Crop confusion

[Dazzer123]

Hi folks,

 

Could anyone clear up some confusion for me?

 

I'm looking to get a Fotodiox adapter in order to use Mamiya RB67 lenses on my A7.

 

On the Fotodiox website they state that in order to know what crop factor you're going to get with this combination of sensor and lens mount (via their adapter), divide the lens length by 2.

 

So a 70mm RB67 lens will give you 35mm equivalent on the A7.

 

But this doesn't make any sense to me. The Mamiya lens has a bigger image circle (i presume) in order to cover the Mamiya's 6x7 "sensor".

 

So i would expect it to be precisely the opposite. As the Sony's sensor is much smaller, when you place it at the same distance (the location of the plane of focus), it can only cover around a quarter of the area ........so shouldn't one double the focal length to know what crop you'll get?

 

Curious if anyone can clear this up for me!

 

Thanks!

Edited May 26, 2023 by Dazzer123

[Pieter]

Focal length is a property of the lens, not of the sensor or the projected image circle. A 50mm Mamiya 645 lens on a Sony A7 will give you the same angle of view as a Sony 50mm FF lens on a Sony A7.

Crop factor really only matters if you want to compare the results from one system relative to another. If you know what the angle of view of your 70mm Mamiya lens on your 6×7 camera looks like, and then put that lens on an A7 camera, you will find that the image produced by your A7 will look like what a 140mm lens on your Mamiya would have given (a smaller part of the image circle is captured, so the image looks more zoomed in). So in that sense you are correct.

However, what that Fotodiox knowledge base tells you is not what your 70mm M645 lens will look like on an A7, but what focal length you need on an A7 to get the same viewing angle as your 70mm lens on a Mamiya camera: 35mm.

Edited May 26, 2023 by Pieter

[Dazzer123]

Thanks for the info, Pieter!

To be honest, i'm still confused, but i think i get it.

You said:

"What that Fotodiox knowledge base tells you is not what your 70mm M645 lens will look like on an A7, but what focal length you need on an A7 to get the same viewing angle as your 70mm lens on a Mamiya camera: 35mm"

But Fotodiox put it like this:

"Using a 80mm Hasselblad (6×6) lens as an example: 80 ÷ 1.6 = 50mm. So an 80mm Hassy lens is going to give a similar angle of view to a 50mm lens when used on a 35mm full frame camera."

(https://fotodiox-knowledge-base.gorgias.help/en-US/faq-adapters-what-is-the-‘crop-factor’-or-35mm-equivalent-focal-length-of-my-lens-198903)

So actually, they're saying the same thing, but in a weird, ass-backward way. Because users of their adapters want to know what the lens if going to look like on the camera with the adapter compared to the original. So they should say something like:

"A 50mm 6x7 lens will give you an equivalent focus length of 100mm on your 35mm camera".

[Pieter]

4 hours ago, Dazzer123 said:

So they should say something like:

"A 50mm 6x7 lens will give you an equivalent focus length of 100mm on your 35mm camera".

No, seems like you're still confused a bit. A 50 mm lens is a 50 mm lens. Doesn't matter if it's a 6x7 lens, a FF lens or an APS-C lens: on the same sensor they all project the same angle of view (except the lenses designed for smaller sensors will show heavy vignette when projecting on a larger sensor).

But indeed, the Fotodiox site does put it wrong and awfully confusing. What it should read:

An 80mm Hassy lens used on a 6x6 camera is going to give a similar angle of view to a 50mm lens (scratch when) used on a 35mm full frame camera.

Or (albeit much less informative):

An 80mm Hassy lens is going to give a similar angle of view to any other 80mm lens when used on a 35mm full frame camera.

[XKAES]

I don't know anything about the Fotodiox Mamiya RB/RZ to Sony e-mount adapter, but I do know about Mamiya lenses, and these are cocked and released by the RB/RZ body.  How are you going to cock and release the shutter on the RB/RZ lens when it is attached to a Sony camera?

More importantly, Mamiya never made a 70mm lens for its RB or RZ cameras.  Can you clarify?????

Edited May 26, 2023 by XKAES

[Dazzer123]

1 minute ago, XKAES said:

I don't know anything about the Fotodiox Mamiya RB/RZ to Sony e-mount adapter, but I do know about Mamiya lenses, and these are cocked and released by the RB/RZ body.  How are you going to cock and release the shutter on the RB/RZ lens when it is attached to a Sony camera?

Sony A7 has it's own shutter.

[XKAES]

I know the camera has a shutter, but to use the RB lens, you have to fire/open the shutter in the lens.  How are you going to do that?

And what lens is it.  Mamiya never made a 70mm lens.

[Dazzer123]

16 minutes ago, XKAES said:

I know the camera has a shutter, but to use the RB lens, you have to fire/open the shutter in the lens.  How are you going to do that?

And what lens is it.  Mamiya never made a 70mm lens.

I mispoke, it's 75mm.

But i don't understand your point.

You mount your Mamiya RB67 lens on the Sony with the adapter. You set the aperture control on the lens to "T". You then adjust the aperture via the aperture ring on the adapter.

So it works just like any other lens would that doesn't have an internal shutter.

What's the problem with that?

Edited May 26, 2023 by Dazzer123

[XKAES]

The RB lenses have an internal Seiko shutter.  To use it on any camera, the shutter has to be open.  How are you going to open the shutter without the lens being on an RB camera.

Have you ever used an RB67?

[Dazzer123]

3 minutes ago, XKAES said:

The RB lenses have an internal Seiko shutter.  To use it on any camera, the shutter has to be open.  How are you going to open the shutter without the lens being on an RB camera.

Have you ever used an RB67?

No, i received my RB67 Pro SD from Ebay today and don't have a lens yet. I have the adapter coming tomorrow. 

But anyway, Fotodiox are obviously scammers, selling a product that doesn't work, see here for yourself:

 

 

[XKAES]

I know nothing about Fotodiox scamming people, but I do know that most people that buy adapters are disappointed because the adapter has limitations -- even if it fits.

I'm sure that the adapter that you are getting will FIT on your camera and RB lens.  Using them together is going to be a challenge -- even if they fit.

You'll find out soon.

Edited May 26, 2023 by XKAES

[tadwil]

50 minutes ago, Dazzer123 said:

No, i received my RB67 Pro SD from Ebay today and don't have a lens yet. I have the adapter coming tomorrow. 

But anyway, Fotodiox are obviously scammers, selling a product that doesn't work, see here for yourself:

 

 

Where's the scam?  The lens' shutter is basically disabled by leaving the shutter on T and the aperture dial is engaged to be controlled manually by the adapter.  If the adapter does what is shown in the video, I can't see any problem with the adapter - which is a moot point until you actually get a lens to shoot with.

Looking at the video, it's going to be a pita to be switching the lens between RB67 body and the A7.

[XKAES]

34 minutes ago, tadwil said:

...it's going to be a pita to be switching the lens between RB67 body and the A7.

My thoughts exactly.  It's can be done, but why use a lens that's twice as large and twice as heavy as your camera? 

If you want 75mm for some reason, you can get a very good, small lightweight 35-90/105mm for a few dollars -- with a SONY mount.

Edited May 26, 2023 by XKAES

[Dazzer123]

1 hour ago, XKAES said:

My thoughts exactly.  It's can be done, but why use a lens that's twice as large and twice as heavy as your camera? 

If you want 75mm for some reason, you can get a very good, small lightweight 35-90/105mm for a few dollars -- with a SONY mount.

If that was your thought, why didn't you say say it?

All you were saying was it couldn't be done, which obviously wasn't correct.

Not trying to be a dick, but it winds me up when "experts" start to get an attitude with a noob.

 

Edited May 26, 2023 by Dazzer123

[XKAES]

You are missing the point completely -- and apparently intentionally.

From the beginning, I've said it can be done, but it is a royal pain in the ass. 

If you want to take five minutes to take every picture, then you are welcome to it.

I know it because I use a an RB67 lens on my large format gear -- and know what a pain in the ass it is to use.

But you can be sure I'm not going to tell you how to do it.

You are on your own due to no one but yourself.

Look in the mirror.  YOU are the one with the attitude.  I was trying to help, but no more.

Edited May 27, 2023 by XKAES