Using GND Filters

[dje]

I have been considering getting a couple of GND filters and a reverse GND filter for a while now but am seeking advice please on the practicalities involved. These would be used on a Sigma 17-70 HSM lens which has a 72mm filter thread. I anticipate using these with sunrise/sunset work. As usual, my budget is not unlimited

One system under consideration is the Cokin P series holder which takes filters that are about 84-85mm wide. Cokin have some GND's and I was considering a 2 stop and a 3 stop, both hard. Would this be a reasonable choice ? I would also like a reverse GND but I don't think Cokin make them. You can however get a Hitech or a Sing-Ray that will fit the Cokin P holder.

One concern I have relates to the possible limited amount of vertical adjustment available on a 72mm diameter lens. Does it matter if the bottom of the filter glass sits above the bottom of the front lens glass ? (I would think yes!) The Sing-Ray filter is 85mm wide and 120mm long and the Hitech is 85mm wide and 110mm long. Would these give me sufficient vertical adjustment ?

Are there other systems I should be considering ?

Your advice would be much appreciated.

Dave

[Colin Southern]

Hi Dave,

I've only got a minute, so ...

1. The transition zone will normally be somewhere between 1/3 down from the top, and 1/3 up from the bottom.

2. I strongly suggest getting filters that are 100mm wide (usually 100 x 150mm). They'll give you more adjustment - easier hand-holding - less vignetting (bigger holder).

I use Singh-Ray exclusively.

[dje]

Hi Dave,

I've only got a minute, so ...

1. The transition zone will normally be somewhere between 1/3 down from the top, and 1/3 up from the bottom.

2. I strongly suggest getting filters that are 100mm wide (usually 100 x 150mm). They'll give you more adjustment - easier hand-holding - less vignetting (bigger holder).

I use Singh-Ray exclusively.

Thanks Colin

I'll have a look at the 100mm series and see if my budget can manage it

Cheers Dave

[Colin Southern]

Thanks Colin

I'll have a look at the 100mm series and see if my budget can manage it

Cheers Dave

Hi Dave,

They're cheaper than buying the 75mm ones - having to sell them at a big loss - and then buying the 100mm ones!

[dje]

Hi Dave,

They're cheaper than buying the 75mm ones - having to sell them at a big loss - and then buying the 100mm ones!

The reasoning is very sound Colin but will my better half buy it !

Cheers Dave

[Colin Southern]

The reasoning is very sound Colin but will my better half buy it !

Cheers Dave

Just show her the price of Lee filter holders or Cokin X-Series, and you'll be fine

[dje]

Colin

One further point - for sunsets/sunrises (where the sun is in shot), I would think that a Reverse GND (say 3 stop) would be the most useful GND. Would you agree ?

Cheers Dave

[Colin Southern]

Colin

One further point - for sunsets/sunrises (where the sun is in shot), I would think that a Reverse GND (say 3 stop) would be the most useful GND. Would you agree ?

Cheers Dave

Hi Dave,

A reverse GND is used when you're trying to attenuate the horizon line, but if the sun is in the shot then that area is ging to blow anyway.

Case in point, my Haulashore Island shot, where I had no less than 6 stops of attenuation over the sky portion ... Not even close to taming the sun!