Altair 26c LCG / HCG

[SkyluxMax]

HI all. I hope someone can help me out?
I have an Altair 26c that I have been using for a while now and been very happy with it. However, I think I could be doing better with regards to its settings and Read Noise levels (in both SharpCap and APT, been using it for a long time for planning/ object DB). Currently, I have been using the 26c by and large at Gain 120, Offset 50 with about 3 Min exposures in Ultra Low noise mode and in LCG mode. I recently ran a Sensor Analysis routine and came up this info (see attached). It would seem that running the Gain level at 300 would be most beneficial?
As I understand, at Gain 300 SharpCap switches over from LCG to HCG? So should I be running APT in HCG or just keep it in LCG at Gain 300? If I do change it to HCG at 300 does that correspond to '300' in both apps as I have seen that these values can change EG 300 in one app means 150 in another?? Confused! I mainly use SharpCap for PA, Focusing, Planetary and Flats.
Also the Offsets in SharpCap started off with 794 should I keep to that?
Hope this makes sense!?

[admin]

Hi,

for the IMX571 sensor in the 26C, the switch from LCG into HCG applies an extra gain of a factor of 3 to the normal camera gain. SharpCap hides this from you by incorporating the LCG/HCG switch automatically into the gain control, whereas other applications may make both controls available.

To give some examples to make it (hopefully) clearer

Code: Select all

Other Application Gain     SharpCap Gain     Total Brightness
100 LCG                    100               1.00x
200 LCG                    200               2.00x
300 LCG                    n/a               3.00x
400 LCG                    n/a               4.00x
600 LCG                    n/a               6.00x
900 LCG                    n/a               9.00x
100 HCG                    300               3.00x
200 HCG                    600               6.00x
300 HCG                    900               9.00x           

In SharpCap once you get to 300 gain (3.00x brighter than minimum gain), HCG is automatically switched on and behind the scenes SharpCap sets the basic camera gain back to 100, so it gets a total gain of 3.00x entirely via the HCG changeover. As gains are increased beyond 300, the camera remains in HCG mode and SharpCap turns up the camera gain to provide the extra brightness boost needed.

The reasoning behind this is that HCG mode provides the benefit of a significantly reduced read noise, with no real downside as far as I am aware, so switching into HCG mode when possible seems to be a win-win situation. SharpCap therefore does this automatically to avoid users needing to learn about LCG and HCG unless they want to.

As a concrete example, to get a total gain of 3.00x minimum, you have two options

1) LCG, 300 Gain, Read noise ~3e
2) HCG, 100 Gain, Read noise ~1.4e

With the HCG approach you can get away with sub exposures that are 4x shorter than with the LCG approach, which might be the difference between getting good subs and having guiding/tracking issues and wondering whether you need a better mount...

chers,

Robin

[SkyluxMax]

Hi Robin
Thank you for the detailed reply. Makes sense.

[8611paulm]

Do these setting's also apply to Zwo 2600mc pro?

[admin]

Hi,

the ZWO camera does the same trick of combining the LCG/HCG switchover into the gain- in fact in the ZWO camera case it is built into the camera control software supplied by ZWO, so *all* software does it that way.

If you look at the product page on the ZWO web site, you will see that the switchover occurs at gain 100 (ZWO cameras measure gain in a different way to Altair ones).

cheers,

Robin