In response to a question about his genre winning photo, Onslow said that he used a Lee filters.   Lee as with Cokin are systems where an adapter  is used to allow use of the same filters with lenses of different diameter.  I do not have either system.

I have two questions. The first is perhaps elementary but I don't know the answer. Does the stacking order of the filters matter?

The more important question is about the filter systems. Why systems with adapter rings and the same filters used for each lens?  The first meaningful thought to me is when wanting to use a circular polarizer.  These are not inexpensive. One large enough for the largest diameter lens I would use it with needs only adapters to use the same filter on smaller diameter lenses. That makes sense.

I see the Lee and the Cokin filter holders and filters. Is there a reason to choose one over the other brand?  Lee does make the polarizer and I really do not know if there is a Cokin counterpart.

Plastic also bothers me some in filters. Sure, eyeglasses use high grade plastics and optically work well in eyeglasses. Scratches of plastic bothers me.  I prefer glass for filters..even if the few I own only fit one lens.

Any comments on filter systems like Lee or Cokin will be appreciated and a comment on whether or not stacking order matters.

Richard, if you see this thread, please chime in. You do have the Lee and can perhaps comment on that system.       

Thanks for any input.           TomDart. 

Attached Link: http://www.cokin.com/

I think the stacking order, or the position in the filter holder if you are using only one filter, can actually matter, and that depends largely on the aperture you use. If you have, let's say, a graduated neutral density filter with a hard dividing edge, you better use it in third position, farther away from the lens, if you want to keep that well defined edge with a wide open aperture. If you want a softer edge, put it in the closest position... It does make a difference.
And if I'm not mistaken, the polarizer usually goes in first position... please correct me if I got that wrong.

Lee offers ployester filters and resin ones.  I wonder how these comare to glass.  They offer glass but the home page does not have a link I could find on glass filter pricing.  I imagine it is a lot more than the plastic versions.

Thanks for the imput so far. This is quite helpful to me.  The info on distance from the lens for graduated nd filters is good to know.  This would seem to add some versatility.  Thanks again.      Tom.

Also noteworthy (but logical): if you plan on shooting with wide angle lenses, like Richard did, you really need the larger filter (and holder) sizes to cover the angles; otherwise you'll have the edges of the filter/holder showing in the corners of your image.
And larger means more expensive...

So, my widest angle lens is a 62mm.  I will likely use filters for lenses of 72mm, 62mm and 55mm.  I am now set on the "need" for a filter system, not knowing to which to put the cash.

I will check into the larger filter sizes but wonder if what works for the 72 will be large enough for the wider angle 62?  Then again, how many filters are stacked will make a difference, I am sure.  Likely, I will start with polarizer, grad ND and ND.  That should cover most of the sort of shots I do now.  

Anyway you look at it, the sum for all comes up to a fairly dear amount.  That is why versatility is so important...to be able to move from one lens to another without problems.   Tom.

Order does make a difference.
 
A polariser has to be at the front to work efficiently - the other filters diffract some light so putting a polariser behind those results in unpredictable results. On a practical note it has to be at the front to be able to adjust it !

If you put an ND filter in first you are not going to see much through the view finder - you won't be able to see where to adjust an ND grad too. 

My preference :
Determine exposure and what filters to use before you do anything else.
ND grads  and adjust as required.
Polariser and adjust as required.
ND filter if required.
Don't forget to adjust your exposure to compensate for Polariser and ND if used.

*"All the Cokin filters I use are glass I've never come across plastic filters" *How odd I have never come across a Glass Cokin filter - unless of course you are including organic glass which is an optical grade plastic used in z pro and x pro filters.  

The difference between Cokin and Lee is quality. 

Even if you decide Cokin filters are good enough for your use - and they are very good especially the z pro range there is simply no comparison between the Cokin filter holder and the Lee filter holder.  
The Lee is a handmade machined product - The Cokin a mass produced moulded plastic.
I'll let you imagine how it feels to use each,  how smooth and easy each operates, and what effect each might have on the filters you have just spent a lot of money on. 

Great info. Thanks.      Tom.