ASI 1600 and Microlensing

[Rodd]

A lot has been written about microlensing causing artifacts around bright stars when using the ASI 1600.  I have noticed several things about this that I would like to add to the discussion.

1) The effect seems to be getting worse over time.  Not sure this is even possible, or real--but it seems that way.  It is not something I noticed up until recently--then again maybe there were not bright enough stars in the FOV.

2) I think the artifact from microlensing--if that is what it even is-may be related to resolution (pixel scale).  I say this because I have imaged the Horsehead Nebula with the FSQ 106 at a pixel scale of 2.46 arcsec/pix and the TOA 130 at a resolution of 0.78 arcsec/pix.  There is no sign of a microlensing artifact around Alnitak at a resolution of 2.46, but there is a severe microlensing artifact around Alnitak at 0.78 arcsec/pix.   I do not think it is the TOA 130 OTA, as stars in general are quite nice. 

Any ideas?  I have images to show as examples but it will have to wait until I get home to post (later tonight). 

Thanks,

Rodd

[vlaiv]

I can offer alternative explanations:

1. Over time, one tends to gather more data, so both SNR and processing skills increase. Microlensing artifact is in fact light signal, so it will be more obvious if you have better SNR data or you improved your processing to push the data further. Don't really think it will worsen on its own - it would mean that composition of coatings is changing or maybe coatings are getting thinner or something.

2. If they are in fact artifacts of micro lens, then resolution should not have impact on it, or at least it should have opposite effect of what you are describing. Star will be tighter on lower resolution, so light will be more concentrated, and that might lead to stronger reflection / diffraction issues, hence stronger micro lens artifact. There is another explanation that can explain difference between two scopes - speed of light beam. I think that there is strong dependence on both wavelength of light and speed of light beam for particular setup.

One setup with for example F/5 beam could have issues in Ha and no issues in OIII, while other setup with F/7 beam could have quite opposite - Ha without issues and OIII with issues for example.

[Rodd]

14 minutes ago, vlaiv said:

Over time, one tends to gather more data, so both SNR and processing skills increase. Microlensing artifact is in fact light signal, so it will be more obvious if you have better SNR data or you improved your processing to push the data further. Don't really think it will worsen on its own - it would mean that composition of coatings is changing or maybe coatings are getting thinner or something.

The FSQ image that has no microlensing artifact has a much higher SNR than the TOA image that has a sever microlening artifact.  Both of these images are simple Ha stacks--not much processing--and the artifact is visible on the raw subs anyway--so processing can be eliminated from the equation.

The FSQ image was captured at F3 (.6x reducer).  I would think the faster the system the stronger the effect, but maybe it works the opposite way.

Rodd

[Adam J]

1 hour ago, Rodd said:

A lot has been written about microlensing causing artifacts around bright stars when using the ASI 1600.  I have noticed several things about this that I would like to add to the discussion.

1) The effect seems to be getting worse over time.  Not sure this is even possible, or real--but it seems that way.  It is not something I noticed up until recently--then again maybe there were not bright enough stars in the FOV.

2) I think the artifact from microlensing--if that is what it even is-may be related to resolution (pixel scale).  I say this because I have imaged the Horsehead Nebula with the FSQ 106 at a pixel scale of 2.46 arcsec/pix and the TOA 130 at a resolution of 0.78 arcsec/pix.  There is no sign of a microlensing artifact around Alnitak at a resolution of 2.46, but there is a severe microlensing artifact around Alnitak at 0.78 arcsec/pix.   I do not think it is the TOA 130 OTA, as stars in general are quite nice. 

Any ideas?  I have images to show as examples but it will have to wait until I get home to post (later tonight). 

Thanks,

Rodd

Its all to do with F-ratio mate more so that pixel scale. Lower f- numbers tend to result in less micro lensing. 

So yes it works the opposite way. 

But its also that larger apertures collect more light resulting in brighter point sources (stars) and so more visible micro lensing. 

Adam

Edited October 15, 2019 by Adam J

[Rodd]

8 minutes ago, Adam J said:

Its all to do with F-ratio mate more so that pixel scale. Lower f- numbers tend to result in less micro lensing. 

So yes it works the opposite way. 

But its also that larger apertures collect more light resulting in brighter point sources (stars) and so more visible micro lensing. 

Adam

Thanks Adam......sort of good news...when I am shooting with the FSQ!  Not so much the TOA.  I think, in the end, its a deal breaker for me--ruins images at times.  I think I will eventually move back to teh STT-8300.  The microlensing effect of that sensor are simply small diffraction spikes on the brightest stars--very small and normal looking  (as far as diffraction spikes are concerned).

Rodd

[Adam J]

35 minutes ago, Rodd said:

Thanks Adam......sort of good news...when I am shooting with the FSQ!  Not so much the TOA.  I think, in the end, its a deal breaker for me--ruins images at times.  I think I will eventually move back to teh STT-8300.  The microlensing effect of that sensor are simply small diffraction spikes on the brightest stars--very small and normal looking  (as far as diffraction spikes are concerned).

Rodd

sell them both and get a QHY600 mate. 

[Rodd]

4 minutes ago, Adam J said:

sell them both and get a QHY600 mate. 

Wow--what I have been asking for for years has finally arrived.  $5,000 though--with no filter wheel.  It definitely is what I want, but it hasn't even been released yet, let alone reviewed.  It would be risky business to dump my imaging ability in hopes that it will 1) actually come out, 2) work as described, 3) be available.  I can see myself getting one in a year or so.  I want the bugs to be worked out.  Also, I notice that it supports binning--though its a CMOS camera, its back illuminated, and it is 16 bit.  Not sure I fully believe all this.  Be sweet if it pans out.

Rodd

[Adam J]

2 minutes ago, Rodd said:

Wow--what I have been asking for for years has finally arrived.  $5,000 though--with no filter wheel.  It definitely is what I want, but it hasn't even been released yet, let alone reviewed.  It would be risky business to dump my imaging ability in hopes that it will 1) actually come out, 2) work as described, 3) be available.  I can see myself getting one in a year or so.  I want the bugs to be worked out.  Also, I notice that it supports binning--though its a CMOS camera, its back illuminated, and it is 16 bit.  Not sure I fully believe all this.  Be sweet if it pans out.

Rodd

The ZWO version will be $4000...but people are still haivng issues with the ASI071mc...

They are coming out for sure mate. Its a sony sensor and already in other products. I could afford a camera, but not with a scope to cover that sensor. You are already half way there. 

Adam 

Edited October 15, 2019 by Adam J

[carastro]

If you're prepared to spend that sort of money Rodd, why don't you go over to CCD, I don't recall ever seeing any-one having Microlensing with a CCD camera.  OK the subs need to be longer, but still I think the same total amount of imaging time.  It may be older technology, but it's tried and tested and it works. 

Carole 

 

Edited October 15, 2019 by carastro

[Rodd]

1 minute ago, Adam J said:

The ZWO version will be $4000...but people are still haivng issues with the ASI071mc...

They are coming out for sure mate. Its a sony sensor and already in other products. I could afford a camera, but not with a scope to cover that sensor. You are already half way there. 

Adam 

My financial situation has changed.  But I'll find a way.  I haven't really been satisfied with ZWO--my filter wheel does not initialize correctly (so I have to shoot flats before every filter change).  An d ZWO just says its within the their tolerance and works as specified.  I am not the only one to have the problem.  So, I would prefer a different brand.  But didn't QHY go uner or something?  Not sure I would want that.  QSI, if they made one, or Atik, or FLI--we'll see. 

Rodd

[carastro]

Quote

But didn't QHY go uner or something? 

Really?  Must check on that as I hadn't heard.

I like the Atik cameras, Atik also do the QSI cameras now.

Carole 

[Rodd]

1 minute ago, carastro said:

If you're prepared to spend that sort of money Rodd, why don't you go over to CCD, I don't recall ever seeing any-one having Microlensing with a CCD camera.  OK the subs need to be longer, but still I think the same total amount of imaging time.  It may be older technology, but it's tried and tested and it works. 

Carole 

 

The problem is there is not a full frame (36mm x 24mm) CCD, let alone one with pixels less than 6um.  The FLI 50100 is close--but it is not back illuminated and I have heard that it has readout problems.   CMOS is the future, and this is a giant leap.

Rodd

[WanderingEye]

4 minutes ago, Rodd said:

My financial situation has changed.  But I'll find a way.  I haven't really been satisfied with ZWO--my filter wheel does not initialize correctly (so I have to shoot flats before every filter change).  An d ZWO just says its within the their tolerance and works as specified.  I am not the only one to have the problem.  So, I would prefer a different brand.  But didn't QHY go uner or something?  Not sure I would want that.  QSI, if they made one, or Atik, or FLI--we'll see. 

Rodd

QHY are still going strong, but QSI were taken over by ATIK... 👍

[Rodd]

Just now, WanderingEye said:

QHY are still going strong, but QSI were taken over by ATIK... 👍

Ahh.....that was it.    I want a full frame back illuminated small pixel camera!!

Rodd

[Rodd]

12 minutes ago, Adam J said:

Its a sony sensor and already in other products.

What products--cameras we can use for AP?

Rodd

[Adam J]

3 minutes ago, Rodd said:

What products--cameras we can use for AP?

Rodd

No not AP applications, I just mean that its real life hardware that is currently fielded as opposed to a pen and paper specification. If you look on astro bin there are some images even from the beta testing. 

[Adam J]

Here: https://www.astrobin.com/5uf7w7/0/?nc=all

[Rodd]

1 minute ago, Adam J said:

No not AP applications, I just mean that its real life hardware that is currently fielded as opposed to a pen and paper specification. If you look on astro bin there are some images even from the beta testing. 

I can't....I will get too excited and will no longer appreciate what I have....which is still pretty cool stuff.  But I will eagerly await the day when this camera is readilly available as it will allow me to capture all of Orion's belt, B33 and the flame, and M42 in one frame.  Man--that would be something.

Rodd

[Rodd]

17 minutes ago, Adam J said:

Here: https://www.astrobin.com/5uf7w7/0/?nc=all

Not the IMX455--the IMX 555 is a 100mp sensor scheduled for 2020--I'll wait!!!

Rodd

[Laurin Dave]

Concur with Adam..  microlensing is worse on the ASI1600 with my Esprit150 (f7) than my Esprit100 (f5)..  I got fed up with it and got a 16200ccd based camera.. it also has microlensing - but only apparent on the blue channel on mag 2 to brighter stars  ..  In a separate thread on here regarding the ASI1600 with integrated fw FLO said they were expecting the ZWO full frame mono camera early next year..  

[Rodd]

2 minutes ago, Laurin Dave said:

Concur with Adam..  microlensing is worse on the ASI1600 with my Esprit150 (f7) than my Esprit100 (f5)..  I got fed up with it and got a 16200ccd based camera.. it also has microlensing - but only apparent on the blue channel on mag 2 to brighter stars  ..  In a separate thread on here regarding the ASI1600 with integrated fw FLO said they were expecting the ZWO full frame mono camera early next year..  

One can sure go broke in this line of work!  I hope they fix the microlensing.

Rodd

[newbie alert]

22 hours ago, Adam J said:

Its all to do with F-ratio mate more so that pixel scale. Lower f- numbers tend to result in less micro lensing. 

So yes it works the opposite way. 

But its also that larger apertures collect more light resulting in brighter point sources (stars) and so more visible micro lensing. 

Adam

Not sure that's the way, I've seen plenty of images with small aperture and focal length scopes with micro lensing effect..

[Rodd]

Just now, newbie alert said:

Not sure that's the way, I've seen plenty of images with small aperture and focal length scopes with micro lensing effect..

For me it seems to be the case.  I have never seen the microlensing on my FSQ 106 with ,6x reducer (F3).  using the TOA 130 at native (F7.7) I see it in broadband and narrow band.  The star does not have to be that bright.  Currently I am working on the eastern veil (witches broom) and the bright star in the handle of the broom is showing signs of microlensing (not as significant as Alnitak--but noticeable). 

I do not think I can tolerate it....the filter wheel does not initialize correctly, and now the sensor is poor.  I guess the ASI 1600 will be my dedicated camera for the FSQ 106 at F3--but that's it.  For all other scopes and configurations I am going back to the STT-8300.

Rodd

[ollypenrice]

This 60 mp 35mm camera is, on paper, what the FSQ106 has been waiting for. I hope it works without microlensing or other issues and if it does I don't see it being resistible! But CMOS cameras have their share of issues so I won't be an early adopter.

To be honest I love working with the old Atik 11000 camera. I've said before that the numbers are lousy - QE and resolution at 530mm - but the data is so sweet. Lovely stars, lovely star colour. 3.5"PP doesn't resolve the finest details but stars are absolutely not blocky. This is a fallacy and the 106/KAF1100 has more APODS than you can shake a stick at.

Olly

[Magnum]

Yes Olly, I must agree about the Kaf sensors, I just bought an Atik 383L and posted the first light image here on SGL. The individual subs are Not as impressively clean as my Sony sensor, but as soon as I stacked the 18 subs I captured last night I was blown away by the smoothness of the data and the tight stars ( probably due to the greater well depth  ) 

I was seriously thinking of getting a 1600 CMOS last week but then looked at Sara Wagers comparison of her QSI KAF 8300 data with her previous Sony version and my mind was made up.

Lee

Edited October 16, 2019 by Magnum