"Good copy"

Clint_Black

Clint_Black

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Hi,
I've seen this term used a lot in regard to lenses.

How do you know whether your lens is a good copy or not and what exactly does it mean?

Thanks
 
Basically its optically good, i.e. sharp is most common reference, although its colour reproduction and distortion levels can also be factors.

Unfortunately you can usually only prove a good copy by actually using it, otherwise its a lottery as to whether you get good, ok, or bad - but dont let this scare you, most lenses by the major manufacturers tend to be good, and some are exceptional.
 
Understood but if I've bought a lens and want to see if it's a good copy what do I use as a reference point?
 
You can use focus charts, a row of items leading away from you at 45 degrees across your view, or the way I do it is just take pictures as you normally would (this maybe less scientific but is definately more practical and real word).

Easiest proof I find is take a shot of someones eye as theres lots of detail in there, if you can get good detail in the eye and lashes then thats good.
 
The traditional way to test a lens is by photographing a chart which shows how many lines per millimetre the lens is capable of resolving. It's also important to test how the lens sharpness falls away from the centre of the lens towards the edges. Again there are patterns with fine lines which can be photographed to show how the lens performs in this respect. All highly technical and a lot of it is way beyond what we'd normally see with the naked eye, which is the bit which really matters.

An easy way to check your lens is to photograph a large page of newsprint or a brick wall which contains enough fine texture and detail in the mortar and bricks for your purposes.

Obviously whether you use newsprint or a wall, it's important that the camera is set up exactly square to your subject for the test to mean anything at all. If all is well then by the time you've stopped down to around f8 you should be getting acceptable sharpness right across the image with a decent lens.
 
Clint_Black said:
How do you know whether your lens is a good copy or not and what exactly does it mean?
Click to expand...

It's easy to get carried away by forum talk about the relative difference between different lenses. Most will deliver good results when used well. What I always do is go walkabout for 20-30 minutes and shoot stuff; anything from doors or pubs, to lamposts and whole buildings.

I'll usually shoot random through the range and at different apertures ... wide open and, say, f8 will usually do. When I get home I check through and the shots should all look well exposed and sharpen up easily.

You need to be careful about handshake leading to fuzzy pictures: that's you and not the lens. Same with depth of field: a 1.8 or 2.8 lens, ie fast aperture, can make some think there is a problem because only the area specific to the focus point/s will be sharp. Also, use centre focus point only when you are testing or periferal contrast areas can attract a periferal focus point and that usually makes the subject seem out of focus.

If I look at my shots and things don't seem right I will use a focus chart. Sometimes a lens will focus just before or just after the point it should be focused on, ie a front or back focus problem. I had that once but it was clear from the 100+ shots I took. All you can do is exchange it or send it the the manufacturer to be calibrated (a better option as it should come back perfect, or at least within specification).
 
i sent a sigma 18 - 50 to sigma for calibration and it returned 100% better than before, the service was friendly and helpful, and if the lens is in warrenty it should be free, otherwise expect to pay around £35
 
Thanks for your help!
 
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