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QHY268M & QHY268C Users Thread (Please share your knowledge and tips)


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As this is still a relatively new camera I though I would start a thread for users to share their knowledge on it.
Of particular interest would be what Gains and modes people are using and why they settled on these settings, also any links to other websites with useful information would be good, and also to report any issue you have had.

If there are useful links or particularly useful info I can update this first post so the info is ready available.

Steve

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Gains, Offset and modes being used

Currently I am using Mode 1, Gain 56, offset 25. I will try to populate this section with other users info so you can see what people are using at a glance.

image.png.ae56bf8e656b01d1518d88b49bc9d4b7.pngUser Settings.xlsx

             
             

 

 

 

Edited by teoria_del_big_bang
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Mono V Colour

image.png.925d40c759c9c6293b5500ed24ea2266.png

Whilst the QHY website states both the mono and colour versions have the same optical window.
I have seen may threads on various forums stating that the mono has a IR cut filter, but the colour does not and requires some sort of IR filter.
The QHY website says it is AR + AR coated, but this doesn't make sense so I am assuming it means IR +AR, anybody know any different ?

 

Edited by teoria_del_big_bang
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Capture1.JPG

image.thumb.png.0358aa970158f792df9987032bc42d60.png

Multiple Readout Modes is a new function for newer QHY Cameras.  Different readout modes have different driver timing, etc., and result in different performance. The QHY268 currently has four readout modes, and more modes will be added in the future. These readout modes are currently supported in the QHY ASCOM Camera Driver, SharpCAP software and the N.I.N.A software.

Readout Mode #0 (Photographic Mode). In this mode there is a drop in the noise between Gain 25 and Gain 26.  We recommend setting the Gain to 26 to begin.  At this setting the full well is 27ke- and readout noise is 2.7e-.  For every long exposures you can lower the gain from this point to increase the full well capacity.

Readout Mode #1 (High Gain Mode).  Please note there is a HGC/LGC switch point at gain55 to gain56. Gain0-55 uses LGC and Gain55-100 uses HGC.

Readout Mode #2 (Extended Full Well Mode).

Now QHY268 adds #3 mode Extend Full Well 2CMSIT (yellow curve). The advantage of this mode is that it has the same full well value and system gain as the #2 mode Extend Fullwell, but the read noise is reduced by about 1.3 times.

This function needs to be used with 2020.6.26 or newer SDK. If your software cannot display this mode, please download the QHYAllInOne installation package to update the SDK in the software.

image.thumb.png.f9448b1197ed3cf571d2a5cd50582916.png

image.thumb.png.0a3213ae918e457e8da04a607ebfc65c.png

image.thumb.png.33775ca3316e1b02befb9a261629621a.png

 

Edited by teoria_del_big_bang
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I too am using Mode 1, Gain 56 Offset 25. Seems to be the consensus that it's a good all-rounder and hard to go wrong with. 

Mode 3 looks interesting for those with fast scopes and large apertures, but be careful. Do not use a Gain of 0 with Mode 3. Up the Gain slightly to around 16 with that mode. See the posts by 2ghouls and my-spot in the link below:

https://www.cloudynights.com/topic/754530-qhy268m-read-out-modes-questions/

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40 minutes ago, Xiga said:

I too am using Mode 1, Gain 56 Offset 25. Seems to be the consensus that it's a good all-rounder and hard to go wrong with. 

Mode 3 looks interesting for those with fast scopes and large apertures, but be careful. Do not use a Gain of 0 with Mode 3. Up the Gain slightly to around 16 with that mode. See the posts by 2ghouls and my-spot in the link below:

https://www.cloudynights.com/topic/754530-qhy268m-read-out-modes-questions/

What sort of sub lengths and any sort of logic behind it or like me its just what seemed to work ?
I ask because there seems to be quite a consensus that more short subs are best way to go, not that they give you better data but that there is nothing to be gained over a certain sub length and that keeping the sub length low means less chance of lost data due to bad subs.

LRGB  should be easy to work out optimal sub length, NB maybe more difficult, obviously considerably longer than LRGB but also will depend on the actual bandwidth of the filters.

Steve

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Nice thread @teoria_del_big_bang I should find this very useful…

Now for a change, let’s talk USB traffic setting, never seen it mentioned, and I guess it’s not really an issue for DSO work, more for planetary video…so what setting do you guys use, it’s goes from 0-60 and mine came defaulted to 0 in NINA, but I changed to 20 and have left it there, does this have any impact with DSO work or any other positive or negative effect I should know about…??

Edited by Stuart1971
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4 hours ago, Xiga said:

I too am using Mode 1, Gain 56 Offset 25. Seems to be the consensus that it's a good all-rounder and hard to go wrong with. 

Mode 3 looks interesting for those with fast scopes and large apertures, but be careful. Do not use a Gain of 0 with Mode 3. Up the Gain slightly to around 16 with that mode. See the posts by 2ghouls and my-spot in the link below:

https://www.cloudynights.com/topic/754530-qhy268m-read-out-modes-questions/

Back to my question, why 56 and not 60, as the drop off starts at 56, but the lowest read noise seems to be at 60 on the graph…??

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22 minutes ago, Stuart1971 said:

Back to my question, why 56 and not 60, as the drop off starts at 56, but the lowest read noise seems to be at 60 on the graph…??

From reading various posts online, I believe the firmware enables HCG at Gain 56. There is no gradual transition between LCG and HCG (unlike what the graph says), you are using either one or the other depending on if the gain is below or above the toggle point.

But in all honesty, whether you use 56 or 60 is such a minor point. 56 gets you a little more FWC, but it would be nigh on impossible to tell the difference between two images taken at Gain 56 and 60. So just pick one, set, and forget 🙂

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42 minutes ago, Stuart1971 said:

Back to my question, why 56 and not 60, as the drop off starts at 56, but the lowest read noise seems to be at 60 on the graph…??

 

15 minutes ago, Xiga said:

From reading various posts online, I believe the firmware enables HCG at Gain 56. There is no gradual transition between LCG and HCG (unlike what the graph says), you are using either one or the other depending on if the gain is below or above the toggle point.

But in all honesty, whether you use 56 or 60 is such a minor point. 56 gets you a little more FWC, but it would be nigh on impossible to tell the difference between two images taken at Gain 56 and 60. So just pick one, set, and forget 🙂

As @Xiga says

image.thumb.png.cd62c22f14f478f76fc0b042095d1470.png

Steve

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On 18/01/2022 at 11:57, teoria_del_big_bang said:

What sort of sub lengths and any sort of logic behind it or like me its just what seemed to work ?
I ask because there seems to be quite a consensus that more short subs are best way to go, not that they give you better data but that there is nothing to be gained over a certain sub length and that keeping the sub length low means less chance of lost data due to bad subs.

LRGB  should be easy to work out optimal sub length, NB maybe more difficult, obviously considerably longer than LRGB but also will depend on the actual bandwidth of the filters.

Steve

It's true that being able to use shorter subs is definitely a benefit. Like you say, less chance of losing a sub due to wind, guiding issues, etc, and even the good subs may well have slightly tighter stars too. 

I go by a simple formula to help me calculate my sub length. I look to swamp the Read Noise by a factor of 10. At a Gain of 56 and an Offset of 25, the formula is:

(10 X 1.6²)/0.45+400 = 457

So as long as my Mean ADU is around 457 then I know I'm swamping the read noise sufficiently and there's no real need to go any higher. For NB, that means 6 min subs so that's what I use. For BB, you will hit the limit in no time, so it becomes a balancing act between too many subs Vs too many blown star cores. All depends which bothers you the most, but something like 90s for Lum and 180s for RGB would be a good place to start from. 

Edited by Xiga
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I'll be following this thread with interest! I think this mono camera will suit my needs just fine, but will need to save the funds first for filter wheel and filters too as this is my first venture into mono. 

For readout mode #1, at Gain 56, offset 25 and luminance exposure of 300s, what sort of ADU value are you seeing on stars? Are stars not fully saturated due to high FWC at these camera settings? 

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25 minutes ago, Xiga said:

It's true that being able to use shorter subs is definitely a benefit. Like you say, less chance of losing a sub due to wind, guiding issues, etc, and even the good subs may well have slightly tighter stars too. 

I go by a simple formula to help me calculate my sub length. I look to swamp the Read Noise by a factor of 10. At a Gain of 56 and an Offset of 25, the formula is:

(10 X 1.6²)/(0.45+400) = 457

So as long as my Mean ADU is around 457 then I know I'm swamping the read noise sufficiently and there's no real need to go any higher. For NB, that means 6 min subs so that's what I use. For BB, you will hit the limit in no time, so it becomes a balancing act between too many subs Vs too many blown star cores. All depends which bothers you the most, but something like 90s for Lum and 180s for RGB would be a good place to start from. 

I assume this relates to the mono version and not OSC…?

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50 minutes ago, Richard_ said:

I'll be following this thread with interest! I think this mono camera will suit my needs just fine, but will need to save the funds first for filter wheel and filters too as this is my first venture into mono. 

For readout mode #1, at Gain 56, offset 25 and luminance exposure of 300s, what sort of ADU value are you seeing on stars? Are stars not fully saturated due to high FWC at these camera settings? 

In short yes.
This is just down to my inexperience and the fact I have done very little LRGB stuff, usually NB.

In fact it is only just lately I have started looking at this and thinking I am doing something wrong.
If I am looking at this right then in LRGB at 300 seconds I am saturating pixels on all the brightest stars for sure and some not so bright, to be fair I have not done any Luminance but even my RGB have some saturation.

And in fact I think the very bright stars are saturated on my NB at 600 seconds, such as Alnitak (which I guess is easily done) but even some other very bright stars.

So this is indeed an area of my imaging I have misunderstood and need to put right.

Steve

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2 hours ago, Stuart1971 said:

Nice thread @teoria_del_big_bang I should find this very useful…

Now for a change, let’s talk USB traffic setting, never seen it mentioned, and I guess it’s not really an issue for DSO work, more for planetary video…so what setting do you guys use, it’s goes from 0-60 and mine came defaulted to 0 in NINA, but I changed to 20 and have left it there, does this have any impact with DSO work or any other positive or negative effect I should know about…??

Now this again is something I have not even given a thought to.

I have just powered up rig to look at what it is set to in EKOS and it was set to 56 and the buffer memory set to 512 bytes. Not sure how it ended up at these figures as it is not something I have set.
I assume the 56 is just a coincidence it is the same as my gain ???

Steve
 

Edited by teoria_del_big_bang
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24 minutes ago, teoria_del_big_bang said:

Now this again is something I have not even given a thought to.

I have just powered up rig to look at what it is set to in EKOS and it was set to 56 and the memory set to 512 bytes. Not sure how it ended up at these figures as it is not something I have set.
I assume the 56 is just a coincidence it is the same as my gain ???

Steve
 

Hmmm, I have 0-60 and I set it in 20, for USB traffic, but no memory setting…I thought there was 2gb memory buffer on these cameras….🤔🤔

Edited by Stuart1971
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15 minutes ago, Stuart1971 said:

Hmmm, I have 0-60 and I set it in 20, for USB traffic, but no memory setting…I thought there was 2gb memory buffer on these cameras….🤔🤔

As I say no idea why they were set to these values and whilst my EKOS agrees with you and the speed can be 0-60 the buffer memory can be set to between 512 and 4096 bytes, no idea what that really means as 4096 bytes is nothing in terms of memory, nobody really talks about anything less than Mb these days.

Steve

Edited by teoria_del_big_bang
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1 minute ago, teoria_del_big_bang said:

As I say no idea why they were set to these values and whilst my EKOS agrees with you and the speed can be 0-69 the buffer memory can be set to between 512 and 4096 bytes, no idea what that really means as 4096 bytes is nothing in terms of memory, nobody really talks about anything less than Mb these days.

Steve

My QHY driver in NINA says 0-60 for USB traffic, not 69

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On 18/01/2022 at 16:22, Xiga said:

I go by a simple formula to help me calculate my sub length. I look to swamp the Read Noise by a factor of 10. At a Gain of 56 and an Offset of 25, the formula is:

(10 X 1.6²)/(0.45+400) = 457

That is certainly a simpler formula than others I have seen on various forums and websites.

But it doesn't equal 457, is the 2nd parenthesis not required, because (10 X 1.6²)/0.45+400 = 457, but (10 X 1.6²)/(0.45+400) = 0.0639 

Also where do the figures 0.45 and 400  come from ?

Steve

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9 hours ago, teoria_del_big_bang said:

That is certainly a simpler formula than others I have seen on various forums and websites.

But it doesn't equal 457, is the 2nd parenthesis not required, because (10 X 1.6²)/0.45+400 = 457, but (10 X 1.6²)/(0.45+400) = 0.0639 

Also where do the figures 0.45 and 400  come from ?

Steve

And to add to the above @Xiga you say "At a Gain of 56 and an Offset of 25" yet those numbers don't appear to figure in the formula so are they irrelevant?

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13 minutes ago, scotty38 said:

And to add to the above @Xiga you say "At a Gain of 56 and an Offset of 25" yet those numbers don't appear to figure in the formula so are they irrelevant?

At gain 56 the readout noise is 1.6e- so indirectly it does appear, and that is multiplied by 10 because the aim is to swamp noise by a factor of 10, I just can't seem to see where the 0.45 and 400 come from., unless 0.4 is the system gain when in mode 1 at gain 56, which I think it is (approximately anyway)

Steve

Edited by teoria_del_big_bang
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@teoria_del_big_bang @scotty38 

Sorry guys, i posted the above in a hurry, and on my phone! Steve, you're right, i shouldn't have put the 2nd paranthesis in there (i've fixed it now, thanks). The figures are not fixed values, they depend on Mode, Gain, and Offset, but seeing as i never change any of these (Mode 1, Gain 56, Offset 25) i just treat them as fixed. 

The formula for determining exposure time is from a guy called Jon Rista. See post#3 below, where he explains it well, but basically the 400 is the 'Offset' (or Bias level) and the 0.45 is the gain in e-/ADU. 

https://www.cloudynights.com/topic/597682-i-need-a-primer-on-read-noise-calc-asi1600/?p=8200280

I realise now that i had just taken rough estimates for my camera gain and read noise, by eyeballing Qhy's graphs. As it turns out, you can get the exact figures from a script called "Basic CCD Parameters" in Pixinsight, so the exact figures should have been 1.56 and 0.33. See the post below as confirmation (or if you have P.I you can just do it yourself):

https://www.cloudynights.com/topic/754530-qhy268m-read-out-modes-questions/?p=11050460

So my own ideal ADU level should be 473 (not 457) and preferably no lower than 422. 

HTH. 

Edited by Xiga
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