IR sharpness issues

[eric.schmiedl]

Hoya R72 filter that I got dirt cheap off eBay. Handheld 1/15s. CV 28/1.9 focused at infinity, f/1.9.
I don't get what's going on, unless the filter is counterfeit... it did come from China.
Full res here:
http://www.ericschmiedl.com/upload/rd1-infrared/_EPS7082.jpg

 

[bellyface]

the problem with IR is the focus shifts. So, if you shot this at F1.9, you'd have to move the infinity symbol over to the red hash mark on the lens focus scale. I know, that seems silly... trust me. Also, use a tripod. Shutter release too. Shoot at iso 400, F5.6-F8, try some brackets shots, 2" @ F5.6-F8. But remember to use your red mark on your focus scale... also be careful with flare, shoot with the lightsource behind you or above you.

 

[pfogle]

For those of us using lenses without a mark for infra-red focusing, I find for many lenses the following works as a starting point: move the required distance on the scale to where the f5.6 DOF mark is. That's usually close enough to start experimenting.

When I find (through trial and error) how far to move the focus point, I stick a tape marker on the lens at that point.

 

[Mike Richards]

As mentioned already, focal shift is the primary culprit here. But moreover, any lens is a compromise among the various factors (aberrations) that tries to optimize images for visible light. Besides simple focus shift, the entire lens design is not optimized for IR. Best bet for IR images is to (1) Use single focus lenses, avoiding zoomers or variable focal length lenses that tend to have worse aberration compromises, and (2) stop down as much as you possibly can.

 

[bellyface]

yes, Mike is correct, but depending on the lens, stopping done can cause aperture hotspots on the image. My experience with IR, on the digital side has been that the simpler lenses, like say, a 50mm 1.8 shot at F11 would cause a burn in of the shape of the aperture blades... IR is a crazy beast, and really what better way to mess with it than digital! So get out there and shoot some, practice 😉

 

[eric.schmiedl]

Focusing at the 5.6 depth of field mark fixed it.

F1.9, 1/30s, ISO 800, R-D1 black and white with green filter mode.

 

[Ronald M]

Pfogle is right. Move infinity to 5.6 and you will be on the money for common IR filters, not for 25 and 29 reds.

In your sample, you are focused at something less.