Exposure time

[Kenza]

I regularly read the Astronomy magazine. The Reader Gallery at the back contains images from amateur astronomers and what puzzles me is the exposure time for the images.

What do they mean when they say for example that the "exposures were 6 hours, 3 hours, 3hours,  respectively". Does this mean that they were taken over a couple of nights?

[oldpink]

could be that or the time for each filter if they are using a Mono camera and Lum frames

[RikM]

There is typically a bit more detail included with the times but it is normal to list the exposure times used with each filter e.g. my current image project has 3.5 hours Luminance, 3 hours H-alpha and about 40min each per colour red green and blue. So far this has been over 3 nights.

[Kenza]

Yes, they usually are mono cameras with LRGB and Narrowband filters. So you do take images over a couple of nights. But how do you know that you have framed the object exactly the same as the night before. They would be different frames each night and isn't that difficult to stack afterwards, or am i wrong?

[RikM]

For DSLR images I use Astrophotography Tool, and this has a feature that you can create a framing mask. You click on bright stars and it records circles. On the next night, you load the mask, take an image and then adjust your mount so the stars line up with the mask circles and you will be in the right place.

For CCD images, I use PinpointLE (within Maxim DL) and this analyses the image and calculates the RA and DEC coordinates of the image centre, the next night you load up a previous image, solve it and then the software controls the mount motors directly to point to exactly the same place.

There is also a program called AstroTortilla which can do the same thing but I never used it myself.

[Uplooker]

There is also a program called AstroTortilla which can do the same thing but I never used it myself.

I am a recent convert to AstroTortilla and can not sing it praises highly enough. there is a bit of flaffing about to get it set up but once done its great. there is a very good guide on here:-

http://stargazerslounge.com/topic/193470-my-tutorial-for-installing-setting-up-and-using-astrotortilla/

The only problem you have then is making sure your camera is orientated the same way

Ian

[Kenza]

So that's how you do it. Which version of MaximDL do you need for mount control and PinpointLE? And also, is it better to buy the boxed version or to download it?

[RikM]

I use V5 Pro as a download. It is expensive, but I use it for almost everything that isn't photoshop.

APT (cheap and very good) will also control CCD cameras and works with AstroTortilla (Free!) and PHD guiding (Free!).

[Kenza]

Thanks for the help!

[lensman57]

I regularly read the Astronomy magazine. The Reader Gallery at the back contains images from amateur astronomers and what puzzles me is the exposure time for the images.

What do they mean when they say for example that the "exposures were 6 hours, 3 hours, 3hours,  respectively". Does this mean that they were taken over a couple of nights?

Hi,

The exposure time ( per single sub ) is rather different to what you are describing as it is more accurately known as total  integration time. If the image was taken with an OSC camera with 12 subs of 600s each then the total integration time is  12X 600=1200s or two hours and can be done in one session. If the image was taken using LRGB or NB filters then each filter has its own integration time of 12X 600s and therefore the total integration time will be an addition of all these times and in particular in the UK due to our fickle weather this data has to collected over many sessions. Hope this helps.

A.G