Friday, 2 December 2016

Digital Infrared Photography with an SLR Film Camera

My digital back Nikon FE can achieve nice results with infrared photography.  I have been incorrect in suggesting that the IR Filter needs to be swapped with a clear glass filter to achieve focus when using the bare sensor for infrared photography. This is a myth as I have found that infrared light works on a slightly different focal length, so no wonder I was having focus issues. On many old SLR lenses there is a red dot on prime and a curving red line on zoom, or a straight red line on zoom lenses like the Tamron SP 35-80 2:8. These red marks are there to re-adjust the focus for infrared film after having first focused on the subject via the split prisms in the view finder. An example is to focus on a subject at 2.5 metres but your red dot or line will be at say 3 metres, therefore you need to turn the focus so the 3 metre mark is on the main focusing mark and your infrared photo will then be perfectly focused when exposed. 
Update 17th Jan 2017 - I have since sanded a bit more off the rebated edge of the sensor so sinking it further into the film plane. This has improved my focus in normal colour (filter inserted) at F1.8 to a very acceptable level. Subsequently with the IR/AA filter removed and shooting on the bare sensor, my focus is much more in line with the normal focus marks on the lens and in the split prism viewfinder. There is still a small amount of difference as IR light travels at a different wavelength. Whether the bare sensor reacts the same as IR film is another matter. If you start adding say red or yellow filters to the front of the lens then this will also change the wavelength to focus. So I think it comes down to rebating the sensor to the best possible tolerance with the IR/AA filter installed and then conduct tests without the IR/AA to see where the focus is at with different lenses shooting in IR. Here is a good article on focussing in infrared.  Focussing in Infrared

Nikkor and two Tamron zooms with red IR focus line.

Another lesson I've had to learn is the dreaded White Balance setting on the Nex. If you use the Auto White Balance setting your photos will have a red tinge and only very blue sky will be blue. But when you use the iOS Photos program and edit filters to Mono, Tonal or Noir, your black and whites will be superb. However you can get a more realistic initial infrared photo in colour if you learn how to custom set the WB to a test photo. These test photos can be of a grey wall or green grass. I suggest you check the Nex manual and the internet to learn how to do this. Once the WB is custom set for the light conditions, you will find that the other colour filters in iOS Photos (or I guess PhotoShop) will provide some exciting filters to your photos and the B&W photos will still be superb with no change from your auto WB setting.

To set the White Balance test photo through the Nikon you need to coordinate the shutters simultaneously at the correct speed. Well that is way too hard. So instead set WB manually on “‘K’ C.Temp/Filter” and try 2900K G9 or G8 as the green strength. This seems to give a pretty good result on a sunny day. Experiment with different K & G settings.
Auto White Balance result
White Balance setting 2900K G9

My previous post mentioned the light meter calibration for infrared. There is about 2 stops extra light striking the bare CMOS sensor than when it has the IR Filter attached (or located within the SLR body). As the SLR light meter is reading light from the mirror before it reaches the sensor, then the SLR is no longer matching the Nex bare sensor reading. My really easy fix is to set the Nikon at 1600 ASA and the Sony Nex at 400 ISO. This brings the light meter to a near correct calibration. I have found in sunny light I get a more exact calibration with the Nikon adjusted to the next mark which must be 2133 ASA.  But a few test shots and some tweaking of the ASA approximately 2 stops above the ISO will give you the correct calibration for the light your working with. You can use the compensation dial to tweak the exposure instead of moving the ASA.

Infrared photography was not my initial reason for inventing this Nikon/Nex hybrid camera. But it has shone through as a fantastic concept for this camera project. Infrared photography opens up a whole new dimension and to be able to combine this with SLR cameras and lenses that were designed to use infrared film is just awesome. If you are thinking about converting a DSLR to infrared then I would strongly suggest you look at this option of using a Sony Nex as the electric film on your favourite SLR kit that has been sitting in the cupboard feeling very unloved for the past 15 years. 

If you are just going to use this camera for infrared then you do not need to worry as to whether or not you can fit the IR Filter up behind the mirror of the SLR. For specifically as a dedicated infrared SLR, you can convert any SLR. Now there is a strong statement but I believe this to be correct. You only need to remove the IR Filter from the Nex APS-C sensor and rebate the sensor to the exact Film Plane measurement. It's your call whether to modify the existing camera back permanently, or make a custom back so you could still change back to film. You should make a custom back for collector cameras and keep the original in tact as good quality film cameras are increasing in value now.

If you have any queries or need advice if tackling this project then I am happy to assist.
Click on the photos to enlarge.

An average front yard transformed to a magic land in IR
Roses are Infrared

Infrared B&W Noir

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