Go Back   Steve's Digicams Forums >

LinkBack Thread Tools Search this Thread
Old Nov 24, 2003, 6:32 AM   #1
Senior Member
shene's Avatar
Join Date: Oct 2002
Posts: 579
Default Two Focusing Problems with A1

Hi A1 shooters,

I am not sure if I am the only one who encountered the following problems. The A1 focuses much faster than my Nikon Coolpix 5700, especially in low light and low contrast situations. But, ...

(1) The A1 has some problems in shooting CRT monitors and TV screens. I used full auto, flexible focus point(FFP) and continues AF to shoot TV screen and CRT monitor at 200mm, and found out that the failure rate is very high. More interesting is that the focus area jumps rather randomly and fail to focus. The 5700 has no such problem as long as it can focus.

(2) In macro mode at 200mm, all three focus modes frequently show false focus (i.e., white dot shows up but it is clear that the camera is not in focus). This is especially true when shooting at the minimum focus distance.

Does any one of you encounter the same problems? Or, is it the problem of my own A1? Any comments and input?


Nikon Coolpix 950/990/995/2500/4500 User Guide
shene is offline   Reply With Quote
Sponsored Links
Old Nov 24, 2003, 7:33 AM   #2
Senior Member
voxmagna's Avatar
Join Date: Aug 2002
Posts: 2,162

Re shooting TV displays: You're picking the most difficult thing to photograph. Your camera is itself a digital sampling device (including the AF which is done in time segments using processor interrupts) whilst the picture on a monitor is from a spot wanging back and forth and up and down, with the image you see produced by persistence in a phosphor and itself a light source, and a big black field blanking interval which your eye is deceived into ignoring - but which the AF will 'see'.

Why don't you try doing a half shutter press on an object at the same distance as the screen to get focus lock, then point at the monitor? Don't forget the point of focus will be a bit further back than the monitor case or glass - but you can stick something at the equivalent distance to focus on, or go down a stop for more DOF. Of course you may still get soft looking pics if your shutter is to long, as the spot is always moving and refreshing the screen! If the text on the monitor case is sharp, then this is likely the problem. However, shorten the shutter and you'll probably catch the black frame bar. VOX
voxmagna is offline   Reply With Quote
Old Nov 24, 2003, 8:35 AM   #3
Junior Member
browntimdc's Avatar
Join Date: Nov 2003
Posts: 20

You shouold use manual focus and the magnifier to photograph a CRT. You should also use a tripod because you need a shutter speed of 1/30 or slower and you need to aim the camera straight at the screen (focal plane parallel to the screen). Lastly, unless the CRT has a flat screen you should set the zoom fairly long (~135mm) and back away from the screen to reduce geometric distortion.
browntimdc is offline   Reply With Quote
Old Nov 24, 2003, 11:03 AM   #4
Senior Member
sjms's Avatar
Join Date: Jul 2002
Posts: 2,735

also don't forget it has both a horizontal and vertical refresh rate

mine is currently running at hoz 85.9khz
vert 85.0khz
screen res: 1280x960


roughly 100%crop

quick snapshot. i don't know looks good to me considering. note the vert phosphor lines

shot from about 12in from screen hand held 200mm eq macro in AF on single shot

oh yeah sorry i didn't clean the screen
sjms is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -5. The time now is 2:51 PM.