ZWO ASI120 Mono and ST4 Guiding

[wave...@talktalk.net]

Following on from my recent discussion on testing connections using the Manual Guide tool ( here ), I have indeed experienced a revelation.

It's apparent that the reason my ST4 guiding failed completely after an OAG adjustment is in the guide camera bit depth. As noted by fellow member bec...@gmail.com , the ZWO driver has a glitch that drops the bit depth from a setting of 16 bit to 8 bit and my thanks go to him for that insight. I have now had chance to test this using the Camera Connection Setting (8 or 16 bit), the LX200 Handbox and LHD2 Manual Guide tool,.all as described earlier. When set to the recommended 16 bit for best centroid detection, the ST4 system fails. Setting the camera to 8 bit in the PHD2 gui enables the ST4 output. Surely this isn't right??

I've posted this observation on the ZWO Camera Forum and await a response.

Cheers,

- Jack

[Richard Beck]

Jack,

If the guiding program expects 16-bit values (max of 65535) and the driver has dropped to 8-bit (max of 255), there will be no stars as far as PHD2 is concerned.  If the 8-bit driver is used, PHD properly assesses the image and selects the appropriate guide star (plural if using multi-star).  I have been getting good stars with SNRs ranging from the 30s to 40s using 8-bits.

I think the ST-4 cable/guiding is a red herring here.

Regards,

Richard

[wave...@talktalk.net]

Hello Richard,

Why would the ASI120 camera driver 'drop' to 8 bit mode? The camera uses the latest version of the ZWO driver, which runs my ASI224 in 16 bit without that happening. The PHD2 Manual Guide tool doesn't actually need stars, so is the Saturation ADU setting relevant?. As suggested in the PHD2 Manual, I'm using it here during the day as a convenient way to test the camera's ST4 to mount signal. The results suggest there's a glitch in how the ZWO driver runs with the ASI120 camera. It's now apparent that I've been guiding my LX200 quite successfully with the guide cam in 8 bit, though I thought it was 16 bit. The use of 16 bit for guiding is frequently recommended, but it's not possible with the ASI120 camera. The tool does work with the ASI224 in 16 bit , so it's rather perplexing.

Cheers,

- Jack

[Richard Beck]

What I know for sure is I posted to the INDI forum about the driver dropping to 8-bits to see if we could fix it.  The lead maintainer for INDI told me it is an ASI feature and it only applies to the 120MM cameras.

I quit trying to use the 16-bit mode and have had no issues with the camera since.

[wave...@talktalk.net]

Hello again bec...@gmail.com,

Indeed, if it wasn't for your earlier post on this, I'd still be pulling my hair out trying to figure where I'd gone wrong.

It sounds like ZWO could fix this 'feature' if the wanted to. Do you know if they are aware of it? It seems to me they're selling a camera that's not as advertised and which breaches trading law, in the UK at least.

Poor do's, I reckon.

- Jack

[Richard Beck]

Jack,

I can operate at 16-bit.  It just doesn't do it reliably.  Being able to operate in 16-bit may be enough to keep it from running afoul of the UK trading law.  (However, being a Yank and not a lawyer, I don't really know the ins and outs of UK's trading law.)

Apparently this is an issue only with the 120MM, and dropping to 8-bits is the ZWO solution.

Regards,

Richard

[wave...@talktalk.net]

Hi Richard, thanks for the info. If Zwo had made clear they have this issue, I wouldn't have bought their ASI120.

Cheers,

- Jack

[wave...@talktalk.net]

Interesting. If you select the ASCOM ASI driver in the PHD2 Profile Wizard and check the Advanced settings, it actually warns you that guiding in 16 bit is not possible. Wonder why isn't that warning issued by ZWO's own driver?

Cheers,

- Jack