Star Streaks

Next time you're shooting star trails, try this: Make your long exposure at a small aperture, then open up the aperture for another five minutes. You'll get a star at the end of the trail, and be able to make out constellations. I like to hang my hat on the camera for a few minutes in between exposures to make a slight gap

A point to remember and contemplate with star photography:

as stars are point sources, the numerical aperture of the lens is not the determining factor in the exposure of stars.

The actual _area_ of the lens is the determining factor.

Thus a 200/4 has as much light-gathering area as a 50mm f1.0 !

So, I had problems recording good star trails on a 45mm f4.0; no wonder !

this has only a 11.25mm effective aperture... that 200f4 has a 50mm aperture !

thus, a shorter lens will need to be faster, or use faster film.

Bear

You recommend a manual camera, because of battery consumtion and this is true for most of the modern cameras, but the old Canon EOS cameras (600-series) feature a mechanical lock of the shutter and draw nearly no current (25 microamps, this means a fresh 2CR5 battery will last for 50.000 houres ...)

Concerning astrophotography and the recording of stars, there seems to be some confusion about f-ratios, aperture, focal lengths, etc. For point sources such as stars, it is the focal length, not the physical aperture, that determines the limits of what will be recorded on film. This is because the amount of background sky included in the picture varies with focal length and thus the amount of magnitude-limiting sky fog goes up as the focal length decreases. Longer lenses include less of the sky and therefore less of the sky fog. Since the stars are points, their light is not spread out as focal length (magnification) increases. This effect results in an increase in the ratio of starlight (point source) to skylight (non-point source) as focal length increases, and fainter stars are recorded before being limited by the sky fog. This light-source ratio is not affected by the f-ratio or physical aperture of the lens. For example, a 50mm lens at a dark site has a limiting photographic magnitude of about 11.5. A 500mm lens has a limiting magnitude of about 16. The magnitude scale is a way of estimating the brightness of an object, with each successive magnitude number being about 2.5 times brighter than the next one (magnitude 1 is 2.5X brighter than magnitude 2). The f-ratio does determine how fast the sky fog limit is reached. Exposures longer than that needed to reach the sky fog limit will not record fainter stars.

For star trails, you should pick an f-ratio that will give you a decent star exposure for the faintest stars you want to record. For a given exposure time, too low a ratio will cause a fast sky fog build up with little contrast between stars and sky. Too high an f-ratio will result in fewer stars against a darker background. The f-ratio you choose will depend on the local sky conditions and the focal length of the lens for the reasons stated above.

In visual astronomy, the physical aperture determines the limiting magnitudes of stars. At the same magnification, a 10" diameter scope will display objects at four times the brightness of a 5" scope at the same magnification. This is probably where the confusion arose.

Regarding long exposure star trail photography with camera lenses, remember that in a lot of climates moisture will condense on the lens surface as the temerature drops to dew point. So, your 6 hour shoot will be ruined by the lens fogging unless you take care to heat the lens element with a "dew chaser" assembly. The Kendrick system, http://kendrick-studio.com, is the best commercially available, or you can make your own using resistors and wire connected to a 12 volt battery source. Consult Sky and Telescope magazine archives for articles on this subject. The object is to keep your lens surface just above the dew point so it will stay moisture free.

When the objective is to image faint stars, the aperture settings and focal settings are critical. Significant improvement will likely occur when optimal settings are used. Usually more sensitivity will be achieved by stopping down the aperture somewhat as reduction in illumination is more than offset by a reduction in the circle of confusion (ie less light but more tightly imaged).

As for focus, while the factory scale is "good enough" for most purposes, the true infinity focus is often different slightly than that indicated. Experimentation pays dividends.

If no time to experiment, a rough guideline is to reduce apperture 1 stop from wide open.

For the curious, the circle of confusion will be reduced as the aperture is closed more than optimal for the above purposes until diffraction effects about the aperture edges add disproportionate degradation. For a typical 50 mm lens, the smallest circle of confusion is found about f/8.

Since no one mentioned it, I'd like to add a quick comment on photographing (or just observing) the moon. The least "interesting" time to do it is during full moon. Since the light of the sun hits the moons surface almost straight on, you won't have the shadows that bring out surface detail like mountains and craters. Half and quarter moons are much more interesting because you can see more of the features of the terrain.

When's sunset? Where's the moon? When's the sun gonna come up? ...Get a Casio Fish-En-Time or Forester for $39 and you'll always know. Just punch your lat/lon into it and it tells you all that and even a graph of where the moon should be right now (if you're indoors and thinking about getting ready to shoot). It also can be set to calculate the events for past/future dates. A must for any star geek. I'm on my third one in 10 years now.

To avoid fogging your lenses, and to make a more overall enjoyable experience when photographing stars, make yourself comfortable. A cheap pup tent of sufficient height can house your expensive tripod, telescope, camera, your equipment, and you. Setup your tripod in the tent and point the camera out the main opening. If you shop around in a good camping store, you'll be able to find a tent that has a large enough opening for you to capture most scenes and leave enough room for you to pass by. (On very cold or windy nights, cut a small flap in the side or top of the tent, point the camera in that direction, and zip everything inside. Your tripod might end up just 1 meter off the ground, or you may need to never enter the tent while filming so as not to disturb the tripod.) You also might want to cut a large hole or flap in the floor of the tent so your tripod can rest on the earth rather than fabric. Now, a small non-combustible heat source placed in the tent will keep the temperature warm enough to prevent fogging. Voila! Your camera is safe(r) from wind, cold, and rain. Plus, you can always sleep in it!

I got an idea from Phil's comment about batteries dying mid-exposure during star trail photography. If you're interested in doing it, next time you get a low-bat light on one of your cameras, immediately take out the battery and save it to open the shutter on a star trail picture. So, next time you're going to shoot the stars, remove your current battery, insert an almost-dead one to open the shutter, and, to close the shutter in the morning, reinsert the original battery. Unless I'm overlooking something important, that should help.

It is worth mentioning that the Canon EOS 3 (with its unique shutter system) doesn't exhaust the battery when performing bulb exposures to anything like the extent of the EOS 5, and other electronic SLRs no doubt. I wish I had one! See http://www.canon-europa.com/Eos/ and look under innovations/rotary magnet shutter.

For those who don't have a lot of money to spend on a camera body with a manual bulb setting, consider purchasing an old Minolta SR-T body with 50mm, 55mm, or 58mm standard lens. There are hundreds if not thousands of these available on the used market at any given time, and you can usually get them complete for under $140 (except the all-black models, as they're more collectible).

They sell for less nowadays due to the fact that the mercury batteries they used are getting harder and harder to find. They're an even better deal if the meter is inoperable -- what do you care, you're not using the meter anyway! I personally recommend the SR-T 101: 1-1/1000 shutter, self-timer, DOF preview, and mirror lock-up.

[Caveat: not all SR-T's which offered MLU when they were introduced had it near the end of the SR-T series' production; for some reason Minolta started mucking around with the features each model offered. You'll know the model you're looking at has MLU when you see the small circular switch on the lens mount housing, above the DOF preview plunger and right next to the self-timer lever.]

For more information on SR-T's, visit the Minolta User's Group.

Roger said:

Next time you're shooting star trails, try this: Make your long exposure at a small aperture, then open up the aperture for another five minutes. You'll get a star at the end of the trail, and be able to make out constellations. I like to hang my hat on the camera for a few minutes in between exposures to make a slight gap.

Another idea is defocussing. Start the exposure with lens at infinity. Then, every so often (1 hour, say, on an all nighter), just barely twist the lens the other way,. You'll end up with a rather unique photo, heck, combine defocus with Roger's idea!

I can recommend f5.6 to f8 for Provia 100F.

View from kilimanjaro, 8-11:30pm

I added a lovely 3.5-hour time exposure from 16,000 feet up Mt. Kilimanjaro just this summer. You can see the big image here.

This is from my series on Star Trails.

I'm surprised no one has mentioned reciprocity failure for long exposures. That is, the color shift that happens as certain films, namely Velvia, are exposed for long periods of time. Velvia will shift to the green pretty quickly, and over 3 hours, you're going to have a seriously GREEN sky. I've had 20 minute exposures with Velvia that haven't been a problem. There are three ways to adjust for this problem.

first, use a FL-D filter. These are normally used to reduce the green tones you get when shooting flourescent lights. they shift back to 'white' by adding magenta. For long night exposures, this is perfect. The sky will shift right back to its correct color. (This may or may not be "black", depending on other gunk in the air that may have its own color.)

Second, use Tungsten film. this is normally used to compensate for indoor shots where "tungsten lights" (normal lamps, etc) are too warm (red/orange). Tungsten film shifts towards blue to balance things out. Again, perfect for sky shooting.

The third alternative is to use Color Negative film, which is not subject to the same reciprocity failure as slide film. I have only tried this once, and while it appeared to work, it's not clear whether it worked because "it worked", or because the lab that made the print balanced it out for me.

im new to this but for star trails i bought a second hand pentax mg for 50 pounds verry cheap and the shutter is mechanical on bulb and there is a set 100x shutter speed for moon picturs on 100 asa/iso film to try youre moony eleven as i call it whith

I have experimented with taking star-trail pictures and have found that my f90's 4-AA batteries just didnt cut it for multi hour exposures,my solution to this problem was to buy a second battery holder and hard wire a battery of any size you like (the right voltage of course) to the battery holder.The battery can then be recharged over and over and it will have plenty of juice.I just bought this stuff for my camera a few weeks ago.6V battery,a piece of coil wire and a new battery holder,it came out to about 50 bucks.now long nightime exposures with todays battery dependent cameras are not a problem!

I've been investigating star trails and use the following setup. Minolta SRT101 (fully manual) batteries removed as you're not going to try and meter on a dark sky :D I use the standard lens that I got with the camera (bargain on ebay I should add) 50mm f1.7. oh, and a cable release. I've been using kodak 100 and 400 film with very nice results. For nice foreground effects try painting nearer object (trees, bushes whatever) with a flashlight. A couple of seconds over the entire area brings up the foreground nicely. Have fun!

With regards to astronomical photography, is not the Olympus OM1 the ideal camera? Fully manual and no batteries required. Still one of the favourites for telescope astronomy.

I picked up an OM1 with a broken meter and 50mm lense for $65, MLU and all what Ray said. It worked well at the amusement park. Now I'm venturing into a Bronica GS1 system. I LOVE the tent idea!

How would you rate nikon F-75 D for night star trail pictures?

Moonshots: the average reflectivity of the moon is about 12%, or approximately 2/3rds of a stop darker than an 18% Zone V grey card. So the f/11 recommendation near the top of the page will over-expose the moon by 1/3 stop, assuming one is aiming for a Zone V reproduction.

But as Ansel Adams pointed out long ago, our impression of the moon from seeing it up in the sky at night is that it's quite light, so higher placement on the tonal scale is typically called for.

Net Result: I recommend giving it at least f/8 at the reciprocal of the film speed, or one more stop than recommended above. This will put it 1 1/3 stops above Zone V, or about like a very light skin tone would normally be.

Even more exposure could be applied for a rising or setting moon where a lot of atmospheric absorption might be present. This also applies to thin crescent phases seen in a deep twilight sky not far above the horizon, since not only is there atmospheric absorption but the angle of illumination from the sun on the moon is then so low (like late afternoon or early morning here on earth) that the part of the moon seen is itself intrinsically dimmer. 4-6 stops more than a typical daylight exposure might be called for, which changes the rule to an f/4 to f/2 rule, though in such cases one may want to meter the brightest part of the sky in the scene and over-expose that about 2 stops -- and then bracket liberally since light is so cheap.

Very interesting topic, but is it possible to achive star trails with Canon G7? I would like to try it out but the limit of the exposure is only 15 seconds.

!!!Cheers!!!

As a G3 owner, I have the same limitation: 15 seconds is too short. You will see very, very short lines, I think. The only way to do it with this camera is to take a series of consecutive 15 second shots and stack them in a photoeditor. There is an article in one of this month's photo magazines that talks about how to do it. Note that you can't use the intervalometer because the minimum interval between photos is 1 minute. I think you have to stand there with the remote and just fire away.

Better yet, go the the camera store and buy an old, used, 35mm manual camera. It'll be wicked cheap, you can get additional kit from eBay and it's great for this sort of thing.

It had remained a very interesting topic with lot of usefull contribution from all. I think, we have been missing one important thing of star trail photograph. How long should you keep your shutter? Two major factors would determine this. One, the fog limit of the location and time. Two, length of the trail you want (Not in term of linear term,but here it should be measured in angular form).

Fog limit is the one that can be determined by giving few test shots.

For angular length of the trails, since here, the subject remains fixed but the Camera moves(Earth with the camera on its surface is moving while stars are still), we find apperent movement of the stars causing the trail on film or CCD or CMOS. Now, earth rotates 360Degree in 24 hours means, 360/24 = 15 Degree in an hour. So, any exposoure of 60 minute would form a star trail of 15 degree (Around the center of the celestial north pole or celestial south pole). You shoot stars closer to the pole, trails would be brighter but with lower linear length and the opposite for the stars farther from the poles.

Take the example of the 6 hr long exposoure. Here try to visualize the full circle of the star trails. Now, take any one of the trails, it is just one fourth of the whole circle or 90Degree.

To add, if you want to shoot just the constellations without any trail, you will have to have the exposoure within a exposoure time that would not give any perceivable trail. For that, forget the complicated astrophotographical equations, as a rule of thumb, 250/effective focal length of the lens used would be the maximum alowed duration of exposoure. This is for the stars of ecelestial equator (The line on the sky that seperates the sky into two parts North and South. It is just above the earth's equator). These stars appear to have maximum linear displacement per degree of angular movement of stars due to usual sky motion. Natuarally, if you shoot stars closer to pole, the exposoure can be further extended. Like a constellation at 45 Degree distance can be shot with even 8 Sec exposoure. I like using my Nikon 50mm 1.4 with FEII. Sometime I use the lens with my D50 where the efective focal length becomes 75mm shortening my maximum allowable exposoure time.