Fstop making night time shots blurry?

[mongoose]

I shot some photos the other night from the top of Mt. Monadnock. I didn't have too much time to experience since it was cold and people wanted to get moving. What I noticed was that photos shot at F/8 were nice and sharp, photos at F1.8 were blurry. Why is this? Does a wide aperture make the lights flare out? I read through my photography book and the recommending aperture settings were f/2.0 or so. Here's a sample comparison.

[Frog]

Your f1.8 has such a shallow depth of field that only one point in the photo is in focus, though I will admit I can't find it.
At f/8 you have much more dof.

[SmartWombat]

Which photography book?


Lenses are usually sharpest when not wide open, but with the aperture closed down 3 or 4 stops.
Your images show that very well, wide open at f/1.8 is not as sharp as f/8

The embedded EXIF in your image shows 30 seconds f/8, you've combined both pictures into one. Did you keep the shutter speed the same for both, at 30 seconds?
I think the f/1.8 image is over exposed.

It's hard to give an exposure to use, it depends on the lights, the weather conditions, the ISO setting ... lots of things can vary you can't control - only a few you can control.
Your meter will be misleading too, it's trying to adjust the exposure for mid-grey and there isn't any in the image. So its best guess may be far away from what you need.

Your best check on the exposure is to use the histogram in your camera.
Look at the Digital Camera Histogram Guide in our Learn section.

[brmill26]

Looks like the exact same problem I had - read this thread, and the link:

Focus problem

[mongoose]

Frog:
Does DoF matter at that distance? It should be focused on infinity.

Wombat:
I double checked my EXIF data for the two images. The first one is: f1.8, 3sec, 250iso. The second is: f8, 30sec, 250iso. I let the camera figure out the exposure, I set the aperture. It's a Nikon D80 with a 50mm lens. The book is "The Basic Book of Photography 4th ed."

I noticed something else when zooming in. All the lens flares move away from the center of the image. They are like searchlight cones on each point of light expanding outward away from the lens center.

I guess the obvious solution is to shoot at f8. I didn't think aperture mattered at that distance.

[SmartWombat]

DoF always matters.
You're not going to have infinite depth of field.
So there is always a compromise.

For your camera & lens you'd need to focus at 230 feet to get a depth of field to infinity.
But at f/1.8 of you focus closer, say at 100ft, then you only get 107 depth of field.
Only another 77 feet beyond your focus point, and 30 feet in front of it.

http://www.dofmaster.com/dofjs.html?...0&units=0.3048

[Greg McCary]

Higher f/stops with night lights will create a star effect with the lights instead of just blowing them out. You can see it in the second shot. Since modern lenses have no DOF markings on them you should focus one third way into the shot. It really isn't a good idea just to focus the camera to infinity.
http://www.vividlight.com/articles/3513.htm

[AgingEyes]

Since modern lenses have no DOF markings on them you should focus one third way into the shot.

It may be kind of difficult with a dark scene like that though

Besides, I think even if he could do it, he still needed a smaller aperture, For landscape photo, I think it should be at least f16. Depending on the lens, f8 may not get you sharpness all the way to infinity. And if you're shooting the sky, things could get even more tricky. Of, I forgot, it's a dark scene so may be it doesn't matter

I hate lens without dof markings. I used to simply set dof through those markings instead of doing the focusing on something. Given today's technology, I wonder why the camera can't show the dof...like actually telling us the dof of 50ft to infinity on the viewfinder. It's just another formula, another calculation, another piece of info to display. No?

[Dylan8i]

Haha so thats what the view looks like from the top. a few years ago i climbed the Mt. in a noreaster, and it was about 5 feet visibility, 60 mph winds, etc.


id deffintly say opening up the aperture should be better, i know for fireworks etc f8 or f16 are usually used.

[SmartWombat]

id deffintly say opening up the aperture should be better, i know for fireworks etc f8 or f16 are usually used.

Ah that's backwards.
Opening up the aperture to let more light in is a lower f/number, closing it down to let in less light is a higher f/number.

[another view]

Looks like the exact same problem I had - read this thread, and the link:

Focus problem

Very similar situation in a lot of ways and a lot of good info here. Thanks for linking it.

As I said in that thread, turning the focusing ring until it stops doesn't always guarantee infinity focus but that's usually more of a problem on longer lenses - some will focus past infinity. I wonder if the focus isn't quite dead on in the first shot. If it isn't, that would make the blur of the lights a little bigger as it shows here.

[Greg McCary]

Very similar situation in a lot of ways and a lot of good info here. Thanks for linking it.

As I said in that thread, turning the focusing ring until it stops doesn't always guarantee infinity focus but that's usually more of a problem on longer lenses - some will focus past infinity. I wonder if the focus isn't quite dead on in the first shot. If it isn't, that would make the blur of the lights a little bigger as it shows here.

That was my thinking on my lens. My focus can be soft at times if I just throw it up and focus to infinity. Just like the old manual focus lenses you have to back off just a little to get infinity. If I focus one third way into the shot my pictures are sharp.

[readingr]

I always use lowest ISO possible 50/100, F11+ normally highest F22, focus on infinity, and a very sturdy tripod. Then bracket the time and check the histogram, but remembering you will have a load of black showing, and check I have not washed out the lights.

Hope that helps.

Roger

[mongoose]

Ok, thanks for the info everyone. I'll stick with an f8 or higher fstop and do a little bracketing next time.

[SmartWombat]

Roger at F/22 aren't you going to find that it's less sharp as you run into diffraction?
You've got a magic lens there !

[freygr]

I have two 50mm lenses a 1.4 AF and a 1.8 AI. With the plain mat focusing screens in the digital AF cameras, it's hard to get critical focus in manual focusing mode. I have a feeling that the l your lens was not focused it infinity.

A good and non-technical web link about exposure, DOF, and lens angle of view: http://web.mit.edu/vap/images/guides/camera_basic.pdf

[readingr]

Roger at F/22 aren't you going to find that it's less sharp as you run into diffraction?
You've got a magic lens there !

I didn't make myself clear - it depends on the subject - the landscape example would be F8/11, I was thinking on some of the night time shots like the Spinnaker Tower shot where I I have used F22 and it worked well but it is very well lit subject.

Roger

[EOSThree]

When I took photography classes a longer shutter speed with a smaller aperture was preferred to a large aperture and shorter shutter speed when shooting at night. Unless you have a variable that needs the faster shutter speed why not use the smaller aperture?

[gahspidy]

I always use lowest ISO possible 50/100, F11+ normally highest F22, focus on infinity, and a very sturdy tripod. Then bracket the time and check the histogram, but remembering you will have a load of black showing, and check I have not washed out the lights.

Hope that helps.

Roger

Alot of good ideas and suggestions already. Roger, just a note about your 5D and ISO 50. I have read on Canons website that the expanded ISO 50 is not actually any better in quality than 100, and in fact has a loss of dynamic range in the highlight areas. So, it really is only to be used if you absolutley must have a slower shutter speed and there is no other alternative. Expanded ISO 3200 on the other hand is very usable and I had great results with it in a Dance theater Performance I shot with it a month ago.

Mongoose, i would agree that your image shot with a 1.8 aperture probably is mainly sufering from a poor focus . whatever was in focus should have came out sharp but would have only suffered from a limited DOF. Night scenes generall look better with a stopped down perture anyway though as the lights tend to get that starry effect and things are a bit sharper all around.

[readingr]

Alot of good ideas and suggestions already. Roger, just a note about your 5D and ISO 50. I have read on Canons website that the expanded ISO 50 is not actually any better in quality than 100, and in fact has a loss of dynamic range in the highlight areas. So, it really is only to be used if you absolutley must have a slower shutter speed and there is no other alternative. Expanded ISO 3200 on the other hand is very usable and I had great results with it in a Dance theater Performance I shot with it a month ago.

Gary

The ISO 50 is used on the Powershot Pro 1 where it does do a lot better than 100. I never take the 5D below 100. Sorry should make things clearer. If I used the AE1 it could be ISO 25 dependant on the film of course

Roger