ND Filter, what am I doing wrong ?

[DaveG40]

I've experimented with filters in the past and have had a CPL and UV for a while, having read nothing but good right ups I recently bought a ND (2) filter, I fitted it to my A500 and to be honest can see little to no difference at all, I took land & waterscape shots with and without the filter and varying shutter speeds, I could'nt tell the difference, I was expecting darker sky tones & smooth water, what am I doing wrong?.

I was using my Minolta (AF) 28-105.

[Malcolm_Stewart]

How dense is your filter? If it's only the equivalent of 2 stops, 4x, then I'd be surprised if you will notice much difference. (Just a thought - does your camera have Auto-ISO ? and is it switched on? This could remove any effect, I would expect.)

Try setting your ISO to its lowest, and have another go - using your shutter time preferred mode, and set to a long exposure time.

HTH

[DaveG40]

Hi Malcolm

I never use Auto ISO and routinely change my ISO to match the conditions/requirement.

I did wonder if the Alpha's dynamic range got in the way ?. It does'nt seem to effect my Polariser's use.

I had read that it's best to have a selection of ND filters and plumped for a number 2, because by all accounts if you only have one, it's the best one to go for ?.

Weather permitting I'll try again tomorrow (lowest iso, shutter priority mode, dr off & longer exposure time).

[RonM]

Probably not a lot Dave, I use ND filters (Grads) usually to hold back the sky to give me some detail here is a shot that I used a combination of a 3 + 1 or 2 stop grad together to ensure I got the sky I wanted



to get smoother water you are probably going to have to look at 4, 5 or 6 stops slower shutter speeds to get any really noticeable effect as you can see above I was holding back the sky 4 or 5 stops to get the detail and depth of colour I wanted.

[DaveG40]

Thanks Ron, Nice shot by the way.

I've tried again this morning (wish I had'nt), the results have been far worse than yesterday, probably to do with the light ?. Yesterday we had bright blue clear sky today it's overcast, everyshot I've taken with the ND fitted has come out out of focus (MF & AF), I've used various shutter speeds and apertures, and I've used both my 62mm lenses (Minolta 28-105 and Sony 18-250), with the nd fitted the shot's are out of focus, as soon as the nd's removed = crystal clear shot. Would i be right in thinking that it's a filter that's of use /beneficial in bright / good light conditions only ?.

If so I'll probably take your advice and get another nd (possibly a grad).

[El_Sid]

I've used various shutter speeds and apertures, and I've used both my 62mm lenses (Minolta 28-105 and Sony 18-250), with the nd fitted the shot's are out of focus, as soon as the nd's removed = crystal clear shot.

Assuming you aren't handholding long exposures then this sounds like a faulty filter - e.g. the surfaces are not parallel or the glass itself is of poor optical quality or some optical issue which is throwing the focus accuracy off. I suppose it's possible the contrast is being reduced to a level where the AF sensors are struggling though that usually results in slow or hesitant AF performance or even a failure to focus at all - characterized by the lens cycling though the full focus range...

Mount the camera on a tripod and focus the lens manually without the filter on and take a control shot. Then, without adjusting the focus, put the filter on and take a second shot. If the control shot is in focus but the filtered one is not the filter is faulty. If the filtered shot is in focus then either it's throwing the AF accuracy off or there is camera shake present in the apparently OOF shots. To determine which switch the AF back on and, still mounted on the tripod and using a remote release (and mirror lock up if possible) take a third shot. If this is defocused there is an AF/filter compatibility issue, if it's sharp then I suspect camera shake...

Would I be right in thinking that it's a filter that's of use /beneficial in bright / good light conditions only ?.

Not really. An ND filter can be used at any time you that wish to adjust the exposure to keep it within the capabilities of the camera/film/sensor or to achieve an effect not possible without the filter present - e.g. long exposures in moderate or even good light. Using an ND filter, especially a very dense one, in low light may adversely affect AF as mentioned but manual focus remains an option.

[DaveG40]

Hi Sid

I did as you instructed; mounted my camera on a tripod, the timer was set to 10 sec's and here's the results (I carried the test out indoors, as the light outside was'nt great).

Photo bucket

AS you can see MF with No ND is clear, MF with ND is probably the worst (slightly out of focus), and AF with the ND is slightly better, but not as good as the control shot.

The 4th photo is a landscape shot i took yesterday with the ND filter on and the camera in AF, which looks fairly good, hence my reason for asking about good light compatability,i tried the same shot without the ND and could'nt tell the difference (I was expecting a fuller sky).

[Stevet]

(I was expecting a fuller sky).

Dave,

Is your filter a graduated ND or a normal one?

If normal, then all it does is reduce the amount of light hitting the sensor equally across all of the sensor area. The camera will adjust the shutter speed or aperture to compensate, so other than depth of field or motion blur, the scene will be recorded just as if the filter wasn't there. Such a filter is used when you want to adust aperture or shutter speed for 'artistic effect' or if conditions are too bright for the camera to cope.

If what you are after is 'darkening' a selected portion of the image (e.g. the sky in a landscape) you need a graduated ND filter.

Note that when using the filter in 'dark' conditions there may be insufficient light transmission to allow the autofocus to function.

Cheers,

[cpfc12]

I think Steve may have the answer here. No problems with my A700 using any NDgrads.I also have a full grad for slowing things down when required. I have Cokin filters and although probably not the best they are pretty reasonable quality and don't cause any Focus issues.