snubbr.com

Can somebody please help me to understand?
Below mentioned formula can apparently be used to determine the exposure time for long exposures..

Set test exposure to AF and ISO to 3200 and the aperture to it's lowest figure for the lens. Observe the shutter speed the camera selects for these settings when you are satisfied with the final exposure..

Test ISO divided by final ISO times your original shutter speed equals final shutter speed for the slow exposure..

Let us assume your hand held shot is set to f 2.8 for the aperture and you set the ISO to 3200 and you get 30 seconds, the final long exposure on the tripod would have to be set to read:.

ISO 200 at f16 with a bulb time of 8 minutes. You dont need a stop watch since the camera will count down the seconds. With other words, your original ISO of 3200 divided by 200 equals 16 and 16 times 30 seconds equals 8 minutes. (16x30 sec=480 sec divided by 60 =8 minutes).

So far so good. However, what does the camera display which is equivalent to 30 seconds?..

Comments (13)

Paul Meusburger wrote:snip.

So far so good. However, what does the camera display which isequivalent to 30 seconds?.

Bearing in mind that many cameras are unable to shoot any LONGER than 30 seconds, or so....

.... in M-anual exposure mode the camera may display something like "30s" to indicate 30 seconds.....

.... or maybe the camera will not set an exposure so long as 30 sec as a shutter speed as such, but instead require you to hold the shutter open on it's 'B' setting, the requisite 30 seconds being timed off your watch. Either way, you will need to employ a remote release to avoid camera shake, of course..

What does your manual have to say about the matter? That is your first recourse for this kind of stuff. Regards,Baz..

Comment #1

When you start tinkering with 8 minute exposure times you don't really care what your camera displays, do you ? .

As long as you know and understand the scales of F-stops and shutter speeds vs ISO values and know how they relate to each other, calculations are fairly easy but, with a digital camera, you can see the results of all combinations on the LCD screen, provided you stay within the limits of your particular camera..

If your camera has a B or T setting and you use that, the in camera metering probably gets switched off because it becomes totally useless..

Go play with your gear, forget theory. In the digital world, the exposures are linear...

Comment #2

Paul Meusburger wrote:.

Below mentioned formula can apparently be used to determine theexposure time for long exposures..

Set test exposure to AF and ISO to 3200 and the aperture to itslowest figure for the lens. Observe the shutter speed the cameraselects for these settings when you are satisfied with the finalexposure..

Formulas are helpful, however, don't let then get in the way of experimentation and out of the box creativity. Inaddition to the math, go outside and experiment and play. That way you'll get a feel for how to do certain shots....

My theory, use ISO 400 or below (you want a smooth photo), use a tripod, use a shutter release, and play with the other variables..

My examples- (no formulas involved).

StarSweep: 15 minutes (bulb mode), ISO 200, f/4.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Twirling Sparkler: 4 sec, ISO 100, f/5.6.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Regards, Mike.

B.R.A.S.S. (Breathe, Relax, Aim, Sight, Squeeze).

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #3

Thanks for your reply Baz and LeRentier.

From what I understand, the guy gives this formula so that you don't have to try out various bulb times only to find out that I have the wrong exposure. With other words, if I set the bulb time for 5 minutes at a given aperture and ISO and set for noise reduction in camera (I have a 5D Canon on loan) and then having waited 5 minutes plus another minute or so for the time the camera takes to remove the noise, if a formula allows me to time it more accurately I have saved 6 minutes of my time. This is a simplified example since some of the scenes would need longer exposures..

What this says is to set the ISO to 3200, let in as much light as the lens allows, which is f4 in my example (24-105 mm IS), let the camera decide how many seconds it needs to get a perfect exposure (Hand-held) and you can now keep this file or apply the given formula, set the mode to Bulb, lock the mirror and remote and put the camera on a tripod. Now dial in the converted time given by the formula and if this conversion is accurate I have close to a perfect exposure. As to my original question if I dial in a shutter speed of 20 on this camera in manual mode is this one 20th of a second and if it is, the next number counting backwards displays 0'3. What does 0"3 represent in seconds? If I continue counting backwards I get to 1", 2" etc until I get to 30" which I assume is a maximum of 30 minutes as Baz has mentioned..

Paul..

Comment #4

Hi Mike,.

Thanks for your reply. Do you employ in camera noise reduction with bulb mode or get rid of the noise in Photoshop?Regards,Paul..

Comment #5

If I am understanding you correctly, your exposure calculations are off. First, I would would personally get used to thinking in terms of "stops". Your formula works for calculating shutter speed changes when ISO changes. I just think in terms of when ISO changes by 1 stop, shutter speed must change by 1 stop. 1 stop = a doubling or halving. e.g.

GIVEN that all are at the same aperture. In your example you stopped down the lens from f2.8 to f16. That is a 5 stop decrease in light that doesn't appear to be accounted for. If the proper test exposure was 30 sec at f2.8 and 3200 ISO, then the proper exposure for f16 and 200 ISO would be 256 minutes, not 8 minutes. I don't do astronomy type stuff, and I know this is hypothetical, but I can't imagine that ever being a realistic exposure..

Comment #6

Hi SM,.

I am quoting a hypothetical shutter speed which yes, turns out to be incorrect. However, I am trying to determine if the formula which states and I quote:.

Test ISO divided by final ISO; times your original shutter speed equals final shutter speed for the slow exposure..

Is of practical use to me..

Regards,Paul..

Comment #7

Paul Meusburger wrote:.

Hi Mike,Thanks for your reply. Do you employ in camera noise reduction withbulb mode or get rid of the noise in Photoshop?Regards,Paul.

I use the Canon 30D, which has a custom function setting for noise reduction, but I never use it..

For the night time shots, motion blurr to me oftentimes add a neat dimension to the photo, so I typically use ISO 400 or less...and this is very subjective I realize, but the images are perfectly accpetable to me, so I haven't fooled around with noise reduction... And when I don't want background motion blurr I'll use my tripod..

In other low light situations, like shots at my church, and at my kids school where I have to set the ISO to 800, honestly, for 8x10 and 5x7 prints I don't worry with noise reduction either...I haven't had to...it seems to me that my 30D produces perfectly accpetable images- I use the 24-105 L and the 70-200L f/2.8 IS..

Not answering your question per say...sorry!.

Regards, Mike.

B.R.A.S.S. (Breathe, Relax, Aim, Sight, Squeeze).

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #8

Paul Meusburger wrote:.

Hi SM,.

I am quoting a hypothetical shutter speed which yes, turns out to beincorrect. However, I am trying to determine if the formula whichstates and I quote:.

Test ISO divided by final ISO; times your original shutter speedequals final shutter speed for the slow exposure..

Is of practical use to me..

Regards,Paul.

Your problem is that you changed both the ISO and the aperture. If you held the aperture constant, your formula is correct, but you changed the ISO by four stops and the aperture by 5 stops or a total of 9 stops. That's a factor of 512 or 30 sec times 512 is 256 minutes. I think something will probably move..

David..

Comment #9

It is partially correct..

It is correct as far as it goes, but it doesn't account for changing the aperture..

For example, if you got a correct exposure at ISO 3200, f/4 and 5 seconds, then at ISO 200, f/4, and 80 seconds you would also get a good exposure. But if you wanted to shoot at f/8, you would have to multiply by 4, because of the two stop difference, giving you a time of 320 seconds..

The formula works if you do the test shot at the same aperture as the real shot. If, in order to get the test shot within the 30 second window, you have to use a wider aperture, then you have to calculate this into the time also. Each aperture stop results in a doubling (or halving) of the shutter time to get the same exposure..

F/4 to f/5.6 = 2xf/4 to f/8 = 4xf/4 to f/11 = 8xf/4 to f/16 = 16x.

Brian A...

Comment #10

With your help I have now adjusted my work-flow, tested the formula on my camera and confirmed my findings. Here is what I wrote:.

Hi Arnold,.

I have read that there is a workable formula to determine the exposure time for long exposures. Try the following:.

(Test ISO divided by final ISO; times your original shutter speed equals final shutter speed for the slow exposure)..

In order to apply this formula, set a test exposure to AF and ISO to 3200 and the aperture to it's lowest figure for the lens. Observe the shutter speed the camera selects for these settings and make a note of it. Take the shot. You might now want to make a few adjustments and take another shot just to make sure the histogram looks good. Ignore the noise just concentrate on the exposure..

Let us now assume that your final hand held shot is set to f 4 for the aperture, ISO to 3200 and the camera indicates that you needed 5 seconds, the final long exposure would have to be adjusted as follows:.

Proceed to put the camera on a tripod  the first exposure was hand-held to get a starting point  and change to Bulb mode, go into custom function 02, switch to Long exp. Noise reduction ON, and still under custom functions go to Mirror lockup and switch to Enable. Insert the lockable timer remote controller. Take a calculator and do the following calculation to determine for how long you need to expose to get a slow exposure with similar results than the hand-held shot..

With other words, youre original ISO of 3200 divided by 200 equals 16 and 16 times your original shutter speed which was 5 seconds equals 80 seconds..

Set the ISO to 200, lock the timer and release it at exactly 80 seconds. You dont need a stop watch since the camera will count down the seconds. You can see this on the top glass. Obviously you have to adjust the tripod so that you can see the counting numbers. Press the LCD panel illumination button frequently so as to not miss the count..

However, if you want to shoot at f/8, you would have to multiply above figure by 4, because of the two stop difference, giving you a time of 320 seconds..

Above formula works only if you do the test shot at the same aperture as the real shot. If, in order to get the test shot within the 30 second window (the maximum on my 5D) you need to use a wider aperture, then you have to calculate this into the time also. Each aperture stop results in a doubling (or halving) of the shutter time to get the same exposure. With other words:f/4 to f/5.6 = 2xf/4 to f/8 = 4xf/4 to f/11 = 8xf/4 to f/16 = 16x.

Note: Since you have set noise reduction, you have to wait a while longer after you released the shutter button depending on the amount of noise the camera has to remove..

Regards,Paul..

Comment #11

A few of corrections,.

That would be "set the test exposure to Av" not " set a test exposure to AF".

The seconds. You can see this on the top glass. Obviously you have toadjust the tripod so that you can see the counting numbers. Press theLCD panel illumination button frequently so as to not miss the count..

Pressing the LCD illumination button during exposure is not a good idea. You should be using a cable release and avoiding all contact with the camera during exposure. A small flash light, well shielded from the lens, is a possibility. A watch or timer is another..

Note: Since you have set noise reduction, you have to wait a whilelonger after you released the shutter button depending on the amountof noise the camera has to remove..

For long exposures the camera is not doing an algorithmic noise reduction it is doing a dark frame subtraction. The amount of time for the noise reduction doesn't depend on the amount of noise, but the duration of the exposure. The easiest way for the camera to do this is to take a frame of the same duration as the shot, but with the sensor not exposed. This dark frame is then subtracted from the image. I haven't timed the dark frame duration on the 5D, and it may be able to calculate how much to subtract from a shorter shot, but in the normal occurrence of things the dark frame duration should be the same as the shot duration..

Brian A...

Comment #12

Thanks Brian A.I will change it as you suggest..

Comment #13

Click Here to View All...

Sponsored Amazon Deals:

1. Get big savings on Amazon warehouse deals.
2. Save up to 70% on Amazon Products.


This question was taken from a support group/message board and re-posted here so others can learn from it.

 

Categories: Home | Diet & Weight Management | Vitamins & Supplements | Herbs & Cleansing |

Sexual Health | Medifast Support | Nutrisystem Support | Medifast Questions |

Web Hosting | Web Hosts | Website Hosting | Hosting |

Web Hosting | GoDaddy | Digital Cameras | Best WebHosts |

Web Hosting FAQ | Web Hosts FAQ | Hosting FAQ | Hosting Group |

Hosting Questions | Camera Tips | Best Cameras To Buy | Best Cameras This Year |

Camera Q-A | Digital Cameras Q-A | Camera Forum | Nov 2010 - Cameras |

Oct 2010 - Cameras | Oct 2010 - DSLRs | Oct 2010 - Camera Tips | Sep 2010 - Cameras |

Sep 2010 - DSLRS | Sep 2010 - Camera Tips | Aug 2010 - Cameras | Aug 2010 - DSLR Tips |

Aug 2010 - Camera Tips | July 2010 - Cameras | July 2010 - Nikon Cameras | July 2010 - Canon Cameras |

July 2010 - Pentax Cameras | Medifast Recipes | Medifast Recipes Tips | Medifast Recipes Strategies |

Medifast Recipes Experiences | Medifast Recipes Group | Medifast Recipes Forum | Medifast Support Strategies |

Medifast Support Experiences |

 

(C) Copyright 2010 All rights reserved.