How To Calculate Bellows Extension For Large Format Macro Photography
In this article, I share a simple method that you can use in your large format macro photography to help you quickly establish the amount of bellows extension you need for your intended image and desired magnification.
You can use this formula to quickly determine if your desired lens will work at each of your desired magnifications (i.e., 1:1, 2:1, 3:1).
There are times when I want a greater magnification than 1:1 and so I will show you how to calculate this scenario as well.
Quick Tip - You really only need to do this calculation one time for each of your lenses and then create a personal cheat sheet.
If we stay with the same 180mm lens that I used in the example for the first article in this series (How To Determine Your Near Focus Limit), and I want a 2:1 magnification (2X size), how much bellows extension will I need for this scenario?
Using the following formula, you can figure out the required bellows exertion for any lens and camera combination.
Tip - If you have not purchased your camera yet, it is a good idea to run your future camera through these calculations to make sure it will meet your needs.
M = magnification ratio
B = bellows extension
F = focal length of lens.
M = (B-F) / F
In our example, we want a 2:1 magnification using our 180mm lens on our camera 4x5 view camera that has a maximum bellows draw of 480mm for example.
M = 2/1, F = 180 B = ?
2/1 = (B -180) / 180
Using basic algebra, we can solve the equation.
(2/1 * 180) = B -180
360 = B - 180
To solve for B, we simply add 360 + 180
Bellows extension required = 540mm
In this example, I don't have enough bellows extension available on my Chamonix camera to achieve 2:1 magnification using my 180mm lens. If I really wanted to use this lens and this magnification ratio, I could use my diopter or I could use my Linhof Technikardan that has enough bellows extension.
I have a 120mm lens that I could use to achieve 2:1 magnification with a required bellows extension of 360mm.
I think it is important to know the math behind these various method, so that is why I share the details with you. However, there is a shortcut that you can do to quickly determine the amount of bellows extension you will need for any given lens and magnification.
Here is my shortcut. For any given focal length, I double it (120 x 2) = 240, and then I add the focal length to that result (+ 120) and this result is my required bellows extension (240 + 120) = 360mm.
For my 150mm lens, it would be 450mm. An even faster shortcut is to triple the focal length for 2X magnification (120mm x 3 = 360mm bellows extension for 2:1 magnification).
In this large format macro photography mini-series, I share three important methods and techniques that will help you quickly plan and create large format macro photographs with total confidence.
In the first article, I shared how you can calculate the near focus limit for any of your shorter standard lenses.
In this second article, I walked you through how you can calculate the required bellows extension for your large format macro photography projects.
In the third article, I teach you how to calculate exposure compensation to ensure you are giving your film enough exposure in addition to some extra bonus tips to take your large format macro photography to a new level.
I use all of these skills that I share with you in this series on large format macro photography on a daily basis as I create my large format botanical photographs.
If you enjoy flowers and botanicals, I have a comprehensive dedicated video workshop where I take you to the deep end on how to create large format floral still life photographs. This is one of my best selling large format video workshops of all time and that makes me very happy to know that so many other large format photographers enjoy creating fine art botanical photographs.
I am actively developing a large format photography resources page where articles like this are all centralized and easy to find. You will find this article on this page along with a lot of other related large format information that I know you will find useful and helpful.
LARGE FORMAT MACRO CHEAT SHEET
For 2 to 1 (2:1) magnification for any lens, your bellows draw will be three times the focal length and the exposure compensation for this will be 3 stops.
For example, let's assume I want to use my 180mm Nikkor lens on my 4x5 view camera for some 1:1 close-up flower photos. I know my bellows extension will need to be 2X 180mm (360mm) and my exposure will be 2 additional stops plus what I metered, plus any filters. I will then apply reciprocity failure times for my film.
New exposure = base exposure x exposure compensation factor + filter compensation and then a correction for reciprocity if applicable.
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Tim, thanks for these very informative and helpful tips on LF photography. I am just getting set up to do 4x5 work, and find your guidance invaluable.
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