My first serious effort at star photos.

[Mr Felix]

I was way out of the city and saw Orion.

Got the tripod and pointed it.

Did a few quick calculations and took the shot.

1 Min 30 and it looked ok.

When I look on the computer screen, ALL the stars have trails.

Would 1 Min 30 be enough for the rotation to show?



Just asking.

[William]

Where's the image so we can tell ?

In answer to your question 1min 30secs will leave star trails

[jasnat]

As a general rule under 30sec with a wide angle lens will have minimal trails.

[ameerat42]

What focal length did you use? I got trailing on Orion with 15 secs and a 24 mm lens. It is at that part of the sky that seems to moves fastest. No, it wasn't camera shake. I got it on 3 shots I tried with a non-SLR camera.
Am.

[gerry]

The longer the focal length the shorter your shutter needs to be, for example, 300mm + 1.7 converter needs under a second to reduce the movement of the planet.

a recent example:

[gerry]

actually here's a better example

30secs at 16mm only very slight movement on full res version.




and 4 secs at 85mm

[Mr Felix]

Ok folks, sorry I wasn't infront of my machine when I posted the question.

(Didn't know I had to be)

Home now and have image - see attached.

I tried a few shots before on other things and they didn't work. So I kind of guessed the time and just tried it.

After the shot I was impressed that it wasn't under/over exposed and it looked ok.

[Mr Felix]

On this, I remember where I came unstuck.

I kind of remember the "Trick" about exposoure calculation you up the ISO speed and get a shutter speed.

Then drop the ISO speed and you increase the shutter speed (or rather time) by the same number of steps.

But, this all falls appart when you run out of time for exposure.


To explain:
Say I set ISO 1600 Shutter speed 30 seconds, F7.

If that is 5 steps up from the desired ISO, what are the next steps after 30 seconds?


(Yeah, I'm gonna cop a flogging for asking.)

[William]

I think what happened, was you posted a question in the Main Critique Forum without an image, Asking for help , Still wondering if you wanted Help or critique on your image , I'm sure you got the help that you needed to try this again with different settings , Good luck for next time you try

[Mr Felix]

Yeah, well I would like to check that the "trails" were from the 1 min 30 sec exposure or movement of the camera?

I was playing with the settings because I couldn't get the exposure automatically. I had to use BULB mode.
And, without the cable release, and in the middle of a field with mosquitoes eating me alive as I am holding the camera, I wasn't sure what the picture is/was.

Now I uploaded the image, I would be interested if anyone can tell me if I am on the right track.

But the new post (18:42) explains my conundrum about how to calculate times when the shutter speed doesn't have numbers that "big".

[ameerat42]

Mr Felix. Don't flog yourself too much. 1.5 minutes where Orion stalks, near the celestial equator, is WAY to much exposure time for almost ANY lens that is not tracking the subject. OF COURSE, though I couldn't be sure, it would be a FAIR BET (you wanna bet?) that what you posted is NOT camera shake but star trailing. Think of Occam's Razor. Why invoke the less probable when the simplest explanation is to hand?

Yes, your focal length was 18mm, but as I said in the earlier post, I had appreciable trailing at 15 sec with 24 mm. Do the trigonometry: 360degrees in 24 hours is 15 degrees per minute, Over a focal length of 18 mm, 75sec (EXIF) is about 0.1mm on your sensor.

Given that it is an approx 1.5 crop sensor, that roughly translates to the trailing you have shown.

ONE Question: Is f/6.3 your widest aperture at 18mm? If you can go wider, ie, go to maximum aperture, and use an ISO of about 800-1600. Do a bit of noise reduction on the result, maybe. Keep it up, though. It's a challenge.
Am.

PS: Just read your last point. You do not "calculate" exposure times for stars. Bulb, widest aperture, most exposure time you can squeeze in before trailing is expected. Meantime, (Much later on summer nights) give the Southern Cross and Pointers a whirl. They are nearer the S celestial pole and their RADIAL motion is less than stars nearer to Orion. (Their angular motion is, of course, the same.)

[Mr Felix]

6.5 is not the widest.

I couldn't focus the stars (obviously) and so gave myself a bit of DOF before taking the shot.

It was DARK, and I wasn't really wanting to take it, but I saw the opportunity and so took it.

A few bad shots, then I guessed about 1.5 minutes.

Took the shot and was pretty happy.


I didn't realise I have the lens at 18mm. It is the 18 - 135 (IS) lens. I thought I zoomed in on Orion to frame the constellation first.

Dunno if the ZOOM is sent to the camea. But..... Anyway.


I didn't want to use higher ISO settings as they give noise and I am not wanting to start learing about that just now.

[Mr Felix]

6.5 is not the widest.

I couldn't focus the stars (obviously) and so gave myself a bit of DOF before taking the shot.

It was DARK, and I wasn't really wanting to take it, but I saw the opportunity and so took it.

A few bad shots, then I guessed about 1.5 minutes.

Took the shot and was pretty happy.


I didn't realise I have the lens at 18mm. It is the 18 - 135 (IS) lens. I thought I zoomed in on Orion to frame the constellation first.

Dunno if the ZOOM is sent to the camea. But..... Anyway.


I didn't want to use higher ISO settings as they give noise and I am not wanting to start learing about that just now.

[MarkChap]

Mr Felix, it is simple exposure calculation, if you halve your ISO, then you need to double your shutter time.

Unless you can achieve ISO 50 on your camera, which i doubt, if I remember correctly you have a rebel ?? then you won't have 5 stops of downward adjustment in your ISO any way.
SO ISO 1600 = 30sec -> 800 = 60 sec -> 400 = 120 sec -> 200 = 240 sec -> 100 = 480 sec.
So as you see, you could only achieve 4 stops adjustment

[ameerat42]

...I couldn't focus the stars (obviously) and so gave myself a bit of DOF before taking the shot...I didn't want to use higher ISO settings as they give noise and I am not wanting to start learing about that just now...

The 1st bit is interesting. You couldn't focus the stars? A 550D and live view? Doesn't it also have some sort of live view magnification? Did you set your camera to Manual and set focus to "infinity"?

"Normal" conditions don't really apply for astrophotography, so you have to take more control of your settings.

This is early in your astrophotography, and you got a fair result, not a bad one by any means. I'm only saying what to look out for. Another thing has occurred to me: did you take it from somewhere in Sydney? If so, you are really battling the light pollution and unclear skies. As such, the result is as good as you can expect for a static exposure as you took it.
Am.

[ameerat42]

Mr Felix.
After the foregoing posts, here's the result I got recently for Orion, as described above. Look at EXIF for details. Magnify it and you will see just the beginning of trailing. Now the only PP done on this was to sharpen it in the RAW converter.
Am.

Orion, Dec 2011.

[Mr Felix]

Mr Felix, it is simple exposure calculation, if you halve your ISO, then you need to double your shutter time.

Unless you can achieve ISO 50 on your camera, which i doubt, if I remember correctly you have a rebel ?? then you won't have 5 stops of downward adjustment in your ISO any way.
SO ISO 1600 = 30sec -> 800 = 60 sec -> 400 = 120 sec -> 200 = 240 sec -> 100 = 480 sec.
So as you see, you could only achieve 4 stops adjustment

Hi Mark.

I have the 550D - or that is what I used to take the image.

Yes, I sort of remember what you explained about ISO/shutter speed. But have forgotten the "extra" numbers.

So where I went unstuck is when I pushed the ISO to a high level, and got the shutter speed to 30 seconds, then wound the ISO back to a less noisy level, but then I didn't know the shutter speed time.

But thanks, now reading your reply, it is "double" if I read it correct.

So if I have ISO 400 and 30 seconds, and take it back to ISO 200, it becomes 60 seconds - right?

[Mr Felix]

The 1st bit is interesting. You couldn't focus the stars? A 550D and live view? Doesn't it also have some sort of live view magnification? Did you set your camera to Manual and set focus to "infinity"?

"Normal" conditions don't really apply for astrophotography, so you have to take more control of your settings.

This is early in your astrophotography, and you got a fair result, not a bad one by any means. I'm only saying what to look out for. Another thing has occurred to me: did you take it from somewhere in Sydney? If so, you are really battling the light pollution and unclear skies. As such, the result is as good as you can expect for a static exposure as you took it.
Am.

As much as you may be correct, you have to understand a couple of other factors.
1 - it was a grass field and it was cool and wet. The mosquitos were eating me alive.
2 - Yes, setting the lens to "infinity" would have worked - probably. But in the past when I have tried, "infinity" is too far and I get blurred images.
3 - the lens focus isn't marked. I am still stuck knowing which way to turn it manually to focus close and far. Yeah, I'm an idiot. I've been told, many times.
4 - it wasn't the main objective of the mini-trip. I was taking images of the moon, some buildings and a party which was going on, and some planes.


No, this photo was taken in the Hunter Valley so the light was not a problem and it really was a nice clear-ish night and I looked up and saw Orion and thought I would "give it a go".


And don't mis-read my reply as upset or annoyed. I am not. I'm just mentioning things - which I maybe should have earlier.

I've got a whole heap of images to go through from other things done those three days.

[ricktas]

So if I have ISO 400 and 30 seconds, and take it back to ISO 200, it becomes 60 seconds - right?

Yes, as long as you do not adjust the aperture at all.

[I @ M]

As much as you may be correct, you have to understand a couple of other factors.
1 - it was a grass field and it was cool and wet. The mosquitos were eating me alive.

A couple of tips ----

You have been given correct advice on the photography side of things, absorb it and put it into practice.

Wear gumboots.

Carry a torch.

Take Aeroguard at anytime you might venture into the great outdoors.

Stop dwelling on the irellavent side issues of mozzies, darkness and damp and concentrate on learning about the correct way to use a camera.