LENSES: Facts and Fallacies - Part II

Gerald · Joined: 25 Mar 2014 Posts: 1196 Location: Brazil

This part of the article explains how to test yourself your lenses using conventional techniques. Thirty years ago, printers for home use were virtually nonexistent and personal computers were not as popular as today. Modern Photography even sold a kit with several test charts and a magnifying glass. Today, printers are ubiquitous, so you can print yourself the necessary test charts. And with digital cameras you do not need to spend a fortune on films to test your lenses.

The article also discusses how the aperture of a lens affects the image quality. As most of you know, besides the image quality, the aperture affects the exposure, depth of field and bokeh.

I would like to remember that the comments in the article are valid for most photographic lenses, but, of course, there are exceptions. For example, there are lenses with correction so good that the peak performance already occurs at wide open.

sichko · Joined: 20 Jun 2008 Posts: 2475 Location: South West UK

The article is confusing. Quotes ...

Optical theory blithely predicts improved resolution as any lens is opened up.

Many aberrations are mitigated as the lens is closed down, thereby improving the resolution. But if yoy step down too far, diffraction (as predicted by optical theory) rears it's ugly head and resolution decreases.

The quotes imply that diffraction only is satisfactorily explained by optical theory, but that aberrations are not. In fact aberrations are also explained by theory.

Gerald · Joined: 25 Mar 2014 Posts: 1196 Location: Brazil

guardian · Joined: 18 Mar 2009 Posts: 1746

I wonder whether it's possible today to buy, new, one of those handy lens test kits.

No doubt a substitute could be put together piecemeal. But having everything together in a kit, well thought through and designed as an ensemble, would be desirable.

danfromm · Joined: 04 Sep 2011 Posts: 595

ForenSeil · Joined: 15 Apr 2011 Posts: 2726 Location: Kiel, Germany.

Should also work fine: Click here to see on Ebay.de
3,2-100lp/mm DINA4 Testchart for 1:40 magnification ratio (2,1m with 50mm lens).
Only problem is that with most good 50mm lenses normal digital sensors won't be high resolving enough and you will need to take photos with high resolving B/W film like Efke 25 - and there with most analog bodies shutter vibration should be limiting.