How would one use filters with the "bulb"-like shape front element lenses?

You really can't use filters with these due to the wide angle of view. You could try to rig up something along the lines of a Cokin style filter, but it would have to be a very large filter to avoid vignetting.

Some lenses, like 400mm and 600mm Nikon teles, have a "drop-in" filter which you slot into a gap in the middle of the lens. Not sure if any fisheye lenses are designed this way

I have the LucrOit system since a week and I'm using it on a Sigma 8-16 with a Nikon D300 and it doesn´t vignette at all, neither vignette on my friend's Samyang 14 on a Canon 5D MkII. We both are very happy with that system, also my father has bought it for his Nikon 14-24 and he's like a boy because he can use filters on his 14-24.

BTW I strongly recomend the ND Prostop filter from Hitech, just awesome, the most neutral filter I've ever seen.

Wish you great shots.

I've been using Lucroit system with Nikkor 14-24 since few months ago and it's really good. The HiTech ND Pro Stop (10 stops) is amazing. You can check these links:

http://1x.com/photo/55827

http://1x.com/photo/56452

Hope it helps you.

A very simple and cheap hack consists in cutting and placing the gel filter behind the lens, that is, between the lens and the camera's body.

You can see a tutorial here:

• YouTube: Hack Tip: Adding ND Filter Gel on Rokinon Fisheye Lens to Block Light

It can be useful to avoid overexposure as seen in the video. Or if you are working with an infrared-converted camera and need to use an orange or red filter.

Or you could hacksaw some ND filters (the plastic ones) as I for one can't find gel swatches in the UK. I've hacksawed an ND8 filter and it fits perfectly behind the lens. Just add a little blu tack to keep in place...now to do with other filters

You could buy the lenses in EOS mount and then buy an EOS R camera and use the EF to R adapter with a built in rear filter holder.

The bulging front element of your lens makes using filters difficult.

• To use a filter in front of the lens, you'd need a very large filter or a bowl-shaped filter that curves around the lens. The filters may be expensive, and you would need to find or make a custom holder for your lens. You may have to correct vignetting produced by the filter or crop the edges of your images.

• Some lenses are designed to use internal filters. Your lens does not appear to be among them. Some people have disassembled lenses to fit internal filters. (eg, DIY Apodization Filter) Flare and reduced sharpness are likely problems, depending on lighting.

• It would be easiest to use a filter behind the lens.

  • Some mount adapters are designed to hold filters. It may also be possible to fit a filter to an adapter not designed to hold one.

  • If you are using the lens on its native mount, without an adapter, trying to attach a glass filter behind the lens would interfere with the DSLR mirror. A gel filter may be thin enough to not interfere with camera operation. Image quality would probably be reduced, but this is probably the best option available to you.

  • You could have your camera modified with a filter in front of the sensor. This is common for astrophotography and infrared photography.

    See: infrared-conversion