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Old 19-08-2017, 03:43 PM
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Sagittarius with short exposures and wide aperture

This is really a test image. I was testing the theory that lenses with a larger aperture make for deeper more noise free images.

So I took 17 x 6 seconds ISO5000 photos at F1.8 with a Zeiss 55mm lens.

Processed them in Lightroom to taste then aligned and stacked them in Pixinsight then final colour in Photoshop cc.

No noise reduction has been done.

So 55m at f1.8 = 55 divided by 1.8= 30.56mm.
Compare that to the Irix 15mm F2.4 image at ISO6400 x 10 second exposures (less overall exposure as only 5 images but its a lot noisier).
15 divided by 2.4 gives 6.25mm. So the 55mm lens is nearly 5X more light and it shows.

Whether or not you are patient enough to take a 26 image panorama with a 55m lens is another story.

So the bottom line seems to be if you use an ultra wide angle lens you are not getting in a lot of light and need to expose longer or take more subexposures and stack to compensate. Or use a longer faster lens (the longer the lens the less the coma is an issue it seems) and take a lot more panels to compose a panorama but they will be very deep. Or use a tracker and use longer exposures on the UWA lenses.

Greg.
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Old 19-08-2017, 04:40 PM
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You've basically just explained why I like mosaics so much
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Old 19-08-2017, 05:22 PM
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Originally Posted by Atmos View Post
You've basically just explained why I like mosaics so much
Yes mosaics tend to overlap and you get a similar effect. But I would use a tracker ideally when doing a mosaic with an ultra wide lens to overcome the lack of signal.

Greg.
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Old 20-08-2017, 12:00 PM
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Quote:
Originally Posted by gregbradley View Post
So the 55mm lens is nearly 5X more light and it shows.
.
Hi Greg.
I think you will find the 55mm lens does indeed have 5 times the apeture but it collects 24 times more light on rough figures.

That is why i like using longer focal length fast primes for milkyway shots too 😊

Cheers, Josh
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Old 23-08-2017, 10:00 AM
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Hi Greg.
I think you will find the 55mm lens does indeed have 5 times the apeture but it collects 24 times more light on rough figures.

That is why i like using longer focal length fast primes for milkyway shots too ��

Cheers, Josh
Working out the area of each and comparing? Yes I suppose once you add pi and square the radius in their the areas get larger quickly.

I take it you don't mind the extra work of taking so many more images to stitch? Do you still stack multiple images at 50mm?

Greg.
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Old 31-08-2017, 10:13 PM
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Originally Posted by gregbradley View Post

I take it you don't mind the extra work of taking so many more images to stitch? Do you still stack multiple images at 50mm?

Greg.
Hi Greg,

No not really, at 50mm I regularly take 80 shot panoramas. I only stack at 50mm when im not doing panoramas or maybe 2 or so frames.

regards
Josh
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