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 Post Posted: Fri Jul 14, 2017 6:53 pm 
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At the Cloudynights forum an odd behavior is described. For exposures above one second the ASI1600MM camera is still recording light. Has something to do with the cutover point for camera-controlled vs. driver-controlled exposure length.

https://www.cloudynights.com/topic/547440-asi1600mm-cool-odd-exposure-behavior/

The current ASCOM driver V1.0.2.25 still show the cutover point at 1 second.

I still have an old driver V1.02.16 with a cutover point at 5 second but that one produces sometimes weird temperature control problem.

The make flats I would like to have a cutover point at 5 or better 10 seconds. Are there drivers available with an other cutover point?

Is there a better solution available?

Han


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 Post Posted: Thu Jul 27, 2017 7:13 am 
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as the camera can transfer data very fast when connect USB3.0
so we adjust the time point to 1s when connect USB3.0
it's still 5s when connect usb2.0

now we already set it to 2s and will release a new version of ASCOM soon
please try this beta one
Attachment:
ASICamera ASCOM Setup V1.0.3.1.zip [787.66 KiB]
Downloaded 10 times

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 Post Posted: Mon Aug 07, 2017 9:27 pm 
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Sam,

Thanks for providing this driver.

I'm currently testing the driver. Yes it works well. I see clearly the behavior changing from 1.99 to 2 seconds exposure. The 1.99 sec is just enough to take some h-alpha flats but with low signal levels. As soon the exposure is 2.0 seconds the gradient comes in.

However using USB2.0 instead of 3.0, I SEE ALWAYS A GRADIENT !!, The gradient with USB 2.0 is always there for any exposure, 0.9 or 1.99 or 4.99 seconds!! It would be nice if with USB 2.0 the switch over point would be at 5 seconds but I don't see it. The same problem with drivers 1.0.2.23 and 1.02.25. The old version 1.01.16 is too buggy to use.

The driver is reported in the ASCOM setup as 6.0.3.1 instead of 1.0.3.1 as in Windows. Same for the old drivers.

Yes this driver is good, but I still would like to have a special version with the switch-over at 5 seconds, or adjustable by the user, or 5 seconds at USB 2.0. Any amp glow can be taken away with flat-darks.

Regards, Han


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 Post Posted: Thu Aug 10, 2017 5:23 am 
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han.k wrote:
Sam,

Thanks for providing this driver.

I'm currently testing the driver. Yes it works well. I see clearly the behavior changing from 1.99 to 2 seconds exposure. The 1.99 sec is just enough to take some h-alpha flats but with low signal levels. As soon the exposure is 2.0 seconds the gradient comes in.

However using USB2.0 instead of 3.0, I SEE ALWAYS A GRADIENT !!, The gradient with USB 2.0 is always there for any exposure, 0.9 or 1.99 or 4.99 seconds!! It would be nice if with USB 2.0 the switch over point would be at 5 seconds but I don't see it. The same problem with drivers 1.0.2.23 and 1.02.25. The old version 1.01.16 is too buggy to use.

The driver is reported in the ASCOM setup as 6.0.3.1 instead of 1.0.3.1 as in Windows. Same for the old drivers.

Yes this driver is good, but I still would like to have a special version with the switch-over at 5 seconds, or adjustable by the user, or 5 seconds at USB 2.0. Any amp glow can be taken away with flat-darks.

Regards, Han


the switch point should be 5s with USB2.0, we will check

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 Post Posted: Thu Aug 10, 2017 7:12 am 
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Hi hank,
I have tried to take the image which you mentioned here。
https://www.cloudynights.com/topic/5474 ... -behavior/
I noticed that the pixel value in your image is small.
But in my image, the pixel value is still much larger than yours, even if I used the lowest setting.
So I want to know your setting and how you shot it.
Thanks
chad

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 Post Posted: Thu Aug 10, 2017 7:49 pm 
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Hello chad,

I guess you referring to the images of user mikefulb. They are not mine. Yes the values are very low.

For my ASI1600MM-cool, I measure a bias value of around 275 in a scale of 0-64k using binx2. After 200 seconds exposure at -15 degrees Celsius it is maybe 330. I only use unity gain settings and binx2.

For flats I try to reach a value of 20k to 30k at binx2. With a h-alpha filter in place, I need about 8 seconds exposure to reach these values using my EL-panel as light source.

Regards, Han


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 Post Posted: Tue Aug 15, 2017 7:38 am 
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Hello Han,
I tried it, but I did not get a gradient .
So can you send me your problematic photo?
Thanks
chad

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 Post Posted: Tue Aug 15, 2017 9:23 pm 
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Hello Chad,

I will make tomorrow new exposures and send them to you.

To see the effect, you need a flat light source in front of the camera. At 1.99 seconds the exposure readout is flat. All pixels have more or less the same value because they are equally exposed by light.

At 2 seconds a different read-out mode is used. The last pixels read-out will have an longer exposure then the pixels of the first read out. At 2 second or longer the camera can't stop pixels recording light photons. So at 2 seconds exposure, one side of the sensor will be exposed at 2 seconds of light and the other side maybe at 2.5 seconds. The effect become less visual at longer exposures since the different will be smaller, eg. 100 second and 100.5 seconds.

It would be ideal if this switch point of 2 seconds can be set by the user in the driver. I think also the default setting of the gain and bias should be at unity gain but that is an other discussion.

The switch point using a USB2.0 connection was selected to be 5 seconds since it takes more time to readout the camera so the effect should be stronger, but I don't see it in the latest drivers.

Regards, Han


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 Post Posted: Wed Aug 16, 2017 3:52 am 
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Hi Han.k,
Waiting for your photos。
Based on the sensor's datasheet, it supports the rolling shutter mode and the global shutter mode. At first, I wanted to use the rolling shutter in long exposure mode. However, it's not stable, sometimes there will be a wrong picture. So I changed it to the gloabl shutter in long exposure mode.
In the global shutter mode, a gradient is possible。As we know, the severity of this problem is related to the readout speed and exposure time. So I changed the switch time from 2s to 5s in usb2.0, and keep it at 2s in usb3.0. we test it and it works well.
As far, it is not easy for us to add a API for user to control the switch time. Because some kinds of sensor have limits for the switch time. A wrong switch time will cause a lot of unknown problems.
Regards
chad

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 Post Posted: Wed Aug 16, 2017 9:02 pm 
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Hello Chad,

Attached an FITS file with exposure of 2.00 seconds at binx4, -15 degrees C.

Below also a JPG image. The difference between top and bottom 2 sec* (23500-21800)/21800=> 0.15 seconds is clearly visible. At next post I will attach an 1.999 seconds exposure.

Is it possible to have simple checkbox in the driver to force the switch point from 2 seconds to 5 seconds? A 5 seconds exposure will allow many users in making good flats.

Regards, Han

Attachment:
UV 2.00 sec binx4.jpg
UV 2.00 sec binx4.jpg [ 237.24 KiB | Viewed 237 times ]


Attachments:
UV 2.00 sec binx4.zip [1.46 MiB]
Downloaded 5 times


Last edited by han.k on Wed Aug 16, 2017 9:14 pm, edited 1 time in total.
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