[milesy]

Hi guys

Using a k5iis and I have a set of nd filters that I would like to play around with ... So step 1 I thought work out how dense a filter it is ... So set camera to manual green button ... Take a reading .. Add filter take a reading

My problem is that a photo taken with the nd filter is considerably darker using the green button than the one without ... I assumed that using the green button it should have adjusted the shutter speed to result in basically the same photo with or without the filter. Just different speeds

Is my thinking wrong ???

[pathdoc]

If you had some degree of exposure compensation set before, the green button resets that. That may be what's happening. I don't have my K5 and ND filters with me right now, but if nobody else has responded by the time I get my hands on them again I'll have a play around and let you know. Either way it will be worth doing and I will report back on what happens to me.

[mattt]

Not sure why you are using the green button. The camera meters through the lens (unless you are using a "pre-A' version lens). You might find with very dens filters the metering is incorrect due to light from the VF affecting exposure (I usually block the VF with some masking tape, a lens cap cover, or even just my ball cap).

In terms of ND filters - The filters are available in various densities. I normally carry a couple of ND8 or 3 stop filters, and an ND400 (9 stops). I normally compose on a tripod with no filter. Set focus to manual, then add the necessary filter for the desireable length of exposure.

[Alex645]

Are you certain they are ND filters and not a linear polarizer? ND filters will not only have "ND" stamped on the ring, but also the amount of EV light loss.

[milesy]

Hi guys .. These are cheap filters they came with 3 ND and 3 GNd filters ...

I'll check ex compensation but I don't think this is the issue as I used the green button in both scenarios

The reason for using the green button was to get a metered Time .. As in to set the meter to a zero point which should give a correctly exposed image

[mattt]

I think you'll find if you make a "normal" exposure, then do the math, you'll get better results than trying to meter through the ND filters.

for example 1/250 @ ISO 100 and f5.6... then add an ND8 or 3 stop ND filter will give you 1/30 @ ISO 100 and f5.6 - 1/30 is slow enough to slick a waterfall.

If you're looking for streaking clouds like those below you need a much longer exposure, but using the same original exposure, you'd maybe stack and ND8 and an ND400 for 12 stops of slow... you'd end up with an exposure like 8" @ ISO 100 and f5.6, and then maybe stopping it down to f11 would give you 30" or, stopping it down to f16 to get a 1' exposure.

[milesy]

Hi mate your probably right but my original action was to determine what value the nd is ... It's been ages since I bought them and there is nothing marked on the filters themselves

[mattt]

Just a suggestion, shoot a regular frame, shoot a frame with the filter, then use the Histogram to determine (like drop it into Light room and find out how many stops are needed to increase the exposure).

Actually, if you shoot a regular frame, then set the camera in manual to those settings, mount the nd filter, the K5IIs ought to give you an idea how under exposed it is in the VF

[milesy]

So taking a manual shot without the filter then adding the filter ( no changes to exposure etc) it takes an exposure change of 4 in Lightroom to pretty much Mach the no filter image ... Is this approximating 4 stops ?

---------- Post added 01-08-16 at 12:05 PM ----------

I may have found my answer :-( I wasn't using the 'hood' when fitting the filter ... If I use the hood then it seems my darkest filter changes the tome required for correct exposures by a factor of 8

[milesy]

A follow on from this ... What's the main difference between a genuine cokin set of filters and the knock of ones from eBay ... Massive difference in price but is there a real world difference

[mattt]

I think the response most would say is colour. Also, if I recall correctly, the Cokin product is made in France, while the cheep knock off's are usually of Asian origin.

For my purposes, I'm using a Formatt-Hitech 85mm 3stop Soft Grad filter in a Cokin P frame.