Rear projection

The rear projection principle offers a number of advantages because it is transmissive.

Reflects less ambient light

                     Fig 28

Rear projection as a general technique has inherent advantages over normal (i.e. non-optical) front projection:

 

> Some ambient light will pass through the screen into the projection room where it will be dissipated by general absorption and cross-reflections in the projection room
> Some remaining ambient light is absorbed or dissipated within the screen material.
> As the screen is so much darker than a front projection screen it will reflect less ambient light, thus creating better black levels in the image and better contrast

 

So called ‘optical’ rear projection screens are vastly superior to conventional rear projection screens (also known as ‘diffusion’ or ‘opalised’ screens). Optical screens use a combination of lens and filter technologies and patents to optimise image quality and minimise the impact of ambient light.

Rear projection screens are superior

                           Fig 28_1

                                      

                             Fig 28_3

 

The following example chart illustrates the impact of ambient light on contrast ratios, comparing front and rear projection.

Contrast ratios

                   Fig 28_2

Using rear projection means that the projection equipment is installed behind the screen in an unobtrusive way, and ventilation noise etc is easy to control.

 

Furthermore, as projection takes place from behind the screen, there will be no projection shadows from a presenter standing in front of the screen.

 

Using rear projection also provides the opportunity of designing the screen as an optical element. By controlling light dispersion effectively (see below), this results in a much higher image brightness than that obtainable from front projection.

 

So what are the drawbacks of the rear projection principle?

 

First of all it’s a little more complicated to design and install an optimal solution. Secondly, rear projection is more costly than front projection.

 

Nevertheless, when comparing the achievable image quality you will see that the price/quality ratio is in the very clear favour of the rearpro (rear projection) solution.
 
<  Projection

 

“dnp’s front/rear demo unit, where one projector (a BARCO 6400) is used for both front and rear projection on the same image. The right hand half of the image is reflected into the booth and then onto the right hand dnp rear projection screen. The left hand half of the image is reflected onto standard front projection screen material. Yes, the difference between rear projection and conventional front projection is really that much!”

 

dnp denmark is the worldwide large-screen centre of Dai Nippon Printing Co. Ltd. With a 65 % market share, dnp is the world’s leading supplier of optical projection screens for high quality display solutions.

The dnp optical screen portfolio includes an extensive range of optical projection screens for both front and rear projection screen applications for all environments including home cinema / home theatre, meeting rooms / conference rooms, control rooms, signage & advertising and more.

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