Glass and mounts for fs100

[Alister Chapman]

An important observation from the test shoot that I did with Den Lennie earlier in the week is that if you are using a lens adapter, we used a cheap e mount to nikon. If you are going to use full frame lenses then it is vital that the adapter incorporates a choke or baffle. Without one you will get some strange flare characteristics. The MTF adapters do have a baffle, I wish we had used one of those and not the cheaper one that we had.

[Terje Rian]

Alister,

Thanks for the tip. But would you mind explaining what a "choke" or a "baffle" is (when it comes to an adapter)? My dictionary isn't very helpful, I'm afraid. I need to know what to look for, if I decide to purchase an adapter. Thank you!

Best,
-terje

[Jason Hampton]

We should ask Birger if they have a choke or baffle for their mount.

[Nicholas de Kock]

So what lenses do you buy to get iris & semi auto focus enabled? I would love to get this camera but I have no idea what F2.8 lenses will work on this body (electronically).

[Piotr Wozniacki]

Originally Posted by Alister Chapman

An important observation from the test shoot that I did with Den Lennie earlier in the week is that if you are using a lens adapter, we used a cheap e mount to nikon. If you are going to use full frame lenses then it is vital that the adapter incorporates a choke or baffle. Without one you will get some strange flare characteristics. The MTF adapters do have a baffle, I wish we had used one of those and not the cheaper one that we had.

Dear Alister,

Please explain to us mortals what a choke or baffle is (preferably with a picture of an adapter).

Thanks

Piotr

[Matt Davis]

PMJI (oops, Pardon My Jumping In) before Alister got a shot, but you know what waiting for uploads can be like...

The choke or baffle Alister refers to would be a simple aperture within the mount to restrict the amount of light going through it, a bit like an 'internal matte box' for the adaptor. Lenses designed to shine their light onto huge great big Full Frame sensor would tend to shine their light over the internal bits around the edges of the smaller S35 sensor, thus perhaps causing internal reflections or glare. By blocking out around the edges and leaving just the middle bit, the stray light absorbed by matte black surfaces, you'll get more contrast, deeper blacks, all that expensive meaty goodness.

Returning you now to your scheduled programming...

[Jason Hampton]

I am sure the Birger mount will have something like that in mind.

[Piotr Wozniacki]

Originally Posted by Matt Daviss

PMJI (oops, Pardon My Jumping In) before Alister got a shot, but you know what waiting for uploads can be like...

The choke or baffle Alister refers to would be a simple aperture within the mount to restrict the amount of light going through it, a bit like an 'internal matte box' for the adaptor. Lenses designed to shine their light onto huge great big Full Frame sensor would tend to shine their light over the internal bits around the edges of the smaller S35 sensor, thus perhaps causing internal reflections or glare. By blocking out around the edges and leaving just the middle bit, the stray light absorbed by matte black surfaces, you'll get more contrast, deeper blacks, all that expensive meaty goodness.

Returning you now to your scheduled programming...

Thanks Matt - got the idea.

Being a mechanical engineer, I couldn't help associating those two names with mechanical "features" I am familiar with (e.g. a "baffle" is a special element of plastic injection mold for cooling narrow and deep cores). Realizing of course we're talking optics here (and not mechanics), I wasn't able to guess without a right hint like the one from you :)

Piotr

[Brian Bang Jensen]

Originally Posted by Nicholas de Kock

So what lenses do you buy to get iris & semi auto focus enabled? I would love to get this camera but I have no idea what F2.8 lenses will work on this body (electronically).

You can use Sony A-mount lenses with the Sony adaptor LA-EA1.
The Zeiss / Sony SAL2470Z is 24-70mm f2,8. this will give you a focal lenght of around 36 - 105mm on the FS100.

[Brian Drysdale]

The focal length doesn't change, it's an equivalent focal length that gives the same angle of view on the different sensor. I suspect people know what you mean, but it can become confusing.

[Nicholas de Kock]

Originally Posted by Brian Bang Jensen

You can use Sony A-mount lenses with the Sony adaptor LA-EA1.
The Zeiss / Sony SAL2470Z is 24-70mm f2,8. this will give you a focal lenght of around 36 - 105mm on the FS100.

Thanks that's what I was hoping for, I currently own Canon glass but I'll easily trade them in for Sony glass if it means I can get them to work electronically with the FS-100. Do you know if you lose any light with this adapter?

[Brian Bang Jensen]

Thanks Brian for correcting me. Of course, a given focal length is always the same.
On a 50mm lens the distance to the focal plane is always 50mm no matter how large or small a sensor the camera it is mounted on has.
I always think of the angle since it is the important thing to get the entire scene framed. Now we're at it, we can also affirm that DOF is always the same with the same focal length as a 50mm lens with a given aperture always gives the same DOF. It is the focal length you need to frame your scene you change and an efekt of that you also changes the DOF.


Nicholas, adapters for different lenses do not contain any optical elements so there is no light loss.

[Brian Drysdale]

BBC TV studio directors and TV studio camera operators used to be trained in angles of view rather than the focal length. In practise that makes a lot of sense when planing and framing shots.

[Alister Chapman]

[QUOTE=Brian Bang Jensen;1647584On a 50mm lens the distance to the focal plane is always 50mm no matter how large or small a sensor the camera it is mounted on has.[/QUOTE]

That's not quite correct. The focal length is the amount that the lens converges light or the optical power of the lens.

The distance between the rear of the lens and the sensor, known as the flange back will vary depending on the design of the camera. On a Canon EF-S camera it is 44mm on a Nikon it is 46.5 and E-Mount is 18mm. That's why you can put a Nikon lens on a Canon or Sony, but not the other way around. A 50mm lens will always be a 50mm lens no matter whether it has a 18mm flange back or 44mm flange back. If you try to use a lens at the wrong distance from the sensor you won't be able to focus it (or at least the focus scale will be off).

It's all very confusing, particularly because people often talk about applying a conversion factor to the lens when really the conversion factor should be though of as applying to the camera as it is the camera and the size of it's sensor that changes, not the lens.

[Liam Hall]

Originally Posted by Alister Chapman

DoF is a function of aperture and focal length. So a 50mm lens at f1.8 will have the same DoF as any other 50mm lens at f1.8, whether its, Nikon, Canon or Sony. The flange back distance makes no difference.

For clarity, that's not quite right.

DOF is is a function of focal length and the aperture, but is also determined by the camera-to-subject distance and the format size or circle of confusion.

You are right that using adapters won't affect focal length, but altering the flange back can affect infinity focus.