When focusing with the bellows

Dear All,

I am new to this forum, introducing myself last week or so. I am representing a group of total beginners in LF photography from Greece, and since none of them speak English very well they have asked me to represent them in forums, etc.

I have a question from a member of the group, which is regards to focusing in LF. It goes as follows:

"When we focus in LF photography, isn't it like zooming a bit? I mean it should have an impact on what we see on the ground glass, as we are moving the lens or film plane backwards or forwards, right?"

I told them that it doesn't work exactly like this, as there are no zoom lenses in LF photography. It is more like - so to speak - moving the whole camera closer or further away from the subject (they are used to 35mm cameras), which will result in a small "zoom" (I explained to her, that I actually mean the going closer or further away with the camera) effect, but we wouldn't call it this.

I might not have explained it very well, that's why I decided to make a post here a well. Was not sure in which category to post, as it has to do with various elements, but I felt that the lens category would be ok for this.

Also I want to try and explain to them the theory behind bellows correction, but I haven't found much. I have seen this video https://www.youtube.com/watch?v=wprcq9HMGVs, but do not know if it's applicable to 4x5 cameras or only to 8x10.

Anybody that can point me to the right direction with an example, a link or otherwise, I would greatly appreciate it.

Thank you all for your time.

Regards...

When you focus any lens on a close object, you are changing the magnification. This is not the same as zooming. Zooming means keeping the object distance constant, while changing the focal length to change magnification.

You need to consider the two options that you have: moving the lens closer OR moving the image plane back.

Each method has its own impact.

best thing to do is break out the camera and start messing around

most questions will be answered that way

But yes it is more like moving the camera back and forth (especially is you are comparing to 35mm at close focus) than zooming.
search for exposure compensation and you will get lots of advice 9more than you want)
http://www.kennethleegallery.com/html/tech/bellows.php
http://www.largeformatphotography.in...nsion+exposure
And welcome

Any time you change the distance from the lens to the the film plane, you change the magnification.

With small changes, this may not be obvious. It definitely is obvious with large changes.

- Leigh

In terms of explaining this to beginners, here are a couple thoughts that may be helpful:

Focus: at a very basic level, when you focus with bellows on a large format camera (any 4x5, 5x7, 8x10 with bellows), it is really the SAME THING that is happening when you focus a 35mm or digital SLR camera: you are changing the distance between the glass of the lens and the film/digital sensor. This makes a particular area in front of the camera lens sharp ("in focus") or not. Typically, what you make sharp is your subject.
With a typical lens on a 35mm/DSLR, the focusing is happening within the "tube" of the lens itself, so you don't see it. With a large format camera, you move the ENTIRE lens forward or backward with the flexible bellows.
This is VERY simplified-- I am omitting any specific optical concepts, the significant differences between SLR and LF lens design, etc. (Not that I could explain these concepts in detail myself!) But I hope this is helpful in getting the general concept across.

Zooming: zooming is changing your effective focal length (e.g. from 24mm to 50mm) and therefore your field of view. Your field of view is how "wide" or "tight" composition in front of the lens is (24mm is wider than 50mm).

At any focal length (whether with a zoom or fixed lens), you still must then focus to make the image itself sharp. So "zoom" and "focus" are different procedures. And where zooming changes your effective focal length (again, e.g. from 24mm to 50mm), that focal length stays the same when you focus (50mm is still 50mm when you are focusing-- how "wide" or "tight" your shot is doesn't really change).

Hope this helps. Apologies for oversimplifications.

To add to the confusion, there are only two ways to focus a camera.

Set magnification and move the camera/lens assembly to put the plane of best focus where desired. This is the way to focus when working close up, isn't very practical for focusing on distant subjects.

Fix the camera's position and change extension. This changes magnification, as has already been said.

Zoom lenses are parfocal, i.e., hold focus when changing focal length. Changing focal length changes magnification. This is why its easy to confuse what happens when zooming with what happens when changing extension. The difference between the two is that zooming doesn't move the plane of best focus while changing extension does.

Varifocal lenses -- they've been made -- change focal length but don't hold focus and must be refocused whenever focal length is changed.

Guys thank you so much for your responses. I have also started reading the book by Simmons regarding the view cameras so I'm getting a lot of info from there as well. Having an active community though is priceless. I also recently bought a very good second hand cambo sc 4x5 but without the rear ground glass and film insertion system. If anybody knows anyone selling a second hand one please let me know. I only have an old lens from my father for now (a 100mm f4.5) but in time will get stuff. Again thanks for the help.


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