# Do lenses have anything to do with noise?



## kkamin (Mar 16, 2010)

Again, do lenses have anything to do with noise?  Can a low grade lens create noise?


Or is noise solely a function of ISO and the sensors size & quality?


----------



## Opher (Mar 16, 2010)

The lens may cause distortion but should not create "noise".  A filter that blocks out some spectrum's of light may help reduce the noise(i think).  If some one more worldly wise could confirm my thoughts that would be great!

Hope that was helpful and more importantly true :er:


----------



## BKMOOD (Mar 16, 2010)

Noise is a sensor / ISO issue.

Actually all pictures have noise. This brings us to the concept of &#8220;signal to noise ratio.&#8221; If the signal (image quality) is really strong, say broad daylight at 100 ISO, the signal ratio is very high and the noise ratio is so low you probably can&#8217;t detect it. It&#8217;s minute. So your picture is, say, 99 percent signal and 1 percent noise. Nice looking picture.

In low light situations when the ISO is high, the camera (or sensor) has trouble seeing.  That's why your auto focus doesn't work so well in low light.  The image signal is not strong enough to keep the noise ratio down so the camera fills in the blanks with noise. It&#8217;s the camera&#8217;s way of saying, &#8220;I really can&#8217;t see that well.&#8221; The signal to noise ration could be, say, 60 / 40. 60 percent picture and 40 percent &#8220;I can&#8217;t see that well&#8221; noise.

Heat also creates noise. Not hot outside but a hot sensor. If your shutter is open for long periods of time (as it is in low light) and your sensor is collecting data, it gets hot, thus helping create noise. Some sensors (and firmware) handle noise better than others.

I&#8217;m sure someone will come along and explain this even more simply than me. But no, noise does not come from your lens. However, really slow lenses can contribute because you must use slower shutter speeds in low light to get the image.


----------



## Hamtastic (Mar 17, 2010)

I would agree that lenses do not affect noise.  For a given sensor the main issues that would increase apparent noise would be increasing ISO, decreasing the signal to noise ratio (underexposure), and the sensor heating up.


----------



## Dao (Mar 17, 2010)

I do not believe they have noise issue back then with the film camera.  (Although there are film grains.) 

So if lens introduce noise to the photos, you should see it in the film.


----------



## Overread (Mar 17, 2010)

+1 to what BKMOOD said. It's a process/result of the sensor which is why Noise improvements (ie being able to have less noise at higher ISOs) is something that is a major feature of new camera bodies and sensors. 

He is right that the only way a lens can affect noise is if you have a slower lens (ie one with a smaller max aperture, eg f5.6) that might mean that you can't get as much light into the camera in dimmer conditions; forcing you to raise your ISO and thus incure more noise on the shot. 

Also remember that underexposure in a shot shows up/produces a lot more noise so if in darker conditions you want to expose the shot as well as you possibly can (eg get that main lump of the histogram over on the right side as much as possible without hitting the far right side limit - ie overexposing) so that less noise is shown/present.

The heat factor is something that you generally won't come across unless you are working around 30sec or longer exposures and many DSLRs have a long exposure noise reduction mode (enabled through custom functions) which is aimed at countering this aspect. Typically the only times I tend to see this setup in use is with astro photography.


----------



## KmH (Mar 17, 2010)

I'm with Overread on the heat issue as a cause of image noise, in so far that it doesn't feature until 30 seconds or so.

A cause not mentioned so far is the quality of the image sensor amplifiers.

One of the reasons entry level cameras don't perform as well at high ISO settings is poor amplifier signal to noise ratio (SNR)  performance


----------



## Hamtastic (Mar 18, 2010)

I have noticed that the long exposure noise is worse on my 5D than on my 20D.  I've wondered if the larger sensor heats up more.


----------



## RyanLilly (Mar 22, 2010)

Because cheaper lenses are often slower, its is often necessary to increase the ISO setting which will cause, more noise. The lens itself will not cause noise, although crappier optics give a softer lower quality image. When you add the use of noise reduction software into the mix, further impacting sharpness and detail, the overall result will look worse than the same picture taken with a better quality lens.


----------



## kkamin (Mar 22, 2010)

I'm the OP.  I'm asking because I have some noise heavy images taken at ISO 100 or 200 with a kit lens.  I was using studio strobes at a shutter speed of 1/125th.  The images were low key, so do you think the fact there were majority dark tones was the variable that contributed to a moderate amount of noise?  

I would think at a low ISO, even with an entry level D-SLR, while using strobes, that it would handle noise better. 

???confused


----------



## Garbz (Mar 22, 2010)

Check your ExIF data. There have been countless times where I have thought I was shooting at ISO200 only to forget that the night before I set my camera to ISO1600 or something. 

Even if you remove the lens you should be able to take a photo, and at 1/125th at ISO100 or ISO200 the picture should be very close to perfect.


----------

