Smart Histogram where to point question

Somewhere to ask questions about the best way to use SharpCap
Post Reply
mAnKiNd
Posts: 172
Joined: Sun Jun 11, 2017 4:55 pm
Location: Long Island, NY
Contact:

Smart Histogram where to point question

Post by mAnKiNd » Thu Sep 13, 2018 7:15 pm

Hi,

I raised this question in another topic I started in Deep Sky Imaging, but felt it needed a seperate topic for clarification.

In the updated manual, in the Smart Histogram tab, under Measuring Sky Brightness, it states "you should point the telescope at an area of sky without nebulosity or many stars to get a good measurement."

What it doesn't state in the manual and what my question is - after you've done this and obtained and entered a value in e-/pixel/s (for example say 5) in the sky brightness dropdown selection, would it be better to:

1) Apply the Exposure/Gain setting recommended from the patch of sky used above that also gave you 5e-/pixel/s for your sky brightness? Use these values for your target, which is in a different part of the sky (either close to before or farther out)?

or

2) Slew to the target that you will be imaging for the night and get new Exposure/Gain recommendations using the manually entered 5e-/pixel/s for your sky brightness you got earlier?

Apologies if this is blatantly obvious to some, but in my mind it would be better to go for option 2, as it would generate exposure/gain recomendations based on your target and not a relatively empty patch of sky.

I will however, leave the verdict to those who know better than me.

Many thanks
Minos
Celestron AVX & SW Az-GTi (EQ)
SW Esprit 80 & 150PL, Canon 300mm f4 (non-IS)
ASI1600MM PRO
EFWmini - HOLRGB
ASI120MM mini for guiding
SC CDC PHD2 DSS PI PS

https://www.astrobin.com/users/minoSpace/

User avatar
admin
Site Admin
Posts: 1898
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Smart Histogram where to point question

Post by admin » Thu Sep 13, 2018 8:07 pm

Hmm,

Let's put it like this...

* Smart Histogram optimises exposure length/gain to minimize noise in the final stacked image
* The bits of the image you care most about noise in are the faintest parts of your target (least signal, so worse signal/noise)
* presumably you want to see the faint parts of the target down as far as possible - the faintest wisps of nebulosity etc
* therefore the instruction to measure the sky brightness on a dark region as the faintest nebulosity you want to see won't be much brighter (but will be a lot harder to find and select!)

In summary, smart histogram is optimizing for the darker parts of the image and leaving the brighter parts to take care of themselves.

hope this makes sense,

Robin

mAnKiNd
Posts: 172
Joined: Sun Jun 11, 2017 4:55 pm
Location: Long Island, NY
Contact:

Re: Smart Histogram where to point question

Post by mAnKiNd » Thu Sep 13, 2018 9:42 pm

Thanks Robin, that does make sense (I think!)

I understand that if I go with my option 2, then there will be a lot more signal in the fainitest parts of the image (because of the target's presence) and the snr analysis won't be as accurate as option 1 (the normal way of doing it).

Hope I'm understanding this right to pick the right settings to start my project tomorrow, as seldom clear skies have been forecast for the weekend.

Thanks again
Minos
Celestron AVX & SW Az-GTi (EQ)
SW Esprit 80 & 150PL, Canon 300mm f4 (non-IS)
ASI1600MM PRO
EFWmini - HOLRGB
ASI120MM mini for guiding
SC CDC PHD2 DSS PI PS

https://www.astrobin.com/users/minoSpace/

User avatar
admin
Site Admin
Posts: 1898
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Smart Histogram where to point question

Post by admin » Fri Sep 14, 2018 5:54 am

Sorry, did not quite understand your question correctly at the first read...

The recommendations from the 'brain' only depend on the sky brightness reading (5e/pixel/s in your example) and the sensor characteristics measured previously using sensor analysis.

That means that you could have the scope out in daylight or with the end cap on and you would get the same suggested gain/exposure values for the same sky brightness level, so I think that means your options 1&2 would give the same results.

cheers,

Robin

mAnKiNd
Posts: 172
Joined: Sun Jun 11, 2017 4:55 pm
Location: Long Island, NY
Contact:

Re: Smart Histogram where to point question

Post by mAnKiNd » Fri Sep 14, 2018 11:16 am

Ah, well that settles that then lol!

Thank you again for your time Robin

Cheers
Minos
Celestron AVX & SW Az-GTi (EQ)
SW Esprit 80 & 150PL, Canon 300mm f4 (non-IS)
ASI1600MM PRO
EFWmini - HOLRGB
ASI120MM mini for guiding
SC CDC PHD2 DSS PI PS

https://www.astrobin.com/users/minoSpace/

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest