Long exposures, noise and cloning

In the fortnightly competition I took a long exposure image of a church by moonlight. This raised some questions!

1. As I was using a tripod I kept the ISO to 400 and used an exposure of 30 seconds. The sky in this image is quite noisy. To minimise noise, is it better to up the ISO and keep exposure time down, or vice versa?

2. A plane flew across my best shot (it would, wouldn't it!). I contemplated keeping it in to emphasise the long exposure but in the end decided it was distracting. When I cloned it out, however, the cloned area is still faintly visible because the noise is, well less noisy. Any tips on how to clone in these circumstances?

Best wishes, Kris.

FWIW I tend to marquee and copy a section and paste it over the defect - to preserve noise characteristics. I use cloning for spot fixes.

C

1. I am doing an experiment.

2. Copy a noisier area. Silkypix Pro and Pixia allows you to copy a small spot from one area of the image to another. The edges of the spot are soft so it blends in. I would expect Photoshop to have something similar.

Some months ago I did some experiments with using several shots to make an exposure "total" bigger and averaging out the noise.

You could have taken you 4 shot at ISO1600 8 s (you get the same exposure right?)
Shots are noisy but if averaged out you get some good shots.

These are some results, handheld and used 2 or 3 shots to get the noise out of it. https://www.pentaxuser.com/forum/topic/test-shots-high-iso-16458
If you've a tri-pod and not doing it hand-held Like I did then you can take a lot more photos.

Also with you plane example if you took several shots, you can easily leave out the one with the plane instead of doing it over again for 30 seconds you only lost 8.

I have done the experiment - with exposures with lens cap on and no noise reduction. I compared 30 sec @ ISO 200, 15 sec @ ISO 400, and 8 sec @ ISO 800 on a K-7. I allowed time for the sensor to cool between exposures.

The longest exposure had the least noise.

I was surprised. I was expecting the compromise shot (ISO 400) to be the best, but it seems high ISO is the worst enemy for noise. Simple as that.

RAW + Silkypix. Exposure bias increased by Silkypix by 2 stops to make the noise more visible. No noise reduction (in pp & camera). Default sharpening. 100% crops.

30 sec @ ISO 200:
[IMG]http://i85.photobucket.com/albums/k59/iceblinker/-Tests-and-demos/K7002907.jpg[/IMG]

15 sec @ ISO 400:
[IMG]http://i85.photobucket.com/albums/k59/iceblinker/-Tests-and-demos/K7002909.jpg[/IMG]

8 sec @ ISO 800:
[IMG]http://i85.photobucket.com/albums/k59/iceblinker/-Tests-and-demos/K7002908.jpg[/IMG]

For a static scene why not use the in camera multiple exposure setting?

Interesting Pete, thank you. I would have taken the shot at 2 minutes at ISO 100 if I had (a) my cable release (b) some means of timing it and (c) it wasn't about minus 4C at the time! I was walking home across the fields when the moon rose and I thought, ah ha!

Anvh. Interesting idea re: multiple exposures but in this particular case it would have messed up my star trails! Amazing how far they move in just 30 seconds. I wasn't sure they would show at all and was worried the "dark frame subtraction" might have got rid of them as hot pixels. Useful idea and I'll keep it in mind for next time.

The glow on the horizon of that shot is light pollution from the town about seven miles away.

Best wishes, Kris.

When you have PS CS use the replace/repair option found under the heal brush or clone brush, I believe.
Draw around the trail you want to remove. Close the form. Then grab and move it to the area you want to use as replacement. This removes the trail but keeps the same noise structure. The quickest way with for this kind of subjects.

Thanks Malo, I didn't know about that one. I'll give it a go when I get home.

Kris.

Be careful with long exposures like that, you will see movement of the moon the same as you did the airplane. The ISO 100 and 2' exposure will create a moon that is oval. I made that mistake with the last eclipse I tried to shoot. As a matter of fact, the moon moved completely out of my view finder in two minutes.

Steven

The moon moves it's own diameter every two minutes hence the oval problem. In this picture the moon was behind me and I wanted the star trails to add to the night-time look. I actually had a problem finding a viewpoint where my shadow wasn't in the foreground!

For shots with the moon actually in the photograph, I think the only real way to get a decent shot is to create a composite with one image shot for all the foreground etc., and one with the moon correctly exposed. I have some shots from my night time walk home across the fields taken with that idea in mind but haven't had time to try my composite idea. It might just be pants LOL...

Best wishes, K.

I agree, I normally use a composite image when i include the Moon in my shots. I use a long exposure for the subject say 20-30 sec and then combine it with one of the photo`s taken years ago on my old K10D during the Lunar Eclipse. I feather the edges by a pixel or two and often brighten it a little to help make it look more natural then re-size it to cover where the original burned out Moon is in the start image.
as for cloning i use either the Patch Repair tool in CS as Malo described or sometimes just the standard Healing Brush if the area allows.

Regards- Pete.