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12-10-2017, 08:13 AM   #16
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Nonsense! The D FA 100mm f2.8 macro is awesome for landscapes. Saturated colors with great contrast, flat focus field, tack sharp from corner to corner at f/5.6-8. It is a perfect complement to my DA 15 and DA 40 Limited lenses for nature and landscape shooting.


Last edited by audiobomber; 12-10-2017 at 08:19 AM.
12-10-2017, 09:33 AM   #17
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If Pentax macro lenses perform well at that longer focusing distances or infinity it means performance at close range can be improved.
12-10-2017, 10:11 AM   #18
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QuoteOriginally posted by Fluegel Quote
If Pentax macro lenses perform well at that longer focusing distances or infinity it means performance at close range can be improved.
Well, the performance of any lens 'can be improved', but if you are saying that a lens performing well at infinity means that it is optimized for long focusing distances and therefore will perform worse at close range, then that is not true. It may be optimized for close range, but still perform well enough at long distances to perform 'well'.

Since you have the means to check this yourself, why don't you try it? You have heard from lots of people here who have, and who dispute what you are saying. I am another. We are not going to be swayed by theoretical arguments when our own experience says different.

My (uninformed) belief has always been that it is harder to engineer a lens which performs well at extreme magnifications than at infinity, so macro lenses are generally made to higher specifications in order to get good quality at close range, and this has the side benefit of increasing quality at long range also, even if it is not optimized for long range. This is really just an educated guess though, which I have arrived at through using lots of these lenses. If it was easy to make lenses perform well in the macro range, then I would have expected to see some manufacturers producing a cheap macro option which is not over-engineered to give good results at longer ranges also, but I never have.
12-10-2017, 10:12 AM   #19
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QuoteOriginally posted by Fluegel Quote
...For objects at distances from about 2 m and more non macro lense give better IQ...
Where are you getting this information? It's wrong. A lens can be very sharp at both 1:1 macro range and at infinity.

12-10-2017, 10:14 AM   #20
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QuoteOriginally posted by Fluegel Quote
If Pentax macro lenses perform well at that longer focusing distances or infinity it means performance at close range can be improved.
Maybe, maybe not.

What is the "physics" relationship between performance at the optimized distance versus other distances? Must a macro lens suck at infinity or might there only be a 1% degradation in performance at the suboptimal distance? Maybe the very very best, most optimized close-focusing macro lens is still a high performer at infinity.
12-10-2017, 10:37 AM   #21
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QuoteOriginally posted by Fluegel Quote
Perhaps a good time to experience what true macro lenses can do at close range?
Sure, show us some examples. Still waiting on examples of a macro lens vs a 'landscape' lens at far focusing distances.

I'm trying to remain optimistic about the motivation of this thread, but I'm losing hope.
12-10-2017, 10:54 AM   #22
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QuoteOriginally posted by Fluegel Quote
Macro lense differ. They not only allow focussing at close range, they hive best IQ at close range. For objects at distances from about 2 m and more non macro lense give better IQ.
Respectfully, that is BS. Macro lenses are optimized for sharp flat field images. Works just fine for landscape or anything else. The only disadvantage is the very long, and often slow, focus throw.

Unless you would care to demonstrate your theory with some carefully taken test images?
12-10-2017, 11:16 AM - 2 Likes   #23
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It's also worth noting that a lens can be optimized for more than one distance if there is more than one degree of freedom in the lens mechanism.

For old-style lenses that have a monolithic assembly of elements all of which move on a single helicoid, it's true that the designer is forced to pick one optimized distance or compromise performance for a range of distances.

But newer lenses such as DFA 100 f/2.8 use a fixed rear group and a moving front group. That means the designer can first optimize all the elements and element locations for highest performance at a close distance and then do a second optimization for infinity by designing which of the elements move and how much they move. The result can be a lens with two sweet spots and high performance across a range of distances.

More complex lenses can be designed to have even more optima. I've seen some zooms with 4 different internal degrees of freedom in the focus and zooming systems that with the use of internal cam-track barrels enables very broad optimization across all focal lengths and distances.

12-10-2017, 12:01 PM - 2 Likes   #24
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QuoteOriginally posted by photoptimist Quote
But newer lenses such as DFA 100 f/2.8 use a fixed rear group and a moving front group. That means the designer can first optimize all the elements and element locations for highest performance at a close distance and then do a second optimization for infinity by designing which of the elements move and how much they move. The result can be a lens with two sweet spots and high performance across a range of distances.
For some added info, Pentax calls this "FREE - fixed rear-element extension" and from Pentax Short Telephoto Prime Lenses it looks like it was added to the A100mm macro in the mid-80s, followed by a redesign for the F100mm macro which looks essentially the same as our DFA100mm. More explanation here: Pentax Lens Terminology.

On my 'to-do' list is to compare an older m42 100mm macro to my dfa100mm at long distances. I'm currently experiencing heavy snowfall (southern Ontario), so all lenses performm equally at far distances. Assuming you're using the default forum colour scheme with a white background, sample photos today all look like the space between these two lines:
____________



____________


Snow- the great lens equalizer
12-10-2017, 12:31 PM - 1 Like   #25
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QuoteOriginally posted by BrianR Quote
For some added info, Pentax calls this "FREE - fixed rear-element extension" and from Pentax Short Telephoto Prime Lenses it looks like it was added to the A100mm macro in the mid-80s, followed by a redesign for the F100mm macro which looks essentially the same as our DFA100mm. More explanation here: Pentax Lens Terminology.

On my 'to-do' list is to compare an older m42 100mm macro to my dfa100mm at long distances. I'm currently experiencing heavy snowfall (southern Ontario), so all lenses performm equally at far distances. Assuming you're using the default forum colour scheme with a white background, sample photos today all look like the space between these two lines:
____________



____________


Snow- the great lens equalizer
Thanks for the info!

What's interesting about the DFA 100mm is that the focus throw is a lot shorter than you'd expect if it were a 100mm simple prime. With a bit of math, one can show that the lens design is similar to a 68 mm f/2 mounted in front of a 1.5 X teleconverter.

LOL on your lens-equilizing landscape conditions. In my neck of the woods, I've got a beautiful line-of-sight to street & building lights several miles on the horizon. But the atmospherics are often horrible with all those nice sharp pinpoints dancing like fireflies on meth.
12-10-2017, 01:28 PM - 1 Like   #26
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QuoteOriginally posted by photoptimist Quote
What's interesting about the DFA 100mm is that the focus throw is a lot shorter than you'd expect if it were a 100mm simple prime. With a bit of math, one can show that the lens design is similar to a 68 mm f/2 mounted in front of a 1.5 X teleconverter.
Possibly - I'm not sure if the FREE bit is equivalent to a TC? I do know the focal length decreases as the dfa100mm changes to the minimum focusing distance. Based on its minimum focusing distance and how it behaves on bellows, my guess is it's acting like a 75mm lens when set to mfd. I don't really know a ton about optics though, what I'd really like to see is a break-down like some of the lenses on this page (mostly Nikon lenses, but I found it extremely interesting): Focal Length and Magnification, by Pierre Toscani


Hmm, meth fireflies, sounds awesome
12-10-2017, 01:36 PM   #27
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The major difference between a macro design and a lens designed for infinity work is the correction of spherical aberration. Macros are corrected for spherical at close distances, while non-macro lenses are corrected for spherical at a distance just short of infinity. However, this spherical aberration at infinity can be negated by stopping down the lens to eliminate the zonal spherical aberration. So yes the macro lens can be used successfully for mid distances and infinity.
12-10-2017, 01:57 PM   #28
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QuoteOriginally posted by BrianR Quote
Possibly - I'm not sure if the FREE bit is equivalent to a TC? I do know the focal length decreases as the dfa100mm changes to the minimum focusing distance. Based on its minimum focusing distance and how it behaves on bellows, my guess is it's acting like a 75mm lens when set to mfd. I don't really know a ton about optics though, what I'd really like to see is a break-down like some of the lenses on this page (mostly Nikon lenses, but I found it extremely interesting): Focal Length and Magnification, by Pierre Toscani


Hmm, meth fireflies, sounds awesome
Interesting link! (In figure 9 you can see that the rear group of the Micro-Nikkor 60 is having a teleconvertor-like effect.)

I know enough about optics to know that when it gets more complicated that a few elements, it's time to bring in the ray tracing computers and the pros. "Thin-lens" optics aren't too hard to understand but when there lots of strange-shaped plano-convex aspheric high-index retro-focus fluorite nonsense, then it's time to treat the lens like a mysterious black box (or black cylinder).
12-10-2017, 02:49 PM   #29
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QuoteOriginally posted by photoptimist Quote
Interesting link! (In figure 9 you can see that the rear group of the Micro-Nikkor 60 is having a teleconvertor-like effect.)

I know enough about optics to know that when it gets more complicated that a few elements, it's time to bring in the ray tracing computers and the pros. "Thin-lens" optics aren't too hard to understand but when there lots of strange-shaped plano-convex aspheric high-index retro-focus fluorite nonsense, then it's time to treat the lens like a mysterious black box (or black cylinder).
There's more on TCs lower down (section 1.4), specifically figures 31 to 33 for macro designs. It's entirely plausable that the dfa100 behaves as in fig. 33, and actually comparing the lens diagrams it looks essentially the same as the Micro-Nikkor AF 105mm f/2.8D. I'm not sure how I didn't see that before, and I'm now pretty convinced the dfa100 has an in-built TC. They're even similar enough that I'm going to start a rumour that the dfa100mm is a nikon design.

It definitely gets more complex than I was exposed to in physics 101/102, so I keep an open mind about anything about optics that I think I know.
12-10-2017, 03:37 PM   #30
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There certainly are some interesting comments here.

Thanks.
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