B4 Lens adapter for C300

S

Starman

Well-known member
I am looking at a B4 lens adapter for the C300

Question, I have to have this doubler on the lens engaged to cover the C300's sensor, BUT, will I lose any wideness in my lens? How much? I have a really nice Fujinon 17x4.6 ENG lens right now. Would this be practical? I am not 100% clear on how this works. Forgive my ignorance in this matter.

https://www.lensadaptor.com/b4-23-canon-ef-adaptor
 
I will ride on Starman's shirt tail and ask what is the crop factor when using a B4 lens with a dumb adapter.

The B4 lens would be double. So, you do loose some bottom end. Some say you loose 4 stops.

The reason you would want to use a B4 is for the parafocus, zooming, and zoom ratio. Alistar Chapman has an article on using a B4 on an F5 with an adapter. Don't remember if smart or dumb.
 
Is the 17x4.6 2/3" or 1/2"? It sounds like a 1/2" model. All of the adapters I've seen are for 2/3" lenses. A simple "dumb adapter"(mechanical only), if they even exist, will not make a 2/3" lens' image circle cover a full s35 imager EVEN with the lenses 2x engaged. The MTF still has optical elements.

Most of the adapters I've seen out there(I've used the IBE) come in two varieties: Full optical correction and partial optical correction. The versions with all of the optical elements to allow a 2/3" lens to cover a s35 sensor are expensive, usually well north of $5K. BUT you do not have to use the 2x that is built into the lens(or have to have a lens with one built-in). You will lose approx. 2.6 stops. The field of view that you had with the lens on a 2/3" camera stays the same on the s35 camera(or at least very very close). The "partial optical adapters" are usually much less expensive and also provide the mechanical connection between the 2/3" lens and the s35 body, BUT they only have optical elements to blow the image up IN CONJUNCTION with the lenses built-in 2x, so you MUST have a 2/3" lens with a built in doubler. But with that you get a cheaper, lighter and smaller adapter. It's still going to cost you about the same 2.5-2.6 stops in the end, though.

And I think the partial(or maybe they're purpose built) adapters that work with the center crop/s16 mode on the F5/55 will cost about a 1/2 to 1 stop.
 
The IBE adapter that Abel sells (that's the one I've used) is a "universal" adapter. The mounts are user swappable, so if you're putting it on a C300, for example, you would buy the EOS mount and it would lock onto the camera natively, no intermediary adapter required. You can also buy PL and Nikon mounts. I think they're about $500 per mount.

Had a quick look through the Fuji site and I can't find a 17x4.6 2/3" HD ENG lens. You must have meant the 17x7.6. BIG difference on the back end... About 30 degrees.
 
There shouldn't be any "crop factor" with these adapters. They are enlarging the native image circle of the 2/3" lens to cover the s35 sized imager. You will lose about 2.6 stops of light, but the field of view will remain the same.

Example: when I put my Fuji 13x4.5 on my C300 with the IBE adapter, it essentially went from a 13x4.5 f/1.8 on 2/3" chips to a 13x11.5 f/4.5 on a s35 sized chip, but the f.o.v stayed approx. 93 degrees.
 
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