Optoma TX7855 Manual page 62

Appendices
Image has vertical flickering bar
Image is out of focus
The image is stretched when displaying 16:9 DVD title
When you play anamorphic DVD or 16:9 DVD, the projector will
show the best image in 16:9 format in OSD. If you play 4:3 format
DVD title, please change the format as 4:3 in projector OSD. If the
image is still stretched, you will also need to adjust the aspect ratio
by referring to the following:
Image is too small or too large
English

Use Frequency to make an adjustment. See page 42 for more
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information.
Check and reconfigure the display mode of your graphic card
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to make it compatible with the projector.
Make sure the lens cap is removed.
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Adjusts the Focus Ring on the projector lens.
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Make sure the projection screen is between the required
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distances from the projector. See pages 24-25 for more
information.
Please setup the display format as 16:9 (wide) aspect ratio type
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on your DVD player.
Adjust the Zoom Ring on the top of the projector.
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Move the projector closer to or further from the screen.
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Press [Menu] button on the remote control or projector panel,
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go to Display | Format and try the different settings.