Has anyone tried adding a filter holder to lens adapters?

ProfHankD wrote:

Honestly, I haven't found filters all that useful with digital cameras except for special purposes. I suppose a polarizer might be worthwhile... but if the adapter is designed to have a filter with a specific optical thickness, you'd need one even for clear to keep the same rear focus distance, which would still degrade IQ a bit.

I do not see much use for them either but an ND and a polarizer is in the bag. The 58mm step up filter ring added to my 3D printer hoods is convenient for the 58mm caps and the use of the two 58mm filters that I have. Sure there is a risk that dirt on the filter shows faster when more extended from the front element but the depth of the hood for my lenses usually goes along with the focal length of the lens. I am measuring the hood depth all around more precisely now in manufacturing.

https://www.dpreview.com/forums/post/62095208

For the 75mm 5.6 scanner lens mounted into an M42 macro extension tube I made a hood that fits in the M42 thread at one side and a 58mm filter thread at the other side. A deeper hood I made for the 100mm scanner lens also mounted in an M42 macro extension tube. The M42 extension tube mounting makes it all quite universal when both side M42 threads, male/female, can be used.  For example in reversing the lens. The diameter of the lens barrel has to be small though. M52 extenders could be used for larger diameters.

75mm on the camera with short helicoid to MC-11 From front to rear; 58mm hood with male M42 rear fit in M42 extender tube with the barrel lens fitted in its center, M42 helicoid,  M42 to EOS adapter, MC-11 adapter. No chip added yet.

100mm on longer helicoid and its hood showing the rear side with the male M42 thread

100mm reversed mounted to the helicoid with a dual male M42 extender

Even projector lenses could be used in M42 female threads when an M42 thread on their barrels is made with a lathe. Studying that possibility; the standard 42 to 42.3 mm diameter lends itself quite good for that work, little to cut off for the thread and enough wall remains. For hoods a female M42 ring at the rear of the hood could be used.

Met vriendelijke groet, Ernst
No photographer's gear list is complete without the printer mentioned !