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01-25-2013, 01:40 PM   #1
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Pentax M 50/4 macro at infinity

Greetings to all,

I'm thinking about buying M 50/4, but before I will purchase another 50 mm lens I want to ask about behaviour of this lens at infinity. Are the edges of the photo soft or sharp when focused at infinity (at digital Pentax)?

I read the lens reviews section, but it is still unclear for me. Some say it is sharp corner to corner, some it has problem with the edges at infinity (without specifying if it is valid for APC-C or film camera).

Maybe one of the Owners of this little lens uses it also as a landscape lens and could answer my question?

thanks in advance

Piotrek (Peter)

01-25-2013, 02:12 PM   #2
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Like all lenses the answer is not as simple as yes or no. It depends on the f stop that the lens is set to.
01-25-2013, 02:15 PM   #3
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And while most lenses are optimized for infinity, most macros are optimized for their max magnification...
01-25-2013, 02:25 PM   #4
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QuoteOriginally posted by vonBaloney Quote
And while most lenses are optimized for infinity, most macros are optimized for their max magnification...
I have heard this said many times, but am not sure where the notion comes from. Macro lenses have very little field curvature (plane of focus is the same throughout the image circle) and that is pretty much essential for technical macro work, but unless the lens employs some sort of floating element, I don't see what difference 2" vs. 10' vs. 10 miles is going to make. The lens does not "know" the subject distance and focus is done purely by moving the optic forward and backward, so I can't see where the close-focus optimization might be applied.

FWIW, I have used my Sigma 50/2.8 Macro for general shooting and it is a great all-round lens, though a little on the slow side and fairly bulky.


Steve

01-25-2013, 02:26 PM   #5
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QuoteOriginally posted by vonBaloney Quote
And while most lenses are optimized for infinity, most macros are optimized for their max magnification...

True, but it does have a VERY flat plane with nearly no curvature. I have a 50/4 Macro in M. It's a very nice lens, although I prefer the M100 Macro personally. I don't use it for much beyond macro work because I have other 50s that are optimized for that work and have f's in the 1.4 range which makes them more useful out in the real world away from artificial light and even illumination.
01-25-2013, 02:37 PM   #6
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I have both the M 50/4 and the M 100/4. I almost never use the 50. I found that the 100 gives a better working distance and allows a variety of lighting sources to be used. Both provide the same magnification and, at least in my copies, the 100 is much sharper and more contrasty than the 50.

Although both have recessed front elements, a hood always helps, especially if you introduce lighting sources in close proximity.

The 100, because of its focal length, allows the use of longer hoods for better contrast; I use a 3" long 62mm-thread metal hood with step down rings.
01-25-2013, 02:40 PM   #7
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I'm not saying that macro lenses turn to crap at infinity, just that long distances were not the priority of the optical engineer when designing the lens. Certainly dealing with spherical aberration at close distances is different than far away, and is the reason why many older telephotos aren't great at close distances.
01-25-2013, 02:41 PM   #8
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The depth of the plane of focus at "infinity" (personally, I can't see that far!) at typical apertures used for landscape shots would make this a non-issue. Using a FF lens on an APS-C sensor should eliminate any differences at the edges anyway.

Most folks are quite happy with using "macro" lenses for normal shooting -- the only downside being the additional expense of a lens optimized for macro use if you don't need that capability and, usually, a slower max aperture than a "normal" lens.

Just try it. If for some reason it doesn't work for you, macro lenses rarely loose resale value and you'll have gained some rare first hand knowledge too often missing in discussions like this.

H2

01-25-2013, 03:34 PM   #9
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Most macro lenses are not so great at longer distance/infinity. I have the K 50 f4, and it is a nice all around lens if you do some macro (e.g., for me backpacking)--but it is soft at infinity. Some lenses internally adjust the element spacing and are better (Nikon 55mm f2.8 is such). To some degree all lenses need to address conflicting requirements. The 50mm f4 is a good all around lens but not really great at most things. For me it strikes the right balance.
01-25-2013, 08:09 PM   #10
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My understanding is that most lenses are primarily designed using calculations based on infinity focus. Macro lenses are intentionally corrected for near focus; this does not necessarily imply that they're therefore worse at infinity. But that doesn't tell us anything about your lens. :-)

I've never tested my macro at infinity, so I just took photos of the moon with my S-M-C Takumar 50mm macro--which I believe is optically the same as your SMC-M macro--and it was almost indistinguishable from my Leica Summicron-R lens, which I prefer over other fifties, including the DA*55, for infinity focus. The Takumar had slightly more glare, and a slightly brighter colored halo, but I had to tweak the processing to make that apparent. I was very impressed by this and might need to test the Takumar more.
01-26-2013, 12:05 AM   #11
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Many thanks, for all replies till now...

...but the behaviour of the lens at infinity is still unknown for me. Maybe I have just try to get it at low rate and get first hand knowlegde.
01-26-2013, 01:24 AM   #12
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QuoteOriginally posted by Piotrek K Quote
...but the behaviour of the lens at infinity is still unknown for me.
Here's a quote from "Stan's Pentax":

William Robb - . . .I have found this lens to be most excellent at close distances, at any aperture.
However, it is not a really great lens beyond a few feet focusing distance.
In normal shooting distances, I would put it on par, optically, with the 40mm f/2.8.
01-26-2013, 10:48 AM   #13
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Part of the question is unstated - compared to what? I think a Pentax-M 50mm f1.7 is a good comparison. They should have similar coatings. If the designers were really considering characteristics and compromises, this is the lens they had around the place. The M50/1.7 is going to have an edge at f4 because it's stopped down, unavoidable.

I think the answer is, they are extremely close, and the macro is possibly just slightly worse.

I did a test this morning. My K-7 was on a tripod. I mounted the M50/4, and adjusted the framing so that a particular mountain was in the lower right corner of the shot. The mountain is 55 miles away, I'm calling that infinity. I focused with live view at 10x on that mountain. Then I took shots at f4 and f8. I switched to the M50/1.7

Here is an array of 100% crops of that lower right corner. I do these by opening RAW files in ACR, setting all the white balances to the same numbers, opening in CS5, cropping out the same details from the image, then pasting those crops into a new composite image. This array has the M50/1.7 on top, f4 on the left, f8 on the right. The bottom pair is the M50/4, f4 on the left, f8 on the right.



I changed the framing to put the mountains in the center of the image. Then I focused in the center of the frame, still using x10 live view. I did another set of crops from the left center of the images, same methods, same arrangements.



These are manual focus lenses and the differences represent a twitch of the focus ring. Focusing is different with each lens. The macro is f4 and therefore a darker viewfinder, though it has almost a full turn of sweep for the focus ring. The M50/1.7 is only a half turn. The details in these crops are really tiny in the viewfinder. I think in the real world, the user would be more likely to make a focusing error that swamps the lens differences, than consistently look at results from the macro and declare them soft. In fact, I really should do this test ten times and see if the results are the same.

The second shot uncropped:
01-26-2013, 12:51 PM   #14
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I have the K50/4 which has the same optics as the M version. I have used it at infinity and as a standard lens, the results are fine. It’s not much different than using a close-up filter or extension tube on a regular 50-55mm lens for macro work.

The end result is that a macro lens is better for macro work and a standard lens is better for regular shooting.

Phil.
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