NIR Pre-flash


#1

It doesn’t appear that there’s any way to utilize this feature on some of the cameras supported by SGP. I see there’s support for scripting after events, but what about after each frame?

Thanks


#2

Probably not externally. It really depends on if the camera is supported via ASCOM or natively. What camera are you wanting this support for?

Thanks,
Jared


#3

It would be any camera with the 16200 sensor, but specifically, I’m referring to a Moravian G3 16200. Banding is an issue (RBI) that can be fixed by preflashing before each exposure.


#4

Since Moravians are supported via ASCOM, they would need to add the option and address it in their ASCOM driver. Such options are not exposed to the client (SGP).

Thanks,
Jared


#5

Moravian already does support preflash in the Ascom driver:

I only just became aware of the banding while taking some 30min OIII subs. I didn’t notice the banding before. There was a recent discussion about this on cloudynights and I’m not sure if it was resolved that the banding was specifically an RBI issue.


#6

BTW, I’ve never encountered the need for RBI preflash before. What is a good setting?


#7

Never used preflash myself either…


#8

I haven’t checked recently but RBI preflash does not work with the Moravian and SGP. For some reason even if I check the preflash option with duration and number of times, it doesn’t do it.
It works fine with Maxim DL.


#9

Just out of curiosity, why are you using preflash? I have the G3-16200 and
don’t use it, but then again I’ve never really understood the purpose.
Also, I seem to recall a discussion I had with Moravian about using/not
using preflash. I’ll see if I can find that.


#10

I am not using it actually.
I had some vertical banding issue and I thought that it might be related to RBI so I wanted to try using preflash. I never did but I plan on trying at some point with maxim.


#11

RBI means “residual bulk image”, where ‘bulk’ means the substrate of the sensor chip. when you run a CCD super-cold, charge from the photosites can leak into the substrate and stay there, such that after you read out the chip and reset the photosites, the charge in the substrate can then leak back into the photo sites, mimicking the arrival of new photons. thus you get a ghost image of the previous exposure in your current exposure.

the RBI pre flash (also called “flood”) floods the sensor with IR light and then reads out (and discards) the flood image before the next real image is taken. charge from the flood is still trapped in the substrate, but hopefully after the flood the charge is uniformly distributed rather than being an image of something.

if you turn on RBI preflash for your lights you also need to do it for your darks and biases, because you need to get rid of the flood RBI somehow. an interesting thing is that you can often see semicircular swirls in the RBI darks - these are caused by slight differences in the crystal structure of the silicon as it is grown in cylindrical ingots. the wafers are cut perpendicular to the long axis of the ingot, and then the chips are cut from the circular wafers into squares.

rob


#12

It’s probably best to cool the camera as low as possible until RBI shows up then back off the TEC temperature by a few degrees. For example if RBI starts to show at -25C, then set TEC to about -20C and not enable RBI. One of the small drawback or side effect of RBI is that it may introduce some noise. So if you calibrate lights at warmer temperature without RBI, you might get better results than at colder TEC temperature with RBI enabled.

The word “banding” was mentioned in this thread but does it have to do with RBI? pfile explained very well how RBI works.

Peter


www.mainsequencesoftware.com