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RedRock, Letus35, and P+S Technik 35mm DOF Adapters, Ground Glass, and Lenses Explained
By Frey | June 4, 2008
Some friends were asking questions about why their Nikon zoom lens was getting vignetting with their new 35mm DOF Adapter (a RedRock Micro35 M2 unit) and Panasonic HVX200 (actually its an HVX200a).
First, we need to talk about frame sizes, for everyone to properly understand the playing field:
The Academy 35mm frame (the standard 35mm Cinema frame) is 22mm×16mm; The Super-35mm/Silent-35mm frame is 24.89mm×18.66mm; Still photography 35mm (aka “135″)/Nikon FX frame is 24×36mm; and finally the Nikon DX frame is 23.7×15.5mm.
Second, as you may have noticed above, there are two different Nikon formats: Nikon FX, which is made for the standard full frame of film and the Nikon DX, which is made for the smaller digital chips. Notice that Nikon DX is smaller than the standard Super35 frame (by 1.2mm in width x 3.1mm in height) as well as shorter than the Academy frame (by 0.5mm), which these slightly smaller frames can make quite a bit of difference when it comes to vignetting.
So, here’s the scoop on why they may be getting vignetting:
Most Nikon F-mount lenses cover the standard still 36mm x 24mm area (designated “FX”). “DX” designated lenses cover the 24×16mm frame (well, almost 24×16mm) area of the Nikon DSLR (digital chip) format. Thus “DX” lenses will produce vignetting when used on still 35mm cameras, or in this case the Ground Glass (GG) of the RedRock M2 35mm adapter.
Nikon FX lenses will work on Nikon DSLRs, but you need to figure in a 1.6x magnification. And even though there’s a “1.6x magnification”, the lens, let’s say it’s a 50mm lens, will still give the same image and angle of view (in other words “the look”) of a 50mm lens made for the smaller DSLR chip. You just record a portion of the actual frame the entire lens can “see” (for lack of better terminology).
Thus a 200mm Nikon FX lens used on a DSLR will have a 1.6x magnification, virtually capturing nearly the same area of information that a 320mm lens would when shooting 35mm still film. But note that it is not the equivalent of a 320mm lens! The area may be roughly the same size, but the field of view will be different! (you will not have the field of view of a 320mm lens, but that of a 200mm lens). [Thusly, a 50mm lens is ALWAYS a 50mm lens, no matter what camera it is placed on, you will just have a smaller frame area]. See this photo submitted by Olivier Satnet to the Konvas Discussion List to get an idea of what I’m talking about. It’s not exactly accurate, as each frame should be centered, but you get the general idea.
UPDATE: I created this page, titled Lens Focal Length Comparisons (Academy vs Medium Format) on konvas.org this morning to help people in understanding the above focal length issues a little better.
Third, the cheaper 35mm DOF adapters, including both RedRock and Letus, are made more with the larger 36×24mm full frames and the cheaper still/full frame lenses in mind.
The more expensive adapters, like P+S Technik and MOVIETube, are made with a lean towards actual Cinema lenses. For instance, I know the exposed area of the gate of the P+S Technik converter will properly cover the Super 35mm film frame. I also know that most modern Cine lenses will also cover Super35.
So, the cheaper 35mm DOF Adapters often make use of the larger still frame for their GG’s and not Super35 or Academy35. I’ve talked with others who have used the RedRock and Letus35 units with Cine lenses and most seem to have had issues with vignetting and/or dark corners to a certain extent.
P+S does not seem to have this issue. A friend shoots commercials every week with his P+S and Canon XLH1, with a set of Cinema lenses. He usually uses a complete set of Leitz Super Speed primes (f1.3 to f1.4) that he owns (you can pick a set up for about $15-20k) and sometimes he adds in few of his standard speed Lomo primes (a 50mm f2.0 and a 200mm f2.9) with occasionally an even slower Lomo Foton zoom (37-140mm f3.5). He doesn’t have issues with ANY of his lenses (unless we’re talking about between the different manufacturers, where the LOMO lenses are warmer than the Leitz).
There’s trade-off in all of the 35mm DOF adapters (including money), but there’s a few ways in which companies like Letus and RedRock can get around charging the hefty “extra” for their adapters, as compared to the more expensive P+S or MovieTube:
A) their glass (possibly even including their achromatic glass) is most likely not as high a quality.
B) their ground glass is most likely not as high of a resolution. I’m not sure what P+S or MOVIETube use, but I am pretty sure they use a very fine grained GG, capable of extremely detailed images.
C) the cheaper adapter makers most likely aren’t precision aligning their GG’s down to the most minute of a fraction of a millimeter, as P+S and MOVIETube most likely are (hot glue and/or plastic is not quite precision material).
D) the cheaper 35mm DOF Adapters don’t really build their adapters to be as rugged as the more expensive ones. I’d hate to think what would happen if I dropped mine from just a few inches in the air…
But, honestly, it’s all cool. The cheaper 35mm DOF adapters have a 36×24mm full frame still lens on the front that’s projecting almost twice as large of an image onto the GG (which, btw, is usually designed for a slightly wider than 36mmx36mm opening), so much less ground glass issues will appear in the final image.
Also too, this means these DOF Adapters will be able to give an even SHALLOWER Depth of Field! Many people really enjoy that latter aspect… After all, they are after a shallow DOF to begin with.
So, if your not dripping too much drool down your shirt from all that super technical information, here’s a list of lenses I’d recommend looking into:
1) Get at least one Fast (say f1.4) 50mm. Since this is the “go to” lens, it’s the only “super” fast lens you’ll really need.
2) I’d get a little longer lens, just to have one, like a 75mm or 85mm. It’ll probably be your second most used lens in your set, but it won’t need to be as fast as the 50mm, so f1.8 will do fine.
3) Get at least one wide-angle lens. A 24mm or 28mm lens (f2.5) will do. Be careful - a lot of the cheaper 35mm DOF adapters have issues with wide lenses and vignetting!
4) And finally, look into getting something a little longer, like a 100mm or 135mm lens. You can find longer lenses that are not much slower than the others (say f2.8, which is still quite fast for a long lens) and you can really dig into places with it when needed.
You may want to get lenses with multi-coating on them. Multi-coating really only helps to better prevent some of those pesky light flares, but everything since the late 50’s has at least some lens coating, so it’s not going to be the “be all, end all” if you don’t get Multi-Coated lenses. Multi-coating will add a lot to the price of the lens, but this is mostly because it implies that the lens is newer. The newer the lens, the better the multi-coating.
BUT: A lens without Multi-coating does NOT mean that it’s going to be a bad lens. It actually doesn’t mean very much at all, except that you may need to be a more careful with light flaring of the lens. It’s honestly not something I’d worry about, especially since Indiana Jones had a ton of lens flares. Don’t believe me? Go see it (again, if you’ve seen it already) and count how many lens flares you see per scene. I actually even think some of them were added in during post…
Expensive lenses don’t always mean better and cheap lenses don’t always mean worse. Since my friends are using an HVX200a with a 35mm DOF Adapter, they’re already fighting certain image limitations. Nothing against the HVX, but it has a built in lens - that is the most severe image degrading factor (if they were to switch to a removable lens camera, the image quality from the same ground glass would take a giant leap upwards). The next step, for the second largest improvement, would probably be to improve the ground glass.
The next two limiting factors are the small Digital Chips (three 1/3″ CCDs is still small, were’ talking close to the size of a super8 frame here!) that are doing both line doubling and stretching (I believe the HVX chip is 540×960 pixels, although those numbers might be off with the newer upgrades done to the HVX200a, which I believe they have improved the chip pixel size - but please don’t flame me here, I’m going off of memory, and I could be getting the camera confused with the Z1U or some other camera for that matter) and the recording medium. Although the recording medium of the HVX is decent, it’s not perfect, and it still compresses the image quite heavily. And don’t think for a second that HDV is any better (or worse) for that matter. It’s a different way to record (ie., different numbers and equations), but that’s about it (ie., roughly the same answer). They both end up with roughly the same degraded image when they are finished.
So what does all this mean? Well, it really won’t matter that much which brand of full frame 35mm lenses go on the front of the adapter (Zeiss, Nikon, Canon, Pentax, Minolta, etc), the expensive lenses just aren’t going to show any real improvements over the cheaper lenses. But, the Nikon FX versus the Nikon DX lenses will definitely show a significant amount of difference, since they are projecting different sized frames and the cheaper adapters do better with the larger frame lenses. You can often save a little extra cash by going with the Pentax K mount lenses or M42 mount lenses. If you already have a Nikon or Canon Mount on your adapter, you can probably pick up an M42 to Nikon F mount adapter ring for pretty cheap.
For night work and other dark sets, you’ll be fighting for light, so at least you can play with your gain a little to get a brighter image. Read heavily how to work around any problems associated with the particular 35mm DOF adapter that you are using, and how it needs to work with certain shutter speeds, gain, and low light.
Even though everyone seems to want fast lenses to buy some extra light, they often find out rather quickly that the shallower DOF creates a whole new set of issues. The biggest being that focus now becomes absolutely critical! At f1.4 on a 36×24mm focal plane (ie, GG), you may be dealing with just centimeters of depth, so someone’s eye can be in focus, while their ear is out of focus. This may be great for a certain look in a given film, but action sequences won’t be able to be pulled properly (you’ll need a full-time focus puller who knows what he/she is doing, plus you’ll have to do a lot of setup time, as well as a lot of walk-throughs). Needless to say, the speed is great, but the best thing you can do is light every scene properly…
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Topics: high definition, other, pre-production |
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