Post by CSLR on Dec 17, 2006 1:48:36 GMT
In another thread Jon asked
As this is a more appropriate place, I am opening this thread to discuss the details.
The picture that we were looking at was this one of the former City Road SB station tunnel:-
Firstly I must clarify what we are looking at.
The above picture is a low resolution copy made for posting and the impression of HDR is purely an illusion caused by the way the image was constructed. To give an example, this is a closeup taken from the image above.
This is the same section of the picture taken directly from the scan that was used to make the low resolution image.
Even this picture will not come through at its best as it is a jpeg compression. The original tiff file was created through a 48 bit fluid scan from a 35mm colour transparency. To view this in all its glory, you should really see it as a 19"x13" print - or larger.
In response to the question of techniques used for multiple flash photography, there are several ways to do this. The most common is to illuminate a subject using a number of flashes that are out of shot and which are fired simultaneously. This is the method often employed in professional portrait photography. It can be used to illuminate railway subjects, but is not really suited to tunnels as there are very few places to hide the flashguns.
The method that I have used here is to eliminate as much of the remaining lighting as I can to avoid it burning out sections of the photograph during a long exposure. This included the tunnel lights which were temporarily fitted with partial deflectors (these lights could not be turned off for safety reasons). The camera was mounted on a solid tripod to avoid any movement from wind or vibration.
When lighting the subject, I moved down the tunnel firing off a flash at one wall at regular intervals. The camera could not 'see' me as I remained in the dark areas. I repeated this procedure another five times, illuminating different stretches of the tunnel on each occasion. With each pass, I filled in the areas of shadow that I had previously been working in. At the end of this I fired off flashes in the cross passages.
At certain points in the tunnel, I varied the interval between flashes slightly to add extra light or to reduce it slightly in order to accentuate the shape of the tunnel and to avoid making everything look flat.
Tips:
1. Wear non-reflective clothing.
2. Carry spare batteries in your pockets.
3. Tape over the red light on the back of the flash to avoid it appearing in the photograph.
4. Place a small light behind the camera so that you can locate where it is in the darkness.
5. You will not have to calculate the length of the exposure as this will be determined by the time taken to fire all of the flashes.
6. The aperture setting is generally the same as would be used for a flash photograph, but with the average distance of 'flash to wall' being substituted for the usual 'camera to subject' measurement. If the subject is dark, you may need to increase the aperture by 1-2 stops.
All of these comments relate to photographs taken on film stock where exposures could be 40 minutes or more.
If you are using light sources other than flash and/or if other light sources are present during the exposure, you are advised to learn about the effects of reciprocity failure - that is beyond the scope of what I am writing here.
For digital photography different rules apply.
Once you get past a few seconds exposure, digital pictures can be affected by noise. Following a discussion with Anne (V3.1), I am now experimenting with methods that will overcome this problem and initial results are promising. It is possible that you might find techniques out there that go some way to resolving this problem, but I prefer to develop specific solutions for my particular requirements.
Note: The pictures on this page were taken during an official visit with a track possession order. For safety and security reasons, public visits are not granted to this site. In addition, the use of flashguns and/or tripods is generally prohibited on the London Underground system during traffic hours. These notes are therefore provided to satisfy the curiosity of the questioner, although they may well be adopted for use elsewhere.
You should be advised that other techniques are available that will give similar results and which may be more practical for you.
These pictures are copyright and are posted here with my permission for discussion purposes only. Please ask if you wish to use them elsewhere.
That first photo is amazing ... I spent part of this afternoon playing with HDR images, and the quality of the image reminds me of that. Out of sheer curiosity, how was the multiple-flash setup done?
As this is a more appropriate place, I am opening this thread to discuss the details.
The picture that we were looking at was this one of the former City Road SB station tunnel:-
Firstly I must clarify what we are looking at.
The above picture is a low resolution copy made for posting and the impression of HDR is purely an illusion caused by the way the image was constructed. To give an example, this is a closeup taken from the image above.
This is the same section of the picture taken directly from the scan that was used to make the low resolution image.
Even this picture will not come through at its best as it is a jpeg compression. The original tiff file was created through a 48 bit fluid scan from a 35mm colour transparency. To view this in all its glory, you should really see it as a 19"x13" print - or larger.
In response to the question of techniques used for multiple flash photography, there are several ways to do this. The most common is to illuminate a subject using a number of flashes that are out of shot and which are fired simultaneously. This is the method often employed in professional portrait photography. It can be used to illuminate railway subjects, but is not really suited to tunnels as there are very few places to hide the flashguns.
The method that I have used here is to eliminate as much of the remaining lighting as I can to avoid it burning out sections of the photograph during a long exposure. This included the tunnel lights which were temporarily fitted with partial deflectors (these lights could not be turned off for safety reasons). The camera was mounted on a solid tripod to avoid any movement from wind or vibration.
When lighting the subject, I moved down the tunnel firing off a flash at one wall at regular intervals. The camera could not 'see' me as I remained in the dark areas. I repeated this procedure another five times, illuminating different stretches of the tunnel on each occasion. With each pass, I filled in the areas of shadow that I had previously been working in. At the end of this I fired off flashes in the cross passages.
At certain points in the tunnel, I varied the interval between flashes slightly to add extra light or to reduce it slightly in order to accentuate the shape of the tunnel and to avoid making everything look flat.
Tips:
1. Wear non-reflective clothing.
2. Carry spare batteries in your pockets.
3. Tape over the red light on the back of the flash to avoid it appearing in the photograph.
4. Place a small light behind the camera so that you can locate where it is in the darkness.
5. You will not have to calculate the length of the exposure as this will be determined by the time taken to fire all of the flashes.
6. The aperture setting is generally the same as would be used for a flash photograph, but with the average distance of 'flash to wall' being substituted for the usual 'camera to subject' measurement. If the subject is dark, you may need to increase the aperture by 1-2 stops.
All of these comments relate to photographs taken on film stock where exposures could be 40 minutes or more.
If you are using light sources other than flash and/or if other light sources are present during the exposure, you are advised to learn about the effects of reciprocity failure - that is beyond the scope of what I am writing here.
For digital photography different rules apply.
Once you get past a few seconds exposure, digital pictures can be affected by noise. Following a discussion with Anne (V3.1), I am now experimenting with methods that will overcome this problem and initial results are promising. It is possible that you might find techniques out there that go some way to resolving this problem, but I prefer to develop specific solutions for my particular requirements.
Note: The pictures on this page were taken during an official visit with a track possession order. For safety and security reasons, public visits are not granted to this site. In addition, the use of flashguns and/or tripods is generally prohibited on the London Underground system during traffic hours. These notes are therefore provided to satisfy the curiosity of the questioner, although they may well be adopted for use elsewhere.
You should be advised that other techniques are available that will give similar results and which may be more practical for you.
These pictures are copyright and are posted here with my permission for discussion purposes only. Please ask if you wish to use them elsewhere.
