Dynax 7D - Long exposure (25min).....Share here

[sulhan]

Hiee Pals.....

I tried out Bulb mode yesterday for an exposure of 1529 secs..~approx 25mins.

Just pointed in the general direction to a star in the sky. Being light polluted here in singapore, image glowed in yellowish color. As you see....in this resized image....its rather noisy but!!! the noise is not rainbowed to red or blue dots. Its grainy like film type of output. Noise reduction is ON.

Initial intend was to doe 5 mins....and i accidentally dozed off....
And well....i'm happy to be able to record a long streak like this.

Now come of another observation....

There is a glowy top left hand corner. This was earlier seen as a red patch in a 4 minutes exposure. Well, i did not close the viewfinder for these long shot and it probably is light from outside. But from the 4mins results and 25mins result....it look like there seem to be some source of inllumination maybe due to sensor...

Ideally the 2mins shots were great without noise.....I'm surprise...

Okay here is the star streak 25mins shot...

Image is resized.

Regards,
Sulhan

 

[Drudkh]

Amazing result!! I wanna try!! :thumbsup:

 

[Timber Wolf]

Hi there. Does the noise seem acceptable to you? When I tried ISO 100 at 717 seconds, the noise really jumped out at me. Quite scary especially when I shot at ISO 100.

Also, the NR only lasts for max 30 seconds even when long exposure is applied. Do you think this could be the cause for increased noise at long exposure?

 

[sulhan]

Hiee...

Well...as far as long exposure is concern, digital imaging till this stage is still not in par with long exposure photography.....

If you need anything more than 1~2 minutes.....then do it on film/slides.
As far as the 25mins exposure that i did was kinda accidental as i dozed off, i had no benchmark in my mind.

Well, unfortunately if you had a rough benchmark that you would like to acheive......then i think ....you need to bring down that benchmark from 10mins exposure to about 2 ~3mins at the most.

* Do multiple 2 secs exposure and merge them digitally......ensure steady tripod...

The electronics simply not designed for that long exposure purpose as in terms of electonics, the camera is actually doing something like *. The Analog To Digital converter need to sample and sample through time and then "add" them through time. Thats why in lower end digicams in the past....in low exposure...you can see the sampling positions....

Dark current in the sensor will cause noises and this is provne by the "pappr" color dots appear even if you take long exposure with the cap closed.

SO to minimise the noise output.....try this out.

- Take a long exposure image with cap on (say 4mins)
- Save this file as A.jpg for example..
- Now take your long exposure 10 mins for example - Image B
- Take the the noisy long exposure Image B and then use PS to merge it up with Image A.
- Put Image A (dark current noise) over image B (your image)
- Use "Layer->Difference"...and see the effect...
- Result will be less noisy image as the "noisy area" cancels during the
in photoshop layer

THe bove method only applied to some type of noisy images for dark sky type of photography....(those that are "known"...in this case due to dark current behaviour on existing sensors)....

Try out with the attached images for the concept.....
more complicated noise need other special handling....

(simulated dark noise)

(Simulated dark noise appearing on black background image...)


If done correctly, the red dots can be deleted and leave the yellow trial line...

rgds,
sulhan

 

[Timber Wolf]

Roger that sulhan. Thx. Didn't think of manually subtracting darknoise. Oh, btw I tried shooting infrared using my mum's trusty infrared light (u know, those for heating up the skin and stuff for health purposes) and I got an exposure of abt 1/15 second ISO 3200 at f/3.5. Hmm. The 7D's not really suited for IR photog issit?

 

[TME]

Roger that sulhan. Thx. Didn't think of manually subtracting darknoise. Oh, btw I tried shooting infrared using my mum's trusty infrared light (u know, those for heating up the skin and stuff for health purposes) and I got an exposure of abt 1/15 second ISO 3200 at f/3.5. Hmm. The 7D's not really suited for IR photog issit?

Maybe u need a IR filter?

 

[Magnus Wedberg]

Roger that sulhan. Thx. Didn't think of manually subtracting darknoise. Oh, btw I tried shooting infrared using my mum's trusty infrared light (u know, those for heating up the skin and stuff for health purposes) and I got an exposure of abt 1/15 second ISO 3200 at f/3.5. Hmm. The 7D's not really suited for IR photog issit?

someone tried shooting IR with filters and stuff, and got nothing. The anti-alias filter seems to be removing IR too.

 

[UY79]

someone tried shooting IR with filters and stuff, and got nothing. The anti-alias filter seems to be removing IR too.

I believe IR and UV affect image quality if they are picked up by the sensor and causes fogging. It's actually a bad side effect if a camera is able to capture IR or UV images. So being not able to capture IR is actually a good thing.

Is this correct?

Cheers!

 

[Timber Wolf]

I believe IR and UV affect image quality if they are picked up by the sensor and causes fogging. It's actually a bad side effect if a camera is able to capture IR or UV images. So being not able to capture IR is actually a good thing.

Is this correct?

Cheers!

Yep. My old Dimage 7 occasionally had very screwed up colours in bright sunlight due to IR interference. I'd prefer if we had the choice, sth like sony's 717/828 series of cams, though not with the crippling of features in nightshot mode. I got an exposure which was decent, but the noise pretty much drowned everything else out. >_<

 

[TME]

Yep. My old Dimage 7 occasionally had very screwed up colours in bright sunlight due to IR interference. I'd prefer if we had the choice, sth like sony's 717/828 series of cams, though not with the crippling of features in nightshot mode. I got an exposure which was decent, but the noise pretty much drowned everything else out. >_<

Build your own camera lor... :blah:

 

[2100]

Sulhan, just glanced through this thread. Just FYI, that top left/right whatever hand corner glow in red/magenta colour is called amp glow.

You can get that too if you set to high ISO like 1600, snap a pic of a couple of minutes (with or without lens cap on). Maybe the D7D is more susceptible to amp glow.

The longest I have managed on D70 is about 15 minutes? No amp glow nor hot pixels but the contrast of the image has degraded slightly. I have read that people have done exposures on the D70 for as long as 6 hours, not too many hot pixels such that the pic cannot be used but there is amp glow at 1 corner. So gotta crop it out lor. Guess you need to use a very wide angle like 12mm for anything to be useful, then crop.

 

[akane]

Wouldn't the CCD/CMOS be burned out if expose for that long :bigeyes:

 

[forbytes]

just realised during my weekend night shoot. in bulb mode, the LCD on the back does not display the stop watch to indicate the duration of the shutter exposure similar with that found in Dynax 7. I was there talking "1 thousand, 2 thousand, 80 thousand, ......" :lovegrin:

 

[deslim27]

just realised during my weekend night shoot. in bulb mode, the LCD on the back does not display the stop watch to indicate the duration of the shutter exposure similar with that found in Dynax 7. I was there talking "1 thousand, 2 thousand, 80 thousand, ......" :lovegrin:

Yeah lor..

wait... it doesn't? :think:

 

[forbytes]

you try bulb mode in both cameras already?

 

[Magnus Wedberg]

just realised during my weekend night shoot. in bulb mode, the LCD on the back does not display the stop watch to indicate the duration of the shutter exposure similar with that found in Dynax 7.

:cry: that's too bad. This was one of the very special features of the 7... it also kept the back light on for the whole exposure if you started it before you fired, all to make night shooting as easy as possible. Just one of the many small details that made the 7F (F for film ) stand out... :kiss:

 

[deslim27]

you try bulb mode in both cameras already?

I've try bulb mode for film 7 before.. haven't try it for 7D..

 

[deslim27]

Just one of the many small details that made the 7F (F for film ) stand out... :kiss:

And DOF and Honey Comb metering display.. ;(

 

[UY79]

And DOF and Honey Comb metering display.. ;(

Just shoot first and chimp!

Cheers!

 

[deslim27]

Just shoot first and chimp!

Cheers!

For metering okay lah, but sharpness is not so easy to judge from LCD leh.