Fixed Focal Zoom vs Prime

[buddhi]

if we compare 16-50mm f/2.8 zoom lens and a 40m f/2.8 or 50mm f/2.8 prime.

does a fixed focal zoom can serve as several primes since it got fixed f and operate within 16-50mm range?

 

[markkuk]

does a fixed focal zoom can serve as several primes since it got
fixed f and operate within 16-50mm range?

There's no such thing as a "fixed focal zoom". A lens with a fixed focal length is also called a prime lens, and a zoom lens has a variable focal length. The fixed maximum aperture of some zoom lenses is another and unrelated feature.

 

[buddhi]

There's no such thing as a "fixed focal zoom". A lens with a fixed
focal length is also called a prime lens, and a zoom lens has a
variable focal length. The fixed maximum aperture of some zoom lenses
is another and unrelated feature.

thanks..

i'm a newbie and not good with terminology and technical aspects.. what i meant was can a 16-50mm f/2.8 serve the need of a 40mm f/2.8 since it has fixed aperture and focal length in the 40mm range?

(am i still getting it wrong?)

 

[mike703]

Yes, it can.

The only difference will be that zoom lenses, usually, have poorer optical quality than prime lenses. A 40mm prime lens is precisely optimised for that focal length. A 16-50mm zoom will necessarily have compromises in its optical design and will show higher degrees of faults such as distortions, chromatic aberration, vignetting, and probably poorer resolution.

This may not be noticeable outside a testing laboratory: it depends how stringent your requirements are. if you want to make big prints with the maximum possible detail and highest optical quality a good prime lens would be better than a zoom. Most people however prefer a zoom for the convenience and versatility, and a decent zoom is good enough optically for most people most of the time.

Best wishes
--
Mike

 

[buddhi]

Thanks heaps mike.. thats what i wanted to know.. I'm thinking of buying the Pentax DA* 16-50 f/2.8 for the K20D than going for a 40mm f/2.8 and more primes covered by the 16-50 range..

 

[Doug J]

BTW, these lenses do not have a fixed aperture. The aperture specified is the maximum (largest) aperture of the lens, this can be adjusted via the camera settings, the smallest setting will be in the neighborhood of f/22-f/32.

--
Best regards,
Doug
http://pbase.com/dougj

 

[buddhi]

BTW, these lenses do not have a fixed aperture. The aperture
specified is the maximum (largest) aperture of the lens, this can be
adjusted via the camera settings, the smallest setting will be in the
neighborhood of f/22-f/32.

true.. but what matters for me is aperture stay a constant and as large as 2.8 (of course when set) in entire 16-50 range.. i'm fine as long as i'm in control..

 

[Dave Martin]

Check Photozone.de for lens comparisons.

 

[chuxter]

i'm a newbie and not good with terminology and technical aspects..
what i meant was can a 16-50mm f/2.8 serve the need of a 40mm f/2.8
since it has fixed aperture and focal length in the 40mm range?

(am i still getting it wrong?)

Sorta wrong? The described lens (ie, 16-50mm f/2.8) doesn't have a fixed aperture. The f/2.8 indicates the widest aperture, but it will be able to ALSO be stopped down, prolly to something like f/22. It would be much clearer if manufacturers and reviewers would use "16-50mm f/2.8-f/22" when describing this lens. For some reason, they think that ONLY the max aperture is important. It can get a bit more confusing when the lens is not a fixed max aperture type. In these instances the lens is commonly described as "16-50mm f/2.8-3.5" where f/3.5 is the max aperture at 50mm. Once you learn these conventions, it ceases to be confusing...

--
Charlie Davis
Nikon 5700, Sony R1, Nikon D300
HomePage: http://www.1derful.info
Bridge Blog: http://www.here-ugo.com/BridgeBlog/
'Experience: Discovering that a claw hammer will bend nails.
Epiphany: Discovering that a claw hammer is two tools...'

 

[buddhi]

true.. but 16-55m f/2.8 stays constant through the entire range if i set it to be so.. that's what matters to me...

 

[buddhi]

Check Photozone.de for lens comparisons.

Thanks Dave, but the Pentax DA* 16-50 f/2.8 has no review there.. May be because Pentax is not so popular as Canon and Nikon..

 

[sherwoodpete]

thanks..

i'm a newbie and not good with terminology and technical aspects..
what i meant was can a 16-50mm f/2.8 serve the need of a 40mm f/2.8
since it has fixed aperture and focal length in the 40mm range?

(am i still getting it wrong?)

The proper term would be "constant maximum aperture", rather than "fixed aperture".

Regards,
Peter

 

[mrxdimension]

Thanks heaps mike.. thats what i wanted to know.. I'm thinking of
buying the Pentax DA* 16-50 f/2.8 for the K20D than going for a 40mm
f/2.8 and more primes covered by the 16-50 range..

Consider that the 16-50mm is quite a bit larger and heavier than 40mm pancake you're comparing it to. Some people prefer the handling of the prime lens over the zoom. For instance, if you were going to shoot street photography the 40 or a similar lens, 35, 43, 50 etc, would be much less intrusive to the subject.

The primes also tend to have a larger maximum aperture, although not the particular case of the lenses you mentioned.

Shooting with primes is a different technique than shooting with zooms. After a while you begin to see as the 40mm or other prime would see and you recognize opportunities. I've never gotten that feeling when using a zoom.

I have a 16-45mm f/4, a 21mm f/3.2, and 43mm f/1.9. In practice the 21 and 43 cover the range the 16-45 does. I tend to prefer to carry two (or three) small primes that are spaced well in focal length instead of one zoom. I rarely change lenses during a day, maybe once or twice at most. As I said, it's a different way of thinking.

Either way I think you'll be happy with K20d and the lenses available for it. The K20 does offer a combination of performance and features that you'd have to pay more for in other brands. Notice on page 23 of the review on this site, the reviewer wasn't sure what to compare the K20d to.

"With the K20D, Pentax has done its usual trick of offering an unambiguously semi-pro specification at much closer to keen amateur prices, which makes it a little awkward when it comes to identifying its peers. The real problem is that some people who might otherwise buy Canon 450Ds and Sony A350s will be tempted to spend a little more to get the better viewfinder and build quality that moving up a level gets you, while its high spec will make it appeal to people considering the Olympus E3, Canon 40D, Sony A700 or even Nikon D300."

 

[chuxter]

true.. but 16-55m f/2.8 stays constant through the entire range if i
set it to be so.. that's what matters to me...

Yes, that's an important feature. But describing it as in "...a 16-50mm f/2.8...has fixed aperture..." is poor use of language. Consider that a 16-50mm f/2.8-3.5 also has a constant aperture at f/3.5...constant is the preferred terminology.

--
Charlie Davis
Nikon 5700, Sony R1, Nikon D300
HomePage: http://www.1derful.info
Bridge Blog: http://www.here-ugo.com/BridgeBlog/
'Experience: Discovering that a claw hammer will bend nails.
Epiphany: Discovering that a claw hammer is two tools...'

 

[neil holmes]

if we compare 16-50mm f/2.8 zoom lens and a 40m f/2.8 or 50mm f/2.8
prime.

does a fixed focal zoom can serve as several primes since it got
fixed f and operate within 16-50mm range?

HI

A constant aperture 2.8 zoom these days is nearly as good optically as a prime in many cases (and in a couple of rare and seriously expensive cases, better than many). Zooms are also much more convienient as well.

The main reasons to use primes....firstly and mainly, in many cases they will be faster lenses than zooms. Ie My Tamron 17-35 2.8-4 zoom is f4 at 35mm. My Nikon 35mm lens (for my Pentax K100d) is a 1.4 lens, this means that in low light if the Tamron at max aperture was at, say, 1/2 a second at iso 3200 I could use the 1.4 lens at 1/30 ...it is 4 stops faster....and 3 stops over every zoom available for anyone (other than 2 Olympus f2 zooms that cost a mint). The depth of field would of course be much shallower but that would be what I would want in many cases...though not always, just means the difference between being able to use it in some cases vs not and gives more options.

secondly, generally with slower primes, they tend to be macro lenses so no need for a really fast aperture (most macros are stopped down to use anyway)....the Pentax 50 2.8 you are considering is a macro lens

http://www.pentaximaging.com/products/product_details?reqID=3094&subsection=Digital_35mm_macro

A third reason to use primes is when you want a really small (in size) lens and that is the 40 2.8 you are considering....it is a pancake lens and one of Pentax limited lens series...which are all high quiality in build and..all round really. The 40 2.8 is one of the smallest dslr lenses made...it weighs 90g and measures 63mm x 15.

http://www.pentaxslr.com/lenses/lens_40

The optical quality of pancakes is high, though not as high as other primes due to trying to make them as small as possible.

So as you can see it is horses for courses...the 50 2.8 is a great macro lens and could be used for portraits as long as you did not want the fast aperture blur of a 50 f2, 1.8, 1.7, 1.4 or 1.2 lens all of whch are available for Pentax k mount...many manual focus and some very cheap (but very good).

The 40 2.8 is a lens to consider if you want a SMALL and a little out of place on a larger dslr like a K20d...will sort of be like a large lens cap in appearance.

neil

 

[buddhi]

Hi Neil,

thanks heaps for your post. I've already bought K20D and 50mm f/1.4 ( http://forums.dpreview.com/forums/read.asp?forum=1002&message=29685437 ). However I'm thinking of getting the DA* 16-50mm f/2.8 in place of few f2.8 primes such as 40mm. Main considerations for that decision are:

• Less lenses to carry, yet serves as a prime in the entire 18-50mm range
• Take advantage of 16-50's good weather protection
• Save $ on buying few primes

I'll have 50 f/1.4 for the sharp and fast needs.

thanks again for the detailed reply..

 

[buddhi]

thanks for the reply.. that was another good input i received.. i feel obliged to write a thank you note for ever constructive reply i receive when the contributor takes time on explaining things and sharing their experience..

some people just go on criticizing the bad usage of photography terminology, yet not giving any constructive input. i think what we need is constructive community that not scorn the newbie (i've clearly mentioned that i'm a newbie) but help them with advice..

thanks again for the reply..

 

[sherwoodpete]

some people just go on criticizing the bad usage of photography
terminology, yet not giving any constructive input.

Apologies if you were offended by my clarification of terminology here http://forums.dpreview.com/forums/read.asp?forum=1002&message=29804410

Still, you did ask "am i still getting it wrong?", I assumed this meant you would appreciate clarification.

I'm not in the habit of correcting every misuse of terms (such as 'depth of focus' instead of 'depth of field' or the hundreds of other inaccuracies in these discussions.

Best regards,
Peter

 

[buddhi]

no offense peter.. i didnt aimed anything at you or anyone specifically..

i was wrong using wrong language and i'm a newbie as well.. i feel that trying to understand what that guy is trying to ask irrespective of what's hes writing would be a great approach than just saying there's nothing like that exist..

we excel in specific subjects and we have lot to learn from others.. your correction which came later was perfect because at that moment i understood i was wrong on language usage.

all i wanted was to know the capability of a lens than terminology. i do agree, knowing the terminology is important.. but not trying to understand my question or not asking enabling questions could have discouraged me to explore and learn from the experts..

if you look at these threads.. they go in to details explaining things.. http://forums.dpreview.com/forums/read.asp?forum=1002&message=29806432 http://forums.dpreview.com/forums/read.asp?forum=1002&message=29802905 which answers what i wanted to know.

as i said.. no offense intended. but those threads and many others gave answers to my questions than telling me i was "doing it wrong"..