Home » All things techie, Featured, Tech

How to Get the right DOF in your macro photographs?

13 November 2008 One Comment

Lets get some things cleared first, the larger the aperture the smaller the depth of field that means the smaller the f stop the smaller the depth of field. I repeat in bold

Large aperture = Small DOF

Small Fstop = Small DOF

So what does that mean when u are using say 2.8 Fstop on your macro lens the depth that will be in focus will be less than when using say 4. I would like to look at depth of field as the volume in focus. Remember that the DOF extends to the front and back of the object in focus but usually more to the back than the front. So when we are taking a Macro photograph our aim is to get the finer details in sharp representation. So it is not about having a large volume in focus or a small volume in focus but to have a ideal balance where we are representing the best combination of the fine details and bokeh.

The DOF gets deeper as you go farther from the subject. For example, if your subject is at 40 feet, the depth of field would be greater than when your subject is at 4 feet, so the closer you are the smaller the DOF.

Another factor that affects the DOF other than the aperture is the Focal length. Longer focal lengths have smaller DOF. That is when you use a 100mm macro and a 50 mm macro the 100 will have relatively smaller DOF than the 50 mm(for similar construction). So when choosing a lens for your macros do take into mind the DOF consideration also. Most medium telephoto to telephoto type Macro lens have very small volume in focus or DOF thus most of the good models have very small apertures also.

Now that covers the basic idea about DOF and what controls it, let us move on to considering DOF in terms of Macro Photography. Remember that most dedicated macro lens are primes so you only have a question of focal length if your kit has more than one macro, even in that case when shooting a picture the focal length remains constant. If you are on a zoom macro i would suggest you keep the focal length fixed and then move your self to frame the picture because this will give you better hold of the DOF.

Let us first deal with the question how much DOF one needs to get the right macro. The best way to do it is to think about the volume that you want in focus, and adjust till you get that correct, the calculation of the volume can be done mathematically and then getting it in focus done by trail and error, so say your trying to get an insect 2mm by 1mm in size, now look at its orientation towards the lens and compensate in the dimensions for this so mostly your looking for a DOF of around 1mm, this calculation should be done mentally and that too quick because the insect wont wait for you. Don’t worry if you can’t do all that, you will get the hang of it in no time. Now we arrived at a DOF of 1mm by mental calculation, now look at some feature in the frame that is near the insect and is around 1mm now adjust aperture so that the whole of that feature is in focus(Do this only until you get the hang of it, you are photographing the insect and ideally you should be looking at it). Now you see that the mental exercise ,of calculating is futile, that was just to give the newbies an idea of how to look at DOF. Basically you should be looking at the image and deciding when the DOF is right.

How do you know when you have the right DOF?

When taking a picture you have an idea of what you want the picture to show. You have the right DOF when the picture has the right message, ok that is if you want to show the insect cleaning its legs and you want the onlookers attention on that a DOF that include a little of the fly’s face, maybe up to the eye and the front legs which it is cleaning should come in the DOF and rest excluded. This is actually up to the Photographer and this is what makes one photo unique from another.

Now the actual part of getting the DOF right is all about experience keep on clicking and you will know when it is right.

That said there are some other factors that need to be given consideration after getting the DOF right but is directly affected by the process of getting the DOF right. The best example is the amount of light coming in when the aperture is turned down.

When you need a large DOF and you bring down the aperture to a large f-stop(remember large f-stop small aperture) you are bringing down the amount of light also. There are some ways that you can compensate for this:

Using a high ISO, when you are in lack of light you should be going to a higher ISO. DO remember that higher ISO can mean an image that is noisy, so reconsider the DOF that you selected because you might end up with an image that has a large DOF but that is too grainy, or if you leave the ISO at a low setting your image will have a large DOF but wont have enough light to show the details that you intended to show with the DOF, so get a balance on the DOF to ISO relation.

Using a flash, there are ring type flashes or flash diffusers or flash directors any of this will suffice but some insects can be scared away by the flash. The ring type flashes can be the best to use due to their least obstructing nature.

Positioning your self properly, look at the subject and position yourself such that your are taking the picture of the best illuminated angle and you are not casting a shadow on the object. If the object in consideration is stationary, like a flower, do make sure that the time your photographing is right. An example would be when photographing a flower in your yard, you have the option of selecting the time at which to shoot that is may be in the morning it lies in the shadow of your house but in the evening or afternoon there is ample light.

Another thing that is directly affected by the DOF is motion blur caused when the shutter speed needs to be brought down as other parameters can not be varied. Motion blur can be reduced by stabilisation systems if any. The safer bet is to invest in a tripod , do remember that the macro lens are usually heavy thus you will benefit from investing in a tripod. If a tripod is out of question consider a mono-pod.

The most important thing about the whole deal is that you need to practice because these are fine skills that you learn while doing, so stop wasting time and start shooting.