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Very Long Exsposures - Way too bright - Help please

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prouds60man

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Hey everyone - I just bought a new Rebel XSi and have been doing quite a few test shots. I have dreamed of being able to do one of those great pictures that is a super-long exposure with a super-slow shutter speed so you can see the star trails, etc. Here is an example I found on flickr:

http://www.flickr.com/photos/bob_west/1155056031/

Notice how it is nicely exposed and everything is pretty clear. I know it is taken by a Pentax, but I figured the answer will still be the same.

Here is the picture I tried:

http://www.flickr.com/photos/kevinalanbaum/3123716927/

I had no idea what to expect with a 30 minute exposure, so I set it at 100 ISO, and F4. The stars streaking look great....except for one major problem - the massive over exposure. On the first photo by Bob West the stats on his photo seem to be similar to mine. What could I change, or what am I doing wrong? Admittedly, there is more light in the area where I took the photo than his probably, but I don't think that is what made my image so overexposed!

Thanks very much!
 
If its over exposed try it again with an 30min at f16 or 22 (maybe an ND filter to let even less light in)

Ray
prouds60man said:
Hey everyone - I just bought a new Rebel XSi and have been doing
quite a few test shots. I have dreamed of being able to do one of
those great pictures that is a super-long exposure with a super-slow
shutter speed so you can see the star trails, etc. Here is an
example I found on flickr:

http://www.flickr.com/photos/bob_west/1155056031/

Notice how it is nicely exposed and everything is pretty clear. I
know it is taken by a Pentax, but I figured the answer will still be
the same.

Here is the picture I tried:

http://www.flickr.com/photos/kevinalanbaum/3123716927/

I had no idea what to expect with a 30 minute exposure, so I set it
at 100 ISO, and F4. The stars streaking look great....except for one
major problem - the massive over exposure. On the first photo by Bob
West the stats on his photo seem to be similar to mine. What could I
change, or what am I doing wrong? Admittedly, there is more light in
the area where I took the photo than his probably, but I don't think
that is what made my image so overexposed!

Thanks very much!
Click to expand...
--
http://www.TheSBimage.com
 
Way too much exposure.

Digital is not like film, there is no reprocity failure, it's just a straight linear exposure, so it's pretty easy to over do it.

Unless you are in some extreme darkness, 30 minutes at F4 will get the results you did. To get the time you want, you almost always will have to stop down pretty far, at least F11. You have to be in the true middle of no where, with no moonlight, no city lights (say crater lake NP) were it's just plain dark to take such a shot at F4.

A quick thing to do, is set your aperture to it's max, and your ISO to it's max. Take some short test shots. Don't worry about noise or any of that. Just keep taking test shots till the exposure looks about right. Say you were able to get it right at F2.8 and ISO 6400, with a 1 minute exposure. So, work the ISO down. so that's 6 stops to ISO 100. Which stretches your exposure to 64 minutes. If you wanted to shoot at F4, then you would need 128 min exposure. Nice to take a 1 minute shot to get it right before wasting 2 hours. Of course now you can see if you were shooting for 30 minutes at F4, that test shot would be much shorter (15 seconds).

So just take that approach before you go for the long exposure. You'll have a pretty good idea of how long it needs to go before taking the shot.
 
prouds60man said:
Admittedly, there is more light in
the area where I took the photo than his probably, but I don't think
that is what made my image so overexposed!
Click to expand...
There's your answer. It might not look much brighter to your eye, but it must have been; your eye compensates for differences in brightness by opening up or stopping down, which is why you can read a book equally comfortably by bright sunlight and a 60 Watt table lamp, which are different in brightness by a factor of at least 10,000.

Best wishes
--
Mike
 
with a normal digital camera you cannot leave the shutter open on bulb and just let it run. the heat from the sensor and the generated noise would be too high. you can, however make series of short shots then use software to link them into one startrail. try Startrails and Registax 4 in google. the 2 software is for different astronomical purposes.

in an observatory the cameras are cooled by liquid nitrogen. you and i cannot afford such a device. the way to get around this is to use software. Startrails is for the trails stars, it simply puts them together. Registax is a program for 1 object in the viewfinder and you shoot multiple shots and the program stacks them, i have seen some excellent pic of the planets done with it; it works.
best of all both programs are free.
 
prouds60man said:
...Admittedly, there is more light in
the area where I took the photo than his probably, but I don't think
that is what made my image so overexposed!
Click to expand...
Make a note of this mistake. It's what happens when you start thinking w/o much knowledge. ;-)

I do that much more often than I'd like. But unlike you, I refrain from posting the evidence for others to chuckle at.

The answer is that ANYTIME, you get a pic that is overexposed, there was more light than you thought there was...

Go to where it's dark at night. It helps to do it on a VERY cold night. Try again. Voila!

--
Charlie Davis
Nikon 5700, Sony R1, Nikon D300
HomePage: http://www.1derful.info
Bridge Blog: http://www.here-ugo.com/BridgeBlog/
'I'm from Texas. We have meat in our vegetables.' Trenton Doyle Hancock
 
I think the first thing you need to do is get out of the city. It appears you're picking up some kind of streetlight glowing. Also, some ambient glow from the city lights is most likely what's blowing your highlights. Next, try stopping your camera down to a smaller aperature. F4.0 is pretty wide open for a long exposure... try F8 or smaller and see how it goes!
--
TANK
'Why is it everytime I need to get somewhere, we get
waylaid by jackassery?' - Dr. Venture
http://www.myspace.com/servantoflove

 
Thank you all for responding. I guess I answered my own question without knowing it :) - too much light in the area.

I tried a couple hours later and put it to F18 and the result was much more viewable. There is just too much ambient light in my neighborhood - I'll have to take a trek out out to the desert sometime!

Thanks.

PS: I also realized I misspelled exposures in the title. 🤦
 
prouds60man said:
Thank you all for responding. I guess I answered my own question
without knowing it :) - too much light in the area.

I tried a couple hours later and put it to F18 and the result was
much more viewable. There is just too much ambient light in my
neighborhood - I'll have to take a trek out out to the desert
sometime!
Click to expand...
And even at that, make sure there's no big cities within a couple hundred miles, or small cities within 50-100 miles, of the direction you're shooting in. One of the darkest places I've been to is Death Valley and you can still clearly see the glow on the horizon from Las Vegas and Los Angeles (about 250 miles away).
 
PhotoTraveler wrote:
.....
PhotoTraveler said:
Say you were able to get it right at F2.8 and ISO 6400,
with a 1 minute exposure. So, work the ISO down. so that's 6 stops
to ISO 100. Which stretches your exposure to 64 minutes. If you
wanted to shoot at F4, then you would need 128 min exposure. Nice
to take a 1 minute shot to get it right before wasting 2 hours. Of
course now you can see if you were shooting for 30 minutes at F4,
that test shot would be much shorter (15 seconds).

So just take that approach before you go for the long exposure.
You'll have a pretty good idea of how long it needs to go before
taking the shot.
Click to expand...
I don't mean to hijack but.....

1) is there a chart I can download somewhere that shows the aperture/shutter speed coralations as shown here "so that's 6 stops to ISO 100. Which stretches your exposure to 64 minutes" I understand the stops but don't know how you came to the 64 min?

another reply stated "with a normal digital camera you cannot leave the shutter open on bulb and just let it run. the heat from the sensor and the generated noise would be too high."

2) how long, under normal conditions, can you leave your shutter on bulb?
--
http://www.kiva.org ...Because I can!
 
Quijibo69 said:
another reply stated "with a normal digital camera you cannot leave
the shutter open on bulb and just let it run. the heat from the
sensor and the generated noise would be too high."

2) how long, under normal conditions, can you leave your shutter on
bulb?
Click to expand...
It varies with the camera. Usually, CMOS sensors don't heat up much unless you clock them, which you don't when you are on bulb. Check with other users of your camera on the associated camera-specific forum.

This was why, in my reply, I suggested to do these kinda shots on a VERY cold night. ;-)

--
Charlie Davis
Nikon 5700, Sony R1, Nikon D300
HomePage: http://www.1derful.info
Bridge Blog: http://www.here-ugo.com/BridgeBlog/
'I'm from Texas. We have meat in our vegetables.' Trenton Doyle Hancock
 
dwalton22 said:
Another approach to this is to take multiple images and stack them
together to piece together a longer star trails photo without the
overexposure. Here is a free program that will do the stacking for
you:
http://www.startrails.de/html/software.html

And this website has some great information on all things
astrophotography. Here is the page specific to star trails:
http://www.astropix.com/HTML/I_ASTROP/TRIPOD/TRIPOD2.HTM
Click to expand...
--Here's another vote for stacking using "startrails.de" one advantage is you can shoot in brighter light areas without blowing out the skys. here is a shot I did using abt 60- 30 second @ f3.5 exposures. This was taken abt 75 km from a city of 200,000. The light on the church was provided by a passing truck.



Brian Schneider

 
Each stop halves or doubles, so 6 stops is: 1) 1 X2 = 2 2) times 2 is 4 3) times 2 is 8 4) times 2 is 16 5) times 2 is 32 6) times 2 is 64.

F stops, each one is half or double. In your camera you will see other f stops, these are 1/3 a stop between these listed stops:

So: f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32

If you are at f8 and need to "open" up your lens by one stop then you set the aperture to f5.6, if two stops open, you set your f stop to ......(?)

If you "close" your lens down by one stop from f8, you set the aperture to f11, and two stops is ..... (?)

How to memorize f stops, memorizie each line so that you can say it equally fast in either direction; review every 6 months for the next 5 years:

1) f1, f2, f4, f8, f16, f32

2) f1.4, f2.8 f5.6, f11, f22

3) now combine the two:

f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32
--
Merry Christmas all & a Happy New Year.
Rationally I have no hope, irrationally I believe in miracles.
Joni Mitchell
 
rsn48 said:
Each stop halves or doubles, so 6 stops is: 1) 1 X2 = 2 2) times 2
is 4 3) times 2 is 8 4) times 2 is 16 5) times 2 is 32 6) times 2
is 64.

F stops, each one is half or double. In your camera you will see
other f stops, these are 1/3 a stop between these listed stops:

So: f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16,
f22, f32

If you are at f8 and need to "open" up your lens by one stop then you
set the aperture to f5.6, if two stops open, you set your f stop to
......(?)

If you "close" your lens down by one stop from f8, you set the
aperture to f11, and two stops is ..... (?)

How to memorize f stops, memorizie each line so that you can say it
equally fast in either direction; review every 6 months for the next
5 years:

1) f1, f2, f4, f8, f16, f32

2) f1.4, f2.8 f5.6, f11, f22

3) now combine the two:

f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32
--
Merry Christmas all & a Happy New Year.
Rationally I have no hope, irrationally I believe in miracles.
Joni Mitchell
Click to expand...
Thanks!
--
http://www.kiva.org ...Because I can!
 
GaryDeM uses a Pentax though.. of course he is going to say that.

Many other DSLR's will do fine with single long exposures.
 
PhotoTraveler said:
You have to be in the true middle of no where, with no moonlight, no city
lights
Click to expand...
Don't be afraid to use a small amount of moonlight. Not everyone wants total blackness in their star trails.

At least moonlight will give you natural colours which can be beneficial for scenery unlike the awful yellow from man-made light pollution.
 
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