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FORUMS Canon Cameras, Lenses & Accessories Canon Lenses 
Thread started 22 May 2014 (Thursday) 20:03
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Need some help with lens choices

 
FEChariot
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May 25, 2014 01:34 as a reply to  @ post 16928195 |  #31

What you have with the tardis is the fact that superzooms like the 15-85 aren't true 15-85s unless you shoot at infinity distances. So while it might start out at 15mm, if you are shooting at close to Minimum focal distance, at 85mm, it might look like 65mm. However at infinity distances, 85mm will look like 85mm. Superzooms like the 18-135s, and 18-200 are especially bad at this due to the nature and design of the lens.

Take a shot of something far away and you will see your 15-85 @ 50 look much more like your 50.


Canon 7D/350D, Σ17-50/2.8 OS, 18-55IS, 24-105/4 L IS, Σ30/1.4 EX, 50/1.8, C50/1.4, 55-250IS, 60/2.8, 70-200/4 L IS, 85/1.8, 100/2.8 IS L, 135/2 L 580EX II, 430EX II * 2, 270EX II.

  
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SkipD
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May 25, 2014 04:59 |  #32

The focal length for ALL lenses for cameras are stated with the lenses AT INFINITY FOCUS. Thus, with closer focus, all bets are off when comparing different lenses' focal lengths. This is especially true with zoom lenses.

Chris - take your 15-85 and your 50 outdoors. Photograph a distant scene with the 50 and the 15-85 set at 50. You will probably find that both are closer to each other in field of view than your close-in examples.

The fact is that ALL lenses for SLR cameras are marked with actual focal lengths. NONE are marked with "35mm equivalent focal length" values. Thus, all Canon EF and EF-S lenses with the same marked focal length should - at least at infinity focus - provide roughly the same field of view.

That said, marked focal length for lenses - especially inexpensive ones - can be in error for several reasons.

  • Manufacturing tolerances will come into play.
  • Marketing folks at lens manufacturers often label lenses' focal lengths to be competitive with the market. For example, if they designed a zoom lens that actually worked out to 73mm to 194mm, it would probably be labelled as a 70-200 because that is a common zoom lens range that this one would compete with in the marketplace.
  • To make a zoom lens that holds the marked focal length at various focus distances and across the focal length range would be a very expensive proposition. Thus, you are more likely to see variations with lower priced zoom lenses than the highest priced zoom lenses.

In the future, I suggest that you don't worry about "crop factor" issues (at least not if you are using only one camera format). Don't worry about differences in apparent focal length variations between different design lenses. Simply choose a lens that will allow you to frame your images the way you envision them.

Skip Douglas
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..... but still learning all the time.

  
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GeekTechLive
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May 25, 2014 08:28 |  #33

hiketheplanet wrote in post #16928195 (external link)
The bottom image looks like classic 50mm to my eyes (on ApS-C of course, I shot that way for a long time). Not surprising the zoom is not quite the same. The markings on the zoom are not always accurate.

Anyway based on everything I've read so far in this thread, I would steer you to the Sigma 30mm f/1.4 Art for EF-S. I gather you're looking to do full body shots & small group photos at these conventions? 30mm on ApS-C should fall squarely in the middle of that requirement. A step or two back or forward accomplishes the zooming you need. It's also got killer IQ and can melt those backgrounds away. Cheers.

So can you explain why when looking at zooms the crop factor applies but not in my example? I hear people on these forums stating that you can get more reach than a FF when using a zoom. I assumed it applies to primes too.


I have a Flickr account HERE (external link) my name IS Chris & these are ALL my images. My Avatar name and Flickr name are confusing people ???<shrug>
Gripped 7D with a Rokinon 8mm, Tamron SP 70-300mm F/4-5.6, Canon EF 50mm 1.4, Canon EF-S 15-85 F/3.5-5.6 and the 18-135 Kit lens .

  
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GeekTechLive
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May 25, 2014 08:38 |  #34

CyberDyneSystems wrote in post #16928183 (external link)
I can't explain what is going on with your images, but 50mm is 50mm
The EF-S moniker ONLY means it can not be used with Canon Full Frame bodies.
The mm designation is constant. EF-S simply means a narrower image circle is required by the smaller sensor. focal length is not changed.

I totally get that focal length is not changed.... IF you look at the Exif on those two images you will see that they are both set to 50mm. It was my understanding that the EF lenses image circle is larger than the EF-S so when used on a crop sensor the image is cropped and therefore looks to be taken with a larger lens. Im my case the EF 50mm prime I used makes a 100% shot that "looks" like an 80mm lens shot it because the image circle is larger than needed on my 7D and so the sensor "crops" the image, which makes it appear zoomed.

Thats really all I am saying... If I want to get am image on my 7D with a FF Lens that looks like it was shot at 30mm At 100% I would need to use a 19mm lens to do that because my sensor would crop the FF image circle.

Oh gosh, please let me not be wrong with this for 4 years!!! :oops::oops::oops::oops::oops:


I have a Flickr account HERE (external link) my name IS Chris & these are ALL my images. My Avatar name and Flickr name are confusing people ???<shrug>
Gripped 7D with a Rokinon 8mm, Tamron SP 70-300mm F/4-5.6, Canon EF 50mm 1.4, Canon EF-S 15-85 F/3.5-5.6 and the 18-135 Kit lens .

  
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SkipD
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May 25, 2014 08:39 |  #35

GeekTechLive wrote in post #16928692 (external link)
I totally get that focal length is not changed.... IF you look at the Exif on those two images you will see that they are both set to 50mm. It was my understanding that the EF lenses image circle is larger than the EF-S so when used on a crop sensor the image is cropped and therefore looks to be taken with a larger lens. Im my case the EF 50mm prime I used makes a 100% shot that "looks" like an 80mm lens shot it because the image circle is larger than needed on my 7D and so the sensor "crops" the image, which makes it appear zoomed.

Thats really all I am saying... If I want to get am image on my 7D with a FF Lens that looks like it was shot at 30mm At 100% I would need to use a 19mm lens to do that because my sensor would crop the FF image circle.

Oh gosh, please let me not be wrong with this for 4 years!!! :oops::oops::oops::oops::oops:

SHOOT NEW TEST SHOTS AT INFINITY FOCUS.

ALso, read my last post carefully.


Skip Douglas
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..... but still learning all the time.

  
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hiketheplanet
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May 25, 2014 08:41 |  #36

GeekTechLive wrote in post #16928675 (external link)
So can you explain why when looking at zooms the crop factor applies but not in my example? I hear people on these forums stating that you can get more reach than a FF when using a zoom. I assumed it applies to primes too.

I'm sure people will come after me with a pitch fork for saying this but here's how I look at it.

A lens produces a big circular image. Full frame superimposes a big rectangle that goes all the way to the edges of that circle. ApS-C superimposes a smaller rectangle on that circle. Of course the physical properties of the lens don't change. The extra "reach" is because you are putting more pixels from your sensor on a smaller portion of the image circle (the "crop").

So if you have a FF camera with a 20mp sensor, and an APS-C camera with a 20mp sensor, the effective "cropped" image from the ApS-C camera dedicates all its 20mp to a smaller portion of the image. Theoretically, to get the same image from the FF camera with the identical lens, distance to subject, etc, you'd have to crop the image in post processing and you wouldn't have as many pixels on that image (you'd have 12.5mp instead).

It of course applies to zooms and primes alike, it has nothing to do with the lens, only the image sensor of the camera.




  
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hiketheplanet
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May 25, 2014 08:44 as a reply to  @ hiketheplanet's post |  #37

And like others have stated, the apparent difference in FL between the prime and zoom can be caused by a myriad of things, like the fact that the zoom is accurate at infinity for the FL. Actually, prime lenses can exhibit this same behavior too.

Every lens is a little different, even two different 50mm primes will not be identical in their apparent FL.




  
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SkipD
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May 25, 2014 08:44 |  #38

hiketheplanet wrote in post #16928700 (external link)
I'm sure people will come after me with a pitch fork for saying this but here's how I look at it.

A lens produces a big circular image. Full frame superimposes a big rectangle that goes all the way to the edges of that circle. ApS-C superimposes a smaller rectangle on that circle. Of course the physical properties of the lens don't change. The extra "reach" is because you are putting more pixels from your sensor on a smaller portion of the image circle (the "crop").

So if you have a FF camera with a 20mp sensor, and an APS-C camera with a 20mp sensor, the effective "cropped" image from the ApS-C camera dedicates all its 20mp to a smaller portion of the image. Theoretically, to get the same image from the FF camera with the identical lens, distance to subject, etc, you'd have to crop the image in post processing and you wouldn't have as many pixels on that image (you'd have 12.5mp instead).

It of course applies to zooms and primes alike, it has nothing to do with the lens, only the image sensor of the camera.

Pixel count has absolutely nothing in the world to do with "crop factor" issues. Field (angle) of view is the only thing that the "crop factor" calculation is all about.


Skip Douglas
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..... but still learning all the time.

  
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hiketheplanet
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May 25, 2014 08:49 |  #39

SkipD wrote in post #16928706 (external link)
Pixel count has absolutely nothing in the world to do with "crop factor" issues. Field (angle) of view is the only thing that the "crop factor" calculation is all about.

So is what I've stated incorrect about how many pixels you'd have on the same image assuming you've cropped the FF image to match the APS-C image?

My point is, of course it's about field of view, getting more pixels on the smaller target within the image circle is a side-affect of that change in field of view.




  
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Dave ­ Kearley
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May 25, 2014 09:09 |  #40

Thought I might add my thoughts on your first question and not the subsequent conversation. The canon 17-55mm 2.8 was a god send for me at the comic cons I've been to (uk only) both on my 50d and 7d it handled lowlight perfectly giving some impressive shots than I'd previously taken with my kit lens. It is a lovely lense on crop.

Since moving to my 5d2 I've used a combo of 24-105 and 50mm lenses both have their place for my needs at comic con




  
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May 25, 2014 09:11 as a reply to  @ hiketheplanet's post |  #41

To the OP, yes there is a change in field of view between crop and FF sensors. Don't concern yourself with it. The FOV on your camera using a 30mm lens happens to be similar to a 48mm FOV on a FF camera. There are plenty of technical discussions you could get into, none of which will help you obtain a better photograph.

I stand by what I said about the Sigma 30mm Art. It's a darned fine lens and would work well for your intended purposes.




  
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May 25, 2014 09:23 |  #42

SkipD wrote in post #16928424 (external link)
The focal length for ALL lenses for cameras are stated with the lenses AT INFINITY FOCUS. Thus, with closer focus, all bets are off when comparing different lenses' focal lengths. This is especially true with zoom lenses.

Chris - take your 15-85 and your 50 outdoors. Photograph a distant scene with the 50 and the 15-85 set at 50. You will probably find that both are closer to each other in field of view than your close-in examples.

The fact is that ALL lenses for SLR cameras are marked with actual focal lengths. NONE are marked with "35mm equivalent focal length" values. Thus, all Canon EF and EF-S lenses with the same marked focal length should - at least at infinity focus - provide roughly the same field of view.

That said, marked focal length for lenses - especially inexpensive ones - can be in error for several reasons.
  • Manufacturing tolerances will come into play.
  • Marketing folks at lens manufacturers often label lenses' focal lengths to be competitive with the market. For example, if they designed a zoom lens that actually worked out to 73mm to 194mm, it would probably be labelled as a 70-200 because that is a common zoom lens range that this one would compete with in the marketplace.
  • To make a zoom lens that holds the marked focal length at various focus distances and across the focal length range would be a very expensive proposition. Thus, you are more likely to see variations with lower priced zoom lenses than the highest priced zoom lenses.

In the future, I suggest that you don't worry about "crop factor" issues (at least not if you are using only one camera format). Don't worry about differences in apparent focal length variations between different design lenses. Simply choose a lens that will allow you to frame your images the way you envision them.

Okay, I did what you said and I was not expecting the images to look the same BUT THEY DO! Its just weird that the close up shots look different.

Can you explain why then that there are posts stating for Zoom lenses that using a FF zoom lens on a crop sensor will get you more reach? Is it because they are not comparing the image at infinity focus?

at this point I would like to apologize for taking my own thread WAAAAAAAY off topic.:o:o:o:o:o
It seemed back when I was shooting full frame 35mm I did not have this same confusion.


I have a Flickr account HERE (external link) my name IS Chris & these are ALL my images. My Avatar name and Flickr name are confusing people ???<shrug>
Gripped 7D with a Rokinon 8mm, Tamron SP 70-300mm F/4-5.6, Canon EF 50mm 1.4, Canon EF-S 15-85 F/3.5-5.6 and the 18-135 Kit lens .

  
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May 25, 2014 09:26 |  #43

hiketheplanet wrote in post #16928744 (external link)
To the OP, yes there is a change in field of view between crop and FF sensors. Don't concern yourself with it. The FOV on your camera using a 30mm lens happens to be similar to a 48mm FOV on a FF camera. There are plenty of technical discussions you could get into, none of which will help you obtain a better photograph.

I stand by what I said about the Sigma 30mm Art. It's a darned fine lens and would work well for your intended purposes.

thank you for helping me get out of a death spiral of analysis paralysis on the never ending debate on FF vs crop sensors. I start second guessing my 7D and start longing to go FF but in the end I don't think it would make me a better photographer.


I have a Flickr account HERE (external link) my name IS Chris & these are ALL my images. My Avatar name and Flickr name are confusing people ???<shrug>
Gripped 7D with a Rokinon 8mm, Tamron SP 70-300mm F/4-5.6, Canon EF 50mm 1.4, Canon EF-S 15-85 F/3.5-5.6 and the 18-135 Kit lens .

  
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hiketheplanet
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May 25, 2014 10:56 as a reply to  @ GeekTechLive's post |  #44

The extra reach on a crop camera is exactly how I explained it above. This has nothing at all to do with the differences you see at 50mm on your prime and your zoom. It has nothing to do with prime lenses vs. zoom lenses. Many lenses exhibit a slight change in field of view when their focus distance changes. This is inherent to all lenses, and also has nothing to do with FF vs. crop.

If you take the same exact picture with the same lens and settings and focused on the same subject at the same distance, you will get a different framing in your final image because of FF sensor vs crop sensor. That difference on the Canon EOS system is 1:1.6. If this lens is a 30mm lens, you will get an image in the crop camera that looks like a 48mm FOV on a FF camera. The FF camera will look like a FF camera does at 30mm. Theoretically, you could be putting more pixels on the target because all of the sensor is dedicated to a smaller portion of the image circle on the crop camera. This is why people call it extra "reach." Some people are of the opinion that this is an advantage that crop cameras have especially in sports or bird photography. Others disagree about any perceived advantage here because a FF sensor has more resolving power (without getting WAY off topic there...)

In the end, it doesn't matter. You simply get a more "zoomed-in" FOV result in your final images from your crop camera. Leave it at that. If you want to know the difference in FOV between FF and crop, simply multiply the focal length by 1.6. You are correct that this knowledge and that a FF camera will not make you a better photographer. These are just the tools of the trade, and it's up to you to create beautiful images. If cameras did all the work, I would not be interested in it at all.




  
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SkipD
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May 25, 2014 11:21 |  #45

hiketheplanet wrote in post #16928715 (external link)
So is what I've stated incorrect about how many pixels you'd have on the same image assuming you've cropped the FF image to match the APS-C image?

I didn't do any detailed analysis of your numbers but it looks OK at a quick glance.

hiketheplanet wrote in post #16928715 (external link)
My point is, of course it's about field of view, getting more pixels on the smaller target within the image circle is a side-affect of that change in field of view.

Field (or angle) of view has nothing to do with pixels. It has everything to do with the focal length and the camera format (size of the film frame or digital sensor). Given film SLR cameras with the same formats as our current crop of digital SLR cameras (pun intended), one would see precisely the same field (angle) of view differences as we do with the digital cameras. You would see the fields (angles) of view in the camera's viewfinders - either film or digital - without capturing even one image on film or as 1s and 0s. Thus, field (angle) of view is pixel-less.


Skip Douglas
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..... but still learning all the time.

  
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