Rokinon/Samyang 7.5 Lens Profiles

Started Feb 22, 2012 | Discussions
kenw
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Rokinon/Samyang 7.5 Lens Profiles
Feb 22, 2012

I recently acquired the excellent Rokinon/Samyang 7.5 Fisheye for m43.

The original review for it on Photozone claimed it was a stereographic projection fisheye. This was incorrect, it is in fact an equal area projection just like nearly all fisheye lenses made (the Samyang 8mm for APS-C is the only exception I know of). I contacted Photozone and they've corrected the review. If you aren't familiar with what projections (or mappings) are, here is something to read:

http://en.wikipedia.org/wiki/Fisheye_lens#Mapping_function

Now, the stereographic projection is nice in that it is a bit less "distorting" than equal area. In the same way you can "de-fish" a fisheye lens to make it look like a rectilinear lens (with a significant loss in angle of view) you can also change the projection to be stereographic (with a small loss in angle of view). Many panorama programs will let you do this.

However, it would be nice to do it directly in LR or ACR. LR and ACR offer "Lens Profiles" but unfortunately the default implementation is to "de-fish" rather than just correct to the intended projection so they aren't all that useful.

I've done a standard calibration of the 7.5 using the Adobe Lens Profile Creator software and then derived modified profiles that will produce any of the typical projections. So now with these profiles you can do any sort of radial projection mapping you want right in LR or ACR. Note that if you want to "fine tune" a profile to get a bit less or more angle of view for a given composition you can use the "distort" slider in ACR/LR to adjust a bit.

Please note, I've removed the CA and vignette corrections from these projections. I wasn't exactly sure how best to transform them so I just left them out. The rectilinear profile does have CA and vignetting correction available (it is the one directly created by the Adobe tool).

The LCP files I generated have XML comments in them describing how to derive the profiles should someone mathematically inclined want to play with them more.

Without further ado, here is the link to a zip with the profiles:

http://dl.dropbox.com/u/46420541/Rok7_5_lcp.zip

And here are some examples of the different projections (camera oriented at an angle so you can see the effect on the corners clearly, really an architectural subject with lots of horizontal and vertical lines would be a better example but I don't have anything like that yet with this lens).

Default (no profile applied):

Equal Area:

Equidistant:

Stereographic:

Rectilinear:

Finally, there are various non-radially symmetric projections that are popular, in particular the Pannini projection that is used by the Hemi de-fishing tool. Unfortunately the lens profile correction models used by Adobe will not support any projections at all like Pannini. So if you want something like that you'll have to export out of LR/ACR to another tool.
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Ken W
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Panda9
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to kenw, Feb 22, 2012

Thanks. I just received my Bower-branded version today. I will have to give your profile a try once I get some proper test shots taken with it.

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amtberg
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to kenw, Feb 22, 2012

Very generous of you. I use PS rather than LR, however. Any idea if the profiles are compatible?

I just got the Rokinon variant of the lens today and I'm exceptionally pleased with it. So much so that I may well put my 7-14 up for sale. I've done a few tests with the Hemi defishing plugin which is also quite brilliant.

This lens is much better than the 7-14 (or other rectilinear lenses) for doing 360 panos.

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ojenfish
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to kenw, Feb 22, 2012

Thank you very much Ken.

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mazzuccato
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to ojenfish, Feb 22, 2012

Thank you very much from me too.
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ginsbu
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to kenw, Feb 22, 2012

Lenstip had confirmed to me that it wasn't a stereographic projection after their review and I reported this to photozone (in the same thread you commented on); at that time they stood by their "near-stereographic" claim. I'm glad you've clarified this definitively. Unfortunately, the photozone review has been only partially corrected: the "Verdict" section still refers to a "near-stereographic" projection.

Thanks for making these profiles available. A simple workflow for converting to a stereographic projection makes the Samyang m4/3 fisheye much more appealing.

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Cani
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to kenw, Feb 22, 2012

Many thanks Ken, these profiles are going to be very useful!

I also acquired this lens very recently and just tested your rectilinear profile on two of my first pics:

Before correction:

Corrected

Before correction:

Corrected:

It's great.

Cani

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Anders W
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to kenw, Feb 22, 2012

kenw wrote:

I recently acquired the excellent Rokinon/Samyang 7.5 Fisheye for m43.

The original review for it on Photozone claimed it was a stereographic projection fisheye. This was incorrect, it is in fact an equal area projection just like nearly all fisheye lenses made (the Samyang 8mm for APS-C is the only exception I know of). I contacted Photozone and they've corrected the review. If you aren't familiar with what projections (or mappings) are, here is something to read:

http://en.wikipedia.org/wiki/Fisheye_lens#Mapping_function

A pity that it isn't stereographic. But in view of how well the lens performs resolution-wise, I guess it will still do quite well even after conversion to that projection.

Now, the stereographic projection is nice in that it is a bit less "distorting" than equal area. In the same way you can "de-fish" a fisheye lens to make it look like a rectilinear lens (with a significant loss in angle of view) you can also change the projection to be stereographic (with a small loss in angle of view). Many panorama programs will let you do this.

However, it would be nice to do it directly in LR or ACR. LR and ACR offer "Lens Profiles" but unfortunately the default implementation is to "de-fish" rather than just correct to the intended projection so they aren't all that useful.

I've done a standard calibration of the 7.5 using the Adobe Lens Profile Creator software and then derived modified profiles that will produce any of the typical projections. So now with these profiles you can do any sort of radial projection mapping you want right in LR or ACR. Note that if you want to "fine tune" a profile to get a bit less or more angle of view for a given composition you can use the "distort" slider in ACR/LR to adjust a bit.

Many thanks for doing this Ken! As you say, it's a great advantage to be able to do this via a profile directly ACR/LR. As you know, I don't have the lens yet, but I immediately downloaded the profiles for future use.

Please note, I've removed the CA and vignette corrections from these projections. I wasn't exactly sure how best to transform them so I just left them out. The rectilinear profile does have CA and vignetting correction available (it is the one directly created by the Adobe tool).

The LCP files I generated have XML comments in them describing how to derive the profiles should someone mathematically inclined want to play with them more.

Without further ado, here is the link to a zip with the profiles:

http://dl.dropbox.com/u/46420541/Rok7_5_lcp.zip

And here are some examples of the different projections (camera oriented at an angle so you can see the effect on the corners clearly, really an architectural subject with lots of horizontal and vertical lines would be a better example but I don't have anything like that yet with this lens).

Finally, there are various non-radially symmetric projections that are popular, in particular the Pannini projection that is used by the Hemi de-fishing tool. Unfortunately the lens profile correction models used by Adobe will not support any projections at all like Pannini. So if you want something like that you'll have to export out of LR/ACR to another tool.

Sorry to hear that but I guess neither of us is all that surprised that this isn't doable (yet, let's hope for a function update ). Any thoughts about where to go in the meantime apart from Hemi? What about Hugin for example? I had a brief look, and it appears to be very capable and is available for free. Any downsides that you are aware of apart from the obvious need to leave LR?

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hybert46
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Many thanks and a few requests!
In reply to kenw, Feb 22, 2012

Wow, this sounds great. Thank you so much for you work.

I still don't have the samyang 7.5mm but it is for sure the next lens on my list (Except maybe if the 75mm f1.8 can be found in two months for less than 400$ ;-)). I have no experience at all with fisheye lenses but these profiles make it a much more versatile tool. I already have dowloaded your profiles for lightroom. I just have to order the lens then I guess.

I have a small request. For someone untrained with fisheye like myself, it is difficult to really understand the difference in all these projections. Could anyone please post pictures of a cityscape with the original projections and then with all different corrected projections proposed in the profiles here? That would be fantastic to be able to compare all different projections directly here in this thread.

Concerning the fisheye hemi projection. It looks very interesting and it is a pitty that it is not supported by LR. Do you think there would be an easy way to achieve this projection with some other (free) software and lens profiles?

Thanks again for these profiles. I cannot wait to try them!

Simon

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hybert46
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to Cani, Feb 22, 2012

Cani wrote:

Many thanks Ken, these profiles are going to be very useful!

I also acquired this lens very recently and just tested your rectilinear profile on two of my first pics:

Before correction:

Corrected

Thanks Cani for posting these. It looks like it works really well. Which correction have you used here exactly? If you have some time, could you please post a picture (the same as above if you want) with each different correction that are in the lens profiles. I would be very interested to see the slightly different effects one can achieve.

Thanks

Simon

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kiri
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to kenw, Feb 22, 2012

Excellent! Can't wait to try this out!

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Cani
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to hybert46, Feb 22, 2012

hybert46 wrote:

Thanks Cani for posting these. It looks like it works really well. Which correction have you used here exactly? If you have some time, could you please post a picture (the same as above if you want) with each different correction that are in the lens profiles. I would be very interested to see the slightly different effects one can achieve.

Here you are :

Original Before correction

Stereographic

Equidistant

Equal Area

Rectilinear

All originals are available at: http://www.flickr.com/photos/cani7575/sets/72157629386788019/

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hybert46
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Great!
In reply to Cani, Feb 22, 2012

Thank you so much for these.

I will have a closer look at them. It is so difficult not to order this lens right now...

But I should really consider if I really need it and get a bit more familiar with my 45mm f1.8 first.

Simon

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Cani
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Re: Great!
In reply to hybert46, Feb 22, 2012

At best, with the rectilinear correction, it is probably not better than a 11mm equivalent (in 4/3 focal length standard), with very poor corner performance, so be cautious, but as a mere fish-eye it's already a very nice lens to have fun with.

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Anders W
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to kenw, Feb 22, 2012

kenw wrote:

The original review for it on Photozone claimed it was a stereographic projection fisheye. This was incorrect, it is in fact an equal area projection just like nearly all fisheye lenses made (the Samyang 8mm for APS-C is the only exception I know of). I contacted Photozone and they've corrected the review.

I just visited the Photozone review again and noticed that they've corrected it only partially. In the conclusion, they still say:

"The near-stereographic projection doesn't look quite as extreme as in conventional fisheye lenses despite the similar field-of-view so its applications are in fact broader and even pretty suitable for movies as well."

So you might want to send them a little reminder about that.

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Anders W
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Re: Great!
In reply to Cani, Feb 22, 2012

Cani wrote:

At best, with the rectilinear correction, it is probably not better than a 11mm equivalent (in 4/3 focal length standard), with very poor corner performance, so be cautious, but as a mere fish-eye it's already a very nice lens to have fun with.

Hmm. Are you sure about that? Just compare Ken's shot with his 14/2.5 posted here (same scene, and, I assume, from the same spot on the same occasion)

http://forums.dpreview.com/forums/read.asp?forum=1041&message=40630885

with the rectilinearly corrected fisheye shot he posted above. I'd say that the fisheye has more than twice the diagonal angle even after defishing.

As to corner performance, after rectilinear correction, could either of you (Cani or Ken) please post a full-size sample?

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Cani
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Re: Great!
In reply to Anders W, Feb 22, 2012

Anders W wrote:

Cani wrote:

At best, with the rectilinear correction, it is probably not better than a 11mm equivalent (in 4/3 focal length standard), with very poor corner performance, so be cautious, but as a mere fish-eye it's already a very nice lens to have fun with.

Hmm. Are you sure about that? Just compare Ken's shot with his 14/2.5 posted here (same scene, and, I assume, from the same spot on the same occasion)

http://forums.dpreview.com/forums/read.asp?forum=1041&message=40630885

with the rectilinearly corrected fisheye shot he posted above. I'd say that the fisheye has more than twice the diagonal angle even after defishing.

As to corner performance, after rectilinear correction, could either of you (Cani or Ken) please post a full-size sample?

Anders, no I am not sure, it's just a back of the envelope estimate based on

and the fact that the vertical angle in the center is preserved with the rectilinear correction (6 squares vertically thus 8 horizontally). My impression is we end up with something like a 90 degrees diagonal angle more or less corresponding to 11mm. But I could be wrong. I have no 7-14mm to compare the de-fished picture with.

For corner performance you can check full-size originals on my flickr gallery.
http://www.flickr.com/photos/cani7575/sets/72157629386788019/

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Anders W
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Re: Great!
In reply to Cani, Feb 22, 2012

Cani wrote:

Anders, no I am not sure,

OK. Presumably, Ken will be able to tell for sure, based on the images he already has and/or the fact that he has the 7-14 as well as the Rokinon.

For corner performance you can check full-size originals on my flickr gallery.
http://www.flickr.com/photos/cani7575/sets/72157629386788019/

Thanks! I'll have a look.

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mfj197
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Re: Rokinon/Samyang 7.5 Lens Profiles
In reply to Cani, Feb 22, 2012

Ken, great job on the profile. Cani, thanks for the images. I noticed something when viewing your image full size that is also readily apparent in your image below - areas of any contrast seem to have a strange lightening shadow on the outside of them. It's almost like a form of CA, but rather than purple fringing it's +EV fringing, increasing towards the corners. The tree trunk to the right of your example shows it very clearly, even in the much-reduced image below, and the plane tree seedheads top right have lightened blobs outside them.

I didn't notice this in Ken's original images though - perhaps there wasn't such a high-contrast element?

Michael

Cani wrote:

Rectilinear

All originals are available at: http://www.flickr.com/photos/cani7575/sets/72157629386788019/

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hybert46
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Indeed!
In reply to mfj197, Feb 22, 2012

Yes I noticed that too,

It seems to appear only in the rectilinear projection however. I have no clue where this could come from.

Simon

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