c8 edge hd ,asi178 and saturn

[iwols]

Hi been doing dso for the last 24 months but just thinking what saturn would look like with a asi 178c ccd,looked the setting up on astronomy tools,with the following but how could i make the image bigger,could a x2 barlow or anything be fitted/worthwhile,any advice appreciated

[vlaiv]

Hm, you are not looking at it properly.

It is hardly that you will be using full sensor surface to capture planet as small as Saturn (anything really apart from the Moon and the Sun).

Best way to calculate what sort of image in terms of size you will have is to compare pixel scale and size of planet at the moment. Planet is now about 18" and rings about 43".

Without barlow, your imaging resolution will be 0.25"/px, so size of planet will be about 72px across, while rings will be 172px.

If we draw a little diagram we can get approx size of planet in the image:

("planet" circle diameter - 72px, "rings" ellipse width 172px)

This is very close to optimal image size that you can get with 8" scope. With this camera, optimum sampling rate is about F/12. This does not mean that you can't make your planet larger by using higher F/ratio, but you won't be able to see any additional detail (much like using higher magnification EP - just blurrier larger image). Since you are using OSC camera, you would benefit from going as high as F/24 in fact - for capture, but for processing you should bring size of planet down (or leave it x2 enlarged, some people do it like that as x2 enlarged image is not going to be very blurry compared to properly sampled one).

Anyway, with 178 sensor you want to use ROI when doing capture - that will save you disk space and enable higher FPS to be achieved (more subs captured). Given the size of the planet, you can comfortably go with 320x240px ROI unless you want to try to capture saturn's moons as well - then 640x480 might be needed.

 

[iwols]

thanks vlaiv,so are we saying i dont need a x2 barlow and the 178 alone will give me quite  large usable image?

On 20/06/2019 at 20:36, vlaiv said:

Hm, you are not looking at it properly.

It is hardly that you will be using full sensor surface to capture planet as small as Saturn (anything really apart from the Moon and the Sun).

Best way to calculate what sort of image in terms of size you will have is to compare pixel scale and size of planet at the moment. Planet is now about 18" and rings about 43".

Without barlow, your imaging resolution will be 0.25"/px, so size of planet will be about 72px across, while rings will be 172px.

If we draw a little diagram we can get approx size of planet in the image:

("planet" circle diameter - 72px, "rings" ellipse width 172px)

This is very close to optimal image size that you can get with 8" scope. With this camera, optimum sampling rate is about F/12. This does not mean that you can't make your planet larger by using higher F/ratio, but you won't be able to see any additional detail (much like using higher magnification EP - just blurrier larger image). Since you are using OSC camera, you would benefit from going as high as F/24 in fact - for capture, but for processing you should bring size of planet down (or leave it x2 enlarged, some people do it like that as x2 enlarged image is not going to be very blurry compared to properly sampled one).

Anyway, with 178 sensor you want to use ROI when doing capture - that will save you disk space and enable higher FPS to be achieved (more subs captured). Given the size of the planet, you can comfortably go with 320x240px ROI unless you want to try to capture saturn's moons as well - then 640x480 might be needed.

 

 

[vlaiv]

17 minutes ago, iwols said:

thanks vlaiv,so are we saying i dont need a x2 barlow and the 178 alone will give me quite  large usable image?

 

Certainly image roughly the size of example I made. How usable it will be depends on seeing conditions and how much data you capture. Interesting thing with saturn is that you can go quite long total capture time and still get usable image - although it's revolution speed is such that you should limit your self to 4-5 minutes, I did up to 15 or more minutes long capture and resulting image looked quite nice - this is due to fact that most features on the planet that you will be able to capture are "horizontal" so some of motion blur due to planet's rotation won't distort the image as much. Not so if you have a larger scope and steady skies and you manage to capture hexagon for example - that one will be quite blurred by rotation.

[iwols]

thanks👍