How to focus in the dark

[mactac]

Viewed on my Nexus 7 and using my reading glasses, I don't see much wrong with your stars. They are rather a long way away so I wouldn't expect to see their alien occupants, if any.

If they are too soft for your liking, have you tried sharpening in post?

The problem is that they are OOF, and therefore creating big bokeh circles. In other words, you're looking at the bokeh of the stars, not the stars. The stars are much smaller.

Sharpening in post sadly won't help, I don't think.

 

[mactac]

Since there aren't any high contrast areas to lock AF focus on you need to go to manual focus set at or near the infinity mark (don't go past it to the extreme end). Live view at 5x or 10x is another option to fine tune it...........

 

[mactac]

Hi, first, everything in the sky/earth is moving so
long exposures defeat the completely in focus
theory. Read up on Hyperfocal distance/
focusing... Read up on Astro photography..
Nice pic '(^_^)'...

Yes, that part I do understand, but the problem that I stated is not that I am seeing star trails. I'm having difficulty focusing on something I cannot see because there isn't enough gain in the sensor.

 

[mactac]

30s will cause stars to be blurry because of movement of earth, 15s is the maximum for a sharp star shot unless you stack or other techniques.

I'm not having problems with star trails, I'm having problems with focus.

 

[mactac]

Often with night shots where you have to 'guess' at the focus and just set to infinity on the lens assuming it will work, you find things can be a little out of focus. Most AF lenses actually allow the focus to be set just a hair PAST infinity - most seem to agree that this allows the AF system the adjustment room it needs at the infinity end to fine tune and adjust for infinity, with the problem being when you switch to manual focus and go all the way to the infinity stop, you're actually a bit past and now out of focus.

You can try to guess where the actual infinity focus is, or test it in daylight conditions...and maybe mark it on the lens for reference. The other suggestion being live view - which can sometimes help as the live-view off a main sensor will often be able to gain up the view significantly allowing you to see objects you couldn't with the naked eye. Plus you usually have the ability to magnify the view on the LCD to allow you to zoom in tight on a very small light source that is otherwise hard to discern, and help dial in the focus accurately.

Sometimes old manual lenses are at a bit of an advantage here, as infinity is usually pretty accurate and there's no extra play beyond infinity - I find shooting manual lenses at night I can slam them to the focus stop point of the lens and fire, and know I'm at proper infinity focus. With my AF lenses, I have to be more cognizant of the play.

 

[zackiedawg]

live view mf

Perhaps I didn't explain myself correctly - that's exactly what I'm trying to do, use MF in live view, but there isn't enough light to actually see what I'm focusing on, hence the 30s exposure.

Mac, I think part of this is 'lost in translation' - the problem is that not all cameras behave the same in 'live view' modes. I believe Nikon does not have an option to display 'exposure simulation'...that's probably what's throwing some folks off. Canon & Sony for example in live view can be set to a mode that significantly gains up the live view to approximate the exposure you will be getting based on your settings - so if you open the aperture, and crank the ISO to 12,800, the screen will be very very bright, and you'll be able to see things that you cannot with your naked eye. Once you set focus, you can turn this function off, or reduce the ISO back to a lower number and take the exposure however you like. Many that are telling you to try live view are probably using cameras that do this exposure simulation...it's likely that you can't on your camera.

 

[mactac]

First... That's a damn fine photo! Viewed on my phone, it's great.

Most SLR lenses have infinity focus points. However, they can often focus beyond infinity for infrared photography. So you need to check the manual to know the mark to use. Usually, the infinity point is marked with a sideways L, and you dial to point where the two lines meet to form the L.

I doubt that focus was your problem. Other possibilities are that your tripod isn't as solid as you think, or wind blew the tripod a bit, or mirror slap. (Your camera may have a mirror lockup feature).If only the stars are blurry, it could be that the stars moved (well, the Earth moved against the starry background).

 

[Steve Throndson]

AF lenses don't actually focus at infinity when they're set that way? Not that I doubt you, I'm just wondering why that is.

Aaron801,

Apparently it's because the autofocus needs to compensate for temperature variations. (according to the Canon instruction manual anyway)

See my post four or five below this one.

 

[Steve Throndson]

mactac,

Your photo would have been wonderful, but for the focus. I hope you'll get another chance on your next camping trip. I've got quite a collection of star shots with similar shortcomings. Shining a strong flashlight on distant trees for a focus target sometimes works, but it looks like you didn't have anything but the distant shore to use for that.

Anyway - you could ask the question in the Nikon forum - 'how to manually focus the 14-24 to infinity?' Maybe there's a trick to it. As I wrote in an earlier post, Canon lenses have an 'infinity compensation mark' that's explained in the instruction book. Nikon must have something similar.

 

[zackiedawg]

See my post farther up the thread on this:

http://www.dpreview.com/forums/post/53715917

I think that's the main reason everyone's advice about live view seems to make no sense...different live view systems perform differently.

 

[EinsteinsGhost]

live view mf

Perhaps I didn't explain myself correctly - that's exactly what I'm trying to do, use MF in live view, but there isn't enough light to actually see what I'm focusing on, hence the 30s exposure.

I have used Live View on my Sony Alpha cameras. If completely dark, it is still possible to find a point source (star), preferably via EVF as it makes identifying a spot easier, and sometimes using high enough ISO (even if that won't be the ISO used for imaging). Set focus manually.

Now, for a closer focus in complete darkness (no visible light, for example a critter), I would take out my ten year old Sony Cybershot F828 and use its night framing mode (it uses IR to acquire focus, although MF is also an option).

 

[mactac]

See my post farther up the thread on this:

http://www.dpreview.com/forums/post/53715917

I think that's the main reason everyone's advice about live view seems to make no sense...different live view systems perform differently.

--
Justin
galleries: www.pbase.com/zackiedawg

Thanks for this.

It appears as though I left out some critical information from my initial post, which might be throwing some people off, namely:

- I am using a Nikon D800 and 14-24 2.8 lens

- I am manually focusing to approximately infinity (approximately because it goes past infinity, so it's a bit of a guess)

- I am using live view, but cannot see anything (or it's all noise) because it's too dark.

- I am using mirror up & a cable release

- The tripod is solid, there is no wind.

- The blur is not star trails or anything else, I'm pretty sure. It looks exactly like OOF bokeh.

There were a few good suggestions IMHO:

- use a laser pointer or light on something closer

- focus on the lights on the shore (duh, why didn't I think of that?), assuming hyperfocal distance works out.

- Focus bracket (yuk!)

It sounds like that's pretty much it?

 

[zackiedawg]

Thanks for this.

It appears as though I left out some critical information from my initial post, which might be throwing some people off, namely:

- I am using a Nikon D800 and 14-24 2.8 lens

- I am manually focusing to approximately infinity (approximately because it goes past infinity, so it's a bit of a guess)

- I am using live view, but cannot see anything (or it's all noise) because it's too dark.

- I am using mirror up & a cable release

- The tripod is solid, there is no wind.

- The blur is not star trails or anything else, I'm pretty sure. It looks exactly like OOF bokeh.

There were a few good suggestions IMHO:

- use a laser pointer or light on something closer

- focus on the lights on the shore (duh, why didn't I think of that?), assuming hyperfocal distance works out.

- Focus bracket (yuk!)

It sounds like that's pretty much it?

I think that about sums it up. Either a laser pointer, or if you can find ANY light anywhere in the distance that is bright enough to focus on - either through the viewfinder or the live view - then once focus is set, recompose & shoot.

Exposure simulation in live view is very useful for this type of shot. I'm not sure why, but Nikon never seems to have offered it in their DSLR cameras that I know of. I can go outside in the kind of darkness that you can't see 5 feet in front of you, and turn on main sensor live view with exp. sim on my camera, and I can see like it's practically daylight...it gains up like mad, and is pretty much like night vision - especially if I go wide open aperture on a fast lens and crank ISO to 12800 or so. Once dialed in on manual focus, I run ISO back down to 100, set my exposure, and fire.

 

[merops]

Thanks for this.

It appears as though I left out some critical information from my initial post, which might be throwing some people off, namely:

- I am using a Nikon D800 and 14-24 2.8 lens

- I am manually focusing to approximately infinity (approximately because it goes past infinity, so it's a bit of a guess)

- I am using live view, but cannot see anything (or it's all noise) because it's too dark.

- I am using mirror up & a cable release

- The tripod is solid, there is no wind.

- The blur is not star trails or anything else, I'm pretty sure. It looks exactly like OOF bokeh.

There were a few good suggestions IMHO:

- use a laser pointer or light on something closer

- focus on the lights on the shore (duh, why didn't I think of that?), assuming hyperfocal distance works out.

- Focus bracket (yuk!)

It sounds like that's pretty much it?

Two additional possibilities:

- Stop down a bit to get greater DoF (you'd have to up the ISO to compensate, to avoid going over the exposure time at which star trails appear)

- Think ahead, focus the camera before it gets dark. Then switch the camera to manual focus (if you used autofocus to focus), and (whether you used manual or autofocus) stick a piece of duct tape round the lens to stop you accidentally changing focus. (Someone who knows much more about this will say how much the change in temperature in the intervening period will muck things up, but I have used this method ...)

 

[Tom_N]

SLR lenses ... can often focus beyond infinity for infrared photography.

So SLR lenses are designed for Buzz Lightyear?

 

[David Strachan]

Hi Mactac

bit hard to get the message through...you are very patient.

Definitely out of focus. Focusing on the distant lights is the best suggestion.

I like star photography too, but electronic viewfinders just don't cut it. Adapters are variable so using manual, or legacy lenses don't focus accurately using the lens barrel settings.

If there are no infinity lights, I try to find the brightest star, Sirius, in my case down here. But it is still very difficult, cranking up the ISO with all that gain. Naturally star pics are best shot wide open to capture as much light as possible, so stopping down is not an option...and that does not achieve critical focus anyway.

My hit rate with digital star photography is very low. Digital sensors also give jaggies, uneven blotchy and stepped images of star rotations which is unpleasant. They often have very short long exposure times too.

I never have this problem with film and optical viewfinder cameras, including SLR's, when I can do a B exposure for hours at a time and get lovely multi coloured stars perfectly focused. So now I use film and scan the results.

Guess we have to live with it.

cheers Dave S

 

[Pantyhose Bandit]

Nobody has said yet what a bloody good photo that is. You nailed the exposure. I'm surprised there are no star trails.

 

[mactac]

Two additional possibilities:

- Stop down a bit to get greater DoF (you'd have to up the ISO to compensate, to avoid going over the exposure time at which star trails appear)

- Think ahead, focus the camera before it gets dark. Then switch the camera to manual focus (if you used autofocus to focus), and (whether you used manual or autofocus) stick a piece of duct tape round the lens to stop you accidentally changing focus. (Someone who knows much more about this will say how much the change in temperature in the intervening period will muck things up, but I have used this method ...)

Great ideas, thanks!

 

[mactac]

Nobody has said yet what a bloody good photo that is. You nailed the exposure. I'm surprised there are no star trails.

 

[SteveL54]

Live View's Exposure Preview mode may brighten up the display enough to allow manual focus on the brighter stars or distant lights.

See page 46 of the English D800 manual.

Steve