Lenses for dummies?

Caiterz

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I have a EFS 18-55mm for my Canon Rebel XT EOS.

Taking a photography class! It's not really all about lenses though.

I'm looking to do some super macro stuff (Clear flower, blurry background), so i'd need small depth of field, and a low aperture, right?

My aperture only goes down to 4.5, but standard goes down to 1. Would I benefit from getting a lens that goes down to 1? Or lower than 4.5?

Also, looking to do pics that are super clear from way far away, so i'd need large aperature. My aperature goes up to 36. Would a bigger one benefit at all?
 
I think I know what you are asking. First, let's clear something: apertures are notated as fractions. When you see one number, it's the denominator (bottom) so larger numbers mean smaller apertures (holes) -- 1/2 is a larger piece than 1/4 so f/2 is larger than f/4.

I'm not sure what you mean by "standard." Most lenses don't have apertures bigger than f/1.4 or f/2.8. Many of the kit lenses you get with the consumer-level cameras typically have a maximum aperture of f/4 or f/5.6.

Depth of field is determined by a few things: the aperture, distance between the camera and the subject, and the magnification. The last two really come into play with macro since you are closer and are magnifying the image to life size.

You should be able to get by with a basic macro (105mm or so) to start with. I typically use smaller apertures (f/11 - f/22) for macros so I can get a depth of field that isn't too shallow.
 
Starting with the macro, your big challenge is probably going to be the minimum focusing distance of your lens -- you may have trouble focusing close enough to properly frame a small-ish flower. Most macros I've shot have a really tiny DOF anyway, so I don't think you need to worry about getting an aperture larger than f/4.5 (large aperture, or lens opening == a small number). To get closer to your subject than your current lens allows, a macro extension tube or a true macro lens would work.

For your "larger" photos, I think you're looking for maximum in-focus distance from near to far, so a small aperture (large number) is the way to go, but f/35 is going to be overkill -- you'll actually start losing sharpness due to diffraction. There's a way to figure out the "best" value for this, but for now, try something around f/16 to start with.

Take a look at these simulators -- they'll help iron out the relationship between aperture and DOF.

Canon Explains Exposure

Bokeh simulator & depth of field calculator
 
I'm not a macro photographer, but I played around with extension tubes 40 years ago just to see what I could do. Extension tubes are hollow tubes that move the lens further away from the sensor, so the image projected from the rear of the lens is made larger. Ideally, you'd want extension tubes that have pass-through contacts, so your camera will control the lens that is up front, just like it normally does.

Perhaps the biggest issue with macro photography is the very thin DOF when the lens is, say...3-4" from the subject...perhaps as small as 1/2". Your current lens has a minimum focus distance of about 9", so that has to be addressed. Extension tubes provide a great way to 'try it out' without spending an arm and a leg.

Of course, extension tubes reduce the maximum f-stop ratio so bright daylight is a good starting point to ensure a fast enough shutter speed necessary to stop an ant walking, or a flower gently swaying in the breeze.

One note, a lesson I learned the hard way 4-5 years ago...do =NOT= waste your money on cheap ebay 'screw on' macro or telephoto lenses. If you are lucky enough for your 18-55 to lock in auto-focus, the image quality will be degraded significantly by the cheap ebay lens. My screw-on literally fell apart the first time I unscrewed it from the Canon lens it was attached to.
 
I think I know what you are asking. First, let's clear something: apertures are notated as fractions. When you see one number, it's the denominator (bottom) so larger numbers mean smaller apertures (holes) -- 1/2 is a larger piece than 1/4 so f/2 is larger than f/4.

I'm not sure what you mean by "standard." Most lenses don't have apertures bigger than f/1.4 or f/2.8. Many of the kit lenses you get with the consumer-level cameras typically have a maximum aperture of f/4 or f/5.6.

Depth of field is determined by a few things: the aperture, distance between the camera and the subject, and the magnification. The last two really come into play with macro since you are closer and are magnifying the image to life size.

You should be able to get by with a basic macro (105mm or so) to start with. I typically use smaller apertures (f/11 - f/22) for macros so I can get a depth of field that isn't too shallow.

Actually aperture sizes are ratios of the lens's focal length to the diameter of the entrance pupil. f/4 for example is actually 1:4 but the '1:' part has been dropped I guess for brevity. For example again, if you are shooting with a 100mm lens at f/4, the diameter of the aperture is 4x smaller than the focal length, (the aperture opening would be 25mm in this case). While looking at aperture as a fraction does work, it is properly a ratio.

Gary
 
I have a EFS 18-55mm for my Canon Rebel XT EOS.

Taking a photography class! It's not really all about lenses though.

I'm looking to do some super macro stuff (Clear flower, blurry background), so i'd need small depth of field, and a low aperture, right?

My aperture only goes down to 4.5, but standard goes down to 1. Would I benefit from getting a lens that goes down to 1? Or lower than 4.5?

Also, looking to do pics that are super clear from way far away, so i'd need large aperature. My aperature goes up to 36. Would a bigger one benefit at all?

There are many elements which affect DOF. The principal elements are:

1) size of aperture;
2) distance from subject to lens;
3) distance from subject to background; and
4) lens focal length.

I do not understand "standard goes down to 1". A lens with the same size aperture opening as its focal length is a very special lens. Yes, you may be able to reap some immediate benefits from such a lens, but special can also be translated into 'expensive'. I doubt that a neophyte will be able to reap an equitable ROI from such an expensive lens. These lenses are big. heavy and expensive.

"looking to do pics that are super clear from way far away, so i'd need large aperature" This isn't very clear as to what you are observing and what is super clear. Usually a way far away image is shot with a telephoto lens. Not all lenses are equal. Typically, a premium lens will be sharper than a less-than-premium lens (premium = expensive). Speaking of a single subject being clear requires different photographic elements to come into play, than speaking of the entire image being clear ... from foreground to background which may require different elements or even similar elements but those elements must be played differently. Photography is much like cooking, after the basics most everything is subjective.

Do not confuse equipment with good imagery. Good equipment will not consistency deliver good images in the hands of a neophyte. Conversely, a skilled photographer can consistency capture good images with less that professional equipment. Do not feel you need to 'buy' your way to good photography. Use what you have and understand what you're using. The best way to climb up the photographic learning curve is by doing ... shooting. Follow your instructions and shoot with what you have (it should be fine). Adding new equipment isn't necessary and will prolong and expand the learning curve. Shoot, shoot again and when you think you're done for the day shoot some more.

Gary

PS- f/4.5 is considered to be on the 'slow' side of lenses. Lenses with aperture openings of f/2.8 or bigger, (bigger aperture = lower numbers), are considered fast lenses. Lenses with aperture openings smaller than f/2.8 are considered slower/slow. All else being equal, a wide open Fast lenses allow significantly more light to hit the sensor than a wide open Slow lens. (Wide open = Aperture is set to its Maximum Opening ... in this case f/2.8 vs. f/4.5) Adjust you other settings, shutter speed and ISO can help compensate for a slower lens. A tripod and/or flash will also go a long way in the compensation department. But there are limits to compensation and those limits are usually dictated by subject matter.

G
 
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When you are focused on an object very close to the lens you have very little depth of field. When I use my 100/2.8 lens to get a macro shot with just a small part of the frame in focus I often end up using about f4-5.6. You really don't need anything faster than 2.8 (lower f number) to get close-ups or macro shots with very little depth of field.
 
I have a EFS 18-55mm for my Canon Rebel XT EOS.

Taking a photography class! It's not really all about lenses though.

I'm looking to do some super macro stuff (Clear flower, blurry background), so i'd need small depth of field, and a low aperture, right?

My aperture only goes down to 4.5, but standard goes down to 1. Would I benefit from getting a lens that goes down to 1? Or lower than 4.5?

Also, looking to do pics that are super clear from way far away, so i'd need large aperature. My aperature goes up to 36. Would a bigger one benefit at all?


Like the others, I think your understanding will be better after the class.
To me, super macro stuff is a grain of rice that fills the frame, or doesn't even fit in the frame. Canon makes a specialty lens like that. You don't focus it, you decide on the magnification then move lens and camera back and forth until what you want is in focus. DOF is extremely thin. Regular macro will fill the frame with a quarter ($0.25), or about 20 grains of rice. Most flower shots are close-up. A regular lens like your 18-55 can do flower photos. When you get into macro lenses the problem is often that you don't have enough DOF, or enough light to use a super small aperture for DOF, when using them as a macro lens. Most macro lenses are prime (a single photo length) lenses. Some zoom lenses have a "Macro" setting which provides improved close focus, but is not as effective as a dedicated macro lens. Teleconverters and extension tubes are also useful for close focus and macro work. With a crop body, you can get a good flower photo with a 10 mm lens, or a 400 mm lens, or any focal length in-between. You can also use a wide open aperture, a partly closed aperture, or the smallest the lens has. Watch out for diffraction, but don't obsess over it.

Canon makes a few f/1.2 lenses. Big, heavy, pricey pieces of glass! f/1.4 lenses are usually much less expensive and you give up very little real benefit. Sometimes you gain because the f/1.2 lenses are generally slower to focus.

I'm not sure how far "way far away" might be. I suspect it might depend on the subject too. A photo of a robin that's a couple of car lengths away will produce a very small bird in the frame, even with 200 mm focal length, so the robin is way far away, relatively. On the other hand, a photo of a mountain or two, and a glacier will fill the frame at reasonable focal lengths, even if you are miles away, which might also be considered way far away. If we are talking about reasonable settings, there are lots of factors that affect clarity more than aperture. Holding the camera perfectly still; high shutter speed; low shutter speed with little ambient light and flash; atmospheric conditions; a subject that doesn't move, all affect clarity.

Finally, a large aperture is a small 'f' number, like 1.2 or 2.8. A small aperture is a large 'f' number, like 22 or 36. How much DOF you can expect from a given focal length, aperture and focus distance is available from calculators like this one: Online Depth of Field Calculator Understanding the concept is more important than having a table with the numbers in your pocket. In the field, you can usually "wing it" and it will be close enough. Your camera also has a DOF preview button that stops down the lens so you can see the effect. I find it marginally effective, but it is there to help you.
 
As mentioned controlling depth-of-field (DoF) is about more than just the lens aperture.
Point of focus (PoF) distance has more of an impact of DoF than lens aperture does.

With a true Macro lens the PoF is very short and the DoF becomes so shallow macro photographers resort to making multiple exposures so they can use a technique known as 'focus stacking' to make the DoF deep enough.

There are lenses - expensive lenses - that have a maximum f-stop of less than 1, like the $11,000
Leica 50mm / f0.95 ASPH. (E60)

Canon makes what is considered by many to be a very good 1-5x, $1050 macro lens -
Canon MP-E 65mm f/2.8 1-5X Macro Lens for Canon SLR Cameras

Canon makes other Macro lenses that range in price from $300 to $1500 - Canon U.S.A. : Consumer & Home Office : EF Lens Lineup


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