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Old May 16th, 2012, 01:30 PM
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sjonee sjonee is offline
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anjin_nav i failed :(

ok anjin_nav i failed at getting the star trails you're so good at getting. i thought i followed your instructions you gave to me a long time ago. Tonight i'm going to have my settings on 22/f instead of 5.8 iso at 100 and still at infinity doing the 1 hour exposure. The other problem i had is that i could find the lil dipper but not the big dipper so really couldn't find the north star so i just pointed my camera to the north. I had fun last night even tho it didn't work so i'm looking forward to doing it again tonight.


this one was done with the instructions you gave me of 5.8/f 3200iso infinity and an hour exposure. As you can "see" it's white lol.


IMG_9281 by ffarah001, on Flickr


This one is 5.8/f 640iso


IMG_9282 by ffarah001, on Flickr

this is 5.8f 100iso and it still was too light so i can use some help


IMG_9283 by ffarah001, on Flickr
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Old May 16th, 2012, 03:04 PM
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Re: anjin_nav i failed :(

i know i addressed this to anjin_nav but anyone who can help me i would love to hear from you
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Old May 17th, 2012, 11:55 AM
RABaker RABaker is offline
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Re: anjin_nav i failed :(

I have done a little astrophotography but never tried star trails. However, I will try to offer something, and I hope it might help.

"The other problem i had is that i could find the lil dipper but not the big dipper so really couldn't find the north star so i just pointed my camera to the north."
At this time of year the big dipper will be upside down above the north star. If you can actually see the little dipper (it is quite a bit dimmer than the big dipper), the end of the handle of the little dipper is Polaris, the north star.

There are some places on the earth where the sky is truly dark and long exposures don't end up showing the effect of light pollution. However, very few of us live in such places. For most of us, the sky is affected by light from the ground as shown by your initial images. [By the way, a bright moon will also add significantly to the general brightness of the sky, even if you are shooting in a direction away from the moon.] It is always a balancing act between ISO, aperture and exposure time. Smaller apertures (larger f-numbers) will yield a darker sky, but some of the smaller, fainter stars will probably be lost from the image. Since the amount of light pollution varies so much from one area to the next, you will have to experiment a little to see what works best at your location. When it comes to the sky's portion of the image, each one stop smaller aperture will cut the exposure in half. So if you shoot at f/8 instead of f/5.6 the sky will by half as bright; if you shoot at f/11 instead of f/5.6 the sky will be 1/4 as bright; if you shoot at f/16 instead of f/5.6 the sky will be 1/8 as bright; and so forth - this all assumes you keep the same exposure time.

Do some testing at different apertures (and different times?) to see what works best for you.

Good luck,
Richard Baker
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Old May 17th, 2012, 01:03 PM
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Re: anjin_nav i failed :(

Sarah, I don't know what instructions Tim (aka anjin_nav) gave you but I doubt it was ISO3200 for long exposures...but maybe it was????

Your series of photos show that wide open, high ISO, and long exposure are WAY over exposing your images.

A couple of basics:
  • You must get the right amount of light to properly expose an image...but you know that. The trick is that night time is VERY low light and we forget that the same principles hold for exposure....it just takes settings that otherwise not used by us.
  • Every change in ISO (ie from 100 to 200 to 400 to 800 etc) INCREASES the sensitivity of the camera's sensor to light 2x.
  • Every change in aperture (ie from f-4 to f-5.6 to f-8 etc) DECREASES the amount of light by 50% (1/2x) for EACH full aperture change.
  • Every change in shutter speed (ie from 1/4 to 1/2 to 1 to 2 to 4 seconds etc) INCREASES the amount of light by 2x.
  • Therefore, I could use several combinations of any 2 controls (aperture, shutter, or ISO), leaving the 3rd fixed, to give me a well exposed image. Using ISO100 I could use f-8 for 1 sec OR f-11 (-1 stop) for 2 sec (+1 stop) OR f-5.6 for 1/2 sec OR several other combos.
The closest image above is the 3rd, ie ISO100, f-5.8 for 1 hr(?). It appears to still be overexposed. What can you do? Let in less light of course. You're already at the least sensitive ISO setting (ie 100)...nothing more you can do there! You could open the shutter for a shorter period, but you probably want the effect of star trails. You could add a polarizer (cuts 1 1/2 - 2 stops of light) or a Neutral Density filter. Most probably your primary option is smaller aperture...but how much smaller?

You COULD trial & error on 1 hr trials....but that takes too long. You could use the relationship between ISO/aperture/shutter to MUCH more quickly zero in on the correct aperture. Look at the difference between image #2 and #3. Image #2 is 2 2/3 stops brighter (ISO640 vs ISO100), assuming shutter speed was the same on both. If you changed your aperture from f-5.6 to f-11 (+2) or f-16 (+3) I'd bet you'd be there. The way to cheat and find out more quickly than a 1 hr trial is to take a 1 minute (-6 stops) or 30 sec (-7 stops) exposure using an OFFSETTING temporary increase in another variable, ie ISO. Change it to 6400 (+6) or 12,000 (+7) if your camera allows such. If not, you'll have to temporarily "cheat" it using a combo of apertures and ISO. If the 1 minute or 30 sec trials show a pleasing exposure on the sky (ie midnight blue, not white or black) and the star trails (albeit very short) are bright enough, then you set everything back to ISO100 and bulb exposure for 1 hr and you're good. If too bright still, smaller aperture (ie smaller). If too dark, wider aperture.
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Old May 17th, 2012, 01:47 PM
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Re: anjin_nav i failed :(

There is also another technique that Tim uses with an intervelometer to create a series of shots over a long period of time plus 1 additional shot with the lens cap on.

The final result from the camera will be say 12, 5 minute exposures over hour plus 1 5 minute exposure with the lens cap on.

Then in post production you can use stacking to create a single image showing the equivalent of a 1 hour star trail.

The lens cap shot is to provide a noise reduction base when stacking.

breaking up the shot like this also will reduce the amount of light pollution coming into the frame from nearby light sources.
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Old May 17th, 2012, 01:47 PM
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Re: anjin_nav i failed :(

thank you both for your answers. i forgot to mention i did use bulb per Tim's instructions....never used bulb before so idk what it is or how it affects pics. my iso only goes up to 6400. I'm still trying to process some of what you guys said some of it is over my head. But i will keep thinking about it so thank you!
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Old May 17th, 2012, 01:49 PM
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Re: anjin_nav i failed :(

Quote:
Originally Posted by agiledogs View Post
There is also another technique that Tim uses with an intervelometer to create a series of shots over a long period of time plus 1 additional shot with the lens cap on.

The final result from the camera will be say 12, 5 minute exposures over hour plus 1 5 minute exposure with the lens cap on.

Then in post production you can use stacking to create a single image showing the equivalent of a 1 hour star trail.

The lens cap shot is to provide a noise reduction base when stacking.

breaking up the shot like this also will reduce the amount of light pollution coming into the frame from nearby light sources.
yeah he gave me these instructions for a second option but was too difficult for me to do. I am using an intervelometer for the 1hour shutter speed.
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Old May 17th, 2012, 01:51 PM
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Re: anjin_nav i failed :(

The intervelometer is a device which will programatically allow you to trigger your camera automatically and hold the shutter open for a specified duration 1 or more times for the full time programmed. Its very important while using this method to have all in camera noise reduction turned off as that will delay between shots resulting in a broken star trail. (they will look like dashed lines rather than solid lines.)
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Old May 17th, 2012, 01:55 PM
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Re: anjin_nav i failed :(

Quote:
Originally Posted by agiledogs View Post
The intervelometer is a device which will programatically allow you to trigger your camera automatically and hold the shutter open for a specified duration 1 or more times for the full time programmed. Its very important while using this method to have all in camera noise reduction turned off as that will delay between shots resulting in a broken star trail. (they will look like dashed lines rather than solid lines.)
what do you mean by camera noise reduction turned off?....i am using the intervelometer.
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Old May 17th, 2012, 02:02 PM
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Re: anjin_nav i failed :(

Most cameras today have built in noise reduction. The way this works with long exposures is the sensor is exposed with the shutter closed after the exposure for the duration of the previous shot to generate a reference for the NR software in the camera to put in noise reduction.

What this means when using your intervelometer with 10 minute intervals for a 1hour exposure you get:

1 exposure 10 minutes, (10 minutes spent with in camera noise reduction) then interval 2 begins with the next 10 minute exposure etc... for the full hour. The 1 10 minute exposure with the lens cap on.

Between each actual exposure there is a 10 minute break for noise reduction and thus 10 minutes of lost trail in the star trail.

You can turn off all noise reduction in most cameras which will eliminate this. The exposure with the lens cap is what is used when stacking photos to eliminate/reduce noise in the shot.

At least that's what Tim explained to me last year when I was trying my hand in this...I may try again in Yosemite this year.
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