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Old 11th April 2014
Alex G. Alex G. is offline
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Metabones OM to m4/3 speed booster

I know there are a lot of users here that have a range of OM lenses so I thought I should share this as many will find it interesting.

Metabones has just announced a new OM to m4/3 adapter.

Taken from their official website:

Increase maximum aperture by 1 stop.
Increase MTF.
Makes lens 0.71x wider.
Optics designed by Caldwell Photographic in the USA (patent pending).
The tripod foot is detachable and compatible with Arca Swiss, Markins, Photo cam ball heads.

The adapter costs $399

http://www.metabones.com/products/de...B_SPOM-m43-BM1
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Old 11th April 2014
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Re: Metabones OM to m4/3 speed booster

And for those interested:

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Old 11th April 2014
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Re: Metabones OM to m4/3 speed booster

It's a very interesting concept, and I know that Ian was trying to obtain one for testing. But it ain't cheap!
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Old 11th April 2014
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Re: Metabones OM to m4/3 speed booster

Hi there Alex!

Thanks for posting this - I am interested in a speed booster but I have to say that I am surprised with some of the lenses it is showing it is compatible with - eg 50/1.2 or 24/2 as they have very large rear elements, and for the speed booster to work they would have to capture all of that light and hence at least match the rear element size - presumably this is the reason for the cost.

In the mean time I am going to continue my own speed booster project to match my 50mm f1.8 - in essence a 2x teleconverter reversed in an OM to m43 converter to hopefully give a 25mm f0.9 with the equivalent depth of field on a f1.8 on 35mm. I've got the bits now, just need some time to play about (total cost of about 12 so far.) If it works out I'll post a how to somewhere on here.

Cheers,

Ralph.
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Old 11th April 2014
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Re: Metabones OM to m4/3 speed booster

Quote:
Originally Posted by Ralph Harwood View Post
in essence a 2x teleconverter reversed in an OM to m43 converter to hopefully give a 25mm f0.9
That sounds interesting! Is it really that simple in theory? (i would imagine actually doing it requires some skills) I would love to see the result of that.
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Old 11th April 2014
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Re: Metabones OM to m4/3 speed booster

I see they don't list the 250mm or 350mm. A 180mm f/1.4 would be fun to try.
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Old 11th April 2014
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Re: Metabones OM to m4/3 speed booster

After a deja vu moment i just remembered i was going to do a comparison shot with the Metabones speedbooster i have. I ended up in hospital a couple times and then went and bought a house and it kinda slipped my mind. I shall get on with it.

This is the first OM speedbooster/focal reducer on the market and a surprise to me. They had stated there would be 2 new m43 speedboosters during 2014 and the OM wasn't one of them.

These guys seem to be the main Metabones sellers in the UK.

http://www.lensadapter4u.com/
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Old 11th April 2014
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Re: Metabones OM to m4/3 speed booster

Quote:
Originally Posted by Alex G. View Post
That sounds interesting! Is it really that simple in theory? (i would imagine actually doing it requires some skills) I would love to see the result of that.
Hi there Alex!

I don't have any qualifications in optics, but my thoughts are that the series of lenses in the teleconverter are adjusting the angles of the incoming light to spread them over a greater area by a factor of 2 - therefore if the same series of lenses are reversed they should bend the light to give a tighter image circle - speed boosters wouldn't be used on a 35mm camera because then you would just have a small bright circle in the middle of the film - from an OM lens you should be able to have a factor of 2 speed booster and still cover the whole sensor on 4/3.

Two words of warning though:- Those great OM lenses you have won't be quite as great as you are used to, as you are used to seeing only through the centre portion of them on a 4/3 or m4/3 camera so you will see more loss of edge sharpness and vignetting. The other issue comes with trying to find a teleconverter with a large enough series of lenses not to have some light loss - as the lenses in the teleconverter have to be as large or larger than those of the back element of the lens you are using. Hence sticking to a relatively small rear element on a 50mm f1.8 rather than the massive one on a 50mm f1.2. Teleconverters don't have this problem as they are only looking at the centre part of the image and magnifying that - hence the loss of f-stops due to the light loss through the lenses being smaller.

If anyone reading this notices a flaw in my cunning plan please mention it by the way - I would rather know before I start sawing up my £5 teleconverter!

Cheers,

Ralph.

Last edited by Ralph Harwood; 11th April 2014 at 10:58 PM. Reason: My typing!
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Old 12th April 2014
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Re: Metabones OM to m4/3 speed booster

Ralph, if you put a reversed TC inside an OM to m4/3 adapter it will be a lot closer to the sensor than it was designed to be so the magnification will be different.
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Re: Metabones OM to m4/3 speed booster

Hi there David!

I agree with you that the rear element of the speedbooster may be closer to the sensor than if I reversed the lenses in the TC and used that, however because of the small diameter of the lenses in the TC they will need to be moved much closer to the rear element of the lens to ensure no part of the image circle is lost, so that effect might not be as great as you might think. As stated above, this is a bit of a trial and error process, and I might just try reversing the lenses within the TC first anyway.

As a point of interest, does anyone know where the focal point is within a 50mm f1.8 lens? If I knew that I could work out more carefully the position for the TC lens assembly in relation to the rear element. Any info greatfully received.

Cheers,

Ralph.
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Old 12th April 2014
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Re: Metabones OM to m4/3 speed booster

Hi everyone!

With reference to the above question my research shows it is also referred to as the nodal point - can't find anything so far but I will keep looking.

Cheers,

Ralph.
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Old 12th April 2014
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Re: Metabones OM to m4/3 speed booster

Things change - even science! Apparently (at least as far as panoramic heads are concerned), it is the 'entrance pupil' that was commonly referred to as the nodal point. There are many references on Google, just search for 'lens nodal point'. A very useful explanation is at http://www.nodalninja.com/nn4/findin...-of-a-lens/13/...

Quote
What is the Nodal Point or Entrance Pupil and why is it important?

We would like to take a moment and dispel misconceptions of the word "Nodal Point". When referring to this no parallax point (NPP), many still refer to it as the Nodal Point. Technically, the point at which you would rotate the camera/lens to avoid parallax is called the "entrance pupil".
The entrance pupil is a floating point located inside the lens, at the point where the light refracts or reverses itself before continuing to the image sensor or film plane. The entrance pupil is different on each lens and changes at different focal lengths

The entrance pupil (incorrectly referred to by some as nodal point) of a lens is the virtual image of the aperture formed by the lens elements in front of it, and is the place where light paths cross before being focused onto the CMOS, CCD or film plane. For a light ray to pass through the lens, it must be directed towards the entrance pupil, which is therefore the center of perspective. Note that the entrance pupil can be outside of the lens and even behind the film plane!

End quote


See http://en.wikipedia.org/wiki/Cardinal_point_(optics) for more info.

Last edited by daved; 12th April 2014 at 05:34 AM. Reason: Spelling :-(
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Re: Metabones OM to m4/3 speed booster

I understand your reasoning Ralph. I'd try reversing the mounts on a TC first. If you get vignetting try mounting the TC optics in the adapter.
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Re: Metabones OM to m4/3 speed booster

Hi there Daved and David M!

Daved - I think what I need is the nodal point rather than the NPP or entrance pupil as I am hoping to use a bit of trig to work out what will happen to the light rays, and since I have an idea of where the image circle is and the flange distances etc if I can find where the rays converge within the lens I should then be able to make some "educated" guesses as to where the TC lens array should sit.

David M - I think that I will have to reverse the lens array within the TC rather than just swap the mounts as the rear element of the TC protrudes from the rear mount and would touch the rear element of the lens with the mounts reversed.

Thankyou both for your helpful comments, I'll keep looking into it and may try reversing the lens array over the weekend.

Cheers,

Ralph.
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Re: Metabones OM to m4/3 speed booster

Bummer, simply swapping mounts would have been a quick conversion. If you could make some way to adjust the lens assembly in the TC body that may be useful in case your conversion loses infinity focus.
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