Old 35mm Film Cameras can go DigitalSaturday 17th September 2016
I have spent half the day sanding down - remounting - testing, sanding down - remounting - testing, sanding down - remounting - testing. To eventually obtain focus on the cupboard knob at Nikon settings of Auto speed + F1:8 using a 1980 Nikon FE + Series E 50mm lens with a digital Sony Exmor 14mp APS-C cmos sensor now successfully mounted at the Film Plane.
|Focus on door knob at F1.8 at approx 3.5 metres.|
Sensor is almost at correct film plane.
My previous posts suggested that if the sensor was to come into contact with the film shutters, then they could be removed from the sensor and a replacement infra red filter could be mounted on the end of the lens. This was incorrect. The IR filter is attached to a thin lens plate. These two have an affect on focus. If removed the sensor has to be moved forward the equivalent distance to obtain focus. So it is a futile exercise thinking this will create space to adjust the sensor before it touches the camera shutters.
To overcome this I mounted the IR & Lens combo at the rear of an SP Tamron with an adaptall Nikon mount. This did work on retaining the same focus but the colour was washed out (probably as I had it round the wrong way).
I then studied the camera internally and could see that there was room behind the mirror to mount the IR & Lens combo against the shutter frame. Using a simple L shape frame of builders flashing with the filters mounted in the middle, this slips nicely in behind the mirror and does not foul any operation of the camera. Now I had a bare CMOS sensor with plenty of adjustment room to the shutters with the IR filters mounted just on the inside of the shutters that provide the necessary focus and infra red filtering.
|Sensor IR Filter & Lens mounted in a L shaped frame.|
This slips in neatly behind the mirror.
The sensor has a frame around it to keep the IR filter & lens above the sensor. Under this frame is a glass screen covering the sensor but this screen is 24.6mm wide. The width of the film rails is 24mm. The sensor could not be moved any closer unless this matter was resolved. I decided to not risk breaking the glass and felt that removing 0.4mm off the side of each film rail would make no difference to the camera being able to shoot film. It would just leave uneven edges if developed as prints - but who does that these days. All my developing involves scanning which crops the film as a neat rectangle anyway. So I filed each rail a bit thinner.
Now I had both plenty of depth to the shutter and width between rails to enable the sensor to move down into the film box rectangle. The sensor mount frame is a very hard plastic and I found the best way to reduce it was with plasterboard finishing sandpaper. After each sanding session I measured the small edges with a micrometer. Once all edges were near equal the sensor was reinstalled and tested. Where the focus disparage really shows up is at F1.8. I placed a chair with magazine copy 1 meter in front of my intended target and this helped identify that the focus was gradually coming closer after each adjustment session with the sandpaper.
|Sensor adjusted for depth with filters removed.|
Still good clearance from the shutters.
Even at the adjusted depth to the film plane, the hinges of the Nikon shutter do not touch the sensor. So now I can move the sensor into the centre. If they did touch the shutter then the sensor IR filter frame could be easily sanded down. This is a real winner for any film camera now. My Canon A1's have a depth to shutter of 2mm so now the adjusted sensor will fit it also. If it fits both the Canon and Nikon then I will assume that this method will work for many film SLR cameras. The issue is no longer the sensor touching the shutter, but rather can the IR Filter/Lens combo be discreetly mounted behind the mirror against the inner frame of the shutters.
As the Exmor CMOS sensor has the small frame to support the IR Filter/Lens a set distance away from the sensor, I theorise that by moving them to the other side of the shutter, so increasing the seperation distance, actually decreased the amount I had to remove from the sensor support to achieve the exact film plane mounting position.
Infra Red Photography
I experimented with removing the IR/Lens and just shooting with the bare sensor. These photos can be easily converted by Photoshop into stunning black and white. See this link. Mingthein Blog But the focus is not correct without the IR/Lens and the sensor would need to be moved further in to compensate. However when shooting with no IR/Lens at smaller apertures the depth of field compensates the focus and the shots are reasonable. So it would be possible to take more off the sensor mounts to make it accurate focus for Infra Red photography and then add set height packers when shooting with the filters on for normal photography. The internal filter frame behind the mirror holds easily in situ with one piece of black tape and can be installed or removed in seconds. A set frame packer could be easy to make for the sensor adjustment. So the camera could be swapped from normal to IR photography in a minute or so. That's one up for film cameras compared to DSLR's.
|Infra Red (in mono) when filter is removed.|
Focus is not correct when IR/Lens are removed.
|Focus accuracy is improved dramatically.|
A bit more sanding and it will be accurate.
My next post will show a number of photos with the sensor correctly on the film plane. I will make them available for download in JPEG and RAW should you wish to check them in your software. By all means check the Exif files. They will read - Sony Nex - ISO 200 - F1.0 - Lens n/a - Speed 5 seconds. The Nikon FE took these photos not the the Sony.
As I have received a few enquiries as to how I am achieving this, once the camera is complete and mounted on the Nikon I will produce an informative manual in PDF explaining all the steps I took. This will save countless hours of work should you now be encouraged to take on this great project.
I can be contacted at email Cross Over Cameras
Please feel free to comment but keep it nice thanks.