Back to forums

Extreme vignetting on this image of M45

Request for feedback M45 Vignetting Messier Objects Open Cluster
11 replies•518 views
Glenn Silverman avatar
Glenn Silverman avatar

The Pleiades
How can I remove the vignetting in this image, taken with my RedCat51, a ZWO ASI294MC Pro and Optolong's 2" L-Pro filter under light polluted skies? I calibrated with darks, bias and flats. Initially, the image looked much worse with flats produced from a light box. I greatly reduced the flats using a tee-shirt and .33 sec exposure to get this image. 

In PIxInsight, I processed mostly with SpectrophotometricColorCalibration and CurvesTransformation.  What additional processing, if any, is needed? 

Thanks in advance for any assistance provided.

Glenn
Well Written Respectful Engaging
andrea tasselli avatar
andrea tasselli avatar
I don't think it is redeemable and not because of the poor flat fielding (which can be bettered if not eliminated), it is because you had condensation on the center of the sensor which is showing with that reddish patch right smack in the middle of the Pleiades where the signal is utterly missing. Chuck and start again, it is the only way I'm afraid.
Helpful Insightful Concise
Ian McIntyre avatar
Ian McIntyre avatar
Hmmm, that doesn't look like vignette. I am only seeing from my phone which shows light  only coming from one side. It looks more like light pollution gradient. There is a gradient removal tool in PI I believe, but I have never used it. I seem to get good enough results from the background extraction tool. 

Look at your flats and make sure they arent dark on that side.
Glenn Silverman avatar
Glenn Silverman avatar
Interesting. I hadn’t thought about dew as an issue. Are you suggesting it’s on the camera lens and not the scope?
Well Written Respectful Engaging
andrea tasselli avatar
andrea tasselli avatar
Glenn Silverman:
Interesting. I hadn’t thought about dew as an issue. Are you suggesting it’s on the camera lens and not the scope?d

It is on the sensor itself and sadly it happened to me more than just few times and had to throw out hours of exposures. The only remedy is to be extra vigiliant and inspect closely the images when downloaded from the camera. If the dew starts appearing increase the temperature to 0 deg (or above but not by more than few degrees). For the residual gradients, which you also have, the tool of choice is DynamicBackgroundExtraction.
Helpful
Arun H avatar
Arun H avatar
It could be on the sensor itself or it may also be on the front glass of the camera which is a bit more likely. The sensor chamber itself is supposed to be sealed and I believe has desiccant capsules to protect against  just this kind of issue - atleast my ASI1600 did, not sure of the 294 MC. The solution to the front glass dewing up is a small resistance heater that ZWO sells that you can stick to the front of the camera. It has a splitter cable that draws power from the main dc power cable connected to the camera. Using that fixed the problem with my 1600 which was quite prone to dew on the front glass. Newer ZWO cameras have such a heater integrated into the front of the camera.
Helpful Concise Supportive
andrea tasselli avatar
andrea tasselli avatar
I reiterate: it is NOT on the window where there are ZERO chances of it ever happening but on the sensor itself and this is a known defect of the ASI294MC Pro and CANNOT be remedied by anything ZWO is pushing you to buy. The camera is NOT sealed AT ALL and the dessicant capsules are a joke and that being gracious…
Arun H avatar
Arun H avatar
I will defer to your experience on the MC Pro specifically and any design issues it has. But as to the possibility of the window getting dew - I can guarantee that it is far from “impossible”, speaking from several hours in Wisconsin fall weather of lost subs that installing the resistance heater fixed 100%. This was on the ASI1600. 

Neither my 2600MC nor 294MM have the problems my 1600 did. My suspicion is that we were beta testers that ZWO used to discover and fix these design issues in future cameras.
Well Written Respectful Concise
andrea tasselli avatar
andrea tasselli avatar
I have chosen my word accurately in saying dewing, which can only occur internally, rather than fogging which could indeed happen either way if the device is badly designed, as you may have suggested. Let's put it in another way: over the course of more than 20 years operating CCDs/CMOS (in my count 6 of them) in the notoriously crappy UK weather it never ever had an issue with fogging of the camera window but plenty with dew/frost on the sensor and that isn't limited to ASI cameras for sure and that includes cameras with window heaters, so there you go.
Glenn Silverman avatar
Glenn Silverman avatar
Could this be solved by simply cleaning the 294 chip with a good lens cleaning solution?

Thanks all for your input.
Well Written
andrea tasselli avatar
andrea tasselli avatar
Glenn Silverman:
Could this be solved by simply cleaning the 294 chip with a good lens cleaning solution?

Thanks all for your input.

No.
Jon Hanson avatar
Jon Hanson avatar
@Glenn Silverman,  as the previous responders have pointed out, you’re probably seeing condensation form on your camera’s sensor as it cools down. I had this happen occasionally with my ASI294MC Pro. In my case the condensation would usually evaporate within 10 minutes of cooling down. The desiccant in your camera is supposed to help prevent condensation and is easy to replace if needed.

You might check your individual subframes to see if the condensation cleared up after the first few frames.  Or you might be lucky and find that the condensation was only there when you took your flats. That happened to me more than once (i.e., my subs were fine–the condensation was only present when I took my flats).

As @Arun H  pointed out ZWO sells an anti-dew heater strip that is meant to prevent condensation on the front window of their cooled cameras. It's only ~$19, but I notice the product description implies that it shouldn’t be necessary for the ASI294:
For ASI183/ASI1600/ASI294/ASI533 cameras, the heat emitting from the TEC will be conducted to the camera case and avoid any dew problems when TEC cooling system working.
Well Written Helpful Engaging Supportive