Tiancao
Newbie
For those who want to tint the viewfinder, this may be of interest: There is a space between the black metal frame (after removing the silver cover) and the viewfinder window that can hold a piece of gel filter. I probed it with paper first, and ended up with a size of about 2 cm x 1.5 cm. The space is bigger but the filter may bend if being too big. The drawback is that the filter may get slightly scratched during entry, so be gentle. My 2 cents. 
Highway 61
Revisited
All Nikon RF cameras can accomodate a gel filter under their main VF front window metal mask.
But apart from putting a Fuji Blue 20 gel filter under the front window mask of the colorless Nikon S3 viewfinder to enhance the RF patch contrast (this has been well documented here thanks to Jonmanjiro) who'd want to "tint" an already green tinted VF with a yellow-orange RF patch ???
richardHaw
junk scavenger
i saw a few with the protective glass replaced with one from a real glass filter its obviously a DIY job
its obviously a DIY job Tiancao
Newbie
I got the idea from the forum and Richard . I just found out I used a Kodak Wratten gelatin ND filter, which is what I have at hand . Not the best option for sure.
. I just found out I used a Kodak Wratten gelatin ND filter, which is what I have at hand . Not the best option for sure.veepeedeepee
Newbie
Yeah, this is exactly what I did some time ago to my own.
richardHaw
junk scavenger
i was about to cut a filter to fit but then i saw something here in RFF and gave it a go since i have the said gel at-hand from my days shooting flash
it saved me some time but it wasnt as nice as the one that I saw using a glass filter.
the real reason why the leica and contax patches are so sharp and contrasty is because they use a piece of "relay prism" to transmit light between the mirror and the splitter. on the contax, its a whole long shard and that made it exceptional. the leica m cameras have a short segment but it helped.
the reason why some Nikons had a feathered edge on the patch is more due to the mask (or the lack of it) on the receiving end of the beam if i am correct. you can improvise by making a square patch mask but that would make the patch smaller. this is probably the reason why the mask was omitted or intentionally made bigger. they settled with a feathered edge but giving you a bigger patch. notice that leicas patches are rather smallish compared to what nikon has.
on the flip side, a canon 7's patch is sharp because it has the mask but the resulting reflection is poor because it only has a dinky mirror and not a prism on the other size of the rangefinder i thought that it was an awesome camera but i cant call it a "classic camera" because it was built like a toy. writing an overhaul article for it next year
it saved me some time but it wasnt as nice as the one that I saw using a glass filter.
the real reason why the leica and contax patches are so sharp and contrasty is because they use a piece of "relay prism" to transmit light between the mirror and the splitter. on the contax, its a whole long shard and that made it exceptional. the leica m cameras have a short segment but it helped.
the reason why some Nikons had a feathered edge on the patch is more due to the mask (or the lack of it) on the receiving end of the beam if i am correct. you can improvise by making a square patch mask but that would make the patch smaller. this is probably the reason why the mask was omitted or intentionally made bigger. they settled with a feathered edge but giving you a bigger patch. notice that leicas patches are rather smallish compared to what nikon has.
on the flip side, a canon 7's patch is sharp because it has the mask but the resulting reflection is poor because it only has a dinky mirror and not a prism on the other size of the rangefinder
i thought that it was an awesome camera but i cant call it a "classic camera" because it was built like a toy. writing an overhaul article for it next year