[newarts]

Here's a Siemens Star resolution test of the Samyang 500:6.3 mirror lens (in the Rokinon version) vs the Pentax DA 55-300:5.8 at F:6.3 with a K100D at ISO 400.

The 300mm image was enlarged to be the same display magnification as the 500mm image. Here are screen grabs of the result (no post processing - top half of the image is the Pentax, Bottom half the Rokinon):

It seems there is no useful advantage of the Mirror lens over the DA 55-300 at f:6.3.

Dave in Iowa

PS a lesson I learned in these tests is that there's no way I can hand-hold a lens at 500mm equivalent (ie. I can't hand-hold the DA 55-300 enlarged to 500 - no way.)

---

Last edited by newarts; 12-12-2009 at 04:27 PM. Reason: explaining comparison image

[Jodokast96]

Too bad the lesson you learned wasn't how to show us the pics, lol.

[newarts]

Too bad the lesson you learned wasn't how to show us the pics, lol.

Thanks for the heads up I suppose?

But I'm not sure I understand. Wasn't it clear that the top half of the image is one lens and the bottom half is the other?

How could the image comparison have been shown better?

Dave

[FotoPete]

Dave, haha, you are missing the point.

You are right that the DA55-300 bears a resolution advantage over the 500/6.3 and if you are after resolution alone, then the Pentax lens is the one for you. (Though if I was nit picky, the enlarged 300mm image shows jaggies. =P)

The 500/6.3 is a totally different lens. It's a 500mm lens. The perspective is totally different. When you see more as you would with the Pentax zoom, your mentality will differ.

the Mirror (while chubby from the doughnuts) is comparatively small with a mere ~10cm x 10cm x 11cm dimension. It focuses down to ~2m. The look is entirely different, DOF, colour etc. If you like a more exacting lens, then perhaps this lens is not the right one for you.

Here's some samples taken with the 500/6.3 mirror (mine is a Rokinon branded one).

#1 and I think #3 are at minimum focusing distance or close it to show tele macro ability.
#2 is among my favourite. I misfocused by like a few inches but love the capture no less.

Attached Images

View Picture EXIF

File Date

 

View Picture EXIF

File Date

 

View Picture EXIF

File Date

 

[Eruditass]

Actually, since he cropped to 500mm equivalent FL, this means he was standing at the same distance as where you would be shooting with a 500mm (unless he did something else), giving the same perspective.

What will be different, however, is the depth of field, which will be shallower on a longer focal length and certainly give a different output.

Anyways, this is just a resolution test and of course doesn't compare other rendering properties (measurable like DoF or not).

[newarts]

Actually, since he cropped to 500mm equivalent FL, this means he was standing at the same distance as where you would be shooting with a 500mm (unless he did something else), giving the same perspective.

Yes, same distance

Anyways, this is just a resolution test and of course doesn't compare other rendering properties (measurable like DoF or not).

F-stop was the same so DOF should be the same.

I think the wide open DA 55-300 wasn't quite as good as when it was stopped down to F:6.3.

These were taken at about 2 meters & focus adjusted in 5mm steps thru focus (DOF less than 5mm or so).

My purpose was to see if there was a resolution difference between the two lenses at the same image size. I conclude that any out-of-the camera difference is minor.

The DA 55-300 is the smaller, lighter, and faster of the two lenses.

Dave

PS I decided to see what effect Focus Magic would have on improving the comparative resolutions of the two lenses for images displayed at the same sizes. FocusMagic's deconvolution improved the mirror lens' resolution sufficiently to win the resolution contest.


I did no diddling with color, white balance, etc. The cross-hatched pattern in the star arms is an artifact of the printer used to make the test chart. It is much more clearly rendered in the mirror lens case.

[Marc Sabatella]

FWIW, even before applying Focus Magic, I could see more detail in the bars from the mirror lens. That could, ironically, be the result of its lower contrast, as the 55-300 rendered those bars much darker.

What I've found comparing my 500/8 mirror to my 50-200 is that when comparing at the 50-200's native size on my K200D (eg, 100% crop from 50-200, 500/8 downsized to match), there is fairly little difference, and indeed, because the DOF is so shallow from the 500, and of course the smaller aperture and lack of AF on the mirror, the 50-200 really wins in practice if you're only looking that big. But when push comes to shove, if you need to blow the image up bigger, looking at the 500/8 at 100% and upsizing the 50-200 to match, the mirror wins pretty handily. Comparing the 55-300 to a 500/6.3 mirror, I'd similarly expect a comparison on the 55-300's terms to be more or less a tossup in terms of IQ with the 55-300 winning on convenience. When one needs more resolution - more than 100% from the 55-300 - I'd expect the mirror to win, if not by as large a margin as it does coapred to the 50-200 (both because the 55-300 is the better lens, and because 300 is closer to 500 than 200 is).

[Marc Sabatella]

Yes, same distance


F-stop was the same so DOF should be the same.

Not if the focal length differs but distance and aperture remained the same. In roughly the same way that ISO, aperture, and shutter speed interrelate such that changing one while holding the others constant will necessarily affect exposure, the same is true of subject distance, focal length, and aperture with regard to DOF.

[newarts]

Not if the focal length differs but distance and aperture remained the same. In roughly the same way that ISO, aperture, and shutter speed interrelate such that changing one while holding the others constant will necessarily affect exposure, the same is true of subject distance, focal length, and aperture with regard to DOF.

Marc, I used the same exposure for both and since I enlarged the 300mm shot afterward (ie the magnification is the same), I think the DOF is the same in theory

In any event the DOF is small for both lenses, measured in mm.

Maybe there's a difference in hyperfocal length. I'll check it out.

Dave

[Marc Sabatella]

Marc, I used the same exposure for both and since I enlarged the 300mm shot afterward (ie the magnification is the same), I think the DOF is the same in theory

I can't do the DOF equations in my head, but I know it doesn't work that way in practice. Magnification from object to sensor and magnification from sensor to view/print size must be separate terms in the equations, because when I've run these tests, the 500 lens has much shallower DOF even when comparing shots upsized/downsized to match. Hopefully someone else can chime in with the math.