How To Calculate Exposure Compensation For Large Format Macro Photography

October 31, 2019  •  1 Comment

How To Calculate Exposure Compensation For Large Format Macro Photography by Tim LaytonHow To Calculate Exposure Compensation For Large Format Macro Photography by Tim Layton In this article, I share a simple method for calculating the exposure compensation for any amount of bellows draw for any large format lens.

In the second article in the Large Format Macro Photography series, I walked you through how to calculate the required bellows extension for any lens and magnification ratio and in this article, I am going to cover the steps for how you can calculate exposure compensation with the extended bellows. 

In the first article, I shared how you can calculate the near focus limit for any of your shorter standard lenses.

Let's jump right in and get to the point. 

Free Analog Photography Journal by Tim LaytonFree Analog Photography Journal by Tim Layton Building off of the example I used in the second article, I wanted to achieve 2:1 (2X) magnification using a 150mm lens.  I determined that I would need 450mm of bellows extension.  If you need a refresher on how to calculate the required bellows extension, please review that article

The last piece of the puzzle after determining the magnification ratio and bellows extension is to calculate your exposure time required for the extra bellows extension. 

Here is my shortcut...

New exposure = base exposure x exposure compensation factor + filter compensation + correction for reciprocity if applicable. 

Let's walk through a scenario so you know how all of this works.

Let's stay with our example of using a 150mm lens for our new macro exposure with a 2:1 magnification.  This scenario requires 450mm of bellows extension and let's say that when we metered our subject, we decided we needed a 2-second exposure before any additional adjustments.  

Formula Legend

B = bellows, F = focal length 

Exposure Compensation = (B / F) squared 

Compensation = (450 / 150) squared or 3^2

Exposure Factor = 3 x 3 or 9 seconds exposure factor (3 stops)

New exposure time = 9 (compensation factor) x 2 (base exposure) = 18 seconds 

Note: based on the film you are using, now lookup the reciprocity failure for 18 seconds and adjust as needed and that is all there is to it!

Tim Layton with Large Format Silver Gelatin Floral Still Life PrintTim Layton with Large Format Silver Gelatin Floral Still Life Print 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.  

LARGE FORMAT MACRO CHEAT SHEET

Tim Layton holding silver gelatin floral still life print. For 1 to 1 (1:1) magnification for any lens, your bellows draw will be twice the focal length and the exposure compensation for this will be 2 stops.

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.

Share your thoughts and comments in the section below.

-Tim Layton

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Comments

Robert Shanebrook(non-registered)
I have always used the dial light meter calculator. It doesn't require any math and is fast. Using the f# dial, align the focal length in inches with 1 second. Measure the distance in inches from the center of the lens to the focal plane. On the f scale read factor that is adjacent to the total extension. No math required. Then deal with the reciprocity.

Reciprocity on modern films i.e. E100, T-Max and Portra is small since the emulsions are doped to efficiently capture and hold electrons. This is done with no sacrifice in other film characteristics. Film with high reciprocity factors expose the grains and then the electrons are lost, the grains fail. Kodak and Fuji implemented this in the 1980s.
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