Ghostless filters

I picked up these little gems today, are they worth keeping, I believe the Ghostless filters are quite rare, I haven't a clue what they are worth though.

I suspect they are not as useful on modern lenses as they already have the ghostless coatings :

What do you think
[IMG]http://i184.photobucket.com/albums/x261/ClarkyinAus/00K73478.jpg[/IMG]

I think they are quite rare but probably not worth a huge amount.
I've got one on the 50mm on my Spotmatic, mainly as a period piece and I haven't tried putting it on a more modern lens.

R

The ghostless filter has a shape that mimics the shape of the front element of the 50mm lens for the Spotmatic - the f1.4 version I think. The theory behind this is that it means the light path is not diverted by a flat filter.

Of course other lenses will have different curvatures, so the filter won't make any difference. The coatings are the same as the coatings of the Pentax lenses of the day.