So...just how do you test a lens?

[blackcloudbrew]

Lately I've been realizing that I really have no clear idea how to test a lens and by that I mean how to really evaluate in a way that I can practically understand, 1) how good it is, 2) what are it's strong / week points, and 3) just whether I like it or want to dump it. Things like color rendering, purple fringing, CA, edge sharpness, vignetting, sharpness, and build quality are all sorts of things that others measure in reviews and that I can observe to some degree myself (if I'm looking). What I'm trying to get at is what do you do to come to a conclusion about a lens from a practical stand point? All to often with me I think it comes down to I like it or I don't like it and too often I reach those conclusions in some unknown way.

So...anyone have a some ideas to share on this?

[spyglass]

I remember as a young boy standing in front of a wall of guitars. I had been playing guitar for about a year. Started with an acoustic (which I still have today). I felt overwhelmed by the selection and the task of having to pick the right one. The salesman was an older man that had been around the block a few times. He told me that you don't pick a guitar with your eye. He said that when I held the one right one I would know. He asked me to close my eyes and said that he would bring a selection of guitars to me. After about a dozen guitars I found it. I felt almost magical. It seemed effortless to play. My fingers seem to glide on the neck. The weight was perfect, the action was so low and no fret buzz. When I opened my eyes I was holding a Fender Lead 2. It looked as good as it felt. It had a gloss black body with a white maple neck.

What is the point? I think we have been exposed to so much technology, testing, reviews, and onslaught of yet another new and improved this or that. We tend to over analyze things and get lost in details that have no measurable value in the real world.  I think with lenses if you feel, and I mean with confidence, that you are getting decent results then the lens is a keeper. If you feel that the results do not match what you see with the naked eye, and find yourself making any effort or mental step to seek a solution, the lens is not for you.


Spyglass

[blackcloudbrew]

Good points that and at some level I know that too. My problem/question here is a realization that unless something is really off in a lens, I can generally get good useful images from all of my (now substantial) collection. Perhaps that's to be expected. I can also say that it may be easier to identify a bad lens from a good lens than a great lens from a good lens. For example I have a Takumar Bayonet 135mm lens which is not an SMC lens. If you get a light source anywhere near the front of it, you will get unacceptable flaring with that lens, in this aspect it clearly sucks, yet with the sun at your back it works fine and clearly delivers good images. In my book it's difficulty in general use has it on my sell off list. I have several FAJ lenses that are cheap, and to my eye, clearly produce inferior images, they live up to the J designation as meaning junk. Yet again, if I put them on a film camera they produce acceptable images.

To expand this discussion I think I also mean how do you go about your own evaluation of lenses. Again for example, I read lens reviews where it's noted that at a certain f-stop you get optimum sharpness. Now I know there are some general rules of thumb on this too but oddly this is one thing that I almost never think about. If my lens is rated to f2.8, I expect to use it at times to that rating and don't say well I shouldn't go below say f8 on this lens.

Anyway, I'm interested in what others do/think on this.

Earl

Spyglass - about guitars, sorry but when I was buying my first one, I was sure that it was how it looked was the only important factor...

[materialsguy]

Probably due to my background and occupation, I am always seeking the sharpest and cleanest images, so I tend to shoot test patterns like this one:

http://www.graphics.corne...estin/misc/res-chart.html

This lets me evaluate a lens for corner to corner sharpness, contrast, and resolution under controlled conditions.  If a lens has a major problem in these areas, or it is generally soft, I am going to see it.  Then I shoot a bunch of images with it at my favorite testing location (Legal Elevator, see below).  I have shot so much film and digital at this location that I know what I expect and what I should be able to see.

Then I'll shoot more images and make some prints, and ask myself if I like what I see.   If yes, then I keep and use the lens. If no, I usually sell it.

Lloyd Chambers  has some really good information on how he tests lenses which is very worthwhile reading, I think: http://diglloyd.com/index-free.html

Regarding optimal aperture, I most certainly test each lens I use for the sharpest and best contrast images, noting the apertures where sharpness and contrast  improve, and conversely where diffraction begins to limit the sharpness. This I do with test patterns.   I absolutely need to know this for each lens for type of images I shoot.

[chongmic]

I'm no expert in lens testing, but would like to share my opinion. I guess it balls down to how much you can afford and what is your perception of good IQ. Different individual have different taste and standard. Review sites are just testing the technical aspect of the lens, without taking into the consideration of what the lens can do in the field to suit different taste of the individuals, and by no means it is easy to review that way. If you are taking shots for a living and eventually the investment will pay off by itself, I guess you will get the best lens money can buy.

My philosophy is simple, trust your eyes, forget about test charts. If the lens falls within your budget and produce results that is pleasant to your eyes, then I think it is a good lens until you can afford something better. Therefore for photography, I take it as lifetime passions and will continuously looking for improvements. Of course as technology matures engineers are able to come out with something better to make your life easier.