Fixed Focal Length vs. Zoom Lens

[IMSushi 0]

Maybe this was covered in photography 101, but I was sick that day So, I thought I might ask for your input. When deciding on a lens to buy, why not buy the one, zoom lens, that will give you more freedom to shoot a variety of subjects rather than purchasing a fixed focal length lens such as a 105mm or 60mm or 10.5mm where your subjects can be very limited? What's the difference between a dedicated 105mm and my kit lens 18-135 zoomed out to 105mm?

 

Coming from a P&S and just hitting the macro button, this sounds like the perfect compromise.

 

At first, my guess is the specific f-value of a dedicated lens will possibly help you shoot in lower light conditions and focus more accurately?

 

Thanks for your help! BTW, maybe next year with my new rig I'll feel comfortable enough to add a picture of my own to the "Best Shots of 2007".

[Rocha 0]

Hi Pat,

 

There are several answers for your question. Here are some:

 

1) The 60mm and the 105mm Nikons that we always recommend here are true macro lenses and have a magnification of 1:1. In other words, you can fill the frame with very small subjects. An 18-135 zoomed to 105 (or 60) wouldn't allow you to do that. You could still take the picture from further back, but you would lose resolution and sharpness. Unfortunately, SLRs don't have a "macro" button like P&S, so you are stuck with macro lenses.

 

2) For wide angles the problem is a bit different. Wide angles require very specific distances between the dome port and the sensor to produce images that are sharp from corner to corner. This distance is closely related with focal lenght, so, when you zoom a wide angle in and out behind a port, the picture will not be good at certain focal lengths.

 

3) Because of #2 above and because they vary in length a lot when you zoom in, it is very hard to design ports that accomodate zooms with a wide change in focal lenghts (such as the 18-135 that you mention).

 

4) The 10.5, 60 and 105 are part of the so-called "prime" lenses, and they have better color, contrast and sharpness than most zooms.

 

I am sure more people will contribute here, but in the mean time, by all means contribute to the "Best of 2006" thread! It can be a great learning exercise, and you will see how much your photography will improve with an SLR.

 

Luiz

[richorn 0]

Luis hit the basics on the head!

 

There is a bit more to the wide angle issue... There are very few (if any) zooms that get to the width of a 10.5 FishEye. Also, any "mid range" zoom will not get to a width that most of us consider "wide". There ARE wide angle zooms, such as the 10-22 and 12-24 mm lenses. These are however wide throughout their range.

 

Mid Range zooms exist in ranges that are "almost" wide, and get to "almost" macro.

 

That said, if you want Wide, you need a wide lens. If you want true macro, you need a macro lens.

 

I (and many others) use a combination of zooms and primes to cover all of the shots we want to take. There is no one lens solution with an SLR.

[Glasseye Snapper 47]

Hi Pat,

 

With zoom lenses there is a tendency to shoot either at the widest or tele-est end of the focal range and for inexpensive zoom lenses image quality is typically worst at these extremes. Because prime lenses can be optimized for a single focal length (although that is not entirely true for internally focusing lenses, which become wider if you focus closer) they can be better for less money, and with a better max aperture. However, expensive modern zoom lenses can now often compete with their prime brethren on most aspects but price. For many of us the medium-price zooms also have good enough image quality and the flexibility of zoom is certainly attractive.

 

On a completely different note. When I asked my very first wetpixel question about which lenses to buy (what else!) some recommended to buy prime lenses to be more focused when shooting underwater. With a zoom it is easy to abuse the zoom to make a subject fill the frame rather than try and get closer. This slows your progress as a UW photographer because getting closer should always be a goal for the highest quality images. There is also the risk of trying to take pictures of everything that comes across your mask. I really noticed that on my initial dives with camera I had tons of images but most showed the fish swimming away, fish pictured from above, fish with head just hidden behind a sea fan etc. At first I was greatly excited by all these images but after a while you don't want your 24th yellowtail snapper shot, just your best possible yellow-snapper shot. Taking a good prime lens underwater with the aim to search for subjects that match the characteristics of the lens means you'll take pictures of fewer objects but they will hopefully be of higher quality with more thought put into composition, lighting etc. That will also make it a better learning experience.

 

Of course there are good uses for zoom lenses and many of the comments above are really more a problem with the photographer than the lens. I just bought a 28-75mm zoom myself and plan to use it on some guided boat dives where the follow-the-leader routine prevents you from spending much time with a subject anyway and where you often don't know in advance what spectacular small or large creatures you are going to find. For shore dives where only my tank pressure limits my time underwater, I expect I will still mostly use my prime lenses with the Canon 100mm macro being my favorite.

 

Bart

[Rocha 0]

Taking a good prime lens underwater with the aim to search for subjects that match the characteristics of the lens means you'll take pictures of fewer objects but they will hopefully be of higher quality with more thought put into composition, lighting etc. That will also make it a better learning experience.

 

Bart

 

This is a very important point that I was going to mention too, but I figured someone else would (and I was right! ). Using primes makes you more disciplined to getting the right shot, and makes you concentrate on the subjects that the lens is good for. Sure you won't be able to photograph that manta ray on the safety stops if you have a 100mm on, but I bet your macro shots will be better than anybody that is using a zoom.

[seagrant 4]

This is a very important point that I was going to mention too, but I figured someone else would (and I was right! ). Using primes makes you more disciplined to getting the right shot, and makes you concentrate on the subjects that the lens is good for. Sure you won't be able to photograph that manta ray on the safety stops if you have a 100mm on, but I bet your macro shots will be better than anybody that is using a zoom.

 

Luiz and Pat,

 

I agree with this. Although I am fairly new to the DSLR world (somewhat like Pat), I decided to go with a prime, the Nikon 16mm, instead of the 12-24 which I originally wanted for its versatility (I could only afford one wide lens to start).

 

I felt that since I was just learning it would be good to learn on the fixed focal lens (get close, close, close) and then add the zoom after I learned the non-zoom. I am happy with that decision. Case-in-point shooting the manatee recently I use the 16mm lens, first times down with it. A very experienced photographer was using an excellent quality zoom lens on a different but somewhat comparable camera to my Nikon d200. Basically my photos came out better......, sharper, etc, shooting the same subjects and conditions.

 

Although I'm sure there are times I'll want a 12-24 zoom and/or other zooms I'm glad I'm not learning on one, for wide or macro.

 

Best, Carol

[Undertow 31]

I agree with all the thoughts so far, but I like to think of it more simply:

 

- If primes weren't much better than zooms noone would use them. Zooms are a compromise in quality for convenience. It all started with primes.

 

I definitely agree with the notion that a zoom will get you a larger variety of lower quality pics and primes will get you a smaller variety of higher quality pics on any given dive. Of course it all depends on the photographer...

 

undertow

[Glasseye Snapper 47]

I agree with all the thoughts so far, but I like to think of it more simply:

 

- If primes weren't much better than zooms noone would use them. Zooms are a compromise in quality for convenience. It all started with primes.

 

undertow

 

I haven't done apples-for-apples comparisons but it seems the thinking on this topic is changing. A good professional quality zoom lens can produce images that are hard to distinguish from a good prime lens when used by professionals. It will be much harder to find quality differences when the lens is used by amateurs and the images are looked at by amateurs. The problem is these lenses also come with a professional price tag. So modern zooms may be able to give you convenience without compromising quality, but they can't do that without compromising your bank account

 

Bart

[Glasseye Snapper 47]

One other point. It is hard/impossible to find a zoom lens with an aperture faster than f2.8. In contrast it is hard to find a (non-tele) prime lens with an aperture slower than f2.8. Canon, and probably other brand, dSLR have a central focus spot that behaves as a more sensitive cross-type sensor when you use a lens with a max aperture of f2.8 or better. I would therefore predict that a fast prime lens gives faster and more reliable auto-focus than cheaper zoom lenses that don't reach f2.8; especially when working close-up or in poor lighting conditions, both of which are common underwater. I'd be interested to hear if anyone has experienced a significant difference in focus ability of f2.8 and non-f2.8 lenses.

 

Bart

[rodriguezfelix 0]

Yep it´s true. Prime lens are really much sharper and produces better colors than zoom does, and as I read in this forum zoom underwater is something you should do with your fins and not with your lens, but If we are talking about learning curve, does not a zoom lens be a good start???, I mean you can learn a lot about lighting, strobe power, angles to shoot, and very different technics not only for wide or macro, as for both.

 

Personally when I start shooting DSLR I was recommended to buy a 60mm cause I only can afford one lens at that time, but Sigma just released 17-70 macro wich get f2.8 on 17mm and 1:2.3 magnification at 70mm, so I bought this lens and later I get 105mm for macro but I learn lots of thing with the zoom lens, and so far I still rather to have the 17-70 and the 105 than the 60, because still covers more angles and technics of shooting.

 

Of course, with time and money I rather to have a 12-24, 10.5, 15, 17-35, 60 and 105 and sure I start using the 17-70 less, but will still be a good scout lens for me.

 

Now I wonder if nikon came up with something like a 15mm-60mm f2.8 with 1:1.5 mag. and a 600$ price, this could be consider a nice UW option...

 

Just my 2 cents.

[Paul Kay 62]

In essence zooms are usually a compromise. They can perform very well in terms of sharpness and many other optical attributes but rarely focus as closely as prime lenses and they often suffer significant distortions. Depending on your requirements, their versatility may outweigh their compromises - distortion for example may be very important for an architectural photographer but of little consequence underwater. Zooms cannot at present compete with 'true' macro lenses in terms of their close focus capabilities but if you want to shoot semi 'underseascapes' to fish in one dive then a zoom might be a good option. If on the other hand you want to shoot creatures which are very small then few ordinary zooms are of much use. I wouldn't be over worried by optical constraints if you are coming from a P&S as most well made zooms will deliver reasonable quality results, but you should look closely at their limitations in terms of close-focus and physical changes during zooming - both may have significant consequences for housing them and using them.