First M51 with cooled 1100D

[Gina]

Sorry its a bit off topic but a big Congratulations to Quatermass who's now showing up as a moderator. :hello2:

Cheers John

I heartily second that

[Gina]

Back on topic DSS now stacking 40 lights (out of a total of 50) having produced a master dark from 56 dark subs. I'll post the result when it's finished.

[Viv]

Great improvements Gina !!

Looking forward to this next one .....

[Gina]

Great improvements Gina !!

Looking forward to this next one .....

Thank you Scarlet I'll be posting it shortly - my main PC has been playing up.

[Gina]

I did a drift alignment last night by just running 2 min exposures in APT and reducing the star trails by adjusting the mount alignment knobs - it was very hit and miss with no way of knowing when you'd gone past the right spot and out the other side.

Since then I've found this post in another thread when trying to find easy ways of drift alignment. It looks a lot easier than the method I used and more accurate

I spent some time last night between clouds using PHD to do a drift alignment, and by George it works a treat.

Method

- set scope to near meridian and celestrial equator start PHD and do a calibration, start guiding with the DEC turned off, turn on the Graph and change the RA/DEC button to dx,dy.

If you see a steady drift in the dy you move the mount to the East or West until the dy graph remains flat, apart from the seeing causing slight random movement.

Repeat the procedure with the scope to the East or West on the Celestrial Equator, calibrate PHD and guide in only RA, watch the dy trace but this time alter the mount up or down until the dy trace flatlines.

This took me about an hour including longish runs to ensure the dy was really flat.

My Mount was slightly out to the East but a fair way out up/down, now it should be virtually bang on.

The nice thing is you can quickly see the affect of each mount adjustment within a few seconds, especially if you adjust in the wrong direction!

[Gina]

Main desktop working again - mainly

Here are a couple of JPEGs from the latest run.

1. Full frame just scaled.
   
2. Stretched etc. cropped and scaled in GIMP.
   

[Gina]

A re-jig of the JPEG

[Starflyer]

I use the PHD drift alignment method and it works a treat

I'm a surprised by the level of noise you're still getting at sub-zero temps, what EXIF temperature are the RAWs showing - Kuso EXIF Viewer? Are you taking plenty of Bias frames, 40 -60 is enough?

For comparison I've attached a single 420s frame at 7C, no calibration, no manipulation at all, just converted to jpg in Photoshop, cropped but still at 100% - 10" f/4.8 newt. Maybe the difference in scopes / exposure times, but to me yours looks too noisy for those temps.

I can see my dark file sizes increase as the EXIF temp increases, to the point where I can now guess the temperature they'll show. Maybe you can check the file sizes of an old, un-cooled dark and a current one?

I found an old un-cooled 420s dark; 36C - 17,461KB, compared with 7C - 11,717KB, that's should give you an idea of the amount of noise the heat can generate

EDIT: - I've just re-read you water cooling thread where you say our EXIF temps are ~ -7C, don't know where the noise is coming from then

[Gina]

I use the PHD drift alignment method and it works a treat

I'm a surprised by the level of noise you're still getting at sub-zero temps, what EXIF temperature are the RAWs showing - Kuso EXIF Viewer? Are you taking plenty of Bias frames, 40 -60 is enough?

For comparison I've attached a single 420s frame at 7C, no calibration, no manipulation at all, just converted to jpg in Photoshop, cropped but still at 100% - 10" f/4.8 newt. Maybe the difference in scopes / exposure times, but to me yours looks too noisy for those temps.

I can see my dark file sizes increase as the EXIF temp increases, to the point where I can now guess the temperature they'll show. Maybe you can check the file sizes of an old, un-cooled dark and a current one?

Edit: I've just re-read you water cooling thread where you say your EXIF temps are ~ -7C

I found an old un-cooled 420s dark; 36C - 17,461KB, compared with 7C - 11,717KB, that's should give you an idea of the amount of noise the heat can generate

EDIT: - I've just re-read you water cooling thread where you say our EXIF temps are ~ -7C, don't know where the noise is coming from then

The temperatures I'm talking about are the EXIF T as read from the RAW files - either at the time in APT or later.

When I was running at -7C I was getting some condensation so I've reduced the cooling in later runs. Last night's was -1C and the night before, -3C. I haven't taken any bias frames yet so maybe that's the problem. The odd thing is that the noise in the lights is way above the amount in the darks.

I'll check the file sizes from the test runs of darks I did. I do know that I could get up to an hour's exposure at ISO 1600 before the noise got near to the level of lights I've been getting at ISO 800 with 3m and ISO 3200 with 2m. I'm very puzzled by this but I'm only at the bottom of the learning curve. I think I need to study the processes in the image sensor and learn more about the sorts of noise and how they're generated. The noise generated by thermal effects with no light is not the noise we're seeing in the lights - this is differently produced noise and several magnitudes greater than the thermal noise.

[Starflyer]

It certainly is a steep learning curve, it still is for me

I'm no expert but here's how I believe it works...

Your lights contain two types of unwanted noise from the camera;

thermal noise and read noise. You aim to remove thermal noise by taking darks at the same ISO / exposure, preferably matched in temperature.

Read noise is introduced by the camera's electronics as it reads and converts the data collected by the sensor into an image file. We can try and eliminate this by taking a dark frame of zero exposure, or as short as your camera will allow, 1/4000s on my 450D. The idea behind this is that the sensor won't have collected any light, and the thermal noise at that exposure should be close to zero - the only noise captured will be generated by reading the sensor - this is your Bias frame. I take around 50 and re-use them for a few months before creating a new set.

Out of curiosity, are your EXIF temps stable during a long run with the cold finger? I get a fairly quick (30 minutes) rise in temp of around 8C if imaging continuously. I limit this by adding a 30s pause between images to allow the camera to cool a bit.

Your engineering knowledge is an inspiration to a lot of people on here Gina, I'm sure you'll have this cracked in no time

[Gina]

It certainly is a steep learning curve, it still is for me

Sure is!

I'm no expert but here's how I believe it works...

Your lights contain two types of unwanted noise from the camera;

thermal noise and read noise. You aim to remove thermal noise by taking darks at the same ISO / exposure, preferably matched in temperature.

Read noise is introduced by the camera's electronics as it reads and converts the data collected by the sensor into an image file. We can try and eliminate this by taking a dark frame of zero exposure, or as short as your camera will allow, 1/4000s on my 450D. The idea behind this is that the sensor won't have collected any light, and the thermal noise at that exposure should be close to zero - the only noise captured will be generated by reading the sensor - this is your Bias frame. I take around 50 and re-use them for a few months before creating a new set.

Ah right - I thought it was something like that - thank you I have some flat frames to take to go with last night's lights and darks so now I see I want to take some bias frames too. Sounds easy enough

Out of curiosity, are your EXIF temps stable during a long run with the cold finger? I get a fairly quick (30 minutes) rise in temp of around 8C if imaging continuously. I limit this by adding a 30s pause between images to allow the camera to cool a bit.

It takes a little while to settle down but once I'm taking a continuous run of lights or darks I can adjust the power supply to get the required temperature and it stays as set for some time generally. If the ambient temperature changes then the EXIF T will change after a while. I shall be making up a control circuit to maintain the cold finger temperature at whatever set point is chosen. Only trouble is, it's goodness knows how many years since I last worked out the damping and stability of feedback control systems - it can be quite complicated.

Your engineering knowledge is an inspiration to a lot of people on here Gina, I'm sure you'll have this cracked in no time

Thank you

[Gina]

Taken loads of flats with the scope pointing as it was when I finished the lights and darks the other night. Sheet of paper over the open dew shield and mainly dark clouds overhead. Camera set to Av and APT running subs at ISO 100 giving histograms at around 50%.

Also taken some bias frames. 1/4000 sec at ISO 3200. I presume the ISO should match the lights and darks. Should the temperature match too or doesn't it matter? I can make sure by turning the cooling on I don't think there's any problem with light getting in with such a short exposure.

[Gina]

A ton of bias frames taken at around EXIF T = 0C within a couple of degrees. With full cooling the temperature comes down in a couple of minutes. Then it's a matter of adjusting the cooling to maintain the temperature - manually ATM, until I build a controller.

Rain is due any minute now and the sky's black as the ace of spades!

[kingboya]

Surely if you are running at such cold temperatures the chance of frost or condensation build up is greatly increased? Just thinking of the 'ice cubes in a glass of water' example.

Just a thought

[Gina]

Surely if you are running at such cold temperatures the chance of frost or condensation build up is greatly increased? Just thinking of the 'ice cubes in a glass of water' example.

Just a thought

Yes, I find I get condensation when I run colder than about -5C but I haven't done anything yet to reduce moisture inside the camera. I'm planning to seal the case with silicone grease (so I can get it open again if I want) and put a number of bags of silica gel inside to absorb moisture.

[Gina]

Taken flats and bias frames and re-run DSS - this is the result - converted to JPEG and scaled for here.

[Chris]

Everytime I drop buy this thread your M51 has got even better:), M51 is my favourite object that I've imaged so far, although I'm yet to let rip on M31 with my zs66, I'm looking forward to that:)

[Gina]

Thank you I'm gradually getting the hang of this lark Gradually improving equipment and getting more used to the processing software Currently just finishing another stack in DSS with different parameters - dying to see if it has improved the result.

[Chris]

I think your doing very well indeed!, you seem to get a lot done and fast, I'm loving your cold finger mod, its tempting to try this with my 350D but It's also tempting to wait until the price of CCD's comes down even more, I don't know how long I'll be waiting though:D

[Chris]

oh I forget to ask have you tried using a 2xDrizzle yet?, I find it worked very well with plenty of subs, it brought out a bit more fine detail compared to previous attempts.

[Gina]

Thank you very much No, not tried drizzle yet.

[Gina]

Here's the result of re-stacking and then changing to JPEG and stretching plus unsharp mask in GIMP

[Chris]

wow! now you must be very pleased with this version, both the galaxy and backgound are great its quality basically a big congrats:)

[jjongmans]

Great improvement!

[Gina]

Thank you Yes, it is better

Here's the TIFF converted to JPEG and scaled with no post processing.