[koolimy]

Hi, this may be the stupidest question ever posted on the forums, but my most recent LBA acquisitions have me confused about everything regarding camera lenses so I wanted to pose this question here.


Background: For a long time my only lens was a Samyang 35mm F1.4. I bought it when I bought the Pentax K-30, and it was my one and only lens. As you may know, it is a very highly regarded lens known for it's sharpness in all apertures and at least to my eyes, yes, it was very sharp at all apertures and the pictures it took were beautiful, only limited by my ability.


Unfortunately, my K-30 broke shortly after I bought it and I didn't take photos for quite a while. I never sold the Samyang however, and recently I bought a Pentax K20D from a forum member to use the Samyang again. In a fit of LBA I also bought a Pentax 80-200mm F4.5, and a Pentax M 50mm F1.7 to go along with my Samyang.


Much to my astonishment (and dismay, LOL) I found that both lenses were as sharp as my Samyang, even wide open! It was a huge shock since each were less than 1/10 the price of the Samyang, and one was an old zoom lens.


Could it be that my eyes are just not trained enough to see the difference between them, or maybe my monitor is not up to par? Would I get the same result with almost any lens, such as the 18-55 kit lens or the 50/2?


Below are pictures taken from each lens. The first is the Samyang, 2nd is the 50mm 1.7, and the last is the 80-200 zoom.

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[FozzFoster]

Definitely not all lenses are sharp - and the 'sharpness' of an image is also affected by sensor resolution.
It's possible (?) that you've hit the resolving ceiling of your K20D 14MP sensor (..?)
Also the 50 M 1.7 is definitely no slouch for image quality, even for more modern sensors.
I have no experience with the 80-200, but being that it's constant aperture probably helps a bunch.

[Cerebum]

No, some lenses are awful lol the M50mm however is a good lens. I can't speak for the 80-200 though. Many old manual primes are superb. Certainly most Pentax and takumar lenses are. Chinons, vivitars, soligors panagors and the like can be a mixed bag, some are incredible, hanimex are rubbish lol. If you see a vintage lens, just google [lens name] review Pentax and you will see the reviews of pf members. These are a great guide. As for your results, it could just be that your technique has improved since the earlier shots. Bottom line, check the reviews, and don't just go off the average scores as these can sometimes be skewed by one owner who really hated his copy

[RICHARD L.]

It is quite rare that a lens can't produce a sharp image, unless it is defective. Modern lenses, designed in Japan or Germany, will always have a "sweet spot" (i.e. a certain focal length or a certain aperture opening where it performs at its best). I have 75 lenses (25 older Minolta MD's, all sharp, and 50 Pentax K, 645 and 67 lenses). The worst lens I ever bought was a Pentax FA J 75-300 mm but I could even produce the following picture with it (see below). Its sharpness level was dismal past 135 mm but it had great contrast. My second worst was the Pentax DA 18-55 mm kit zoom and this one was poor at all focal lengths and at any aperture. It was badly decentered and produced sharp left sides of pictures but fuzzy right sides. I also have a Pentax A 35-70 mm f/4 that is not too bad on the 16 Mpx sensor of the K5 but unusable on a K3 or a K1. Sensor resolution will thus determine the level of performance of a lens.

So it all depends on A) aperture opening B) focal length C) sensor resolution, presuming the lens is in good mechanical condition. Of course the proficiency of the photographer himself will also affect the final results. You need an interesting framing, precise focusing, solid support, middle apertures and good light. Never forget it is the light that is sharp ...


Taken with my worst lens ever, an FA J 75-300 mm on a K20 @ 75 mm FL and f/11.

P.S. Remember that a good lens can also produce poor images if used improperly.

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Last edited by RICHARD L.; 04-21-2021 at 04:28 PM.

[Bob 256]

Don't forget monitor resolution (and display size). It's usually the bottleneck in the pixel resolution chain whereas the lens and sensor pixel resolutions are substantially higher in many cases. Your final image is limited to the lower of these. Things like chromatic errors, distortion, and flare are not as subject to resolution related limitations but plain old image quality and sharpness depend on the lens, sensor, and display resolutions. If you have a poor display device, then the best camera and lens in the world won't help that much.

A good example was how well some movies appeared using VHS tape on a small monitor. Try that with a big screen UHD display and see if your opinion changes (it will).

[stevebrot]

In short, some lenses are dogs and some of those dogs have been branded Pentax. Conversely, most Pentax-branded lenses are worth owning and some are highly desirable.

Sharpness is only one aspect of what divides the dogs from the others and no lens is sharp if poorly focused.


Steve

[biz-engineer]

In short, some lenses are dogs and some of those dogs have been branded Pentax.

Out of topic, English not being my mother tongue, is a "dog" lens better or worse than "lemon" type lens?

[FozzFoster]

Also some lenses are designed 'soft':
SMC Pentax-F 85mm F2.8 Soft Reviews - F Prime Lenses - Pentax Lens Reviews & Lens Database

[stevebrot]

Out of topic, English not being my mother tongue, is a "dog" lens better or worse than "lemon" type lens?

Lemons are bad from the maker's hands (manufacturing defect, usually due to poor QA). Dogs are bad by design or material choices.

Added: The owner may refer to their lens as either a dog or a lemon depending on reputation or degree of disgust. I currently own one lens that is definitely a dog and probably not a lemon...Auto Eyemik - Quantaray 28/2.8.


Steve

[swanlefitte]

A grain of sand added to a few grains is still a few grains but a some point you call it a pile. Sharpness is the same except more when you can distinguish the grains from the pile. That depends on many things. Viewing distance, eyes, what you record on and view on, at what size. In general for most cases, most lenses are sharp enough but you don't take photos in general without a specific purpose. So yes all lenses are sharp but not neccessarily sharp enough.

[TedH42]

The 80-200 f4.5 (either K or M, they have the same optics and weight) was known in its time as a quite good zoom lens. Mine from back in the day (1980s) performed quite well. It is actually better than some of my modern lenses wide open, such as DA 55-300 ED WR @ 200mm f5.6. Check out the user reviews reviews at:

SMC Pentax-M 80-200mm F4.5 Reviews - M Zoom Lenses - Pentax Lens Reviews & Lens Database

Good lens. Keep enjoying it!

[MossyRocks]

My opinion about lens sharpness is that most lenses when shot in most normal cases are sharp enough. There may be some slight differences wide open to stopped down a bit on a lens but for the most part unless one is really pixel peeping there isn't a huge difference. Granted there are some lenses that don't follow this like the SMC A 50/1.2 where it has an almost ephemeral softness to it but other than a handful of lenses that have a similar behavior I've not found a lens that wasn't sharp enough. I will say that a damaged or worn out lens can produce unsharp images but again that is the exception.

The only type of shooting that I consider sharpness and actual measurements or extreme pixel peeping of lenses is for astrophotogarphy. However for most images there is more to a lens than just sharpness. On that list is the maximum aperture so being able to shot a 35mm f/1.4 instead of a 35mm f/2.4 can make a big difference since you basically can gather an extra 1.5 stops of light, and have that shallower depth of field. Also there is how a lens renders things. The DA 35/2.4 is a much liked lens by a lot of people, however I just find how it renders things boring and not to my taste. I really like how the SMC A 50/1.2 and DA 77 ltd render things when stopped down a bit. Wide open I still like the SMC A 50/1.2 with its soft glow and I also like the Vivitar Series 1 135/2.3 for the same reason.

[koolimy]

Thanks a lot for the replies, there are quite a lot of things to parse through but I learned a lot. My takeaways so far:

1. There are bad lenses, some "dogs" LOL. Some lenses are also actually designed soft! That 85 F2.8 is pretty interesting, it really has a dreamy quality to the photos.

2. The sensor matters. My camera is an older model so maybe I hit the resolution ceiling of the lenses and I can't distinguish any differences.
3. My Pentax lenses are actually good! It's not too much of a surprise they have good sharpness.

4. The viewing medium matters! My monitor is not the best, it's a $60 21 inch 1080p IPS HP monitor, so on the bottom rung of modern monitors. Also, to be honest, I do most of my pixel peeping on the back screen of my K20D, as I need to check if my picture is in focus. That's where I noticed mostly the lack of difference in sharpness. I did do some pixel peeping on my monitor but it seemed to confirm the results on the back of the screen so I stopped doing it after a while.

5. A lot of lenses are sharp enough! What is enough depends on a lot of factors, including the person and the purpose, so what is a dog to stevebrot may be a gem to me, LOL. I have been exporting most of my pictures 900 x 599 for convenience reasons, and I find that at that size even out of focus pictures are sharp enough. That probably means that unless I become an avid pixel peeper, most lenses will probably be sharp enough.

6. Maybe most importantly, lens sharpness probably doesn't matter that much! I would love to someday be able to take a photo like the one posted by RICHARD L. I should probably not worry about my Samyang being outclassed by my other lenses and just appreciate all lenses for what they give, and most importantly try to take better pictures! In the end it's the photo that matters, and how you got the photo probably matters very little.

[mikesbike]

I do not find any of your examples as particularly sharp. I was a regular K20D user for a number of years, passing up the then new K-7 to get a new leftover one at half price with a 5 year Pentax warranty. I have numerous results from it demonstrating impressive sharpness, and using top-quality lenses, both zoom (like the DA* 50-135mm f/2.8) and prime like your F 50mm f/1.7 or my FA 77mm f/1.8 and others. I still have it and use it on occasion when I want its extra-rich color capability. But now my main camera is the KP.

A definite problem here is you cannot expect reliable maximum sharpness when shooting live subjects with a shutter speed of 1/90s and even more so at 1/45s on top of that with a handheld zoom lens of 80-200mm. The one from the Samyang lens looks perhaps better, but the photo appears for the most part not in focus, perhaps from using a very large aperture, which will of course greatly reduce DOF.

The best way to evaluate sharpness is using subject matter that is solidly unmoving, has well-defined edges and containing some clear fine detail. Some statuary, an ornate streetlight in daytime, are two such examples. Then still use a high enough shutter speed for handheld shots to bring sharp results. if using a tripod, watch out for wind shake.

---------- Post added 04-08-21 at 07:24 PM ----------

Definitely not all lenses are sharp - and the 'sharpness' of an image is also affected by sensor resolution.
It's possible (?) that you've hit the resolving ceiling of your K20D 14MP sensor (..?)
Also the 50 M 1.7 is definitely no slouch for image quality, even for more modern sensors.
I have no experience with the 80-200, but being that it's constant aperture probably helps a bunch.

Indeed, this can be a factor also. I noted a step or two forward in image quality upon acquiring my K-5 IIs but then it does omit the AA filter for better fine detail, in addition to better dynamic range and better performance for low light/higher ISO use. I notice even greater improvement when using the KP.

[mikeSF]

Every lens has its own performance parameters and you will find sharpness is all across the board.
I remember the first time I tried something besides my 18-55 kit lens, the M 50/1.7, and the difference was striking.

These days, I'm using 645 format, and I was even more astonished the first time I mounted the D-FA 90mm f/2.8. That is by far the sharpest lens I've used, ever.