The Big Dipper

The general appearance was achieved from one frame but the sky was a bit noisy because of the 6400 iso. setting used.

Because of the star rotation I couldn't just stack frames for the entire image because if I had aligned them for the edges or the watch post there would have been multiple images of the stars.

By aligning the stars instead, there would be multiple images of the stonework and foreground so that had to be masked out of the upper two layers.

The advantage of doing it this way is the rotation means that the re-aligned sky falls on slightly different parts of the sensor.

When the layers are set to the darken mode any random lighter pixels, which are caused by noise rather than the stars appearing in all three frames, are blended to the darkest value of the three layers which eliminates any hot pixels and most of the troublesome noise.

Interesting explanation, I learned something, thank you.

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Originally Posted by Nicks Pics

I'm using a bridge camera; however,

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Bridge cameras I have seen use the 'equivalent focal length' on their lens rather than the actual which in turn is found around the front of the lens ....ie 25-600 on the lens barrel and 5.5- 132 arouind the lens so I have never bothered about the crop factor until I got a MFT camera :)

The crop factor would be hard to figure out with such a small sensor and fixed superzoom lens.

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Originally Posted by Nicks Pics

So did you not need more than one image to make that general appearance, apposed to using HDR, or something like that?

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While I have never seen the Milky way but with limited knowledge taking astrophotography, I would say a couple of frames at enough integration time should suffice for the milky way. In the case of the Orion image above, I took 30 secs x 50 frames and then stacked them together ( Raw only ) to reduce noise as well as by stacking to obtain more data to stretch in Photoshop etc.,

I would assume if the location was dark enough and only lit by the bulge of the Milky Way, there should be enough light to capture with a 20 secs at ISO 1600. If the Milky way is very dim then perhaps you need to stack multiple exposures of 20 secs to obtain a good signal.

I did not consider originally that the Milky Way was not visible to you. Maybe you'll get to see it sometime anyways. Did you mean you took 50 shots of the same scene and combined them all? Are longer exposures preferable in astro photography, or is a shorter exposure preferred? In other words: Would you like to be able to use a long exposure, or would you like it if you didn't have to use a long exposure on a given scene?

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Originally Posted by Nicks Pics

I did not consider originally that the Milky Way was not visible to you. Maybe you'll get to see it sometime anyways. Did you mean you took 50 shots of the same scene and combined them all? Are longer exposures preferable in astro photography, or is a shorter exposure preferred? In other words: Would you like to be able to use a long exposure, or would you like it if you didn't have to use a long exposure on a given scene?

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Yep I took 50 exposures in Raw at 30 secs each and then stacked them together with Deep Sky Stacker. Longer exposures are preferable as long as you don't washout your "Lights" ( lights are the Raw captured in astrophotography terms ), however for longer integration work you need dark skies without the city light dome and light pollution. I am limited in this regard thus the 30 secs or max 50 secs without washing out my lights. To answer your question specifically, both attain the goal similarly but the signal to noise ratio may get accentuated depending on the object. There are objects with good surface lumonisity, eg., Andromeda galaxy or low luminosity like Horsehead nebula for example. Therefore for objects such as Andromeda galaxy, one could capture a whole lot of sub frames and stack them together whereas for Horsehead nebula, you may need to expose long enough to let in photons to obtain detail. You either take short exposures into x number of frames or longer exposures into x number of frames, as long as there is enough signal to process your image with detail and colour.

On the question of noise, what we normally do is after taking in our light frames, we then take "Darks", at the same ISO and exposure as the Lights. We then take "Offset / Bias" frames which are done using the fastest exposure speeds but at same ISO. We then combine the Lights / Darks / Offsets ( all Raw ) with use of Deep Sky Stacker and stretch the histogram and then process with Photoshop etc.,

The Dark frames substracts the noisy pixels from the lights. Alternately you can use the in-camera noise reduction feature but your Lights will take double time to finish, i.e., a 30 secs will take a minute. Normally we take darks separately for fear of clouds rolling in.

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Originally Posted by Nicks Pics

The crop factor would be hard to figure out with such a small sensor and fixed superzoom lens.

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The crop factor has been worked out and is mentioned occasionally but it is immaterial to using Wayland's interesting formulae so long as you know the equivalant focal length being used. I seem to remember it is around 5.5x . In using the guideline one should also include the degree of cropping to be performed in post, if any. In using the 280mm AoV of my MFT with a quarter crop the effective AoV is 560 if my maths is right :)

Alternatively when using my bridge with its x26 rig, a quarter crop gives me a 1900mm AoV and OIS gave satisfactory results at 1/400 shutter which bears out the claims for OIS of 2<3 stops.

Thanks I found this interesting.

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On the question of noise, what we normally do is after taking in our light frames, we then take "Darks", at the same ISO and exposure as the Lights. We then take "Offset / Bias" frames which are done using the fastest exposure speeds but at same ISO. We then combine the Lights / Darks / Offsets ( all Raw ) with use of Deep Sky Stacker and stretch the histogram and then process with Photoshop etc.,

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The crop factor has been worked out and is mentioned occasionally but it is immaterial to using Wayland's interesting formulae so long as you know the equivalant focal length being used. I seem to remember it is around 5.5x . In using the guideline one should also include the degree of cropping to be performed in post, if any. In using the 280mm AoV of my MFT with a quarter crop the effective AoV is 560 if my maths is right

Some of this I did not fully understand so much, AoV and OIS are not very familiar terms to me, too much of a novice. Sorry...

Thought I join in the conversation.

Haseeb Modi or anyone interest about shooting milky way in light polluted areas. See the works of Justin Ng Photography where he shot the milky way over highly light polluted Singapore. It can be done. I joined his tour to shoot the milky way in Mt Bromo.

Interesting stuff. As he says, most people would just fake it and come away with a better looking image.

Must be frustrating to get it right and not be believed.

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Originally Posted by teokf

Thought I join in the conversation.

Haseeb Modi or anyone interest about shooting milky way in light polluted areas. See the works of Justin Ng Photography where he shot the milky way over highly light polluted Singapore. It can be done. I joined his tour to shoot the milky way in Mt Bromo.

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It can be done ofcourse and I have done so but not satisfied with the results. However I cannot see it. I have been in Singapore many times and I can safely say my city where I live is far more light polluted than Singapore.

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Originally Posted by Nicks Pics

Some of this I did not fully understand so much, AoV and OIS are not very familiar terms to me, too much of a novice. Sorry...

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Sorry in return :)
AoV = Angle of View
OIS = Optical Image Stabilisation [ if in the lens ]
and IBIS = In Body Image Stabilisation [ when in the camera itself ]

Some people are more familiar with quoting the actual angle in degrees ... which I have never managed to understand and simply quote the effective focal length in 35mm film camera terms, though it is all relative and I have absolutely no idea of what angle is what.