Depth of field - Tamron 17-50mm vs superzoom

<p>I posted last week on the merits of a Tamron 17-50 versus a Canon 18-200 (or alternatives, like the Tamron 18-270) for low light photography. Where depth of field is concerned, would the Tamron's constant f2.8 offer enough flexibility over a superzoom to be a dealmaker?</p>

<p>I've tried both lenses briefly in store, and (in my unpracticed judgement) think I notice the Tamron's greater capacity to obtain a shallow depth field. I'm trigger happy and think I'll appreciate the capacity to isolate subjects at will. So I'd find it a nuisance having to change between a superzoom and a faster lens (say the 50mm f1.8) for this kind of shot.</p>

<p>I'm trying to decide if this issue tilts the balance in favour of a two-lens combo with the Tamron, over the convenience of a superzoom. Apart from low light performance, this seems the only reason to go with the Tamron, since I doubt that I'd notice gains in image quality (e.g. sharpness , distortion) over a superzoom at my level of photography.</p>

<p> </p>

<p>Go with a 2 lens setup, you will be much better off. When it comes to depth of field and separating the subject from the background I am no expert, but I do know it has a much to do with focal length and subject distance as it does to F stop. </p>

<p>Yes it is possible to squeeze a bit of bokeh out of this lens, at 50 mm, f/2.8, at close focusing distances (e.g. headshot).<br>

http://www.arievandervelden.com/HaarlemParis/1732YellowTulips.jpg<br>

http://www.arievandervelden.com/HaarlemParis/1785Diana.jpg<br>

These days I rarely reach for my 50/1.8 unless I really really need that extra stop of light.</p>

 

<p>If you really dont care about image quality, I think you are better of with EFs 18-200 IS and 50/1,8. You will save weight and bulk, and get 1,3 stops faster lens at 50mm. With a Rebel/EOS XX0 body you will also get a very light combo with 50/1,8 that are very handy to use with just one hand.</p>

 

<p>According to the <a href="http://www.lensplay.com/lenses/lens_depth_of_field3.php">DOF Calculator</a>,</p>

<p>total DOF=0.164 m for a focal length of 50mm at f2.8 and subject distance of 2m</p>

<p></p>

<p>total DOF=0.328 m for a focal length of 200mm at f5.6 and a subject distance of 8m (for similar framing of subject).</p>

<p>thanks everyone. As for image quality, I do care - it's just that when you're going to be on the road for several months, a superzoom looks mighty appealing </p>

 

<p>As Songtsen indicates the DOF is almost entirely due to the focal length and f stop selected and not the lens. Having said that the 'quality' of the bokeh is very much determined by the lens. My 70-300 IS DO lens has entirely different bokeh from a non DO lens at the same focal length and f stop.</p>

<p>John Lee - your OP bounces almost randomly between concerns for low light and depth of field which suggests you don't know what your priorities are and only you will know that. The best camera in the world is useless if it stays in the hotel room so ask yourself how willing are you to lump a camera bag around with you - if the answer is 'not very' then go for the convenience of a superzoom; if you know you will make the effort then the 17-50 plus another zoom becomes a more reasonable proposition.<br>

From the way you wrote about the 17-50, you were impressed with the shallow depth of field on the f2.8 so if you really want to achieve that then the 17-50 is the only choice. The question is what do you get for the longer focal lengths? You say that it is a 'nuisance' to swap supersoom to 50mmf1.8 - but if you get the 17-50 you will also have to swap that anyway for the 'other lens'. Take your pick. If concerns about bulk overrides picture quality then the 18-200 will do you fine.<br>

Personally, I am convinced you <em>will</em> notice the difference between the superzoom and the 17-50 (for instance you have already said you like the depth of field on the 17-50). Go back to the store with a CF card and take a picture with both lenses. Plug the card into a printing station in the shop and spend a few bucks printing those pictures out - concentrate on pictures at the wide end f8 (typical landscape shots) and about 50mm at about f4 (typical portrait) as that is where most differences will be and if possible do some blow-ups from off-centre regions. Then go home and look at them closely and make your decision,and maybe ask a few friends to look at the pictures (without telling them which is from which lens). </p>

<p>I always have this same issue: How much do I want to carry? I say if your thinking of taking a superzoom just go with an advanced point and click. If you want higher quality use a 2 lens set up and get a good bag so taking it along is no problem. </p>

<p>The superzoom is much more than an advanced point-and-shoot. No point-and-shoot that I've ever seen has the responsiveness of my 18-200 on an SLR. All that I've seen have motorized zoom, which is far slower than a twist of the wrist. They also have inferior viewfinders and autofocus. They have smaller sensors, so more noise in bad light. If a point-and-shoot existed that was as responsive as an SLR, I'd gladly buy it.</p>

<p>As I see it, the biggest advantage of the 18-200 is it lets you react and get shots you'd otherwise miss. I travel with my family and my goal is to get great photos of my kids in action. The superzoom is perfect for this, if I had to dink around with changing lenses, I'd miss the shot 90% of the time. Going from pretty wide to fairly long with the flick of a wrist is awesome.</p>

<p>But, the image quality is noticeably inferior. I notice the barrel distortion, the vignetting, and the lack of sharpness at anything under f/8. Do I care? Well, better image quality is always nice, but I still get better images than I would with a P&S <strong>and I get the shot. </strong> My photographs are there and gone, no time for contemplation or setup.</p>

<p>If you have more time to set up your shots and switching lenses is no big deal, then you might be happier with two lenses. If my travel was more focused on the photography and less on having fun with my family, I'd definitely pack a few sharper lenses, take more time to compose my pictures, and ditch the superzoom.</p>

<p>At the long end, the superzoom has pretty shallow DOF, even stopped down a bit- that's true of all 200mm lenses. In the 18-50mm range, its not very shallow-f/2.8 or f/1.8 is going to be noticably shallower than f/3.5-5.6.</p>