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11-26-2017, 04:22 PM   #16
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All very good demonstrations. As in Norm's snake photos, control of depth of field (DOF) by means of the aperture you select, is very important to impart a visual impression of sharpness. This is especially true if the subject is agains a distracting or busy background that has no relevancy in the overall composition. In this case, however, the rocks, etc do have importance as part of the snake's habitat, and there are very dark parts behind the snake so it will stand out against the background even with the rocks in focus.

As tests of the K-70, and the KP have revealed, set sharpness to "F" (Fine Sharpness) in the custom image menu. This will improve rendering of fine detail. I have employed this practice for years, although I do not have the K-70.

Learning is indeed fun, and you certainly have a fine, comprehensive setup for doing so. A future addition you might consider is a fast lens (having a larger aperture capability, meaning a smaller f/ number) if you enjoy doing low-light and/or action shooting, or portraits or other subjects where you want to blur the background even more. Your DFA 100mm macro lens is very good for portrait work, although being a little bit longish in focal length for getting the best perspective. An inexpensive lens in a portraiture focal length, and for action, like the DA 50mm f/1.8, or a "normal" focal length like the FA 35mm f/2 for night shots or action would be two suggestions. They are very high-quality primes for great sharpness in any use as well.

11-27-2017, 08:56 AM   #17
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QuoteOriginally posted by Alex645 Quote
Although not as thorough as the ones listed above, DXOmark has done tests and in order of sharpness report:

Camera Lens Database - DxOMark

"Best results" = sweet spot:
100mm f/4 on K-50 but f/2.8 on K-3
55-300mm f/5.8 @ 300mm on both K-50 and K-3

From experience, I question their results here as almost always, the sweet spot are f/stops midway between the largest and smallest apertures. In most wide-to-tele zooms the sweet spot is around 35-50mm. Telephoto or wide angle zooms are more complicated: At the best performing aperture, they are usually sharpest at a mid-focal length, although some have been designed to perform best at their extremes and many will have unexpected resolution at other aperture and focal length combination.

You may also find anomalies based on focusing distances.
Hi, Thanks for your response but the database does not include the Pentax K-70 in the "mounted on" column. Perhaps the K-70 is close enough to another model to make the database useful?

---------- Post added 11-27-17 at 08:57 AM ----------

QuoteOriginally posted by Alex645 Quote
Although not as thorough as the ones listed above, DXOmark has done tests and in order of sharpness report:

Camera Lens Database - DxOMark

"Best results" = sweet spot:
100mm f/4 on K-50 but f/2.8 on K-3
55-300mm f/5.8 @ 300mm on both K-50 and K-3

From experience, I question their results here as almost always, the sweet spot are f/stops midway between the largest and smallest apertures. In most wide-to-tele zooms the sweet spot is around 35-50mm. Telephoto or wide angle zooms are more complicated: At the best performing aperture, they are usually sharpest at a mid-focal length, although some have been designed to perform best at their extremes and many will have unexpected resolution at other aperture and focal length combination.

You may also find anomalies based on focusing distances.
Hi, Thanks for your response but the database does not include the Pentax K-70 in the "mounted on" column. Perhaps the K-70 is close enough to another model to make the database useful?
11-27-2017, 09:53 AM   #18
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QuoteOriginally posted by normhead Quote
Falconeye once went through a mathematical proof as to why the absolute best lenses are shaprest at 2.8, and the next bunch like the 31 ltd and 77 ltd. being sharpest at 4, and your standard every day kit being sharpest at 5.6, I know enough to know he may be on to something, but not enough to repeat the proof. Apparently some ZIess lenses are sharpest at 2.8. There are enough lens reviews around on Photozone you can check this out empirically if you choose.

Having your lens sharpest at 4 or 2.8 makes for some really nice smooth out of focus areas on portraits, without having to open to ridiculously wide apertures and killing your depth of field.

At least I assume it would. Those lenses are out of my price range.
I may have been a little unclear - I was specifically referring to f/5.6 being the sharpest point for the dfa100mm macro. I've no comment on the performance of the lenses that are also out my price range.

I don't think the dfa100mm falls into the 'absolute best' from an optical criterea alone, but I do wonder if it was intentionally designed to be sharpest stopped down a bit given how it's likely to be used or if this was just a given after other design considerations (size/cost). I've drooled a few litres over the Voigtlander APO Lanther and it's interesting to see how it has an even smaller change in sharpness as you range across the aperture settings (tested on a different camera so the numbers aren't directly comparable to the dfa100mm chart you showed). The cost is double the weight and maybe 4 or 5 times the price of the dfa100mm (it's also tough to find).
11-27-2017, 11:09 AM   #19
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QuoteOriginally posted by BrianR Quote
I may have been a little unclear - I was specifically referring to f/5.6 being the sharpest point for the dfa100mm macro. I've no comment on the performance of the lenses that are also out my price range.

I don't think the dfa100mm falls into the 'absolute best' from an optical criterea alone, but I do wonder if it was intentionally designed to be sharpest stopped down a bit given how it's likely to be used or if this was just a given after other design considerations (size/cost). I've drooled a few litres over the Voigtlander APO Lanther and it's interesting to see how it has an even smaller change in sharpness as you range across the aperture settings (tested on a different camera so the numbers aren't directly comparable to the dfa100mm chart you showed). The cost is double the weight and maybe 4 or 5 times the price of the dfa100mm (it's also tough to find).
I really would like an all WR kit. It is just peace of mind in so many of the situations I find myself in. The sharpness of the 100 macro is not an issue for me. It may be far from the sharpest, but, it gets the job done and is just a lovely lens to work with.

11-27-2017, 11:51 AM   #20
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QuoteOriginally posted by Joyce Keay Quote
Hi, Thanks for your response but the database does not include the Pentax K-70 in the "mounted on" column. Perhaps the K-70 is close enough to another model to make the database useful?[COLOR="Silver"]
Yes, I wish they would keep up. IMO the K-70 is going to get results most similar to the K-3 as both are 24MP sensors.
11-27-2017, 11:59 AM   #21
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QuoteOriginally posted by Alex645 Quote
Yes, I wish they would keep up. IMO the K-70 is going to get results most similar to the K-3 as both are 24MP sensors.
Except for the part where the K-70 has the new image accelerator unit in it which should increase low light performance about a stop. That's actually pretty huge.
11-27-2017, 12:27 PM   #22
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QuoteOriginally posted by normhead Quote
Except for the part where the K-70 has the new image accelerator unit in it which should increase low light performance about a stop. That's actually pretty huge.
Agreed except my interpretation of the OP trying to find the "sweet spot" as mostly a sharpness/resolution inquiry. I'm not saying the results from a K-3 are identical to the K-70....just that it's the closest on that site.
11-27-2017, 01:08 PM   #23
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And if one is old enough one remembers a Vietnam era photographer comment: "f/8 and be there". I've used this in a pinch and out of a pinch for years and found that for normal printing and viewing sizes it is plenty close enough for all the lenses I own. I prefer to use the M 400 at f/11 to reduce the Chromatic Aberrations to minimum, but f/8 still works with a bit more post processing, and in many birding situations I have used f/5.6 (wide open) to get my shutter speed up.


Last edited by Canada_Rockies; 11-27-2017 at 01:13 PM.
11-27-2017, 01:14 PM   #24
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QuoteOriginally posted by Canada_Rockies Quote
And if one is old enough one remembers a Vietnam era photographer comment: "f/8 and be there". I've used this in a pinch and out of a pinch for years and found that for normal printing and viewing sizes it is plenty close enough for all the lenses I own. I prefer to use the M 400 at f/11 to reduce the Chromatic Aberrations to minimum, but f/8 still works with a bit more post processing, and in many birding situations I have used f/5.6 (wide open) to get my shutter speed up.
ƒ8 for FF, ƒ5.6 for APS-c. It's a DoF thing.

They didn't have APS-c in Vietnam.
11-27-2017, 01:47 PM   #25
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I use f/8 on APS-C, too, unless I'm looking for restricted DoF.
11-27-2017, 05:01 PM   #26
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I never thought I'd say this, but there's a point where sharp enough is sharp enough, at least for any use I could conceivably make of an image. On the Photozone charts for the DFA 100 macro, at f16 the numbers drop to "only" 1749/1707. But that's plenty for my purposes. Even as a large print I doubt that any greater resolution would make a significant difference for an image like this.
11-27-2017, 06:48 PM - 1 Like   #27
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1749 is 1749 distinct lines per picture height,. On a 16x20 inch print, that's more than 100 distinct lines per inch0 .01 inch, quite a bit more if you realize line patterns aren't complexly extinct for another 400 lwph more.

At it's sharpest it is roughly 2200 lines or roughly 137 distinct lines per inch or .0072 distinct lines per inch. The difference is .0028 lines per inch or 2.8 thousandths of an inch.

There are people who tell me they can see the difference, but until I see it proven in a blind test, I'm not buying it.

Last edited by normhead; 11-28-2017 at 09:12 AM.
11-27-2017, 07:39 PM   #28
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What I'm taking away from this discussion is that if possible on my two zoom lenses (18-135 mm and 55-300 mm) I should try for an aperture of f/5.6 if that is appropriate for how I want the background to look, and try to stay away from both extreme ends of their zooming capability. For the macro, I will try for whatever aperture gives me what I need for depth of field. I've got a ring light on order so according to one youtube video, when using that, I can set the camera at f/22 and 1/250. Thanks again.
11-27-2017, 08:20 PM   #29
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If you are only interested in shooting at the sharpest aperture, the camera will do this automatically in Program mode. Just select MTF in the Program Line menu. Of course this ignores depth of field. I try to shoot with my 18-135 and 55-300 at f/8 whenever possible. I rarely feel the need to go to f/11. I regularly shoot shoot macros at f/13 or even f/16. Shooting at f/22 on APS-C is well into diffraction territory and will carry a heavy sharpness penalty.

I've owned the original DA 55-300mm and the HD DA 55-300mm WR. Neither was acceptably sharp at 300mm wide open.
11-27-2017, 08:48 PM - 1 Like   #30
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QuoteOriginally posted by Canada_Rockies Quote
And if one is old enough one remembers a Vietnam era photographer comment: "f/8 and be there".
You may have remembered "f/8 and be there" because Weegee died in 1968 during the Vietnam war...but Weegee's hey day was more like the 1930's and 40's. Perhaps he was clairvoyant and knew that one day, they'd be making Pentax lenses in Vietnam!

f/8 and Be There - What We Can Learn From WeeGee's Philosophy | Shutter Photo Magazine
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