I have made some comments recently re issues with infra red conversions. Here are the 2 points explained -
Calibration – Infra red light focuses at a different point to normal light. The old style cameras that you set the aperture on the lense, and focused on the lense, had a red line next to the normal focus line, which represented the mark that you set the focus of your lense to when using infra red film. Modern camers don’t have this, but when you have a conversion done, you have the camera focus (for auto) calibrated based on the lense used when shooting infra red. This meens that the auto focus will proprly work, and your images will be sharp. You can use other lenses, butthe auto focus may be out, and you will need test shots for each image to get the manual focus right. You cannot see the focus correct through the viewfinder, it is at the sensor only that it will be noticed.
In relation to diffraction, I have been told that anything over f11 in infrared will suffer from this. Following is a desciption of what diffraction is.
Diffraction is an optical effect which can limit the total resolution of your photography— no matter how many megapixels your camera may have. Ordinarily light travels in straight lines through uniform air, however it begins to disperse or “diffract” when squeezed through a small hole (such as your camera’s aperture). This effect is normally negligible, but increases for very small apertures. Since photographers pursuing better sharpness use smaller apertures to achieve a greater depth of field, at some aperture the softening effects of diffraction offset any gain in sharpness due to better depth of field. When this occurs your camera optics are said to have become diffraction limited. Knowing this limit can help you to avoid any subsequent softening, and the unnecessarily long exposure time or high ISO speed required for such a small aperture.
I hope I have enlightened you all.
Karl Schlemmer
Its good to know this Mark. Thanks mate!
Karl Schlemmer
Mark, the reason I don’t do too many landscapes is because I get so bloody frustrated. Yeah, I know I own a Nikon but surely I should be doing much better than what I can manage now. There seems to be so many trade offs when deciding optimum camera settings and I think I have tossed this subject in the “too hard” basket. I always shot landscapes on a tripod using the smallest aperture (largest f stop) that my lens can handle. Now I know what I am doing wrong. I wasn’t aware of diffraction and now that makes sense to me because all my landscape images turn out very soft. I thought it was because my Nikon is just not built for the task. So, having said all that. what do you think would be an optimum aperture for Landscapes.?
Mark Jones:
Hi Karl.
The diffraction thing was more applicable to Infrared stuff in the infrared group, but having said that, the principle still applies in colour. I must say, I most always shoot at f22 though, and had not applied this problem to my landscape stuff because I didn’t notice it. but I hope it has helped.
Karl Schlemmer
Oh well, back to the drawing board for landscapes. Must get a sturdier tripod then.