Star trails / landscape in moonlight

[josphy]

I have gotten really interested in night photography recently since

taking some photos of the city skyline. This upcoming weekend I'm

going to be out in the Texas hill country for a family reunion, and

it seems like a good opportunity to try some star trail shots. I'm

always amazed by how many zillions more stars I see when I go out

there versus the city.

 

I was hoping it would be pitch black while I was there, but it looks

like I'm going to be there only 3 days after the full moon. The

place I'll be staying is by a river with a huge cliff face. My

thought was to use a longer lens (I have 135mm and 200mm) to isolate

a section of the cliff face with star trails behind. I may also try

some wider shots including the river/cliff illuminated by moonlight

and star trails. So I have a few questions...

 

As long as I leave the moon out of the frame, can I still get away

with this? My assumption is that instead of a several hour

exposure/long star trails, I will have to settle for a several

minute exposure/shorter star trails.

 

Can someone also shed some light (terrible pun) on what f-stop I

will want to use? My understanding is that the actual area of the

lens is the important factor, so a 200mm @ f4 would give a 50mm

aperture which would basically be equivalent to a 50mm lens @ f1.0.

This is making my brain hurt, but is it feasible to stop down my

135mm or 200mm lens down to like f5.6 or f8 to cut down on some of

the moonlight somewhat but still get a decent star trail (since that

would be like the equivalent of a 50mm @ f2 as far as the star

trails themselves are concerned).

 

Jeez that was complicated, but just trying to wrap my mind around

all this. If someone with a little more experience can give a

little clarification or even a suggested starting point for time/f-

stop I would really appreciate it.

[josphy]

Oh, and I don't mind bracketing shots at all -- but just trying to get an idea of some starting points and what other people's strategies might be when it comes to dealing with pretty strong moonlight and trying to combine the moonlight with star trails or minimize the moonlight.

[christian deichert]

Night landscapes are tough to combine with star trails. Star trails require a relatively wide aperture and a long exposure. However, with a full moon, the longer the exposure, the more washed out the foreground may become. You may want to experiment with a graduated neutral-density filter.<p>

 

Here are two shots I took in Tucson Mountain Park a few years ago. Neither of them are great shots, but they illustrate my point. If I recall correctly, both shots were taken with the Minolta Rokkor-X 58/1.2. I don't remember the aperture used, but I think I was using an exposure guide I bought from another photographer, sort of a slide-rule setup. I wish I had it in front of me so I could tell you who I bought it from, but it's in Germany and I'm stuck in Kuwait. The exposures were in the minutes, that's all I can remember. Obviously the first one has a longer exposure than the second.<p><center>

<img src="http://cldphoto.com/saguar_moon1.jpg"> <p><img src="http://cldphoto.com/saguar_moon2.jpg"> </center><p>

Keep in mind you're going to have to worry about reciprocity failure as well, assuming that you're using film. This was shot on Kodak E100VS. Note the odd color shift for the first shot; it's not as noticeable for the second. That's reciprocity failure, and there's no getting around it, there's only compensating for it (or hoping for the best).<p>

 

Hope this helps.

[josphy]

Thanks, Christian -- I'm going to be using Provia 100F, and I've found some reciprocity data going out to about 20 minutes.

[pvp]

When the moon is full, or nearly full, it will definitely limit the length of your exposures. For a full moon, you can use a "rule" that is similar to the Sunny-16 rule: <P>

<center><B>Exposure Time at f/4 = 1 / (ISO Film Speed) * DAYS</B></center><P>

So for ISO-100 film, an exposure of 1/100 of a day (at f/4) will give an exposure roughly equivalent to daylight. Since there are 86,400 seconds in a day, that's about 864 seconds, or 14.4 minutes. If you stop down to f/8 you get about an hour. My experience is that you can double that time to allow for reciprocity and get good negatives, though I haven't used transparencies in this scenario.<P>

So, at f/8 and with color negatives, you can use a 2 hour exposure and you'll get nice blue sky with star trails visible, though faintly. Cutting back to say 30 minutes will give a darker sky and the star trails should be more obvious.<P>

I've heard from numerous sources, that it's the overall area of the lens front element that determines performance for stars. It makes sense in an intuitive way, but I've never tested it.

[andy_depaulo]

"I've heard from numerous sources, that it's the overall area of the lens front element that determines performance for stars. It makes sense in an intuitive way, but I've never tested it."

 

Depends. Resolving stars is totally dependent on the physical aperture, NOT the f/ratio. Thing you need to remember is that telescopes and camera lenses change their f/ratios in different ways. Telescopes change there f/ratios by changing the focal length. Camera lenses change the ratio by modifying the aperture.

 

Take two 4" telescopes (100mm aperture). One is an f/10, one is an f/4. The f/10 scope will have a FL of 1000mm, the f/4 will have a FL of 400mm. The f/10 will have a lot more magnification, but since it has the same physical aperture (100mm) as the f/4 scope, they will resolve and expose stars identically.

 

When you adjust a camera lens's f/ratio, you are changing the physical aperture of the lens and not changing the focal length. So when exposing stars with a camera lens, f/ratio plays a huge part in exposing/resolving stars.

[andy_depaulo]

and by the way, shooting anything at night for longer than several seconds when the moon is up (especially right around full) will give a picture that looks just like one taken on a clear, sunny day.

[kirk_keyes]

Andy wrote: "Take two 4" telescopes (100mm aperture). One is an f/10, one is an f/4. The f/10 scope will have a FL of 1000mm, the f/4 will have a FL of 400mm. The f/10 will have a lot more magnification, but since it has the same physical aperture (100mm) as the f/4 scope, they will resolve and expose stars identically."

 

This has to do with sources of light that are considered to be "point sources".

 

Another way to think about this, from a camera viewpoint, is that the larger that effective aperature of a lens is the brighter it will record the stars. A normal lens for 35, a 50 mm, at f/2.8 lens has an aperature of 17.9 mm, while a normal lens for 4x5, a 150 mm, at f/5.6 has an aperature of 26.8mm. The 150 mm lens at 5.6 on the 4x5 will record stars brighter than the 50 mm lens on the 35 at f/2.8.

 

Of course the lens at f/2.8 will record detail in the landscape faster than the lens at f/5.6, so there is a trade off here.

 

Kirk - www.keyesphoto.com

[phule]

<< and by the way, shooting anything at night for longer than several seconds when the moon is up (especially right around full) will give a picture that looks just like one taken on a clear, sunny day. >>

 

Which is not to say you won't get a (great?) image with star-trails in it.

 

Using the moon as a way to illuminate other subjects in a star trail shot is pretty neat, IMHO.

[josphy]

Well it looks like bracketing is definitely in order...not just of exposure times, but different f-stops to see what gets the best balance of moonlight to starlight. This is gonna be fun!

[bonsignore_ezio]

I will agree that taking photos of objects illuminated by a full moon will result in a nearly daylight scene, although with its own flavour, and I will also subcribe to the necessity of braketing. This photos of the Trango Towers in Karakorum was taken at an altitude of about 4,000m with an exposure of 4m, and is the best shot in series of ten with exposures from 30 sec. to 8 min. No start trails are visible, but the long exposure has resulted in "puffy" clouds. The moonlight was so strong that starts were barely visible anyway, and of course the shorter exposure times with a much darker sky and less reflection off the cliffs just produced a few faint light points.

[christian deichert]

FYI to Ezio: TIFF files aren't normally displayable in browsers, and uploading a TIFF file is pretty much an invitation for folks to steal your photo for their own purposes...