LF bellows extention question

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Graeme
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Being new to LF I was just working out an exposure of a test shot i was doing. I was aware I need to take the bellows extension into account but I wanted to check if it's always needed?

Foma 100ISO, I had extended to 180mm with a 135mm lens at f/45 which gave me a result of 1 minute 48 seconds

So, do i always need to take account for it or is it scene dependant?

Cheers
 
Large format zero to hero thread, p58, post 2319 and the answers thereto.

Sorry I can't post a link from my tablet.
 
The bottom line is, bellows extension compensation is bellows extension specific, and as far as I am aware not at all dependent on the scene.

While the extension is only 1.(something small) that of the focal length of the lens, it really can be ignored, especially so for negative films. For slide films, one might want to start accounting for correction by about half a stop. Again, this is, to the best of my knowledge, never scene dependent.
 
@Woodsy just started a train of thought (always a bad thing when you're stuck indoors with not enough to more actively occupy you). I strongly advise that these musings are taken cum grano salis, as I don't even convince myself of them...

One of the potentially large sources of in camera flare is the bellows. When you photograph close up, two things follow.

1. There is a larger area of bellows extended and an increased reflective surface area and
2. Only the centre of the image is being used, so there is more non image forming light bouncing around.

One of the beneficial effects of flare is reduced contrast. It will give more exposure to the shadow areas. This could potentially imply that due to the reduced contrast, the dynamic range of the film is increased, and hence high contrast scenes in close up may be able to cope with reduced exposure.

And that is my (I think defective) reasoning for scene dependence.

I just want to add that there was a very informative quantified article on sources of flare in the British Journal of Photography Almanac in around 1961 from memory.
 
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@Woodsy just started a train of thought (always a bad thing when you're stuck indoors with not enough to more actively occupy you). I strongly advise that these musings are taken cum grano salis, as I don't even convince myself of them...

One of the potentially large sources of in camera flare is the bellows. When you photograph close up, two things follow.

1. There is a larger area of bellows extended and an increased reflective surface area and
2. Only the centre of the image is being used, so there is more non image forming light bouncing around.

One of the beneficial effects of flare is reduced contrast. It will give more exposure to the shadow areas. This could potentially imply that due to the reduced contrast, the dynamic range of the film is increased, and hence high contrast scenes in close up may be able to cope with reduced exposure.

And that is my (I think defective) reasoning for scene dependence.

I just want to add that there was a very informative quantified article on sources of flare in the British Journal of Photography Almanac in around 1961 from memory.

Flare within an optical system and light path is rarely a serious issue these days. baffles within cameras and lenses, and the use of good lens shades reduce the effects to a minimum.
Large format cameras ( or any camera with poor baffling) can produce internal reflections. However these can be minimised by a suitable matt finish, and by the uses of an adjustable lens hood, as are available for most large format cameras. They can be adjusted to limit the field of view, so as to block any light sources from falling anywhere out side the required image area and onto any internal structures.

While flare can reduce contrast by diffusion, it is rarely even over the entire image, as it is largely formed by the Peripheral image circle falling on to one or more sections of the bellows, especially the sky region. this gives a somewhat uneven added exposure.
As I mentioned above this is best controlled by a bellows lens hood or by the use of flags.

Good large format technique, virtually eliminates these problems.

However Bellows extensions, and the exposure compensation require and calculated from the inverse square law. is always an issue. both in large format or when using extendable macro lenses or extension tubes.

However when the exposure is measured at the film plane or sensor this is automatically taken into account. Sinar and others have produced large format film plane exposure meters for this purpose.
 
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