about gnd，which material is better ，glass or resin？ how do it choose？

[Bornfect]

hello all
resin gnd cheaper than glass one。I do a simple testing about image of definition，below 70mm ，looks like the same，and most lens which need gnd filter is wide lens。
and 2 or 3 piece using together ， also show the same effect，not casting colour， so I feel both can make the same work，but many people prefer to glass filter。
or any aspect which I do not consider ？ thanks

[Manfred M]

Any GND filter will be resin. I can't think of any way of producing the effect in glass. If you find a glass one, I suspect that you are likely looking at a sandwich construction with a piece of resin sandwiched between two pieces of glass.

Glass filters are heavier and break more easily than resin ones, but are more scratch resistant. Optically there is no difference.

[Black Pearl]

I have seen a few glass GND filters over the years but the biggest issue with them is not whether they are optically better or worse than resin filters its that their fixed horizon position makes using and composing a shot with them very rigid. With the square/rectangular filters and a slot-in holder you are able to position the graduation line on your horizon almost regardless of where it sits in your image.

[Manfred M]

I have seen a few glass GND filters over the years but the biggest issue with them is not whether they are optically better or worse than resin filters its that their fixed horizon position makes using and composing a shot with them very rigid. With the square/rectangular filters and a slot-in holder you are able to position the graduation line on your horizon almost regardless of where it sits in your image.

I had not seen this Hoya design before, but it is unusual in terms of how the GND is manufactured. Glass filters have to be mass dyed, and then doing a bevel cut will certainly be one way of introducing a gradient, but there would be a very thin and fragile edge in the beveled area that requires some protection.

Most of the other "glass" grads seem to have a dyed resin piece sandwiched between two sheets of glass.

[dje]

Most of the other "glass" grads seem to have a dyed resin piece sandwiched between two sheets of glass.

Yes Manfred I think that is the case in general however I notice Formatt Hitech have a new technology out they call "Firecrest", see here. They ain't cheap!

Dave

[Manfred M]

Dave - I know some people that have used the Firecrest filters. So far as I can figure out, they are using a vacuum deposition approach for bonding a material directly to a glass substrate. I've heard some comments that they are not as neutral as Formatt Hitech claims, but haven't used them myself. I understand that they are really hard to get hold of right now. I have no information on how they hold up as thin film deposition on glass has tended to be quite fragile.

I knew that they used this process to make ND filters, but was not aware that this process was being used on GND filters.

[Bornfect]

glass gnd get developed in past two years， so far，“gradual process is not enough gradual” is solved 。one piece of glass make into GND，in our area，we call it “metal coating” which is similar ”uv coating”，but difference ， “mental coating ”will cause strong light of reflect。 it can not be solved for now。
and sandwich gnd is not uesd by resin。
i take some landscape when light and shadow is complicated ，I found traditional size by holder ，like 100 150 ，150 170 ，100 100， can not make a perfect ， because sometimes only need reduce a small area lighting，probably only need 10 10，或5 10 new size by handhold。