Pre digital lens focal range.

Galaxy66

Galaxy66

Jeremy Beadle
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My name is Mal not Jeremy :)
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I have the 24-105 IS L as my main lens on the 40D, I also have a pre digital Cosina 19-35 which I know will work on the 20/30/40D. Not wanting to change the lens unnecessarily if I can help it can anyone tell me if the 24-105 would cover the range of the Cossina and if so what would then be the true focal range. It will be straight over to classified if it is covered by the L lens.
 
The focal length of a lens is the focal length irrespective of it being digital or not. The difference with some digital lenses is they are designed for smaller sized sensors to they don't give good coverage with full frame cameras.

You Cosina is more of a wide angle than the 24-105, but much shorter a telephoto.
You may find it useful if/when the 24 mm range of you lens is not wide enough.

You might want to do some image tests to see if the image quality is up to your expectations
 
Mmmm, I had it in my head that the older lens increased the focal range, for example:thinking: have I read that the older Canon 35mm 75-300 was equal to 120-480 on today's new digital slr's.
Am I getting confused with something else ?.
 
Afaik Canons have a crop factor of 1.5. That would mean your Cosina 19-35 would give you a Field of View of 29-53mm in 35mm film equivalent on your 40D. So your 24-105 IS L has a greater zoom range: it is slightly wider at the wide end, and almost double at the tele end. Also it is an IS L lens.
 
Yeah it can be confusing because no-one seems to tell anyone how it works, but its actually pretty simple.

Most digital cameras have cropped sensors which are 1.5 or 1.6 times smaller (and thus cheaper to make) but it means that a lens which is, say 50mm, will actually cover the equivalent of a 75mm lens (or slightly more on a cropped canon sensor)

Great for telephoto lens but not so good for wide angle lenses and especially fisheye lens. Also the level of bokeh is reduced on a cropped sensor too.

Also, lenses that are designed for cropped sensors will show heavy vignetting on a full frame camera, or worse will just have a massive circle but then these lenses on cropped sensors are better especially when it comes to things like lens flare and the like.

One benefit of using lenses that are meant for 35mm sensors are that on a cropped sensor you get to enjoy the lens sweet spot, which is the center, so less vignetting and sharper shots too.

Hope that made sense :)
 
So looking at the photonotes site, http://preview.tinyurl.com/2l23ds ,
my 24-105 IS L has the same field of view as a 38-168 mm lens on a 35mm camera so it would not be wider than my Cosina 19 -35mm lens which would then be 29-53mm field of view.
So after reading the replies and looking at the links I am still trying to get my head round this:thinking:, using the 24-105 I capture less of the scene on the 1.6 crop sensor with my 40D than I would on my old (full frame) EOS 10 35mm camera.
But, the field of view is 38-168, would the object/scene I was wanting to capture be larger in the image at the long end of the zoom on the 1.6 crop 40D than it would on my EOS10.
:thinking:
 
Yes life can be a bit confusing. Let's see if this helps.

What is happening is with a smaller chip you are using only part of the image that the lens is producing. A bit like a selective enlargement. The crop factor is simply a way of saying that if you were using a full size sensor you would need to have a lens with this focal length to get the same effective view , as you would with the smaller sensor.

Simple example

50 mm lens . The sensor on you 40D will give you an image that would be the equivalent of an 80mm lens on a full frame camera. The lens hasn't changed it's focal length. it's the effect the smaller sensor gives.

The image does not get bigger, it just seems to
 
Thanks chappers I was half way there already and the rest has now just fell into place.:clap::clap::clap:

Simple isn't it:)
 
And thanks to the others of course, I was just a bit slow in adding it all up, bit like trying to get my head around algebra until it all clicked into place........ but that was a long time ago.:)
 
Chappers said:
The focal length of a lens is the focal length irrespective of it being digital or not. The difference with some digital lenses is they are designed for smaller sized sensors to they don't give good coverage with full frame cameras.
Click to expand...

This is something I've been meaning to clean up in my head for some time. If newer 'digital' lenses provide poor coverage on fullframe sensors, does this mean that they do not give the full 1.5x crop effect when used on the digital bodies they're designed for?

And if so, do old lenses therefor give a longer effective length than newer 'digital' lenses of the same length when used on a cropped sensor?
 
Focal length is defined as the distance from the optical centre of the lens to the focal plane (sensor) when the lens is focused to infinity. So a 50mm lens is 50mm regardless of the size of the sensor as the focal distance stays the same.

Focal lengths for "digital only" lenses are the same as they would be if the lens were used on a full frame body - because the focal distance is still 50mm, etc.

The difference between digital lenses and full frame is the size of the image circle they project onto the focal plane. With a digital lens the image circle is smaller and wouldn't cover a full frame sensor so you'd have extreme vignetting. But the distance from the optical centre to the focal plane is still what defines the focal length.

Crop factor can be used as way to calculate what focal length you'd need on a full frame to capture an image with the same coverage. If you take a shot on a 1.6 sensor with a 100mm lens you'd need a 160mm lens on a full frame to get an (almost) identical image. Alternatively you could crop the image by a factor of .625 (1/1.6) which would give an identical image. Shooting with a 160mm lens would have differences in perspective compression and DoF.

Perhaps the best way to understand the difference between full frame and cropped sensors is to imagine you're looking out of a window. With a cropped sensor you simply have a smaller window, everything else stays the same.
 
pxl8 said:
Perhaps the best way to understand the difference between full frame and cropped sensors is to imagine you're looking out of a window. With a cropped sensor you simply have a smaller window, everything else stays the same.
Click to expand...

That is the simplest, most succinct and technically accurate explanation I have ever heard. :clap::clap:
 
There's an awful lot of misinformation in this thread.

pxl8 is spot on. Focal length is focal length is focal length. Lenses do not change their focal length depending on what body they're attached to. So a 19-35 goes wider than a 24-105, because 19 is less than 24. It's as simple as that.

What does change is the field of view. As pxl8 says, using a crop sensor is like looking out through a window; you don't see the whole scene.

Time to post my visualisation again, I think. The left hand image simulates the view through a conventional lens that will fit 35mm film cameras and "full frame" digitals like the Canon 5D. Canon EF lenses are like this. The right hand image simulates the same view through a "designed for digital" lens with the same focal length. Canon EF-S lenses are like this.

Crop-factor-demo-3.jpg


I would suggest that the only relevance of the "crop factor" is when you're trying to compare lenses on different camera bodies. So for example, I used to have a 28-80mm lens on my old film SLR. Dividing both these number buy 1.6 tells me that a lens on my 350D (1.6x crop factor) that has the same field of view would be 17-50mm. But if you never shot film, or if you don't aspire to owning a full-frame camera, then you really don't need to worry about this.
 
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