What is the difference between a good and a bad lens?

[willem_leenen]

I have an EOS 300D with a kitlens and a 50mm F1.8. The first one is

generally considered bad, the second one as 'very good'. I made a

test were I made some pictures in raw-format, and tried to see if i

can see any difference between a kitlens at 50mm and the 50mm prime.

I've got to admit that i didn't see much difference. Perhaps the

aperture of F8 was within a sweet spot of the kitlens? Or is the

difference between a good and bad lens not so great? ( carefull, i

might put you to the test ;-) )

[dcardoso]

The first comparison is the kit lens max aperture is f3.5 I believe compared to f1.8. There's also less of a difference between lenses when you stop down.

 

Now you did mention "i didn't see much difference"...which means you did see a difference. That's the difference ;-). Some people can live with the difference, others wouldn't.

 

I would also factor lens construction.

[lester_wareham]

The 50mm should be much sharper although the kit lens IQ is not as bad as its build quality might suggest.

 

However it can be difficult to see this in ordinary photographic subjects. Try photographing newsprint with both lenses using a solid tripod and mirror lockup. You should be able to see the difference a bit easier.

[rustymadd]

>What is the difference between a good and a bad lens?<

 

Some would say that a good lens does what you want, a bad lens doesn't.

 

On the other hand, if you're a gearhead then, a bad lens is the lens you have, a good lens is the one you want. ;-)

 

C Painter

[marknagel]

Willem,

 

Here is a comparison of several "good" lenses. When I say good, I mean $400+ with good reputations. You can see the differnce in sharpness and contrast. A kit lens wide open should fall short of these...should. But, you should be able to see the differnce between the $400 zoom and the $1200 zoom and the $450 prime.

 

http://www.nagelhome.com/Test%20Final.jpg

 

Mark

[mark u]

There's a nice mouseover illustration of several kinds of lens problems here:

 

http://www.cambridgeincolour.com/tutorials/camera-lenses.htm

 

There's some more in depth discussion of particular problems with illustrations here:

 

http://www.vanwalree.com/optics.html

 

Some defects show more clearly for particular kinds of subject, lighting, focus distance and aperture choice, and whether you are using a hood or not. Good lenses used with a hood (which should really be considered part of the lens and its design) perform well in all circumstances for which they are designed (though "faults" might show if you use the lens outside its design parameters - e.g. with extension tubes, unmatched teleconverters, etc.).

[jan_thomas1]

This can be quite subjective, and depends on the criteria that are important to you, or for the type of work you do.

 

Max aperture, resolution, contrast, focusing accuracy/speed, chromatic aberations, susceptibility to flare... you could make an almost endless list.

[ken munn]

A good lens produces shots YOU are pleased with.

 

A bad lens doesn't.

 

Price doesn't (necessarily) come into it.

[pjmeade]

Hello Willem, I'm not sure if the difference between the 50/f1.8 and the kit lens is that one is good good and one is bad, so much as they have good and bad reputations.

 

The kit lens is not a bad lens, it's just mediocre, but people tend to compare it with L lenses and it doesn't measure up to that standard. The 50/f1.8 isn't an L, but it is a good lens because it's reasonably sharp and is quite fast and above all it's cheap.

 

I have the 50/f1.8 and have produced some very nice images with it, but they are not jaw droppers and I've had some nice images from the kit and have been very pleased. I replaced the kit lens with two L lenses (17-40 and 24-105). So if it takes that level of expenditure to replace it, the kit lens can't be that terrible.

 

Just my 2p.

 

Pete

[John Crowe]

It is important to understand that generally speaking all lenses preform better with respect to contrast and sharpness as you stop down from wide open to around f5.6 to f11 then get a little worse as you go from f11 to f32. For instance while the 50/1.8 is useable wide open it gets progressively much better as you stop down even 1 or 2 stops.

 

 

In your test shooting them both at f8 means both lenses are indeed in their sweetspots and testing any lens at this aperture is going to make discerning the differences more difficult. Even in their sweetspots you may find considerable differences in colour rendition and contrast if you look for them. Sharpness is not the only gauge of an excellent lens but it is the one most referred to and for me the most important.

 

 

I have two very fast and very good telephoto lenses but when used for sports, which is often, I rarely have the opportunity to shoot them at anything but wide open. As good as they are wide open I know that by f4 they are much sharper so when I use them for landscapes I try to shoot them at f4 at least to reap the sharpness rewards. So, it is important to test your lenses so that you know what to expect from them in various situations.

[kin_lau]

F8 is the great equalizer. At F8, it'll be hard to tell the difference btwn _most_ lenses in the 35-135 focal length (35mm equiv) unless it's exceptionally good, or bad. At the 35-135mm equiv, distortion should not be a problem at all, chromatic aberations, vignetting and most faults for that matter, can be minimized at F8. At both the wide angle & tele end, it gets harder to fix, and some faults such as distortion cannot be fixed by stopping down.

 

So why buy the 50/1.8? Because you _can_ use it btwn f1.8 to f5.6, and it's pretty sharp thru the whole range.

 

The kit lense isn't _bad_, it's just not great, and if you can shoot at f8, then it's good enough most of the time. For the price you pay, you won't find a better lense.

 

The difference btwn a very good wide-angle, and the kitlens with be more.

[alexandru_petrescu]

FRom my experience, a good lens is one that can open at or below 2. Usable w/o flash in much more situations, most of my subjects are most of the time indoors. Additionally, a DoF at 1.8 gives a very nice effect of "bokeh": suddenly all distracting background (objects around subject appearing sharp distract attention, a coke can) becomes a very smoothly painted concentration support for the main sharp subject.

 

In 1995-2000 the difference between a 50/1.8 and a 35-70 kit lens at same apertures were immediately obvious on film. A kit lens for 300d is probably not better than the 35-70 MTF-wise, and putting a 35-70 on a digital sensor gives images with much more "pop" than common film. Colors being enhanced to give "pop" right out of the camera is one factor that makes think the kit lens is good enough.

 

A good lens is one allowing one to print very large. Some lens differences are visible only when enlarging pictures.

 

Other people may consider good lenses the longer focals. Actually, there is no "kit" or "bad" lens above 135mm, they seem to be all good. The differences between them are relatively subtle.

 

Other people love the versatility of zooms, a 28-300 can shoot so many types of photos, from NYC city-scape to eagle wildlife to the Moon.

 

Re color, this lens gives better color than that lens, I think it's a matter of fashion. I don't think there's any lens that can approach reality of any sort. It's just that one's eyes are more acustomed to some color balance, because the current TV sets or magazines use most expensive lenses actually. There are people tweaking Photoshop trying to imitate the "look" of the 1930s or any other period. In 100 years there will be no better lens in terms of colour, just different balance, and they'll photoshop to get the look of the 2000s.

[alexandru_petrescu]

<em>I made a test were I made some pictures in raw-format,</em>

<p>

Yes, but what kind of processing were applied to the raw files? DPP? A really raw file out of camera is not very impressive at all. Comparing two non-impressive linear gamma dark files may be difficult.

[stephen hazelton]

If you're shooting 4x6 prints, you may not ever see the difference. That's great, lets you do more with less.

[phyrpowr]

The only test for me is the quality of the print

[robert_hall2]

Willem's question refers to judging print quality, and with the great gear we have, it takes lots of practice and experience to see the differences. Norm Koren suggests a way to test your lenses. Print the armed forces lens test print, put four or five on a poster, illuminate evenly, and shoot full frame at various focal lengths and f-stops. You can see the differences on the screen, and even more in prints. That's a start. Then there is color and contrast, not so easy to test easily. Hope this helps.

[bellavance]

To me, a good lens is one I can use wide-open on my 5D to control depth of field, and still get good (sharp and contrasty) results. These lenses, when made by Canon, usually have the letter "L" in their description.

 

Pierre

[john falkenstine]

Since you haven't posted any images its difficult for any of us to really judge what's happening with your lenses.