Dithering again and cooling

[alan potts]

After testing the patience of a saint getting dithering off the ground with my Canon 40D, I rather like this approach to the final image and have basically dropped Darks.

Can I still continue to dither instead of using Darks when my Zwo 071 arrives which should be in the next day or so.

I also wonder about the cooling as it is at least 10-15 degrees hot of a night here than England, any recommendations, even at 11pm it can be 30 degrees

Alan

 

[symmetal]

Yes, dithering is beneficial no matter what the camera. With CMOS cameras it would still be useful taking darks as well. With set point cooling they are more matched to your lights for proper calibration compared to your DSLR darks. The ASI071 doesn't exhibit very noticeable 'amp glow' like the ASI1600 but would still benefit from darks. A set of darks should be fine to use for a year or more before possibly needing to be redone, (if taken at the same temperature as your lights).

I've noticed that my 071 only cools to about 30 degrees below ambient compared to my 1600 which can cool by 40 degrees. You'll just manage to reach about zero degrees at +30 ambient so for the moment use zero degrees for your set point cooling and take darks at this same temperature. In the winter you can cool to -15C or so which is better noise wise so another set of darks at that temperature would need to be taken.

Alan

[alan potts]

8 minutes ago, symmetal said:

Yes, dithering is beneficial no matter what the camera. With CMOS cameras it would still be useful taking darks as well. With set point cooling they are more matched to your lights for proper calibration compared to your DSLR darks. The ASI071 doesn't exhibit very noticeable 'amp glow' like the ASI1600 but would still benefit from darks. A set of darks should be fine to use for a year or more before possibly needing to be redone, (if taken at the same temperature as your lights).

I've noticed that my 071 only cools to about 30 degrees below ambient compared to my 1600 which can cool by 40 degrees. You'll just manage to reach about zero degrees at +30 ambient so for the moment use zero degrees for your set point cooling and take darks at this same temperature. In the winter you can cool to -15C or so which is better noise wise so another set of darks at that temperature would need to be taken.

Alan

Many thanks for that, in winter it can go down to minus 25 here very easily. Plus 30 is maybe rare of an evening but 20-25 would common in June, July, August and early Sept.

Alan

[symmetal]

You could then try for -5 or -10C in the summer which would be reachable for most days. On the noise vs temperature graph shown on your last thread, at -15C the noise graph pretty much levels out so the benefit of cooling below that is not so much. I'd just leave the set point cooling  at say -25C in the winter even if the ambient temperature goes below that just to save possibly having to take another set of darks at the cooler temperature. 

Alan

[ollypenrice]

I've no experience of CMOS cameras but some seem to have a big amp glow and dithering won't take this out. Only darks will do that. Please regard this post as no more than a 'Heads up' because it doesn't come from experience and merely draws on posts I've read from users. The necessary homework should be straightforward.

Olly

[Annehouw]

Hi Alan,

Do both. Really.

I use a QHY168C which uses the same IMX071 chip as your ZWO071.

- It has no amp glow (not my camera at least).

The rest of the pre-processing frankly is the same as with CCD:

- Use a fair amount of dithering (every 2-3 exposures) to combat fixed pattern noise and help the statistical outlier rejection algorithms in the software of your choice (I use AstroPixelProcessor and it is a brilliant and very user friendly piece of software).

- Dark frames are fast and easy, why not use them as well?: I have a library for my 2 exposure settings (50sec for L, 300sec for narrowband). Darkframes for  summer (-10C or -15C) and for winter (-20C).  Do an average of 30 darkframes, make a master dark. You can use those masters easily for a year.

- Generate a bad pixel map (of a defect map) in your software of choice. Again..can be reused for at least a year.

- No bias needed if you use master darks with the same exposure time at the same temperature as the exposures.

Working with a temperature regulated camera is convenient and efficient compared to a dslr where you have to scale darkframes due to temperature fluctuations.

 

Regards,

Anne

 

[Annehouw]

I now see that I could have said: What symmetal said......

[alan potts]

Just dawned on me I wouldn't know what amp glow looked like and would try to stretch it.

Thanks to all for help, I will try both and Just Darks as it seems as if you don't have to do them every night. At least with a cooling setable I could do them in the day if it were not too hot.

Alan

[symmetal]

1 hour ago, alan potts said:

Just dawned on me I wouldn't know what amp glow looked like and would try to stretch it.

Thanks to all for help, I will try both and Just Darks as it seems as if you don't have to do them every night. At least with a cooling setable I could do them in the day if it were not too hot.

Alan

This is the effect of 'Amp glow' on an ASI 1600 dark frame. It's heavily stretched to make it obvious but the raw ADU difference shows the magnitude between the centre and corners. Without calibrating using darks, when stretching the image during processing the corners would show noticeable brightening. Up to 60s the glow isn't too noticeable and you can get away without darks to some extent, but for longer exposures they are needed.

CMOS cameras exhibit it as the sensor read-out electronics, amplifiers and multiple A/D converters etc. are all incorporated on the sensor chip itself so certain areas of the  chip can become hotter than others causing 'Amplifier Glow'.

By comparison CCD sensor chips have all their read-out circuitry and the single A/D converter on separate circuit boards so it's easier for all the sensor to be maintained at the same temperature all over.

i don't have a similar length ASI071 dark to post for a direct comparison but it's nowhere as bad as the 1600.

As you say you don't need to take darks every night, once a year or so is normally good enough. Just take a set for each exposure duration you're likely to use (to avoid using dark scaling which isn't as accurate.) I take them on nights when it's cloudy, (plenty to choose from ) as it's easier to get the right temperature.

Alan

 

 

[alan potts]

5 hours ago, symmetal said:

This is the effect of 'Amp glow' on an ASI 1600 dark frame. It's heavily stretched to make it obvious but the raw ADU difference shows the magnitude between the centre and corners. Without calibrating using darks, when stretching the image during processing the corners would show noticeable brightening. Up to 60s the glow isn't too noticeable and you can get away without darks to some extent, but for longer exposures they are needed.

CMOS cameras exhibit it as the sensor read-out electronics, amplifiers and multiple A/D converters etc. are all incorporated on the sensor chip itself so certain areas of the  chip can become hotter than others causing 'Amplifier Glow'.

By comparison CCD sensor chips have all their read-out circuitry and the single A/D converter on separate circuit boards so it's easier for all the sensor to be maintained at the same temperature all over.

i don't have a similar length ASI071 dark to post for a direct comparison but it's nowhere as bad as the 1600.

As you say you don't need to take darks every night, once a year or so is normally good enough. Just take a set for each exposure duration you're likely to use (to avoid using dark scaling which isn't as accurate.) I take them on nights when it's cloudy, (plenty to choose from ) as it's easier to get the right temperature.

Alan

 

 

Many thanks for that, didn't understand everything but at least I know what to look for.

If you have time can you let me know, what sub lengths you find best and what sort of gain and other settings you use, feel it will take me a while to get use to it. The canon was second nature to some degree as I have had so many other models and understand the setting.

Alan

[symmetal]

9 hours ago, alan potts said:

If you have time can you let me know, what sub lengths you find best and what sort of gain and other settings you use, feel it will take me a while to get use to it. The canon was second nature to some degree as I have had so many other models and understand the setting.

I would just start with the unity gain setting as selected in the Ascom driver, gain 90, offset 65. The offset looks fine for all gain settings (no black clipping) so there's no need to change that. I've only had my camera for about a month and haven't been able to take any real images with it, just a few tests so can't recommend a starting exposure at the moment. Others who've had the camera for longer can give more practical advice there. For my 1600 I found 180s was optimum for RGB so that the sky background level swamped the read noise. It depends on your level of light pollution as to what the optimum is. I was going to start with 180s with the 071 (assuming the Star Adventurer can manage that without star trails) but may have to limit it to 120s. I may have to mount it on my AZ-EQ6 if I need longer exposures.

Others advocate using half unity gain (gain 30 for the 071) for RGB and twice unity (gain 150 for the 071) for narrowband imaging, but this means having to take a set of darks for each gain setting so I stick with unity gain.

If you're interested the sky background ADU (16 bit) to swamp the read noise (where the sky b/g is ten times the square of the read noise) is 526 for the 071 at unity gain and offset 65 but that may be more than you want to know. 

The other setting in the driver is USB3 speed limit. If you have a fast enough imaging PC you can set it at 100% to get the shortest download time but if you experience problems with corrupt or missing images you will need to set it to a lower speed limit.

Alan

Edited August 21, 2019 by symmetal

[alan potts]

22 minutes ago, symmetal said:

I would just start with the unity gain setting as selected in the Ascom driver, gain 90, offset 65. The offset looks fine for all gain settings (no black clipping) so there's no need to change that. I've only had my camera for about a month and haven't been able to take any real images with it, just a few tests so can't recommend a starting exposure at the moment. Others who've had the camera for longer can give more practical advice there. For my 1600 I found 180s was optimum for RGB so that the sky background level swamped the read noise. It depends on your level of light pollution as to what the optimum is. I was going to start with 180s with the 071 (assuming the Star Adventurer can manage that without star trails) but may have to limit it to 120s. I may have to mount it on my AZ-EQ6 if I need longer exposures.

Others advocate using half unity gain (gain 30 for the 071) for RGB and twice unity (gain 150 for the 071) for narrowband imaging, but this means having to take a set of darks for each gain setting so I stick with unity gain.

If you're interested the sky background ADU (16 bit) to swamp the read noise (where the sky b/g is ten times the square of the read noise) is 526 for the 071 at unity gain and offset 65 but that may be more than you want to know. 

The other setting in the driver is USB3 speed limit. If you have a fast enough imaging PC you can set it at 100% to get the shortest download time but if you experience problems with corrupt or missing images you will need to set it to a lower speed limit.

Alan

Thank you for that, we are in a spell of 18 nights clear at the moment and more to come, would happily let you have a couple. Er yes keep it simple for me. I only have USB 2 laptops so that will not worry me. I am going to try DSLR and the 071 on teo scopes, but I will use another laptop for the 70mmED, just for APT.

Alan.

[symmetal]

1 hour ago, alan potts said:

we are in a spell of 18 nights clear at the moment and more to come

Wow! I wonder what that's like.  I think the most clear nights I've had in a row is about three.

Alan

[david_taurus83]

Hi Alan,

 

Have you got Sharpcap? It has a sensor analysis tool where it measures the read noise of the camera. You need to follow a few on screen instructions where it simply takes a batch of darks and flats at various exposure length and gain strength. Once the values have been measured they are saved in Sharpcap.

 

This then opens up its Smart Histogram feature. Similar to above, this is carried out at night and Sharpcap takes exposures of your sky conditions and works out the optimum exposure length and gain value for you based on your cameras sensor values. It's very good!

[alan potts]

3 hours ago, david_taurus83 said:

Hi Alan,

 

Have you got Sharpcap? It has a sensor analysis tool where it measures the read noise of the camera. You need to follow a few on screen instructions where it simply takes a batch of darks and flats at various exposure length and gain strength. Once the values have been measured they are saved in Sharpcap.

 

This then opens up its Smart Histogram feature. Similar to above, this is carried out at night and Sharpcap takes exposures of your sky conditions and works out the optimum exposure length and gain value for you based on your cameras sensor values. It's very good!

Feel I need to consider software a bit more seriously than I do at the moment. I have a feeling Sharpcap is a free program or very cheap. I would like to get some processing software too, Gradiant Ex and a few others. At the moment I just have PS.

I have a small set back with the 071 in the shape of the IR/UV filter, Flo have sent me 1.25 inch filter and said there was an adapter to fit it close to the sensor, I fee they were mistaken as the sensor is bigger than the filter and requires a 2 inch without a doubt in my view. If I'm wrong I would love to know how to fit it. Still it will not stop me learn the ropes.

Alan

[symmetal]

21 hours ago, alan potts said:

Feel I need to consider software a bit more seriously than I do at the moment. I have a feeling Sharpcap is a free program or very cheap. I would like to get some processing software too, Gradiant Ex and a few others. At the moment I just have PS.

I have a small set back with the 071 in the shape of the IR/UV filter, Flo have sent me 1.25 inch filter and said there was an adapter to fit it close to the sensor, I fee they were mistaken as the sensor is bigger than the filter and requires a 2 inch without a doubt in my view. If I'm wrong I would love to know how to fit it. Still it will not stop me learn the ropes.

Alan

APT is a very reasonably priced program for imaging too which many people here rate highly too. I assumed Sharpcap was more geared towards planetary video imaging though I'm willing to be proved wrong. 

The small printed manual included with my 071 was actually the manual for the 1600 which does show a 1.25" filter thread on the rear of the 1.25" nosepiece adapter which may have confused FLO. The actual 071 manual downloaded from the Zwo website just mentions 2" filters which are M48 threaded in reality.

Alan

[alan potts]

59 minutes ago, symmetal said:

APT is a very reasonably priced program for imaging too which many people here rate highly too. I assumed Sharpcap was more geared towards planetary video imaging though I'm willing to be proved wrong. 

The small printed manual included with my 071 was actually the manual for the 1600 which does show a 1.25" filter thread on the rear of the 1.25" nosepiece adapter which may have confused FLO. The actual 071 manual downloaded from the Zwo website just mentions 2" filters which are M48 threaded in reality.

Alan

Thanks Alan

The guy that does APT live in Sofia here. Well I have just spent most of the day in less than ideal 36 degrees trying to understand this camera and have given up. I got the various drivers loaded with issue which is strange for me but as for Sharpcap I cannot understand a thing apart from the cooling. I don't understand the way it works what so ever, and I have tried to read the instructions and give up.

Even APT that I sort of know didn't do a thing, wouldn't take a picture, wouldn't cool the camera yet claimed it was connected. I have come away from a beautiful clear sky because I will do something I regret.

Alan

[symmetal]

59 minutes ago, alan potts said:

Even APT that I sort of know didn't do a thing, wouldn't take a picture, wouldn't cool the camera yet claimed it was connected. I have come away from a beautiful clear sky because I will do something I regret.

That's a pity. The manual says that the camera draws 0.5A (without cooling) which is the limit for USB2 and is why they recommend USB3 which can deliver 1A. However it also says if the 12V power is connected to power the cooler the camera will use that instead of the USB power so that should be OK for you. You do have the 12V connected I presume and your USB2 cable is plugged into the USB3 connector on the camera and not the USB2 sockets. As it does nothing apart from recognising the camera does imply a power problem somewhere.

Also look in 'Device manager' on your PC and check if the camera is there under 'Imaging Devices' and has no yellow exclamation mark next to it which would imply a driver problem.

Alan

Edited August 22, 2019 by symmetal

[Dragon_Astro]

On 21/08/2019 at 17:48, david_taurus83 said:

Hi Alan,

 

Have you got Sharpcap? It has a sensor analysis tool where it measures the read noise of the camera. You need to follow a few on screen instructions where it simply takes a batch of darks and flats at various exposure length and gain strength. Once the values have been measured they are saved in Sharpcap.

 

This then opens up its Smart Histogram feature. Similar to above, this is carried out at night and Sharpcap takes exposures of your sky conditions and works out the optimum exposure length and gain value for you based on your cameras sensor values. It's very good!

I use SharpCap with my cmos camera, and I can concur the Smart Histogram is very good for measuring your skies and working out the correct exposure, gain etc.

SharpCap Pro version is £10 a year and find it more stable than APT, which I found froze all the time with my cmos.

[david_taurus83]

Hi Alan,

 

The camera requires a separate 12v supply for the cooler alone. The camera/imaging itself runs off the USB cable. Forget Sharpcap for now is it is very different to APT if your used to that. What version of APT are you running? Do you update it regularly?

[symmetal]

3 hours ago, david_taurus83 said:

The camera requires a separate 12v supply for the cooler alone. The camera/imaging itself runs off the USB cable.

That's what the other ASI cameras state which have a 12V cooler supply. But the manual for the 071 at the end of the 'Power Consumption' section states 'ASI071 and USB hub is powered from the 12V DC power supply if you connect it.' Whether that's true or not remains to be tested. 

Alan

[alan potts]

8 hours ago, symmetal said:

That's a pity. The manual says that the camera draws 0.5A (without cooling) which is the limit for USB2 and is why they recommend USB3 which can deliver 1A. However it also says if the 12V power is connected to power the cooler the camera will use that instead of the USB power so that should be OK for you. You do have the 12V connected I presume and your USB2 cable is plugged into the USB3 connector on the camera and not the USB2 sockets. As it does nothing apart from recognising the camera does imply a power problem somewhere.

Also look in 'Device manager' on your PC and check if the camera is there under 'Imaging Devices' and has no yellow exclamation mark next to it which would imply a driver problem.

Alan

Thanks Alan,

After a bit of a cool down I went back for a look, I have done all you said correctly and do have the Zwo transformer connected. It also appears in Device manager. How I actually came to look at that I am not sure but I saw it whilst I was checking a problem which stopped the mount moving, I was checking to see if EQdir still had a port, which it did. Once I removed the Zwo camera from the laptop onto another laptop, it started working again. Oddly I reconnected it by accident thinking it was the guide camera and the mount was still working, strange what can happen. I then after PHD told me there was a Darks Library problem took a set of Dark files with it thinking it was the guide camera.

I am sure the camera works, as I believe I have taken a set of Darks. I set it going on a 15 shot run early in the day and it said it was averaging them, to me meaning you end up with one or a stack of them. this seems to have happened. There is a what looks like a Dark frame with time stamp in the folder, that took an age to find until I noticed an icon on the Desk Top screen.

I am just not very good at all at understanding what all this means, I find the whole thing very frustrating.

Alan.

[alan potts]

7 hours ago, david_taurus83 said:

Hi Alan,

 

The camera requires a separate 12v supply for the cooler alone. The camera/imaging itself runs off the USB cable. Forget Sharpcap for now is it is very different to APT if your used to that. What version of APT are you running? Do you update it regularly?

Hi Dave,

I am running the PHD which was loaded about 3 months back so must be fairly new, I don't know the number but putting the latest PHD in is easy enough for me. Your right in Sharpcap is very Different. Grant said I would be fine running the 071 on USB with the 12v transformer connected, it was a question I asked as I don't actually have a Laptop with USB3 even though I have 5 of them all fairly decent high spec models for their time, their time was about 6 years ago in the best case.

Why can't IT be a bit easier,

Alan

 

[alan potts]

8 hours ago, Dragon_Astro said:

I use SharpCap with my cmos camera, and I can concur the Smart Histogram is very good for measuring your skies and working out the correct exposure, gain etc.

SharpCap Pro version is £10 a year and find it more stable than APT, which I found froze all the time with my cmos.

Thanks for you reply, at the moment getting any exposure would be nice to look at, I aim for about 2-3 minutes judging by what others do, my sky id very good here as I am miles from any real problems and directions like South West and North, I have nothing for tens -hundreds of miles. I am though finding APT locking up at you say and it is running on a separate laptop at the moment which is doing nothing else but what the 071 requires, plenty of computing power for that I would have thought.

Alan

[bottletopburly]

1 hour ago, alan potts said:

APT locking up

 Alan Drop ivo @Yoddhaa message on APT forum he may be able to help or at least let him know issue for that particular camera