.  Itorex is also a no-name brand and this lens is intended for use on either video or Super-8 gear.  It achieves the "Macro" setting by letting you unscrew the rear element and use it alone on the camera.  This works as a simple close-up lens.  All of these wide angle attachments are of the same design and if you can separate the front from the back, you can also use it as a Macro (close-up) attachment. 

The third attachment I tried was the Sony VCL-MHG07 High Grade item.  I was given this one when I went to the Sony shop to try the HG lens as listed in my PC110 brochure.  In the end this turned out to be one intended for use on other video cameras as it was able to be mounted on a larger diameter lens.  That however, should have made it perform better overall on the smaller PC110 lens.

Itorex 0.7x Yashica 0.6x Sony VCL-MHG07 Sony VCL-HG0737

The relative sizes of these pictures are not accurate.  The Yashica is around 5cm across, the Itorex 6cm, the flat Sony is the largest at maybe 10 or 12cm and the other Sony is just a bit larger than the Itorex.

The fourth and final lens I tried out (on the right) was the one I really wanted to know about all along.  Funnily enough, the shop staff had never even seen one until the day I walked in and asked to see it.  They had only that day received their first one ever.

Anyhow, I screwed it onto the camera and took a couple of snaps around the store as I had done the previous week with the other Sony lens.  The results can be viewed on the next page.

 

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    2001 R.I.Axford