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Old May 27, 2008, 10:58 AM   #1
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I only yesterday got my first DSLR, so naturally I have some questions. I will be using Canon terminology, since that is what I know (even though I know very little).

I got the 450D, which has a crop factor of 1.7, so a 100m lens will have an effective 170mm.
But that is with EF lenses. What about the "made for digital" EF-S lenses, which are specifically made for the smaller sensors? Is their focal length accurate, or do you still have to apply the 1.7 modifier?
I am fairly certain my kit lens is an actual 55mm at 55mm.

I saw a lens with a 1:2 macro. What does that mean?
Where can I see how close the the lens it will focus?
Will I be able to use the full telephoto on all macro lenses, or how do I know what I can use?

Most importantly, where can I find good lens reviews. Mostly of cheap lenses, as I will never buy a $1000 lens.
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Old May 27, 2008, 12:05 PM   #2
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Carrots,

A couple points: First, the factor is 1.6 for that camera, not 1.7. And the factor applies to both EF and EF-S lenses. In fact all manufacturers have stuck with using film-like measurements. Even though it is no longer the real focal length of the lens. It just makes it simpler. Bottom line, any lens you can use on that camera should have the 1.6x multiplier applied to what the lens is described as.

Every lens will have the minimum focus distance specified in the technical specs. When in doubt, simply look at the manufacturer's website - they will all have the technical specs for the lenses they manufacture (which will include minimum focus distance).

As to using the full telephoto on a macro lens - sure you can always use the lens in a non-macro fashion. But you should realize - cheap consumer zoom lenses are often quite poor at full zoom. You should also be aware of the fact that true macro lenses will give you a 1:1 ratio (i.e. the subject will appear in the viewfinder at actual size). That's a rare feature in budget macros where you are more likely to see the 1:2. But in any case you can use the lens for non macro use - you don't have to focus on something really close with a macro lens. You should also note however that many true macro lenses are designed for focus precision not speed. So they can focus a bit slower. But it sounds like you might be after consumer zooms with psuedo-macro capability - in which case you lose both speed and precision :G

www.fredmiranda.com has a number of lens reviews. Although you might find it difficult to find reviews on re-branded cheap lenses (e.g. Quantaray and such which are often re-branded budget Sigma or Tamron lenses).
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Old May 27, 2008, 12:14 PM   #3
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Carrots wrote:
Quote:
I got the 450D, which has a crop factor of 1.7, so a 100m lens will have an effective 170mm.
Actually, the 450D, along with most other Canon dSLRs, has a 1.6X Crop Factor [ See http://www.usa.canon.com/consumer/co...elTechSpecsAct], so a 100mm lens with an angle of view equivalent to the angle of view of a 160mm lens on a 35mm film SLR.

Carrots wrote:
Quote:
But that is with EF lenses. What about the "made for digital" EF-S lenses, which are specifically made for the smaller sensors? Is their focal length accurate, or do you still have to apply the 1.7 modifier?
I am fairly certain my kit lens is an actual 55mm at 55mm.
The Crop Factor doesn't actually change the focal length of a lens;it justaffects what the image sensor can record. A 55mm lensstill has a focal length of 55mm, but because of the smaller image sensor, that 55mmm lens has a smaller angle of view on that camera body.

Carrots wrote:
Quote:
I saw a lens with a 1:2 macro. What does that mean?
Where can I see how close the the lens it will focus?
A 1:2 Macro lens can focus so close that the image projected onto the image sensor will be 1/2 actual size. A 1:1 Macro lens will project an image onto the image sensor that is the actual size of the subject.By comparison, aregular (non-macro) lens projects an image onto the image sensor that is sever times smaller than the actual subject. Naturally, to do that, the lens has to be able to focus very cose, but the 1:2 or 1:1 does not actually indicate the closest focusing distance.

Carrots wrote:
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Will I be able to use the full telephoto on all macro lenses, or how do I know what I can use?
Yes. Macro lenses can focus to infinity. But because they are designed to precisely focus on close objects, they are often slow to focus on objects that are far away.

Carrots wrote:
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Most importantly, where can I find good lens reviews. Mostly of cheap lenses, as I will never buy a $1000 lens.
PhotoDo.Com, SLRGear.com and PhotoZone.deare good sources for evaluatinglens. CameraLabs.com and PopPhoto.com are also quite good, buttest fewer lenses.

And KEH.com is a good source of used lenses, so you don't actually have to spend $1,000 on a $1,000 lens.
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Old May 27, 2008, 12:15 PM   #4
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Carrots wrote:
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I only yesterday got my first DSLR, so naturally I have some questions. I will be using Canon terminology, since that is what I know (even though I know very little).
Congrats.

Quote:
I got the 450D, which has a crop factor of 1.7, so a 100m lens will have an effective 170mm.
It should be closer to 1.6x to see what focal length you'd need on a camera with a larger 35mm size sensor or film to get the same angle of view.

Quote:
But that is with EF lenses. What about the "made for digital" EF-S lenses, which are specifically made for the smaller sensors? Is their focal length accurate, or do you still have to apply the 1.7 modifier?
Use 1.6x. Yes, the same thing applies to both. The only difference is that the EF-S lenses can be made with a smaller image circle (you just don't use the entire image circle on a camera with an APS-C size sensor).

You will have a narrower angle of view (more apparent magnification) for a given focal length if you use a smaller sensor or film size. You will have a wider angle of view for a given focal length if you use a larger sensor or film size.

Quote:
I am fairly certain my kit lens is an actual 55mm at 55mm.
Nope. The reason that most kit lenses for dSLR models start out so wide at 18mm (versus kit lenses for 35mm cameras that typically start at around 28mm), is because you'll have roughly the same angle of view with an 18-55mm lens that you'd get using a 29-88mm lens on a 35mm camera.

Quote:
I saw a lens with a 1:2 macro. What does that mean?
It means that the smallest subject you can fill the frame with is going to be twice the size of the sensor or film. With a zoom lens, you may be limited to the long end of the zoom range to get the rated macro ability.

A true 1:1 Macro (only in fixed focal length versus non-zoom lenses) can fill the frame with a subject the same size as the film or sensor it's being used on at it's closest focus distance.

Quote:
Where can I see how close the the lens it will focus?
The specs pages of lenses on manufacturers sites will show you that kind of thing, and you'll see it in the specifications at some vendor sites, too. Try http://www.bhphotovideo.com listings for a specs tab.

Working distance is what you worry about with focus distance. That doesn't make any difference for a given Macro magnification rating (since both focal lengths can fill the frame with a subject the same size). If you have two different focal length lenses like a 50mm and 100mm, and they are both 1:1 Macro, you'll be able to shoot from further away with the longer lens, and still fill the frame with a subject the size of the film or sensor being used.

Sometimes a longer macro lens is preferred to a shorter lens if they both have the same magnification rating, since you can get further away to keep from casting shadows, spooking subjects, etc. Tamron 90mm f/2.8 Macro and Sigma 105mm f/2.8 Macro lenses are popular choices, as are the camera manufacturer's lenses in similar focal lengths.

Quote:
Will I be able to use the full telephoto on all macro lenses, or how do I know what I can use?
Most lenses like that have a minimum focus distance that is available at all focal lengths. The term Macro is used rather loosely by lens manufacturers. Just look at the magnification specs for one (1:4, 1:2, 1:1). Yes, you can use it throughout it's range. But, you don't get to the rated macro magnification unless you zoom in all the way.

It depends on what you want to take photos of (the size of your subject) and desired focus distance what you buy.

Quote:
Most importantly, where can I find good lens reviews. Mostly of cheap lenses, as I will never buy a $1000 lens.
http://www.photozone.de

http://old.photodo.com

The lens forums here.


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Old May 27, 2008, 12:26 PM   #5
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I didn't realize this thread already had two replies by the time I finished answering it. I removed some of it and changed some of it. Not enough coffee today. ;-)

I moved this thread down to our Canon Lense forum for you, where you'll get more discussion from Canon shooters on lenses. Let them know what you want to use one for and the specific brand/models you're looking at for more info.

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Old May 27, 2008, 1:46 PM   #6
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Thanks to everyone who replied.

It seems i misread the crop factor, and it sucks that to get true wide angle on what I have, I need to get a 5D, or a 10mm or something lense. Both of which are steep.

For macro photography it seems that my kit lens might be good enough. I cant find specs, but will experiment a bit to try and deduce it. If i understand correctly, for a 1:2 rating I should be able to fill the frame horisontally with a subject that is twice as large (horisontally) as my sensor's horisontal size. (something like 22mm if I remember correctly)

So, to photograph something that is as large as my sensor, I will have to be far enough away that it only fills half the frame.

If I understand correctly, a macro lens can focus on anything at any distance, as long as something that is twice the size of the sensor (for a 1:2 lens) fills the frame, or less?

I also have a Canon S5, which can focus on something touching the lense. That has a sensor about 10mm across, so lets say the lens has a 20mm diameter, then it means that it also has a 1:2 macro, since something touching the lense twice the size of the sensor, will only fill the sensor?

On the crop factor issue, when the spec says that the optical viewfinder displays 90%, is that 90% of what will be recorded by the sensor, or 90% of what "enters" the lens?

edit: This is what I've got: http://www.usa.canon.com/consumer/co...elTechSpecsAct
I see it can focus up to 25cm, but there's no macro ratio. I also looked at other Canon lenses, and also dont see a ratio listed there. Any other way to deduce it?


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Old May 27, 2008, 2:47 PM   #7
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Carrots wrote:
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If I understand correctly, a macro lens can focus on anything at any distance, as long as something that is twice the size of the sensor (for a 1:2 lens) fills the frame, or less?
No. The maximum magnification for a lens occurs at it's closest focus distance. For a zoom lens, the specified magnification will only be at it's longest focal length and closest focus distance.

If you move further away, your subject is going to take up less of the frame. ;-)

Quote:
On the crop factor issue, when the spec says that the optical viewfinder displays 90%, is that 90% of what will be recorded by the sensor, or 90% of what "enters" the lens?
90% of what the sensor will see when the mirror flips out of the way and lets the light from the lens get to it when you take the photo.

You'll have to find a formula for the rest if you really care. What you want to know is how much of the frame you can fill with a given subject size, and if the minimum focus distance required is acceptable. There is probably a fomulae you could use based on it's closest focus distance, actual focal length, and sensor size somewhere.

You don't normally see macro ratings on non-dslr models.

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Old May 28, 2008, 3:13 AM   #8
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1:2 macro is pretty good for most purposes.

Certainly good enough for flowers, butterflies, even dragonflies, big spiders too.

Because you will easily fill the frame with those subjects. If your subject is 2x the dimensions of the sensor then you are filling the frame and getting the full 12Mp.

If you want to go down to things with the dimension of small spiders or flies then you might want 1:1. In fact there are specialist macro lenses or attachments that will give you even bigger magnification than that. I think Canon makes a 5:1 specialist lens. The kind of thing you would want if you were looking to fill the frame with an ant.

Most Canon lenses will give a macro ratio of around 1:4 or 1:5, which is still actually probably good enough for things like flowers and butterflies. Do some experiments with your current lens and check out the macro ratio to get a better idea of what you might need.
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Old May 28, 2008, 2:04 PM   #9
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Keep in mind that the macro rating is going to be for the full zoom end of the lens using most lenses, if the minimum focus distance is consistent throughout the zoom range. The specs are a bit unclear on it. But, I'd keep in mind how far away you'll need to be for your subject to fill the desired portion of the frame.

If focus distance is consistent throughout zoom range, then at shorter ends of the focal range, you're probably down below a 1:4 Macro rating or even rose (which is about what you get with most kit lenses in the 18-55mm or 18-70mm range).

It looks like this Tamron has a macro switch that allows focusing at 37.4 inches. (almost one meter).

http://www.tamron.com/lenses/prod/70300_di_a017.asp

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