[captainbert]

Hi,

I am looking to do long exposure photos of seascpaes and have bought a Hoya ND400, a nine stop filter to use on a Sigma 10-20. When i attached today to try out it the K5 gave me way too inaccurate readings for a proper exposure ie every image was dramatically underexposed. I'm a noob at photography but i presumed in aperture mode the camera would give a relevant reading and the only way i was able to get a proper exposure was to dial in some serious EV compensation at times up to +5. Is this pure stupidity on my part and is this the norm?

[Macario]

in the film era there was a phenomenon called reprocity failure Reciprocity (photography) - Wikipedia, the free encyclopedia How it excactly works, is difficult to explain. But basicly it is like this: when having a 30second exposure at f4, you would need a 3 minute exposure at f8. so instead of increasing the exposure time by 2 when decreasing the fstop by 2 doesn´t work. you need to increase it by 6. and the longer the exposre is, the more you must compensate. I do not know how this excactly works for digital. but I always compensate when doing night time shooting or using ND filters (as I do with film) and it works for me

[captainbert]

in the film era there was a phenomenon called reprocity failure Reciprocity (photography) - Wikipedia, the free encyclopedia How it excactly works, is difficult to explain. But basicly it is like this: when having a 30second exposure at f4, you would need a 3 minute exposure at f8. so instead of increasing the exposure time by 2 when decreasing the fstop by 2 doesn´t work. you need to increase it by 6. and the longer the exposre is, the more you must compensate. I do not know how this excactly works for digital. but I always compensate when doing night time shooting or using ND filters (as I do with film) and it works for me

Thanks a lot Macario. I'll have to read up on that and try and get my head around it. I really appreciate your response!

[DAZ]

Exactly it has to do with the range that the metering system is usable. There is technically reciprocity in any system that is not liner but in the digital world it is very small and only at the edge (just be for clipping and at the bottom with the noise) so can be ignored for exposure. There is reciprocity in the metering system but is is best just staying in the middle so it is not a problem. The system is best in more normal lighting conditions. Just like at night if the scene is to dark the system can not meter accurately. As the scene gets darker the metering system will get less linear. Putting the filter on and then metering is the same as it being to dark for the metering. When using something like a ND400 with 9 T/stops it is best to meter with out the filter then do the math (9 T/stops in this case) and use that as the starting point for your exposure. This is only the starting point. You will still need to expose and chimp to get the exposure you want. Also be advised that with such long exposes that light leaks in the system (lens/filter, back of camera) can be a problem. This will look like a color shift with a shorter then expected exposure. Just find the leaks and block them then you will be good to go.


DAZ

[captainbert]

Thats fantastic Daz. I'm really getting an understanding now. Much obliged for the great response!

[mysticcowboy]

Reciprocity failure isn't much of an issue for digital cameras. It's a interesting subject, but probably not the answer to your question. The simplest way to use a ND filter is to take a meter reading before adding the filter. I use my iPhone for a light meter, either way works.

Using that setting, go to manual mode and adjust your time down to match your ND filter. Say you have a 3 stop filter and your metered reading is for 1/125 at F8. Subtract three stops. Cut your speed in half each time. ie. 1/125-> 1/60 -> 1/30 -> 1/15. If that's too fast, lower your ISO, or narrow your aperture, or both. Again, each EV will cut your shutter time in half.

[demp10]

Some ND filters actually use polarizers to dim the light. If that's the case with yours, then you can get inaccurate exposure reading because of the linear polarization. Try to rotate the filter by partially unscrewing it 90 degrees either way and see if the exposure measurement changes. If it does then the filter uses linear polarizers.

As mysticcowboy mentioned, try to measure the exposure up front, adjust it for the ND filter and then take the picture in manual mode. You can do that by removing the filter and measure as normal. Since you are doing landscapes, a better approach will be to switch your camera to spot metering and take several reading (without the filter) of the areas with most interest, (or from the dark and bright ones if you want to use a zone-like system) and then calculate the average. After adjusting for the ND filter, use that as the starting point and bracket the exposure in 3 or 5 frames. One will be the best.

[captainbert]

Reciprocity failure isn't much of an issue for digital cameras. It's a interesting subject, but probably not the answer to your question. The simplest way to use a ND filter is to take a meter reading before adding the filter. I use my iPhone for a light meter, either way works.

Using that setting, go to manual mode and adjust your time down to match your ND filter. Say you have a 3 stop filter and your metered reading is for 1/125 at F8. Subtract three stops. Cut your speed in half each time. ie. 1/125-> 1/60 -> 1/30 -> 1/15. If that's too fast, lower your ISO, or narrow your aperture, or both. Again, each EV will cut your shutter time in half.

Thanks a lot Mystic Cowboy... i was thinking about how to work out the maths element after the last response but thats help a lot to say the least. Much obliged for taking the time to share your wisdom!

[captainbert]

Some ND filters actually use polarizers to dim the light. If that's the case with yours, then you can get inaccurate exposure reading because of the linear polarization. Try to rotate the filter by partially unscrewing it 90 degrees either way and see if the exposure measurement changes. If it does then the filter uses linear polarizers.

As mysticcowboy mentioned, try to measure the exposure up front, adjust it for the ND filter and then take the picture in manual mode. You can do that by removing the filter and measure as normal. Since you are doing landscapes, a better approach will be to switch your camera to spot metering and take several reading (without the filter) of the areas with most interest, (or from the dark and bright ones if you want to use a zone-like system) and then calculate the average. After adjusting for the ND filter, use that as the starting point and bracket the exposure in 3 or 5 frames. One will be the best.

Had no idea of such things Demp. I'll try what you suggested tomorrow by using spot metering in the areas of interest and deducting an average and take it from there. Thanks a lot sir for enlightening me!

[newarts]

Hi,

I am looking to do long exposure photos of seascpaes and have bought a Hoya ND400, a nine stop filter to use on a Sigma 10-20. When i attached today to try out it the K5 gave me way too inaccurate readings for a proper exposure ie every image was dramatically underexposed. I'm a noob at photography but i presumed in aperture mode the camera would give a relevant reading and the only way i was able to get a proper exposure was to dial in some serious EV compensation at times up to +5. Is this pure stupidity on my part and is this the norm?

Perhaps light leaking in through the viewfinder was causing the underexposure. Your 9 stop filter is allowing about 2/1000 of the light into the lens so any light sneaking in through the viewfinder can make a big difference depending on camera design and exposure mode.

[captainbert]

Perhaps light leaking in through the viewfinder was causing the underexposure. Your 9 stop filter is allowing about 2/1000 of the light into the lens so any light sneaking in through the viewfinder can make a big difference depending on camera design and exposure mode.

Hi thanks for that. I actually just tried it out there but to no avail unfortunately. Much obliged for the response!

[HawaiianOnline]

Hi thanks for that. I actually just tried it out there but to no avail unfortunately. Much obliged for the response!

Try using the live view mode, and covering up any potential light leaks around the filter itself. If this doesn't help, try using the manual mode to lock the ISO and aperture where you want them and adjust the shutter speed until you get the exposure you want.

[captainbert]

Try using the live view mode, and covering up any potential light leaks around the filter itself. If this doesn't help, try using the manual mode to lock the ISO and aperture where you want them and adjust the shutter speed until you get the exposure you want.

I think that sounds like the way forward as ive been trying to work out how to calculate 9 stops difference in shutter speed and my non mathematical brain wont cooperate I think manual mode indeed and adjusting the shutter speed is what i will do. I actually already tried getting an accurate reading whilst covering up the eyepiece when in live view but it didn't help. Cheers again and i think you've clarified what is the way im going to go about this. Very best regards!

[FrankC]

Do you remember what your exposures were with and without the ND filter? The problem could be that with the ambient light and the massive reduction of the light from the ND filter, that your exposure system was not sensitive enough.

On the other hand nine stops is certainly a huge reduction in light getting to your sensor. Most cameras are limited to how long of an exposure it can provide in Program, Av, Tv, and manual modes. This is usually 30 seconds. Your under exposure problem may not be entirely due to reciprocity. Let's say for example that without the filter your camera's indicated exposure is f/22 at 1/2 second. Now attached the 9-stop ND filter and you'll need a shutter speed of 256 seconds or 4.26 minutes. Because the camera is limited to a maximum exposure time of 30 seconds, in this example then you would be under exposing the image by 3 stops.
With the filter attached to the lens in this scenario, the camera would indicate that the shutter speed required cannot be set due to the limitations of the camera. This is typically shown as a blinking shutter speed.
However, if you used exposure compensation and you saw an improvement, then my theory is busted.

[captainbert]

Do you remember what your exposures were with and without the ND filter? The problem could be that with the ambient light and the massive reduction of the light from the ND filter, that your exposure system was not sensitive enough.

On the other hand nine stops is certainly a huge reduction in light getting to your sensor. Most cameras are limited to how long of an exposure it can provide in Program, Av, Tv, and manual modes. This is usually 30 seconds. Your under exposure problem may not be entirely due to reciprocity. Let's say for example that without the filter your camera's indicated exposure is f/22 at 1/2 second. Now attached the 9-stop ND filter and you'll need a shutter speed of 256 seconds or 4.26 minutes. Because the camera is limited to a maximum exposure time of 30 seconds, in this example then you would be under exposing the image by 3 stops.
With the filter attached to the lens in this scenario, the camera would indicate that the shutter speed required cannot be set due to the limitations of the camera. This is typically shown as a blinking shutter speed.
However, if you used exposure compensation and you saw an improvement, then my theory is busted.

Yeah i was getting the flashing digits alright but i did find that i was able to get an accurate exposure by adjusting the shutter speed. Because of the terrible weather here i haven't been able to get a chance to properly explore this fully. Thanks very much for taking the time to write!