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-   -   Century Optics Telephoto converter for GL2 (https://www.dvinfo.net/forum/canon-gl-series-dv-camcorders/52035-century-optics-telephoto-converter-gl2.html)

Julian Kehaya September 30th, 2005 05:52 PM

telephoto vignetting question
 
I currently own a Century Optics 2X telephoto converter for my GL2. Already i learned the hard way about vignetting in the true frame vs. vignetting in the viewfinder. One thing that concerns me is that when fully zoomed out or when any vignetting occurs the top left and right corners vignette more than the bottom corners almost as though the lens is not properly alighned. Does anyone else have similar vignetting with their teleconverters? Is my lens possably defective? There does not seem to be any distortion when zoomed through the vignetting. It is also the bayonet mount version if that makes a difference. Any help is much appriciated!

-Julian

Bill Ball October 2nd, 2005 09:01 AM

I have their widescreen adapter. I likewise get a bit of offset on the vignetting where one side does it more than the other on the GL2. I dont think there is anything unusual with you camera. I think imaging chips are not always perfectly centered but as long as they pass quality control with the standard setup they are put on the market by Canon. It's when we start adding the aftermarket stuff that the trouble occurs. I do wish Century would have designed in a little extra leeway on their add on lenses so this would not have happened.

Meryem Ersoz October 2nd, 2005 04:23 PM

julian, i posted a set of test shots using the 2x, which illustrates the vignetting problem. the vignetting on mine seems fairly uniform....you can look at it on this thread:

http://www.dvinfo.net/conf/showthrea...t=2x+test+shot

i plan to limit my own use of the century optics 2x teleconverter to fully zoomed in, because the vignetting shows up in the viewfinder *after* it occurs on the monitor screen. in other words, unless i'm using a GL2 hooked up to a monitor (which i'll probably never do, since it is almost exclusively a field camera for me), i won't be able to perceive vignetting in the viewfinder before it actually takes place. therefore, that seems like the safest use of the teleconverter.
hope this helps.

Julian Kehaya October 2nd, 2005 07:44 PM

it would be cool if i cold limit the ammout i am able to zoom out so that i would never mistakenly get vignetting. I film a lot of surfing and it's great to be able to get cose to the action while safely on the beach. Unfortunatly for me in this situation i like to use zoom in my shots because i like the way it looks in certain situations. I'm sure witha little practice i can get to where i can keep my zooming within a safe range. I don't think i can sacrifice my personal style for safety hehe.

Meryem Ersoz October 2nd, 2005 09:41 PM

you probably could get a bit of zoom in there if it's important to you, but since vignetting occurs at around 60-65% of zoom, it might not be all that satisfying. i shoot a lot of climbers, and the choice to zoom at all is about showing perspective (size of miniscule climber set against size of gargantuan peak), and 2x vignetting kind of limits the range of that perspective. so while it is pretty nice for getting close in, i can't really think of too many uses of the limited zoom for me personally. still, everyone, as you point out, has their own style.

Meryem Ersoz October 4th, 2005 01:48 PM

Century Optics 2x and Chromatic Aberration
 
i was just out playing with my GL2 and Century Optics 2x again and noticed that the 2x at full zoom produces some chromatic aberration which i had not noticed under previous lighting conditions. i shot these short clips at about 9 am on a cloudy morning. shooting against a blue sky on a clear day, there was no purple fringing, but shooting against a white sky yielded some different results. julian, you might be interested in taking a look these images, since you might be shooting against a similar background....

here's the link:

http://ia300133.us.archive.org/3/ite...aberration.mp4

i still think this is a nice piece of equipment but am learning its limits. thought i would pass it on....

Julian Kehaya October 4th, 2005 03:45 PM

wow that is interesting thanks a lot. I will have to more closely review some of my footage to see if i am getting that as well. I do often contend with overcast skies in my area.

Tom Hardwick October 5th, 2005 08:08 AM

A few points of interest maybe. All lenses give a circular image at the film plane, and the gate simply places a 4:3 or 16:9 mask at that film plane. It's not at all uncommon for the chips to be off axis with the true centreline of the lens, as for all general photography this doesn't matter a toot.

But when you get vignetting using a wide or tele converter that really shows up any offset. The filter threads and /or bayonet also have quite large offset production tolerances about the zoom's central optical axis, so any A lens is going to be quite a big compromise anyway. Hense the XL range.

If you look carefully at the images your Canon lens gives at full tele you'll most probably see the chromatic aberation there as well. Telephoto lenses (even fluorite ones) are very prone to this, and telephoto converters simply exagerate it. The FX1 has it very badly, and that's supposed to be a posh Zeiss zoom.

A telephoto converter is really only designed to increase the focal length of your zoom, and you can believe that they all vignette the image as you zoom back towards wide-angle. Don't forget too that the very best tele converter in the world is losing you image quality, so if you want to shoot at 60 mm say, take off the converter and use the camera's zoom naked.

tom.

Meryem Ersoz October 5th, 2005 08:49 AM

that's good info, tom, thanks. i was shooting two cameras yesterday, for the very purpose of making some comparisons, and do have video images of the identical bird, shot on an XL2 with a canon EOS 70-200mm, and there is no chromatic aberration at full zoom. none whatsoever. the XL2 image is very crisp and detailed, down to individual feathers and highly individuated pine needles, without any fringing. if i have something coming up, i always like to test the limits of new equipment in advance, because i don't always notice the mistakes i am making during crucial shooting moments.

as i said before, i still think the 2x is a good addition, i just am trying to ascertain its limits, especially compared to the XL2, mostly to see if, under certain conditions, the difference in images justifies lugging the extra gear and weight, because those differences are *considerable*. let's see, a GL2 on a light tripod with a 2x, which fit in a backpack my 4 year old can carry, or an XL2 with several lenses, an adapter, a 516 head and big fat legs, several more batteries for the energy-sucking 35mm lens....which i need to pack into a car to drive to site....hmmm.

Alan Craven October 5th, 2005 10:47 AM

The Sony 1.7X telephoto adaptor exhibits just the same off-centre vignetting, and the viewfinder does not show the full extent of the vignetting. I am not aware of any visible chromatic abberation though - perhaps I am just not that critical!.

Tom Hardwick October 5th, 2005 11:29 AM

It's not the telephoto converter that causes the off-centre vignetting as I'm sure you're aware Alan. It just shows up what the camera manufacturer would rather you didn't see. I agree - I hate the v'finder masking on cameras. Nice that on the Z1 you can dial it out.

tom.

Julian Kehaya October 7th, 2005 11:31 AM

i wonder if there is any way to convince manufacturers to change the LCD and viewfinders to include the whole image being recorded. Or what their reason for not doing that in the first place is.


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