Wavy ripple-like distortion with tele lenses

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umit kivanç

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Wavy ripple-like distortion with tele lenses

PostTue Dec 24, 2013 1:01 am

Hi all,
I am struggling with a strange phenomenon since I am using an old Nikkor 300 mm ED AF lens with Mark II and III. The image is brilliant (is sharp, has right colors) but never stabil. It is wavy and "moves" like ripple. It is something I see the first time in my (not so short:) life. With BMPCC is this worst now. And even with an old manual 200 mm Nikkor lens I have the same waving pattern. I've used this lens with Mark II and III without this phenomenon. The image quality, sharpness etc. with both lenses + BMPCC are excellent, even unbelievable!
What I could find until know are:
- With wide open iris the waves are weeker, the distortion is less, with 16 or 22 it is worst.
- With the full censor cameras, Mark II and III, the distortion is less, with BMPCC it is much more.
- It has no impact if I record to the card in the camera or via output to Ninja recorder.
- This phenomenon shows itself only with the mentioned tele lenses.
Please write to me if you know or can think anything about this.
Thank ahead, regards
Ümit
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Denny Smith

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Re: Wavy ripple-like distortion with tele lenses

PostTue Dec 24, 2013 1:50 am

What is the temp. Where you are shooting? In warm to hot weather, a long tele lens will show heat waves in the air movement. A 300mm lens is an extreme tele, with crop factor becomes 800+mm lens!
Denny Smith
SHA Productions
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adamroberts

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Re: Wavy ripple-like distortion with tele lenses

PostTue Dec 24, 2013 7:51 am

2 things that could be causing the issue.

1, as Denny said, heat haze and air movement refracting light. On the BMPCC those lenses become extreme telephoto lenses. The 200mm has a field of view closer to that of 576mm on a MKII and the 300mm close to 864mm. At those focal lengths heat have and air movement will become much more noticeable.

2, rolling shutter. At those extreme tele lengths any vibrating will be picked up by the sensor. You'll need an extremely solid tripod on a very solid surface to avoid picking up the slightest vibration.
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Michael Sandiford

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Re: Wavy ripple-like distortion with tele lenses

PostTue Dec 24, 2013 9:03 am

As they say you either have a rolling shutter problem but with the times 2 crop factor I reckon you've stumbled upon the technique the great DP Freddy Young used to create the mirage in Lawrence of Arabia. Don't look at it as a problem but instead a technique to add to your tool box.

If I were you I'd be getting out and playing and experimenting with it. Also post your results see if you can emulate the famed shot.
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Mac Jaeger

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Re: Wavy ripple-like distortion with tele lenses

PostTue Dec 24, 2013 10:03 am

I'd also blame this on the very high magnification, it's what you'd expect to see in telescopes when the tube has not had time to cool down. You will clearly see ripples and wobble through a 750mm scope with your naked eye, and a 300 mm lens on a Pocket cam has even longer (effective) focal length! The effect lessens when you open the iris, because there are more light rays to be bent, equalizing each other.

I don't think rolling shutter is to blame here, but it may amplify the effect.
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umit kivanç

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Re: Wavy ripple-like distortion with tele lenses

PostTue Dec 24, 2013 3:10 pm

Hi,
thank you very much to you all for these quick responses.
Believe me, I know that the 300 will be something like 850 with BMPCC. This is one of the reasons why I have buyed BMPCC as a videographer with Mark II and III in his hands. And considering the quality, sharpness and tones of the shots with this combination, I am not so wrong with my expectation.
It makes sense to search the causes out of the camera and "on the air" because with Mark II and III I could shot some scenes without this distortion. I will work further on this. Please write to me if you come to anything across which can help.
Thanks again for the responses.
Best from Istanbul
Ümit
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umit kivanç

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Re: Wavy ripple-like distortion with tele lenses

PostTue Dec 24, 2013 9:46 pm

Hi all,
I've uploaded a 1'30 min video with sample shots here:

Maybe you'll take a look and say something.
Thanks ahead
Ümit
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Tom

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Re: Wavy ripple-like distortion with tele lenses

PostTue Dec 24, 2013 10:37 pm

The shots where you can see it less or not at all are not looking through the same amount of atmosphere as the shots where the distortion is more visible.

It is nothing to do with the camera or the lenses, it is 100% caused by natural refractions in the light caused by fluctuations in temperature.

Such effects are less visible when focusing on a subject which is closer - because you are looking through less atmospheric space.

This is completely normal and not a fault.
Tom Majerski
http://tetragrade.com/
http://www.imdb.com/name/nm5157752/
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Mac Jaeger

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Re: Wavy ripple-like distortion with tele lenses

PostTue Dec 24, 2013 10:46 pm

Thank you for the demo shots. Now that i've seen the shots i'm even more convinced that this is normal tele wobble, there's nothing you can do about (unless you want to buy adaptive optics mirror system, that's the way modern telescopes try to solve the problem).
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umit kivanç

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Re: Wavy ripple-like distortion with tele lenses

PostWed Dec 25, 2013 12:22 am

Many thanks, Geoff, Tom, Mac,
I've got what you've explained to me.
Geoff, it was not a hot day, we had only 10°C here. I have shots, made in snowy winter days with 300 mm and Mark II (where 300 is 300:) with the same distortion.
Does it mean that the maximum focal length which can be used in video even with full frame DSLRs is something like 200? It is hard to accept it:)
Thanks again.
Ümit
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Mac Jaeger

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Re: Wavy ripple-like distortion with tele lenses

PostWed Dec 25, 2013 12:57 am

Temperature doesn't have to be hot for this to happen, as long as there are temperature differences you will see that kind of wobble in the air. Cities are a bad place for this, so many heat sources, and cities at the sea (like your marvellous home town) even more so, because there's always a temperature difference between the city and the sea.

I've just been testing my nikon 70-300 at the tele end - same thing. Not as much as in your example, but this is a rural area, and it's been mild rainy weather for days now, ground and air at similar temps.
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Peter J. DeCrescenzo

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Re: Wavy ripple-like distortion with tele lenses

PostWed Dec 25, 2013 12:59 am

FYI:
http://en.wikipedia.org/wiki/Atmospheric_refraction

When air has reletively little turbulence in it, this refraction will be very minimal. As conditions change, so does the clarity of the air.

A photographer/cinematographer can either shoot a scene as planned (such using a long lens through turbulent air or whatever), or instead "shoot around it": If possible re-block the scene and use a shorter lens, or point camera in a different direction, or shoot at a different time of day when conditions may be better, or move to a different location, and so forth.

You can defintely shoot with very long focal length lenses on Blackmagic -- or any camera -- conditions permitting.

John Brawley posted an detailed summary of how he used very long lenses on one of his productions in the BMCuser forum. The link to his post and video examples are here:
http://herefortheweather.wordpress.com/ ... ng-lenses/
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umit kivanç

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Re: Wavy ripple-like distortion with tele lenses

PostWed Dec 25, 2013 6:01 pm

Hi,
Thank you very much. I've learned from this conversation. It is something very valuable.
And it was so quickly!
Thank you all for trying to help me. I hope I can do the same for anyone who needs this.
Ümit
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umit kivanç

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BMPCC + tele lenses - new experiences

PostFri Dec 27, 2013 3:37 pm

Hi all,
I am trying different combinations and settings with BMPCC + tele lenses so maybe we can collect some useful info here.
I've shot with a Tamron 28-300 f3.5-6.3 at the 300 range and had the wavy distortion in 5-6 in 50 shots. The result was much better than a much better lens: Nikkor 300 mm. During these shots the lens were targeted to only shadowed places. (It was a partially cloudly day with ca. 10°C.) But the aberration sometimes in the whole frame was (yes, in some shots) very high and not acceptable.
I've made new shots with Nikkor 300 mm ED with ND on cloudy days without sun and absolutely diffused light: gray, with nearly no colors around:) I have only in 4-5 of the 85 shots the wavy distortion. The iris was always f4, rarely f5.6 during shooting.
Some thoughts:
- Using BMPCC with extreme tele lenses (300 is ca. 860) is a matter of "try and see". But, if you open the iris while using NDs and avoid the sunlight or sunny parts in the frame you have much more chance to get a clean picture.
- If you follow an animal, a bird etc. you can use these extreme lenses because the movement prevents or can hide the unwanted effect.
I will upload a video to vimeo with all these shots soon (I will send a message here when I'm done).
Thanks for your helps
Ümit
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umit kivanç

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BMPCC with heavy tele - an example

PostWed Jan 01, 2014 8:26 pm

Hello,
I've uploaded a video to vimeo with some explanatory info:


I can say that BMPCC with heavy tele lenses is an amazing experience. Yes, it is hard, has many limitations but amazing.
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Tom

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Re: BMPCC with heavy tele - an example

PostWed Jan 01, 2014 10:31 pm

umit kivanç wrote:Hello,
I've uploaded a video to vimeo with some explanatory info:


I can say that BMPCC with heavy tele lenses is an amazing experience. Yes, it is hard, has many limitations but amazing.



your caution regarding using tele lenses is applicable to any camera, digital or analogue - its not specific to the pocket cam.
Tom Majerski
http://tetragrade.com/
http://www.imdb.com/name/nm5157752/
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umit kivanç

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Re: Wavy ripple-like distortion with tele lenses

PostWed Jan 01, 2014 11:13 pm

Analogue-digital or big-small censor etc. some factors change of course the impact of using heavy tele.

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