A lens question...

Chr1stof

Chr1stof

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Chris
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Hello all
Im still very much a noob and most of the time I find the answers to my questions by a lot of reading on here. However, Im struggling to get my head around some of the queries and comments made on lenses, especially in the f/s section. I was looking at some of the shorter focal length lenses such as 10-20 etc and read stuff like this-
"I've just bought a 5d and 70-200 and this could be spot on to get me up and running if the IQ is ok. I'm interested in the extreme corners at f8 to f11." (regarding a 27-70)
"Kept it as I always thought I'd get another 1d, but looks like I'm stuck with a cropped sensor and i really need something wider"
(regarding a 12-24)

I think Im just not getting the whole croped sensor and how various lenses will interact with them. Probably pretty obvious but :shrug:
Thanks!
 
I think it's like this:
On a cropped sensor a lens will produce an image that appears to have been made by a slightly longer lens.

I have a Nikon D7000 which has a DX sensor (cropped) I have a 35mm lens, it makes pictures that are similar to those that would be made by a 50mm lens on a full frame sensor.
 
There are various sizes of sensors but for Canon DSLRs they are normally APS-C, APS-H and FF.

APS-C is a 1.6 crop - APS-H is a 1.3 crop and FF means Full Frame (no crop)

Full Frame means that the sensor is the same size as the old 35mm film frame size - i.e. 24x36mm.

All sensor crops are relative to a Full Frame sensor and describe the Field Of View (FOV) which any lens will give when attached to various crop cameras.

So a 100mm lens attached to a 1.6x crop will give the same FOV as a 160mm lens on a Full Frame camera - the calculation is 100mm (the REAL focal length) x 1.6 (the crop) = 160mm.

And a 300mm lens on a 1.3x crop will give the equivalent FOV of a 390mm lens on a FF camera - 300mm x 1.3 = 390mm.

But on a 1.6 crop the same 300mm lens will give the equivalent FOV of a 480mm lens on a FF camera - 300mm x 1.6 = 480mm.

Note that the FOCAL LENGTH of the lens doesn't change, just the FOV.

Also note that with Canon an EF lens can be used on any DSLR but the EF-S series can only be used on 1.6 crop cameras e.g 350D, 450D etc.

Hope that makes it a bit clearer.

.
 
Chris.

Probably the easiest thing to think, if you're a complete newbie, is that the cheaper, entry level cameras are almost always Crops (Canon are 1.6x, think Nikon are 1.6x or 1.5x).

As you get to more expensive, more professional bodies, you start seeing full-frame cameras (I wouldn't worry too much about the 1.3x crop bodies as, by the time you're spending £3-5k on a body, you'll know what's what....you'd hope).

So - for entry level (and by that, I mean upto about £1,200 for the body....so probably 90% of all DSLRs that are bought)...you're talking Cropped bodies.

Peter's explanation about the different calculations etc are right - so a 100mm lens on most DSLRs will be the same as a 150-160mm lens on an old film SLR.

I'm not 100% up on the Ultra Wide Angle lenses (the 10-22 type ones) but I seem to remember there's issues with them at the widest ends (the 10mm) where it's so wide that the sensor can't read it all and you get black corners (like you'd see on something like a cheap Lomo Fisheye although not as extreme).

Your other point about F numbers....that relates to the Aperture. That's the size of the hole in the lens which you vary according to how much light you want to let in. The smaller the number, the bigger the hole (there's lots of threads on here dealing with Aperture though and it's a bigger discussion than a quick post on here).
 
I understand the description of sensor size and the maths of how big/small it makes an image look, its just how it all relates to the lens being used and how the image is captured Im not sure on.
For example, if using a wide lens which gives that curvy almost "fishe eye" type effect, is some of what would end up on a FF sensor lost on a cropped sensor? To try and illustrate what I mean, imagine an overhead projector (your camera's lens) aimed at a screen (your sensor) thats too close and some of the image around the edges is missing the screen and getting lost. Is this what one of the posters I quoted meant about using a cropped sensor?

The link wont work as my PC says I need PSP :(
 
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Full frame is like looking at the world through a toilet roll tube.

Crop sensor is like looking at the world through a kitchen roll tube (with a narrower diameter). The world is the same size, you just see less of it. It looks bigger, but it isn't, it's just a side effect of your field of view encompassing less of the world in front of you.


After a bit of head scratching thinking about what you're decribing, yes, your OHP example is a reasonable one.
 
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:)
I guess it depends if you think of it as the sensor "looking" through the lens or as the image (light) travelling down the lens onto a sensor.

Shamelessly ripped off wiki-
Lenses produced for 35 mm film cameras may mount well on the digital bodies, but the larger image circle of the 35 mm system lens allows unwanted light into the camera body, and the smaller size of the image sensor compared to 35 mm format results in cropping of the image compared to the results produced on the film camera.

Know I understand why I see pros with such massive lenses at bike racing, Im guessing they are using full frame?
 
Chr1stof said:
:)
I guess it depends if you think of it as the sensor "looking" through the lens or as the image (light) travelling down the lens onto a sensor.

Shamelessly ripped off wiki-
Lenses produced for 35 mm film cameras may mount well on the digital bodies, but the larger image circle of the 35 mm system lens allows unwanted light into the camera body, and the smaller size of the image sensor compared to 35 mm format results in cropping of the image compared to the results produced on the film camera.

Know I understand why I see pros with such massive lenses at bike racing, Im guessing they are using full frame?
Click to expand...

Possibly, possibly not. The ones on full frame would need even more massive lenses!

Try this - you have a full frame camera and lens. Now without changing anything else, get some tape and mask off the top, bottom and sides of the sensor so that you are left with an area the size of a crop format sensor in the middle. You have now converted the camera to crop format - that's all there is to that bit of it.

Obviously, you have also cropped away a lot of the image so to restore the field of view, you now need to fit a shorter focal length lens which takes in a much wider field of view in the first place, so that when you have done with the masking tape you can still get all of the same scene in the picture.
 
So then, thinking about one of the comments I quoted earlier-
"Kept it as I always thought I'd get another 1d, but looks like I'm stuck with a cropped sensor and i really need something wider"(regarding a 12-24)-

Is there anything I need to think about specifically if Im looking for a wide lens for my 550d?
 
(regarding a 12-24) "Kept it as I always thought I'd get another 1d, but looks like I'm stuck with a cropped sensor and i really need something wider"
Click to expand...

What's being said there is that they want a FOV in the range 12-24mm, and the 12-24mm lens which they have will give that FOV on a full frame camera. However, as they're using a copped sensor, the same 12-24mm lens is actually giving them a FOV of 19-38mm, which is not as wide as they'd like.

With regard to anything specific you should be on the look out for to fit your 550D, it really depends on how wide you want the lens to be. Only you can answer that one, and it's far easier to judge by looking at images as opposed to looking at statistics.

Your best bet, if you haven't already, is to try a few different lenses on your camera; if you take it to a local camera shop (Jessops, Jacobs, etc) most of them will allow you to test different lenses on your own camera in the store, so you can see the different results.
 
Chr1stof said:
So then, thinking about one of the comments I quoted earlier-
"Kept it as I always thought I'd get another 1d, but looks like I'm stuck with a cropped sensor and i really need something wider"(regarding a 12-24)-

Is there anything I need to think about specifically if Im looking for a wide lens for my 550d?
Click to expand...

Not really. How wide do you want? Short answer is a Canon EF-S 10-22mm :thumbs: If that's within budget, there's nothing better.
 
paulhinch said:
Chris.

Probably the easiest thing to think, if you're a complete newbie, is that the cheaper, entry level cameras are almost always Crops (Canon are 1.6x, think Nikon are 1.6x or 1.5x).

As you get to more expensive, more professional bodies, you start seeing full-frame cameras (I wouldn't worry too much about the 1.3x crop bodies as, by the time you're spending £3-5k on a body, you'll know what's what....you'd hope).

So - for entry level (and by that, I mean upto about £1,200 for the body....so probably 90% of all DSLRs that are bought)...you're talking Cropped bodies.

Peter's explanation about the different calculations etc are right - so a 100mm lens on most DSLRs will be the same as a 150-160mm lens on an old film SLR.

I'm not 100% up on the Ultra Wide Angle lenses (the 10-22 type ones) but I seem to remember there's issues with them at the widest ends (the 10mm) where it's so wide that the sensor can't read it all and you get black corners (like you'd see on something like a cheap Lomo Fisheye although not as extreme).

Your other point about F numbers....that relates to the Aperture. That's the size of the hole in the lens which you vary according to how much light you want to let in. The smaller the number, the bigger the hole (there's lots of threads on here dealing with Aperture though and it's a bigger discussion than a quick post on here).
Click to expand...

Incorrect, at 10mm there are no issues and the sensors can certainly "read" it all! I think you must be thinking of people that have adapted the canon 10-22 (crop lens) to a full frame camera?

Certainly onto bodies it's designed for they work perfectly. And I wouldn't call a xxd or 7d body entry level either!!
 
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