Long Lenses Always Wide Open?

[Ronald Jackson]

I use an XLH1 with EF adaptor and a small selection of Canon and Sigma "long" zoom and prime lenses.

I always, as near as possible, shoot fairly wide open, near to maximum aperture, often via the use of ND filters.

I do this because I read , somewhere here on DV Info, that this was "de rigeur" when shooting video with "35mm" lenses.

Is this in fact the case? In my stills days with long lenses stopping down within reason (and available light) was the ideal, not so much for increased depth of field which was negligible, but for that extra bit of sharpness.


Ron

[Cees van Kempen]

The advantage of 35mm is the shallow depth of field. That however refers to the sensor size, not to the lenses you use. It is for this reason that cameras like Sony's F3 and FS100 weer long waited for.

However, shooting wildlife with long telelenses brings a reasonable narrow depth of field anyway. You don't have to aim for maximum aparture. In the contrary. Most still camera lenses perform best when stopped down at least 1 or 2 or even 3 stops. At maximum aparture image often becomes softer and I have noticed a lot more CA with my still lenses with wide apartures. I believe quality of your images will certainly improve if you properly stop down.

[Kin Lau]

The answer is "it depends". With my Sigma 50-500, f8 works well, all the way to f11 when I'm using my T3i with the extra 3x tele-crop factor. When I'm shooting stills or video with the just 1.6x crop factor, I can shoot wide open @ f6.3, but that extra magnification requires stopping down.

I do find that "sharpness" in video is not as much of a requirement, unless the softness is visible. Shooting at 1/50 or 1/120 means sharpness will be limited anyhow, contrast is more visible.

[Willard Hill]

Ronald,

I think the reason for this is the same reason they put the built in neutral density filter in the XL-H1 which is to avoid prevent loss of sharpness from diffraction, which is caused by the combination of small sensor and small f stop. I think you can easily get away with f8 and maybe f11 with the eos lenses and still maintain satisfactory sharpness I am not sure of the actual stop where serious degradation begins as I usually the ND filters too, but only if I am going to have to go smaller than f8.

The T3i should work at even smaller apertures without problems as it has a larger sensor. I avoid the ND filters with the DSLRs in most cases as they are very difficult to focus accurately and in many cases in shooting wildlife it is a plus to have greater depth of field. I only use the ND filters with them if it is extremely bright or I want shallow depth of field for a particular reason.

[Ronald Jackson]

Thanks all. The "standard" lens on the XLH1 won't stop down beyond F11 before expecting you to engage a ND filter so I guess that is a partial answer. Maybe therefore best to have similar self imposed restrictions with "EF" lenses.
Interesting article about DOF in another forum I subscribe to over here under "DV Doctor". I understand some of it!

I do feel sad, actually sad, that Canon appear to have given up on a replacement for the XLH1 based on the XF305. You see BBC Wildlife using EX3s with nanoFlashes strapped to them, but the Beeb also use XF305s "out of the box".

There is thus a market for lightweight broadcast quality cameras for the likes of wildlife programmes, which are increasingly popular. Canon were/are in a very good position to supply it.

Sorry to digress!

Ron

[Brian Drysdale]

With smaller sensors you need lenses with higher resolution because you need to extract the information from a smaller area than with larger sensors. The wide open aperture is more a style thing than a technical requirement, so stopping down a stop or two does help the optical performance of the lens. Although, with the smaller sensors, you need to be aware of diffraction at the other end.

[Vishal Jadhav]

Long Lenses wide open work fine most of the times, yes the DOF is shallow and i do enjoy it some times.
Using the Nikkor 800 MM manual focus lens i do notice that the images are pretty sharp at wide open but as Cees rightly pointed out in his comment the CA is high wide open and pulling down a stop normally gets rid of it. Its just a choice we make.
However when it comes to improvement of DOF its really not that big when you stop down , yes it does increase but not that much.

[Sabyasachi Patra]

I use a Canon EF 400 f2.8 L IS USM lens. It is very sharp at f2.8

It is another issue that the depth of field is very less at that aperture and the margin of error is less.

Cheers,
Sabyasachi

[Alan Emery]

Hi Ron;

I use a long lens (Nikon 80-400mm and an 80-200mm) on a Canon XLH1s and notice a significant fall-off in sharpness and picture quality when shooting in bright light. I ran a series of tests under the same conditions of bright light and found that at any focal length on this lens, the picture quality fell off significantly at f numbers above f8, and even f8 was quite not as good as f5.6. The f numbers were adjusted by using neutral density filters. Actually I am not sure it was entirely a loss of resolution, there seemed to be a degradation of the picture quality overall including the ability to hold the light under control as if there several types of optical aberration occurring. I could see what one could describe as small flares and even colour changes at the edges of brightly-lit objects in the frame.

For those interested in close-ups using long lenses and extension tubes on a small-sensor video camera, the same principle holds. It is very tempting to close the aperture down to increase the depth of field when doing close-ups. Be sure to test the balance between wider DOF and sharpness when using these extreme lenses. I also used a Nikon 60mm macro to be certain of the resolution with the extension tubes and found in bright light I could go to f11, but smaller apertures did not appear to improve the DOF much and picture quality fell off a little.

These are simple tests to carry out with your own lenses. If you do not have neutral density filters, for the purpose of the test (not your actual shooting), you can alter the shutter speed to open and close the aperture. So it is worth testing the concept.

My practice now with any long lens (attached with an adapter and or with extension tubes) is to try to stay around f5.6. This only applies to the small sensor video camera.

With a large sensor camera, I assume you are using a great deal more of the lens so the likelihood of optical aberrations is smaller.

Hope this helps,
Alan

[Bob Hart]

Alan.


As I understand things, there are two things which may be going on with your lens-camera combination.

Firstly, your lens is not optically compensated for use on a 3 chip camera which uses a three way prism split to feed the image to three sensors. Unless your adaptor mount has optical compensation built in, you might observe some vertical chromatic abberation on hard contrasts. This will be seen as a coloured border on a horizontal white edge. It may also be apparent on vertical edges.


Secondly, 1/3" three-sensor cameras are more prone than larger format cameras to displaying an artifact defined as "diffraction" when tight ( high numbers ) apertures like f16 are used. A non compensated lens might even aggravate this trait. The effect is a sort of "hard look" to the image with colours not looking all that good and focus appearing to be off.

ND filtering the lens so that you can adjust iris in the ballpark f4 to f6.3 as you are already doing is as much as you can to keep this under control.


Ideally for best production value adding, you would be attempting to use the lens in its sweet spot anyway which is what you have already found.


Please heed advice published by such as Chris Barcellos and Charles Papert over my comments. As much as I like to massage my ego, I really a tourist in this business compared to those folk who have done it for a living and refined their craft over years of experience.

[Sverker Hahn]

Use ND filters to use iris on the "standard" lenses within the 2.8 -5.6 range, to avoid diffraktion.
Also use ND filters to keep the shutter speed around 180°, e g 1/50th s with when your framerate is 25 fps. Do you wonder why? Shoot a moving object - like a person walking - with shutter speed 1/250 - and compare it with normal 1/50. You get an unpleasant strobing effect with a fast shutter.

[Alan Emery]

Bob and Sverker,

Thanks for the replies. I am very new to trying to do it all on my own and have been experimenting to find the best compromises for all the various cameras, lenses, and shutter speeds while trying to learn enough about the craft of nature documentaries to make engaging stories with excellent images on the video camera.

The technical and artistic learning curves have been steep, but I am getting closer. I realize that the next part of the game is improving the technology to reach full BBC broadcast standards, but in the meantime the combination of the Canon XL H1s and a nanoflash is impressive. Unfortunately my artistic and story-telling skills are not yet the equal of my current technology. Once they outstrip the technical then I will invest in better technology.

Alan