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Thread: Please explain:::

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    Member Wannabe photopro's Avatar
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    Please explain:::

    Hi there,

    I need some help in understanding a few things please. I would like to buy a new camera. From recent research and reviews the Canon 7d looks like a good buy. I have always had my heart set on buying a 24-70mm lens, my first serious L series lens. I need a great everyday walkabout lens. My main subjects are my 3 daughters and everything to do with their lives.
    If I put this lens on the 7d does the actual mm change? Due to the 1.6 crop of this camera? What is a full frame camera then? Many times I take pictures indoors in low light. Will the 24-70mm be better suited therefore than the 24-105mm? I don't intend on using the tripod everytime I take a picture.

    Please help me to understand this before I make a mistake in my purchases...

    Thanks

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    It's all about the Light!
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    Check the New to Photography forum equipment guide before purchasing - lots of good advice.


    Full frame (a misnomer, as 35mm is small compared with medium format and larger) refers to the
    sensor being the same size as a 35mm film camera. This is documented in the NTP forum.

    Focal Length is exactly that.
    All the happens on an APS-C sensor is the image is cropped by 1.6 in Canon land, 1.5 everywhere else.
    The crop gives an appearance of more zoom, its not, its just a crop.

    FF is suited to landscape and portrait, APS-C is better for wild life and sport.
    But, APS-C is also usually much lower cost.
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    It's all about the Light!
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    This explains the sensor sizes...
    http://www.ausphotography.net.au/for...ad.php?t=24359

    Dave's post illustrates the crop...
    http://www.ausphotography.net.au/for...ad.php?t=36999

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    What gear have you now ?
    Darren
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    Hi

    Firstly lenses are hardware, they are manufactured to be a specific size etc. They cannot magically change size depending on what camera you put them on. If they could, why would we buy differing lenses at all? Your 24-70mm lens is a 24-70mm lens no matter what camera it is on!

    what does happen is the term we call 'crop factor'. Think of it this way. You have a wall in your house with a window in it, that window is a metre across and you get a lovely view out the window from you dining table. This window is the equivalent of a full frame sensor. Now for some reason your house needs renovations and part of that is replacing the window with one that is half a metre across. When you look out your new window from the same place at your dining table, you still have a nice view, but cause it is only half the size of your previous one, you cannot see as much on each side. This is your cropped sensor.

    A cropped sensor reduces your field of view (just like the window). It doesn't magically change your lens, it just reduces the size of your field of view.
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    Firstly what Rick says is right, but I will add, that you still have plenty of megapixels crammed into that smaller sensor, so it will appear as there has been some zoom. You will often hear people use terms like 'apparent focal length' as everyone likes to compare their lenses to when they are using them on a full frame (or 35mm) camera.

    This can be difficult to get your head around so take your time with it. Here is a great tool for comparing different focal lengths and you can click on the "35mm" or "Digital" to give you an idea of what the same focal length will look like on each camera type. Yes 24mm is still 24mm, but on each camera type it will give a different result.

    http://www.tamron.com/lenses/learnin...comparison.php

    Regarding your other question, the 24-70 has a maximum aperture of F2.8 whereas the 24-105 is F4. The F2.8 is one stop bigger than the F4 so that will help in low light meaning you can shoot at one stop faster shutter speed (reducing chance of blur) OR one stop lower ISO (improving noise). But the trade off is you miss the zoom of the 105mm. Everything is a compromise!

    Hope that helps, don't be afraid to ask more questions. The focal length/crop sensor is a difficult one to understand and everyone has their own way of explaining it!
    Mic

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    In Training MarkChap's Avatar
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    Focal length does NOT change regardless of what body you attach a lens to.

    The two lenses you mention are both fine lenses.
    The 24-70 is a constant f2.8 which is always good in low light, barring the obvious depth of field (DoF) issues, f2.8 = smaller DoF
    The 24-104 is a constant f4, but has the image stabiliser, so in effect you can probably shoot at shutter speeds about two stops slower than normal, so equivalent to having an f2.0 lens, in theory, practice is always another thing.

    The 24-70 f2.8 will allow you more creative control over DoF than the 24-105 f4.0

    I can't fault my 7D for the shots I cam get at 3200 iso, so indoors with either lens should be ok
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    I think you are confusing the poor bloke.

    True a 24mm is a 24mm lens.

    But taking a photo through it on a 1.6 crop camera (Canon 7D) will give an apparent focal length of 24x1.6 = 38.4 mm.

    This is particularly important at the wide angle end of things. eg. a 10mm lens on a FF camera will give a very wide view. On the crop, you get far less angle.

    Same at the other end... 200mm seems like 320mm.

    Scotty
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    It's all about the Light!
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    This might help...


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    Thats a great illustration Kym, pictures worth a thousand words!

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    Ausphotography Regular bobt's Avatar
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    Quote Originally Posted by Scotty72 View Post
    I think you are confusing the poor bloke. True a 24mm is a 24mm lens. But taking a photo through it on a 1.6 crop camera (Canon 7D) will give an apparent focal length of 24x1.6 = 38.4 mm.
    I'm inclined to agree with you on this one. The perception of a greater focal length is actually more relevant than the reality. If we were still using 3 megapixel cameras then perhaps things might be different, but with the huge image sizes of today the "apparent" focal length is probably more relevant to the average photographer than the true focal length.

    As for which lens to choose, I agonised over this for months, and eventually decided on the 24-105 on the basis that the reach was more important than the other considerations. This lens has an almost universal good feedback from everywhere with the most frequent comment being "if I could only have one lens this would be it".

    Unfortunately, although I did eventually buy it, my wife won't let me have it until my birthday - so it's sitting in a cupboard until next weekend! I cannot therefore comment on the lens from personal experience.

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    I can't speak highly enough of the 24-105. It spends most of it time on the camera as it'a a excellent all round lens.

    Even though it is f4 the 7D has excellent ISO capabilities so you can just bump the ISO up to achieve a faster shutter speed in low light.

    With the money you save you can but a 50 1.4 which I use for low light shooting all the time. Used this on my 50D most of all for indoor shots and anything where the light started to dim.

    As I'm learning I'm starting to trust bumping the ISO more and more whereas in the last few months I wouldn't have.
    AKA Sean

    Canon 5D MKII - 24-105L - 70-200 F4L IS - 70-300 IS USM - 28 1.8 - 35L 1.4 - 50 1.4 - 85 1.8 - 100L Macro - 200L 2.8II - Tamron 17-35 2.8 - Sigma 150-500 - 430EX - and a stack of other bits and pieces.

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    Ausphotography Regular bobt's Avatar
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    Quote Originally Posted by ausguitarman View Post
    it'a a excellent all round lens.
    ...... and so much better than the square ones!

    (Sorry ... can't help myself - I see 'em and simply can't resist.)

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