Question on wide angle converters

Antworten
jan lameer

Question on wide angle converters

Beitrag von jan lameer » 7. Apr 2003, 22:35

Hi, perhaps someone with optical knowledge might help me on this:

The basic question is: are there wide angle converters on the market that are placed behind the lens on a 35 mm photo camera? A sort of tele extender that makes the focal length shorter instead of longer.
Now I don't mean a wide angle converter that goes in front of the lens, but one that goes in between the lens and the film.
From advertisements in Sky & Telescope I know that there are so called focal length reducers (factor .6 or .7) for telescopes, a sort of negative barlow lens (or should I say, a sort of positive barlow lens?).

Why do I need it? Well, on the 35 mm Eclair movie camera that will be in operation soon, I want to place Nikkor lenses. Since the 35 mm cine format is only approximately 24 x 16 millimeters, all my focal lengths are doubled. For instance, a 24mm f/2,0 becomes 48 mm f/2,0.
Worst of all, the 8 mm f/2,8 Nikkor fish-eye that I intend to buy, doesn't get a full circle on the negative since it becomes almost the equivalent of 16 mm on 35 cine format (the projection circle is 22 mm).
So a .6 or .7 wide angle converter would be nice, wouldn't it. Even better, with such a converter, my 24 mm f/2,0 would become something like a 28 mm f/1,4 which is great, and a 20 mm f/2,8 would even become a 24 mm f/2,0 or so.

The main problem is: Nikon doesn't have one :-(
I can imagine that the reason for that is that such a converter should be exactly made to fit only one type of lens...

I've tried the Kenko fisheye adaptor but it gives a lot of flare and I want the sun and moon walking through my time-lapse movies. Only real good wide angle lenses, like the Nikkors fish-eyes are without flare...

I hope someone can help me on this. I wouldn't mind refitting an existing wide angle convertor to Nikon bajonet, that is common practice in cinema: it is not uncommon to use Zeiss, Canon, Nikkor, Kinoptic and Angenieux lenses on the same cinema camera.

Oh well, I hope it makes sense, it is quite a difficult and practical problem...

greetings, Jan Lameer

Bernd

Re: Question on wide angle converters

Beitrag von Bernd » 9. Apr 2003, 10:46

Hi Jan,

are you sure, that it is possible to change the "Auflagemaß" (distance between film plane and the plane where the lens touchs the camerabody) of a fix optical system? In your example with the focal reducer for teleskopes it is a little bit different because you can change the distance of the camera (film plane) with an adjusting screw, thus the "Auflagemaß" is variable. I think converters between lens and camerabody do not exist because they are technical impossible.

In addition, I don´t understand your problem with the 8mm Nikkor fisheye: If the image diameter is 22mm, you get a lot of "black space" on a 24x36mm film, but on your 16x24mm film it should work great.

Regards,

Bernd

> Hi, perhaps someone with optical knowledge might help me on
> this:

> The basic question is: are there wide angle converters on the
> market that are placed behind the lens on a 35 mm photo camera?
> A sort of tele extender that makes the focal length shorter
> instead of longer.
> Now I don't mean a wide angle converter that goes in front of
> the lens, but one that goes in between the lens and the film.
> From advertisements in Sky & Telescope I know that there are
> so called focal length reducers (factor .6 or .7) for
> telescopes, a sort of negative barlow lens (or should I say, a
> sort of positive barlow lens?).

> Why do I need it? Well, on the 35 mm Eclair movie camera that
> will be in operation soon, I want to place Nikkor lenses. Since
> the 35 mm cine format is only approximately 24 x 16 millimeters,
> all my focal lengths are doubled. For instance, a 24mm f/2,0
> becomes 48 mm f/2,0.
> Worst of all, the 8 mm f/2,8 Nikkor fish-eye that I intend to
> buy, doesn't get a full circle on the negative since it becomes
> almost the equivalent of 16 mm on 35 cine format (the projection
> circle is 22 mm).
> So a .6 or .7 wide angle converter would be nice, wouldn't it.
> Even better, with such a converter, my 24 mm f/2,0 would become
> something like a 28 mm f/1,4 which is great, and a 20 mm f/2,8
> would even become a 24 mm f/2,0 or so.

> The main problem is: Nikon doesn't have one :-(
> I can imagine that the reason for that is that such a converter
> should be exactly made to fit only one type of lens...

> I've tried the Kenko fisheye adaptor but it gives a lot of flare
> and I want the sun and moon walking through my time-lapse
> movies. Only real good wide angle lenses, like the Nikkors
> fish-eyes are without flare...

> I hope someone can help me on this. I wouldn't mind refitting an
> existing wide angle convertor to Nikon bajonet, that is common
> practice in cinema: it is not uncommon to use Zeiss, Canon,
> Nikkor, Kinoptic and Angenieux lenses on the same cinema camera.

> Oh well, I hope it makes sense, it is quite a difficult and
> practical problem...

> greetings, Jan Lameer

jan lameer

Re: Question on wide angle converters

Beitrag von jan lameer » 9. Apr 2003, 22:28

Hi Bernd

Yes, changing the distance between lens and film plane is possible since I'm machining a new front to the camera myself in order to attach Nikkor lenses.
I am afraid that wide angle converters are impossible indeed, my optical knowledge isn't good enough to exactly understand why, but if it were possible, they would exist.... (like tele converters).
Why I like a circle on the film: well it is a nice geometric figure to play with ...

regards, JanL

Antworten

Wer ist online?

Mitglieder in diesem Forum: 0 Mitglieder und 4 Gäste