Month: September 2022

How many MP do you need in your camera?

The Megapixel war

Camera producers know that many consumers look to parameters and arguments that are easy to compare. So a camera with a certain amount of megapixels must be inferior to a camera that has double the megapixels, right? That is at least what the producers want you to think, so you buy a new camera or a new smartphone with better technical specs. But it may not necessarily be so that 24MP is better than 12MP. Let me explain why.

The need for MP

You actually need less MP than you think. Obviously, the more MP and the more resolution on your sensor, the more fine grained the image is and all things equal that must be better, right? Yes and no. Notice what you do when you view an image: instinctively you hold it in a distance so you can take in the entire scene. If you hold it too close, then you feel like you are watching a tennis game: your eyes ping pong all over the place, and it does not feel natural.

You can try this with your TV: If you go very close to it, you can probably spot the individual pixels, but as you move away, it all gels together to lines and curves and colors and shades. So the viewing distance is key to determine how much resolution you need. And the further you move away, the less resolution you actually need! I have not tried this, but the rumors has it that a billboard only has 1-2MP!! So the further away, the less resolution you need!

There are however some situations where lots of resolution can be useful.

Cropping

If you often find that you crop a lot in post processing of your images, then obviously the more MP’s you got, the more you can crop and still have an acceptable number of pixels left for the final image. And the more you have to start with, the more likely it is that the final result has sufficient resolution.

Viewing distance

Sometimes your viewers do not hold a natural viewing distance, simply because they use your image in another way than traditionally. For example I often stand in filled trains with – if not billboards – then large adds, and in those cases I get very close to the ads and hence the resolution needs to be good in order for me not to see a lot of unrelated dots. It can also be an exhibition where the audience find it natural first to view your image from a distance, and then go close to the image to study a detail. Also here the viewing distance is the parameter the necessitates lots of pixels.

Post processing

In some cases when you do post processing of your images, and especially where you use one part of a picture to repair or fill in another part of the image, it can be easier to do if the material is more fine grained when you work zoomed in several hundred percent. Again, it is because your post processing work takes an “unnatural” viewing distance.

How much is enough?

I have with my Nikon D700 (12 MP) printed images in size 70×100 cm and the client was very happy with the result. That is how little you need to print large. So if you just want to print large with a viewing distance, then in most cases 12MP will suffice. Also, if what you primarily do is upload your images to social media, it will undergo a lot of compression etc, so you have no benefit of a higher resolution. But, admitted, it seems like the normal resolution for a good enthusiast camera – both APS-C and FF – is around 24 MP.

Any disadvantage to high MP?

The file size will grow with increasing MPs and your hard disk and  computer will feel the weight if you shoot RAW especially. Also, camera shake is more likely, as the fine grained sensors will be super sensitive to even the smallest movements, where there is more forgiveness in a sensor with big and fat pixels. Also, because the light is being hashed up to smaller and smaller units, the exact reading of the amount of light becomes more difficult and precise micro contrast is more difficult to obtain with a high resolution sensor.

Bottom line?

I shoot with anything from 12MP (Nikon D700), 16MP (Nikon D4), 24MP (Nikon Z6ii) to 36MP (Sony A7Rii). And one of my biggest disappointments was to work with the Sony files in LR. I may have had expectations beyond what is reasonable, but I must say that I did not reach the true “nirvana” that I had hoped for.

My experience tells me that it is much more important that you have a great lens that can feed the sensor with the best light possible combined with a sensor able to read the light precisely, than it is to have lots of megapixels. And that is probably why so many photographers in this day and age still hold on the their Nikon D700 coupled with some AI-S glass from back in the days, as it still delivers images with 3D feel and micro contrast far beyond what many more modern and high res sensors can deliver. But it is a complicated message to convey, and not one that makes the marketing headlines easy to make, and hence we will probably continue to see the pixel war continuing for years to come.

 

 

Should you buy a fast lens or not?

To speed or not to speed

There are arguments for and against a fast (or faster lens), and in this short blog I want to go through some of the pro and cons of a fast lens. I will not make a recommendation, as I think the decision is yours as you have to live with the consequences of the choice you make, not me. So I think it is important that the decision stays with the decision maker: you.

Fast versus less fast

One of my favorite lenses: The 135mm DC from Nikkor. Also comes in a 105mm version,

Fast glass is glass that will allow you to go to a small f-stop number i.e. a large aperture. This is also referred to as shooting wide, as the lens’ aperture blades are opening up as wide as they can to make use of all the glass in the lens.  When you have fast glass, the glass will allow you to shoot at fast shutter speeds, as the exposure time can be kept down (= fast) because the lens takes in a lot of light.

There is not absolute definition of what fast glass is, but I would say that from around f/2 and wider (say f/1.4 or f/1.2) we are talking very fast glass. And some glass can go down to f/0.95, but when talking Nikon, I believe their fastest glass is the 50mm f/1.2.

One characteristic of fast glass is that the front glass is BIG, and the longer the lens, the bigger it gets. For a short lens like 24mm, you will probably not notice if the glass is f/2.8 or f/2, but the longer the lens gets, the more “crazy” big the front glass gets. You have probably seen bird or wildlife photographers with long, long lenses and crazy big glass at the far end of the lens. They need all the light they can get to freeze a bird in flight with a fast shutter speed.

Weight and size

This brings me to the first point about fast glass: it is heavy, and you will need to be prepared to carry a significant weight if you want to have fast glass. And the longer the lens, the worse it gets. Secondly, the sad observation is that ONLY when you shoot very wide will you benefit from the glass at the edges of the lens – the rest of the time you only use the center part. So if you shoot wide very seldom, you will carry a lot of glass for some very rare occasions. It may not be worth it, if weight is important to you.

Lens design and image quality

I am no expert on lens design, but I have shot with so many different lenses that I can tell that the wider the lens gets, the more difficult it is for lens designers to maintain the good characteristics you see when you are shooting with middle-of-the-road apertures. Lenses wide open often suffer from being soft overall, being extra soft in the corners and if you shoot into the sun or stark contrast, these lenses also tend to suffer from chromatic aberrations to a significant degree. If you are willing to buy an expensive lens, then the lens designers can mitigate these issues, but – as far as I can tell – there is something that makes a fast lens difficult to design with good control of sharpness and aberrations. You can study the MTF chart of the lens to get an idea about how it performs wide open.

Depth of field

Shooting wide gives a wonderful shallow depth of field, and if that is what you are after, then a fast lens can be wonderful. However, be mindful that depth of field is not only a question of aperture, but also distance to the subject. So you can actually get a shallow depth of field if you (zoom out and) move close to your subject. Of course this may not work if you are shooting with a prime, but try it out and see if moving close to your subject will give you the depth of field you seek. Any macro photographer is suffering the opposite issue: even though they are shooting at say f/22, they are so close to the subject that the depth of field is super shallow anyway!

Shooting with a shallow depth of field can give wonderful background blur.

Better sensors

The world moves forward, we get better and better technology, and the image sensors in cameras are no different. Today they can be “starved” with light and still come out with decent results. I think this is both due to the sensors getting better and better, but also because the noise reduction software in the cameras gets more and more advanced and can do computing that is much more advanced than just 10 years ago.

The camera image sensor, here from the Nikon Z50. In a mirrorless camera the sensor is completely exposed when the lens is removed; on a DSLR the sensor is hidden behind a diagonal glass.

I often shoot at ISO 800 with no problem, and I know that I can go higher. So to some extend a modern sensor can compensate for a lens that does not take in much light. And that is why you will see that more and more new lenses are designed with a not-so-impressive maximum aperture. Lens designers prioritize other factors (weight, size, etc) over the speed of the lens.

Price

As you have probably guessed, the price if a fast lens is high, simply because there is more or larger glass involved. You can get fast glass that is not too pricey, but I ask you to study the MTF charts before you invest! You may find that the lens quality wide open is not what you hoped fore. Many lens producers use the speed of the lens as a marketing tool, and hence the engineers are pressured to design a fast lens with the image quality being second to the speed. So learn how to read an MTF diagram, and study it well before you invest.

 

Psychology

The last thing I want to mention is pure psychology, and maybe not much to do with the images you bring home. But if you can choose between say a f/2.8 lens and a f/4 lens, and you go for the f/4, then every time you come home with an image that suffers from either camera shake or subject blur, you will ask yourself if this was because you did not go with the fastest lens alternative. If you buy the fastest and the best lens of the two, then you have taken out that excuse and know that the issue is due to you and not your gear.

Conclusion

I hope the above was useful. I may just have confused you at a higher level, but I hope you see my point that I really don’t want to make the decision for you. I hope this post has helped you make a (more) informed decision – best of luck!