Thoughts on the GH2's tele conversion feature

R

richtrav

Active member
I was wondering if anyone at Photokina had the chance to play with the GH2 and got to try out the tele conversion function. It sounds like it's using a full center scan at the maximum telephoto length, which will produce 1080p videos that in theory I guess should look like a 100% crop of a 1920x1080 center of a still image. This is what the Canon T2i and 60D do already with their crop mode, just at VGA resolution.

But what I'm really curious about is how will the camera get from a tele length of 0 to the max of 2.6? Is it just a simple "on" button where it goes straight to the full 2.6 or will it be like most digital zooms and let you zoom in at any length? Or will it have a variety of preset choices, like 1.3, 1.7,2.0,2.6? If it is NOT going straight from no zoom to 2.6 (which is what I'm guessing) then something has to be going on with the camera's binning and scaling routines (unless they're just cropping and scaling the original until you got to the full 2.6, in which case anything in between would look like cr@p). What I suspect is going on is several different sampling routines will be employed along the way as it zooms in more and more, and in between each routine a simple upscaling (or downscaling) process will be used. To illustrate this, I've borrowed how one chip maker (Cypress) performs its subsampling routines and extrapolated it to what might happen in a tele conversion process on one of their chips. If say the original subsampling routine for live view/video mode looks like this:
skip1.jpg


then as you zoom in to a cropped portion of the sensor you should get subsampling routines that are closer and closer together:

skip2.jpg
then
skip3.jpg
then
skip4.jpg


Finally at some point (where???!) a full sensor scan will be used. If it is before the full 2.6x mode (say it were to kick in at just 2x) then you'd get better quality at 2x since it'd be using a full sensor scan then presumably downsampling to get to 1080. It'd be particularly interesting to know what happens at 1.29x when the cropped portion off the sensor is 3840 pixels wide. I'm guessing there will be certain "sweet spots" along the way where image quality will be optimal for a given routine.

Note the above is NOT how I believe Panasonic implements their video mode - nobody seems to know - but is instead just a simple representation of the general process.

If anyone had a chance to use the feature and inspect the quality of the video as you zoom in I'd love to know their impressions. To me it's the most interesting part of the GH2 and could be more significant than people realize (especially if the full sensor scan mode starts before 2.6x)
 
Interesting discussion, but the way Panasonic has worded the feature, I'm fairly certain it's an on/off proposition, with no "in-between" setting (other than perhaps normal, resolution-losing digital zoom).
 
It is an on off switch

It is an on off switch

It is an on off switch. However, the amount of zoom does vary depending on your movie resolution with a 2.6x for 1920x1080 video. You can get more of a zoom with 720p and 480p video.

My prediction is that the GF2 or G3 will come with the world's first automatic zoom in an interchangeable lens camera. It will feature a zoom toggle just like on point and shoot cameras. However, this feature will be a purely digital zoom. It will also be nearly lossless since the resolution of the sensors is so much greater than the video and Panasonic's binning process is so good.
 
Theoretically, the EX tele Zoom feature should have no sub sampling at all. It should offer 1:1 pixel mapping and perhaps better image quality than the non EX tele Zoom mode. This could be our answer for the fast 50mm lens for video. Think 20mm F1.7 + 2.6x lossless zoom!
 
mpgxsvcd said:
It is an on off switch. However, the amount of zoom does vary depending on your movie resolution with a 2.6x for 1920x1080 video. You can get more of a zoom with 720p and 480p video.
Click to expand...
mpgxsvcd said:
Theoretically, the EX tele Zoom feature should have no sub sampling at all. It should offer 1:1 pixel mapping and perhaps better image quality than the non EX tele Zoom mode. This could be our answer for the fast 50mm lens for video. Think 20mm F1.7 + 2.6x lossless zoom!
Click to expand...
Well, the 1:1 pixel mapping is only at the maximum zoom setting, which is 2.6x for 1080 mode. The language of official feature description
The Extra Tele Conversion function virtually extends the zoom range up to 2.6x, thus the max. 728mm* in AVCHD Cinema / FSH mode
Click to expand...
makes it sound like in between settings, like x2 are possible. However, demo clip shows smooth variable optical zoom and discrete switch to 2.6x Tele Conv zoom in the end. I guess we'll just have to wait for someone to reliably test this feature.
 
No it is a discrete switch. It is either on or off. For 1920x1080 video it is 2.6x or nothing. If you take the resolution of a full resolution picture and divide it by 2.6 you will get 1920x1080 with some decimal rounding.

However, you can increase the zoom from 2.6 by using a lower video resolution. For example you can get 3.9x with 720p video. This is because you are cropping out a smaller image on the sensor to coincide with the smaller frame of the 720p video.

They say that 2.6x is the maximum because they are referring to 1920x1080 mode for the 14-140 lens specifically. It would be misleading of them to state the maximum zoom for something less than Full HD resolution.

I believe the image below shows that the setting is an on/off switch.
recmenu.gif

http://www.dpreview.com/previews/panasonicdmcgh2/page3.asp
 
mpgxsvcd said:
No it is a discrete switch. It is either on or off. For 1920x1080 video it is 2.6x or nothing. If you take the resolution of a full resolution picture and divide it by 2.6 you will get 1920x1080 with some decimal rounding.
However, you can increase the zoom from 2.6 by using a lower video resolution. For example you can get 3.9x with 720p video. This is because you are cropping out a smaller image on the sensor to coincide with the smaller frame of the 720p video.
They say that 2.6x is the maximum because they are referring to 1920x1080 mode for the 14-140 lens specifically. It would be misleading of them to state the maximum zoom for something less than Full HD resolution.
Click to expand...
Yes, thanks for posting that picture. Technically it only shows the OFF setting. We don't know if the other setting(s) is/are ON or 1.1x, 1.2x, 1.3 up to 2.6x for HD mode :)
 
svecher said:
Yes, thanks for posting that picture. Technically it only shows the OFF setting. We don't know if the other setting(s) is/are ON or 1.1x, 1.2x, 1.3 up to 2.6x for HD mode :)
Click to expand...

I am confident that it is an on/off switch. The magnification is determined by the camera and the video resolution you are using.
 
i vote on the discrete switch. this is consumer camera body. lower the expectation. the kit zoom can change FOV at 2.6x. lossless zooming? prolly not. nothings free. less sensor size implies worse noise control.
 
On the panasonic website, their little graphic shows a continuous arrow from 10x optical all the way to 26x digital, as well.

extra_image02.gif


The ordinary digital zoom on Gh1 has 2x and 4x under a similar menu option. Ah, whatever, I suppose we'll find out very shortly. I'm waiting for Philip Bloom to do a blog on the thing.
 
Just got a line on a used Nikon 400mm 2.8 (manual focus) in supposedly great condition. It's local and I'm going to check it out tomorrow.

Am thinking Tele Conversion equivalent of 2080 at f/2.8. OMG. Even without the Tele Conversion feature it should be pretty sick.

Have never read anything but raves about this lens in any of its many iterations. Anybody have any experience with one of these monsters?
 
tflak said:
Just got a line on a used Nikon 400mm 2.8 (manual focus) in supposedly great condition. It's local and I'm going to check it out tomorrow.

Am thinking Tele Conversion equivalent of 2080 at f/2.8. OMG. Even without the Tele Conversion feature it should be pretty sick.

Have never read anything but raves about this lens in any of its many iterations. Anybody have any experience with one of these monsters?
Click to expand...

Remember this extended tele conversion feature is really only useful for video. It works because video resolution is limited to 1920x1080. Since the sensor has so much more resolution than that you might as well just crop out the center and still retain all of the 1920x1080 or 1280x720 resolution.

For pictures this setting will work. However, it will produce pictures with resolution smaller than full size. If that is ok for your application then it will work much better than the “digital zoom” feature. I will only use the tele-conversion feature for video though. That is where it has the most promise.

For videos over 100mm(35mm equivalent) you will need some sort of image stabilization. I doubt that 400mm F2.8 has that? What are you planning to get pictures/videos of with the 400mm? If it is the moon then a cheap telescope is a much better option.

Imagine using the GH2 with the 14mm F2.5 and being able to get 14mm, 36.4mm, and 54.6mm focal lengths for 1080p and 720p videos respectively. Talk about a versatile lens. Those are pretty much the ideal focal lengths and F2.5 is a great aperture in light absorbing respects.
 
mpgxsvcd said:
Remember this extended tele conversion feature is really only useful for video. It works because video resolution is limited to 1920x1080. Since the sensor has so much more resolution than that you might as well just crop out the center and still retain all of the 1920x1080 or 1280x720 resolution.

For pictures this setting will work. However, it will produce pictures with resolution smaller than full size. If that is ok for your application then it will work much better than the “digital zoom” feature. I will only use the tele-conversion feature for video though. That is where it has the most promise.

For videos over 100mm(35mm equivalent) you will need some sort of image stabilization. I doubt that 400mm F2.8 has that? What are you planning to get pictures/videos of with the 400mm? If it is the moon then a cheap telescope is a much better option.

Imagine using the GH2 with the 14mm F2.5 and being able to get 14mm, 36.4mm, and 54.6mm focal lengths for 1080p and 720p videos respectively. Talk about a versatile lens. Those are pretty much the ideal focal lengths and F2.5 is a great aperture in light absorbing respects.
Click to expand...

Appreciate the feedback, but almost never shoot stills so hadn't even thought about using this lens other than for video.

I shoot a lot of wildlife and anything less than 200mm rarely cuts it. I have an old Bogen 3061 with a 3066 head. Figured that along with the 13 lb. Nikon 400 (and a forklift to move it all) should be pretty stable using a remote to trigger.

I'll also have the new 100-300 with OIS on my GH13. The Nikon idea was to get some really sick close ups to intercut with. However, I've never actually tried a 400mm so maybe it indeed can't be used for some reason without OIS, even on a rock-solid tripod for a locked down shot.

While I have shot a few moons in my time, it never had anything to do with photography. :laugh:
 
mpgxsvcd said:
I have a 400mm F5.0 Canon lens that I have used with two 2x teleconverters to shoot the moon at 3200mm equivalent. With the GH1 I will be able to shoot the same video as below with the lens only and still get 3120mm equivalent. There is a gigantic difference between F5.0 and F20.
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Very cool videos! To be honest had never considered shooting the moon, etc., but this opens up some new possibilities. Thanks for sharing!
 
I think the real question is what happens with respect to hand held stabilization with this extended tele-conversion feature. If you have an unstabilized lens then your body’s natural corrections will get exaggerated as you increase the focal length. However, the new tele-conversion feature doesn’t actually change the focal length.

Does that mean we might be able to shoot with something like the 20mm pancake at 80mm unstabilized? Or perhaps we could shoot the 300mm at 1170mm hand held? I am curious to see how the extra zoom affects stabilization.
 
I wouldnt bet on the 14mm. I just saw sample images from the 14mm. No visible barrel distortion. Prolly heavy software correction. The cropping will inheritantly make DOF deeper and worsen the noise control and camera shake. i.e. no more shallow dof, more noise, more shake, more digital feel. im guessing iso 100 is only practical for this mode to yield good IQ. yes tripod a must. i hope im wrong about this.
 
mpgxsvcd said:
I think the real question is what happens with respect to hand held stabilization with this extended tele-conversion feature. If you have an unstabilized lens then your body’s natural corrections will get exaggerated as you increase the focal length. However, the new tele-conversion feature doesn’t actually change the focal length.

Does that mean we might be able to shoot with something like the 20mm pancake at 80mm unstabilized? Or perhaps we could shoot the 300mm at 1170mm hand held? I am curious to see how the extra zoom affects stabilization.
Click to expand...

No I don't think so... If you take the 20mm or any lens for that matter and use the focus assist, you can see what I mean.
 
mpgxsvcd said:
I think the real question is what happens with respect to hand held stabilization with this extended tele-conversion feature. If you have an unstabilized lens then your body’s natural corrections will get exaggerated as you increase the focal length. However, the new tele-conversion feature doesn’t actually change the focal length.

Does that mean we might be able to shoot with something like the 20mm pancake at 80mm unstabilized? Or perhaps we could shoot the 300mm at 1170mm hand held? I am curious to see how the extra zoom affects stabilization.
Click to expand...

Normal rules should still apply, I think, so if you wouldn't shoot handheld or on a shoulder rig with an 80mm lens, you shouldn't with (4x20) either. If you can get the camera stable enough for 80mm (steadicam?), then it should be fine either way.
 
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