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09/02/2007 02:36:06 PM · #1 |
Does anyone know of a place I can get a general explanation of lenses. I just bought a Canon Rebel XTi, and I haven't a clue of what lenses are used for what. I have been reading the forums, but they all assume a certain level of knowledge.
I can't make sense of all the numbers. What do the mm number (focal length?) ranges mean, and how do the f stop numbers relate to those mm numbers? I have been working with point 'n shoot cameras and understand 10x and 12x optical zoom, but don't know how that relates to all these specialized lenses.
The letters are confusing too. I know IS stands for Image Stabilization (I understand that), and I found out what some of the other acronyms are such as: USM (Ultrasonic Motor), MM (Micro Motor), and AFD (Arc Form Drive), but don't know which is best.
There must be something on the Internet that will be simple and comprehensive, but I can't find it. |
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09/02/2007 02:57:35 PM · #2 |
For the XTi you've got a few manufacture options.
Canon EF, and EF-S lenses.
Sigma
Tamron
Tokina
These are your best options. Anything new that says for canon mount should work on your camera.
the MM values on the lens tell you how much reach a lense has. Anything longer than 50mm is generally considered a telephoto lens. After 300mm it's getting into super telephoto. generally the widest of the wide is about 10mm. There are wider lenses but they're specialty lenses. If a lens says something like 18-55mm then it's a zoom lens rather than a prime lens. A zoom lens can zoom in and out without you moving. A prime lens can only zoom if you move closer or farther from your subject.
Apertures. This is the 3.5-4.5 or 2.8 or 1.8 etc you see on the lens. Generally the lower the number the better. This number is a ratio between the focal length of the lens, and the size of the aperture. The lower the number, the more light can get to through the lens. With a zoom lens 2.8 is about as good as it gets. With prime lenses you can see all the way down to 1.0 (for thousands of dollars). Some lenses have variable apertures, this is less desireable but they're cheaper than fixed aperture lenses.
USM is a good thing. This is what you usually want with canon lenses.
A lot of the other terms on lenses don't really tell you that much about the lens. A lot of times they tell you what kind of glass was used, or what type or sensor they are for, of if they're designed for digital. Since you have the XTi none of this really matters very much, and Any of the newer (last 15 years or so) canon mount lenses will work. |
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09/02/2007 02:58:47 PM · #3 |
photozone.de, canon's site has some good info. Probably some others I can't think of this sec.
Someone also posted a site that had a picture on it and a slider beneath where you could see how the same picture would look when shot with different lenses (different mm).
Message edited by author 2007-09-02 14:59:25. |
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09/02/2007 03:01:00 PM · #4 |
Just look around here, all that information and much more is readily available.
To get you started though...
The focal length is essentially the distance to the focal plane. The higher the number, the narrower field of view and the more it magnifies things far away (good for wildlife, sports, etc). The lower the number, the wider the field of view adn you can fit much more into the frame (good for landscapes and interior work).
The f stop numbers are always shown as f/x.x. This means the focal length divided by the aperture value gives the physical size of the aperture. The smaller the number, the more light it lets in because the opening is physically larger. This also means the cost of the lens goes way up since the lens elements need to be larger to allow that large opening. Lenses with f stop numbers as f/x.x-x.x mean that at the widest end of the zoom the f stop is the first number and at the long end it will be the second. The switch will happen somewhere in between.
USM, as you know, stands for ultrasonic motor which uses sonic pulses to quickly drive the focus of the lens. This is much quieter and faster than micro motors. USM is a Canon name. Other companies use the same technology but call them different things. Any sonic focus drive is said to be better than a micro motor.
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09/02/2007 03:03:18 PM · #5 |
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09/02/2007 10:57:06 PM · #6 |
| Thank you all very much. This information is exactly what I needed. I really appreciate the time you took to respond so thoroughly and quickly. I have stopped hyperventilating, and think I will survive this leap I just took. |
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09/02/2007 11:57:33 PM · #7 |
Originally posted by JuliBoc:
Thank you all very much. This information is exactly what I needed. I really appreciate the time you took to respond so thoroughly and quickly. I have stopped hyperventilating, and think I will survive this leap I just took. |
Get the basics. Near, far and/or macro. After that the most important thing to do is ask yourself what you want to take photos of. Find a lens or lenses that help you accomplish that and don't look back. You'll always want more lenses. Just get your basics, and then specialize once you have a better feel for what kind of photographer you want to be.
My kit lens is my "near" lens. It's an 18-135. A pretty good walk around lens. When it came to my telephoto I got the best far reaching Nikon I could afford at the time. It was my first purchased lens, and I was a little chicken to go offbrand on that.
When I started to look for my macro I picked a couple photographers with the same brand of camera as mine. I looked at what lenses they had.  ursula and  hotpasta were who I looked at. I've always loved ursula's macros, so I picked her macro lens and guess what, hotpasta had the same lens; Sold! (especially when jmsetzler, who wrote that lens buying for dummies, put a near brand new used one up in the buy/sell forums, heh.)
It's been about a year now, and my basics have kept me satisfied. I'm finding that I'm craving a really wide angle lens. That's probably where I'll be looking for my next lens, but for now, I'm satisfied. |
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09/09/2007 12:26:47 PM · #8 |
I was looking for some information on the difference between a 10x zoom and a slr lens
my Question is: what is the equivlant mm for a 10x zoom and a 12x zoom?
scwalsh |
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09/09/2007 12:43:24 PM · #9 |
Originally posted by scwalsh:
I was looking for some information on the difference between a 10x zoom and a slr lens
my Question is: what is the equivlant mm for a 10x zoom and a 12x zoom? |
SLR lenses aren't measured in terms of 'zoom', but max and min focal lengths. So, the way to compare P&S lenses to SLR lenses is to find the P&S model at www.dpreview.com (click camera database on the left). What you are looking for in the camera spec are the 'zoom wide' and 'zoom tele' figures. These have already been converted into 35mm equiv. terms for you.
btw, when talking about comparing focal lengths of lenses, everything is converted into '35mm equiv' to allow like-for-like comparisons, this is because of the differences in sensor sizes.
So, the Fujifilm S700 has a 38mm-380mm lens, compared to say the kit lens I got with my D40 which is 27mm-82mm (18mm-55mm multiplied by 1.5 crop factor)
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09/09/2007 12:45:12 PM · #10 |
Originally posted by scwalsh:
I was looking for some information on the difference between a 10x zoom and a slr lens
my Question is: what is the equivlant mm for a 10x zoom and a 12x zoom?
scwalsh |
This is a *really* common question... unfortunately it's one without a hard answer. When a camera says "10x" what they mean is that the focal length (in mm) of the telephoto setting is 10 times the focal length of the wide angle setting. Example:
a camera's lens is marked 5-50mm. The 50mm setting is the telephoto end, the 5mm setting is the wide angle end. 50 divided by 5 is 10, so this camera has 10x zoom range. Another camera with a 10-100mm lens also has a 10x range, but the end focal lengths are different.
What makes this all even more confusing is that different cameras use different sensor sizes. The result is that even if the lens focal lengths are the same, two cameras with different sensor sizes will have different field of view.
To add yet more confusion, the focal lengths are sometimes advertised as "35mm equivalent."
For SLR lenses, here are some things to remember:
- On APS-C cameras (pretty much all DSLRs except some Canon and one upcoming Nikon model) a 30mm lens is about "normal" or what you'd have gotten from a 50mm lens on 35mm film.
- Longer focal lengths are telephoto, shorter are wide angle.
- The "crop factor" of your camera (1.6 for most Canons, 1.5 for most Nikons) is what you multiply a lens's focal length by to get the "equivalent 35mm" focal length. This is the focal length that, on a 35mm camera, would give the same field of view.
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09/09/2007 01:30:25 PM · #11 |
So, the Fujifilm S700 has a 38mm-380mm lens, compared to say the kit lens I got with my D40 which is 27mm-82mm (18mm-55mm multiplied by 1.5 crop factor)
thanks that was basicly what i was looking for.
im in the market for an slr, but have become use to using the zoom on my camera and was wondering what kind of zoom lens i will be to get to come close to the zoom i have now.
Message edited by author 2007-09-09 13:31:29. |
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09/09/2007 01:34:24 PM · #12 |
Check this link out. It a simulation for depth of field for which you enter the distance, focal length, etc.
It will give you a good idea as to how everything works together. |
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09/09/2007 01:52:37 PM · #13 |
Hi. I don't have any specific websites to help you with lens fundamentals (I've noted others have posted some good stuff), but when you have gotten some of the lingo down and you're looking to build your lens collection, I HIGHLY recommend this site for reviews of Canon lenses.
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09/09/2007 06:00:42 PM · #14 |
Here is a camera simulator that will let you learn about aperature, shutter speed, and Iso relationships.
SimCam
Tim |
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09/09/2007 07:54:18 PM · #15 |
Originally posted by atupdate:
Here is a camera simulator that will let you learn about aperature, shutter speed, and Iso relationships.
SimCam
Tim |
some nice tutes there and nice to use their simulator |
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09/09/2007 08:19:28 PM · #16 |
This is fun tool to get a visual idea what the different lens do as far as focal length.
Tamron Focal Lenght Tool |
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09/09/2007 09:04:04 PM · #17 |
Originally posted by scwalsh:
im in the market for an slr, but have become use to using the zoom on my camera and was wondering what kind of zoom lens i will be to get to come close to the zoom i have now. |
The one thing about DSLR lenses is that very few have the zoom range of a point & shoot. There are some lenses that cover a 10x range, but they are "optical compromises." So in the end, you will need to make choices between a single lens that may be optically less capable (not as sharp, more distortion, needs more light) or a more capable lens with a smaller zoom range. |
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09/11/2007 08:31:24 PM · #18 |
Originally posted by kirbic:
The one thing about DSLR lenses is that very few have the zoom range of a point & shoot. There are some lenses that cover a 10x range, but they are "optical compromises." |
Note that an "optical compromise" is only relevant because this is an SLR, and people demand higher quality from an SLR. This had me a little depressed when I first looked at SLRs, that my P&S camera had a really good quality mega-zoom, and all the SLR megazooms were said to be 'bad'. But it's just a different viewpoint. There are a few megazoom lenses for SLR cameras, and they are just as good quality, if not better then P&S megazooms. It's just that with an SLR, you have a much higher quality option when choosing not-so-mega zooms. :) A P&S megazoom that gets raved about as a great lens is probably of a quality that would get thrown out of any serious SLR discussion.
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09/11/2007 08:40:08 PM · #19 |
Originally posted by scwalsh:
im in the market for an slr, but have become use to using the zoom on my camera and was wondering what kind of zoom lens i will be to get to come close to the zoom i have now. |
I was worried about this too. However, moving from a 12x zoom P&S, to the 18-55 kit-lens, I really didn't find I was missing it much at all. I found I'd much rather have the extra wide end than the long end. But add a 300 tele-zoom, and you've got the whole range covered and more at both ends. Very occasionally I get a scenario where I'm swapping lenses more than I'd like to, but that's a small tradeoff for the extra quality.
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09/11/2007 08:50:59 PM · #20 |
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