Exposure latitude of CMOS cameras

[StuartT]

I shot this last night. Moderately good seeing. Only my second attempt at the moon.

It's the best 50% of frames from a 2min video captured in SharpCap, then stacked in AS3! and (gently) tweaked in Registax.

Shot at prime focus of an Esprit 150mm ED APO using a ASI 2600MC

Reasonably happy as a try out of my setup and processing, but it's a bit too blown out at the bottom. Maybe the latitude of these cameras isn't that wide?

Anything I can do about that without underexposing the terminator?

Edited August 28, 2021 by StuartT

[DaveS]

What gain setting did you use? The IMX 571 cameras should be good for 14+ bits of DR. How was the histogram? No saturated pixels?

[StuartT]

8 minutes ago, DaveS said:

What gain setting did you use? The IMX 571 cameras should be good for 14+ bits of DR. How was the histogram? No saturated pixels?

according to the settings file generated by SharpCap the gain was 571 (I think I put it up high to try and get a faster frame rate).

Not sure about the histogram (sorry, I am new to this stuff). SharpCap has generated an excel file called histogram, is that what you mean? Attached

01_19_10.Histogram.csv

[DaveS]

571 sounds like the sensor designation rather than gain, but looking at the graphs on the FLO site going much above Gain 100 will lead to lower DR and Full Well. Going to Gain 400+ will cause catastrophic loss of both. Looking at the spreadsheet and scrolling right down to the bottom I see an awful lot of saturated pixels.

For the next try I would keep the gain no more than 100 (Where the HGC kicks in. I might even go for Gain 0 to maximise Full Well. The Moon is a bright target!

BTW "Exposure Latitude" is something I used to hear about with film photography (Been there, done that).

[StuartT]

7 minutes ago, DaveS said:

571 sounds like the sensor designation rather than gain, but looking at the graphs on the FLO site going much above Gain 100 will lead to lower DR and Full Well. Going to Gain 400+ will cause catastrophic loss of both. Looking at the spreadsheet and scrolling right down to the bottom I see an awful lot of saturated pixels.

For the next try I would keep the gain no more than 100 (Where the HGC kicks in. I might even go for Gain 0 to maximise Full Well. The Moon is a bright target!

BTW "Exposure Latitude" is something I used to hear about with film photography (Been there, done that).

Ok, I am not sure what full well or HGC is, but I think the take home is to keep my gain low. I guess I was trying to get a good frame rate, but as the moon doesn't rotate, perhaps I was worrying about that unnecessarily.

Thanks!

[CraigT82]

2 hours ago, StuartT said:

Anything I can do about that without underexposing the terminator?

Before you start capturing you want to set your exposure to correctly expose the very brightest parts of the moon without any white clipping, preferably with a good bit of headroom too.  Don't worry about the dimmer parts, they can be brightened up later in the processing flow.

As with planetary imaging you want short exposures to freeze the seeing, so 5ms of thereabouts. You wan't to set the gain to allow you to achieve this short exposure time so if it has to be high gain then that's fine, but the moon is so strong a signal you may find you can get those short exposures with low gain. 

You want to be able to capture as many frames as possible during the still moments so yes you want as many frames per second as you can get, not sure what that is with the full sensor size of your camera? The moon doesn't rotate relative to us so you can capture for as long as you want really. Well until the shadow lengths start to change anyway. 

 

[StuartT]

10 minutes ago, CraigT82 said:

Before you start capturing you want to set your exposure to correctly expose the very brightest parts of the moon without any white clipping, preferably with a good bit of headroom too.  Don't worry about the dimmer parts, they can be brightened up later in the processing flow.

As with planetary imaging you want short exposures to freeze the seeing, so 5ms of thereabouts. You wan't to set the gain to allow you to achieve this short exposure time so if it has to be high gain then that's fine, but the moon is so strong a signal you may find you can get those short exposures with low gain. 

You want to be able to capture as many frames as possible during the still moments so yes you want as many frames per second as you can get, not sure what that is with the full sensor size of your camera? The moon doesn't rotate relative to us so you can capture for as long as you want really. Well until the shadow lengths start to change anyway. 

 

Thanks Craig. This 2600MC is an APS-C sensor and doesn't get super high frame rates. But as you say, I can afford to shoot for longer with the moon.