Streaks ruined my m18

[JohnH]

Help,

I took 20 3 mins iso800 shots of m18 last night, took darks and flats too. Stacked and processed in IP2.75 as I have done many times before and the result - diagonal streaks appear when I used DD to bring up the nebulosity. What is causing this? I have tried reprocessing a number of times but cannot eliminate the problem. It seems to me the darks are not good - I have some residual amp glow showing too (crpeed out of the image attached though)

I should say this was all done with the camera set to LARGE/FINE (jpeg), is that the problem? (I have done this before too), advice/opinions/ideas welcome?

[JohnG]

Try shooting all your images in RAW mode (lights, darks, flats and bias), if your not using it, try Automatic Image Set Processing.

Looks like a JPEG artifact.

Cheers

JohnG

EDIT: I am asuming here that you are using the 20D.

[asimov]

I had the same trouble with a modded toucam on the triffid last night. Doesn't matter in my case, just having a play.

[JohnH]

JohnG,

Yup t'was the 20d - and it could be the JPEGging....I will try again with RAWs when clear...

[bojan]

I think this is not jpg artefact... They tend to be around high contrast details, but never extended to the end of the image.
This looks to me like the RF interference I had in my modified QuickCam, and it turned out it was a faulty cable (when I shortened the cable by cutting off 10cm from each end, getting rid if parts of the cable where it was stressed and bent, the streaks dissapeared).
Maybe you had used your mobile phone while taking this picture?
Bojan

[rogerg]

Are your images reduced (to remove dark & bias) ? It looks to me like you had trailing, corrected for by aligning and stacking the sub frames but because of the guide error you have the noise trailing.

I'd suggest you need to remove the noise (if you're alrready doing reduction on your images then find some other way to hide it - darken the image, processing techniques of various kinds...).

Remember that because your stars have been align correctly that means the noise is now drifting and hence you end up with streaks of noise instead of streaks of stars.

Roger.

[bojan]

To determine if this is a noise or not, try to take only dark frames under same conditions ....

[JohnH]

Roger, you nailed it, reviewing my uncalibrated images shows a drift over time aligned with the streaks, not sure quite why that shold be as the shots were autoguided and IIRC there was no reported drift reported in the s'ware....that combined with not enough signal means these shots are not useable. Oh well ...

Bojan - the darks were collected immediately after the imaging run - typically as I pack up so they should be a good match to the lights.

[bojan]

So there is nothing like that on darks?

[JohnH]

Nope they look normal - hot pixels, amp glow and random(ish) noise...

[bojan]

Well, that certainly rules out the EMI.....

[Garyh]

Hi John, I have had this with my 300d. I put it down myself to a combination of noise, hot pixels and (moire patterns-which are more noticable when the canon uv/ir filter is removed or replaced) and there is some sort of drift or sag between exposures-hense the streaks. Also on a warmer night it is more noticeable as well. I find my 300d sometimes rotates slightly on its adaptor as there is some play in it which does it so I have to be careful not to bump the camera at all.
Hope theres something useful there for you..
CS...Gary