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
 
Necktie Boy

Necktie Boy

Well-known member
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.
 
R

Run&Gun

Well-known member
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.
 
R

Run&Gun

Well-known member
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.
 
Necktie Boy

Necktie Boy

Well-known member
Thanks for the information R&G.

If I read right, the crop factor with the adapter Starman linked is 2.7.
 
R

Run&Gun

Well-known member
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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