- #1
guyburns
- 32
- 7
I have some questions about projection lenses and screen brightness.
Background
I may be purchasing a BenQ PU9730 (http://www.benq.com.au/product/projector/pu9730/specifications/) for use in a large venue, projecting an image 3 x 5.3 metres. The projection booth is 18m from the screen (maximum distance), but the projector could be placed amongst the audience.
BenQ offers a choice of several lenses, and I will probably choose between the Standard and the Semi Long, with these considerations:
Standard Lens
Semi Long Lens
Ques 1
Comparing the two lenses, and assuming the same size image on the screen (obtained by moving the projector while changing lenses) – is the Standard lens always going to throw a brighter image than the Semi Long lens?
Ques 2
For a single lens, and assuming the same size image on the screen (obtained by moving the projector while altering the zoom) will the brightness change as the zoom changes?
Ques 3
Assuming the brightness does change in Q1 and Q2, where does the energy in the wasted light go when the screen image is less bright?
• Does it heat up the lens? In particular, for the same size image, will the Semi Long lens runs hotter than the Standard lens?
• Is the wasted light reflected back into the projector, so the projector runs hotter?
Thanks in advance for any comments.
Background
I may be purchasing a BenQ PU9730 (http://www.benq.com.au/product/projector/pu9730/specifications/) for use in a large venue, projecting an image 3 x 5.3 metres. The projection booth is 18m from the screen (maximum distance), but the projector could be placed amongst the audience.
BenQ offers a choice of several lenses, and I will probably choose between the Standard and the Semi Long, with these considerations:
The Standard lens has a lower f-number (brighter?), but it would have to be placed amongst the audience. And because it has less zoom range, I would be more restricted in where I could place it, in this venue and others.
The Semi Long lens would allow projection from the projection booth (away from the audience), but I think it would project a less-bright image. For use in other venues, though, it has a much larger zoom range.
The Semi Long lens would allow projection from the projection booth (away from the audience), but I think it would project a less-bright image. For use in other venues, though, it has a much larger zoom range.
Standard Lens
• focal length 26 ~ 34mm
• f-stop 1.64 ~ 1.86
• f-stop 1.64 ~ 1.86
Semi Long Lens
• focal length 33 ~ 54mm
• f-stop 1.86 ~ 2.48
• f-stop 1.86 ~ 2.48
Ques 1
Comparing the two lenses, and assuming the same size image on the screen (obtained by moving the projector while changing lenses) – is the Standard lens always going to throw a brighter image than the Semi Long lens?
Ques 2
For a single lens, and assuming the same size image on the screen (obtained by moving the projector while altering the zoom) will the brightness change as the zoom changes?
Ques 3
Assuming the brightness does change in Q1 and Q2, where does the energy in the wasted light go when the screen image is less bright?
• Does it heat up the lens? In particular, for the same size image, will the Semi Long lens runs hotter than the Standard lens?
• Is the wasted light reflected back into the projector, so the projector runs hotter?
Thanks in advance for any comments.