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Newbie Question - Closer (and smaller) or Further (but bigger)

harlanz

Standard Member
The wife has finally given the go-ahead on a ceiling mounted projected in our living room, and it looks like we're going with the Optoma HD72 (the other option was the Infocus IN76. I've posted on the kit elsewhere so won't go into details here). We'll use a decent quality DVD player (Denon 2930). We're waiting for the site visit from Sevenoaks to finalise the screen and other details. No doubt they'll advise well but I really value opinions on this forum.

We can mount the projector and drop down screen across the length or the depth of our living room. Basically, the otpions are:

1. Throw of 4 meters (and we'd have room for a screen of about 78-84 inches across, which is fine per the Optoma website calculator), or

2. Throw of 5 meters, and screen size limited only by the projector (which per Optoma website could be up to 120 inches across).

My question is about the tradeoff between sitting a bit closer and having a smaller screen, and sitting further back and having a much bigger screen. Of course, bigger is better generally, but when the picture begins to degrade, brightness decreases, or whatever, maybe it's not necessarily better in my case. I just don't know.

Please could you give me any subjective thoughts you have.

Thanks a lot.
 

reevesy

Distinguished Member
i'm sure most would say the bigger the better...personally i'm stuck to having a 5ft screen from nearly 3ms away but a big screen is still a big screen.
....picture quality wise i think you're better off being a bit further away if possible as the closer you are ,the more likely you are to notice any imperfections if there are any.
 

cyberheater

Prominent Member
The other thing you need to factor in is your Zoom settings.

Using the zoom to the max to make the picture biggest will increase the brightness but reduce the contrast.
Likewise, having the zoom at it's smallest will make the picture slightly dimmer but increase your contrast. (which is what I do with mine).
 

Jammyb

Prominent Member
zoom to the max to make the picture biggest will increase the brightness but reduce the contrast.
How come? the image brighness will surely go down?

Likewise, having the zoom at it's smallest will make the picture slightly dimmer but increase your contrast. (which is what I do with mine).
surely it's the other way round

I agree about the contrast though.
 

Peter Parker

Distinguished Member
It's all to do with F stops and how the light goes through the optics.

It's expensive to make a constant aperture lens (they're usually very large), so as you zoom the lens the aperture changes. With the likes of the Ruby and Pearl, that can mean as much as 20% more light is available with the lens opened up to give a bigger image - the image through the optics is larger and more light scatter through the lens occurs, so you contaminate the blacks in the image.

When you zoom the image smaller, the light beam is smaller with less scatter so more contrast, but less light output. It's similar to cameras, the f stop numbers on the lens tell you how much light it will let through, so a cheaper lens will allow less light through and you may need a faster film for the same exposure.

Gary
 

Peter Parker

Distinguished Member
I've a few problems with PJcentral so I'm not sure how accurate their calculator is overall. If you use the diagonal rather than the throw range then the image brightness will drop because you're making the image bigger. if you use the throw range (image size stays the same) their calcualtor gives constant nits (or foot lamberst which is what I prefer cos I'm Old School :p). I was using the Sony Ruby as the example as I know that pj does drop brightness when you move the image back for a given screen size.

It may not be the case with every projector, but those that have been measured recently have proved the theory at least, and the new JVC appears to do much the same, despite originally being led to believe it was going to be constant lumens throughout the zoom range.

HTH

Gary
 

Peter Parker

Distinguished Member
Hi Harlan,

If you prefer a brighter image then the shorter throw and smaller image with the pj closer will give you that, plus you've more chance of getting a reasonable image if you're not watching in totaly dark conditions. With a brighter image it can highlight any 'noise' from the source but at 7ft wide I'd think you'll be getting a big enough picture that will remain bright for a much longer period of time due to lamp ageing. If you have the pj closer to the screen rather than further away, you should get some extra brightness from it, (though how much more I don't know since I've not seen any measurements of the projectors you mention).

If you get a screen that has some gain to it then that will help add some brightness and help negate any room reflections from the bright walls to a small degree. 1.2 to 1.3 should work well, though a grey screen with gain can work even better, but getting the right one for your situation may be a bit tricky so to be on the safe side a white screen should do fine, especially if you're going to be doing most of your watching at night.

Gary
 

harlanz

Standard Member
Thanks, Gary for the great explanation.
 

Barcoing Mad

Prominent Member
It also depends on the size of your room. If a screen on the wall about seven feet wide puts your sofa say 12 feet away with a bit of space between it and the back wall, then you've got a good size to watch and also acoustically things will be better. If your sofa is pushed up against the wall, then speaker positioning is harder (and bassy standing waves become moro obnoxious).
 

Timbo21

Prominent Member
Hi Harlanz,

I think the larger you can get your screen, the more it will feel like being at the cinema. So, personally, I would be trying to go for the 5m viewing distance with the bigger screen. When I first bought, I didn't go for the maximum screen size, because I thought it might be too big :rolleyes: . I later regretted it, and eventually bought a bigger screen.

SMPTE (Society of Motion & Picture Television Engineers) have calculators for size screen vs. viewing distance. THX do also, but they tend to go for a slightly larger screen.

If you are viewing from 15ft away (approx. 5 metres), then SMPTE would recommend a screen width of 96.5" viewing area, which is a 110" diagonal viewing area measurement for a 16:9 aspect ratio screen.

THX works out at 117" wide, and 134" diagonal for same distance.

The calculator is here:
www.myhometheater.homestead.com/viewingdistancecalculator.html

Just scroll down and enter in the "Distance to main viewing location" & hit calculate. Then scroll down for results.

Personally I would go nearer the SMPTE one, or just slightly larger, since you may start to see artifacts if you go much larger at that distance.

HTH,

T.
 

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