Hi Everyone
Here is a challenge - what caused the mottling on my subs of Eta Carinae a few weeks ago? (See below).
With rotten weather here in Tassie it wasn't until the very end of March that I managed to set up my gear (WO GT102 Apo refractor, the new ZWO ASI071 and Sky X Pro software. It was a warm and humid night (ambient=20 degrees C) and the camera struggled to reach the -20 C temperature I had set. I mucked around with gain and other settings trying to get focus right and I also reset the temperature to -15 and then -5 (as well as turning it off completely). This produced unusable darks as the settings were all over the place, including the gain. I wrote to ZWO who told me (twice) that the mottling on these subs was caused by dew. My mates down here disagree with this analysis. What do you think? The gray scale is just a snipped file of a sub; the colour one is part of the same sequence (60 secs).
It’s not easy to see on the Dow samples image but does it look anything like the top part of this image?
If so, it’s kinda dew. ZWO cameras moreso than QHY cameras suffer from frosting of the front cover slip on the camera. On a dewy night it can be good to slowly cool down the camera or even just wait and it’ll slowly disappear. My ASI094 does have an anti-dew setting but it still takes time to work if I cool down too fast.
Hi Everyone
Here is a challenge - what caused the mottling on my subs of Eta Carinae a few weeks ago? (See below).
With rotten weather here in Tassie it wasn't until the very end of March that I managed to set up my gear (WO GT102 Apo refractor, the new ZWO ASI071 and Sky X Pro software. It was a warm and humid night (ambient=20 degrees C) and the camera struggled to reach the -20 C temperature I had set. I mucked around with gain and other settings trying to get focus right and I also reset the temperature to -15 and then -5 (as well as turning it off completely). This produced unusable darks as the settings were all over the place, including the gain. I wrote to ZWO who told me (twice) that the mottling on these subs was caused by dew. My mates down here disagree with this analysis. What do you think? The gray scale is just a snipped file of a sub; the colour one is part of the same sequence (60 secs).
Cheers,
Richard
Looks like frost to me, perhaps dew. If its dew simply have a look and you'll see. If its frost you'll need to shine a bright torch at an angle on the sensor and you'll see it shining.
It’s not easy to see on the Dow samples image but does it look anything like the top part of this image?
If so, it’s kinda dew. ZWO cameras moreso than QHY cameras suffer from frosting of the front cover slip on the camera. On a dewy night it can be good to slowly cool down the camera or even just wait and it’ll slowly disappear. My ASI094 does have an anti-dew setting but it still takes time to work if I cool down too fast.
Thanks for the comment, Colin. In your image the mottling looks a bit different; the pattern on the sensor in my shots does look more like a systematic grid - would dew do this? Maybe it does!
You're right about the need for gradual cooling; I maxed out the power (100%) and it probably cooled too quickly in the humid air (after which I eased up on the temperature and settled on -5).
Looks like frost to me, perhaps dew. If its dew simply have a look and you'll see. If its frost you'll need to shine a bright torch at an angle on the sensor and you'll see it shining.
Greg.
Thanks for the comment, Greg. I never thought about ice being the cause, let alone dew. It's the grid patterning that has puzzled me. The ASI071MC Pro has a built-in dew heater which defaults to 'on'. When I checked in Sky X Pro under camera settings, it was on (though the 'on' setting, counter-intuitively, is 0, not 1).
Some night soon, I might get to do some astrophotography, but not from my backyard which looks south and has no other quadrant of the sky).
Hi Richard. I can see a grid pattern of dots. That is not dew or frost related. In fact, I don't think I have ever seen this problem before. No suggestions for you sorry.
I am with Paul, I have never seen anything that looks like that before. It is not microlens issues (I don't believe the 071 suffers themin the first place and they show up as reflections/spikes rather than "Holes")
Are they single subs or integrations? And what software are you using to produce those? What do you get on flat frames?
I see a similar checkered pattern on my 071 wihen there's dew/icing on the sensor. As Greg says, shine a torch on the sensor and you'll see it. And it's really obvious when you do the flats
Recharge the desiccant. Just takes 2min in microwave, and/or put in the extra desiccant in the side port. I seem to have do redo mine every few months. If I see it, pushing it back up to+5C then taking it back down to 0C also works.
Also, I only cool mine to 0 or -5C. More often just 0 nowadays as it doesn't really need that much cooling.
Wow, that is a very different pattern to what frosting makes on the ASI294. When I needed to dry the dessicant out on mine it showed up as a blocky, crystalline pattern in the center of the image, most obviously on flats.
I found that it does tend to sublime away in the ASI294 so I just cool the camera to -15 well before I want to use it. I know that the 071 is more prone to frosting than most though, from what I had read it is down to the different sensor package of the IMX071 to most others making it more prone to frosting up, and it is an IMX071 issue rather than a ZWO issue, just QHY may have managed the chamber sealing better?
Thanks everyone for your replies and advice. The grid pattern did disappear on later subs that night, once I had the temperature back to just -5. next time I will take things more slowly and then see what happens!
I am such a newbie at this and that was only the second time I used the camera.
Thanks for the comment, Greg. I never thought about ice being the cause, let alone dew. It's the grid patterning that has puzzled me. The ASI071MC Pro has a built-in dew heater which defaults to 'on'. When I checked in Sky X Pro under camera settings, it was on (though the 'on' setting, counter-intuitively, is 0, not 1).
Some night soon, I might get to do some astrophotography, but not from my backyard which looks south and has no other quadrant of the sky).
Cheers,
Richard
I am hardly an expert on ZWO cameras but I did read on Cloudynights that ASI cameras dew control is not that great compared to QHY. Frost can take on different looks. I have seen some that look like fibres on the sensor, wormy.
Perhaps your dew heater is reducing some of the frost but not all of it leaving the pattern.
I am hardly an expert on ZWO cameras but I did read on Cloudynights that ASI cameras dew control is not that great compared to QHY. Frost can take on different looks. I have seen some that look like fibres on the sensor, wormy.
Perhaps your dew heater is reducing some of the frost but not all of it leaving the pattern.
Greg.
Thanks for the observation, Greg. I think I was just too impatient to cool down the camera under warm, humid conditions and perhaps asked too much of it. When you live in Hobart, clear skies are increasingly rare now, unfortunately, so you get set up quickly, polar align and go for it.
Do you have access to the inside of your camera? If so try to purge it with argon and try again see if it is really dew or something else. Dew will bloat stars straight away. That looks like a bayer pattern on the sensor, or micro lensing.
When it's warm or humid, try to cool in steps as not to max out your power. I usually go to 10c, then 0c, -10c then -20c in steps and let it settle a couple of minutes in between.
A CMOS camera like the 071does not need to go below-5C. I've taken long darks: -10C & -15C is really no better than -5C (and 0C ain't much different). Have a look at the dark current specs.
I would recharge some desiccant - 2min in a microwave oven. Put it in the small side holder for extra desiccant.
