Home Theory Megapixel, sensor size, aperture, ISO

Megapixel, sensor size, aperture, ISO

by Güray Dere

The basic terms in the article title are familiar to everyone who is interested in photography. So I will cut short of what they are and be more interested in how they play a role in macro photography.

What we want is very simple! The framing is of course very important, but at the moment it is out of question. We want a clear, sharp and bright picture. In general, the more detail we see in the macro, the better it is. For more details, we are getting closer and closer. In terms of clarity, megapixel – sensor size – aperture – ISO values play a role. But there are some limits that we can not reach the details we want to capture even if we have the magnification. For this, it is necessary to know the basic concepts first.

Aperture is a sensitive subject and we have a direct control of it. Let’s discuss it first.


Aperture has the same function as our pupil’s constriction and dilation against the light. In its simplest terms, it is a mechanically dimension-changing aperture that adjusts how much light will enter inside. If the diaphragm is open we can take plenty of light and shoot in dimly lit environment.

We generally glorify lenses with wide apertures. For example, when someone says f1.2, it attracts attention. Whereas in the macro world, especially in handheld shooting, aperture is often used at f10-14 range. Most modern macro lenses are f2.8. But if you don’t use that lens in portraits, f2.8 doesn’t really mean that much. It is unfair to underestimate an older, higher aperture macro lens without researching just because of its starting F value.

So why do we close the aperture? We’re losing the light, everything is getting darker. We have to increase the exposure time and we are fighting the vibration.

depth of field table
Depth of field table for various magnification and aperture values

You know we’re increasing the depth of field by closing the aperture. Someone who had not previously taken macro, may be surprised in the first photo that  only one antenna of the insect may appear sharp and everyhing else is blurred. In a 1: 1 magnification, even at f11 aperture, clearly visible area will only be 1.32mm deep. Only the eyes of a fly can be displayed clearly at this value 🙂 As the magnification increases, the DOF (depth of field) problem will also increase.

In addition, the lenses often produce the sharpest image in the mid-aperture. You can see this difference by closing the aperture 1 or 2 stops from the wide open value. Usually values such as f5.6 – f8 produce quite sharp results.

Many sources on macro says “close the diaphragm for image clarity” and you may think i say the same. But keep in mind that closing diaphragm has serious limits. We don’t go beyond f16 unless we have to, and we open the aperture again as we increase our magnification. Otherwise we lose sharpness.


We closed the aperture. This time the light is not enough, what will we do? We know that by increasing the ISO value, the picture is brightened again and we can reduce the exposure time. In digital machines the increase in ISO works by multiplying and increasing the electrical signal value read from the sensor. Let me try to explain this with an example.

Let’s consider a pixel in the photo. Let us assume that its numeric value must be 100 to give us a bright and beautiful image. These numerical values tell us the color and amount of light.

We did a shoot at ISO 160 in a sufficiently lit environment. Our pixel looks pretty good to us. But when we look at it carefully, we see that its value is 101. Because our sensor is not perfect. Electronic components carry noise. Our sensor added +1 unit of noise. And sometimes it reads 99 indicating -1 unit noise. But they all look the same way. Dots of the same color lined up side by side. Some are 99, some are 100, some are 101 but they all look the same color. Everything is OK.

Now, let the light go down 10 times. We can for example closed the aperture. What are we gonna do? The first thing that comes to mind is increasing the exposure time. If we expose 10 times more, we can still have a nice, bright picture. But we don’t have a tripod. We can not make handheld shooting with a 10 times more exposure! Then we will increase the ISO.

If we now take the same shot at ISO 160, our sensor will read the numerical value of the pixel as 10. That’s too dark. We set the ISO to 1600 to make the reading as our desired value of 100.

In fact, our sensor continues to read the pixel as 10. But let’s remember the noise. Our sensor adds +1 or -1 noise. So the value that should be 10 comes from the sensor as 9 or 11. ISO 1600 multiplies the read signal mathematically by 10. So our pixel becomes 90 or 110. There is a problem now. Some of the side by side pixels are 90, some are 100, some are 110. In fact, they should all be the same color, but each point looks a little different now. The image is grainy!

As we increase the ISO value, we also raise the noise signals within the numerical values indicating the amount of color and light coming from the sensor and cause noise in the photo. The more we increase the ISO, the greater the noise signal.

Grain/noise in the macro is a situation that we do not want at all, but a grainy photo is better than not to take that photo. If we don’t have a long exposure chance or a lighting device, we will increase ISO. As sensors develop, we can use higher ISOs in each generation. With K-x, I can go up to 1600 ISO. I couldn’t have imagined it 10 years ago. High ISOs are not bad if the resulting photo is not too dark.

Now I can get details on the Sony A7II at ISO 3200s. The sensor noise level is very low on special bodies such as the Sony A7S series, which can be take clear pictures at  hard-to-believe ISOs. Even values such as ISO 56k can be used.

There are some options you can find in the body settings as “noise reduction”. Here you can find out how much grain cleaning is done at which ISO values. I prefer to turn them off completely. Instead of using the body with limited processing capacity, I use stronger softwares on the computer for noise cleaning. It’s not only more effective but maybe I’m saving some battery power because I turn off a function in the machine.

Sensor size

Basically, the larger the sensor we have, the better. From compact machines to APS-C, and then to full-frame classes, the sensor size increases.

Sensor size

Assuming we use different sensors to get the same photo, the larger sensor collects more light, more details. As the image projected on the sensor by the lens is larger, it is less affected by diffraction and maintains sharpness at small apertures. Our sensor makes light / color measurement more accurate as a single pixel occupies a larger area as it grows. The noise is still low when we increase this signal with low error margin by increasing the ISO. We can use higher ISOs more conveniently.


You actually have to think of it as the megapixel / sensor size. If our sensor tries to produce very high megapixels, even if the sensor is large, the quality may be reduced as the area per pixel is low. Of course, this comparison can be applied to two sensors with similar technological features. Every day, changing technology and increasing megapixel values say otherwise.


There’s a lens thing. Lens resolutions may not saturate high megapixels. If you try to pass 24 million pixels through a small hole with the aperture closed, your lens will probably not be able to handle it. Looking at the full size image we will see a non-sharp picture.

After a certain size, large pictures may begin to produce difficulties in practical use. My Pentax K-x with 12.4 MP, 12-bit color depth sensor produce an average of 10MB of files in RAW. Pentax K5 with 16:28 megapixel, 14-bit color depth sensor has 20 MB RAW files. I can feel that above 24MP bodies will cause performance problems in image processing programs and will fill hard drives over the years. Computers need to be renewed at the same speed.

Briefly, the subject of megapixels will be one of my latest points in a camera. If you take a high quality 1MP image and double the size with Photoshop, you can get a better-looking photo than an image from a sensor  forced to be 4MP. Do not fall into the megapixel trap, especially on compact machines.

Update – May 14, 2015

Now I use a Sony A7II, 24 MP full-frame body. The big files I mentioned above make me a little headache. The RAW file format with Sony ARW extension is a compressed format, but it takes 24MB per photo. When i switch off compression it takes 50MB per shot. Compared to Pentax, my productivity has fallen slightly. Photo processing began to take 2-3 times longer. I also consume my storage capacity quickly. But it’s worth it. Sony has come to a very good place in photography in recent years. I can say that I’ve reached the level of detail I’ve been looking for.

You may find interesting

Leave a Comment