1000d max useable sub time?

[Uranium235]

Hiya,

Last night I did my first test with the 80ED DS PRO, guided by the 6" Newt. It all worked well apart from one thing - beacuse the 80ED is f7.5 i upped the sub time from 2.5min to 5min to compensate (and get the same luminosity as i would with the f5 newt). The test target was M81/M82.

However, LP didnt seem to be the big problem when going up to 9min... it was noise.. and lots of it. its kinda wierd noise too.... looks like a "texture".

Yes, i did make the exact number and length of darks to match, with flats and bias, but the 3x9.5 min subs were a shocker when i stacked them with the rest.

Is there a useable time limt to an ISO800 exposure with the 1000d? It seemed to be about 6minutes before any noticeble amount of noise/ampglow showed. I know there are a fair few people who have used the same setup so it would be nice to get some sort of general agreement on what is the most useable sub time @ f7.5 ISO800.

[Psychobilly]

What do the darks look like ... I have pushed my 1000D to 1800s (yes 30 min) subs at ISO 800...

You are taking bias frames - how many? - they have a greater effect on image quality than darks with the 1000D at sensible sub lenghts... quick to take so use quite a few

Peter...

In terms of general agreement you need to test your camera as I have seen a fair bit of variation between cameras...

[johnrt]

At iso 800 after 10 min I get a fair amount of noise, they look like coloured flecks across the image, mainly green and red.

At iso 400 there is hardly any noise whatsoever.

[Uranium235]

Hi peter,

I looked at the darks (with the canon software, not DSS cos the all look reddish there), there are a few hot pixels and when you zoom in you can see loads of red & white dots (I guess thats normal).

I used 10 bias frames for the 90 minutes worth of subs. Is that too few?

How many should I be aiming for? Thanks!

[Psychobilly]

I'm uploading ISO 800 Master Darks (300,450,600 and 900s) and and Bias for my 1000D it will take a while as its 100MB+ of tiffs

I'll post links when they have finished...

Peter...

[Psychobilly]

Theres a lot been discussed about the right number...

This is just what I do...

In general is use "40" of each of the calbration frames... I tend to use Library darks that are close to the temp when the light were taken.. I often leave the camera running doing dark sequences in the obs all day...

For better temp control pinch the fridge...

I dotn get any "glow" in my darks unless i have been using liveview when its visible on the left hand edge of the frame whilst the sensor cools down...

I do run with "external" PSU rather than internal batteries and leave 30s between subs never mind how long they are...

Peter...

[Uranium235]

Thanks, will try that now. Its a clear night again so im gonna set up and give it another bash.... 40 bias & 30 sec between subs (i was using 5sec).. got it!

Will report any findings later...

[Psychobilly]

the last of my Master Darks and Bias are uploading

Master Darks are from 20 darks at each exposure...

http://www.graigolaobservatory.org.uk/1000D/MasterDark_ISO800_300s.tif

http://www.graigolaobservatory.org.uk/1000D/MasterDark_ISO800_450s.tif

http://www.graigolaobservatory.org.uk/1000D/MasterDark_ISO800_600s.tif

http://www.graigolaobservatory.org.uk/1000D/MasterDark_ISO800_900s.tif

Bias...

http://www.graigolaobservatory.org.uk/1000D/MasterOffset_ISO800.tif

[Uranium235]

Peter... youre a STAR!

Did as you said, and used 40 bias frames and the noise vanished!

I added another 10x5min subs to what I got on saturday night so the total exposure time on M81/82 is now 2h25min - plus a little bonus of M44

I will probably do as you did and keep a stock of bias & darks & flats to save the hassle (I rarely change the cam focus or orientation). Ive taken a look @ your darks, heh heh I guess theres no point in me "borrowing" them as you took them with a different scope to mine.

If the weather holds out this eve I might throw in some 20min subs to try and get more detail out of M81 - heres what ive got so far:

[Psychobilly]

Glad the advice based on practical experience helped you out...

Peter...

[jgs001]

Whilst this is not directly related... it is in some way.. I went looking for info on Bias frames, as I stopped using them... it was causing too many hard to process out issues... and I found this

Digital SLR Astrophotography

Look right down at the end.

What's your thoughts ?

I've shot 20 minute subs with the 450d and I did push it to a 35 minute once as an experiment (it didn't work) and the images were full of hot pixels.

[Psychobilly]

John,

I have seen so much variation camera to camera...

So I base my methods on my own practical results and loads of testing with the actual cameras I use and they way I want to use them....

I still need to see how the 500D is going to pan out...

Peter...

[dph1nm]

Yes, depends on the camera I think, and how many frames you stack. My 1000D has horrible bias structure, and as I only do many short (~1min) exposures this structure rapidly appears once you stack the frames. So bias frames are a must for me (or darks, which have the bias in anyway of course).

NigelM

[Psychobilly]

Ive taken a look @ your darks, heh heh I guess theres no point in me "borrowing" them as you took them with a different scope to mine.

Just to clarify...

Darks are camera and temperature but not scope dependent..

Flats are Camera and optical train dependent

Bias are Camera dependent...

Peter...

[sgazer]

the last of my Master Darks and Bias are uploading

Master Darks are from 20 darks at each exposure...

http://www.graigolaobservatory.org.uk/1000D/MasterDark_ISO800_300s.tif

http://www.graigolaobservatory.org.uk/1000D/MasterDark_ISO800_450s.tif

http://www.graigolaobservatory.org.uk/1000D/MasterDark_ISO800_600s.tif

http://www.graigolaobservatory.org.uk/1000D/MasterDark_ISO800_900s.tif

Bias...

http://www.graigolaobservatory.org.uk/1000D/MasterOffset_ISO800.tif

hi,

what temperature are these darks taken at?

Thanks

[Psychobilly]

I would have to check when I get home to see if i recorded all the info...

I have noticed my cameras darks dont vary dramatically with temp... and even at room temp they aren't too bad...

I have been meaning to get a temp logger to use in the obs during darks run...but havent found a cheap one...

Peter...

[sgazer]

ok thanks. Perhaps the temp build up in the sensor and the insulation provided by the camera body outweigh the external air temp some extent.

ps. I noticed your darks weren't.....dark! Well not completely, the 300s, ISO800 one gives about 93% black according to Photoshop. I don't know if this is important or not or what affect it might have.

[Psychobilly]

I'm happy with the way they work

[Uranium235]

Just to clarify...

Darks are camera and temperature but not scope dependent..

Flats are Camera and optical train dependent

Bias are Camera dependent...

Peter...

Ahhh.. i see

Thanks!

[sgazer]

I'm happy with the way they work

sorry, hope I wasn't sounding negative, I was just comparing them with some of my 1000d darks, to see if any variations between the cameras were noticeable and noticed they looked a shade more grey when side by side. I can tell from your images that they work very well though .

[Psychobilly]

Sorry i didn't mean it as a dismissive reply...

I just let DSS do it's thing and don't pay much attention to what the calibration frames look like unless the resulting stacked image looks wrong...

One thing I have found with DSS is to make sure you are providing all the frames for one of its "legitimate" calibration methods as described in the DSS help files... or in this thread http://stargazerslounge.com/imaging-discussion/99867-yet-another-calibration-question.html

Peter...

[sgazer]

Thanks for the link, I use the dark, flat, dark-flat routine.

ps. back on the thread subject; I've tried a 10 min sub ISO1600 with my 1000d and it didn't seem too bad at all (100% crops, RAW converted to jpg, no calib, attached below). I don't like long subs though, as something is twice a likely to go wrong than with a 5min sub (tracking, plane, cloud etc etc), so I usually stick with 5mins.

pps. I'm sure I tried a 20min sub once and it was rubbish, but I can't find it at the mo'

[yesyes]

Ahaaa... So that would be something to do when there's clouds.

As I understand it it would make sense to just leave the 1000D outside to cool down put the body cap on the camera and then take loads of darks (long exposures) and bias frames (exposure as short as possible).

With APT programmed to do all the necessary exposures this should be rather easy...

Slightly off-topic: With a brand new 1000D how many hot pixels should be acceptable? Mine has 3 red pixels, one just above the middle and 2 bottom left.

[Psychobilly]

I think taht would be fine... At least you would have problems with persuadign Canon to swap it as they would argue that they won't "appear" when the camera is being used for its intended purpose (theirs) with long exposure NR enabled...(effectively auto dark subtraction)

Peter...

[sgazer]

I found my longest sub, it was 15mins at ISO800 with the 150p-ds, the one above was 10mins ISO1600 with a C80-ED so it's difficult to compare.

The 15min sub will be 1.5x brighter due to the exposure length, 2.2x brighter due to the scope, but then 0.5x brighter due to the lower ISO which I think is a total of 1.65x brighter.

I haven't posted the 15min one as it was quite blown out due to thin cloud, but after stacking 1 15min sub with some flats and comparing it to the 10min sub with some flats, (no darks) it didn't look too bad.

So, I think 10mins subs at ISO1600 and 15mins subs (poss 20mins) at ISO800 are reasonable (based on a sample of 1 sub each!)