After posting my ‘review’ of the Industar 50-2 lens, I decided to get a determination of what settings I should use with the lens (50mm) on my Olympus e-510 (2x crop).
An hour or so later, after plowing through a bunch of mathematical drivel on many websites, I had a thought (and, yes, it did hurt – a lot!). In the olden film days, most lenses had DOF (depth of field) markings on them.
These, since they were from mainly the film and early autofocus 35mm sized film/full frame sensor days, were simple to adjust to hyperfocal (the largest DOF possible including infinity). Set the aperture to the desired size and set the focus with the infinity sign on the same aperture mark. A look at the distance lined up with the other matching aperture mark gave you the closest focus point.
An example >> With the lens set at F22, the infinity mark at F22, and the other mark at 5 feet (for example here only!); everything from 5 feet away to infinity would be in focus.
Ah ha!
Full Frame = use the same values
Now, the mumbo jumbo well known on the Internet, where everything is made as complicated as possible in order to be known as an expert out standing in the field (old joke – I know). The bottom line after reading between lines was- a full frame lens has less depth of field when used on a crop sensor. Simple so far. How much less you ask, well – following directions; using a TI 2943 function calculator and Kentucky windage; it comes out that a 1.5X crop sensor will work out to be about 1 F stop less on the lens markings. Examples: Using a 1.5/6 crop sensor – set the aperture to F8 and use F11 for the infinity mark. Using a 2.0X crop sensor – set the aperture to F5.6 and use F11 for the infinity mark.
Sounds pretty good. Off to the field (OK no more field jokes) to check out this wisdom. Canon XTi (1.6X crop) with the Industar 50mm lens and it works as determed by the SWAG method above. (Mr. Spock, how long until the dilithium crystal containment explodes, and us with it? Well, Captain, since my sensor array is offline, my best Scientific Wild Ass Guess is .. massive explosion follows..) OK, on with the Olympus e-510 (2X crop) and it works again. Good enough for my street shooting anyways.
The images below are shot with the Olympus e-510 and the Industar 50-2. The lens is set at F8 and the focus with the infinity at F16. I felt F11 would be too dark in a lot of places in NYC and the lens is only marked to F16, so I picked F8. The closest shot to the lamp pole was 60 feet from the round bushes that are nicely in focus as is the lamp post. Why use the lamp post? Well I figured it would pretty well pose as a person’s height without asking for minimum wage. The lens markings show 5 feet as the minimum and infinity as the maximum. Well, due to the loss of actual DOF due to the crop value, the focus falls off pretty much at about 10 feet close to 100 feet distant in real world as can be seen in the pictures. I stepped back about 10 feet for each image. In the last image the bush is about 90 feet away. So, I have arrived at a setting that is approximately 10-100 feet in focus. Good enough for street shooting for me. (I did change the distance on the lens from meters to feet. I also fudged a bit when converting infinity from meters to feet)
Remember to read my warning at the bottom of the right hand column for my weasel room if you follow my instructions. They worked for me, but, perhaps not for you.
OMG !!! AM I GUILTY OF INTERNET MUMBO JUMBO ? After checking above, I see no place where the use of a calculator or my phone a friend is needed. Phew ! 8)
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