Help with setup

[Kenboy]

Hi all! Happy weekend 

I'm a beginner, hoping to get some good shots today 

I have an astro modified Canon 550d on Sky-Watcher star adventurer tracker & Canon 50mm f/1.8 lens, Bortle 4 sky 

Any suggestions for my camera ISO and exposure length? Would you suggest ISO 800, or higher? 

Thanks ! 

[barbulo]

I've never used the 600D (same sensor as yours) with a lens. With telescopes I use ISO800 (supposedly the sweet spot for this cameras) and the exposure time depending on the target and the conditions. As a starting point, take pictures with different durations and looking at the histogram choose the exposure time that places the peak between 1/3 and 1/2 of the scale. Don't forget to take flat frames at the end of the session. Stack, post-process and enjoy.

HTH

[Daf1983]

I used my 600d with a 135mm Carl Zeiss lens, which was much slower than your 50mm. I had it on a Omegon Minitrack, which could only manage subs of about a minute before star trailing. I always used either iso 800 or 1600, with some decent results.

You will probably manage longer subs than me with your mount/lens combination. Personally I would start off at iso800, as  that is the sweet spot for that sensor

[drjolo]

I think ISO800 is a good starting point, however as far as I remember this Canon 50/1.8 lens requires to be stopped down. Just make several images of some star field with the same EV to compare, so f/2 at 30s, f/2.8 at 60s, f/4 at 120s and then inspect the images on the monitor to find out the optimal f stop, when stars look good. 

Edited January 29, 2022 by drjolo

[rickwayne]

The very best way is to experiment. Fortunately this need only take a few minutes. Stop down the lens a bit, take a series of progressively-longer exposures, and examine each histogram as it appears. When the big peak of the histogram clears the left edge of the graph, stop -- that's long enough. You want your exposure to be long enough that you're not clipping any of the image to black (including the sky background), but otherwise as short as practical, to avoid problems with star trailing, satellites, airplanes, etc. Stacking integrates total exposure time, which is much more important than the length of a single sub-exposure.

I've seen advice to put the top of the big histogram peak at 1/4 scale, 1/3, even 1/2, but all you really need is a little bit of flat no-signal space between its left edge and the edge of the graph. Too long a sub-exposure time (or too high an ISO) can give you the opposite problem, white clipping at the right side of the graph. Since stars are the brightest thing in astro images, that means your stars will lack color.

Shorter sub-exposures means you need to shoot and stack more of them to achieve a given total integration time, which can place practical limits -- nobody wants to manage 3,600 sub-exposures if they can avoid it!

As for total integration time, shoot as much as you can stand to image and process. For deep-sky objects, more is really better, although you hit diminishing returns pretty quickly. But think hours, not seconds or minutes.

Likewise, as drjolo recommends, have a squint at the stars to determine if the f-stop suffices to your needs.

[Kenboy]

6 hours ago, rickwayne said:

The very best way is to experiment. Fortunately this need only take a few minutes. Stop down the lens a bit, take a series of progressively-longer exposures, and examine each histogram as it appears. When the big peak of the histogram clears the left edge of the graph, stop -- that's long enough. You want your exposure to be long enough that you're not clipping any of the image to black (including the sky background), but otherwise as short as practical, to avoid problems with star trailing, satellites, airplanes, etc. Stacking integrates total exposure time, which is much more important than the length of a single sub-exposure.

I've seen advice to put the top of the big histogram peak at 1/4 scale, 1/3, even 1/2, but all you really need is a little bit of flat no-signal space between its left edge and the edge of the graph. Too long a sub-exposure time (or too high an ISO) can give you the opposite problem, white clipping at the right side of the graph. Since stars are the brightest thing in astro images, that means your stars will lack color.

Shorter sub-exposures means you need to shoot and stack more of them to achieve a given total integration time, which can place practical limits -- nobody wants to manage 3,600 sub-exposures if they can avoid it!

As for total integration time, shoot as much as you can stand to image and process. For deep-sky objects, more is really better, although you hit diminishing returns pretty quickly. But think hours, not seconds or minutes.

Likewise, as drjolo recommends, have a squint at the stars to determine if the f-stop suffices to your needs.

 

Thanks all, very helpful 

 

How do I improve from this, my histogram looks way off? 

 

Edited January 31, 2022 by Kenboy

[rickwayne]

If I'm reading that display correctly, you're way overexposed. Try closing the aperture  another stop (f/4) and decreasing the exposure time by half or more -- try 30 seconds.