ISCO anamorphic adaptor mechanical focus solution

[Anton Zimin]

Well, 

I'd like to buy a ISCO adapter and in the same time seeking for a cheap focus solution. My first though was that there are has to be a mathematical dependence between taken lens' focus and adaptor's focus. I wonder if there is a way to do it just mechanically by using gears with a right ratio. The idea is that you use a follow focus gear but with gears of different sizes that rotates two lenses simultaneously with a right ratio in a way that it focuses just right. What do you think? 

[Julien416]

Hello,

It's definitely possible. Rapido Technology even sells such a gear :

http://www.rapidotechnology.com/products-services/rapido-single-focus-solution

Now, what you need to know. Anamorphics changes their compression ratio when you focus closer. It's called breathing. The first CinemaScope lenses back in 53 worked this way. But it quickly became unacceptable as it made actors look fat onscreen as the close up had a ratio closer to 1.6 instead of 2. This problem was first fixed by Dyaliscope, an obscure french lens maker of the 50's. But it was only with Panavision in 57 that the solution was widely adopted in the industry and from that moment Panavision became the de facto king of anamorphic. 

Now, if you built such a gear, or use the one from rapido, you'll basically be using the equivalent of a 1955 lens. It can be pretty cool, but you have to understand the shortcomings. As much as I do love the old CinemaScope, I'd rather shoot without too much breathing. So a single focus solution is probably a better path to shoot anamorphic. Problem it can be expansive and make your setup heavy.

Well it's anamorphics, no simple solutions unfortunately.

 

[Anton Zimin]

Julien,

 

Don't you think the breathing effect depends on the lens? I don't see much breathing effect on Rapido Solution. Anyway it is more convenient and cheaper than all these focus systems adding chromatic aberrations )

[Anton Zimin]

Also, as for the  Rapido solution, I didn't get why they did it motorised. I definitely makes all the system more expensive. Can't it be done just with gears? 

[Julien416]

4 hours ago, Anton Zimin said:

Also, as for the  Rapido solution, I didn't get why they did it motorised. I definitely makes all the system more expensive. Can't it be done just with gears? 

Probably, but they avoided complicated gear train by doing it with an arduino and some basic step motors. Going the gear train way would require skills I do not have even though it's pretty basic mecanical stuff. They did it this way in the 50's

Example taken from the excellent filmoscopeFR website

20 hours ago, Anton Zimin said:

Julien,

Don't you think the breathing effect depends on the lens? I don't see much breathing effect on Rapido Solution. Anyway it is more convenient and cheaper than all these focus systems adding chromatic aberrations )

It depends on the lens indeed, but even the best ones breathe a lot. I used to shoot with a Kowa 8z without rectilux and was forced to resize with a 1.8 ratio at minimal focus distance. A face 10% larger than usual doesn't look too good honestly.

I went the rectilux way and even though it - very slightly - degrades the image, it's so much easier to focus without being bothered by breathing that I haven't looked back. But of course, the FM lens and the rangefinder aren't so good and bring a lot of CA...

[Hans Punk]

5 hours ago, Anton Zimin said:

Also, as for the  Rapido solution, I didn't get why they did it motorised. I definitely makes all the system more expensive. Can't it be done just with gears? 

Absolutely could be done mechanically, but you’d be limited to the precise throw of one specific taking lens per mechanical calibration, and/or the transport distance of optics throughout the focus range (which is often not linear).The advantage of a motorised route is that you can set custom waypoints along a lens’s throw, allowing offset focus sync between various taking lenses throughout the range.

[Anton Zimin]

4 hours ago, Julien416 said:

It depends on the lens indeed, but even the best ones breathe a lot. I used to shoot with a Kowa 8z without rectilux and was forced to resize with a 1.8 ratio at minimal focus distance. A face 10% larger than usual doesn't look too good honestly.

I went the rectilux way and even though it - very slightly - degrades the image, it's so much easier to focus without being bothered by breathing that I haven't looked back. But of course, the FM lens and the rangefinder aren't so good and bring a lot of CA...

Can you show me please your breathing examples? I don't see much breathing here https://vimeo.com/206798264

 

3 hours ago, Hans Punk said:

Absolutely could be done mechanically, but you’d be limited to the precise throw of one specific taking lens per mechanical calibration, and/or the transport distance of optics throughout the focus range (which is often not linear).The advantage of a motorised route is that you can set custom waypoints along a lens’s throw, allowing offset focus sync between various taking lenses throughout the range.

Agree with you) I'm just looking for a cheaper solution. Also I think I can switch the gears for each lens. But I will also try calculate DIY motorised solution . Just wonder how they measure the rotation of the first lens.