TOPIC: Digital Projector Features.

Last Update 19 October 2005

Nothing on this page constitutes a recommendation for any product

URL/Contact	Comments
www.projectorcentral.com	A thorough site with discussions on the technical choices to be made when choosing and using a projector. Comments on LCD v DLP technology. Importance of matching computer resolution to projector resolution, which for laptops or other computers with LCD displays will also mean matching to screen size. Forum discussions on many topics and including review of projector models. Models may be US rather than UK
www.ivojo.co.uk	Commercial site with advice, and a full listing of projectors from numerous manufacturers. (Site is linked from Maureen Albright)
http://palimpest.stanford.edu/byauth/vitale/digital-projection/	A personal paper discussing the resolution limits of film versus digital projection. Notes that film still has the edge although slide projectors are not perfect.
Steve Brabner, Amersham PS (CACC)	At Amersham PS we found the procurement process for a digital projector in 2003 to be particularly difficult because we did not find anywhere that could show us a significant number of projectors 'lit up'. Typically they obtain one after you have ordered it and they have few, if any, available for demo. We were eventually pointed to Image AV at Didcot http://www.image-av.co.uk/ by Ian Bateman (Wantage CC, CACC) and they did manage to demonstrate about 7 projectors and let us borrow 4 for a couple of nights. After trialling these in our club room with a group of members, we chose the Panasonic PT-L735E. This has proved to be effective and reliable. At 2600 lumens there is a minority view that this is too bright but on economy setting most of us continue to be very pleased with the image quality. I would warn against using the software keystone adjustment as this destroys image sharpness. Far better to adjust the height of screen or projector as necessary. We chose an LCD projector because of a) the DLP rainbow effect b) the supposed colour accuracy and c) guidance from the Photographic Society of America that LCD projectors were more 'photographic' whereas DLP projectors were more 'Hollywood' in character. After nearly two years of regular use we have only clocked up about 300 hours so have not purchased a spare bulb. (Ed Note: Useful comment on the lumens value may put an upper limit on what is suitable for Club style use.)
www.dlp.com	As its name suggests, this is a site extolling the virtues of DLP over LCD. Claiming independently reviews of long-term use, it suggests that LCD projectors are subject to loss of contrast and to colour changes, where such effects are not seen with DLP. The life of an LCD projector, on their figures, is quite similar to the expected life of a single projector bulb, making projector replacement rather than bulb replacement the expected outcome of an LCD purchase. But they would say that!
Why LCD	While DLP projectors are agreed to have a higher (?better) contrast ratio, some consider that LCD projectors have a more realistic look with better colour saturation.
LCD v DLP	Despite intense competition leading to technical advances, LCD projectors tend to have lower contrast ratios. Basically, the contrast level determines how good a black is obtainable, given that photographic use is likely to involve a blackout (unlike presentation use). All LCD projectors require more complex optics and the panels are subject to deterioration, which may be differential. While some have chosen LCD after comparison (see Amersham PS), both the RPS and the Wessex Digital group have chosen DLP. DLP uses simpler optics (until the highest cinema range is reached), but needs a colour wheel. Contrast is high, usually >1000:1, while all the usual brightnesses are available. Differential colour deterioration is not possible at the single panel level, although the colour stability of the wheel is not discussed.. Some people are affected by ‘rainbow’ from the DLP wheel, especially on moving images. Some projectors counteract this by having more wheel segments and/or faster spin rate.
LCOS	The third available technology is LCOS, using three colour panels but in a reflective rather than solely transmissive mode. LCOS is typically more expensive, either because it is a newer technology with lower demand (so far) or because resolution may be higher. LCOS projectors may come to be judged superior to both LCD and DLP for photographic realism.
Luminance	The luminance of projectors is described in ANSI-Lumens. The ANSI standard ANSI/APM IT7.288-1997 is usually cited, but this standard was replaced in 2003 by IEC 61947-1. The two standards are effectively the same. However, this does not particularly help us decide on a necessary projector luminance. The lumen is a unit of total flux of illumination whose definition has varied, but is now equated with the candela (SI unit). This is not immediately helpful in choosing a projector, as we require the unit of luminous intensity (candela per sq.m) resulting from the available lumens being spread across the screen, and projector manufacturers do not usually suggest an adequate level for this. Three factors in a typical setup are clearly relevant. One is the screen size as the inverse square law will apply. A 6’ screen (image diagonal 7.5’), a 9’ screen (image diagonal 11.25’) and a 12’ screen (image diagonal 15’) have an image area relationship of 1: 2.25: 4, and a projector will have a luminance relationship on these screens of 100%:44%:25%. Audience size is often used as a proxy for expected screen size. Two is the lamp setting, as many projectors have an economy mode. This can be set dim for smaller screens, and bright for larger screens to compensate luminance for various audiences - but only if the bright setting is adequate for the larger screen in the first place. Three is lamp deterioration, where projector specifications give lamp life. This is not the expected time to failure, but is the expected time to 50% luminance.
Epson	Range of LCD projectors such as the 7-series. Typically contrasts of 400:1, and various brightnesses. Preset modes eg sRBG should be available. More expensive models have network capability.
Sanyo	Highly regarded for projectors and high proportion of all sales. LCD projectors. Products in the XU series have contrasts not much more than 350:1, with various brightnesses. Some with wireless/card options
Sony	Some projectors, but the company seems to have a poor reputation. Site not easy to search, and no more listed here.
HP	Using DLP technology gives higher contrast. Example is the vp6120 with 2000:1 and 2000 lumens.
InFocus	Using DLP technology. Example is the LP600 with 1000:1 contrast and 2000 lumens, with optional extras available.
BenQ	Using DLP technology. Curiously, many in the microportable 2200 range have an SVGA panel although claiming XGA native resolution. Better may be examples such as 6200 and 6210 with 2000:1 contrast and 1700 to 2000 lumens.
NEC	Ranges of projectors using both LCD and DLP technology. DLP types include the small LT20 and LT180 with contrasts over 1000:1 and 1500-2000 lumens. LCD types include the standard sized VT575 or 670 with contrast 400:1 and 1500-2000 lumens. Unusual feature is correction based on the screen colour. On rereading the manuals, this seems to be a manual setting. In that case, Epson has something similar. This would not be required for photographic use.
3M	LCD projectors with 400:1 contrast. X45 with 1200/1500 lumens, and X55 with 1500/2000 lumens.
Panasonic	LCD projectors with 400:1 approx contrast. Micro PTLB20VEA at 1600 lumens, and PTLB20NTEA at 2000 lumens, with the latter having wireless. Portable PTL735E (see Amersham PS, CACC) and PTL735NTE at 2600 lumens, with the latter having wireless and SD data card.
Optoma	DLP projectors with contrasts approx 2000:1. Make used by Wessex group (model H56). EP729 at 1600 lumens, and EP739H at 2500 lumens can be set on sRGB space. Also ‘H’ series intended for home cinema features a fast multi-segment colour wheel.
Dell	DLP projectors from this highly rated direct sell company. Contrasts approx 2000:1. Model 2300MP at 2300 lumens and 3300MP at 1700 lumens. The latter has video modes and optional card reader.
Canon	LCD projectors with 400:1 contrast. LV-X4 with 1500 lumens and LV-5220 with 2000 lumens. Latter has card/networking option.
Reviews by ‘Digital Photo’	Digital Photo reviewed some projectors in their Oct-04 issue. From then until Jun-05, they awarded Gold to the NEC-VT46 projector. A recent review of the NEC site shows that the VT46 model is not current, and may have been replaced by the VT47. The NEC-VT series are all LCD types. The main problem with the DP review is that all the models were SVGA, perhaps because DP set a cost limit of £1000: see below why SVGA is ruled out. However, there were useful comments about the requirements for brightness.
Some comments	XGA resolution is the current essential. Take care that the LCD/DLP panel really is XGA as some BenQ projectors claim XGA native resolution while using an SVGA panel. If in doubt, DLP seems preferable for contrast, so that good blacks are possible. This tends to rule out very well known manufacturers like Epson and Sanyo. Perhaps, test against an LCD model before purchasing, and check with several people that rainbow effect is not obvious. Jessops lists Canon and Epson projectors, which are all LCD. With the requirement for consistent colour setup, check colour preset options and make sure sRGB is available. Not all data sheets confirm this. Dynamic per-image colour adjustment may not be a good idea. Lumens are usually equated with audience size, which is a proxy for screen size. A higher rating, but using lamp economy mode may be more robust in the longer term. If the projector may be used with a larger group, consider more than 1500 lumens rather than less. Amersham PS feels that 2600 lumens is too much, unless reduced by economy mode. Be prepared to record the projector setup so that it can be kept constant, and then the colour profile adjustments on the PC will be fairly stable. All projectors have a short throw compared to usual photographic experience with slide projectors. And, the lens cannot be changed. Consider how this might interfere with normal audience seating layout. Some compensation as lens tends to be shifted vertically off-centre to avoid too much need for tilt. Projector may offer motorised lens shift as a better option than keystone adjustment on tilt.