self modding man needs reassurance

graham.hobart (Graham stevens) · #1 09-12-2011, 08:12 PM

Hi folks, just taken my self modded 450D outside to the rig to take some darks with the new set up i.e no IR filter on sensor and with new field flattener. I know it's not dark yet but have covered every oriface well and seem to be getting far more hot pixels on my 8.3 minute darks (iso 800 500 secs)
Is this normal for a bare sensor or have I buggered it up?
Can I still rely on my darks/flats to extract this noise?
Need kindly hugs from self modding experienced peeps

Graham

rcheshire (Rowland) · #2 09-12-2011, 08:39 PM

Desperate measures, but worth the effort. And you can see stars from where you live. Which makes you very fortunate. I can only see clouds

Should be OK Graham. If you are worried about an increase in the number of hot pixels, which seems unlikely, post an image. Let's have a peep...

graham.hobart (Graham stevens) · #3 09-12-2011, 09:25 PM

Row my man, only stars I can see are when I hit my head on the door frame. Is totally clouded out - even the cricket stopped today across the river after a biblical storm and deluge. Antediluvian optimism evaporates in reality!
Still -am taking darks outside under a canvas or two. Will post when I finish the run. Have ordered 30 x 500 secs and 30 x 240 secs so could take a while.
Temperature EXIF was quite warm as well-my outside thermometer is 16'c and my EXIF currently is 31'c!!
Need to get that cooler going I think
addit- there is no airflow around the camera at the moment as it is well wrapped for the rain and light, so maybe I will unwrap it a bit now and see if that lowers the EXIF.

leon · #4 09-12-2011, 09:31 PM

You are running pretty hot for dark's with out noise, best to take your dark's along with your lights, or very close to the same time and temp.

Leon

adman (Adam) · #5 09-12-2011, 09:45 PM

Hey graham, you are one little hive of activity down there!

You don't have to have the camera on the scope to take your darks. It is a good idea to take them at the same time as your lights -especially with a DSLR to get similar temps, but I often do them when I am packing up. I just take the camera off the scope and put the little canon cover over the bayonet mount and set it clicking away while I get everything packed up.

The ones that really matter to leave the camera on the scope (and in the same orientation / optical setup as your light frames) are your flats.

I find that my sensor will be about 10 degrees above ambient most of the time, so your high temps and noise are probably due to having the camera swaddled up.

Cheers, Adam

graham.hobart (Graham stevens) · #6 09-12-2011, 10:30 PM

The thing about the swaddling- I guessed as much but now it's dark I am reticent to take covers off with threatening clouds. Plus it's near Christmas and traditionally swaddling clothes are in the nativity play (next to the Canon DSLR from Nazareth)
I wanted to shoot a series of 500 sec darks so when I finally get some clear sky I could directly contrast my last set of lights on the Rosette with the modded cam; same exp, same iso etc. Obviously now have realised need to shoot the darks at the scene of the crime as it were.
This is a bugger as apart from processing, shooting darks is the only excuse I have for playing with my telescope on a cloudy night. I won't tell my wife though, have to keep shooting darks till I get it right. Also, late at night, under even a cloudy sky, with just the shutter going-that's just about the best peace a man(or woman) can get. So even if I have to re-shoot my darks at the next time I do lights, tonight I continue to do darks!
Thanks to all for advice thus far
Peace & harmony all

Graz

ballaratdragons (Ken) · #7 09-12-2011, 10:37 PM

Yep Graham,
Leon and Adam summed it up exactly.

Take your darks in the same temps as your lights (or as close as possible).

The ones you took are taken in temps waayyyy too hot. No wonder you have so many hot pixels!
I found it easier to use ICNR while imaging even though it can cut my imaging time down. But the results are worth it

graham.hobart (Graham stevens) · #8 09-12-2011, 11:16 PM

ICNR? please explain

graham.hobart (Graham stevens) · #9 09-12-2011, 11:40 PM

Experiment thus- I took the swaddling off and within 3 exposures of 500 secs the EXIF has dropped from 31'c to 25'c. Crazy what a beanie, bathtowel and three layers of tarps can do. Kept it dry though.

Poita (Peter) · #10 10-12-2011, 12:08 AM

Quote:

Originally Posted by graham.hobart

ICNR? please explain

In camera noise reduction? I'm only guessing though.

graham.hobart (Graham stevens) · #11 10-12-2011, 12:37 AM

Good point Poita, though I had set the camera for this before, and found download times to be a bit churlish. Anyway will try all when the cummulus has left my parish.
Was ok before the mod, so I would assume it would be ok after. Though thinking about it, once powered up, I had to put date/time etc in it so maybe it has defaulted back to factory?
Will instigate closer looks tomorrow.
Tonight, now I am going to watch Senna and maybe have a glass of good red. Seeing as the seeing is like midnight in a wrestler's armpit!
Graham.

ballaratdragons (Ken) · #12 10-12-2011, 01:30 AM

Quote:

Originally Posted by Poita

In camera noise reduction? I'm only guessing though.

Yep, 'In Camera Noise Reduction'.

It takes the dark immediately after the light, then subtracts it for you then downloads as usual, so it arrives at your PC already dark subtracted

Download time should be the same as for an image without using ICNR.
Mine downloads in about 2 - 3 seconds with my Canon 350d.

Yes it will halve your imaging time but I still prefer it myself.
The trick to having successful darks is taking them at the same temp as the light and ICNR achieves this perfectly every time

rcheshire (Rowland) · #13 10-12-2011, 10:03 AM

Alternatively, automate dark frame acquisition. When you have finished imaging, take bias and flats and leave the darks firing away. DSLR Shutter should do the job.

Auto off setting to turn the camera off when finished. More sleep. Don't be a slave to calibration.

Darks are only part of the puzzle. Dithering is essential and will improve SNR out of sight. Doesn't need to be exact, just move the target around the sensor between shots.

midnight (Darrin) · #14 12-12-2011, 02:48 AM

Good luck Graham!

I have a modded 40D and it's a new world.

I have had success with doing many light frames and then at the end of the night, take the camera off and put the Canon bayonet cap back on and set it to do 25 or so darks using the little hand controller while I go to bed. The Exif delta from start to finish is only about 2-3 degrees over my entire session at worse. There's some very interesting reading about dithering and ICNR vs separate darks. Do a search around

Unfortunately for me, I don't think I can dither with my Nexguide as it simply locks on and that's it!

Stick with what works best for yourself!

Darrin...