Advice Needed!

[rylinho]

Hi all,

I have noticed a problem today whilst out shooting long exposure sunsets.

On exposures over about 10 seconds, it looks like there are some dust particles on the lens or sensor, but these are not there on shorter exposures.

Does anyone have any idea what this might be?

thanks in advance

Paul

[beejaybee]

"Hot" pixels ... try turning on long exposure noise reduction, or making matching "darks" (same exposure, same temperature, lens capped) & subtracting.

[rylinho]

here is an example - is there anything permament i can do about it?? (round ish dots at top middle of frame and darker ones towards the bottom)

Paul

Click to view - 640 pixels

Moderators Note: Your image has been changed to a link as it exceeds the forum limit of 600 pixel for the longest edge

[danny1985]

looks like dust to me mate. could be wrong though. (only going on what my shots looked like before i got my sensor cleaned)

[Kettering_Jeremy]

I have noticed a problem today whilst out shooting long exposure sunsets.

Judging by the picture you posted you have bigger problems than dots. There appears to be a radiator, and wall getting in the way of the scene.

It is easily rectified though, just step around the wall, using a door if necessary, keep passing through similar spaces in the walls until you are outside!


Seriously though, I think it's probably dust; And I'm guessing minute particles too. Not sure quite why they are not visible on shorter exposures. I have two theories. First shorter exposures may make the picture so dark that the particle cannot be seen. Second, the shorter exposure is required because the scene is very much brighter. The strong light in such a scene effectively burns around the shadow caused by the dust. The example picture is very dark – I’m guessing if it was correctly exposed the spots would disappear.

The solution is the same regardless, clean the sensor.

Do it in as dust free an environment that you can. I use an Arctic Butterfly and Loupe. The money saved on professional cleaning (which probably uses the same apparatus anyway), quickly pays for the item.

Good luck.

[AlexMonro]

Certainly looks more like dust than hot pixels to me, but it's hard to tell from a small jpeg. If you stopped down to get your long exposure times, that would make the dust spots more obvious.

Try taking some shots of featureless sky at various apertures. If the spots get larger as you stop down, it's dust, and a few puffs with a Rocket blower might be worth a go. If they stay the sme size, but get brighter, hot pixels are more likely, especially if they go away or get dimmer when you turn on long exposure noise reduction.

[rylinho]

Thanks all for the advice, I will use some of the your ideas at the weekend. I guess it isn't a massive problem as only occurs on 15 second or longer exposures but still a bit annoying.

Jeremy - your help is greatly appreciated, you are indeed a wise man!

Thanks again

Paul