Lens Calibration on IR conversion

[Herb Cunningham]

I am sending a camera to a group that does IR conversion. They recommend I get the lens I will use calibrated to the IR filter. ($125 extra). Anybody have experience with this? Depth of field is important, although my lens would be a 24mm, used on a crop sensor camera, or 1.6x.
And thus the depth of field would be pretty good to begin with.
Don't want to be cheap, but it seems a charge I might do without.

[pellicle]

Hi

I am sending a camera to a group that does IR conversion. They recommend I get the lens I will use calibrated to the IR filter. ($125 extra). Anybody have experience with this?

well, not with DSLRs but I found that the contrast detect AF works a treat without any calibration on my Coolpix although on my panasonic I expect it needs a conversion as the sensor sees only blackness for the viewfinder and needs long exposures.

I guess it depends on if the phase detect can see much.

Alternatively you could do what I always did on my Film SLR and that is to work on a tripod, focus, fit filer, correct focus and take

[Mike Richards]

I assume you're referring to an SLR of some type, where the visible light focus in the viewfinder won't match the focus of the IR sensor. Not sure what it involves to calibrate the lens, but you can run a series of tests on any lens wide open on a tripod at varying focus settings to determine the offset for IR. This will be different for each lens. Once you get the offset right, you need to crank it in after focusing visually. You can then run DOF tests by varying the aperture. This is basically what I've done with a converted Nikon D100, and it seems to work out ok. I use a manual focus 28mm Nikor AI almost all of the time and got some great images. I was not offered any lens calibration when I had this done some 4 years ago, so I'd like to know what the $125 does? Does it affect autofocus lenses only?

[Herb Cunningham]

Mike, I am not sure about the autofocus question. Once the camera is converted (Canon 50d)
the story is that IR is adjusted automatically.

I will ask the vendor about it and post a reply.

[sanking]

Mike, I am not sure about the autofocus question. Once the camera is converted (Canon 50d)
the story is that IR is adjusted automatically.

I will ask the vendor about it and post a reply.

I am very interested in how this turns out as I have a 50D and am thinking about having it converted to IR. Not so long ago I had a Canon G9 converted to IR by the folks at www.maxmax.com and I very pleased with the results, but when all is said and done I would probably be happier with an APS sensor since I am looking for MF type sharpness in print size up to 13X19. Amazingly, the converted G9 is not far off, with some interpolation.

Prior to having the G9 converted I had not done much work with IR. Now I am pretty amazed at the kind of imagery that one can find in full sun with scenes of high contrast where it would be impossible to do any interesting work with regular B&W.

Sandy King

[Walt Calahan]

I had my camera (Nikon D200) converted to Infrared. The company conversion process was set for a Nikkor 18-70 mm zoom. If I wanted to use a different lens on the camera there would be an additional $125 charge for calibrating the CAMERA to that lens.

The lens is not calibrated. The camera sensor is calibrated to the lens of your choice. Once calibrated you can attempt using other lenses, but you'll have to test them to learn whether the depth of field will carry to cover the IR focus shift that all lenses have.

Hope that is helpful. Once done, I've loved the results. The auto-focus tracks perfectly in IR.

[Herb Cunningham]

I had my camera (Nikon D200) converted to Infrared. The company conversion process was set for a Nikkor 18-70 mm zoom. If I wanted to use a different lens on the camera there would be an additional $125 charge for calibrating the CAMERA to that lens.

The lens is not calibrated. The camera sensor is calibrated to the lens of your choice. Once calibrated you can attempt using other lenses, but you'll have to test them to learn whether the depth of field will carry to cover the IR focus shift that all lenses have.

Hope that is helpful. Once done, I've loved the results. The auto-focus tracks perfectly in IR.

Ok, I spoke with the vendor, and he explained that they calibrate focus with a lens wide open. If it is a zoom, they use halfway as the focal length.

Since mine is a prime, I can shoot wide open and not worry about being in focus, as that is where they calibrate the lens. Makes sense. Also means I will have to check out where other lenses might have a problem at wide apertures.
The wide open fits my agenda perfectly, as I planned to do some old buildings in shade with bright sun peeping through parts of them.

Sandy, I will post a shot or two when I get the camera back.

[sanking]

Ok, I spoke with the vendor, and he explained that they calibrate focus with a lens wide open. If it is a zoom, they use halfway as the focal length.

Why would the calibration matter if you use focus with live view, which is what I would plan to do with the 50D?

Sandy King

[Don Bryant]

Hi


Alternatively you could do what I always did on my Film SLR and that is to work on a tripod, focus, fit filer, correct focus and take

Correcting the focus was totally unecessary IME, particulary when hyperfocal distance focusing.

Don Bryant

[Mike Richards]

The lens is not calibrated. The camera sensor is calibrated to the lens of your choice.

Doh! Should have thought of it. This makes perfect sense.