Remove vignette by using a teleconverter?


Mythmaker

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Oct 8, 2011
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#1
I have a Tamron 18-270, which is able to mount on a full frame. Unfortunately like most lens designed for crop sensors, it gives a strong mechanical vignette at all focal lengths:



Now the question is, does anyone know if I am able to remove the vignette via using a 1.4 TC?
 

catchlights

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#2
I have a Tamron 18-270, which is able to mount on a full frame. Unfortunately like most lens designed for crop sensors, it gives a strong mechanical vignette at all focal lengths:



Now the question is, does anyone know if I am able to remove the vignette via using a 1.4 TC?
you can try, you will lose two stops of light, hope that lens still able to auto focus, and the quality don't deteriorate too much..


but what is the point of have a full frame camera but pair with not so great lenses?
 

Rashkae

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Nov 28, 2005
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#3
but what is the point of have a full frame camera but pair with not so great lenses?
bingo. Lenses like the 18-250, 18-270 are designed for the "basic consumer" who does not value image quality and just wants "zoom" and convenience.

A TC will, by it's very nature, deteriorate IQ and cause a light loss. (note: 1.4x is not too bad, but really obvious with 2x).

If you want to use an 18-270, just pair it with a cheap APS-C cam.
 

ArchRival

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Sep 17, 2006
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#4
Use a white balance filter cap for frame calibration.
 

Mythmaker

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#6
I understand that I will lose 1 stop of light, and AF would not be able to work (f6.3 down to f9.0) for sure. But the only time I'll need to use a zoom lens for my 5d3 is during casual visits to dark places (no flash, but requires telephoto) like underwater world, sea aquarium, etc and I'm not sure if I want to get another lens just for these very rare occasions... the photos will only be taken more of a remembrance, not looking for fantastic shots >.>

In normal casual trips (zoo, bird park etc) with adequate lighting, I would use it with my 550D instead. Pairing it with a FF is just for casual trips to dark places... >.<

18-270 is a fun lens, when I'm doing serious work like weddings or events it won't be inside my consideration no worries :)
 

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Rashkae

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#7
I understand that I will lose 1 stop of light, and AF would not be able to work (f6.3 down to f9.0) for sure. But the only time I'll need to use a zoom lens for my 5d3 is during casual visits to dark places (no flash, but requires telephoto) like underwater world, sea aquarium, etc and I'm not sure if I want to get another lens just for these very rare occasions... the photos will only be taken more of a remembrance, not looking for fantastic shots >.>
Uhm. You do understand how dark it is, and that you will use mainly wide angle, right? Totally wrong lens combo. You'd be better off with a 25-105 f/4 or something, not a compromised f/9 lens...
 

ArchRival

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#8
Actually the answer whether a 1.4 tc will work is already in the image.

TS posted an image 480x320.
The diameter of the illuminated circle, coincidentally, is ~480 pixels (width of the image).
However looking closer, the diameter is actually < 480, so we use an estimate of 420 pixels to be on the safe side.

The diagonal of the image is 577 pixels.

With a 1.4 tc, the image scale will increase by 1.4x. The diameter of the illuminated circle will likewise increase by 1.4x. Hence 420x1.4 = 588 pixels.
The enlarged illuminated circle must cover the image diagonal, which is 577 pixels. Since the enlarged illuminated circle is 588 pixels, it does cover the image diagonal.

So short answer: yes the 1.4 tc should work, or at least drastically reduce vignetting. However the margin is pretty narrow, TS may want to try out at the shop before committing to a purchase.
 

Mythmaker

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Oct 8, 2011
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#9
Uhm. You do understand how dark it is, and that you will use mainly wide angle, right? Totally wrong lens combo. You'd be better off with a 25-105 f/4 or something, not a compromised f/9 lens...
Actually I'm looking towards close up photos of the fishes or something... haha. I understand alot of the minute details wont be there, but if it looks like a fish and most of the major details are there, I'm fine with it :D

The pics are just for remembrance sake... haha

Actually the answer whether a 1.4 tc will work is already in the image.

TS posted an image 480x320.
The diameter of the illuminated circle, coincidentally, is ~480 pixels (width of the image).
However looking closer, the diameter is actually < 480, so we use an estimate of 420 pixels to be on the safe side.

The diagonal of the image is 577 pixels.

With a 1.4 tc, the image scale will increase by 1.4x. The diameter of the illuminated circle will likewise increase by 1.4x. Hence 420x1.4 = 588 pixels.
The enlarged illuminated circle must cover the image diagonal, which is 577 pixels. Since the enlarged illuminated circle is 588 pixels, it does cover the image diagonal.

So short answer: yes the 1.4 tc should work, or at least drastically reduce vignetting. However the margin is pretty narrow, TS may want to try out at the shop before committing to a purchase.
Thanks for the analysis! I guess I have to drop by a shop then... >.<
 

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ArchRival

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Sep 17, 2006
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#10
Uhm. What link? Do you even understand his question?
Yes i do. TS wants to eliminate vignetting.

By snapping an image using the setup through a white balance filter, you get an image which is neutral white but also captures the vignetting. This is commonly called a flatfield.
The image you take of an object with the undesired vignetting is called a lightfield.

The common treatment people use is to divide the lightfield by the flatfield, then rescaling the pixel values to 255 or whatnot depending on your bitdepth. This is called flatfielding and it serves to remove vignetting, among other things. There are free programs to do this.
 

Rashkae

Senior Member
Nov 28, 2005
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#11
Yes i do. TS wants to eliminate vignetting.

By snapping an image using the setup through a white balance filter, you get an image which is neutral white but also captures the vignetting. This is commonly called a flatfield.
The image you take of an object with the undesired vignetting is called a lightfield.

The common treatment people use is to divide the lightfield by the flatfield, then rescaling the pixel values to 255 or whatnot depending on your bitdepth. This is called flatfielding and it serves to remove vignetting, among other things. There are free programs to do this.
Yeah, I know flatfielding, but it won't help if all his edges and corners are totally black as they are outside the image circle. Flatfield would work with correcting vignette on normal images.
 

Rashkae

Senior Member
Nov 28, 2005
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#12
Ts: honestly, don't risk the small f-stop and image degradation. Just crop. You'll get a sharper image and not need to push ISO like mad to compensate for the smaller f-stop
 

Blur Shadow

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Sep 17, 2005
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#13
Rashkae said:
Ts: honestly, don't risk the small f-stop and image degradation. Just crop. You'll get a sharper image and not need to push ISO like mad to compensate for the smaller f-stop
Those were my first thoughts too. Won't cropping the image be so much easier and cheaper?
 

Mythmaker

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#14
I'm not really sure about the degradation part actually. I know by nature the TC degrades the image quality for EF frames designed for EF use. But so far from what I have seen over the internet, mounting the 1.4x TC on Sigma 10-20 and a modified Canon 10-22 does really improve the quality by a bit, giving it slightly more contrast and making it sharp throughout (otherwise corners are soft). I'm thinking that TC might actually improve performance for mounting EFS/EF lens designed for Crops on FF, but if anyone had tried it out (using TC on EFS lens on FF) please feel free to correct me :)
 

daredevil123

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Oct 25, 2005
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#15
I'm not really sure about the degradation part actually. I know by nature the TC degrades the image quality for EF frames designed for EF use. But so far from what I have seen over the internet, mounting the 1.4x TC on Sigma 10-20 and a modified Canon 10-22 does really improve the quality by a bit, giving it slightly more contrast and making it sharp throughout (otherwise corners are soft). I'm thinking that TC might actually improve performance for mounting EFS/EF lens designed for Crops on FF, but if anyone had tried it out (using TC on EFS lens on FF) please feel free to correct me :)
Personally I don't buy the bull that mounting a TC will improve optics. You will be better off cropping a picture in post.

and the lost of 1 stop of light is big if you are to shoot in low light situation, especially when your lens is already such a slow one.
 

catchlights

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#16
I'm not really sure about the degradation part actually. I know by nature the TC degrades the image quality for EF frames designed for EF use. But so far from what I have seen over the internet, mounting the 1.4x TC on Sigma 10-20 and a modified Canon 10-22 does really improve the quality by a bit, giving it slightly more contrast and making it sharp throughout (otherwise corners are soft). I'm thinking that TC might actually improve performance for mounting EFS/EF lens designed for Crops on FF, but if anyone had tried it out (using TC on EFS lens on FF) please feel free to correct me :)
got such thing meh?

anyway, you can always rent a tele-converter to try it out yourself, and DO remember tell us what is your finding.
 

Rashkae

Senior Member
Nov 28, 2005
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#17
I'm not really sure about the degradation part actually. I know by nature the TC degrades the image quality for EF frames designed for EF use. But so far from what I have seen over the internet, mounting the 1.4x TC on Sigma 10-20 and a modified Canon 10-22 does really improve the quality by a bit, giving it slightly more contrast and making it sharp throughout (otherwise corners are soft). I'm thinking that TC might actually improve performance for mounting EFS/EF lens designed for Crops on FF, but if anyone had tried it out (using TC on EFS lens on FF) please feel free to correct me :)
If it could "improve" the image quality with such a cheap solution, don't you think Canon would have thought of it already?
 

mamypoko

Senior Member
Dec 18, 2007
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#18
Yes it would remove the vignetting, but it would be blatantly pointless to shoot in the dark at f/9.0.
 

ricleo

Senior Member
Mar 13, 2004
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Eastern Singapore
#19
I tend to agree with the consensus here.

kind of pointless to use the 1.4x convertor method on a 18-270. why not buy a 3rd party 28-300 instead. Tamron does one for full frame right?

makes abit of sense to convert EFS wide angle for full frame for those on a budget and just upgraded to full frame.
 

dodgethis

Senior Member
Nov 15, 2011
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#20
Rather than sitting around, why not go rent a teleconverter and test it for yourself? Just because it happened on one lens doesn't it will apply for others.
 

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