mwsilvers Loc: Central New Jersey

From my perspective either a lens is good or it is not good regardless of how much it costs. The least expensive lens I have ever owned is the tiny TTArtisan 35mm f/1.4 manual focus prime lens with a Nikon Z mount purchased new for only $66 USD on Amazon last year. It also turned out to be one of the sharpest lenses across the frame that I have ever owned. I also have owned very inexpensive lenses that were truly mediocre. While purchasing a cheap bad lens is a much less painful investment, IMHO, it has no added value just because it was cheap, and I would most likely discard it. Why waste time with a mediocre optic when better options are available?

User ID

Okaaaay ! You mean one of those awkwardly physically long refractors. I think I still have one somewhere. Your mention of purple CA fringing clued me in. Somehow I thought we were discussing the cheap 500/8.0 reflector lenses cuz some post had mentioned about a "fixed f/8.0"... and reflector lenses acoarst have only their one fixed aperture.

My reason I call a mirror lenss one fixed stop "minimum", even though it is simultaneously maximum, is that Im always regretting I cant close it down smaller, cuz even at f/8 a 500 has about Zeeeero DoF. Being me, acoarst I happen to have a 500/5.6 reflector with less than zero DoF.

Yes, some of you lust for a 600/4.0 refractor. Useless to me, but at least those have the important option of stopping down ! Attached below is an example image from the 500/5.6 reflector lens. Also attached is a pic of my 250/5.6 reflector, which has the DoF of a 500/11 ... very slightly better than zero !

Likely my most expensive yet least useful lens

(Download)

"Less than zero" DoF for all you bokeh cultists

(Download)

dustie Loc: Nose to the grindstone

Isn't it true:
.....diffraction is directly related to aperture?
.....diffraction affects what we perceive as reduction in sharpness / clearness of detail?
.....an f-stop number is not a specific dimension as .005" is a specific dimension, rather it is related to focal length ÷ effective aperture of lens?
.....physics of light behavior when passing through an aperture will be consistent to physics of light regardless what humans do in designing camera lenses?

If any of the questions above have the answer "true", doesn't the camera sensor also have a part in the search for clearness/sharpness? Isn't there a relationship between the size of the cone of light produced by the light passing through the lens aperture and the size of the pixels on the sensor?
If that is true, wouldn't a lens performance be affected by what sensor is behind it, maybe even the dimensions involved in rear lens element to sensor distance?

If none of these are true, never mind......maybe I'll understand it better a few years down the road.

R.G. Loc: Scotland

Optical quality varies greatly between lenses but diffraction due to aperture size is consistent because it's determined by the laws of physics. When you use a smaller aperture you reduce the amount of glass that's being used and for most lenses that means an increase in quality where sharpness, distortion, fringing and vignetting are concerned. If it wasn't for diffraction the quality would go on increasing as you decreased the aperture, but diffraction comes into play typically round about f/11 and continues to get worse as aperture decreases.

For some the increase in quality due to the smaller aperture may outweigh the decrease in quality due to diffraction. So with cheaper lenses there's something to be said for preferring smaller apertures. Of course the suitability of smaller apertures is very dependent on circumstance, and bright, expensive glass is a way to bypass that limitation.

ronpier Loc: Poland Ohio

Years ago when I started my journey I was told to buy ‘good’ glass but have never been able to find the exact definition of what is good glass.

imagemeister Loc: mid east Florida

Wow, it took you only 60 years to figure this out and yes, I totally AGREE - except that shallow DOF is about 50% of the ARTISTRY of photography and best done at wider apertures !
.

imagemeister Loc: mid east Florida

"GOOD" glass is the lenses you cannot afford

Rick from NY Loc: Sarasota FL

[quote=JohnSwanda]That's fine if you never shoot in low light, or situations where you need a lot of DOF.[/quot
Uh - all other things equal, your 50mm @1.4 will have LESS dof than at f8.

rjriggins11 Loc: Colorado Springs, CO

If there i no back or forward fucus issues, most lenses are sharp wide open. I've calibrated hundreds back focus issues on all types of lenses and some aren't possible but by and large the majority of them come out sharp as a tack. The ones that don't are usually impact damage or are the very cheapest of lenses.

With today's cameras, this can be done in the camera to a certain extent and this works fine most of the time but some lenses actually require physical calibration to work correctly.

JohnSwanda Loc: San Francisco

[quote=Rick from NY Uh - all other things equal, your 50mm @1.4 will have LESS dof than at f8.[/quote]

Of course. I'm talking about two different situations. f1.4 for low light and little DOF, smaller apertures for more DOF.

bikinkawboy Loc: north central Missouri

Correction #3, I didn’t even think about the mirror 500s even though I knew the are a set aperture.

That second image, is that a B2 bomber breaking the sound barrier, the Loch Ness monster sticking his lips through the water’s surface or scissors pressing against Saran wrap?

And yes, a crappy lens is a crappy lens. And a $38 Korean made Kalimar 500 in on one end of the crappy spectrum while a $2,500 Nikon is on the opposite, less smelly end of the spectrum. However, I will pony up $38 for the low image quality recreational-play value where I’m not going to spend $2,500 for a high quantity play thing when I need to get a new roof on my shop, split a 15,000 pound tractor to replace the rear main seal and build a quarter mile of new woven wire fence. I know that a $6,000 Benelli 12 gauge shotgun is far superior to the old 1920s vintage I have setting behind the bedroom door but I haven’t used the old one in years. And neither have I used the Kalimar in over a year, meaning I don’t need a high buck lens or the image quality it would provide.

one_eyed_pete Loc: Colonie NY

I also had the 100-400L. It was very sharp at f 5.6 - f 8.0 even w/ the 1.4X extender. But, not quite as sharp as the 70-200. I used the 70-200 for a model shoot and got some incredible head shots. So sharp I had to soften them down w/ negative clarity. (tiny blood vessel in the eye sharp)

JD750 Loc: SoCal

To each his own. You should definitely do what works for you.

However readers should also be mindful that there is a LOT more to high-quality optics than sharpness at F8.

Given that, the focusing on sharpness at F8 is a little bit myopic. (Puns intended)

E.L.. Shapiro Loc: Ottawa, Ontario Canada

All lenses are not necessarily at the "sharpest" at f/8. The kinda sometimes rule of thumb is about 2-stops dawn for the top is the "sharpest"- SOMETIMES!

First of all most modern lenses in today's current market are pretty sharp. It is rare to find a real dud even in the moderately low price range. You can't evaluate every lens by the same standards because there are differet focal lengths. formula, types (such as n zoom and primes), and different applications such as macro, tele, super wide, etc. Nor can you always rely on reviews- depends on the source and degree of precision investigation.

Years ago, Modern Photography Magazine maintained a lab with state-of-the-art electronic/optical analyzation equipment. They issued reviews that indicated the so-called "sweet spot" of each lens as well as the degree of falloff at the edges of the field. Better lenses had less falloff. Lenses of lesser quality might be tack shap, at a particular aperture, at its center, but perform poorly at the edges. If the review does not include this rating of edge sharpness across the field, the review is somewhat invalid.

There are other factors such as contrast, the potential for flare, and a host of possible aberrations that affect performance sharpness. I am sure that today's optical/electronic analization gear is even more sophisticated and accurate than their ancestors. I often wonder if some of the reviews are just opinions or based on real data. Another consideration is a tiny defect or abberatio that shows up on a precision instrument under "optical bench" standards is even perceptible to the naked eye.

Going back to the film days of those photography magazine reviews- things and standards were differet. Shooting in low light, the proverbial" black cat in a coalmine at midnight" scenario required super fast lenses, the widest aperature, very high IOS settings and/or forced film processing. You had to sacrifice quality for depth of field. Many photojournalistic images made with existing light were super-grainy, contrasty, and laced in shad detail- but were quite acceptable inthe day. Nowadays the digital pixel-peepers and sharpness freaks can have their cake and eat it too. They can use extremely high ISO settings without super-noise, stop down for DOP in low light, and not have to worry about IQ. Nowadays, if you want that old-grainy look, you have to add a "texture" in post-processing.

I'm an old-school guy in that I buy my lenses through a local dealer. If I buy an expensive lens, I get to test it out and if it ain't up to my expectations, I will swap it up for a better model. I have reunited one lens in 30 years- not bad! Nothing like a live demo under YOUR shooting conditions!

Alafoto Loc: Montgomery, AL