morkie1891

I have been reading and occasionally posting in UHH for a few years, mostly Active Topics, and now want to explore deep space object photography - with a mirrorless Sony and no tracker. In researching technique it seems some recommend a longer exposure - 30 sec and others recommend Stacking 200-300 short exposures using calibration frames and Astro stacking software. I don’t understand how stacking the Short exposures achieves a proper exposure. (I do understand the resulting noise reduction). I plan on using my A6500 with either a sigma 30mm or Sony 70-300mm. Could someone please explain how stacking the short exposures results in appropriate exposure? Thank you

Paul Diamond Loc: Atlanta, GA, USA

Hi, I'm definitely not the best resource here. But, the earth rotates and makes pictures of stars into "trails" with longer exposures. You said you don't have a telescope or star tracker mount. Due to technology we can now use, our camera sensors allow us to record multiple recorded images of a star, etc. before it is blurred by the earth's rotation. Stacking these images will combine the un-blurred images into one. Other exposures, like a dark field, will record the way that the software will treat the non-stellar areas of your image as 'black', increasing the contrast and appearance of your stellar images.

morkie1891

Thank you Paul

SonnyE Loc: Communist California, USA

Hi Morkie, and Welcome to the Astrophotography section!

OK, in a nutshell, what stacking does is to take a bunch of images, each having what data they caught, and it combines them into a single rendition of the image.
Programs like Deep Sky Stacker do this by aligning key stars it finds to get the clearest stack of images. Best part: It's Free.
And there are You Tube tutorials to help you get into it.

I don't do that. Never had a camera good enough.
Instead, I use an Atik Infinity camera which is a One Shot Color camera (OSC). And it stacks the images it collects automatically for me. Perfect for a lazy dummy like me.

If you find you like this sport, you will eventually want to delve deeper into it.
When I was considering AP, I took a month to convince myself I wanted to. There are literally billions of images on the WWW. I decided, Yes, but they aren't MY images.
Then it was WHAT do I want to get out of this? Me, I like Nebula, but the Moon, Planets, Star Clusters, The Sun (with proper filters), and on, interest folks.
As I researched how to do what I wanted to, DSO, the telescopes got smaller and more refined. And I realized to value of guiding, and of dedicated Astronomy cameras.
I made several mistakes in the beginning. Trusting old names, buying equipment I could afford that was less reputable than dog doo.... I've over come most of those errors.

I began imaging the Moon with my DSLR and Tamron 150-600 mm lens. Then started shooting Star Trails.

This isn't an inexpensive sport, and there are no regulation balls or equipment. Rather take advice as generic and apply it to your goals.
Can you get by with less expensive trackers? Sure, but like relationships you'll be compromising.
If you think you will be getting into the sport up to your eyeballs, the age old advice of getting the best equipment you can afford applies.

Besides these guys, some of the best advice I found was from Forrest Tanaka. http://youtu.be/9d0292TBMHo

JimH123 Loc: Morgan Hill, CA

It is true that stacking many short exposures can improve the image. There are also options for stacking that can operate in accumulation mode to build up those exposures.

The best exposures are those that produce a histogram that moves toward the center of the screen. You don't want to expose so long that pixels start to saturate. But you have to track for that.

And you don't want ISO so high that that noise is so bad that it is hard to recover from.

The 1st image I am posting is one from a stack of images taken at ISO 1600 for 10 sec each. And then, after stacking 10 of them using the free SW sequator and setting up the appropriate conditions, image #2 was produced. I did treat the noise in the final image. I did very little stretching.

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morkie1891

Thank you, I need to experiment with settings and time.