DSLR and lense selection, fixed vs variable focal length/zoom?

[Banon]

I've been playing with P&S UW cameras for a while (Sea&Sea DX3000 followed by Olympus SP-350), and am now THINKING about DSLR. There are some great, and tempting, threads out there. I particularly enjoyed the recent one about using a borrowed Canon 400D with the SeaTool housing, and how the author listed the perceived negatives of moving from P&S to DSLR followed by her revised thoughts on why those negative impressions might not be entirely accurate.

So I've started putting together what I might like... and what it might cost...

Size/weight is a big factor for me, but with the smaller DSLRs and housings like the SeaTool, size is now into my "acceptable" range. I'm also going to start with a single strobe. It's worked for me with the P&S cameras, so I'm going to stick with it initially with the DSLR setup.

Finally to the heart of my questions, I'm trying to figure out which lenses I might want/need...

Coming from P&S, this idea of "lense selection" is new to me. My world includes terms like ISO, shutter speed, f-stops, and zoom.

Zoom is the one that is causing me confusion, specifically in how it relates to lense selection. I read Alcina's excellent camera overview thread including the part about DSLR lenses, but I still don't get it.

What is the difference between the Canon 100MM Macro lense and a lense that spans 100MM, such as one that goes from 28MM to 135MM? If the latter lense was set to 100MM, would it produce the same shot?

Is it mainly a matter of how close you can get and still focus on the subject and how fast the camera will auto focus at that distance, or is picture quality impacted as well?

Here are two lenses I'm looking at:

• Canon EF 28-135mm f/3.5-5.6 IS USM Auto Focus Standard Zoom Lens, Closest focus 1.6ft
• Canon EF 100mm f/2.8 Macro USM Auto Focus Macro Lens, Closest focus 1ft

If I'm generally shooting at f5.6+ to get depth of field, is my only tradeoff between these two lenses about 7" of difference in how close I can get to my subject and still focus? (I'm not saying that's not important, just trying to understand.)

Thanks for any help!

 

[Kingpatzer]

fixed focal length lenses have fewer components, produce crisper images, less aberration etc. They are also lighter since there are fewer lens elements.

A macro lens does not compare to a non-macro lens, so the answer to your 100mm macro versus a 28-135mm is that the 28-135 won't have the 1:1 image ratio of the macro lens.

Personally, I'm a low f-stop *****. The lower f-stop not only means that you can shoot in lower light if you need to, it also generally means higher quality optical elements, better lens arrangement, and thus crisper images at the same f-stop number compared to lenses with higher minimums.

In any case, use a macro lens for macro shots, use a non-macro lens for everything else.

 

[Thalassamania]

The real bottom line is summed up in the phrase, "there's no free lunch." When it comes to lenses everything is a trade off, the more zoom, the more light needed, the softer the image, etc. You never get anything for free, all you can do is optimize your tradeoff(s) and maybe pay a lot more money for fancier glass that will perform better, but within that class of glass the trade offs will still rule.

 

[Banon]

Thanks you two. Both replies help quite a bit with my understanding... although it kills my sense of "just in case" to be stuck with a single lense choice on a dive. (I know I know... and I agree... most dives you know generally what you will see in advance... it's just the CHANCE of seeing something else!)

I have to admit I was hoping for a "free lunch" answer suggesting some alternative "super" lense that would allow great macro shots but still let me shoot the occasional ray or turtle that stopped in to say "Hi." Alcina's thread suggests that the 60MM macro is pretty good for that sort of thing.

I've been reading a bit more and came across the Canon EF 24-70mm f/2.8L USM lense, which won't exactly do 1:1 macro but it will get somewhat close... at the bargain basement price of $1000+...

Any experience or comments on this one? I know it won't be quite as good as either the 60mm Macro or 100mm Macro lenses when taking macro, but it may be a tempting alternative to buying both macro and non-macro lenses and ports. I'd be curious to know if anyone has this lense, and their thoughts/experiences with using it underwater for both macro and non-macro shots.

 

[Thalassamania]

Your pictures will be better if you shoot to an assignent (self imposed is fine) use fixed focal length with the right port. No fudging. Carry a Nikonos around your neck with the opposite setup (e.g., maco vs wide angle) if you need to feel prepared for anything.

 

[alcina]

What is the difference between the Canon 100MM Macro lense and a lense that spans 100MM, such as one that goes from 28MM to 135MM? If the latter lense was set to 100MM, would it produce the same shot?

A macro lens is a dedicated purpose lens. This lens is fabulous and will give you a 1:1 reproduction ratio. Why do you want this? For shooting small stuff. Simplisticly, you use a zoom, for instance, the subject will be smaller in the frame. Being able to get 1:1 or approaching that, just makes the subject pop more instead of getting lost.

The zoom lens you talk about will not give you the same frame at 100mm. Go into a camera store and look through each. See where you have to be and how big the subject is in the frame? Remember, closer is better underwater.

One of the gems for underwater work (and above water it's no slouch!) is the Sigma 17-70 macro...it doesn't quite do 1:1, I think it's like 1: 2.3 or something. It is an excellent compromise between having some flexibility on a dive and still being able to shoot those tiny crabs and nudibranchs. This particular lens is pretty darned sharp so shooting with the aim of cropping is also viable and something I do almost every time I use the lens.

Is it mainly a matter of how close you can get and still focus on the subject and how fast the camera will auto focus at that distance, or is picture quality impacted as well?

Yes

Here are two lenses I'm looking at:

• Canon EF 28-135mm f/3.5-5.6 IS USM Auto Focus Standard Zoom Lens, Closest focus 1.6ft
• Canon EF 100mm f/2.8 Macro USM Auto Focus Macro Lens, Closest focus 1ft

Skip that zoom for underwater work. The 100mm is an awesome lens. You may also want to check out the 60mm macro - still 1:1 but the wider frame allows you to shoot divers, fishes, turtles etc more easily. The 60mm can be easier to learn to use and is more versatile than the 100mm. Both are fabulous and eventually you'll likely end up with both.

If I'm generally shooting at f5.6+ to get depth of field, is my only tradeoff between these two lenses about 7" of difference in how close I can get to my subject and still focus? (I'm not saying that's not important, just trying to understand.)

I doubt you'll be at f5.6 much underwater with macro lenses. Yes, shallow depth of field can be used to good effect but mostly you'll be at least f8 (the depth of field is still VERY shallow at this setting and I only use this wide of an aperture when I was a totally exaggerated effect). I am usually at f13 or smaller with the 100 or 60 and you still have to get the focus point right to get what you want to get in focus. Dslr f stops and compact f stops are NOT the same - you can google to find out why or you can just accept it

No, distance is not your only trade off.

It's not that you can't use lenses that are outside the initial list in the Sticky, it's just that those listed are tried and true lenses that will give you the best results possible for the widest range of shooting. There are also specialty lenses for specific purposes and some of the general lenses, such as the zoom you mentioned and the kit lenses, can be used. But there are sacrifices that will have to be made that, imho, aren't worth it at all.

What do you want to shoot? Where will you be shooting?

I, too, used a single strobe for a very long time. Nothing wrong with that at all and perfectly capable of great results.

 

[BurBunny]

As the author of the "I was an idiot" thread you referenced, let me jump in with some of the knowledge I've recently aquired about lenses and choices. First, it's not just choosing a lens, but it's also choosing a lens which has a port which works with the housing you're wanting. For example, right now, Seatool's housing for the XTi has 4 available ports - one for the 100mm, 1 for the 60mm (which also works with the kit 18-55 lens), and 2 dome ports for the Tokina wide angle. They're looking at soon making another port for the Sigma 17-70 (possibly just an adapter for the 60mm port). But you can't just choose any lens and automatically use it in your housing.

Sometimes people choose a housing by the ports available, rather than by other factors such as size, weight, or cost. There are several ways to approach your ultimate decision on which camera/housing/lenses/system is right for you.

Now as to aperture. Beleive me, when you have apertures above f8 available to you, especially on macro, you're going to be wanting to use them. Makes a huge difference in the crispness of your images. When I was trying the Seatool housing a couple weeks ago, I never went below f11, mostly was at f13. And like you on a compact, I did a lot at f5.6. DSLR is just a different critter with more flexibility and tools which benefit us as underwater photogs.

As an FYI, I only used the 60mm for the shots I posted with that thread. Feel free to contact me directly for any questions you have. I wrote the post to be a guidepost to others on the same path looking at DSLRs, but that was just a start to what I've been learning. Happy to share!

 

[Kingpatzer]

I use the Canon EF 24-70mm f/2.8L USM as my "walking around" lens, but I don't use my canon under-water, so I can't comment on it for that use.

As a general purpose lens, it does it's job very well and I have no complaints about it.

 

[Banon]

Thanks all for the excellent feedback.

I've been playing with different camera/lens/housing/strobe options. I guess that's at least one advantage of moving to DSLR... you get to pick from all the latest and greatest stuff without trying to match with what you already have.

Back to my research...

Thanks again.