It’s great to hear from readers of my blog at any time, but particularly when they’re having trouble with their cameras or need some advice. This gives a chance to explore their problem and everyone can learn from it, including me. Steve recently wrote to me about problems he was having with getting sharp photos using his new Tamron lens. This is what he wrote:
“I use aperture priority and with a Nikon 18-300mm lens all is well. Shifting to the Tamron 150-600mm I have trouble getting pin sharp pictures. I shoot on single point, but my friends are saying matrix is better! What are your thoughts on this please..?”
This is a very interesting question, and one which I know will resonate with other readers: you invest in a better lens, take the time to get to know it, and yet it’s still hard to get the sharpness you are looking for in your images. I’m not going to be able to answer Steve’s question precisely without knowing quite a bit more about his technique and camera settings, but I can offer some ideas that readers can work through to diagnose their own problems.
Before we go on, I want to clarify a couple of points in Steve’s initial question. Firstly, he has given info on the lenses that he has been using, but not about the camera. But given that he is also talking of the Nikon 18-300mm lens (which is designed for cameras will smaller sensors), I assume that he has a cropped-sensor camera. This means that his effective focal length is multiplied by 1.5; a 300mm lens is operating as a 450mm lens, in terms of magnification, the importance of which will be apparent later. Secondly, he talks about using “single point” and also about “matrix”. Single point refers to acquiring focus using a single focus point (that can be moved around within the frame) and is my preferred method of instructing the camera to focus on a particular part of the scene. Matrix – on Nikon – refers to the way the camera measures the light from the scene and has less impact on getting sharp images, except in how it affects the shutter speed as part of the exposure. We’ll look at this later.
When looking at images from your camera, it’s really important to determine if the lack of sharpness is down to “blur”, “poor focus” or “softness”. These are 3 very distinct problems that I deal with in much more detail in this blog. Please take the time to read this – it opens in a new window – before proceeding.
I’m going to work through some possible problems that Steve might be facing with his new lens, with the knowledge that readers are familiar with the terms “softness”, “poor focus” and “blur” as explained in the blog linked above.
- Photos that lack sharpness are often quickly dismissed as “out of focus”, when in fact this may not be the most likely explanation. When using a 150-600mm lens on a cropped-sensor camera, the effective focal length at the long end is 900mm! This is an incredible level of magnification, which will certainly bring subjects nice and close, but also magnifies any shake in the camera or movement in the subject. The old rule of using a shutter speed no less than 1/focal length would therefore suggest that a minimum shutter speed of 1/1000sec is required for sharp images with this lens. Image stabilisers will help – though not with subject movement – but it’s still unrealistic to think that sharp handheld shots can be achieved at much below 1/500sec at full zoom. Magnification of very slight camera movement at this very long focal length is a very likely cause of image softness.
- Following on from this, it’s also worth a quick mention that the maximum aperture of a long zoom such as this will heavily restrict the light entering the camera. At f6.3 – for example – the light entering the lens is less than half that of a lens at f4, resulting in a much reduced shutter speed. It will often be difficult to maintain a high shutter speed of 1/1000sec especially when the light levels are low, but checking the shutter speed during a shoot and adjusting the ISO when needed should assist with keeping the speed high enough.
- Image softness may also occur when the depth of field is very small. It may be that the image is sharp (i.e. taken with accurate focus and at a fast enough speed to freeze movement) but that the depth of field is so narrow that “nothing” appears to be in sharp focus. This is especially the case with a very long lens like a 600mm Tamron. Using the helpful Depth of Field Master calculator we can work out that the depth of field in an image shot with a 600mm lens at f6.3 on a cropped-sensor camera, with the subject 10 meters away will be just 7cms! Bring your subject in to 3 meters (perhaps a butterfly) and the depth of field is 1cm….not even enough to cover the whole butterfly. So what appears to be softness could simply be that the subject is not fully covered by the depth of field either side of the plane of focus.
I tend to advocate shooting with lenses wide open, but it’s worth considering whether small depth of field plays a part in images that seem not to be sharp.
- Of course, there is also a chance that the images could be out of focus. Achieving sharp focus with modern cameras is easier than ever, but it’s still helpful to assist the camera by understanding how the autofocus system on a camera works. The small square (or dot) that is used to represent a single autofocus point in the camera’s viewfinder will likely be much smaller than the total focus area represented by that point. The camera therefore might find greater contrast to lock onto outside the edges of the focus point that you have carefully laid over the subject’s eye. Take time to consider how to help your camera get the best focus, and employ those techniques next time.
Given that there is much written in the link above about achieving sharp focus with a long lens, I will only summarise the my recommendation that for best image sharpness results, a single focus point should chosen, paired with continuous/servo focus mode, and fast frame rate. This allows the user to choose which area of the frame should be focused on, and then allows the camera to continually search for best focus, with the insurance policy of several images from each situation to ensure that at least one is as sharp as possible.
[It is possible that the combination of camera and lens do not achieve accurate focus….something that can be remedied by autofocus calibration. But this is usually not necessary and will, in any case, only fine tune the focus not provide a cure if there is a problem. Refer to your camera’s manual for how to run this calibration.]
- My final suggestion to explain why images from a Tamron 600mm zoom lens might not be as sharp as other lenses is that zoom lenses always give up some sharpness (compared to primes) for the flexibility that they offer. I am reluctant to offer this explanation for the lack of sharpness of a lens since no one reading this wants to consider that their lens cannot create sharp images. But the results from any piece of camera equipment have to be evaluated against the range of equipment on offer. Consider the vast difference in price, weight, portability and availability between the Tamron 150-600mm and the Nikon 600mm f4 prime…the results will be different. It’s worth wondering whether we are looking too critically at the final images.
Having said that, very few people need to be able to print huge images which are pin sharp, and we sometimes get caught up in 100% views of small sections of images, rather than keeping the real-world uses of our images at the fore-front of our minds. I say this with a guilty smile on my face as I am certainly known to do this sometimes! I should say that I absolutely believe in the pursuit of sharp images – or at least the sharpest images that our kit and the conditions allow – but that it should not be the yardstick against which all our photographic work is measured.
This article aims to answer the question of a reader without full knowledge of that reader’s situation. It is not meant to be a diagnosis but a list of possible options to explore. I may be wrong and it could be that the lens has a problem and needs to be returned to the seller (an option to consider if all the above fail to explain the cause) and in which case I hope to have helped narrow down that requirement.
As always, I will be happy to answer questions or responses below!
