test exposures with Alt-az tripod

Here's some test images with an alt-az mount. The purpose of the test was to experiment with focal lengths and exposure times to estimate acceptable exposure times without excessive blurring of the image. Processing was minimal. All images taken in RAW mode of course. Images not cropped.

100mm focal length; f/4.5; 4sec exposure; ISO200
www.astroshot.com/Wide%20Angle/Test%20Im...4.5-4secs-iso200.jpg

100mm focal length; f/4.5; 6sec exposure; ISO200
www.astroshot.com/Wide%20Angle/Test%20Im...4.5-6secs-iso200.jpg

400mm focal length; f/5.6; 4sec exposure; ISO200
www.astroshot.com/Wide%20Angle/Test%20Im...5.6-4secs-iso200.jpg

400mm focal length; f/5.6; 4sec exposure; ISO200
www.astroshot.com/Wide%20Angle/Test%20Im...5.6-4secs-iso200.jpg

400mm focal length; f/5.6; 6sec exposure; ISO200
www.astroshot.com/Wide%20Angle/Test%20Im...5.6-6secs-iso200.jpg

250mm focal length; f/5; 6sec exposure; ISO200
www.astroshot.com/Wide%20Angle/Test%20Im...-f5-6secs-iso200.jpg

250mm focal length; f/5; 10sec exposure; ISO200
www.astroshot.com/Wide%20Angle/Test%20Im...f5-10secs-iso200.jpg

100mm focal length; f/4.5; 10sec exposure; ISO200
www.astroshot.com/Wide%20Angle/Test%20Im....5-10secs-iso200.jpg

Lessons learnt? Exposures are limited to about 2-3 secs when in alt-az mode; ISO200 and RAW help keep the images really noise-free and I need to take more test exposures.

All look great to me. I really like No.4

Actually now i look AGAIN...............No.5 onwards seem to lose detail. Lots more blurriness in them. So stick to the settings of the 1st four.

A thorough test there Michael, even at 100mm, trailing will occur after about 3 seconds (if you are using a canon dslr, chances are you are using the x1.6 multiplication factor as a 35mm camera size is 1.6 times bigger than the sensor in the dslr, so effectively 100mm = 160mm)

So with alt-az, it's all about capturing the most amount of light in the least amount of time. don't worry so much about ISO as 3-5 seconds at ISO 800 upwards is not really going to be a big probem unless it is really warm outside, or your camera is warm from inside your house.

Set the aperture f stop as wide as you can, and step down if your subject is too bright, mainly this will be the moon, because anything else will only benefit in general from more light gathering power.

Also, is it a zoom lens you are using, if so, the higher the focal lenghth, the less the maximun f stop you will be able to use.

I think you are getting through the pain barrier (I learned with film !!!! :evil: ) and these tests will hold you in good stead.

Keith..

Thnaks Paul and Keith.
I'm mainly trying these exposures with the solar eclipse in Russia in mind. I'm hoping to just use a standard alt-az tripod rather than bringing a mount with me. The test has been useful to see the extent of diurnal motion in short exposures at these focal lengths.
Next time, I'll limit my exposures to less than 2secs and try ISO400 for comparison.
Cheers,

Michael, you're pretty much coming to the same conclusion I did when I was testing my scope rig for the eclipse in Turkey, I found 1 second was the max I could use at 500mm focal lenght without noticeable trailing and I had to use iso400 to get an image bright enough, this is why I was thinking of getting a motor for the skylux.
Of course the difference here is that I'm using a F5 4" aperture.

Keith g wrote:
I think you are getting through the pain barrier (I learned with film !!!! :evil: ) /quote]

:shock:

Good grief!
I did photography in art college for a few months and boy did
we waste a shed load of film!
(all a learning curve though)
With digital, you can learn so much faster.

Mike,
Thanks for posting this up.
It makes for a great test card for the different settings.