A very long time ago, ancient history it seems already, I was selling Kodak slide projectors in Australia. In fact I was doing the same back in Germany before I came here.
The difference was, that in Germany, people usually bought the best lens available. Regardless if it was fixed focal length or a vario lens.
Here in Australia I noted that while the customers generally appreciated the high quality of the projector and were willing to pay a bit more, they often selected the lowest cost lens, the one with plastic housing and plastic or lower cost, glass elements.
But why is this critical in projection in the first place, regardless of the image source, film, LCD or DLP?
We can talk in length about the mechanical stability of the lenses and how the constant warming and cooling of the lens could impact its optical precision. We could also discuss the mechanical and optical stability of plastic lenses and the impact of higher temperatures on the colours and transparency of the material. But some of these factors are becoming less relevant with the advances of laser projectors, which are developing less heat.
So why better projection lenses?
If you buy a camera you often have the choice of a kit lens, one which is bundled with the camera or you can select other types. The kit lenses are often of lower quality. For example, I bought some time back a DSLR camera from a well known Japanese Brand. It came with a lens, which looked ok. Later I bought a much more expensive replacement lens and the difference was as chalk and cheese. Not only in sharpness, but in contrast, evens of illumination, colour errors and edge focus.
So we understand that good lenses are important for the image quality of our pictures or videos, but why is this critical in projection in the first place, regardless of the image source, film, LCD or DLP?
If you can do a side-by-side projection comparing a cheap and en expensive lens, you would see the difference, regardless of the image processing.
We could clearly demonstrate that the more expensive lens provided the much superior image. Better contrast, better colours, sharper, better edge brightness.
Projection lenses further have another critical performance criteria. These lenses are always used wide-open. No aperture stepping down to improve quality. If you are not familiar with the concept, here it works.
In cameras the exposure control, of manually, not only is the shutter speed adjusted, but also the lens aperture. In fact if you reduce the aperture, the lens not only increases the depth of field, but generally gets better in quality, sharpness, etc.. Up to a point.
But in projection we want to maximise light output. This is why we do not step down the lens. We operate wide open and here the optical quality becomes very apparent.
Maybe in the earlier years of VGA and XGA projection this was not as much of an issue. But with 4K and higher resolution we need again to get every pixel, distortion free and sharp on to the screen. A test yesterday in our projection set-up demonstrated again that the better optic does not only provides the before-mentioned benefits, but an overall clearer, cleaner picture.
Of course, here starts the problem. Most projectors, except in the higher price and light bracket, have fixed lenses. So you have no choice. Or do you?
Here the problem starts.
If you buy on-line. You will often get much reference to the light output, resolution, scan rates, etc.. But very little about the lens.
I have read dozens of projector tests and the most the reviewers refer to the lens is the focal length and vary range and if they are really very good, to the sharpness and illumination. Rarely about the colour, contrast and other factors.
Maybe they don’t know how to rate it or maybe it is just difficult and therefore not on their radar.
True, image quality on the screen is much of a personal thing and because we can adjust the projectors so much, we may not consider the lens. What is really good?
Here is the crunch. Ideally you should be able to compare projectors. But there are few, if any dealers, which can give you a comparison, who have a suitable projection set-up and a variety of projectors.
So, do we give up? No need, you can always assume, that as cheaper the projector is, as more the manufacturer must have cost controlled all components and therefore the lens may not be the utmost best quality.
If you climb up the ladder and look at Canon, Sony, Panasonic, Fujifilm, Barco, Christies and others, you will find that the piece of glass in the projector improves as the price goes up. While you may not have all the test data, you can safely assume that the lens is also of better quality.
So it is definitely worth to consider the image quality. As I said before, the higher your resolution and maybe the bigger the image, the more critical becomes the proctor lens. By the way not only for film and video or pictures, but also for PowerPoint and Spreadsheet projection.
Next time we will talk about the image the projection screen can have on your image and why not all screens are created equal.