Share:
Notifications
Clear all

Please note our new Downloads page here

2023-01-19: APP 2.0.0-beta13 has been released !

!!! Big performance increase due to optimizations in integration !!!

and upgraded development platform to GraalVM 22.3 based on openJDK19

 

We are very close now to  releasing APP 2.0.0 stable with a complete printable manual...

 

Astro Pixel Processor Windows 64-bit

Astro Pixel Processor macOS Intel 64-bit

Astro Pixel Processor macOS Apple M Silicon 64-bit

Astro Pixel Processor Linux DEB 64-bit

Astro Pixel Processor Linux RPM 64-bit

Gain 0 imaging with QHY268C


(@tsk1979)
Main Sequence Star Customer
Joined: 4 years ago
Posts: 52
Topic starter  

I normally shoot Gain 30, Offset 50 on Photographic DSO mode for everything.

 

I was wondering if I should try imaging with gain zero for brighter objects? What is the recommended offset for Gain zero with this camera?


ReplyQuote
(@vincent-mod)
Universe Admin
Joined: 6 years ago
Posts: 5206
 

Could you explain what photographic DSO mode is? Don't really know about that.

Gain 0 is fine and will give you the best dynamic range, but it also requires you to check well if the exposure lengths are good enough to get all data not being clipped. Offsets should not be changed, 50 seems a bit high maybe, but that will depend on what is normal for your camera. When you have that set right, just never change it.


ReplyQuote
(@anofeles)
White Dwarf Customer
Joined: 4 years ago
Posts: 21
 

I'm going to answer you but I guess that kind of questions about a specific feature of a specific camera has more appropriate forums....
I always use gain at 26 (I've made attempts with gain 0 and gain 56 and they didn't turn out any better). The exposure time will prevent you from burning or not the heart of the stars (I have done the Pleiades with that gain). I usually work with 180 seconds.
On the subject of offset. It depends on many factors. The best you can do and the less time it will take you is to make a bias (very short exposure, telescope covered) with an offset, for example of 30. Look at the histogram. Check that the left part of the peak is separated from the Y-axis. If not, increase the offset until you see it clearly separated. In my case, I use an offset of 80.
I hope you find it useful....


ReplyQuote
(@tsk1979)
Main Sequence Star Customer
Joined: 4 years ago
Posts: 52
Topic starter  

Thanks

I also use gain 26 and offset 50. Gain 26 is the unity gain of qhy 268C

 


ReplyQuote
(@davidharris11)
Brown Dwarf Customer
Joined: 2 years ago
Posts: 12
 

@tsk1979 A little late to the party here, but just found this thread for the first time.

I have the QHY268C and I have imaged extensively at gain 0 with an offset of 30. I arrived at the offset 30 setting after doing a some camera analysis in sharcap, which has some useful tools for analyzing cameras. I have had very good results using gain 0, offset 30 in photographic mode for the RGB portion of my images & am working in heavy light pollution within the city limits of Charlotte, NC. My house is bortle 7, not far from a bortle 8 area.

With narrowband images I use gain 30, offset 45 also in photographic mode (think L-Extreme filter).

I've tried several different modes with this camera & various gain/offset combos, but those two that I mentioned have become my go-to's & work well. So, I've built my library of dark frames around these at various exposure lengths.

For broadband: gain 0/offset 30.(120 or 180 sec subs, depending on target, usually 120 with my light pollution)

For narrowband: gain 30/offset 45 (I can go either 180, 240, or sometimes 300 sec subs with narrowband here, but the 3 or 4 min sub exposure length seems to work well, I just accumulate more subs this way, which is fine.)

I'm certainly not saying that the above is what you "should" do, only that it has been working well for me & I have used the above in some combination for the vast majority of my images for about the last year, which is as long as I've had this camera. I did a lot of initial testing, analysis with sharpcap before settling on these gain/offset settings in the beginning, so I didn't get there just by guessing.

What I've outlined above has been working very well. This camera is still VERY sensitive at gain 0. Even when I go out to a dark site I have access to, I still stick with gain 0 when imaging broadband with just a UV/IR cut filter & the subs really pop even at gain 0. Your dynamic range is pretty much the same at gain 26 or gain 60, but I do like the fact that you have greater well-depth to work with at gain 0, which I think probably helps when out at a dark site. At the very least, it certainly doesn't hurt & does produce great results.

Hope this helps.

David


ReplyQuote
(@tsk1979)
Main Sequence Star Customer
Joined: 4 years ago
Posts: 52
Topic starter  

@davidharris11 

Thanks! I have started doing Gain 26 offset 50 now and I image mostly from Bortle 4 or darker. It gives me very good results at 180s. However for very faint objects even with F4 newt I feel this is a bit too dim. Maybe I should try the high gain mode on the very faint dark nebulae

 


ReplyQuote
(@davidharris11)
Brown Dwarf Customer
Joined: 2 years ago
Posts: 12
 

I experimented using high gain mode for a while, at various gain settings, also using an F4 Newtonian & my experience was that high gain mode created noisier images without a big benefit over photographic mode in my opinion. I was not a fan of high gain mode, personally & I did use it quite a bit for a period. If you’re looking for the fainter detail there’s also the full well mode available.

I have found that I can get plenty of dark nebulosity detail in standard photographic mode at gain 0 with just a UV/IR cut filter at the dark site I have access to. 3-4 min exposures with my Newtonian work well there. The dark site is bortle 3-4, so similar conditions as yours. There’s also zero nearby local light pollution in the immediate area around that site, so this may be a factor. I can almost always pull out all the detail I was hoping was there in the image in post processing just with gain 0, 3-4 min subs at photographic mode from the dark site. 

I always use gain 30 with narrowband. My thinking on using 30 vs 26 gain is that 26 is just right on that cutoff line where you suddenly get the bump in dynamic range with this camera, so I’d rather bump it just past this & not be straddling that line. 


ReplyQuote
(@tsk1979)
Main Sequence Star Customer
Joined: 4 years ago
Posts: 52
Topic starter  

I used qhy268C extended fullwell mode Gain 0 and offset 50. Looks good to me. 


ReplyQuote
Share: