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The Canon Thread - Page 139

post #2071 of 2659

OK, I'm really confused now about crop factor.....

 

I have a crop sensor camera (Rebel T1i).  Lately I've only gotten "only for APS-C" lenses because if I get lenses for Full frame "and/or" crop sensors....then I have to take the crop factor into consideration.....so if it's a 50mm lens...multiply it by 1.6 making it more like:  78 or so.

 

From what my friend told me (which seems to differ from some reviews--not all--is that if you get a "crop sensor only" lens, what you see is what you get....so 50mm means 50mm).  This seems to make sense to me...........because:

 

  • for example, my Rokinon (Samyang) fisheye lens is made only for crop sensors.  The fisheye is normal--like it should be.  If put on a full frame--is is kinda unusable--distorted and I think there is a black ring around the picture--but not like a fisheye that's made for a full frame.
  • The lens I have now--Tamron f2.8 17-50mm is a terrific lens that is ONLY made for crop sensor - it is very wide.  In fact a little wider than my standard kit lens 18-55mm that came with the camera......  so does that mean I'm still only seeing 17-50 X 1.6 because of the crop factor??  
  • The Tamron f2.8 28-70mm (I think) works on BOTH crop and FF.  28mm was really too narrow to be my all purpose lens.  I had to stand too far back........I'm guessing this is because it's 28mm times the 1.6 crop factor....making it more like........44mm
  • I've had the common f1.8 50mm canon lens (I think only for APS-C) and that is pretty narrow.......50mm makes sense when compared to the 44mm (28mm x 1.6) on my previous lens..

 

So.. this Sigma 30mm f1.4 that I've decided to buy is only made for crop sensor....is it gonna be 30mm?  I've read in some reviews that it'll be more like 50+mm........maybe the reviewer didn't know what he was talking about?  He also recommended the Canon 28mm f1.8 which was more sharp and about the same price, BUT for a crop OR full frame........and I believe he said on a crop sensor it'd be more narrow than the sigma 30mm...

 

so I'm confused..    I'm guessing it doesn't make sense for me to get the Canon 28mm b/c it'll be way more narrow than the Sigma 30mm......am I correct in assuming this?    People were recommending the 28mm canon if you ever planned on going to full frame....which I dont plan on for probably 10 years......I think once I upgrade to a 7D in the next couple years or so, I'll be set for 10 years...  -_-

 

Thanks


Edited by hyogen - 5/23/12 at 7:58pm
post #2072 of 2659

Short answer: crop factor always applies.

 

Long answer: anytime light passes from one medium to another (from air into glass or plastic, for example), it bends (refracts).  So, as light passes through a lens, it refracts twice: once as it enters the lens, and once again as it leaves the lens.  Very simply, light refracts around the "nodal points" of a lens (there are two for each lens).  The focal length of a lens is determined by the distance between the rear nodal point and the distance to the image capture plane (film, sensor, whatever).  So, a 135mm lens has a rear nodal point which is 135mm from the film or sensor.  A 50mm lens has a rear nodal point which is 50mm from the sensor.  This is a fixed PHYSICAL attribute.

 

So, if were talking about Canon EOS cameras, a 50mm EF-mount or EFS-mount lens is always a 50mm lens as the distance from the rear nodal point to the sensor is fixed.  However, a crop sensor camera, whether APS-C or APS-H, has a smaller sensor which only captures light from a portion of the image circle projected by the lens.  So you have crop factor.  This means that an APS-C lens, with a crop factor of 1.6 sees the equivalent of an 80mm image when using  a 50mm lens.  I.E., if you put an 80mm lens on a 35mm film camera (don't confuse 35mm film with a 35mm lens) or full frame digital camera, the amount of "stuff" in the image would be the same as a 50mm lens used on a APS-C camera.

 

So, the Sigma lens you reference: it is a 30mm lens.  However, it will give the same image as a 48mm full frame lens when used on an APS-C camera.

 

Confused?  Remember the short answer.  Crop factor always applies.

 

Me?  I looooove me some wide angle so I couldn't use a crop camera.  Full frame or nothing for me!
 


Edited by leftnose - 5/23/12 at 8:21pm
post #2073 of 2659
Quote:
Originally Posted by leftnose View Post

Short answer: crop factor always applies.

 

Long answer: anytime light passes from one medium to another (from air into glass or plastic, for example), it bends (refracts).  So, as light passes through a lens, it refracts twice: once as it enters the lens, and once again as it leaves the lens.  Very simply, light refracts around the "nodal points" of a lens (there are two for each lens).  The focal length of a lens is determined by the distance between the rear nodal point and the distance to the image capture plane (film, sensor, whatever).  So, a 135mm lens has a rear nodal point which is 135mm from the film or sensor.  A 50mm lens has a rear nodal point which is 50mm from the sensor.  This is a fixed PHYSICAL attribute.

 

So, if were talking about Canon EOS cameras, a 50mm EF-mount or EFS-mount lens is always a 50mm lens as the distance from the rear nodal point to the sensor is fixed.  However, a crop sensor camera, whether APS-C or APS-H, has a smaller sensor which only captures light from a portion of the image circle projected by the lens.  So you have crop factor.  This means that an APS-C lens, with a crop factor of 1.6 sees the equivalent of an 80mm image when using  a 50mm lens.  I.E., if you put an 80mm lens on a 35mm film camera (don't confuse 35mm film with a 35mm lens) or full frame digital camera, the amount of "stuff" in the image would be the same as a 50mm lens used on a APS-C camera.

 

So, the Sigma lens you reference: it is a 30mm lens.  However, it will give the same image as a 48mm full frame lens when used on an APS-C camera.

 

Confused?  Remember the short answer.  Crop factor always applies.

 

Me?  I looooove me some wide angle so I couldn't use a crop camera.  Full frame or nothing for me!
 


thanks for clearing this up....but hmm... I've seen some pretty wide pics using the crop-sensor-only 10-22mm lenses........so the full frame wide angle 10-22mm lenses will be even more wide?? 

 

so I guess the 28mm canon (full frame and crop sensor) and the 30mm sigma (only crop sensor) will have about the same image, right?

post #2074 of 2659

The 10-22's fullframe equivalent is 16-35, and 16mm is plenty wide. There aren't many full frame lenses (rectilinear) that go wider than that -- just a handful that I recall are the Canon 14mm prime, and the Sigma 12-24. But yeah, they exist and are truly ultra-wide.

 

I wouldn't say 28 vs 30 would give the same image though... very close, but not exactly the same. But the Sigma is only built for crop sensors and wouldn't work on fullframe, whereas the 28 will work on both.

post #2075 of 2659
Quote:
Originally Posted by MadCow View Post

The 10-22's fullframe equivalent is 16-35, and 16mm is plenty wide. There aren't many full frame lenses (rectilinear) that go wider than that -- just a handful that I recall are the Canon 14mm prime, and the Sigma 12-24. But yeah, they exist and are truly ultra-wide.

I wouldn't say 28 vs 30 would give the same image though... very close, but not exactly the same. But the Sigma is only built for crop sensors and wouldn't work on fullframe, whereas the 28 will work on both.

It all makes sense now. Thanks
post #2076 of 2659

So I bit the bullet and bought a 100 L Macro and a 430 EX II for my 5D2.

 

Note that I have ZERO experience with macro photography or using an accessory flash with a tilt/swivel head.  But. I played around with the set-up this evening a bit and managed to capture this in the first few minutes.

 

IMG_1523.jpg

 

and a 100% crop from the in-focus area (or, at least it was 100% until the forum software did its thing):

 

IMG_1523-2.jpg

 

Click on it to enlarge.

 

I have a couch which, by coincidence, is pretty close to 18% gray so I laid the subject down on it and bounced the flash off the back of the couch.  I had to take the lens hood off because it was casting shadows.  These JPGs wer generated from the RAWs by LR4 with no post processing other than a slight WB adjustment.

 

The lens does seem to be front focusing just a bit so some adjustment might be in order there but I need to spend some time with it on a tripod instead of hand holding at such close distances!

post #2077 of 2659

More fun!

 

IMG_1545.jpg

post #2078 of 2659

what do you do to adjust front or back focusing?  I think the sigma 30mm i'm about to get is known for a little backfocusing issue

post #2079 of 2659
Quote:
Originally Posted by hyogen View Post

what do you do to adjust front or back focusing?  I think the sigma 30mm i'm about to get is known for a little backfocusing issue


It's a feature of certain bodies, basically the full frame bodies, 50D, and 7D.

 

Basically, you take a series of photos while changing the MFA (microfocus adjustment) setting on the body.  Dial it in for front or back focus as necessary and voilà, adjusted focus.  Older cameras remember the setting but will apply the same setting to all copies of a given lens model mounted to the body.  The newer bodies, I believe, remember the adjustment for specific copies of lenses and can even adjust for multiple focal lengths of a zoom lens.

post #2080 of 2659
Quote:
Originally Posted by leftnose View Post

So I bit the bullet and bought a 100 L Macro and a 430 EX II for my 5D2.

 

 

The lens does seem to be front focusing just a bit so some adjustment might be in order there but I need to spend some time with it on a tripod instead of hand holding at such close distances!

Front focusing?  You are not supposed to be using auto focus for macro shots!  Just kidding.  100L's AF actually works decently at Macro distances compared to some others, e.g. Sigma macro.  

 

I just found out that my Bower (aka Phoenix) macro ring flash does not work with 5D MkIII, with the whole ETTL (which is the only mode avail) going haywire and firing full strength.  A bummer since I found out my Kenko 1.4x extender does not work well with 5D MkIII, either.  

This should teach me to avoid third party accessories in the future, as there is no guarantee they will continue to work with newer Canon products.  

 

I'm looking at the Canon ring flash and twin macrolite, which are over $500 and $800 respectively.  Darn, Canon does charge what it likes to charge..

post #2081 of 2659
Quote:
Originally Posted by Jon L View Post

Front focusing?  You are not supposed to be using auto focus for macro shots!  Just kidding.  100L's AF actually works decently at Macro distances compared to some others, e.g. Sigma macro.  

 

I just found out that my Bower (aka Phoenix) macro ring flash does not work with 5D MkIII, with the whole ETTL (which is the only mode avail) going haywire and firing full strength.  A bummer since I found out my Kenko 1.4x extender does not work well with 5D MkIII, either.  

This should teach me to avoid third party accessories in the future, as there is no guarantee they will continue to work with newer Canon products.  

 

I'm looking at the Canon ring flash and twin macrolite, which are over $500 and $800 respectively.  Darn, Canon does charge what it likes to charge..


If you ever want to attempt an exercise in futility, try hand holding a modern DSLR and MF a high magnification shot.  You can't see the focus through the viewfinder so that leaves live view.  You can't focus with live view unless you zoom in and then you can't compose properly.  Not fun.  I think I see a tripod like a Manfrotto 055XPOB with a tilting center column in my future.

 

I've acquired my gear slowly over the last 15 years and I've always gone original Canon.  When I first started, 15 years ago, the big complaint about third party lenses was AF speed/accuracy.  Part of the reason why I went Canon over Nikon was for the improved AF--at the time, Nikon still only had AF motors in the body--so I've sort of stuck with Canon lenses ever since.

post #2082 of 2659
Quote:
Originally Posted by hyogen View Post

what do you do to adjust front or back focusing?  I think the sigma 30mm i'm about to get is known for a little backfocusing issue

 

Only some Canon bodies have micro adjustment on the body.  The full frame cameras, 7D and 50D have it, while newer crop bodies like my 60D and entry level DSLR's like the Rebel series do not have it.  

 

If you're getting that Sigma 30/f1.4 and have focusing issues, one option is to send your camera body and the lens to Sigma for them to calibrate the lens for you.  Thankfully, my Sigma 30/f1.4 didn't have focus issues and it's been a neat little lens that opens up some good opportunities for creativity.  

post #2083 of 2659
http://www.kenrockwell.com/sigma/30mm-f14.htm

Looking at this side by side comparison would you strongly not recommend the Sigma? Friend says I should definitely spend 50 more for the canon 28mm f1.8 over the Sigma 30mm 1.4.....or even the canon 35mm f2.0

That the Sigma will be too soft

The Sigma is aps-C sensor only, bit I don't really plan on upgrading for a long time to a ff... At least 5 maybe 10 years maybe never
Edited by hyogen - 5/25/12 at 9:02am
post #2084 of 2659
Quote:
Originally Posted by daigo View Post

Quote:
Originally Posted by hyogen View Post

what do you do to adjust front or back focusing?  I think the sigma 30mm i'm about to get is known for a little backfocusing issue

Only some Canon bodies have micro adjustment on the body.  The full frame cameras, 7D and 50D have it, while newer crop bodies like my 60D and entry level DSLR's like the Rebel series do not have it.  

If you're getting that Sigma 30/f1.4 and have focusing issues, one option is to send your camera body and the lens to Sigma for them to calibrate the lens for you.  Thankfully, my Sigma 30/f1.4 didn't have focus issues and it's been a neat little lens that opens up some good opportunities for creativity.  

Oh wow I did not see this. I'm in my car and posting from my phone. Thanks!
post #2085 of 2659
Quote:
Originally Posted by hyogen View Post  http://www.kenrockwell.com/sigma/30mm-f14.htm
Looking at this side by side comparison would you strongly not recommend the Sigma? Friend says I should definitely spend 50 more for the canon 28mm f1.8 over the Sigma 30mm 1.4.....or even the canon 35mm f2.0... That the Sigma will be too soft... The Sigma is aps-C sensor only, bit I don't really plan on upgrading for a long time to a ff... At least 5 maybe 10 years maybe never

 

See for yourself with The Digital Picture's resolution chart comparisons... Honestly, I wouldn't worry about wide open performance. Even at f/2.8, I'd worry about center performance only. I only start to worry about corner sharpness from f/8-11

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