Jump to content

Single pixel noise depending on shutter speed


Recommended Posts

Hello together,

 

For time lapsing stars at night, i wanted to try, which ISO setting is usable, before visible noise  appears.

 

I'm using the a6500 with the 18-105. Firmware of both is up to date (Body: 1.04, lens: 04)

 

For this test i just left the cap on the lens and tried different ISOs with different shutter speeds:

Starting with ISO100 and 120s Shutter speed (external controled), going on doubling shutter speed and ISO up to ISO51200 with 1/4s.

I saved and evaluated both, JPG and ARW (converted in TIF with Sony Image Data Converter Ver. 5)

 

At first it looked good until ISO800 didn't produce any perceptible noise. But then, i discovered something strange:

At ISO6400 with an shutter speed of 2s (internal controled), there appeard some bright pixels, but with ISO12800 with 1s shutter speed and also higher ISOs there isn't.

 

By the way, StadyShot, NoiseReduction at long exposure and Silent Shooting is off. E-Front Curtain Shutter is on.

 

I thought it belongs to an special ISO Value, so at the next test i tried everx ISO setting between 3200 up to 12800, always with an Shutter speed of 2s (internal controled).

At this test i had single bright pixels in every single picture, getting brighter with higher ISO settings.

 

Then I thought, let's again look at lower ISO settings, but now with 10s fixed shutter speed. Changing ISO from 100 up to 3200.

Now, there weren't bright pixels at all, even with ISO3200, where i had bright Pixels at an shutter speed of 2s.

 

At this point, i understood, that the appearing of bright pixels seems to change with shutter speed, but not with ISO settings.

Next, i testet all shutter speed between 1s up to 10s with ISO3200.

And in this test, the bright pixels only appers at shutter speeds of 1s up to 3.2s, getting brighter at longer exposure. At an shutter speed of 4s and longer, they disappeared.

 

Because the bright pixels getting brighter at longer exposures, according to my imagination, it cannot be an EMC issue with the shutter, because this would always give us the same brightness. Regardless of this i also tried to just use the electonic-shutter with the setting "Silent Shooting" and reverse just using the mechanical shutter by putting "e-front cutain Shutter in Off-position, but both didn't change anything on the appearing of the bright pixels.

 

Following two pictures, the first one with ISO3200 and 3,2s, the second is ISO3200 at 4,0s.

Because i can upload just smal files, the picture is cropped, you can see just the upper left corner (1/4) of the real picture.

By uploading the pictures here, they getting compressed even more. I also tried the gallery, but it also compressed them. But i think, You get the point, even the noise is not that sharp anymore.

I also brightened the pucture two times with +150 with  Adobe Photoshop. Now you also can see noise in the picture shot at 4s exposure time, but it's much less, even it should be a little bit more because of the longer time.

 

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

 

What is the reason for this behavior. Can someone confirm it. It's not difficult to reconstruct, just use the same settings. What can I do against it.

 

One more little question:

Can someone tell me what to do to make the camera display the picture number? It shoes a number, but this is just a counter of pictures on the SD-card. So, if i delete some pictures, this number doesn't match to the picture number anymore.

 

Greetings

Jörg

Link to post
Share on other sites

Jörg,

what you are experiencing is Sony's infamous 'star eater' algorithm. There's a lot to be found on it on the web:

https://www.google.nl/search?q=sony+star+eater

 

Basically, you're screwed if you want to do astrophotography with exposures over 3.2sec: hot pixel noise is removed from you photo but so is a substatial amount of stars, as the algorithm can't differentiate between them.

Link to post
Share on other sites

Hey thank You very much for Your answers.

 

Jörg,
what you are experiencing is Sony's infamous 'star eater' algorithm. There's a lot to be found on it on the web:
https://www.google.nl/search?q=sony+star+eater

Basically, you're screwed if you want to do astrophotography with exposures over 3.2sec: hot pixel noise is removed from you photo but so is a substatial amount of stars, as the algorithm can't differentiate between them.

 

Hi Pieter,

that's exactly the issue, i was talking about. Thank Your for this hint.

To know now, what is giong on, is good, but it's still very unpleasant, that Sony does not give us a setting to switch off this algorithm at all.

 

I read about this issue now on a view sites, and it seems to me, that Sony is thinking about fixing the issue.

Or at least i hope so, even if astrophotography was not the reason for me to buy the a6500.

 

   

IIRC display options are cycled thru by 

pressing the top edge of the rear dial. 

One or more of these options includes 

displaying the actual file names, which 

are unique numbers for each image. 

 Hy Username,

 

thank You for reading my post to the end :D

But i checked it again:

Of course, the camera is showing this picture-number in playback-mode.

But this semms just to be the actual position of the viewed photo of the library, which the camera is creating from the pictures stored on the sd-card.

Let's check, if we are talking about the same:

In Plyback -Mode at two of three Display-Modes, there is be shown e.g. 305/350 in the lower right corner, meening, that you watching photo 305 of 350 saved photos on the sd-card.

But this number is not the number, the picture is named, e.g. DSC01230.

They don't match, and i don't find the option so that the camera shows me the name of the photo.

But that is what i need, e.g. i try some settings while taking pictures. Than i wan't to be able to write down the number (name) of the picture, so that i know, which setting i used at which picture, when im looking at them on pc later.

This should be possible!?

 

Thank You for Your help so far.

 

Greetings

Jörg

Link to post
Share on other sites

Somewhere in the "Live view" settings menu there is 

a way to choose which information will be displayed. 

You get to choose as many or as few viewing formats 

as you wish. Cycling thru the "DISP" button ... which 

is actually the top edge of the rear dial ... you cycle   

thru all the formats you chose for inclusion.   

   

The above holds true for viewing when photographing. 

I don't recall if the live view menu is also where you 

get to choose viewing formats for PLAYBACK as well. 

Maybe. But if not, then expect to find the options in the 

playback menus. 

    

My camera is a 6000 and the menu system in a 6500 

is somewhat different in detail, but it offers the same 

features and options. I can only generalize about how 

you do things. A pathway thru my menus is not going 

to be correct for your menus ... but be persistent, cuz 

it's in there somewhere !   

    

Actually, I have 5 different Sonys ... no 2 alike. So I've 

had to just get accustomed to thinking like a Sony, cuz 

it's pointless to memorize 5 different menu systems :-( 

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...