Jump to content

Thoughts on sharpness of B4 mount lenses?


Recommended Posts

One of the reasons I don't use my Ursa Mini 4K very much is due to the PL mount. PL lenses are stupidly expensive. But I do know the UM4K has a B4 mount adapter available, and B4 lenses are cheap. There are some Canon and Fujinon zooms out there in good shape. Are those cinematic at all? Soft or sharp?

 

They might be what I need for some green screen work, if sharp enough. At the moment I only have a Helios 58mm and an Angenieux 25-250 in PL. The Angenieux is a moose. Some of those B4 zooms might be more manageable.

 

What I wish I had was a 35mm prime, but I don't see any B4 primes.

Link to comment
Share on other sites

also designed for 3 chip CCD sensors... when I very first got my F5 I used my Fujino B4 lens .. with a small adaptor for centre crop .. if works but its such a waste of sensor.. and I dont think you would ever want to project the image onto anything large.. probably better off with an actual 16mm zoom ?

Link to comment
Share on other sites

  • Premium Member

I think it can be.

 

The optical performance is not what you'd get from a DSLR lens, but then it wouldn't be.

 

The sheer performance of these lenses, the size, weight and flexibility, is enormous.

 

c224b199cc14230c1f8c24caff4fff1f_XL.jpg?

 

Ursa Mini 4.6K with Canon HJ11x4.6B

 

P

Link to comment
Share on other sites

Much as I respect Alastair Chapman, this adaptor really only seems to make sense if you already own expensive B4 lenses. A 2.5 stop light loss is considerable. Also, using the 2x extender to increase the image circle is going to soften the image no matter what sensor is behind it, even without the additional relay lens in the adaptor.

Link to comment
Share on other sites

  • Premium Member

I assume you're cropping the sensor. Just how badly does it vignette (or rather porthole)?

 

This is a complicated question because various lenses project larger or smaller images and various cameras have various sizes of sensor.

 

There are a combination of approaches (which I'm sure you're aware of) which I will list here for completeness:

 

- Crop the sensor in the camera

- Engage the doubler on the lens

- Use some degree of optical expansion.

 

The depicted configuration uses the extender and a very small amount of optical expansion to fill the cropped area of the Ursa Mini 4.6K's sensor. The adaptor is made by MTF (Mike Tapa is the guy holding the camera.)

 

Optical correction is critical in any case, because B4 lenses do not perform well on single chip cameras without it. Below f/4 the glow and flare becomes unacceptable, because of their expectation of a 3-chip block. The optics need to correct for this.

 

Yes, it is probably only worthwhile if you own the B4 lens, although there may be some argument on this for specific circumstances. That lens goes for under £4500 on eBay. You cannot get anything which does even nearly what this setup does for even double the money.

 

P

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...