Hi all! I have a small question about crop factor and dof adaptors:)

So, I'm probably going to buy a used inexpensive M2 adaptor with a nikon mount for 2 or 3 upcoming projects. I'll be using the adaptor for only a short time so I'm not going to buy lenses. I'll only be borrowing them. But the problem is most of my friends from whom I could borrow lenses have DX lenses.

So my question goes: with using a DX lens I will have to zom more into the ground glass. Is this a problem? Would I lose any picture quality doing this? What is the size of the M2 ground glass anyway?

Thanks!
Sanjin

For better chances at success try to find older manual nikkors.

Have you checked if the lenses you will use have manual aperture rings?

Mostly I think they are af. I know it's not the best setup but I'll live...

the m2 ground "glass" is a spinning disc made of special plastic like polymer. It can give you s35mm like area of projected image if your lenses are for full frame. Zooming in for dx lenses might produce vignetting and slight enlargement of ground glass grain structure.

af lenses usually can be switched to manual.

Your problem is if your lenses dont have manual aperture rings.

You need fast and bright lenses also, meaning that f1.2-1.4 up to f2.8 is ideal. anything slower than 2.8 will not be ideal for the m2.

The only DX lens I have tried is a Nikon 12mm-24mm f4 zoom. It vignettes from about 14mm wider. Being f4 wide-open leaves only 1.6 f-stops before groundglass artifacts may become apparent. The M2 should be more forgiving of this than the vibrating adaptors.

CADILLAC - BEHIND THE SCENE - PYROS. By Bob Hart On ExposureRoom (http://exposureroom.com/members/DARANGULAFILM/a12fff28227a449b9aba4ac4a5830b07/)

The window blow-out in middle of this clip was shot with the lens on a Letus Extreme/Sony HVR-Z1P.

Other DX series wide angle prime lenses may vignette on a groundglass adaptor. It would be best if you could fit and test.

Otherwise measure 46mm (46.5mm ) from flange face of the lens, (where it butts against the mount face). Maybe make a little cardboard frame to hold the distance exactly. Get a piece of white paper. Draw a rectangle about 24mm wide by 18mm high. Hold this piece of paper behind the lens at the 46mm distance, aim the lens at a broad bright light source, observe the width of the projected image circle from the lens which is seen on the paper.

You can also do this with waxed paper, architect's tracing paper, lighting diffuser or a microscope slide made into a groundglass by grinding with five micron aluminium oxide. These translucent materials can be viewed from behind and will give you a better idea of what to expect from the lens on an adaptor.

If the projected circle edges fall just outside of the coners of the rectangle, the lens should work. There may be corner brightness falloff with wide-angle lenses.

the m2 ground "glass" is a spinning disc made of special plastic like polymer. It can give you s35mm like area of projected image if your lenses are for full frame. Zooming in for dx lenses might produce vignetting and slight enlargement of ground glass grain structure.

af lenses usually can be switched to manual.

Your problem is if your lenses dont have manual aperture rings.

You need fast and bright lenses also, meaning that f1.2-1.4 up to f2.8 is ideal. anything slower than 2.8 will not be ideal for the m2.

Yeah I know I need manual aperture:) It was late and didn't read your post quite good... Most lenses that are within my grasp don't have manual aperture. So I'll probably need to carry a Nikon camera with me.

Bigger grain structure you say. Heh I guess that would happen - it is logical. Do you think that the results would be visibly apparent?

Hey Bob. Why didn't you zoom in more if the lens started to vignette?

Thank you Bob for that nice explanation. I didn't read it until now.

Why does the circle need to come close to the edges for it to work? Can't I just zoom in more with the camera?

So I shoot with the redrock and a 50mm nikkor 1.4 MF. I was surprised at how unsharp the picture was at anywhere accept at the centre. The set-up I used was HPX171 -> 55mm macro adapter -> redrock M2 -> 50mm 1.4 MF.

The lens on the HPX wasn't fully opened I tried to kept it as close to f 5.6 as possible. Does anybody know - is this normal?

Sanjin.

The HPX and Redrock M2 are something I am not familiar with.

However, soft corners in the relayed image should not be happening. I looked up the camera specs and found that the filter mount diameter is 72mm.

The sensor size is 1/3". The lens is 51mm zoomed in so should be capable of seeing a standard 35mm movie sized frame of 24mm approx width through relaying achromatic dioptres of power 4+ to 7+ on a flip adaptor with 4+ being preferred for best edge-to-edge sharpness.

You mention a 55mm "macro adaptor". I guess, maybe wrongly, that you may be using a single-element close-up lens of about 10+ power with a 55mm diameter lens in it and a 58mm threaded mount fitted via step-up rings.

There is one around of that size possibly by Hoya I think. Any single element close-up lens or 'macro adaptor will not give you edge-to-edge sharpness. There may be radial distortion or smearing of the image closer into the corners and chromatic issues, which make the colour reproduction a bit muddy, also towards the edges and corners.

It should be possible to zoom through a close-up lens which has a 55mm exit pupil. You might pick up corner vignettes and have to zoom through to a smaller area of the groundglass before they swell out of the corners of your camera image.

I think what you may need will be an achromatic dioptre. This lens is also a close-up lens. It has two elements in it. Corner-to-corner sharpness should be good with this lens and very little or no chromatic abberation should be apparent.

I have used a Century Optics 4+ achromatic dioptre for a PD150 with its 58mm filter diameter on a Sony HVR-Z1P which has a 72mm filter diameter. I even used this lens on a Sony PMW-EX1 which has a 77mm filter diameter.

Now I stray into areas of unknowns. Your Redrock M2. - Does this flip the image upright or is the image the camera sees upside-down. I would need to know this before I could make any guess at a suitable achromatic dioptre.

Redrock may have their own dioptre for the HPX camera as a separately available part, so that would be my first direction of enquiry.

Wayne Kinney had some surplus achromatic dioptres for his superseded SGPro model which were said to work fine on the Redrock M2 some time back. He may have sold his stock down by now but who knows?


As for camcorder iris setting of f5.6, it is generally agreed that the sweet spot for most camcorder lens iris setting is in the zone of f4 - f6.3 and that you should try to stay with this iris setting by using the camera ND filters.



So the questions in summary before we can advise you furthur :-


1. Is your Redrock M2 a "flip" adaptor which presents its image to the camera the right way up?
2. Is your 55mm "Macro adaptor" a lens which has only one piece of glass in it? ( If it is, it will be from front to back, about 6mm thick.)


If possible, maybe post some jpg images of your M2 and "macro adaptor" and the assembly as fitted to your camera.

Sanjin.


Furthur to my post above, Redrock do have relay achromatic dioptres of 5+ power. It seems these are for flip adaptors. They would work with a non-flip adaptor but there might need to be an extention tube of approximately 3" or 75mm between the camcorder/achromatic dioptre and the M2. For ease of use, I recommend using a flip adaptor.

Send Redrock an email. Even though your adaptor is used, they may still offer support and advice for it.

Redrock Micro Achromatic Lenses (http://store.redrockmicro.com/Catalog/AchromaticLenses)

First off - thanks for all the help!

What I have is a non flip M2 adaptor and the macro lens is about 1 cm thick. The macro lens is from Redrockmicro. It's a 55mm macro and as far as I know it came with the package... It looks exactly as the one in your link only it's 55mm not 72mm.

Further more: this M2 that I have is not the "fixed" version. It has a soft "rubber-ish" mount (that I don't really like...) on the camera end. Maybe (and I'm just thinking here) the macro lens that I have is meant for the flip version. I'll investigate on this further...

Sanjin.


At 1cm thick, the "macro" lens could be an achromatic dioptre. If it is supplied by the vendor for the M2, I would be surprised if it was not.

The M2 as I recall was an earlier less matured development. I also vaguely recall there were some issues with the HVX-200 which required some custom fitment to make it work at best but I am not sure on this now. I think both the HVX-200 and your camera were released to the market after the M2.

A quick test you can do, is to mount the "macro" lens to the camera without the M2 attached. Make some close-up shots of anything with straight edges at about 5" or 120mm distance from the camera. It would be even better to draw an accurate 22mm x 18mm rectangle with gridlines across it on white paper, frame tightly upon it with the zoom and make images of that.

If you can achieve a sharp image without distortion of the gridlines, try moving the paper closer to the camera, refocus and see if you can still achieve sharp focus without corner softness or distortion.

Experiment with closer or furthur distances between camera and paper, with different zoom settings and different focus settings on the camcorder lens. Illuminate the paper and/or use in-camera ND so that the camera lens iris has to be wide-open so that a most accurate focus position can be found due to the camcorder's own shallow depth-of-field.

In making home-made adaptors, dioptres seemed to perform best when they were as close to the camera lens as they could be but not always.

There is another optical interaction which should not be adversely affected by camera to groundglass distance. That is, most adaptors will have a condenser lens inside in a position close to the groundglass.

This interaction may also cause edge/corner softness and chromatic aberration ( rainbow effect ) if the position of the "macro" is not ideal or both lenses are not an optical match. The closer the condensor lens is to the groundglass, the less apparent this adverse interaction should be when the "macro" lens is also in an ideal sweet position.

With different camera types there seems to be a unique sweet spot for the position of the "macro" lens between the groundglass and camera lens. The ideal distance of the groundglass from the camera lens remains more or less constant. If it is too close and you have to force sharpness by focusing closer than the lens and the "macro" are suited for, then you may find that soft edges will occur.

The close-up lens can be moved a little furthur from the camera towards the groundglass which affects the corner sharpness without affecting the centre sharpness. Eventually the edges of the exit pupil ( rim ) of the macro lens will vignette the corners of your camera image the closer to the groundglass it is moved. In the first 15mm or so from the camcorder lens, any sweet spot will likely be.

The P+S Technik Mini35 and Mini35C relay optics are set up ex-factory so that camcorder focus is very close to the infinity end of the lens focus range. There are apparently good reasons but I don't know them. It takes a lot of engineering precision to do that. P+S design precisely each relay lens for each camera type which is why they are so costly.

The alternative adaptors like M2 have been expected to fit across a broader range of camera types. Some of these alternative adaptor builders play safe and set the relay optics up so that the sharp focus position is well way from the infinity focus mark where the focus is more controllable and a larger range of camera types with fewer relay lenses is doable.

I don't know how much space there is between the front of your camera and the groundglass of the M2. I expect there would need to be at about 6" to 7" ( 150mm - 175mm) distance for a close-to-infinity focus position on your camcorder lens, less distance with the camcorder lens focussed closer.

I expect you will have to use a zoom position of about 45mm - 55mm to achieve a tight frame on the 24mm x 18mm frame drawn on the paper.

I expect you may have to make up a tube extention of about 3"- 4" ( 75mm - 100mm ) to fit between your camcorder and the M2 to achieve the ideal camcorder lens to groundglass distance for distortion-free images into the HPX camera. This will mean it will become a long awkard machine. The upside is that the longer focussing less powerful 5+ "macro" lens gives you a better image than a more powerful one of 7+ to 10+ when edge/corner distortion/softness becomes harder to control.

I expect you may have to mount the "macro" lens separately from the M2 body and mount it close to the camcorder lens. If you leave the "macro" mounted to the rear of the M2 body, you may find there is a bad vignette or corner softness with the M2 mounted more distant from the camera.

Good results have been achieved by users of the M2 and one indie feature is known to have achieved theatrical release.

If you have the budget to buy in the flip module, I would recommend it. Setting up and shooting indie movies is hard enough without the extra problem of an upside-down image. If you don't have a monitor screen you can use to rotate the image upright, any camera moves will be almost impossible.

When shooting with an adaptor, use a siemens star or similar focus target ALWAYS for every setup and take. Focussing by eye with the camera LCD, eyepiece or even a larger monitor is simply not reliable, especially outdoors when LCD screens and monitors can become next to useless without hoods.

Ideally, do not use front lens aperture settings of wider than f3.5 unless you want really shallow depth-of-field for creative reasons. It will be just too hard to manage focus and will draw audience attention away from the sotry towards the technology behind it. Please ALWAYS add light or select in-camera ND to enable this f3.5 aperture setting to be useable. Try to keep your camcorder iris in the zone f4 - f6.3.

Please be mindful that I am not an optical engineer so my comments are really only guesswork and my advice may be incorrect for your problem.


I hope this is helpful.

My god you wrote a lot!:) Thanks! I'll get to it as soon I can (I'm swamped at the moment)! On a quick note: I think there is no condenser lens in front of the GG...

These clips might be of interest :-


My own clips


YouTube - AGUS35 APVE PARTIAL DISMANTLE (http://www.youtube.com/watch?v=CnweOEEqlRY)

YouTube - AGUS35 APVE TO HVR-Z1P DEMO. - PELENG FISHEYE. (http://www.youtube.com/watch?v=Cx-GTXQLF6A&feature=related)

YouTube - AGUS35 FILMS MINI35 (http://www.youtube.com/watch?v=Cu46tmYmRY0&feature=related)


Other youtube clips about the M2.


YouTube - Red Rock M2 Follow Focus setup (http://www.youtube.com/watch?v=gIMLFJS0HsA&feature=related)

YouTube - HDFilmtools: Red Rock Micro M2 Cinema Lens Adapter - Part II (http://www.youtube.com/watch?v=qcpZ6QVnoqU&feature=related)