Optimum image quality - short throw with maximum zoom or long throw with no zoom?

Brogan

Novice Member
As the title really.

I'm just about ready to mount my 7210 on the ceiling and was wondering which is the optimum position.

I can mount it anywhere from 3.92m to 4.88m from the screen to get an image 234cm wide x 132cm high.
If I mount it at 3.92 I will have to zoom to the maximum of 1.25.
If I mount it at 4.88 there will be no zoom, it will be at 1.0.

So, is there any difference between the two extremes?

Coming from a photography background, different lenses behave differently at different zoom lengths in terms of image quality, etc.
Ideally of course a fixed aperture would be best but this is not the case with the 7210 lens - it is a Carl Zeiss lens and ranges from F2.7 (wide) to F3.1 (tele).
I presume wide is with the zoom wheel at 1.0 and tele is maximum zoom?

At F2.7 I would expect this would give the brightest image and therefore I wouldn't need to increase the brightness on the PJ thereby saving the life of the bulb, reducing heat, fan noise, etc.

However at F3.1 the image may well be better quality.
Certainly with some lenses in the photography world you get better quality if the lens isn't wide open and you take it down a couple of steps.

So does anyone know or am I reading too much into it? :D
 

Wild Rumpus

Standard Member
I guess that the safest bet would be to go for the middle of the focal range, but with a CZ lens the performance should be bloody good right through the focal range.
 

Brogan

Novice Member
I would expect so but my thinking is if I can get the projector to work less hard that should help to prolong the life of it and the bulb, reduce fan noise, etc.

Just not sure which is the best position for this and whether the quality of the image would be better or worse at wide open or not.
 

cyberheater

Well-known Member
Brogan said:
I would expect so but my thinking is if I can get the projector to work less hard that should help to prolong the life of it and the bulb, reduce fan noise, etc.

Just not sure which is the best position for this and whether the quality of the image would be better or worse at wide open or not.
If you worrying about the optimal position in terms of zoom settings of your PJ then your done. The zoom setting on your lens has the smallest impact to quality of your system compared to your environment/video source/cables/calibration etc....
 

Peter Parker

Distinguished Member
Like Cyber says, there are differences depending on the optics, and they can be measured, but the chances of you noticing them are quite small.

Some lenses will give more lumens when zoomed big and placed closer to the screen (something like 25% brighter in some cases), whereas having the image smaller can allow more contrast as the beam is tighter and so less light is scattered in the optics to contaminate the black level.

If you have light coloured walls, you will get less light reflected from the screen onto the walls and back onto the screen (which can wash out colours and dark detail to some degree) if you have the pj further back with a tighter beam as the angle the light will reflect at will be tighter too.

Gary
 

Brogan

Novice Member
Gary Lightfoot said:
If you have light coloured walls, you will get less light reflected from the screen onto the walls and back onto the screen (which can wash out colours and dark detail to some degree) if you have the pj further back with a tighter beam as the angle the light will reflect at will be tighter too.
Thanks Gary, just the kind of useful information I was looking for.

As I do indeed have light coloured walls I'll push it as far back as it goes.
This is also my preference as it won't be as noticable near the back wall as it would if it was directly above the sofa.

Just need the screen and mount now (hopefully arriving tomorrow) and I should be able to get it all installed before the end of the weekend.
 

gingercat

Active Member
Gary Lightfoot said:
If you have light coloured walls, you will get less light reflected from the screen onto the walls and back onto the screen (which can wash out colours and dark detail to some degree) if you have the pj further back with a tighter beam as the angle the light will reflect at will be tighter too.
Gary
Aha - so presumably having the projector mounted as high as possible is also best, as this will result in less light reflecting back up to the ceiling? (And more reflecting down to the viewer?). :smashin: Or am I being daft :suicide:
 

Brogan

Novice Member
gingercat said:
Aha - so presumably having the projector mounted as high as possible is also best, as this will result in less light reflecting back up to the ceiling? (And more reflecting down to the viewer?). :smashin: Or am I being daft :suicide:
I recall a response to one of my threads stating exactly that.
Beacuse of the angle the light hits the screen, if it is ceiling mounted it will be reflected back to the viewer whereas if it is table mounted it will be reflected up towards the ceiling.
I'm not sure who posted it, possibly Gary.
 

gingercat

Active Member
Right, so actually, trying to place the projector bang in the middle of the screen to avoid lens shift etc. actually results in more light relected to all surrounding walls, which is particularly bad if you have light walls. So my setup in a white walled spare room with the PJ located centrally to the screen is the worst possibly setup... Her indoors won't allow ceiling mounting though :(
 

cyberheater

Well-known Member
Paint your walls and ceiling matt black guys. It's the only way...
 

Brogan

Novice Member
cyberheater said:
Paint your walls and ceiling matt black guys. It's the only way...
His wife won't even let him ceiling mount so he's got 2 hopes of doing that....:D

I've been testing mine for the last 2 evenings and although it's unwatchable during the day, at night it's fine and that's just projecting onto a wall.
It should be even better when I get the screen up.
 

Peter Parker

Distinguished Member
The angle the light reflects at also depends on the screen - if it's a high gain the light reflects back more to the viewer from the pj (and ambient reflects back in a similar fashion so effects the image you see less). Some screens are retro reflective like the Optoma GreyWolf and Da-Lite Hi Power, and they reflect back to the source, so in those cases the high gain is only realised if your head is near the same projection plane as the projector.

But ultimately Cyber is correct - to take the room out of the equation and to get best results, it has to be black non reflective surfaces all round. :)

Gary
 
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