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Comment by dylan604 | Hacker News Reader

Curiosity begs why(and how) do you do exposures for that long rather than stacking? With my 5D mkII (yes I still shoot on that old carcass) when shooting in West Texas, I get hella heat noise on 20 second exposures. I recently modified a small pelican case to hold my camera, and I was going to use those re-freezable ice packs for cooling the temps in the case down. I haven't been able to take it out for testing though.

I still want to pick up an a7sII. We mounted that to a telescope and cranked up the ISO. We could identify DSO as the telescope slewed to the next subject. It made framing super simple. Once framed, we'd drop the ISO back to realistic numbers for the actual image to be taken. With my DSLR, I'd have to take a 15 sec exposure just to see what I was looking at, and rinse-repeat for each adjustment.

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Yes I do mean stacking. Usually I do 30-60 seconds for a single exposure but often stack 1-4 hours worth of data.

The fact that the sensor is on for about 95% of the time through that process means that the heat isn't any different than a mirrorless setup.

Dark frame subtraction corrects reasonably well for this anyway. Cooled camera would perform better but that's a lot more trouble than it's worth for me as a hobbyist. I wouldn't recommend cooling with ice packs though. You want your sensor at a constant temperature through most of the data collection so that your dark frames actually work. If the temperature of the sensor fluctuates, your dark frames become not representative of the actual dark currents most of the time.

Can you configure the camera to take photos till you stop it, or do you have to buy an external device that connects the camera for this?

The device you are looking for is called an intervalometer. They come in all sorts of shapes, sizes, and prices. Each camera manufacturer uses a different connector as well as different connectors from the same maker, so you have to make sure you get the right one. Some cameras have one built-in (or can run hacked firmware to use one). The advantage is no external device needed. There's also software you can run on a laptop connected to the camera that will not only control the camera but also save the image directly to the computer. Lots of ways to skin the cat.

I use modified camera firmware to do this. With certain Canon camera models you can load Magic Lantern, an open source alternative firmware -- it includes intervalometer out of the box, and you can also write your own plugins and run scripts on the camera. (Separately: In general hackability is the #1 priority in deciding what gear I buy.)

For those playing along at home, be aware that the intervalometer from Magic Lantern has some issues with it depending on which camera body you are using. First, you cannot reliably shoot a timelapse with an interval of less than 5 seconds. This is something the ML tells you, and it is a known issue. If you try it, it will not take images at regular intervals as expected. It is very inconsistent by skipping one, double snapping on the next one, and other weird things. With a wired external intervalometer, I have no issues taking 1 second intervals.

That is pretty much the only thing that I have found about ML that I don't like. Everything else about it makes my camera a much better system. ETTR is my fave!

Ah yes. For astrophotography it isn't an issue though since each exposure is typically at least 15 or 30 if not more seconds.

It is admittedly hard to get the intervalometer to switch off though, often it keeps restarting itself after several restarts of the camera but eventually gives up.

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