SLR Lens (Sigma 100-300mm) versus ENG Lens on EX3? at DVinfo.net

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Old November 20th, 2010, 06:33 PM   #1
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SLR Lens (Sigma 100-300mm) versus ENG Lens on EX3?

For a few years now I've been using a Sigma 100-300mm on my EX3 (with an adapter of course) for wildlife work. At times it works great, other times the image seems soft. So I'm looking at buying a true video lens for the EX3, such as a Canon KH21ex5.7-IRSE.

Of course the Canon is very, very expensive so I'm hoping for some input from anyone that has used a SLR lens (ideally the Sigma) on their EX3 and a Canon lens (like the one mentioned above or any lens with a long focal length) and how big a difference there is in image quality and any other thoughts they have on the pros and cons of each. Cheers.
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Old November 21st, 2010, 08:42 AM   #2
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Hi Dan,

I am a beginner, but here is my experience.

I have a different camera (Canon XLH1s) and a different lens (Nikon 80-400 & Nikon 80-200), but the same challenge. I shoot wildlife subjects as well and make good use of the far end of the lenses. I also noticed that sometimes the images were great and sometimes pretty soft. I began to look at super expensive lenses both from still cameras and others designed for video.

By chance one day (before I had spent my fortune!), I was waiting in a blind for some wood ducks to fly into where I was set up. They took a long time to get there so I thought I would shoot some establishing material with the long lenses. I was also trying out my first external HD monitor. The day was bright for most of the pond, but part of the pond was in shadow. I could not get the bright areas to be sharp (f16 to f22 at appropriate 1/60 shutter speeds). However, when I used exactly the same lens and camera combination at exactly the same distance, but shooting into a shaded area (f4 or f5.6 at 1/60), the picture was sharp.

At first I didn't clue in, but later that week I got some neutral density filters. Back in the blind, I repeated the experiment, but this time shooting bright areas at high f numbers compared to bright areas at low f numbers with the ND filters making that possible. The difference was remarkable. As soon as the f numbers drop below f8 using the ND filters the sharpness returns.

I repeated the experiment on my DSLR and the differences were much less pronounced, but still present.

Before you spend your fortune on a new lens, you might try this same experiment for yourself and see if the same issue is present with your current cam/lens combination, and if it can be solved in a similar fashion.

Hope that helps,

Alan
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Old November 21st, 2010, 09:03 AM   #3
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Alan - Thanks! That's great feedback and not inconsistent with my own experiences. In fact, I try to stay in the "sweet spot" in terms of aperature (around f5.6-11). (You'd think the the higher f-stops would be sharper, but that's not my experience either.)

The fact that the images do sometimes look very sharp with the Sigma 100-300mm, and other times soft suggests that the user (i.e., me) may be the problem (either focus, f-stop, too great a distance, or other factors).

Of course there's still the question as to what looks real sharp to me with the Sigma 100-300mm may actually be even sharper with a real video lens like the Canon KH21ex5.7-IRSE. Thoughts???
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Old November 21st, 2010, 09:38 AM   #4
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My understanding and somebody like Charles Papert or Chris Barcellos, please correct me if I am misleading, is that :-

Stills-camera lenses are designed to convey an image to a single focal plane, as in film or single sensor.

Most video-camera lenses are designed to convey a lens image to what in effect is three focal planes or sensors via a long optical path through a prism which splits the image off into three different directions to land on individual sensors. Additionally those three sensors are arranged for three primary colours each which have different wavelengths and very slightly differing focal planes.

The image from say, an 8mm focal length lens, actually has to travel furthur than 8mm through the prism to land on the sensors. There is some optical trickery built into a 3 x sensor lens to enable this to happen and I understand there are micro-optics on the sensors themselves which do something clever the likes I have no knowledge of. A lens with compensation built-in for three sensors will not confer a satisfactory image to a single sensor.

If a simple stills-camera lens image lands on a single large sensor, any difference in focus between colours is apparently not such a big deal. Some keep the colours together better than others

On a small sensor, any error is magnified. Split that to three sensors and the possibilties of error multiply.

At the f11 - f16 end, there may occur a defect in the imaging referred to as diffraction. This I understand and maybe wrongly is the beginnings of the separation of colours. I am assuming that the three channel prism path may aggravate this defect in the image.

My understanding and again likely wrong, is that a very small aperture begins to resemble in its own right a simple lens (pinhole camera) which may not have the same focal length as the lens's own optical design, so the pinhole lens image is out of focus whilst the true lens image remains in focus.

The pinhole camera's inherent depth-of-field is apparently very deep. As the "true" lens's image becomes duller with a tighter aperture, the pinhole image becomes apparently more coherent and also competitive in brightness. - Again please, anyone with a greater ounce of optical expertise than mine, offer correction to my comments if they are misleading.

When a stills lens is wide-open and connected to a three sensor camera, you may observe an unwanted colour fringe above or below a bright object against a darker background. This appears to diminish or even disappear when the aperture of a stills lens attached to a three sensor camera is within the sweet zone.

At the f2.8 end or whatever the widest aperture your lens provides for you to choose, your lens may also go softer and may also flare ( lose contrast ),

By using ND, you are bringing the light level down to within the lens's "sweet spot" when the image conveyed is at its purest.

Please take heed of the opinions of others far more qualified to comment than I.


A 2/3" ENG lens is designed to confer image via a prism to a three-sensor system. It may not be optically true to the shorter prism path of small-sensor cameras so you may still get some colour separation or "chromatic aberration". It is going to perform better than a simple single-sensor lens.


In the opposite direction, I decided to try an old TV-Nikon ENG lens on a single-sensor camera, the SI2K, which normally works fine with motion picture film or stills lenses. It was a rather sad outcome, an unacceptably soft image. The same lens with a IMS-B4 adaptor (contains a big long piece of optical glass) works fine to the SI2K.

Last edited by Bob Hart; November 21st, 2010 at 10:06 AM. Reason: error
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Old November 21st, 2010, 10:16 AM   #5
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Quote:
Originally Posted by Dan Licht View Post
In fact, I try to stay in the "sweet spot" in terms of aperature (around f5.6-11).
Dan,

As Alan suggests, this is where you have gone wrong. You're shooting at too small of an aperture for a 1/2" sensor. The sweet spot on the EX3 is not f/5.6 to f/11. It ends at f/5.6. The sweet spot is from f/2 to f5.6. Personally, I never shoot anything over f/4 and usually try to shoot at f/2.8 so I still have some leeway either direction.

To answer your question about using a real ENG broadcast lens, you'd see a little improvement but probably not enough to justify the expense of the lens. I own a Fujinon 18x5.5 lens that I used on my EX3 as well as several Nikon lenses (including a 300mm f/4 and 80-200mm f/2.8). I always preferred the image from the Fujinon, but it didn't have the reach I needed for wildlife. The main reason I used the Fujinon over the stock lens was ergonomics. I can shoot faster, better, and follow focus on almost anything with that lens. I can point you to some clips at Vimeo that were shot with that lens if you are interested in seeing what an ENG lens can do.

Getting back to your original question, have you considered that the Canon lens you are considering is only 120mm when zoomed all the way in? How's that going to compare to your Sigma 100-300? Not too good for wildlife! You're better off sticking with the SLR lenses even if you need to upgrade from your Sigma. But at Alan said, shoot almost wide open and you'll see a marked improvement in sharpness. I always tried to use my Nikon lenses on the EX3 nearly full open and I was very happy with the results -- and I could see a difference whenever I had stopped down.
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Old November 21st, 2010, 10:37 AM   #6
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Doug.


My personal preference is to use when I can stick to it, the zone f4 up to just over f5.6 and to ND down, either with camera internal or an external ND. I am however using an EX1 not the EX3.

Your observations. - Are they in relation to the EX3 camera's own Fujinon zoom or all lenses attached to the camera. - It it a characteristic of the camera from the lens-mount rearwards.
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Old November 21st, 2010, 10:56 AM   #7
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Bob, my recommendations apply to any 1/2" or 1/3 camcorder using any lens you want to choose.
If you do some research you'll find that it all boils down to the physics of shooting with cameras that have very small sensors and has nothing to do with the lens-mount rearwards. But the science behnd it doesn't matter, because you can see the results with your own eyes and that's why the discussion of soft images keeps popping up over and over again on these forums. And the diagnosis almost always turns out that the OP has been shooting at small apertures. The solution is easy: stay almost wide open!

Besides that, if you're shooting wildlife, sports, interviews, portraits, etc. you generally want to keep a shallow DoF anyway. So you kill two birds with one stone. I wouldn't be caught using a lens at f/16 even it looked perfectly sharp at that f-stop. Even on my F800 (2/3 sensors) I keep my f-stop above f/5.6. I could go smaller and not suffer the same diffraction problems that appear with 1/2" and 1/3" cameras, but I choose not to for reasons of aesthetics.
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Old November 21st, 2010, 11:10 AM   #8
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Wow! Great responses.

Bob - I'm no physicist, but what you said is the best explanation I've heard.

Doug - Good advice (although my Sigma only opens to f4 - for some reason I've preferred using 5.6, but as you suggest maybe I need to lean toward the f4 and avoid f8-11 whenever possible). Regarding the Canon lens I'm considering, it does have the 2x converter so the maximum focal length is 240mm. Still not the reach of the Sigma SLR lens, but if the quality is better I'd consider it (it obviously has other benefits as well, e.g., servo iris, zoom, etc.).

Keep the input coming, its been great (and reassuring as its mostly consistent with my own experiences). Cheers.
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Old November 21st, 2010, 11:27 AM   #9
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Ummm no...

You can use lenses designed for cameras with 3 CCDs on cameras with a single CMOS.

The reason why you'll get out-of-focus shots shooting with a small aperture and nice crisp images when you open up is simply down to diffraction. Every lens and sensor combination will have its sweet spot, most lenses function at their best between f/4 and f/11. Be aware that the smaller the sensor on your camera and the longer the lens you use, the more diffraction you'll get - it's due to the circle of confusion, which is a good subject to google on a long night:)
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Old November 21st, 2010, 04:01 PM   #10
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Just as important, when using long lenses (designed for 35mm cameras) on your EX3, get a sturdy tripod with a good video head. I have been using the Manfrotto 503 head and it is nowhere good enough for the EX3 and long lens combination. I am now using the new 504HD head which is a vast improvement, but I am still looking for something better.
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Old November 21st, 2010, 04:53 PM   #11
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I use an O'Connor 1030B with 35L carbon fiber sticks and even that isn't enough sometimes.

FYI, the sweet spot for a lens isn't necessarily he same thing as the sweet spot for the camera it is attached to. For example, a given lens may be at it's very best optically at f/11 when it's being used on a 35mm SLR, but on a 1/2" camcorder f/4 might look better -- even though technically the lens isn't quite as good at that f-stop.
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Old November 21st, 2010, 05:42 PM   #12
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In my own experience I found that zoom lenses for SLR cameras do not perform as well with the EX3. I have a series of Nikon prime lenses which include 85, 105, 135, 200, 300 and 500mm as well as the 55 micro Nikkor. These all produce outstanding quality on the EX3, at apertures of f4 or 5.6. At wide open they do not perform that well, far too much light bouncing about in the camera. You can pick up most older style manual lenses on e-bay for a song, everyone wants autofocus these days. I have a few zoom lenses but rarely use them on the Sony, although I did use my 70-300mm Nikkor on a wildlife shoot in Africa, using the zoom gave my quick response with moving wildlife.

Don't bother with anything wider than 85mm as the results will be very poor, I also have the 18, 20, 25 and 35mm lenses, they produce all sorts of weird effects - maybe one day if I move into producing horror films then I might give them another go.
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Old November 21st, 2010, 05:55 PM   #13
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Vincent, yes I agree with you about zooms. The picture quality on my 80-200 f/2.8 was acceptable with a little grading, but the cheaper 300mm f/4 was sharper and had much better contrast. The contrast really made the difference. I reccommed sticking with primes.

Also, It makes no sense to use any SLR lens wider than 80mm because that falls within the range of the focal length of the stock lens. And with the stock lens you get better focusing, zooming, lower f-stop, and stabilization.
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Old November 21st, 2010, 07:13 PM   #14
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Hi All,

Short lenses do sometimes have their place on small sensor video cameras.

Although I am just in the learning stages still, I did one other experiment that was interesting and revealing about lenses on small sensors. I wanted to do some extreme close-up work (examining individual seeds of milkweed plants, bullrushes, diasies, goldenrod etc.) and discovered that the kit lens on the XLH1s was not able to get anywhere near close enough. I purchased the diopter lens that Canon supplies, but it was just not sharp enough, nor could it deliver as much magnification as I wanted.

I happened to have the 60mm Nikon macro lens (a superb lens for the DSLR). By adding an extension tube (no glass) to the macro lens before putting it on the XLH1s, I was able to get close to microscopic shots. One milkweed seed or one daisy seed or one bullrush seed fills the frame and it is tack sharp. At these magnifications, it is absolutely essential to have a solid tripod for steady shots. I tried panning with my hands (like an earthquake going on), then my fingers just gently touching the handle (my heart beat roars through the fingers to the handle) and you can see the shake. Finally, I was able to do smooth pans using a rubber band tied to the handle of the tripod head. The rubber absorbs the jiggles and allows for a smooth start and finish to the pan.

Alan
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