exposure time

[larrym1972]

Celestron SCT 11"

ASI294MC

focal reducer will be here on wednesday. Sky is about 21 mag. i know that these variables like light pollution, fog, brightness of the object, with or without reducer and more.

will out a reducer exposure time is max at 30 seconds before stars get little tales. is there a chart, guide, rule of thumb a book.

i did google search on this topic. i find information on dslr including chartsbut very little zwo series camera or similar.

i have 60 to 100 degree of sky for imaging other worth 4 to 6.5 hours

M104

exposure 20 sec

50 frames

80% gain

it not bad but its not great

[happy-kat]

What mount are you using?

[Anthonyexmouth]

As above, what mount are you using that limits you to 20 secs. 

[vlaiv]

It looks to me that your scope is out of collimation.

How about fixing that first, or at least confirming that it's not the case?

[happy-kat]

If you are using an altaz mount you might like to see this thread. Link here though take a look from the first page.

[larrym1972]

Cgem ii is the mount. F/10 is the focal length but the makes correction it show it the image I would like to know how long exposure do I need a good image I getting tired of guessing that's why something to go buy 

[vlaiv]

I just stretched that image a bit for everyone to see:

Stars in the image show serious coma. Before you start trying to do anything else - collimate your scope and then you will be able to tell how long exposures you can pull off with your mount.

Even with 50 subs of 30 seconds you have some serious signal in that galaxy - but it is all too blurred by misaligned optics to tell. This should be your number one priority now - collimate your scope properly.

[larrym1972]

i will collimate the scope tonight i get some dark frames and half moon 

 

[vlaiv]

4 minutes ago, larrym1972 said:

i will collimate the scope tonight i get some dark frames and half moon 

 

Take a test shot of 20-30s after you do collimation - just as a comparison. It does not matter if the moon is out - no need for subs to go deep, just to confirm star shapes are ok. Maybe near dense star field or open star cluster

[larrym1972]

i do that next clear night it over cast