Long Exposure of Starry Night

[dan428s]

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Have anybody here done any long exposure of the night sky? I been using my M8 mainly for street shoot, but once in a while I will be on a trip somewhere, where I wanted to do a long exposure of the night sky and I don't have my 1Dm3 on hand, but the images I been getting have just been very noisy. I have the asa set at 160, exposure at 32s and aperture wide open at 2.0.

 

Is the noise just something that comes with the nature of the CCD sensors?

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[wparsonsgisnet]

Dan, the noise is probably coming from the long exposure. A long exposure heats up the sensor, producing noise.

 

Try a higher ISO and something under 1 second. Since you can see what was captured, a little playing around will get the stars against the black background.

 

If you were trying to get clouds as well, that's a bit tricky as they aren't giving off so much light. To do that, try 2 exposures and overlay them in the computer.

[jaapv]

Bill, the M8 is very clean up to the limit of 32 seconds, especially at ISO 160. That is what the black frame exposure is for, and it seems to be 100% effective, so I am very surprised at the report of the OP..This is a 160 ISO image at 32 seconds:

 

 

 

[karl101]

You could always take a series of photos and use some image stacking software

 

Cheap: Image Stacker

 

Example: Stacked Images: Streaks and Trails

 

 

Karl.

[wparsonsgisnet]

Bill, the M8 is very clean up to the limit of 32 seconds, especially at ISO 160. That is what the black frame exposure is for, and it seems to be 100% effective, so I am very surprised at the report of the OP....

 

Cool. Nice pic, too.

 

I haven't done any long exposures (at least intentionally, when the cap was off), so didn't reallize that the black exposure was cleaning stuff up so well.

[farnz]

I agree with Jaap; I've taken many long exposures and at ISO160 the noise is very low. At first it's annoying having to wait for the additional (32 seconds) black frame exposure each time but the results (as shown in Jaap's lovely picture) are worth the wait imho.

 

Pete.

[brucek]

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Maybe the OP hasn't enabled the black exposure compensation?

[jhs1963]

Wow thats one of the best pics i've seen of landscape..... and at night. Bet thats not in Holland! The more i see of all your photos the more i see life. I do not have a camera yet but that is what is in my imagination. Photos like this are art and like art i can look at them for ages.

Cracking photo Jaap!

[farnz]

Maybe the OP hasn't enabled the black exposure compensation?

As far as I know it's enabled by default and I don't think it can be disabled.

 

Pete.

[Tom Johnston]

i have a few night shots w the elmarit 21 on the m8. experimented with ae as well as bracketing- iso 160, 32s, and a variety of shorter times...

can be seen here: night works

and, nice one jaapv

[jeff_clegg]

;)Jaap: Can you explain to me what "black frame exposure" is?

Thanks,

Jeff C

[farnz]

;)Jaap: Can you explain to me what "black frame exposure" is?

Thanks,

Jeff C

Jeff,

 

After a long exposure the M8 takes a second exposure of the same length with the shutter closed and then subtracts the noise from the second exposure from the first one. What this does is to remove any spurious or random noise generated by the M8's sensor, commonly called shot noise.

 

Unfortunately this can't remove sensor noise that is generated when the sensor's signal is weak and typically occurs at high ISOs.

 

Pete.

[h00ligan]

I'm sure you guys all know this but i'll chuck it in anyway, you can stack easily in photoshop by assigning each shot to a layer, one by one, using a layer option of difference to line then up, remove the difference option and merge down - works great for very large scans that have to be scanned in 10 passes or whatever. Anyway, just in case anyone hadn't used that option - great for panoramic line ups too.

 

I'd never heard of black frame exposure, what a neat trick!

[jeff_clegg]

Jeff,

 

After a long exposure the M8 takes a second exposure of the same length with the shutter closed and then subtracts the noise from the second exposure from the first one. What this does is to remove any spurious or random noise generated by the M8's sensor, commonly called shot noise.

 

Unfortunately this can't remove sensor noise that is generated when the sensor's signal is weak and typically occurs at high ISOs.

 

Pete.

 

Pete,

Thanks for your response. It appears from your response that using the fastest aperature and lowest ISO is preferable.

Jeff

[farnz]

Pete,

Thanks for your response. It appears from your response that using the fastest aperature and lowest ISO is preferable.

Jeff

Jeff,

 

Lowest ISO, yes, but the aperture will depend on what you're shooting; for example, if it's a far away object that's stationary then a smaller aperture, within diffraction limits, is likely to be suitable.

 

One of the things to be wary of is long exposures with light sources in the frame, which can cause flare and spot burn out, especially when using an UV/IR filter; I always remove it for these shots if I can (or if I remember:o). Sometimes including light sources is unavoidable and it's best to let the spot(s) burn out but ensuring that the camera's not including it/them in its exposure calculation. In these instances its better to use a wide aperture (if the desired depth of field allows it) so as to minimise the opening of the shutter and therefore minimise burnout.

 

Pete.

[jaapv]

Pete, it is not an absolute that specular highlights will produce problems. As you see the bright light in my shot only produced a star-shape, and I was using a IR filter. Iirc this one was taken with the Elmar-M 50 @ f2.8. On the other hand I have had some shots spoiled by green reflections in akward places, so your advice is sound. Always chimp in this kind of shots, often moving the camera a bit or removing the filter is all that is needed.

[farnz]

Pete, it is not an absolute that specular highlights will produce problems. ...

That's a good point, Jaap, and the 'starburst' effect can add to a photo to as it has in yours. My concern is more with heavy burn out where blooming can become a problem.

 

Pete.

[jeff_clegg]

That's a good point, Jaap, and the 'starburst' effect can add to a photo to as it has in yours. My concern is more with heavy burn out where blooming can become a problem.

 

Pete.

 

Thanks Pete & Jaap for the heads-up. I got some experimenting to do with my M8.

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Hallo,

Look here: Leica M

[amedick]

I was also plesantly surprised by how well the M8 handles long exposures, I assumed noise would make photos unuseable. Both pictures below were trials at 32 seconds and lit by moon lighting, or camp fires in this Bedoin village. Lens was 24/2.8, believe ISO setting was 160. Want to try something similar on M9.

 

Regards

 

John

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[bsmithy]

Jeff,

 

After a long exposure the M8 takes a second exposure of the same length with the shutter closed and then subtracts the noise from the second exposure from the first one. What this does is to remove any spurious or random noise generated by the M8's sensor, commonly called shot noise.

 

Unfortunately this can't remove sensor noise that is generated when the sensor's signal is weak and typically occurs at high ISOs.

 

Pete.

 

From the "just in case you care" department, here's a slightly more detailed but basic explanation:

 

Depending on the sensor, much of the noise in long exposures can be thermal noise, which is an increase in a pixel's value due to electrons accumulating in the photosite as a result of heat rather than photons.

 

Note that this is not the same thing as shot noise (or "photon noise", in the case of digital imaging). There are many sources of noise for a sensor, including thermal, shot, readout, and reset noise.

 

In order to do a proper dark frame subtraction, the camera must allow the sensor to integrate for at least the same period of time as the original shot, only with the shutter masked to prevent light from striking the sensor. Theoretically, this provides a perfect image of the thermal noise (and any other time-constant noise) present in the original shot. This "black frame" is then subtracted from the original shot to effectively remove the noise from the image.

 

This is a huge deal for the specialized digital cameras used for astrophotography as exposure times can easily be many minutes. In addition to dark frame subtraction, cameras used for astrophotography are usually actively cooled (via a Peltier cooler, for example) to reduce thermal noise from the original image. This allows the photosites to use their "electron well" capacity for more of the actual signal, which increases signal/noise and allows for longer exposures before a photosite reaches its full-well potential (i.e. saturation voltage -- picture a bucket full of electrons).

 

Speaking of which, I think blooming was also mentioned by someone in this thread. Once a pixel is saturated, blooming (charge "spilling over" into neighboring pixels) can occur unless the sensor is equipped with anti-blooming gates to drain charge from a pixel once it has become saturated. Blooming produces (typically) vertical and/or horizontal light streaks in the image (depending on the type of sensor and the layout of its pixels).

 

OK, enough of that; back to our beloved M8: According to the M8 user's manual, the camera will institute dark frame subtraction for shots as fast as 1/30 sec, "but this can vary as a result of other menu settings."

 

And, as Pete mentioned, noise will increase as ISO increases. The reason for this is that the ISO setting on a digital camera is mostly a representation of "gain", or multiplication of the signal from each pixel. Of course the gain increases *all* of the components of the signal, including the noise portion, so signal/noise is reduced. As you probably know, increased ISO/ASA in silver-halide based film emulsions results from an increase in the size of the silver-halide particles and hence an increase in "grain". So it's not quite an exact comparison between digital ISO settings and film ISO values, but eh, close enough.

 

If you made it this far without getting really irritated with me, here are a couple of links that provide better and more complete explanations:

 

the astroscopic labs - article: Thoughts about Image Calibration for low dark current, unregulated Amateur CCD Cameras to increase Signal-To-Noise Ratio (SNR)

Shot noise - Wikipedia, the free encyclopedia

 

Cheers,

Brad

 

This may be my first post here -- it's at least been long enough that I don't remember. Since many people post their pile 'o equipment, here's mine:

M8 / Rollei 35 / Rolleiflex 2.8f / Canon 20d, 1DMk3, and 5D / Horseman 612. Plus lenses and stuff