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Need help understanding zoom lens please.

Discussion in 'Photography & The Digital Darkroom' started by willnabby, Mar 24, 2008.

  1. willnabby
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    willnabby RS-one day soon!!

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    Sigma 55-200mm Lens Olympus Evolt E-510 E-410 E-330 E-1
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    Can anyone tell me if the Sigma (55-200mm) lens is more powerful than the olympus (40-150mm) that I already have? I'm after a bit more zoom & I don't still yet understand all the numbers:think:, I'm still a newcomer to the world of SLR's,

    Any help appreciated.
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  2. FactionOne
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    FactionOne Administrator Staff Member Administrator

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    In short, yes. The Sigma lens will get you a bit closer to the subject.

    The two focal lengths quoted (55mm and 200mm) are the shortest and longest extents of the lens. In plain english that translates to how wide a field of view and how narrow (zoomed) a field of view it will give. So at it's widest setting, the Sigma glass will be a bit more zoomed than your current lens, and at the fullest extent will be quite significantly more so.

    If you can hang on until tomorrow I'll do you a couple of test shots (one at 150mm and one at 200mm) to give you an idea of how much closer it will bring the subject.

    I've got an EOS and the first lens I bought to go with my 18-55 kit lens was a Sigma telephoto zoom. The one I got was the 70-300 APO DG Macro; and I'm pretty happy with it. Obviously it's not a patch on an f/2.8 300mm image-stabilised lens costing a grand or three, but in terms of 'bang per buck' I can't really fault it. I don't know if the lens you currently have has ultrasonic (quiet) focusing motors, but I don't think the Sigma you're looking at has. Mine hasn't, and it's rather audiable - but that's not a problem at all for me because I rarely shoot wildlife (which is one of the few times ultrasonic motors make a difference - you don't want the noise to scare off the subject!).

    I guess there's not much else to be said really - the other important thing to consider when buying a lens (which I touched on above), is its maximum aperture. This is basically the largest 'hole' to let light in that the lens can be set to. Aperture is described by an 'f number' - and confusingly, the numbers work back to front - a high f number is a narrow aperture, and a low f number is a wide aperture. The key thing here is that with a wide aperture (low f number), the lens can capture more light and therefore allow a correctly exposed photograph at a higher shutter-speed. This of course is important if you want to take photos of moving subjects. The other consideration is 'depth of field'. With a wide aperture (low f number), the subject will be in sharp focus and anything in the background will quickly become blurred giving a nice effect, especially in portraiture and similar styles. A narrow aperture will give focus to the subject and things further into the background, this is sometimes useful, but can often detract from the subject or clutter the photograph. I've just bought an f/1.8 lens for portraits and automotive photography. One final note about aperture - a narrow aperture (high f number) combined with a longer exposure (increased shutter-time) can be useful in night photgraphy as it will create 'stars' around intense light sources.

    In this case I'd say the Sigma lens' max aperture will be on a range of around f/3.5-5.6 (dependant upon the focal-length you're working at - if the lens is zoomed-out the widest aperture will likely be f/3.5 or f/4.0 while it'll be f/5.6 when zoomed all the way in). That's likely to be a similar range for the maxium aperture to the lens you already have.

    I wouldn't worry about the minimum aperture too much - most lenses will go to f/22 or beyond, and you'll rarely need that much (or rather little!).

    Anyway, as I say I'll make some test shots for you tomorrow to help you get a better idea of the zoom you can expect and post up some links.

    Hope this post is of some help, and that I've not waffled too much on things you already know!

    Regards,

    Rob
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  3. willnabby
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    willnabby RS-one day soon!!

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    Thanks Rob for that easy to understand explanation, the book I was reading to try and understand it was confusing the hell out of me:uhm:

    what I'm after is more zoom on a budget see(£71 &£13 postage from america), hence the sigma for when I go to the british grand prix in july although now I'm not sure if the F4-5.6 is suitable for F1 cars now after reading your explanation??
    It will be helpful to see what the gains are when you post up a couple of shots for me, thanks again for the help.
    Cheers,

    Martin.
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  4. FactionOne
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    FactionOne Administrator Staff Member Administrator

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    No worries mate! Hope it's all helpfu!

    As regards shooting F1 action... I won't lie to you, the professionals will be using f/2.8 or lower lenses, possibly with Image Stabilisation. The latter is another interesting one though, as there are a lot of misconceptions surrounding the subject. Manufacturers will often quote things like "IS technology effectively allows you to shoot the same image at one or two aperture stops lower" - that is true, but only in certain circumstances. IS technology counteracts lens movements and will steady the whole frame; but if you've got your camera on a steady footing, perhaps on a good tripod, the frame itself will be pretty steady - it's only the fast-moving subject within it which would blur, and IS won't help too much with that.

    This is all pretty academic though, as f/2.8 telephoto glass starts at about £800 - £1,000; and a particularly long lens with IS can run to £4,000 - £5,000.

    It'd be unfair to say that shooting F1 cars with something at f/4 or f/5.6 would be impossible though - there are a few other factors to be considered.

    First of all is the weather and position of the sun. Obviously if the sun is in the background, you're going to struggle regardless of the glass you're using. However if you can get in a spot with the sun pretty much behind you (and shining straight onto the subject), and you're lucky enough to get some bright weather, you'll be running the maximum aperture you can (probably f/5.6 at maximum zoom), but hopefully there'll be enough natural light to allow a quick shutter speed. I'd be hoping for 800-1000 and above for good shots.

    The other thing you could consider is the direction the cars take through your picture. Obviously if they're passing perfectly right to left (or vice-versa), you're going to need a pretty quick shutter to freeze the action with no blur. If however, you can position yourself so they're at a shallower angle in your picture, the movement will effectively be slower, affording you to be using slightly longer shutter speeds.

    You can also consider the ISO sensitivity setting on your camera. In a perfect world you'll want to shoot as much as possible at ISO100, where the sensor is at its least sensitive - but delivers the best quality. If you need to though, you can bump this up and for each step you'll probably gain a stop or two of aperture (and therefore shutter-speed). Avoid going too high though, because this is where you'll get colour-noise coming into the picture. I normally shoot everything at ISO100 for quality, but if pushed I'll go up to ISO200 or ISO400. I'll rarely use ISO800 because this is generally where a lot of cameras start to get a little noisy, and at ISO1600 and above you can really see the noise in the pictures.

    The final thing I'd advise is to shoot in RAW. I've not shot a JPEG with my camera for a long time now, because for starters when you do any post processing, you are basically trying to polish a turd. The image has been compressed and a lot of the colour and luminosity data is lost straight away. This data is very important in post-processing, as with something like RawShooter Essentials (free, discontinued, but still available to download), Adobe Camera RAW (in PS), or Adobe Light Room you can adjust exposure compensation, contrast, saturation and a host of other parameters almost losslessly. The same cannot be said when working on a JPEG. In short if you shoot JPEG you're not getting the full benefit of your camera's potential in your photos. There is one caveat to shooting RAW on fast-action though - the number of shots you'll get in 'burst' or 'continuous drive' mode will be fewer. Your camera might be able to fire off 10, 20 or more shots continuously in JPEG, expect 3-6 depending on aperture, shutter, light etc. in RAW mode. I wouldn't let this push me into using JPEG though, I'd just be more careful with my timing of the squeeze of the shutter-release.

    The other thing you can do, if lighting etc. demands it - is try to 'track' your subject as you shoot. What I mean by that is if the car passes right to left, pan the camera right to left as you shoot. This is tricky to get right, but to be honest if you can get the technique it can produce some fantastic results, with a car perfectly focused and the background (crowd in grandstand etc.) with some great-looking motion-blur. I would advise some serious practice at this though - it is very tricky to get it right. The bonus is that on the day at least you'll have enough laps to do some attempting to track, and some trying to maximise the settings (ISO etc.) to keep the camera still. For practice it might be worth heading along to the side of a motorway or fast-road and spending an hour or two getting used to the technique. You might get some odd looks, but if it helps you get the photos you want at the Grand Prix it's gotta be worth a go!

    Anyway, on to some zoom samples for you...

    Firstly I have to say apologies for them not being great shots - It was a little windy and I didn't have the camera on the tripod so that made shooting a little more complicated.

    The second thing to note is that the guide on the barrel of my lens is only a guide, so when I was going for 200mm I actually got 190mm; but it's not far off.

    Anyway, the following images are (in order):

    70mm, 100mm, 149mm, 190mm, 300mm

    Regards,

    Rob.
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  5. FactionOne
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    FactionOne Administrator Staff Member Administrator

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  6. willnabby
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    willnabby RS-one day soon!!

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    Thanks for doing me those shots, I think I know what I need to be looking for as far as the lens now, I've read what you said quickly now because I've got to go out in a min but I'll read it in depth again in a bit, but it does look like I need to set the camera up manually if I understood you right?, I was going to put it in sport mode and mount it on my monopod, & take hundreds of shots hoping I'd get maybe half a dozen good ones, I think maybe I should go on a course or something because I am getting really intrested in photography now, by the way I think the way you explain things is fairly easy to understand, you would make a good teacher, I'd ask you to teach me if you were nearer, lol.

    if you think of any other tips that may help me generally, let me know.

    Cheers Rob.:icon_thumright:
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  7. L1 HCS
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    L1 HCS Active Member

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