Is Tamron 70-300mm lens gives more noisy picture than 18-55mm Nikon kit lens for same ISO?

Question

I am new to photography and have recently purchased a Tamron 70-300mm Telezoom lens without VR.

I understand that a 70-300mm lens is quite different to 18-55mm lens but I just was just checking the picture quality of both the lenses for the same scene under same lighting conditions (evening, low light).

I found that the pictures taken by Tamron lens were quite noisy for the same ISO setting (even if I decrease the shutter speed) on shutter priority mode (took pics between a shutter speed of 1/20 to 1/200).

Question: Is it normal to have more noisy pics with telezoom lens?

Answer 1

Noise has nothing to do with focal length or the lens per se - it is a by-product of the digitalization of the photo.

Noise usually comes from:

• Amplification: Digital amplification makes far more noise than analog amplification, so increasing the ISO is always better than increasing the exposure in post-production.
• Lack of light: as less photons hit the sensor, there is more margin for error, a.k.a. noise. Imagine 500 000 photons (in total) hitting the sensor - it might well be that shadowy areas of the frame are still hit by ~500 photons per pixel, so if plus/minus 20 pixel will not result in noise, as it is only a small change in relation. Now imagine 5000 photons (in total): the same shadowy area will be hit by 5 photons per pixel - entropy alone is enough to result in clearly visible noise.
• Heat / Entropy: as the sensor gets warmer, the resulting picture will get noisier; mostly from hot pixels (pixels that are more sensitive to light than the average), but also because of thermodynamic effects on electronics. This will usually only be visible in mirrorless cameras and/or with very high exposure times (say: >5").

So if everything is the same - f-number, exposure-time, ISO - it might come down to a smaller t-stop of your Tamron tele-lens and amplification after capturing the photo.

The t-stop...

[...] shows how much light a lens can really transmit. For example, a Nikkor 70-200mm f/2.8 VR II appears to be T/3.2 - it can transmit the same amount of light as an F/3.2 theoretical lens could. This discrepancy is not an engineering fault, but rather a fact of life.

_{Source: "What is T-number / T-stop?" on this site.}

Answer 2

Noise in the jargon of digital imaging describes a lack of uniformity seen in an image. This is akin to “grain”, a similar effect, different cause, common to film photography.

In digital photography, the lens projects an image onto the surface of a digital sensor that is covered with millions of photosites. During the actual exposure, light energy is converted to an electrical charge. This action happens independently in each photosite. The resulting charge is feeble, thus an amplifier built-in to each site boosts the charge independently. The amount of amplification applied at any given site is based on the ISO setting and the brightness of the image playing on that site.

Now all the amplifiers should work alike, but each operates at different efficiencies, so the amount of amplification applied will be slightly dissimilar. This is the root of what plagues us as “noise”. Noise is worse when the image projected by the lens is feeble. Under these conditions, the amplifiers are turned up high. The result is a lack of uniformity due to each site applying differ amounts of gain.

As to noise differences between different mounted lenses: We use the f-stop system as a means to compare image brightness, lens-to-lens. In theory, any lens set to the same f-stop should yield an image with identical brightness. The problem is that the f-stop is a mathematical computation. We divide the focal length by the working aperture diameter to derive the f-stop. This method does not take into account light loss due to the fact that the glass is not flawlessly transparent. The f-stop does not take into account light loss due to reflections off the polished glass surfaces. In other words, the f-stop system is imperfect. Some lenses are calibrated using a “T-stop”. This is an f-stop with improved accuracy based on actual measurements made of image brightness.

So to explain your experience, more noise from one lens vs. another. Likely the lens with more noise projects a feebler image and the camera’s chip logic is turning up the amplification to mitigate. You are thus seeing the effect of uneven amplification. Additionally, your camera yields a JPEG image. This is a file compression algorithm that will under certain circumstances promote more noise.