Inexpensive DOF adapter...

[Peer Landa]

I'm curious to know if this DOF adapter is just a waste of money:
DIY 35mm DOF lens adapter with Nikon mount ! - eBay (item 160309712286 end time Mar-13-09 18:24:59 PDT)

I'd appreciate any suggestions/pointers for other adapters. The camera I'm gonna fit it on is a Canon XL2.

-- peer

[Bob Hart]

Peer.


No one seems to have chimed in so here goes sticking my own nose in where maybe it does not belong.

Firstly, whilst I have home-built these appliances, I did not progress my own to more than an enthusiast level of image quality or utility so please do not hold my opinions to any worth. I am looking at this adapter from a distance.

In the making of 35mm groundglass based adaptors, getting to about 85% of image quality with a non-flip adaptor is relatively easy. I can do it with a Pringles can, microscope slide, grinding paste and a close-up lens and iris settings on hot lenses absolutely wide-open for next to nothing.

But there is no such thing as a free lunch.

The $350.00 you are being charged for this device likely represents an honest costing for the materials and living wage labor required to produce it, so nobody is ripping anybody off here. Let's get that straight for a start.

If you want to operate at an enthusiast and hobbyist level, then this appliance will serve you well enough.

Image quality-wise, as good as the quicktime download is, I prefer to reserve my judgements until I see the vision face-to-face.

The groundglass motion appears to be adequate with no apparent dead zones in the excursion or focal plane pulsing effects. Unfortunately for me, all the vision appears to have been shot with the lens near to wide-open which will eliminate groundglass texture even on coarse textured static adaptors. So the adequacy of the movement cannot be assessed validly from the posted clip.

The declared 10 micron texture is a little on the coarse side when 5 micron seems be what home-builders have settled on. The builder has wisely chosen the larger groundglass to get around the resolution hit a coarser groundglass introduces.

The larger area introduces potential problems of brightness falloff to corners and edges. The coarser groundglass does not produce this defect as noticeably as a finer groundglass.

The bokeh rendition of a coarser groundglass is superior and this adaptor's bokeh rendition appears to be fine.

Light loss with a coarser groundglass is an issue. You have to drown it in light which then can take a lens out of its sweet spot into softness and internal flare. Flare from diffusion across the groundglass also becomes more apparent. This is seen as a loss of contrast and colour depth.

With wider groundglass areas viewed, added optical elements in the path are required to deal with brightness falloff to edges and corners.

The use of the Nikon focusing screen, either as an unmarked original or a marked one refinished as a groundglass and viewfinder optics as a condenser is a well known solution for home-builders and valid at an enthusiast level.


OBSERVATIONS.


There are visible artifacts in the clip. My own jury is out on what they are caused by.


There was jitter in locked off shots which might have been tripod shake or looseness in the lens itself (Some Sigma f:1.8 28mm auto lenses are bad for this). It could also be a lens fit into its mount not being firm. Can't judge this one for you.


There seems to be a soft area to right of frame unrelated to the selective focus. This could derive from several causes -


Angular deviation of the camcorder optical centre axis from adaptor optical centre axis which will bring one side of the groundglass closer and out of critical camcorder focus.

It seems the adaptor mounts via threaded rings which should eliminate this as a cause. However case compliance in most consumer/prosumer camera bodies can introduce an angular deviation if the case is stressed by mounting on a rails system or the adaptor and the weight of its lens is supported only by the camcorder filter thread.

This deviation will also move the camcorder view across the groundglass into possible areas of less sharpness at the edges.


Parallel deviation of the camcorder optical centre axis from adaptor optical centre axis. This can move the groundglass image area seen by the camcorder out of the sweet zone and bring in an edge which is soft but might not otherwise be seen if the image is centered.

Again, the use of the tubular structure and threaded joints for the front lens mount and adaptor to camcorder junction should entirely eliminate this as a cause.

Some camcorders however do not have the optical centre axis coincident with the sensor center. The Sony VX2000 camera family is one such. Whilst the image fall onto the sensor is correct for sharpness, the center of image moves as the camcorder lens is zoomed in.

This is a distinct hassle when trying to set up the camcorder to the confined image pathway of some adaptors. This can have the effect of "walking" an apparent centered image when seen in wide view across the frame as the camcorder is zoomed in.

A known soft area, thought to be out of frame in the wide position is slipped across into the frame and the zoom has to be moved in furthur to get inside it, resulting in a loss of groundglass image area and an unwanted crop effect.


The condenser element and focus screen are rectangular objects. The focus screen position is not critical with regards to centering so long as it is square-on to the focal plane and larger enough that there is not edge vignette.

The condenser is another matter. This has only to be a part of a millimetre off-centre and the image will be adversely affected. Accurately mounting this element within a circular structure offers its challenges.

Accurate centered mounting might only be established by measurement from the centre of each of the condenser's rounded corners but I would expect that Nikon quality control would have the flat sides of the condenser accurate relative to the center axis.

Parallel deviation of a condenser element off the adaptor optical center axis which will bring in a soft edge and maybe an asymmetrical CA artifact as well.


Angular deviation of the groundglass panel from the focal plane. This will cause a soft edge in both the image on the groundglass itself and in the camcorder image of the groundglass.


There were a few spots in the image, probably buts of dust which one expects. There was one white artifact on right portion of frame which changed with focus pulls. It may be an internal reflection from the groundglass which is one of those things you mostly have to live with.

If it is an internal reflection between a cover glass in front of the adaptor and the lens, the moving the front cover glass forward or rearwards may make this go away. This cover glass should be as thin as possible to have it as the backfocus or collimation of wide-angle lenses is adversely affected.


I would like to see images shot of a resolution chart with the lens at all stops from wide-open to f5.6 and at least one slow pan across a large plainly coloured and texture object like a car or bus in a shot or including an area of sky, before I passed judgement or thought about endorsing the product.


I would recommend the builder-vendor produce such videos for the website so people can judge for themselves.


For your XL2, there may be some issues. The front element of your standard lens is fairly wide. If the achromat which comes with the 35mm adaptor has a small exit pupil, say about 44mm, you may encountere an unavoidable vignette. You may also have to play around with positioning the adaptor closer or furthur from the Canon lens with spacers and rings to achieve best results.

You will end up with a very long and unwieldy combination, whatever adaptor you choose.

You will likely have to invest in a monitor to achieve satisfactory critical focus and to flip the image for shooting. Flipping in post ads another layer of complication. There are two layers of focus and iris adjustment, the objective lens on front of the adaptor and the camcorder's own lens.

[Peer Landa]

Originally Posted by Bob Hart

Peer. No one seems to have chimed in so here goes sticking my own nose in where maybe it does not belong. [...]

Hey Bobby, all I can say is WOW -- thank you so much!

So now, after such a comprehensive write up, I'm a bit hesitant to ask if you could also comment on this DOF system -- I sure would greatly appreciate it: Cine DOF Adapter + Follow Focus + Rail System gear Free - eBay (item 350170015478 end time Mar-01-09 19:57:51 PST)

-- peer

[Bob Hart]

Peer.


Happy to oblige. Just don't forget me when your cargo plane comes home and brings good things for the people and drops 5 mill film funding in your lap. Fly me over and give me a job for six weeks.

Just kidding. - (maybe).


This product is out of Chandrigagh India I seem to recall. Despite concerns of others relating to ordering from India, I can attest that my three orders from there have come promptly, well packed and as described.

The vendors in my case, "cine-city", have also followed up to make sure the items were received. Obviously they would want their eBay feedback score to be maintained, however their communications have been polite and courteous.


I had had two jumbo matteboxes. For the price, you expect one or two little glitches and ability to hold the upper flap tight with thumbscrew friction was one. One has to recourse to propping the upper flap on the side flaps. However we are using them as is and have not modded them. They have not broken. The fit-up seems to be adequate and the finish good albeit paint or powdercoat on the flaps and not anodised. At the price they are not gold-standard Chroszeil nor should be expected to be but they get the job done.

The CineDOF adaptor. There might be a bit of a contention over the use of this name as another groundglass relay device was and may still be marketed by the same name from Europe. The maker/vendor is a member here.

The Vimeo clips are of too small a format for me to validly make judgement as with the "Hollywood" adaptor.

However I am impressed with the fact that the Indian vendor has posted "warts and all" vision which is representative of what users might expect as the vision is not perfect.

The upper clip is more representative of the best potential of the adaptor. Even there, the use of a f2.8 zoom is a bit more than a fair test. Ideal lenses would have been f1.8 or f1.4 primes, however the real world dictates that f2.8 primes and zooms will be used if the camera operators can get away with it.

In one of the shots in the first clip, there is some apparent radial distortion. This might be more of a backfocus issue related to the zoom lens. It would be interesting to know if the lens mount flange to focal plane adjustment (assuming there is one) was set up correctly.

There appears to be a hint of fixed pattern artifact in some of the shots. However it is just too difficult to tell from the posted clips if it is an artifact or the groundglass motor was inadvertertently not turned on.

The second clip by Dustin Gurley is possibly honesty gone a bit far and the vendor again is to be commended for linking to it. There is no misrepresentation here.

There is a distinct brightness fall-off on the sides and a hint of it on corners. This suggests to me that the camera operator did not zoom the camcorder lens in far enough or maybe the zoom range runs out before the image can be brought close enough.

The darker left edge suggests a bit of sideloading on the camcorder adaptor junction and a bit of vertical loading as well as the lens image centre on the groundglass does not co-incide with the camcorder optical centre.

This could be a build quality issue however centres on a "project box" styled non-flip adaptor as this is, are not all that hard to set up. Stack drilling the screw holes and centre pilot holes in the front and back covers as pairs would eliminate any error. It is highly likely it is done this way as it is more efficient, so I doubt that the centres are that badly off.

The Nikon 50mm f1.8 lens may have been a DSLR lens which would cast a smaller image area onto the groundglass hence the edge and corner brightness falloff. I don't know the type so I cannot vouch for my own comment here.


This adaptor on the surface appears to have a better apparent resolution compared to the other product. The bokeh however appears to be less solid.

A hint of aerial image passthrough on the wildgrass shot suggests a finer grade of groundglass texture was used. There may be less light loss with this adaptor than the other one. However the size of the vimeo clip does not permit me to make this observation with confidence. It could also be an introduced digital compression artifact.


This adaptor requires no innovation to design added fittings to support it on rods as this is integrated into the whole package. Care would be required during assembly to make sure no sideloading on the camera/adaptor junction occurs.


The rods kits with the matteboxes from Chandrigagh have had considerable available lateral and vertical adjustment. I imagine this appliance will provide the same adjustment facility but again this is speculation.