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Long exposures

Discussion in 'Beginner's Corner' started by ipbr21054, Aug 12, 2017.

  1. ipbr21054

    ipbr21054 Active Member

    Being new I'm shooting in Aperture mode & getting on fine with it.

    I have some ND filters on order & I understand I need to now shoot in manual mode & using a cable shutter switch but my question is,
    If I set the ISO to 100 the APPERTURE to F13 how do I know how long to hold the shutter open for ?
    I understand it will be different each time & ND used but is there a calc for this so it can be worked out.

    Please could you advise, thanks.
  2. PeteRob

    PeteRob Well-Known Member

    The problem with strong ND filters is you can't see much. So you have to set up without the filter to focus etc. then adjust the exposure according to the fikter strength. It should say how strong it is. You extend exposure time accordingly, doubling it fir every stop of filtration
  3. ipbr21054

    ipbr21054 Active Member

    Thanks for the reply.
    ND6 & ND8 ordered.
    Can you explain the doubling it for every stop of filtration part.
  4. RogerMac

    RogerMac Well-Known Member

    You do not say what type of camera you have and I probably am not familiar with it. However some cameras are perfectly capable of metering very long exposures in aperture mode without any manual intervention, It would be worth checking the manual to see, or just experiment to see if it copes. Try both live view and normal view. Having said that I suspect that manual focus will probably be needed.
  5. P_Stoddart

    P_Stoddart Well-Known Member

    Interestingly this is one of the advantages of mirrorless and SLT cameras :)

    I have a ND16 (4 stops) and can put that on my Sony A58 and can compose image with the EVF. :)

    As for metering the camera has no problem giving me the correct exposure. AF still works as well.

    But if you look through it you can hardly see things at all. LOL

    I am sure I did a test with both the ND4 and ND16 on and still could see through EVF.

    But to the naked eye very blacked out LOL
  6. PeteRob

    PeteRob Well-Known Member

    That does surprise me! (you mean ND 12 for 4 stop? )
  7. PeteRob

    PeteRob Well-Known Member

    the filter series, as you go higher in number, progressively cut the light they pass. So if a filter were to half the amount of light you would need to double the exposure time so as to keep the total amount of light for the exposure the same as for the unfiltered case.

    I always thought the naming went as log10(2) of the strength.
    .3 => 1 stop (half of light).
    .6 => 2 stop (1/4)
    .9 => 3 stop (1/8)
    1.2 => 4 stop (1/16). etc.

    but different companies may have different nomenclature: the series ND2, ND4, ND8, ND16 would account for the other post being 4 stops at ND16 rather than being named ND1.2 (as I just posted )
  8. Roger_Provins

    Roger_Provins Well-Known Member

    The chart here gives all the nomenclatures (scroll right down).
  9. ipbr21054

    ipbr21054 Active Member

    I have read the replies,thanks very much
    Some i dont even understand "being new" so not to sure how to even take them on board.

    I thought i was going to achieve it like this.
    Set the ISO to 100
    Set the APPERTURE to F13
    Then knowing the ND filter in use ND6

    Input this info into a calculator to be then told "hold the shutter button down for 1m 35s"
  10. Benchista

    Benchista Which Tyler

    You need to meter the shutter speed without the filter first, then apply the filter factor. But in all honesty, unless it's a VERY strong filter, it's much easier to just use aperture priority, and meter with the filter on and let the camera sort it out.
  11. ipbr21054

    ipbr21054 Active Member

    The filters ordered are ND6 & ND8
    Lets say i i use the ND8
    I would press the shutter button half way & see what speed is being shown "without filters fitted" lets say its 1/30
    Then this speed is calculated using the filter number 8
    So once i then fit the filters i would need to keep the shutter open for 8 seconds.

    Does that sound the basics of it.
  12. Roger_Provins

    Roger_Provins Well-Known Member

    An N8 filter reduces the light transmission by 3 stops so your 1/30 sec measured without the filter would need to be increased to 1/4 sec with the filter.

    Here is another chart.
  13. ipbr21054

    ipbr21054 Active Member

    So if i changed the speed to 1/4 is it then just a matter of operating the shutter button.
    I mean no need to hold it for 4 seconds etc ?
  14. ipbr21054

    ipbr21054 Active Member

    I forgot to mention.
    Looking at the chart you have supplied if i look at 8 stop filter & 1/30 it advises to hold the shutter open for 8 seconds.
  15. Roger_Provins

    Roger_Provins Well-Known Member

    An ND8 filter has F-stop Reduction (EV) of 3 stops NOT 8.

    For long exposures you need to mount the camera on a tripod and use a remote release to operate the shutter.
  16. Geren

    Geren Well-Known Member

  17. ipbr21054

    ipbr21054 Active Member

    My mistake.
    I was looking at ND8 filter but on that chart i used it as 8 stops.
    Now looking correctly at the chart i do see 3 stops at 1/30 = 1/4 so this can be achieved by the just pressing the shutter button.
    Otherwise & depending on exposure length if it then starts to go into seconds i will use tripod 7 shutter release cable.
  18. PeteRob

    PeteRob Well-Known Member

    In normal use you set the exposure time - say 1/4 of a second and press the shutter release. The camera does the rest. The camera will have a maximum setting of a few seconds - depends on the camera. If you want longer exposure then many cameras have a B setting where you do have to "hold" the shutter open. You would use a remote release for this as you can't hold pressure on the actual button without shaking the camera. For anything longer than 1/30s you are much better using a remote release or the camera self-timer to avoid shaking the camera.
  19. ipbr21054

    ipbr21054 Active Member

    Many thanks,i have seen the bulb mention after 30 seconds but just needed to brush up on how long to keep the shutter open for.
    I have a tripod & shutter release cable
  20. P_Stoddart

    P_Stoddart Well-Known Member

    It get better than that :)

    I just done a test took 2 images one without ND at all got 1/3200 f3.5 100ISO

    I then put the ND16,ND8 & ND4 onto camera could see image no problem on EVF :)

    The exposure drop to 2.5" f3.5 100ISO

    More surprising the AF still locked on to subjects. :)

    I could barely see through the filters with the naked eye :eek:

    Of course not good practice to combine NDs because you lose image quality with each layer of glass
    Last edited: Aug 13, 2017

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