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DSLR Horizontal Banding...?

AndyUK

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MikeWilson

MikeWilson

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He probably kept a few "stubbies" in that box too :)

I'm also considering somethings else, Andy. Selling my 1000D + EOS Clip + MPCC + accessories 'n' all and then trying to get together funds for a cooled CCD.

The QHY8L (it's a OSC) looks achievable this way.

Sorry for hi-jacking your thread!

Mike

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joselin

joselin

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Mike - He also has a version 2 on there as well... which is basically what Psychobilly's mentioned (a fridge dangling off the tube!)...

And then there's the (for me) fairly DIY intensive v3, which MIGHT just work (without looking at a "Cold finger").

Hi Joselin Yes, the bands are in the lights. What Mike and I are considering is building up a library of temperature, exposure length and ISO-based folders full of darks.

After taking a session of lights, we'll then review the exif data so that we can then select the correct temperature darks to subtract.

Assumimg that this noise/banding in the lights IS temp related(?), hopefully the same noise should also be contained in the matched temp dark and thus will be subtracted (:)).

It's worth a shot anyway...

I'll hopefully be doing long exposure with my dslr shortly as well so knowing its limitations will be useful, I just get the feeling your trails might be in vain as effectively the darks are just lights (just the dust cap is on). The conditions to replicate these banding's should be easily repeatable should they not ? Possibly indoors in a dark room ?

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MikeWilson

MikeWilson

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I'll hopefully be doing long exposure with my dslr shortly as well so knowing its limitations will be useful, I just get the feeling your trails might be in vain as effectively the darks are just lights (just the dust cap is on). The conditions to replicate these banding's should be easily repeatable should they not ? Possibly indoors in a dark room ?

Hi Joselin,

That's right. This is repeatable - I've had this problem before but not quite as bad as Andy's (as expected as my images were taken at colder ambient and were slightly shorter in length).

The darks will have the banding. The lights will have the banding.

Now take the lights and subtract the darks and voila - no banding.

Mike

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joselin

joselin

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Hi Joselin,

That's right. This is repeatable - I've had this problem before but not quite as bad as Andy's (as expected as my images were taken at colder ambient and were slightly shorter in length).

The darks will have the banding. The lights will have the banding.

Now take the lights and subtract the darks and voila - no banding.

Mike

Yep I see what you are trying to achieve there I just wonder if the banding will result in losing good info as well ?

I wonder if it would be better to find the camera's limit and keep below it.

anyway its all good info for me

we could all just invest in a cdd or one of these

Cooled DSLR

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MikeWilson

MikeWilson

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Yep I see what you are trying to achieve there I just wonder if the banding will result in losing good info as well ?

I wonder if it would be better to find the camera's limit and keep below it.

anyway its all good info for me

we could all just invest in a cdd or one of these

Cooled DSLR

You probably would lose a bit of signal, it's impossible to eliminate the noise completely. But we're all in the game of increasing the signal to noise ratio as high as possible and we can do this with darks.

However those darks have to be at the same temperature as the lights (in order to have an equivalent amount of noise). We also need a lot of darks (to average out the random noise).

Those custom modified DSLR's seem as expensive as an equivalent CCD.

Best,

Mike

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Psychobilly

Psychobilly

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We also need a lot of darks (to average out the random noise).

Do we..? thats news to me as most of the time I dont bother with them at all....:)

Here's a links to a couple of Autosave.html files from DSS... renamed... whats missing B)

http://dl.dropbox.com/u/8191904/Autosave001%28NAN%29.html

http://dl.dropbox.com/u/8191904/Autosave001%28Pacman%29.html

http://dl.dropbox.com/u/8191904/Autosave001%28Veil%29.html

http://dl.dropbox.com/u/8191904/Autosave001%28Cocoon%29.html

http://dl.dropbox.com/u/8191904/Autosave001%28GCN%29.html

http://dl.dropbox.com/u/8191904/Autosave002%28M31%29.html

Billy...

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AndyUK

AndyUK

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No worries Mike... If the 40D wasn't my "only" DSLR, I'd consider doing something similar...

Billy - I'd love to see a photo of that...! That link that Mike listed has a v2 which seems to be pretty much based on using the entire fridge as opposed to just the peltier and fan... Again v3 looks quite nice though (if only I had the skills!)

Joselin -

The conditions to replicate these banding's should be easily repeatable should they not ? Possibly indoors in a dark room?
You're probably right... although the starting ambient temp the other night (going by the temp of the first sub) was 8C, but I don't know what the temp did after that, so It wouldn't actually be possible to replicate the exact same conditions...

However, if this banding IS temp related, I could simply take some "room" darks (ambient 20C) and then set the camera off taking 20x 600s @ ISO800, stack those and stretch them - If the theory's correct, then they will also show the banding (and I might expect it to be worse due to the higher ambient start temp).

Re: using darks, I know a few people don't use them - Just flats and bias... which is actually where I started with this image. I then replaced the bias with darks and flat darks to see how that would turn out.

I seemed to get slightly better results WITH the darks, although Nadeem's image versions posted in this thread DIDN'T use darks (and the bands are all but non-existant).

(I think I'm right in saying that if there were a lot of hot pixels in the images and you still didn't want to use darks you could potentially use the hot pixel removal option in DSS?)

EDIT - Billy - Just seen your html log files - I see that you apply those cosmetics :) - Thanks for confirming... I haven't tried them yet...

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Psychobilly

Psychobilly

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Getting warmer :)

Or dithering and statistical stacking methods..

Or...

I dont deliberately dither as there is enough "drift" to take care of it but not so much as to show up in the images...

Whenever I get a new camera I spend a lot of time "testing" it to find a sweetspot B)

Luckily my 1000D and 500D are both pretty darn quiet...

Billy...

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GrantEb

GrantEb

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Ok, so I have been doing some experiments today (as I have nothing else to do)

It was just to get an idea of temperature trends with my 1000d.

All of this was done inside, with an ambient temp of 18 deg C, and using APT to control the camera.

I first took a 5 sec exp to extract EXIF temp, and read 18 C (my thermometer read 17, so close enough)

I exposed for all sorts of durations, and came to the conclusion, that at the max temp the CMOS was going to reach was 26 C. I found it would reach this temp, with long (10min) exposures, and short (1 min) exposures.

I only had a 5 second pause between shots. This was just to allow the file to download to the PC, and to get more accurate readings, as the EXIF is read at the beginning of the exposure.

The offset between ISO800 and ISO1600, was about 3 degrees (ISO1600 higher)

It seems it reaches operating temp (highest) very quickly, around 3 minutes, and stays there.

So, in my opinion, a long cool down period between shots, is of no use, as you are going to reach the high temp very quickly, and are going to get inaccurate EXIF temps, as it takes this at the beginning of the exposure, which after a long cool down, would be much less than end temp, and actual temp during exposure.

Blowing air aver the camera body with a desk fan, dropped the max temp, at ISO800, from 24, down to 21. (not a huge difference, but it did help)

A metal container of ice, with salt added (-2C), just pressed up against rear of camera body, dropped the max temp back down to ambient, 18C, within 15 minutes.

I then moved up to ISO1600, and couldn't get it to raise above 18C.( 30 mins)

The interesting bit came in, when using liveview. From ambient, switching on liveview for 10 mins, warmed the CMOS up to 32 C. It took 10 mins to cool back to ambient.

So I would allow 10 mins of cool down, after using liveview, before exposing. (that is if you use liveview to focus)

I will plot all the details on a graph sometime, after I have finished putting together the cooling device.

Hope this helps a little.

Cheers

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MikeWilson

MikeWilson

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So, Billy,

No dark frames at all? That's incredible. I hadn't thought that it were possible to not use dark frames. I imagine that your flats presumably take care of some of the noise - or do you simply not get any noise as you favour shorter exposures?

Mike

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Deneb

Deneb

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So, Billy,

No dark frames at all? That's incredible. I hadn't thought that it were possible to not use dark frames. I imagine that your flats presumably take care of some of the noise - or do you simply not get any noise as you favour shorter exposures?

Mike

Actually I've found darks to be quite noisy tell you the truth especially when using ISO1600... Billys the expert about this :)

Nadeem.

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AndyUK

AndyUK

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Hi Grant - That's a really useful post - Thanks! It also goes to show the value of switching off the image display when on a run, and also the value of "warming" the camera up and "wasting" the first frame or two (whilst setting up)... and the fact that extended periods between exposures really isn't that necessary - With 10 min exposures, I'd sometimes been leaving a 90s delay, but it would seem that I can shorten that significantly without any loss.

This also confirms the review of my darks library and some of the imaging runs I've made, especially wiht the longer exposures. Admittedly, the 30s and 60s don't get up to anywhere near the temps of the 240/300/600s but they do indeed level out. It would be interesting to plot a graph of ambient temp vs max chip temp, although I suspect that this may well be camera-specific. However, I shall certainly be paying a lot more attention over the next few months to the ambient temp...

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Psychobilly

Psychobilly

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So, Billy,

No dark frames at all? That's incredible. I hadn't thought that it were possible to not use dark frames. I imagine that your flats presumably take care of some of the noise - or do you simply not get any noise as you favour shorter exposures?

Mike

I personally wouldnt call 300, 600 and 900s subs short ones :grin:

Although you can have some longer 1800s and 3600s ones if you like :)

Wherever possible Plenty of subs , dont try an push the data to far and use statistical stacking methods...

I just go with what works for me with my camera's... I dont try an get too involved in the "maths" and theory (Which Is why I have largely kept out of the earlier discussion) and just go with what works in practice :p

Colder is always better .... B)

Billy...

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Deneb

Deneb

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Andy I used the same workflow which is in the M51 Vid, apart from using darks instead of the bias frames. Also for filtering the noise I used Noiseware Pro with a touch of Topaz Denoise to get rid of the Banding...

Nadeem.

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Psychobilly

Psychobilly

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Just one more result from the method I use..

Baader BCF Modified Canon 1000D on CPC 800 XLT @ approximately f6.3

Hutech IDAS P2 2" filter

33 light frames made up of...

4h 24m @ ISO800 including 3h of 30m subs

4h 45m @ ISO1600 in 15m subs

Master Flats for both ISO800 and ISO1600 Produced from 50+ random selected skyflats from 100+

Master Bias for both ISO800 and ISO1600 Produced from 50* bias frames selected at random from 100+

No Dark Frames

Crop from Full frame...

M27-Traditional_800.jpg

Peter...

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