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ZWO ASI294 MC pro

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#176 sharkmelley

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Posted 10 June 2018 - 01:58 AM

Hi Jose,

 

I downloaded your test images:

  • Calibrated 5s master flat
  • Calibrated 1s master flat
  • Uncalibrated 60s raw light of M13

The good news is that the two master flats calibrate each other perfectly.

The other good new is that there are no odd features (such as histogram gaps often found in DSLRs) in the uncalibrated raw.

 

There are some odd effects in the master flats though.  For instance if I white balance the master flat then colour saturate it, this is what I see:

SaturatedFlat.jpg

 

If I divide one colour channel by another e.g. blue/green and stretch the result I can see weird structures such as diagonal streaks:

DiagonalStreaks.jpg

 

Is this an artefact of the sensor or an artefact of the optics?  The only way to know for sure is to try the camera on various different optics. 

Does it matter?  Probably not - as long as it also appears in the light frames and therefore calibrates out.

 

I wasn't able to calibrate the raw light because you didn't provide a master bias (or master dark). 

 

All in all, the tests I've done give no real insight into the cause of colour variations in the backgrounds of calibrated lights.

 

Mark


Edited by sharkmelley, 10 June 2018 - 01:59 AM.

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#177 CCD-Freak

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Posted 10 June 2018 - 09:11 AM

Don't know if this will help but I learned a trick some years back of doing a half pixel x and y shift to remove the color info from my master flat.  AstroArt 6 has a shift function which makes this easy.  This has helped with calibrating my Atik 383L+OSC images and I am using the technique with my recently acquired ASI 1600MC-Cool V3 camera.

 

John

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#178 tjugo

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Posted 11 June 2018 - 12:46 PM

Hi Jose,

 

I downloaded your test images:

  • Calibrated 5s master flat
  • Calibrated 1s master flat
  • Uncalibrated 60s raw light of M13

The good news is that the two master flats calibrate each other perfectly.

The other good new is that there are no odd features (such as histogram gaps often found in DSLRs) in the uncalibrated raw.

 

There are some odd effects in the master flats though.  For instance if I white balance the master flat then colour saturate it, this is what I see:

attachicon.gif SaturatedFlat.jpg

 

If I divide one colour channel by another e.g. blue/green and stretch the result I can see weird structures such as diagonal streaks:

attachicon.gif DiagonalStreaks.jpg

 

Is this an artefact of the sensor or an artefact of the optics?  The only way to know for sure is to try the camera on various different optics. 

Does it matter?  Probably not - as long as it also appears in the light frames and therefore calibrates out.

 

I wasn't able to calibrate the raw light because you didn't provide a master bias (or master dark). 

 

All in all, the tests I've done give no real insight into the cause of colour variations in the backgrounds of calibrated lights.

 

Mark

Mark,

 

An interesting pattern you have found in your test. For instance, the pattern looks very similar to what I see after stacking, an overcorrected master light.

 

FWIW this is the 60s master dark I used for dark calibration of my lights. The master was created using 128x60s dark frames.

 

https://drive.google...dUhJWUBBxajTdua

 

Regards,

 

Jose



#179 tjugo

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Posted 11 June 2018 - 12:49 PM

 

If I divide one colour channel by another e.g. blue/green and stretch the result I can see weird structures such as diagonal streaks:

attachicon.gif DiagonalStreaks.jpg

 

Is this an artefact of the sensor or an artefact of the optics?  The only way to know for sure is to try the camera on various different optics. 

Does it matter?  Probably not - as long as it also appears in the light frames and therefore calibrates out.

 

Regarding the streaks, I've no idea where they are coming from, the images were taken with an Epsilon 160. I will try to take another set of falts with a refractor to check if the streaks go away.

 

Cheers,

 

Jose



#180 ve1drg

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Posted 11 June 2018 - 01:46 PM

Ah ok, I have never used pixinsight, its too expensive for me :/ I hear it works great though

It's a first class piece of software.




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#181 glend

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Posted 11 June 2018 - 04:06 PM

It's a first class piece of software.




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You should not need to buy PI to be able to use the 294MC. If that is the case then ZWO should supply a free copy with each 294MC it sells.  ZWO needs to fix the issues with this camera or withdraw it from the market and admit their mistake. In the rush to release more and more models they were bound to get one wrong eventually.  Its not like the IMX series issues were unknown.


Edited by glend, 11 June 2018 - 04:09 PM.


#182 jgraham

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Posted 11 June 2018 - 04:51 PM

Hmmmm, it is unfortunate that some are having problems with this camera. I haven't had any problems processing the images from my ZWO ASI294MC Pro and I'm not doing anything special that I haven't been doing for the past 15 years. The only problem that I have had with the  ASI294MC Pro is that it works so well I'm having trouble finding the time to use my other cameras.

 

Curiouser and curiouser…


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#183 tjugo

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Posted 11 June 2018 - 05:14 PM

Hmmmm, it is unfortunate that some are having problems with this camera. I haven't had any problems processing the images from my ZWO ASI294MC Pro and I'm not doing anything special that I haven't been doing for the past 15 years. The only problem that I have had with the  ASI294MC Pro is that it works so well I'm having trouble finding the time to use my other cameras.

 

Curiouser and curiouser…

Yeap, the specs of the camera are fantastic! I really hope we can sort out the problem and find a solution easy to implement. The size of the sensor is also very convenient cause you don't need premium optics to fill it up.

 

Clear skies,

 

Jose



#184 jdupton

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Posted 11 June 2018 - 09:42 PM

ASI294MC Camera Enthusiasts,

 

   I have tried in a couple of places to make a point about the influence of electronics packaging but have apparently not been clear enough. I'll make another attempt to see if any of this makes sense to others here with respect the the ASI294MC-Pro. This is very long but maybe it help others sort out some of what they read here and elsewhere.

 

   I keep seeing a lot of comments in this thread and others about the "problems with the ASI294MC camera". I do not (yet) own one but am still seriously considering a purchase even in view of the negative comments. (If they were in stock at any of the usual suppliers, I might have already hit the Add To Cart button.) I will try to explain below why I don't think it is quite fair to call the issues with this camera "problems" -- not that they are not issues or concerns. I consider a problem to be something that is a mistake or error and can potentially be corrected. Others have stated their belief that these are design flaws that the camera manufacturer must correct or else withdraw the camera from the market. I do not believe that is the case here. What we are seeing with this camera falls into the realm of the "nature of the beast", in my opinion. My thoughts and (considerable) conjecture regarding explanations are discussed below.

 

Let's start by laying out what facts are known about the camera and its sensor.

  • It uses a Sony IMX294CJK CMOS sensor. [Ref: ZWO Website] [Ref: Sony Sensor Flyer]
     
  • The IMX294CJK sensor is packaged in a 248 pin ceramic LGA (Lead Grid Array or Land Grid Array) package (A standard chip package.) [Ref: Framos Website]
     
  • LGA packages have electrical contact points on the back of the ceramic package rather than pins or leads on the sides of the package. [Ref: Wikipedia]
     
  • The IMX294CJK sensor uses a BSI (Back Side Illuminated) architecture. [Ref: Sony Sensor Flyer] [Ref: Adomrama BSI FAQ]
     
  • Some users are reporting and have demonstrated that deep images show a gradient effect in both the raw and processed images after stretching. [Ref: CN Thread "Help me with this artifact - ZWO ASI294"]
     
  • A ZWO contact (Sam) has reportedly acknowledged that the cold finger in the camera is slightly smaller than the sensor size itself. [Ref: CN Thread "Help me with this artifact - ZWO ASI294"]
     
  • I think a ZWO contact (Sean?) has also reportedly commented that the thermal sensor for the camera TEC control may not be optimally placed directly on the back of the sensor. [Ref: Cannot Find Link Again]
     
  • BSI Sensors have a generally higher dark current compared to front illuminated sensors due to a side effect of the way the charge wells are built. [Ref: Wikipedia]

 

Implications of the LGA Sensor Packaging

 

   The electrical contact array on the back of the LGA package takes up room around the periphery of the chip. The image below will give you an idea of what an LGA sensor package might look like. Note that this is not the Sony IMX294CJK package. The Sony sensor is larger and the land contact points are probably arranged in only two or three rows around the periphery leaving the center open. (I base that assumption on the sensor size, the number of contacts, and the typical land pitch for similar packages.) The Cold Finger in the ZWO ASI294MC-Pro camera likely covers most of the central clear area but is not as large as the silicon sensor chip itself. The cold finger cannot be placed over the contacts as then there would be no electrical connection between the chip and the camera's PCB (Printed Circuit Board).

 

{Image of example LGA Sensor Package -- Not the Sony IMX294CJK}

28-megapixel-aps-c-cmos-image-sensor_2.j

 

 

   The layout of the LGA package is most likely at the heart of most of the issues users have encountered. Since this is probably a sensor packaging issue, it is unlikely that any camera manufacturer will be able to completely work around them. For that reason, I think it is a stretch to "demand" the issues be "fixed". In my opinion, such demands are as likely to be met as an economy car user base demanding a 600 HP engine that gives 35 MPG. It is what it is and we can either accept the nature of this particular sensor and try to make the most of it or move on.

 

   In addition to limited space for the Cold Finger on the back of the sensor, there is also likely no room for thermal sensors for TEC control. On most pinned packages for sensors, a thermal sensor can be added to the back of the chip package itself. LGA packages make that most difficult. As a result, there may be a few tenths of a degree discrepancy between actual sensor temperature and TEC readout based on where the manufacturer was able to place the thermal sensor.

 

Dark Frame Patterns

 

   Contrary to the comments about the sensor having "warm edges" due to the undersized cold finger, Dark Frames which have been posted in various places seem to show the opposite. Below is the Dark Frame posted on the ZWO Website. Using the PixInsight FlatCountourPlot script, it can be seen that the edges are generally a bit darker than the center indicating better cooling and less dark current there compared to the center of the frame. Of course the exception is the considerable amp glow along the right and left edges of the chip. I have noticed the same trend in the Dark Frames posted by users here on CloudyNights.

 

{Image of FlatContourPlot for ZWO Sample Dark Frame}

ASI294MC_PRO_dark_frame_300s_10degree_HDR_settings_contourPlot.jpg

 

   It is just pure conjecture on my part but I think this may indicate something about about the mounting of the silicon sensor to the ceramic LGA package. 

 

Implications of a BSI Sensor In a TEC Cooled Environment

 

   Normally when packaging the silicon chip into its packaging, a bonding agent is applied to "glue" the chip in place. It is then wire-bonded out to the pin connections of the package. The use of the chip-to-package substrate contact gives very good thermal conductivity for removing heat from higher power chips or for cooling chips as used on cooled camera astronomy applications. Normally the surface of a typical chip has wiring layers covering most but not always all of the active chip surface. Sensor chips minimize this area and use micro-lenses to concentrate light away from the wiring channels on the chip's surface. This top layer of a typical chip or sensor is, by its nature, fragile and susceptible to chemical contamination which can render the circuits inoperable.

 

   Now, think about a BSI sensor. The active surface of the sensor is really the back side which would otherwise be bonded to the ceramic package if this were a normal chip. In a BSI, however, the "back side" (as in non-light-sensing side) needs to be mounted to the ceramic packaging. This may present a problem. I have a suspicion that the sensor is bonded mainly around the top and bottom edges where there are few or no critical electrical circuits -- only off chip drivers. 

 

   This is usually done in "Flip-Chip" packaging designs using microscopic "solder balls" between the chip and the ceramic packaging. This would mean that thermal contact may be better at those points of contact between the actual silicon sensor and ceramic compared to areas where no electrical connections are present. That might explain why the dark frames I have seen appear to be better cooled around some edges. In any case, flip-chip packaging will have lesser thermal contact area between the silicon and ceramic carrier when compared to normal full bottom bonding methods.

 

   We can see the gradients produced by the slightly uneven cooling. That smacks of thermal conductivity differences across the chip resulting in dark current differences we can see. The real question may be just which parts have the best thermal conductivity. While the TEC / Cold Finger may not cover the edges of the ceramic package out to the edges, the ceramic to silicon attachment may not cover the center of the sensor as well either.

 

   To the best of my knowledge the ASI294MC-Pro may be the first consumer grade BSI sensor astronomy camera to hit the market. I hope it is not the last. Some of these issues discussed about the camera could be a common condition with BSI sensors in general for the reasons just given. I would like to find out more about the first-level packaging of BSI sensors but have not been able to find much in my research. BSI offers the lure of much higher QE for the sensors but packaging concerns may work against us at the end of the day.

 

  Advantages of the Sony IMX294CJK CMOS sensor as I see them are:

  • BSI architecture gives rise to considerably higher QE for more "sensitivity"
     
  • 14 bit DAC, low read noise, and large full well capacity are well suited to astronomy
     
  • 4/3" Format and moderate pixel size hit the sweet spot of many optical systems we use for AP
     
  • Rolling shutter and high readout speed helps for many astronomy applications
     
  • BSI may enable easier Micro-Lens and Bayer Filter removal in the future. (Less worry about damaging sensor wiring structures as they are on the other side of the chip.)

 

   My own conclusions after this research and reading are as follows. I am still interested in the camera due to the reasons just listed. The issues with the camera are in my opinion issues with the sensor and not necessarily with the camera's design or implementation. I think that demanding that ZWO fix the sensor's packaging are simply unrealistic. Again, in my opinion, we should be looking for novel ways to address and mitigate the issues to get the most out of this camera. I am still intrigued and would love to try one out.

 

   Hopefully this long boring diatribe will clear up some of the misconceptions about this sensor and camera. While much of this is guesswork (as I have no inside knowledge), it is based on what we know and my own experiences of working in the electronics industry for over 30 years. I have tried to weave a story around what we know and what we have observed that fits with the technology being used.

 

 

Respectfully,

John


Edited by jdupton, 12 June 2018 - 07:42 AM.

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#185 AdamJ

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Posted 12 June 2018 - 10:17 AM

Has anyone actually tried taking the Darks at the same time as the flats / lights? Does it then calibrate correctly? Because if not then we are all barking up the wrong tree. Also I do not personally see why cooling irregularities would result in color variation? Surly the variation in dark current with temperature is the same for Red Green and Blue pixels?



#186 AdamJ

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Posted 12 June 2018 - 10:35 AM

Yes! I can’t believe I hadn’t thought of that. We should take a series of subs with no cooling then stack them with no darks and see if the artifact is there.

Would the cold finger not still act as a passive heat sink across part of the chip? Even so the effect should be seriously diminished if the causes are as suspected. 



#187 sharkmelley

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Posted 12 June 2018 - 11:23 AM

Also I do not personally see why cooling irregularities would result in color variation? Surly the variation in dark current with temperature is the same for Red Green and Blue pixels?

A good question.  Cooling irregularities can potentially explain the background green/purple background seen here:

https://www.cloudyni...act-zwo-asi294/

 

I'll attempt to explain:

Let's suppose that the dark does not exactly match the light because of a non-repeatable patchy temperature variation - non-repeatable in the sense that the dark is different to the light.  As you rightly say, any such variations in pixel values would affect R, G & B equally.  But remember that the red and blue channels are boosted during white balancing (typically by a factor of 1.5 - 2.0) because they are the weaker channels in terms of the sensor's sensitivity to light.   Subtracting the dark may end up with some areas of the sensor having pixel values a fraction of a digital unit brighter than they ought to be and other areas a fraction of a digital unit dimmer.  This would simply appear as patchy variations in brightness until the channel multipliers for the white balancing are applied.  At this point the brighter areas become purple and the dimmer areas become green.

 

Patchy mismatches between the dark and the light can definitely lead to purple/green patchiness in the background of an image.

 

Mark


Edited by sharkmelley, 12 June 2018 - 11:24 AM.

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#188 glend

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Posted 12 June 2018 - 12:50 PM

Would the cold finger not still act as a passive heat sink across part of the chip? Even so the effect should be seriously diminished if the causes are as suspected. 

Any cooling solution that does not evenly cool across the entire sensor area is pretty useless, and is not what we usually expect from a modern AP camera. Uneven cooling is the sort of hack job that we used to see in early DSLR cooling conversions.  The chip simply is not capable of being effectively evenly cooled with TEC type cooling due to its architecture. The TEC is pulling heat out from the center and of course this gives you gradients through the substrate.  Other cooling methods, such as refrigerated dry gas circulation through a chamber might be more effective, but likely significantly more expensive.  I really can't see how ZWO is going to make it work. You might be better off with an uncooled version, shooting very short subs, thus an EAA platform.


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#189 Susan2613

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Posted 12 June 2018 - 01:07 PM

Has anyone actually tried taking the Darks at the same time as the flats / lights?

Yes same result.

With my camera there's no difference in using the darks from february or from the same night.

 

I did a test with 10 x 30 second subs with the power plugged in but not set (it cools 10 degrees C below ambient so ended up at 3 degrees Celsius) and it showed the same pattern, with the power unplugged 10 x 30 second subs did not have the pattern. Don't know if it eventually shows up without cooling if you would make more or longer subs. Clouds came so I couldn't do more tests.



#190 bulrichl

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Posted 12 June 2018 - 01:35 PM

Hi John,

this was an interesting contribution for me. I don't have the knowledge about sensor structure like you, but..

 

 To the best of my knowledge the ASI294MC-Pro may be the first consumer grade BSI sensor astronomy camera to hit the market.

there are other cameras: QHY has launched the QHY183 (mono and color version; Sony IMX183), QHY178 (Sony IMX178), QHY290 (Sony IMX290) and QHY42 (GSENSE400BSI). All of these have backside-illuminated sensors. However, I don't know whether these sensors are constructed similarly to the IMX294 (concerning heat dissipation).

 

I also can imagine that the issue is caused by inhomogeneity of thermal conductivity. The question that has to be answered is: why does this issue arise in spite of a calibration with a master dark (made from dark frames which were taken at the same temperature and the same "exposure time" like the lights)? In other words: Why should dark frames be affected in a different way than light frames?

 

I thought about my process of dark and light frame acquisition. The difference is: in case of dark frames, I continuously shot the frames with a pause of only 5 s. In case of light frames, I do dithering, and due to my restrictive settling conditions, this took about 45 s on average. My guess was: Maybe thermal equilibrium is reached when I take darks, whereas with the lights a heating / cooling cycle (periodical fluctuation of thermal flow) results from the dithering pauses. So I took dark frames with a pause of 45 s and made a new master dark. However, the colored background artifact showed up as well when using this new master dark.

 

Another possibility could be that the absence / presence of light falling onto the sensor makes the difference. However, I have no idea, why this should be that way.

 

Bernd

 


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#191 Jeff2011

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Posted 12 June 2018 - 02:40 PM

What is the capture software and drivers (ASCOM or native) used by those having issues calibrating?   If not already doing so, you might want to try capturing lights, darks and flats in SharpCap and native drivers and then calibrating and stacking those in PI or whatever software you use.  You don't need the Pro version of SharpCap to do that.  You do need the Pro version for SharpCap to do the calibration and stacking.


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#192 jdupton

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Posted 12 June 2018 - 02:44 PM

Bernd,

 

   Thank you for correcting me regarding other BSI sensors that have been released. I have never gone to look up all of what Sony is offering these days.

 

   You have asked a very good question about the other BSI sensors. They all would need to be using Flip-Chip packaging. I checked the specifications for each of the other Sony sensors you listed and all are using LGA first level packaging. That adds mystery to why these others are not showing similar effects. I made a list to try to note any differences:

Chip      Size X  Size Y  Diagonal   Area  I/O  I/O per Area
IMX290LQR  5.64    3.18     6.48    17.94  110     6.13
IMX178LQJ  7.43    4.99     8.95    37.09  128     3.45
IMX183CQJ 13.54    8.90    16.20   120.52  118     0.98
IMX294CJK 19.30   13.08    23.31   252.32  248     0.98

   The main things that pop out are that the IMX294CJK is the largest sensor by diagonal, area, and pin count. I thought it might be related to number of I/O connections per unit area. The two smaller chips clearly have more solder balls (and hence thermal conductivity) per unit area but the IMX183CQJ appears to be about the same as the IMX294CJK so something else might be at work for those. I don't recall having seen any complaints about dark calibration with the 183 cameras. Something else must be at work.

 

   Your question as to why dark calibration is problematic is right on the mark. If we knew the underlying answer to that question, it's quite possible a calibration methodology could be worked out to mitigate the gradients. I especially liked your experiment with delaying similar times between lights and darks. (I think you had the description of cooling soak time after an exposure backwards for lights / darks but I followed the point you were making.) I would have bet on that going a long way to resolving your calibration. At least we have another data point for what doesn't seem to help.

 

   Like you, I cannot imagine what is different between taking lights and darks at the same set point and ambient.

 

 

John


Edited by jdupton, 12 June 2018 - 03:49 PM.

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#193 bulrichl

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Posted 12 June 2018 - 03:47 PM

What is the capture software and drivers (ASCOM or native) used by those having issues calibrating?   If not already doing so, you might want to try capturing lights, darks and flats in SharpCap and native drivers and then calibrating and stacking those in PI or whatever software you use.  You don't need the Pro version of SharpCap to do that.  You do need the Pro version for SharpCap to do the calibration and stacking.

Hi Jeff,

 

for all frames (lights, darks, flats and flat-darks) I used the ASCOM driver and SGP as acquisition software. I know that the intensity values in the raw FIT files are scaled (14 -> 16 bit, i.e. multiplied by factor 4). Are you saying that I should try SharpCap and the native driver? Why?

 

Calibration, debayering, aligning and integration was done with PixInsight.

 

Bernd



#194 tjugo

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Posted 12 June 2018 - 03:51 PM

Hi Jeff,

 

for all frames (lights, darks, flats and flat-darks) I used the ASCOM driver and SGP as acquisition software. I know that the intensity values in the raw FIT files are scaled (14 -> 16 bit, i.e. multiplied by factor 4). Are you saying that I should try SharpCap and the native driver? Why?

 

Calibration, debayering, aligning and integration was done with PixInsight.

 

Bernd

I used MaximDL5 and ASCOM for capture. Calibration and stacking in Pixinsight.

 

Cheers,

 

Jose



#195 Jeff2011

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Posted 12 June 2018 - 04:08 PM

Hi Jeff,

 

for all frames (lights, darks, flats and flat-darks) I used the ASCOM driver and SGP as acquisition software. I know that the intensity values in the raw FIT files are scaled (14 -> 16 bit, i.e. multiplied by factor 4). Are you saying that I should try SharpCap and the native driver? Why?

 

Calibration, debayering, aligning and integration was done with PixInsight.

 

Bernd

Hello Bernd.  Last Friday I imaged with a friend who used an ASI294 with SharpCap, native drivers and he had no calibration issues.   Just something to try.  Not saying it is the problem, but it would not be the first time SGP with the ASCOM drivers had issues with a ZWO camera.   Not trying to get you to change your image capture software.  I image with SGP and ASCOM drivers myself but with an ASI1600.

 

Here is my friend's thread:  https://www.cloudyni...mcp-8se-cem60/ 

You can ask him questions if you want to regarding his calibration


Edited by Jeff2011, 12 June 2018 - 04:11 PM.


#196 Mert

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Posted 13 June 2018 - 01:38 PM

Anyone used APT with this camera and had isues with calibration?



#197 AhBok

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Posted 13 June 2018 - 04:06 PM

Yes. I use APT, but APT is just for post processing. The “Wipe” function in APT deals with this pretty well,

Last night I tried stacking using bias frames rather than dark flats. That eliminated most of the artifact. I stacked using DSS and afterwards APP. That makes no sense to me, but I am thinking my Dark Flats May be problematic.

#198 rlsarma

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Posted 13 June 2018 - 11:17 PM

Yes. I use APT, but APT is just for post processing. The “Wipe” function in APT deals with this pretty well,

Last night I tried stacking using bias frames rather than dark flats. That eliminated most of the artifact. I stacked using DSS and afterwards APP. That makes no sense to me, but I am thinking my Dark Flats May be problematic.

You probably mean to refer "Star Tool". The "Wipe" function is there in "Star Tool" only which is a post processing software. APT is an image capture software.



#199 AhBok

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Posted 14 June 2018 - 12:52 PM

Yes, I’m old and sometimes confuse myself 😵🤦🏼‍♂️
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#200 AhBok

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Posted 14 June 2018 - 01:07 PM

I do use APT as well and calibrate using APP or DSS. I see the artifact with any combination, but do not have problems calibrating otherwise.


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