Sagittarius

[PaulSthcoast]

Once again,
I thank Raymo and Martin for the inspiration to post an image.

While looking through my mobile I rediscovered a few images
taken with my DSLRS.

I enjoy taking single shots with various lenses, and most times they
are taken with an asi-air, mobile phone and at times a Skywatcher
Star Adventurer Pro, purely for ease and instant viewing, (Electronically Assisted Astronomy).

This image was taken on 22.09.20 with a modded Canon 1100D.

Single 5 second exposure, 135mm f2.5 Asahi lens, ISO 1600.

Thanks for looking.

Paul.

[raymo]

Good effort Paul, you should take some single exposures of 30 to 60secs unguided with your Star Adventurer reasonably well polar aligned, and using a much longer lens if you have one, say 250- 500mm. This is 30 secs unguided of Eta Carina with my 8" Newt at prime focus [Fl 1000mm]. With such long single exposures you won't get the noise control that stacking provides, so enable in camera long exposure noise reduction, and high ISO noise reduction features, remembering that the camera will take a dark sub of the same duration as your original sub, so the image won't appear on the screen until that process is complete. I apologise for teaching my grandmother to suck eggs as the saying goes if you are already familiar with these features. Have the noise reduction on the strong setting when taking only a single frame.
Actually, Eta Carina would look good at 250mm.
raymo

[astro744]

Well done Paul. Now that is what I expect to see with a single short exposure with settings similar to what I used with film all these years ago. I understand the camera is modded hence the nice colour of the nebulosity in M8 and M20 but the stars are all colourful too and this makes for a nice shot. Tracking of course is important for the longer focal length lenses.

[raymo]

Also remember that Paul's lens is more than a stop faster than mine was.
My 100mm f/2 shows a little colour at these short exposures; my zoom was operating at f/4.
raymo

[astro744]

40mm focal length, 7 secs, f/4, ISO 12800, (effective aperture 10mm)
135mm focal length, 5 sec, f2.5, ISO 1600, (effective aperture 54mm)

I had considered the slower lens at f4 but also thought the difference in ISO and slightly longer exposure would have made a difference. Perhaps reciprocity failure also affects some digital sensors and not only film. However there is a big difference in effective aperture at the given f stops. Could this be the reason irrespective of the speed/f-stop/ISO triangle. (Correct me if I’m wrong here calculating this).

[Startrek]

That’s a really good wide field Paul
Well done !!!
Just gotta get that HEQ5 and scope up and running hey. The weather lately has been poor for astronomy especially on the east coast of NSW ( up and down like a yo yo ) the forecasters said it will be be a wet summer with unstable weather patterns , they are dead right
Cheers
Martin

[raymo]

Something is wrong somewhere, because light gathering power of optics
is the diameter squared, so 10mm is 100 and 54mm is 2376, so the 54mm has 23.76 times the light gathering power of the 10mm, which seems a bit
ridiculous. I imagine that somebody with a younger/better brain than mine will help us out.
raymo

[astro744]

Yes of course area of the lens not the diameter is the factor determining light gathering. There is a huge difference in light gathering between the two lenses and whilst the ISO is 3 stops greater on the slower lens, even given its slightly longer exposure; the light gathering of the 100mm f.l. Lens at the slightly over 1 stop faster aperture but 3 stop slower ISO is clearly a key in capturing more colour. Like I said in my other post in the other thread, I will experiment myself a little further.

Didn’t mean to hijack your thread, Paul. I do like what you’ve achieved in 5 seconds. A few of those stacked and it will be stunning as Raymo achieved with his. Well done!

[Zuts]

You are correct, it's (D1/D2)^2, not that I have a better brain, and certainly not a younger one :)

I guess it sounds a lot but then a 60mm Tak will give good views and images, not sure of the mileage you would get from a 10mm scope...

Cheers
Paul

[raymo]

No further input from Paul. I apologise for your post getting hacked.
raymo

[PaulSthcoast]

Thank you everyone for your comments.

I didn't expect my post to create such interest and open discussion.

I am both honored and flattered by having it generate conversation and input.

Raymo, I am planning to post a few more images I have taken,
as this is the beginner astrophotography area, and if I cant post them here, well......we all start somewhere....right ?

Martin, thanks to you too.....you probably endure my images more than anyone here, and again, I thank you for your patience and encouragement.

Astro and Zuts, thanks for the input too !

Again, many thanks.

Paul.