Asi 533 offset setting

[Craig a]

So I’ve just received my new 533mc pro and plan it’s first light at gain 100, thats the point the read noise drops, but what offset do I need to use if anybody has got this camera thanks in advance 

[Adam J]

3 hours ago, Craig a said:

So I’ve just received my new 533mc pro and plan it’s first light at gain 100, thats the point the read noise drops, but what offset do I need to use if anybody has got this camera thanks in advance 

At gain 100 you have huge dynamic range so I would just stick it at 50 and be done with it as its sufficiently high to be sure to prevent black clipping and your not going to see any real advantage to lower settings.

Adam

 

[Craig a]

Ok thanks Adam I shall set it to 50 😀

[Craig a]

So do these newer cmos sensors still require darks if the images are dithered? Also are dark flats required or can you just get away with normal flats be enough? Being new to these cameras I’m not at all clued up on the calibration required, on my canon I just used a bad pixel map and plain old flats 

[CCD-Freak]

The default offset setting in the ASCOM driver is 70 which seems high to me and I plan to try going down to 50 or maybe as low as 20 but I will have to be careful not to clip the bottom of the histogram.

Let us know how the 50 offset works.

 

John
CCD-Freak
WD5IKX

[Adam J]

14 minutes ago, CCD-Freak said:

The default offset setting in the ASCOM driver is 70 which seems high to me and I plan to try going down to 50 or maybe as low as 20 but I will have to be careful not to clip the bottom of the histogram.

Let us know how the 50 offset works.

 

John
CCD-Freak
WD5IKX

Honestly if you can see any difference at all between 50 and 70 then I would be shocked. Hence if the default is 70 just leave it there, more improtant things to be worried about. 

Probably not worth putting the effort in to test it as the advantage of lower bias (at gain 100) is an insignificant increase in dynamic range.

Adam

Edited August 28, 2020 by Adam J

[CCD-Freak]

31 minutes ago, Adam J said:

Honestly if you can see any difference at all between 50 and 70 then I would be shocked. Hence if the default is 70 just leave it there, more improtant things to be worried about. 

Probably not worth putting the effort in to test it as the advantage of lower bias (at gain 100) is an insignificant increase in dynamic range.

Adam

I, like you, think there will be little difference lowering the offset so I have not been in a rush to experiment with it.  I will continue to run the gain at 100 since that is where the low noise mode kicks in and the dynamic range and well depth are the highest.  I am really happy with the ASI-533MCP so far and look forward to more "quality dark sky time" with it.

John
CCD-Freak
WD5IKX

[Craig a]

9 hours ago, CCD-Freak said:

The default offset setting in the ASCOM driver is 70 which seems high to me and I plan to try going down to 50 or maybe as low as 20 but I will have to be careful not to clip the bottom of the histogram.

Let us know how the 50 offset works.

 

John
CCD-Freak
WD5IKX

I’m hoping for a clear spell tonight to have a quick first light, the moon is around so not ideal, I did do a bias frame at offset 50 and that gave me a median of around 1750 I’m not at all technical when it comes to this but I’m taking it that number gets added to light frame after it’s been shot?

[Craig a]

9 hours ago, Adam J said:

Honestly if you can see any difference at all between 50 and 70 then I would be shocked. Hence if the default is 70 just leave it there, more improtant things to be worried about. 

Probably not worth putting the effort in to test it as the advantage of lower bias (at gain 100) is an insignificant increase in dynamic range.

Adam

Dynamic range is about 13.5 at gain 100 and well depth about 20,000, my scope is f4.5 was thinking of using 3 min exposures, does that sound About right to you? Will I saturate stars in 3 mins? I spose I could test but I don’t really want to be wasting precious time if I get a clear spell, I’ve seen people say gain 0 is the way to go and longer exposures on these newer cmos cameras then others say shorter exposures at unity gain 

Edited August 29, 2020 by Craig a

[CCD-Freak]

So far I have not shot longer than 120 second subs with my ASI-533.  At F3.8 many of the stars are saturated so I may try 60 second subs with that scope next time I have it out.  I plan to use a 10" F4.7 Newt when I go out to New Mexico in October if it tests OK from my light polluted garden.  I know what you mean about wasting "sky time".

The ASI-533 is very sensitive.....This test image of M3 was only 10 second subs at F10 (60 x 10 seconds...10 minutes total)

 

John
CCD-Freak
WD5IKX

 

Edited August 29, 2020 by CCD-Freak

[Adam J]

16 hours ago, Craig a said:

Dynamic range is about 13.5 at gain 100 and well depth about 20,000, my scope is f4.5 was thinking of using 3 min exposures, does that sound About right to you? Will I saturate stars in 3 mins? I spose I could test but I don’t really want to be wasting precious time if I get a clear spell, I’ve seen people say gain 0 is the way to go and longer exposures on these newer cmos cameras then others say shorter exposures at unity gain 

Unity gain should work great. Optimal exposure depends on sky brightness and read noise but 3 mins seems longer than necessary.

[Craig a]

Ok I just did a 3 min exposure at gain 100 and offset of 50 but my mean pixel stat for entire image is 3700? I’m using an idas lp filter but even so I thought the background would be higher than that? And the moon is out? I’m wondering if nebulosity isn’t applying the gain as I’m capturing in nebulously 

Edited August 30, 2020 by Craig a

[Craig a]

On 29/08/2020 at 18:49, CCD-Freak said:

So far I have not shot longer than 120 second subs with my ASI-533.  At F3.8 many of the stars are saturated so I may try 60 second subs with that scope next time I have it out.  I plan to use a 10" F4.7 Newt when I go out to New Mexico in October if it tests OK from my light polluted garden.  I know what you mean about wasting "sky time".

The ASI-533 is very sensitive.....This test image of M3 was only 10 second subs at F10 (60 x 10 seconds...10 minutes total)

 

John
CCD-Freak
WD5IKX

 

Can I ask what your mean adu value was per sub? I’m doing 3min exposures and getting around 3500 with the moon out, I am using an idas lp filter but for gain 100 I would of thought it would be higher than that? My dslr on a 3min exposure would be up at around 20000 

[CCD-Freak]

Here is a screen grab from AA7 of a single sub of M3

John
CCD-Freak
WD5IKX

[Craig a]

So your average is lower than mine, that is to be expected as you have 10 second subs, but my 3 min subs only 1000 adu more in the background is confusing me, I always thought we should aim for histogram to be roughly 1/3 to the right? I tried the same 3 min sub is asi studio and got the same result so I don’t think it’s an issue with nebulosity. It may not be an issue at all and I’m making a mountain out of a molehill. I’m only comparing to my dslr, I selected ascom camera in neb and that brought up the ascom controls to set the gain and offset 

[CCD-Freak]

As I understand it the Offset is used to keep the bottom end of the Histogram from going below 0 which would be clipped.  The default in the ASCOM driver is 70 which seems a bit high to me.  I want to try some lower Offset values but I don't want to spend too much of my hard to come by clear sky time.  The default value works fine so I will use that for now.  One thing to remember....If you change the offset value you will need to shoot your Darks and Flats at the same setting.

After looking at a stacked image of 2 minute subs I think the 70 Offset is good. 

John Love
CCD-Freak
WD5IKX

Edited August 31, 2020 by CCD-Freak

[Campster]

On 28/08/2020 at 06:40, Craig a said:

So do these newer cmos sensors still require darks if the images are dithered? Also are dark flats required or can you just get away with normal flats be enough? Being new to these cameras I’m not at all clued up on the calibration required, on my canon I just used a bad pixel map and plain old flats 

 

I'm also using the ASI533MC Pro and it's always a good practice to take Darks, Bias & Flats to help attenuate noise in your image.  Dark Flats don't seem to be a regular practice with most amateurs though.

Glad to see the discussion about Offset here.  Being a recent convert from DSLR photography I've been trying to get a handle on the baseline settings.  The recommendations of 20-70 help me get a feel for where I should be setting that value in APT.  I think I'm going to be using 40 or 50 and see where that takes me.  

Regards, David