[Rainer]

I'm just experimenting a bit with my Fuji x100 and some

screw-on teleconverters. Most will lead to heavy vignetting,

but some interestingly do not vignette at all. Nevertheless,

even most of those that do not vignette have poor borders

an very pronounced pincusion distortion along with heavy CA.

 

I do not have a PTlens-profile for any of my test-objects, but

eventually I can get along for now if I use the profile of a

completely different lens that also produces strong pincushion

distortion.

 

So far, my best find is the Canon EF 70-300 (non L , non DO)

at 300mm on fullframe. (2.58%) ... I need to apply this profile

two times (which already overcompensates a little).

 

Anyone of you knows a lens that has more pincushion distortion

(regardless of camera system and sensorformat or lens and

focallength)? I just want to try some other PTlens profiles

in order to check if a converter along with stopping down and

correction of the distortion and CA might serve as a 50 - 80mm

substitute for the x100.

 

Rainer

[David Parsons]

Canon 17 - 85 EF-S 4.01 @17mm? Ooops wrong way, thats barrel...

[JJ_SO]

Why don't you photograph a wall with some rectangular structures and create a lens profile?

[stevenb]

Samyang 14mm 2.8 should be able to deliver the pincushion distortion.

[Rainer]

Canon 17 - 85 EF-S 4.01 @17mm? Ooops wrong way, thats barrel...

 

Indeed, I also thought of the 17mm side of the 17-85 first ... but that's, as you

gathered, the wrong type of distortion.

 

Why don't you photograph a wall with some rectangular structures and create a lens profile?

 

Well, I want to find out if it's really worth the effort. In PTlens (the tool I use to correct

lens distortions) you cannot create your own profiles anymore ... Tom Nieman

decided to get rid of the textfile based database quite a while ago.

So I want to check the possible quality of the results before I hand in a testimage to Tom.

If I find a valuable candidate for a teleconverter, I will see to get the profile available

in PTlens.

 

 

Samyang 14mm 2.8 should be able to deliver the pincushion distortion.

 

Nope ... 14's typically produce hefty barreldistortion, or at best mustache ...

but no pure pincushion.

 

 

Thank's for your suggestions guys ... seems like the 2.5% that I have now are

about as bad as it gets ...

 

Rainer

[Brightcolours]

Nikkor 24-85mm f3.5-4.5 VR offers more (2.74%).

 

Maybe you need a lens which offers less, since you apply it twice now. Like the Nikkor 18-300mm DX with 2.36% at 85mm or 2.15% at 150mm.

[Rainer]

Nikkor 24-85mm f3.5-4.5 VR offers more (2.74%).

 

Thanks for this one! ... I did recall there is a Nikkor with strong

pincushion distortion, but couldn't find it (I only looked at the

older non-VR 2.8-4 version of the 24-85).

 

This profile plus the profile of the EF 70-300 along with CA reduction

produces the "best" results so far. With the current converter (an older

Raynox 1.5x) I still don't think its a way to go ... too much losses at

the borders (albeit there is a minimal win in the center compared to

crop and upscale). Next candidate is a Sony 1.5x which might be better

(havent got the stepupring yet) bus is also bigger and heavier.

 

If I ever get usable results, I will post some pictures.

 

Rainer

[Rover]

Nikkor 28-300 looks atrocious at 100mm as well. I remembered that part well.

http://www.opticallimits.com/nikon_ff/57...ff?start=1