Exposure?

[Samop]

Hi,

I'm just having my first go at astrophotography.

I've done "ordinary" photography for many many years so I know about exposure (when I first started it was all manual) but I'd like some guidance on how to calculate shutter speed. 

I could of course set the camera to spot metering and trust that my object is dead in the centre. Is that what you do or is it more hit-and-miss?

[tomato]

I would have a go at photographing the moon, it is bright enough for your metering system on the camera to work. 
Before you proceed further see if you can get hold of a copy of “Making Every Photon Count” by Steve Richards. It covers all the fundamentals of astro photography and will set you on the right track. 
I think it is fair to say that astro photography requires a very different approach to terrestrial photography.

[michael8554]

For the Moon, sub-1sec manual exposures would be less hit-or-miss than auto-exposure, adjust for best result.

For dim Deep Sky Objects such as Galaxies and Nebulae, much longer exposures are required, 10 seconds or more.

Michael

 

[vlaiv]

For astrophotography, you have to "unlearn" all you know from regular photography.

Common knowledge in regular photography is full of "shortcuts" and "implied knowledge" - and, while the same principles govern both types of photography - they operate in completely different regimes and hence you can't use shortcuts and implied knowledge - you must have complete understanding - or learn another set of shortcuts / implied knowledge - which is totally different.

In astrophotography - we work in light starved regime / photon counting. In regular photography - most of the time we have plenty of light so we don't have to worry about discrete nature of light and signal to noise ratio.

Signal to noise ratio is the key in astrophotography and you should think in terms of SNR rather than in terms of exposure. Total exposure in AP is usually measured in hours rather than seconds. We achieve this by stacking single exposures. This is for DSO / long exposure AP.

For planetary, we employ yet another technique / another aspect - called Lucky planetary imaging. Here it is also about SNR - but we approach it from a different angle. We have atmosphere to content with and we use extremely short exposures that are governed by how long we can expose for before atmosphere ruins the show (think of motion blur in sports in daytime photography) - and we take tens of thousands of such exposures and stack them to get good SNR (in planetary astrophotography normal exposures are order of 5ms and even less if target is bright enough - like moon or white light solar)

Another aspect of how long exposure should be is precision of tracking.

In any case, what do you want to image and what equipment do you want to use? If we know that, we can start discussing how to determine good exposure value (is it minutes or milliseconds ).

[Samop]

Thanks guys,

At this point, as an aged (😄) astronomy newbe I'll be trying to photograph the moon and planets.. 

Deep sky will be some time in the future..

 

 

[vlaiv]

8 minutes ago, Samop said:

Thanks guys,

At this point, as an aged (😄) astronomy newbe I'll be trying to photograph the moon and planets.. 

Deep sky will be some time in the future..

 

 

If you want to photograph Moon, and you have DSLR - it is fairly easy - start with single shots of moon. Set your exposure to somewhere in range of 1/500 to 1/200.

If atmosphere is stable - you can go even longer to say 1/100

Image will probably be too dark - but you can fix that in post processing by adjusting brightness.

Image will look noisy. Here you start encountering noise issue and SNR and next logical step is to:

1. Watch youtube video that explains how to stack multiple exposures in software like RegiStax or AutoStakkert!3

2. Take multiple exposures (say dozen or so) of moon and apply above technique

3. Process resulting image to same brightness and you will notice it has less noise - or better SNR

Next step would be to get dedicated astronomy camera that can capture hundreds of images per second (without compression or distortion), a laptop with SSD drive and apply above technique to that data.

Also watch youtube videos that explain how to do this with movie recordings from planetary cameras (We call those movies since they are just bunched up frames into single file like a movie).

Learn about pixel scale and optimum sampling rate and wavelet sharpening and other sharpening techniques for processing of planetary images.

[900SL]

Assuming you have a DSLR and telephoto lens, from Nasa:

'lunar photographers actually have a rule of thumb called the Looney 11 that can be used as a starting point to photograph the Moon. At its most basic, the rule is to set the aperture at f/11, and make the ISO and exposure time the same. So if the ISO is 100, the exposure time would be 1/100. If the ISO is 200, the exposure time would be 1/200. Aim for a low ISO since the Moon is so bright ― 100 is a good place to launch your experiments'

For planetary, forget it unless you have very long focal length .. planetary needs 2000mm upwards, a mount and most shoot video to stack the best frames

[Samop]

12 hours ago, 900SL said:

Assuming you have a DSLR and telephoto lens, ......

 

Well 900SL,  I do have a DSLR but the telepohoto lense ins my telescope, which doesn't have adjustable apeture 😐

But those rules of thumb are still a good starting point so thanks for that.

Also, thanks Vlaiv

I just need to wait for a clear sky and a free evening.

[900SL]

What telescope and camera are you using?

[Samop]

My 'scope is a skywatcher Explorer 150p (with the 6"mirror) and the camera, I have the choice of a Nikon 200D or an Olympus EP8 Pen. Preference is the Olympus as it's lighter and the sensor has more pixels

[Mandy D]

1 hour ago, Samop said:

My 'scope is a skywatcher Explorer 150p (with the 6"mirror) and the camera, I have the choice of a Nikon 200D or an Olympus EP8 Pen. Preference is the Olympus as it's lighter and the sensor has more pixels

The Olympus has a micro four thirds sensor, which is smaller than the crop sensor of the Nikon, but you will fit the full Moon on either sensor with the 1200 mm focal length of the 150P. You'll just have to chase the Moon more with the small sensor. It will also be better on the planets with the smaller pixels. The advatage of the Nikon is a much wider selection of lenses to choose from for other photography.

Edited November 9, 2023 by Mandy D