Basic projector install question...about to buy an HC6800

shottel

Standard Member
Guys i tried to find this info elsewhere on the site but couldn't find it so let me know if i'm lost. i'm about to order up an HC6800 (my first projector project) for a ceiling mount install. I plan to mount the projector perpendicular to the screen at about the top of the screen. My basic question is when i use lense shift to get the picture "down" on the screen will i still have to do a keystone correction ? This may go back to the basic question of how does lense shift work? Is it just mechanical reposition of the lense (same as tilting the entire projector down) or is it digital and correct the keystone automatically?

thanks for sharing your knowledge....
 

tom1379

Active Member
No, you will need no keystoning correction when using the lens shift :thumbsup:

Cheers,

Tom
 

Tight Git

Distinguished Member
How does lens shift work? Is it just mechanical reposition of the lens (same as tilting the entire projector down) or is it digital and correct the keystone automatically?

Welcome to the Forum, Shottel. :)

I'm installing a ceiling mounted projector shortly and was wondering exactly the same!

Perhaps one of the experts can give an explanation. :lease:
 

Tight Git

Distinguished Member
I've tried Google, but all the sites explain WHAT lens shifting is, without saying HOW it's achieved. :thumbsdow

Basic physics says that if you aim a picture at an angle, then you must get keystoning. :lesson:

Is there no one who's prepared to have a go at explaining this apparent anomaly? :)
 

Zone

Moderator
Lens shift as it implies is simply the physical movement of the lens within the housing!

There is a lens used in 35mm photography called a tilt shift lens that corrects perspective especially when taking pictures close up of tall buildings, if not used the end result looks as though the building is falling backwards due to the fact that the film plane (now digital sensor :D) needs to be parallel to the sides of the structure! If not the sides appear to converge at the top and give the illusion of the building falling backwards!

Hopefully this little picture will give you an idea of how it works!

tiltshift.jpg
 

Tight Git

Distinguished Member
Many thanks, I think I understand now. :smashin:

So the lens itself (or combination of lenses) are shaped in such a way that the keystone correction is applied physically within the lens structure?
 

Zone

Moderator
So the lens itself (or combination of lenses) are shaped in such a way that the keystone correction is applied physically within the lens structure?

Sounds good to me :D
 

shottel

Standard Member
thanks for the replies guys but I still don't think we have the whole story yet. I have not been able to find an engineering description of lense shift online so maybe a call into Mits/Panny will get this answered...stay tuned.

The pictorial above is good but i don't understand how just (assumably) a small vertical movement of the lense can equal such a large movement on the screen. I can't imagine the lense actually moves in more than a 1/2 inch window of travel. the only way i could imagine is if the lense didn't just move vertically but also rotated/tilted. This rotation/tilt would induce a keystone.
 

kuro_man

Standard Member
Taking an ill-informed guess, I would imagine that you may be over-simplfying the optics involved. The lense may not just be a simple single piece of glass but an array within a zoom barrel.

The projector is designed to send an image out onto a screen from a relatively fixed range, not capture one like a camera, so the lens' natural angle is going to be set up to do this. Also, the image inside the projector is tiny, so minor lens movements could make a big difference.
 

The latest video from AVForums

Star Wars Andor, Woman King, more Star Trek 4K, Rings of Power & the latest TV, movies & 4K releases
Subscribe to our YouTube channel
Support AVForums with Patreon

Top Bottom