8mm Rokinon Fisheye

MetroRuss · Mar 21, 2013

Hello,
I just bought this lens off Amazon, was thinking this lens was not focusing properly. I read that users should try to be at f8-f11 and have a longer exposure time.

This photo was at f16, iso100, focus infinity, 1/30
Please let me know what you think, I feel its a pretty nice shot in regards to composition, textures of the clouds, wood, rocks and ocean all together.

This is Ambleside beach in West Vancouver.

timor · Mar 21, 2013

What do you mean by "not focusing properly" ? It doesn't look like much of a fisheye unless pictures you present are crops of just the middle of the frames. Sharpness seems to be Ok. but there is some problems with horizontal level. Did you use a tripod ?

MetroRuss · Mar 21, 2013

timor said:
What do you mean by "not focusing properly" ? It doesn't look like much of a fisheye unless pictures you present are crops of just the middle of the frames. Sharpness seems to be Ok. but there is some problems with horizontal level. Did you use a tripod ?

Hi timor,

Thanks for looking.

Many of the first shots I took with this lens were blurry. The user reviews on amazon said the lens was nice and clear. I read that one should try to use f8-11 with longer exposure time. I tried it and these are the results.

The pics are not cropped, only reduced in size.

Handheld, no tripod.

timor · Mar 21, 2013

OK. So, this is not real fisheye but very wide rectilinear lens. By "blurry" I understand not very sharp or soft. This is quite common story with lower quality glass; or are not corrected properly during the design stage or QC is very relaxed and below f8 images are just crap. The funny thing is, that Samyang is capable of making high quality glass and they do for other brand lenses, but they keep their own brand as a low quality and low cost product. Not long ago I bought Vivitar Series 1 19-35 zoom for Minolta SR (MD) mount. No idea how old this lens is, Minolta stop making manual focus cameras very long time ago, but this lens was never used. First pictures came out not bad, even on the max aperture which is f3.5, but then Series 1 had always high QC.
With such a short lens you should be careful with the horizon or correct the perspective in PP. Our friend ceeboy14 has a great skill in that (and many other digital manipulations of course to). If in doubt ask him.

tirediron · Mar 21, 2013

These lenses tend to be very hit and miss as far as quality; some people report outstanding results, others, not so much. It might be worth attempting to return it and get another copy, in the hopes of improvement.

MetroRuss · Mar 21, 2013

timor said:
OK. So, this is not real fisheye but very wide rectilinear lens. By "blurry" I understand not very sharp or soft. This is quite common story with lower quality glass; or are not corrected properly during the design stage or QC is very relaxed and below f8 images are just crap. The funny thing is, that Samyang is capable of making high quality glass and they do for other brand lenses, but they keep their own brand as a low quality and low cost product. Not long ago I bought Vivitar Series 1 19-35 zoom for Minolta SR (MD) mount. No idea how old this lens is, Minolta stop making manual focus cameras very long time ago, but this lens was never used. First pictures came out not bad, even on the max aperture which is f3.5, but then Series 1 had always high QC.
With such a short lens you should be careful with the horizon or correct the perspective in PP. Our friend ceeboy14 has a great skill in that (and many other digital manipulations of course to). If in doubt ask him.

Hi timor,

Its a fisheye, in those 2 photos I was trying for the non fisheye look and trying to utilize the 180 degrees only. I saw a website where the fellow takes landscapes with the same lens.
http://www.focusonnewfoundland.com/gallery_449568.html#photos_id=10902354 this fellow also has instructions on how to calibrate the rokfish focus with the focus ring. But Im debating returning it instead of voiding the warranty.

Do you think the 2 pictures could be in better focus or its ok for a $330 piece of glass?

Here is a close up photo with my rokfish.

Have great day

MetroRuss · Mar 21, 2013

tirediron said:
These lenses tend to be very hit and miss as far as quality; some people report outstanding results, others, not so much. It might be worth attempting to return it and get another copy, in the hopes of improvement.

Hi tirediron

I read a how to about calibration of this lens. But Im a little timid about trying it. It was a 1st time buy from amazon. I think ill read up on the return policy.

Thanks

KmH · Mar 21, 2013

Since f/8 to f/11 is recommended, why did you use f/16? Focus sharpness can be softened by 'diffraction' caused by using small lens apertures.

Lens focal length is one of the factors that determine DoF. As focal length gets shorter, lens aperture and point of focus distance has less and less affect on DoF.
The far DoF limit of an 8 mm fisheye lens is pretty much always infinity (see 3rd image below).

timor · Mar 21, 2013

I am a bit confused, when you say "focus". What is the problem ? Are you, let say, focusing 3 meters in the front of you but the lens focuses on infinity ? You focus on infinity, but the lens position the focus 1 meter in the front of you ? Is that the problem ? Or is the lens just soft, not very sharp. Any optical system can focus one distance only, not everywhere, focus is, where the circles of confusion are the smallest (still might be not very sharp with bad lens), everything else is out of focus (but still might be visually rendered sharp with given magnification). So what is the case ?
Looks like your perspective correction from fisheye to normal is quite successful, I am sure with the time you will gain even more experience. The gentleman you are mentioning is, I believe, an active member of Rangefinder Forum.

MetroRuss · Mar 21, 2013

KmH said:
Since f/8 to f/11 is recommended, why did you use f/16? Focus sharpness can be softened by 'diffraction' caused by using small lens apertures.

Lens focal length is one of the factors that determine DoF. As focal length gets shorter, lens aperture and point of focus distance has less and less affect on DoF.
The far DoF limit of an 8 mm fisheye lens is pretty much always infinity (see 3rd image below).

Hi KmH
Thanks for the charts. I am gonna have a closer look at these.

I was using f16 because the screen looked over exposed. At this situation should I stay at f8 or 11 and use the ev adjustment?

KmH · Mar 21, 2013

The rear LCD cannot accurately be used to judge exposure.
Judging exposure is best done by looking at the histogram:
Understanding Digital Camera Histograms: Tones and Contrast
Understanding Digital Camera Histograms: Luminosity and Color
Optimizing Exposure
ETTR
Exposing to the right - Wikipedia, the free encyclopedia

If you have enough shutter speed adjustment and no specific motion stopping goals, I would open the lens and speed up the shutter rather than dial in any exposure compensation.