Zoom lenses

[MarkBarbieri]

Without IS, the rule of thumb for a 200mm focal length is a shutter speed of 1/200. Given that you use a 1.6x body (if I recall correctly), that should be adjusted to 1/320. At f/4.0, you can shoot in even bright overcast conditions with a reasonable ISO.

Check the shots you've taken in different conditions and look at the shutter speed, aperture, and ISO settings. That should give you a reasonably good idea.

I love having IS on my 70-200mm, but it would still be a very, very useful lens without it. That would be true even at f/4.0 I fact, I would wager that a small majority of my shots are taken with a shutter speed that does not require IS and I usually use f/4.0 unless I'm trying to absolutely maximize light gain or minimize DOF.

 

[Charade]

Without IS, the rule of thumb for a 200mm focal length is a shutter speed of 1/200. Given that you use a 1.6x body (if I recall correctly), that should be adjusted to 1/320. At f/4.0, you can shoot in even bright overcast conditions with a reasonable ISO.

.

Ok, now you're confusing me. I thought the 1.6 CROP factor was just that, a crop factor. If you're suggesting to alter the 1/XXX rule to allow for a 1.6 CROP factor, wouldn't that mean that it changes the focal length (or magnification)? Magnification is the reason for the 1/XXX rule.

 

[MarkBarbieri]

I thought the 1.6 CROP factor was just that, a crop factor.

For camera shake purposes, the crop factor effectively increases the focal length of the lens. It would just be a crop factor is you scaled everything, including your final print/screen image, down when you scaled down the sensor. However, you probably magnify the cropped image more so that it is as large as a full frame image would be. In that case, you have also magnified camera shake.

Let's use some real world sizes to compare what happens. Let's assume that you take a picture of a brick wall 10 feet away using a 50mm lens. On a full frame body, your image captures 7'2.4" x 4'9.6" of bricks. On a 1.6x sensor body, your image captures 4'6" x 3'0". Presumably, you will print them both on the same size paper (or display them on the same size screen). In that case, the bricks from the copped sensor appear larger, which is another way of saying that they are displayed with greater magnification. Now, while you took the picture, the amount of actual camera shaking was probably not affected by the sensor size. However, since you magnified the final image more with the cropped sensor, you also magnified the image problems cause camera shake more as well.

It's functionally the same as taking the full frame image, cropping it to match the smaller sensor image, and then enlarging it back to the original size. In both cases, you have magified the subject by the same amount. You may have jacked with your resolution, but camera shake is resolution independent.

The crop factor also affects DOF. You get more DOF with a smaller sensor image than a larger one, but the explanation is much more complicted.

The crop factor does not directly affect perspective. Perspective is the same regardless of focal length and sensor size and is only changed by moving the photographer or the subject. Typically using a different focal length of crop factor causes the photographer to move to get the composition that they want, but it is the movement of the photographer and not the change in focal length or crop factor that changes the perspective. A 17mm lens and a 400mm lens have the same perspective.

 

[Charade]

Let's use some real world sizes to compare what happens. Let's assume that you take a picture of a brick wall 10 feet away using a 50mm lens. On a full frame body, your image captures 7'2.4" x 4'9.6" of bricks. On a 1.6x sensor body, your image captures 4'6" x 3'0". Presumably, you will print them both on the same size paper (or display them on the same size screen). In that case, the bricks from the copped sensor appear larger, which is another way of saying that they are displayed with greater magnification. Now, while you took the picture, the amount of actual camera shaking was probably not affected by the sensor size. However, since you magnified the final image more with the cropped sensor, you also magnified the image problems cause camera shake more as well.

.

This is true but that magnification occurs in the post processing. The amount of camera shake that might have influenced the image quality didn't change because the focal length didn't change. So I don't see the need to modify the 1/xxx rule. Anytime you use a faster shutter, you reduce the chance of introducing camera shake.

 

[0bli0]

deja vu? i'm sure this has come up a few times. the reason the 1/over rule includes the crop factor is you have to consider motion against the medium. yes, the focal length doesn't change, but the physical size of the recorded image does. so 'movement' as represented as a percentage of the total recorded image increases by a factor 1.6.

if you have a full frame camera and a long zoom, you can do a real world image test by taking a picture of the moon with a slow shutter speed and well stopped down aperture. you will see the moon moves farther across the recorded image on the crop shot than it does on the full frame.

 

[MarkBarbieri]

This is true but that magnification occurs in the post processing.

That is true, but it doesn't matter. Magnification is magnification. However you slice it, you are magnifying the errors from camera shake more with a cropped sensor than a full frame sensor and so you must hold the camera steadier to get back to the same sharpness. The difference in magnification is directly proportional to the difference in effective focal length, so you should treat a 100mm lens on a 1.6x body the same as you would a 160mm lens on a full frame body for camera shake purposes.

 

[Andrew Bichard]

Without IS, the rule of thumb for a 200mm focal length is a shutter speed of 1/200. Given that you use a 1.6x body (if I recall correctly), that should be adjusted to 1/320. At f/4.0, you can shoot in even bright overcast conditions with a reasonable ISO.

That is true, but it doesn't matter. Magnification is magnification. However you slice it, you are magnifying the errors from camera shake more with a cropped sensor than a full frame sensor and so you must hold the camera steadier to get back to the same sharpness. The difference in magnification is directly proportional to the difference in effective focal length, so you should treat a 100mm lens on a 1.6x body the same as you would a 160mm lens on a full frame body for camera shake purposes.

And, of course, if you have enough pixels and it is your intention to crop tight at the printing stage to enlarge your target even further, or to make big enlargements, you should use an even faster shutter speed than this rule of thumb would suggest as you will be increasing the blur as well as the image.

Andrew

 

[Charade]

deja vu? i'm sure this has come up a few times. the reason the 1/over rule includes the crop factor is you have to consider motion against the medium. yes, the focal length doesn't change, but the physical size of the recorded image does. so 'movement' as represented as a percentage of the total recorded image increases by a factor 1.6.

if you have a full frame camera and a long zoom, you can do a real world image test by taking a picture of the moon with a slow shutter speed and well stopped down aperture. you will see the moon moves farther across the recorded image on the crop shot than it does on the full frame.

If that's true, then the crop factor is also a magnification factor. When I think of crop factor, I think of a mask. Like taking a 5x7 matte and putting it on an 8x10 picture. The magnification didn't change. You just see a cropped portion of the 8x10 picture. However, if you want the 5x7 masked area to fill an 8x10 matte, you'll have to enlarge the image.

Again, if what you say is true, then why are there "DX" (digital only) lenses? DX lenses do not work properly on film SLRs because they mask (or vignette). It would be interesting to see what the picture looks like when a DX lens is used on a film camera.

Regarding your example of the moon shot. The moon movement distance won't be any different as long as you account for scale if the magnification factor doesn't change. If indeed the crop factor is also a magnification factor, then the movement will appear different using the same lens on a film vs. a digital camera (not full frame). However, if the magnification doesn't change, neither will the movement. If the movement is 5mm at 1:1 scale, then the movement will appear to be 10mm at 2:1 scale. Or 2.5mm if the scale is 1:2.

Or..... I could be completely wrong!!!

 

[Charade]

And, of course, if you have enough pixels and it is your intention to crop tight at the printing stage to enlarge your target even further, or to make big enlargements, you should use an even faster shutter speed than this rule of thumb would suggest as you will be increasing the blur as well as the image.

Andrew

Right but that applies to any camera. Personally, I'd take my chances with less optical and more post processing "zoom" if I couldn't get the shutter fast enough (or a lack of a stable support) to eliminate camera shake. It's a lot harder (or impossible) to work with an image if the image is blurry from camera movement vs. a slightly less raw pixel count.

IOW, I would shoot at 100mm vs. 200mm and the do a 200 percent post processing digital resizing/crop if I couldn't get the 200mm shot stable enough to eliminate camera movement.

 

[MarkBarbieri]

If that's true, then the crop factor is also a magnification factor. When I think of crop factor, I think of a mask. Like taking a 5x7 matte and putting it on an 8x10 picture. The magnification didn't change. You just see a cropped portion of the 8x10 picture.

I'll agree with you only on the condition that when a typical user moves from a film camera to a Rebel, they switch from 4"x6" prints to 2.4"x3.6" prints.

Let me walk through the process with two specific cameras to help illustrate my point. I'll use the Canon 5D and the Canon Rebel XTi.

With the 5D using a 100mm lens, an image is captured on the 1.41 x 0.94"sensor. With the Rebel XTi, using the same lens, an image is captured on a 0.87 x 0.58 " sensor. The image is different in that the the Rebel XTi has cropped the image generated by the lens, capturing only the portion that landed on the smaller sensor.

Now let's assume that both photographers decide to make 6 x 4" prints. The 5D photographer magnifies the sensor image 4.26 times to enlarge the sensor image to 6 x 4 inches. The Rebel XTi photographer magnifies the sensor image 6.90 times to enlarge the sensor image to 6 x 4 inches.

However, if you want the 5x7 masked area to fill an 8x10 matte, you'll have to enlarge the image.

That is precisely the point I'm trying to make in saying that the inverse focal length rule should be modified based on sensor size. At the point of capture, while the image is on the sensor, no magnification has occurred on the Rebel XTi. However, we don't tend to view images on our sensors. We enlarge those images with output devices (monitors, printers, etc). Because the sensor image is much smaller on the Rebel XTi, it is enlarged more when we view it. When it is enlarged, the shake blur is also enlarged.

So if the inverse focal length rule worked for you with film and you want to apply it to a non-full frame DSLR, you should either adjust the rule based on the increased magnfication you will be using to view your images or you should print smaller.

 

[Groucho]

Deja vu indeed.

Color me right in the middle on this one. I think the crop matters, but I do think that it's no different from actually cropping a larger image. If we take a digital photo and crop off the edges, we still say that it's the original focal length, even if 1/3rd or more of the original is removed. Furthermore, the sharpness of the focus is the same no matter how much you crop off. If your original photo was sharp, it's still sharp when cropped. If it was out of focus, it'll still be out of focus.

An out of focus picture may look a little better when cropped, though, as the smaller image will hide it. But I don't really buy that you need to use the same rule for shooting, say, a 400mm on a DSLR as you would a 600mm on a 35mm.

I think that the truth, as it usually does, lies somewhere in the middle.

 

[Groucho]

One other thing to remember is that we rarely look at the photos in their native resolution. At native resolution, you can be hypercritical of focus and sharpness, but much of that resolves itself when shrunk down to a more viewable size. Similarly, you probably won't notice such issues too much on a 4x6 print versus an 8x12 or larger.

There are just too many factors for one "rule" to cover everything.

 

[Charade]

I'll agree with you only on the condition that when a typical user moves from a film camera to a Rebel, they switch from 4"x6" prints to 2.4"x3.6" prints.

Let me walk through the process with two specific cameras to help illustrate my point. I'll use the Canon 5D and the Canon Rebel XTi.

With the 5D using a 100mm lens, an image is captured on the 1.41 x 0.94"sensor. With the Rebel XTi, using the same lens, an image is captured on a 0.87 x 0.58 " sensor. The image is different in that the the Rebel XTi has cropped the image generated by the lens, capturing only the portion that landed on the smaller sensor.

Now let's assume that both photographers decide to make 6 x 4" prints. The 5D photographer magnifies the sensor image 4.26 times to enlarge the sensor image to 6 x 4 inches. The Rebel XTi photographer magnifies the sensor image 6.90 times to enlarge the sensor image to 6 x 4 inches.


That is precisely the point I'm trying to make in saying that the inverse focal length rule should be modified based on sensor size. At the point of capture, while the image is on the sensor, no magnification has occurred on the Rebel XTi. However, we don't tend to view images on our sensors. We enlarge those images with output devices (monitors, printers, etc). Because the sensor image is much smaller on the Rebel XTi, it is enlarged more when we view it. When it is enlarged, the shake blur is also enlarged.

So if the inverse focal length rule worked for you with film and you want to apply it to a non-full frame DSLR, you should either adjust the rule based on the increased magnfication you will be using to view your images or you should print smaller.

Are we in agreement that the crop that we get on a APS sensor is caused just by the fact that the sensor is physically smaller than the film frame and not by any magnfication of the image before it hits the sensor?

If I take a piece of paper and cut a hole in it to mask out 37 percent of the last element (the one closest to the body) of the lens, I've effectively created the same thing as putting that lens (without the paper mask) on a DSLR (assuming a crop factor of 1.6). The film will just "see" 37 percent less of the scene and the same amount of the scene as the digital sensor will "see".

I understand fully what you're saying but where I think I'm losing you is that crop factor is just that. It's not a magnification factor that happens at the sensor. Magnification of the image to make the print output the same size happens during post processing. Of course any flaws in the image would also be magnified. But that happens with any lens/camera combination whenever you optically magnify the image that's dropped on the film or sensor. If you use different magnifcation ratios to get the prints to be the same size, you've introduced another variable. And of course the detail or flaws in the image that's been magnified (all other things being equal) will not be the same as the image that had a lower mag ratio.

IOW, to fully compare the output from a 5D to an Xti and eliminate the extra variable (the different mag ratios to get the prints the same size) you would have to compare a (approx) 5x7 print (from the 5D) to a 4x6 print from the Rebel. The scale would be the same. The Rebel print would just be a crop of the 5D print.

 

[MarkBarbieri]

It sounds like we are pretty close to agreeing.

Magnification of the image to make the print output the same size happens during post processing. Of course any flaws in the image would also be magnified.

I agree with this, but I see this as critical to the inverse focal length rule and you appear not to.

Magnification of the image to make the print output the same size happens during post processing.

Why do you think this is relevant? What difference does it make whether the magnification occurs before the image is recorded, after it is printed, or even by the observer moving closer to the image? The visual impact of motion blur the same regardless of how it is enlarged.

IOW, to fully compare the output from a 5D to an Xti and eliminate the extra variable (the different mag ratios to get the prints the same size) you would have to compare a (approx) 5x7 print (from the 5D) to a 4x6 print from the Rebel. The scale would be the same. The Rebel print would just be a crop of the 5D print.

I agree with this and agree that if you are comparing what shutter speed you need to take a reasonably sharp 5x7 with a 5D vs a 4x6 with a Rebel XTi, then you can use the same rule. However, if you are trying to determine what focal length you can hand hold for similar same sized prints, you need to compare the effective focal lengths and not the actual focal lengths.

Let me illustrate that point by bringing in a third camera, the Canon S3. It's sensor is 0.28x the size of a piece of 35mm film, so it has an effective focal length multiplier of 3.5x. It's longest physical focal length is about 120mm, which results in a 35mm equivalent focal length of 420mm. If we didn't need to adjust the inverse focal length rule, you could hand hold (without IS) at 1/120 of a second (using the inverse focal length rule). Try it sometime. You'll see that it is a hold lot more like trying to handhold a 400mm lens than it is a 120mm lens.

 

[jann1033]

uhummm, readers digest condensed version please then you may all continue your discussion .
so basically since i have a rebel xt, i am crazy to even think about general use of a 200mm lens without some kind of added stability, correct?

 

[boBQuincy]

uhummm, readers digest condensed version please then you may all continue your discussion .
so basically since i have a rebel xt, i am crazy to even think about general use of a 200mm lens without some kind of added stability, correct?

I don't think so, I sometimes use my 70-200 at 200 without a support and get decent images. Not as sharp as if I used a support, and they probably wouldn't look good at 13x19, but still decent and very useable.

Go for it!

 

[JR6ooo4]

TIME!

3 months 13 days 4 hours 12 seconds since the last Crop factor / camera shake discussion.

WHo picked the closest to that time in the betting pool?

John is holding the money.


MIkeeee

 

[Charade]

It sounds like we are pretty close to agreeing.

Good!


The implication made earlier in this thread is that the inverse focal length rule must be modified because of the crop factor. That's where we disagree. The addition of the crop factor doesn't change the focal length of the lens (nor it's optical magnification (same thing)).

You could also argue that the inverse focal length rule must be modified if you desire to print 16x20 prints from a film camera vs. a 4x6 from the same negative. If 1/300 will not produce visible motion flaws in a 4x6 print but might be visible in a 16x20 print, then the inverse focal length rule must be adjusted. I've never heard of that being suggested until the digital crop factor is brought into the discusion in this thread. The inverse focal length rule is a minimum setting rule for handheld shots. Put the camera on a tripod (another variable) and the rule doesn't apply as much any more.

Let me illustrate that point by bringing in a third camera, the Canon S3. It's sensor is 0.28x the size of a piece of 35mm film, so it has an effective focal length multiplier of 3.5x. It's longest physical focal length is about 120mm, which results in a 35mm equivalent focal length of 420mm. If we didn't need to adjust the inverse focal length rule, you could hand hold (without IS) at 1/120 of a second (using the inverse focal length rule). Try it sometime. You'll see that it is a hold lot more like trying to handhold a 400mm lens than it is a 120mm lens.

Well now you've brought up an interesting point. At 120mm, the S3 has the same magnification as a 35mm film camera with a 420mm lens. That's why your illusration is valid and I agree. The inverse focal length rule deals with camera motion blur intruduced by magnification. So the S3 would have a different rule than a 35mm camera system. It would be 1/the 35mm equivelent focal length.

 

[0bli0]

if the xti had 1.6x less pixels than the 5d, then yes... it would be merely a crop. but because this is not the case, the physically recorded detail resolves more detail of the camera shake. i completely that there is no difference to the focal length and that all things being equal and reasonably small (i.e. not blown up very large - say on a 4x6) it's not going to make much of a difference. but if you were to crop a 1000x1000 square of the 5d image and 1000x1000 square of the xti image, you will be able to notice any apparent camera shake more in the xti's image.

a so-called digital lens will work on a SLR (when they fit). i have used a sigma 30mm on a canon film body. it just vignettes at the edges. it does so on my 1dmk2, but far less noticeable.

 

[handicap18]

Jan, I would probably say that prime lenses 300mm and above would need a tripod for the majority of the people. Some people would need to use a tripod/monopod all the time for a 70-200mm f/2.8 whether it has VR/IS or not as it is a heavy lens. The 80-400mm lenses that Nikon and Sigma put out are very large. Not quite as long as the 70-200mm f/2.8's, but are thicker and heavier. Now that I look at it, the 200mm f/4 lens will probably need mono/tripod. Its really dependent on the person using the lens. Me being 6' 275 (and at one time a heavy weight lifter) can hand hold lenses that my DW, at 5' 4", wouldn't even think of touching.

Plus, I think that any lens that comes with a mono/tripod mount probably means that you should think about using a mono/tripod with it.