Confused About Lens Lengths

[gunghorjc]

I can't really seem to find a "direct" answer w/ google, and I've looked in the stickies for this board and can't find them there either.

So I'm confused how lens lengths affect the type of photos you'll produce. I'll be purchasing my digital SLR within a month and I'm debating going with just the kit lens to start off, or with another one as well.

Does the longer lens (i.e. 300mm) allow you to get a great depth of field for scenic shots? Or are the longer lenses for more extreme close ups for flowers, bees, bugs, etc?

I hate to be redundant if I this has been asked a gazillion times but it is something I'd like to know. Any links anyone could supply that explain it would be really awesome too! Thanks.

 

[DerekSalem]

Well long confusing story short...the bigger the maximum length (300mm in your example) the more it can zoom. There's a lot of math involved in figuring out exactly how the number correlates but the bigger the number, the more zoomed in.

For depth of field your looking for a lower f number (like f/1.8). Lower numbers mean a bigger aperture on the lens

 

[Vinny]

The longer the focal length, the closer the object appears to be. Also the longer the focal length the objects that you are looking at appear to be closer together. A lens has a minimum length that it can focus to and you can zoom in howerever much as long as you remain at that distance. The exception being a macro lens - it's function is to focus close distances.

I would advise going to the library if you can and get a photography book but Nikon has a lens selector to show what it's like: Nikon | Imaging Products | NIKKOR Lenses Simulator

 

[pbelarge]

Gung
this is strictly my advice, I am sure there are others who may not agree, which is fine.

If you can afford not to purchase the kit lens, I would look to buy a different lens. The $64,000 question then would be...which lens.

So, you have to ask yourself what you want to shoot.
Landscape, wildlife, macro, night, portrait, glamour, architecture, abstract, weddings, etc...
There are some lenses that overlap some of the types of shooting, and then there are lenses that are very specific, such as macro lens.

You can follow this google link Google , which will help you get started in your choice of lens.

Take a look and get back to the site there are some guys here who are really knowledgeable with lenses.

 

[JSD]

Does the longer lens (i.e. 300mm) allow you to get a great depth of field for scenic shots? Or are the longer lenses for more extreme close ups for flowers, bees, bugs, etc?

Longer lenses such as a 300mm are often used for subjects that cant be gotten close to such as wildlife, and have less depth of field than shorter lenses. Wide angle-shorter- lenses such as 24mm have much more depth of field. Often, but not always, short lenses are used for scenics/landscapes becasue of their huge depth of field. Macro lenses are for getting really close as with bugs and flowers, and have very little depth of field even when stopped down to a small aperture such as f16. Remember: The smaller the aperture the bigger the f- number (i.e. f16) and the more depth of field. Larger aperture= smaller number (i.e. f1.8) and less depth of field. BUT: f16 on a 300mm does not equal f16 on a 24mm in terms of depth of field. Hope this helps...JSD

 

[SrBiscuit]

the faster the lens the better DOF.
but even zoomed all the way, with the ap wide open, a slower lens should still get decent DOF...provided your subject is well in the foreground. (the bokeh might not be ideal)

keep in mind too that if youre shooting with a crop body the length will be multiplied by roughly 1.5x. i.e., a 300mm lens on a 1.5 crop body will be 450mm.

 

[KmH]

Depth-of-field is a function of several factors:

• the apparent lens focal length
• the lens aperture
• the subject to image sensor distance
• the subject to background distance.

Lens for making closeups of bugs are quite specialized and the good ones are expensive. They are known as macro lenses though some lens makers use the term as a marketing aid more than as a true description of a lenses capabilities.
Many of them have focal lengths from 60 mm up to about 200mm. The longer focal lengths for macro lenses mean the lens can be further from the subject so as to not scare it off or to make lighting it easier.

The longer focal length non-macro lenses offer what is called more 'reach' or magnification, like shooting sports from the sidelines or making images of birds of prey in flight. Generally, as focal length increase so does lens cost.

 

[--ares--]

Not to throw this thread off topic, but does focal length and range have any direct bearing on magnification? Or does it change from lens to lens?

 

[Nameless]

Gung
this is strictly my advice, I am sure there are others who may not agree, which is fine.

If you can afford not to purchase the kit lens, I would look to buy a different lens. The $64,000 question then would be...which lens.

So, you have to ask yourself what you want to shoot.
Landscape, wildlife, macro, night, portrait, glamour, architecture, abstract, weddings, etc...
There are some lenses that overlap some of the types of shooting, and then there are lenses that are very specific, such as macro lens.

You can follow this google link Google , which will help you get started in your choice of lens.

Take a look and get back to the site there are some guys here who are really knowledgeable with lenses.

I would have to disagree with this slightly because I think it is dependant on which camera/kit the OP buys. The Canon 7D kit comes with a 28-135mm IS, which is a pretty good lens for someone starting out. The Nikon D90 kit comes with a 18-105mm VR, which is also pretty decent for the money.

 

[gunghorjc]

Thanks everyone for the replies! Really great information.

As to what kit, I'm still debating between the Nikon D3000 kit or the Canon Rebel 350D kit. Both come with a an 18-55mm lens I believe.

I guess what I'm really getting at. How do you determine what lens for how far away you are from a subject? Such as if the subject is 100, or 200 feet away.

 

[chaman]

I would suggest to get the kit lens and start shooting, and shooting! You want to start right away, right? Then as you gain a bit more experience consider a zoom lens or a better all around alternative. My advice...whatever you do, get a 50mm prime lens...!

 

[Derrel]

Not to throw this thread off topic, but does focal length and range have any direct bearing on magnification? Or does it change from lens to lens?

Within a format, like APS-C, or FX digital, or 645 rollfilm or 120 rollfim,and so on, the shorter a lens is in focal length, the wider its angle of view, and the lower its magnification. Focal length of a lens is computed and specified with the lens at Infinity focus; as a lens is focused closer, it typically will lose focal length--sometimes quite a bit, especially in the case of macro lenses, or lenses which are corrected to deliver flatter field and better close-up performance. So, when talking about focal length, it must be measured with the lens at Infinity focus.

The relationship between focal length and image size is directly linked. A 25mm lens will produce an image that is half as large as a 50mm. A 50mm lens will produce an image one-half as large as that of a 100mm lens, and a 200mm image will produce an image size that is twice as large as that of a 100mm lens. So, the relationship in Image size is direct, when the different lens lengths are used on the same camera format.

It's important to note that the optical industry has about a 10 percent maximum tolerance in labeling on lenses and MANY lenses cary specified focal lengths that are a slight bit off in their actual, measured lengths; a 300mm labeled single focal length lens may actually be a 285mm lens, or a 307mm lens when measured critically. Same with wide-angle lenses, and zooms like 24-70mm, which could easily be a 25.1-68mm or some such thing.

 

[maris]

I guess what I'm really getting at. How do you determine what lens for how far away you are from a subject? Such as if the subject is 100, or 200 feet away.

The key concept is magnification. If you want the image on the sensor of your camera to be (say) a hundredth of the size of the subject the focal length of the lens must be a hundredth of the distance to the subject. Other ratios work the same.

Here's a worked example: Suppose you want a 1 inch high sensor image of a 6 foot tall man standing 12 feet away. The magnification is 1/72 (1 inch divided by 6 feet alias 72 inches). The focal length required is 1/72 of the distance. Dividing 12 feet by 72 gives 2 inches, alias 50mm. Voila, a 50mm lens will do the job!

All you have to know the size of the lens image you want, the size of your subject matter, and the distance.

 

[Breaux]

The longer lenses also have the effect of compressing distance: ie, the mountains far behind a horse in a field will be magnified proportionally more than the horse, and therefore seem closer than with a normal view.

I would start with the kit lens (they're usually a good deal) and, after some shooting, you will know how, or if, it limits you.

 

[icassell]

Here are 3 focal length simulators which might help you.


Focal length comparison tool, Tamron USA

Canon USA Consumer Products - EF Lenses 101 - Focal Length Comparison

Nikon | Imaging Products | NIKKOR Lenses Simulator