tips for focussing with IR filter on

lurker · 15th June 2005

how? turn the focus ring to infinity? tried it today, don't think it works.
Focus will be out if i turn the zoom ring (17-40) even tho the focus is at infinity.

Any tips from the IR guru's here? other than taking the IR filter on and off to focus.

8sec, f5.6, iso 400
pic done with 300D, 300mm f4

Del_CtrlnoAlt · 15th June 2005

if your object is in distance over your lens range.. (i think your 17-40 is max 3m?) the pic is still blur, i think you need to send pic for calibration liao...

teerex · 15th June 2005

Can you tell which camera you're using?

lurker · 15th June 2005

Originally Posted by Del_CtrlnoAlt

if your object is in distance over your lens range.. (i think your 17-40 is max 3m?) the pic is still blur, i think you need to send pic for calibration liao...

my 17-40 focus fine without the IR on. Just that i want to learn how to focus with the IR aka 'shoot blindly'. As in shooting a series of pics with IR on and recomposing 'blindly'

lurker · 15th June 2005

Originally Posted by teerex

Can you tell which camera you're using?

stated in my 1st post
300D with 300mm f4 from that pic i attached.

deadpixel · 15th June 2005

Use hyperfocus.

The hyperfocal point is a distance you focus on for a given focal length and aperture that will give you max focus. For example, on the Nikon DX format CCD with its 1.5x crop factor, a 15mm lens set to f/5.6 and focused at 2m will give you max focus.

You'll need to do a search on the net for Hyperfocus Chart or Table or Calculator and remember that the crop factor for the 300D is 1.6 (if I remember correctly).

However, as you are focusing for IR, you'll also need to compensate for reduce the focusing distance slightly. That is to say, if the HF chart says 2m, you'd want to focus around 1.8 or 1.9 instead.

This all might sound confusing, but once you've tried it, you'll find it quite easy.

Cheers,

Matt

15th June 2005	#1
lurker Member Join Date: Dec 2004 Posts: 187	tips for focussing with IR filter on how? turn the focus ring to infinity? tried it today, don't think it works. Focus will be out if i turn the zoom ring (17-40) even tho the focus is at infinity. Any tips from the IR guru's here? other than taking the IR filter on and off to focus. 8sec, f5.6, iso 400 pic done with 300D, 300mm f4

15th June 2005	#2
Del_CtrlnoAlt Senior Member Join Date: Feb 2003 Location: Outside the Dry Box. Posts: 16,342	if your object is in distance over your lens range.. (i think your 17-40 is max 3m?) the pic is still blur, i think you need to send pic for calibration liao... __________________ Logging Off Permanently. Those who need to contact me will know where to contact me.

15th June 2005	#3
teerex Moderator Join Date: Mar 2003 Location: Singapore Posts: 4,650	Can you tell which camera you're using? __________________ *Before you embark on a journey of revenge, dig two graves.* teerex@myinfrared.com

15th June 2005	#6
deadpixel Member Join Date: Apr 2004 Location: East Posts: 1,252	Use hyperfocus. The hyperfocal point is a distance you focus on for a given focal length and aperture that will give you max focus. For example, on the Nikon DX format CCD with its 1.5x crop factor, a 15mm lens set to f/5.6 and focused at 2m will give you max focus. You'll need to do a search on the net for Hyperfocus Chart or Table or Calculator and remember that the crop factor for the 300D is 1.6 (if I remember correctly). However, as you are focusing for IR, you'll also need to compensate for reduce the focusing distance slightly. That is to say, if the HF chart says 2m, you'd want to focus around 1.8 or 1.9 instead. This all might sound confusing, but once you've tried it, you'll find it quite easy. Cheers, Matt __________________ My Gallery IR Photography Black & White