Olympus E500 long exposure noise -- help!!

Recently, a friend and I went out on a night shoot. I was using a Fuji E900 P&S, and he was using the Olympus E-500 DSLR. We were shooting long exposures from tripods between 8 and 10 seconds.

I was shooting ISO 80, he was shooting ISO 200. Both shooting JPGs.

His ISO 200 pictures, with a long exposure, were dotted with large (roughly 10x10 pixel size) chrominance noise "blocks." They were primarily red and blue dots, and while some were smaller than 10x10, they were definitely bigger than single pixels. These dots were visible at all practical sizes(no zooming required to see them), and they would be evident at any print size. Noisa Ninja didn't touch the noise with a 10ft pole, even using the appropriate Olympus plug-in profiles/settings. The noise wasn't just a small irritation, it made the photo completely unusable.

His Noise Reduction (NR) feature was turned off.

He also tried a simple test by leaving the lens cap on, switching his ISO to the lowest (its ISO100), and taking a long exposure. Exactly the same results.

Now note that he has shot PLENTY of shots at HIGH ISO's, and the noise there is completely acceptable for all reasonably short exposures, under a few seconds.

If he activates the NR feature, then the dots go away completely across all exposure times, and he is left with a good quality photo. The NR feature, however, really slows down the processing of his camera, and takes roughly double (or more) the exposure time to process the image.

This didn't happen just once, it was on upwards of 100 pictures -- and is a repeatable problem.

My pictures, on the other hand, were completely clean, and had very minor luminance noise, and this was only visible in dark, solid shadow regions. Noise ninja(on a weak setting) was easily able to perfect the image. This noise was very small light gray specks which would be invisible in most print sizes. The resolution was maintained, images not overly soft, and so on, so Fuji isn't applying aggressive in-camera noise reduction, pixel binning, etc.

So, questions,

1> what the heck are we seeing here? I know astrophotographers(this a term?) have to deal with cooling their sensors for very long exposures, is this a heat thing?

2> Larger sensors(4x area of my Fuji) in SLRs should outperform small sensors(like the one in my Fuji) in regards to noise, but this CLEARLY isn't the case here. Why not?

3> Has anyone seen this before on their E500 ? Anybody bored enough to try that cap test I mentioned? Anyone do night photography with their E500 or similar?

Thanks for any insight.

Keith

The RGB block are called "hot pixels" and they occur at long exposure because those photosites get physically hot (presumably from electrical current).

The way to get rid of them is call dark frame subtraction which only occurs when the noise reduction (NR) option is on and the exposure is longer than 15 seconds if I recall correctly.

The camera takes a second exposure without opening the shutter for the same duration as the original exposure, and takes the difference of the two frames. This will remove all the color spots from the long exposure.

It's frustrating (but necessary) when you have an 8-minute exposure, and have to wait an additional 8-minutes to shoot again.

HTH.
--

• Adam

Equipment in plan

the noise reduction feature works by first exposing the image then exposing the sensor for the same time with the shutter down. (since heat affects the performance and will cause noise)

this way the noise seen in the image is removed by using the second exposure to remove the noise from the first.

the fuji has the sensor active all the time and will not have a problem with the heat the sensor is at. the camera firmware/software will deal with the noise without a problem.

--
if you can imagine the picture, then do all you can to make it

DFS = Dark Frame Subtraction, and it's why his camera took so long to process the shots after each exposure with NR turned on. It's necessary to take a dark frame, find the "hot pixels" and subtract it from the actual image to get a clean image. It's just the nature of the imaging sensor, and most if not all DSLRs do it at long exposure times. Both the hot pixel noise and the method of dealing with it are completely normal and standard.

trisweb said:

DFS = Dark Frame Subtraction, and it's why his camera took so long to
process the shots after each exposure with NR turned on. It's
necessary to take a dark frame, find the "hot pixels" and subtract it
from the actual image to get a clean image. It's just the nature of
the imaging sensor, and most if not all DSLRs do it at long exposure
times. Both the hot pixel noise and the method of dealing with it are
completely normal and standard.

Click to expand...

Adam, Kevin, trisweb, thanks for quick education. I actually just learned about DFS yesterday, but didn't realize his NR == DFS.

I guess what isn't so obvious to me is why SLR sensors have hot pixels and require DFS for long exposures, but much cheaper P&S cameras/sensors have no such limitation? Noise (whether it be high ISO or otherwise) should be a clear advantage to the SLR, but in this case, the P&S is the winner.

While NR does in fact solve the problem for my friend, the feature takes so long that it really slows down his shot-to-shot times. As Adam pointed out, waiting an extra 8-minutes (or 8-seconds or whatever), certainly isn't convenient. It takes a fast camera and in essence slows it down. NR for long exposures is absolutely required........

Kevin said.... "the fuji has the sensor active all the time and will not have a problem with the heat the sensor is at"

Are all P&S sensors active all the time? Why do they not have heat-related issues like SLR-sensors? Both the fuji sensor (5th generation SuperCCD HR) and the E500 (Kodak 4/3) are both CCDs. Is there some tradeoff for a physically larger sensor and heat-induced noise? Are smaller sensors cooler?

Last, but not least, since it's possible to do DFS by taking a "lens-cap" image and pasting it into a new "blend mode=difference" layer with blur, is taking only one image just prior to the shoot (once camera has warmed up) sufficient to counteract these hot pixels? If one could, for instance, setup an action that does this automatically in PS, maybe we could skip the extra processing time IN CAMERA. This would at least preserve shot-to-shot times.

Thanks

Keith Monahan said:

Are all P&S sensors active all the time? Why do they not have
heat-related issues like SLR-sensors? Both the fuji sensor (5th
generation SuperCCD HR) and the E500 (Kodak 4/3) are both CCDs. Is
there some tradeoff for a physically larger sensor and heat-induced
noise? Are smaller sensors cooler?

Click to expand...

i'm no expert, but the tiny size of a P&S CCD compared to a SLR sensor does make a big difference. Some sensors react differently to the hot pixels, but a great deal of SLR sensors - be it CCD, CMOS or nMOS - suffer from this problem.

I have a Fuji E550, and i know that there is alot of proccessing which takes place in the camera after the shot is taken so most probably, the hot pixels are mapped automatically.

Keith Monahan said:

Last, but not least, since it's possible to do DFS by taking a
"lens-cap" image and pasting it into a new "blend mode=difference"
layer with blur, is taking only one image just prior to the shoot
(once camera has warmed up) sufficient to counteract these hot
pixels? If one could, for instance, setup an action that does this
automatically in PS, maybe we could skip the extra processing time IN
CAMERA. This would at least preserve shot-to-shot times.

Thanks

Click to expand...

i don't know about you, but i really wouldnt bother with that lens cap image, because the hot pixels aren't always going to be in the same spot. you have it in the camera and it works perfectly, so why not use it?!
And what are you shooting that you need so fast shot-to-shot speeds?!

generally when you are shooting long exposures the thing you're shooting doesn't move a great deal - hence being able to shoot it slowly in the first place.

I think a bit of patience will quell your worries mate.

--
Cheers, Tom
If you can't be the best, then be different!
http://home.iprimus.com.au/yankoslogistics/

My P&S (a Panasonic LX-1) also has DFS as does, as the other end of the scale, the full-frame EOS 5D (which uses a CMOS sensor), and indeed the Fuji S5.

Nothing to get hung up about.

John

Once the shutter clicks closed and is starting the DFS frame you can move the camera around and set it up for the next shot. This is what I was doing for my 60 second exposures last week.

On the e-1 there are 2 set of bars - both lit for the start and just one lit for the DFS frame.

--
Thanks,
Brent

http://www.pbase.com/brent