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Understanding lenses
http://www.x404.co.uk/forum/viewtopic.php?f=17&t=18985		 Page 1 of 2
Author:  cloaked_wolf [ Sat May 18, 2013 9:55 pm ]
Post subject:  Understanding lenses
This is something I'm still struggling with despite doing my best to read around.

I understand you can have prime lenses, which are fixed and have no ability to zoom eg 50mm ("nifty fifty").
I understand you can have zoom lenses, which have the ability to zoom eg 70-200mm, and that you can have telephoto zoom, superzoom, and wide angle zoom.
I understand that lenses have an aperture eg 50mm f/1.8

Where I struggle is relating those values to real life figures.

How can I work out what 50mm means to me? How do I know how far away I can autofocus with a 400mm?
How do I know whether I want the camera to come with a 15-85mm lens 18-135mm lens?

If a lens has an aperture of f/1.8 but my camera goes to f/1.4, does this mean when I attach the lens, the aperture won't open beyond f/1.8? Or will there be no difference between f/1.4 and f/1.8?

Working out lenses seems to me to be more difficult that working out which camera to buy. I need help please :(
Author:  timark_uk [ Sat May 18, 2013 11:43 pm ]
Post subject:  Re: Understanding lenses
cloaked_wolf wrote:
How do I know how far away I can autofocus with a 400mm?
The lens will have a minimum focal distance. This is different depending on the lens.
See any documentation that came with the lens or look it up online.
cloaked_wolf wrote:
How do I know whether I want the camera to come with a 15-85mm lens 18-135mm lens?
Think about what you want to photograph and how you want to photograph it, then base your choice on that.
Also compare lenses for quality/price/durability.
cloaked_wolf wrote:
If a lens has an aperture of f/1.8 but my camera goes to f/1.4
I don't understand this … the lens has an aperture, not the camera. Unless some cameras do and I'm just not familiar with this.
If the camera is able to handle an f/1.4 but you put on an f/1.8 then you'll get the maximum aperture of the lens that's on, in this case 1.8

Mark
Author:  cloaked_wolf [ Sun May 19, 2013 5:48 am ]
Post subject:  Re: Understanding lenses
The aperture question was a bit of a ditzy one. What I was trying to ask was how does it know what the max aperture is? Eg lens aperture goes to f/4. When I fiddle with the setting on an SLR, will it limit me to selecting f/4, or will i have to remember it's an f/4 lens and try not to set the aperture wider. I've not used an interchangeable lens camera much other than to fiddle with.
Author:  HeatherKay [ Sun May 19, 2013 6:04 am ]
Post subject:  Re: Understanding lenses
cloaked_wolf wrote:
When I fiddle with the setting on an SLR, will it limit me to selecting f/4, or will i have to remember it's an f/4 lens and try not to set the aperture wider.


The lens dictates to the camera what apertures it can handle. Therefore, an f/4 lens will only open to f/4 and you won't see any options below it.

I see this at the other extreme. Some of my lenses will close to f/32, but most will only go to f/22. All I do is twiddle* the aperture until it stops.







*Technical photosnaptic term.
Author:  petermillard [ Sun May 19, 2013 8:58 pm ]
Post subject:  Re: Understanding lenses
Just to add, modern lenses are 'smart' enough to let the camera body know what the limits of the lens are.

Back in the day, with Nikons anyway, when you changed lenses you would twist the aperture ring all the way left, then right, to set the min/max aperture of the lens with the camera body's meter. Later on, this would happen automatically, and we'd have the giddy technical sophistication of a little prism that would show the set aperture in the viewfinder - yes, literally a little prism that showed you top of the aperture ring, which was fantastic until you started taking pictures in dark conditions...

FWIW a 50mm 'standard' lens was the focal length included with most 35mm SLRs (the 'kit lens' of its day) because 50mm was approximately the diagonal of a 24x36mm 35mm frame, and also the focal length that most closely reflects what you see with the naked eye. But modern digital SLRs often have smaller sensors (ASPC) than 35mm ('full frame'), so there's a focal-length fiddle-factor to take into account; for example, the 15-85mm you mention is equivalent to a 24-136mm on a full-frame 35mm SLR, so just be sure that you're comparing like-for-like.

HTH Pete
Author:  ProfessorF [ Sun May 19, 2013 9:25 pm ]
Post subject:  Re: Understanding lenses
I've got a powerpoint I use to teach with - -I'll gladly email it to you if you fancy.
Author:  cloaked_wolf [ Sun Jun 16, 2013 5:56 pm ]
Post subject:  Re: Understanding lenses
Okay so I've been trying to read around and I'm understanding a bit more. Where I struggle is knowing which focal length range I would need. I got bored so I knocked up this:

Image

Now I'm happy with a little better understanding of wide angle and telephoto lens ranges.

Where I'm struggling is mainly in the standard zoom range. How would I know whether what I need is a 15-85, 17-55, or 18-55?

I'm trying to work out which lenses I would need. I figure maybe a 35mm for the "nifty fifty" on an APS-C sensor, and maybe a lovely 70-200/300 - both of these I'd buy well into the future.

But what would be great as a general purpose lens?
Author:  timark_uk [ Sun Jun 16, 2013 11:03 pm ]
Post subject:  Re: Understanding lenses
Well, my general purpose lens is 24-120mm, if that helps?

Mark
Author:  veato [ Mon Jun 17, 2013 5:26 am ]
Post subject:  Re: Understanding lenses
My most used lens is the Tamron 17-50. It offers a similar range to the 'kit' 18-55 lenses (24-70 on FF) but is better optically than what generally comes bundled with the camera.

I guess for that reason it is my general purpose lens although arguably on APS-C a 18-135 or similar would be better suited. Personally (and with a limited budget) I wouldn't want to sacrifice image quality by going for something with a bigger range.

Sigma do a 17-70 which is a nice range (pair it with a 70-300 DG APO and that's a lot covered for not a lot of money!) but it doesn't have the constant f/2.8 of the Tamron.
Author:  cloaked_wolf [ Mon Jun 17, 2013 6:22 am ]
Post subject:  Re: Understanding lenses
timark_uk wrote:
Well, my general purpose lens is 24-120mm, if that helps?

Mark

It does. I've been looking at the canon 24-105mm as a general purpose lens. Supposed to be better than the 18-135mm that is the standard kit lens.

Guess I need to do more research on lens reviews now.
Author:  HeatherKay [ Mon Jun 17, 2013 10:18 am ]
Post subject:  Re: Understanding lenses
cloaked_wolf wrote:
It does. I've been looking at the canon 24-105mm as a general purpose lens. Supposed to be better than the 18-135mm that is the standard kit lens.


Yes, it will be better, but don't forget the 1.6x crop factor. The kit lens is designed for the APS-C type sensor, so replacing it with a near equivalent (such as the 18-50mm or 18-70mm) is something to consider.

For my 7D, I'm looking to get the Tamron 18-50mm f/2.8 for a "standard" walkabout zoom. Right now, I have the 35mm EF f/2 as my "standard" lens, but the extra wideness and small zoom will be very useful, and fills a gap between the 10-20mm silly wide angle, the 28-300mm (not a fixed aperture) and the 70-200mm f/2.8 bazooka.
Author:  cloaked_wolf [ Mon Jun 17, 2013 10:45 am ]
Post subject:  Re: Understanding lenses
Yeah the other one I was looking at this morning in between patients was the 17-55mm f/2.8 IS USM from Canon.

I've honestly not looked into third party lenses by Sigma and Tamron.
Author:  HeatherKay [ Mon Jun 17, 2013 12:12 pm ]
Post subject:  Re: Understanding lenses
cloaked_wolf wrote:
I've honestly not looking into third party lenses by Sigma and Tamron.


You ought to really. While they don't necessarily have the cachet of the badge, the quality is just as good - if not better in some cases - and they're definitely cheaper. 8-)
Author:  Tsar [ Mon Jun 17, 2013 1:55 pm ]
Post subject:  Re: Understanding lenses
HeatherKay wrote:
cloaked_wolf wrote:
I've honestly not looking into third party lenses by Sigma and Tamron.


You ought to really. While they don't necessarily have the cachet of the badge, the quality is just as good - if not better in some cases - and they're definitely cheaper. 8-)


+ 1

and the BETTER is norm for them
Author:  ProfessorF [ Wed Jun 19, 2013 5:39 pm ]
Post subject:  Re: Understanding lenses
Tsar wrote:
HeatherKay wrote:
cloaked_wolf wrote:
I've honestly not looking into third party lenses by Sigma and Tamron.


You ought to really. While they don't necessarily have the cachet of the badge, the quality is just as good - if not better in some cases - and they're definitely cheaper. 8-)


+ 1

and the BETTER is norm for them


I don't know about better, but I'd pick Sigma over Tamron at the moment.

cloaked_wolf wrote:
timark_uk wrote:
Well, my general purpose lens is 24-120mm, if that helps?

Mark

It does. I've been looking at the canon 24-105mm as a general purpose lens. Supposed to be better than the 18-135mm that is the standard kit lens.

Guess I need to do more research on lens reviews now.


Ok. As with everything, there will be areas you need to compromise on.
What do you think you're going to be shooting mostly? What is your intention?
If you're into photographing wildlife, or air shows, or sports, then a 24-105mm isn't going to cut it. Ideally you'd want something like a 70-300mm. Unless you're going to spend loads on a nice lens with a constant f2.8, then you're going to have to accept that you'll push the ISO to gain speed, as the aperture will probably got to f5.6 at the widest, when at the long end.

On the other hand, if you're photographing things closer to you, then the kit lens is, in fact, not bad. It's not great, but it's perfectly serviceable in most situations. That's why they bundle it.
Again, it won't open up that wide, but during the day, it's unlikely to be an issue. If you were wanting to get more creative with shallow depth of field during daylight, then really you'll be into using filters to cut down the light entering the lens.

So, really, think about the type of stuff you're likely to want to photograph, and how creative you're expecting to get. The kit lens is perfectly adequate for a lot of things - I've used it at weddings and events and next to the stuff I've shot on a prime lens you'd honestly be hard pressed to spot what was taken on what, primarily because you can correct a lot of lens distortion in software after the event.
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