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To the original poster - any particular lens (with or without an extender) does NOT "become" anything other than its actual focal length (an extender changes the actual focal length by its multiplier) when mounted on different format cameras.

 

A lens' focal length and aperture range does not change when it is mounted on a 35mm film camera or a DSLR with a "crop factor" (indicating that its sensor is smaller than a 35mm film frame).

 

The only thing that changes when using a particular focal length on cameras with different film/sensor formats is the field of view, and that is purely a function of the image capturing area built into the camera (film or sensor size).

First off, it sounds like you don't have enough light from your flash unit. Lose the silly diffuser. The Lightsphere and all other "tupperware" diffusers waste a lot of light by blasting it in all directions. If you do not have nearby reflective surfaces to return all that light to the subject's area, you have just lost the effectiveness of the flash unit.

 

Like others have said, you don't need a fast shutter speed to "stop action". The burst of light from the flash is far faster than your 1/640 second.

 

The easiest way to work would be to try the "P" exposure mode and just point your flash in the direction of the subjects. Use fully automatic mode on the flash unit. If you have a white wall or ceiling very near by, you could aim the flash to bounce the light off those surfaces for a softer look, but forget the "tupperware" for now.

>>>> Does a crop sensor SLR mean that an f2.8 200mm lens is 'slower' (as it's 320mm) or the same speed? <<<<

 

NOTHING about a lens' characteristics changes when you put it on different format bodies. A 200mm lens is still a 200mm lens whether it's mounted to a 35mm film camera or an APS-C format body like a Canon 30D. If the maximum aperture is f/2.8 it's always f/2.8 regardless of the format of the camera it's mounted to.

 

The only difference when you use a particular lens on different format bodies is the field of view of the captured image. An APS-C camera will record less of the image than a 35mm film camera will, for example.

You can set your 20D's shutter speed to 1/250 if you are connected to the AlienBees lights with a cable. The 1/125 caution in the manual is for larger and slower-to-fire studio lights. You can prove this easily. Shoot in a dimly lit space, with the room lit only by the AB lights. Try several shutter speeds, including faster than 1/250. When you get to the point of being too fast, you will see a black bar at one edge of the image.

 

One problem you may have outdoors is syncing all the lights together. The lights using their built-in slaves may not "see" the master flash. For this purpose, I use Wein Peanut slaves (Wein is the manufacturer, Peanut is the brand name for the specific slaves) on the end of the cords that came with the AB flash units. I aim the Peanut slaves at the master flash unit. That works great.

You want to make absolutely sure that you have backup equipment for a wedding. Even though you may not be getting paid for it as a professional, the bride would never again consider you a friend if there are no photos because your one camera failed.

 

Rent or borrow a spare camera and lenses.

Be sure that you don't make the mistake of being too close to the car using a wide-angle lens setting. Being too close will give you a distorted view of the cars. You want a medium telephoto focal length and a position for the camera that will give a "flattering" perspective of the cars. Being up in the air a few feet (like with the camera atop an 8-foot step ladder) would probably be a very good thing.

I always leave IS turned on - mode 1 - with my Canon 70-200 f/2.8L IS lens.

 

If I use it on a very sturdy tripod, the lens will detect lack of motion and disable the IS. However, if I turned it off manually and forgot to turn it back on after using the lens on a tripod, Murphy says that I would have needed it when it was off the next time I used the lens handheld.

David - I wonder how many folks will refuse to believe us? :-)

I've been reading a lot of mis-information in this thread about "distance compression" and variations of that topic. Every post that suggests that certain focal lengths do more or less "distance compression" are totally incorrect.

 

"Distance compression" is merely a perspective issue. Perspective, as related to the relative sizes of objects at different distances, is controlled by one thing and one thing only. That is the DISTANCE BETWEEN THE VIEWER (or camera) AND THE SUBJECT(S). This is an absolute and there is nothing that can change it. Here's an experiment you can do to prove it to yourself:

 

Find a scene with distant objects (mountains, distant city-scape, etc.) as well as objects that are moderately close to you (say ten yards or more) and objects in between them and the distant objects. Put the camera on a tripod and take a series of photos of the scene with a variety of lenses FROM THE SAME POSITION (don't move the tripod or the camera). Use a wide-angle lens, a "normal" lens, and whatever telephoto lenses you may have. A typical selection for a "crop" camera might be 18mm, 31mm, 55mm, 100mm, and 200mm. Now, print the shot from the longest lens. Using it as a reference, crop all the rest of the shots to include the same amount of the scene as the shot from the longest lens.

 

What you will have is a series of virtually identically-framed shots. Yes, the ones with the maximum cropping will have less resolution than the rest. However, all will have EXACTLY the same amount of "distance compression", to use the term that has been used above. In other words, the relative sizes of the near and far objects will be absolutely identical, as long as you took all the shots from the same location.

 

If you are a non-believer, I challenge you to try the experiment.

35mm film cameras have a film frame size of approximately 24x36mm, while the Rebel XTi has an APS-C sized sensor, measuring approximately 15x22mm.

 

When camera manufacturers started designing digital SLR's, they decided that they should be about the same physical size of their 35mm SLR's. For that reason, they concluded that they could use the line of lenses they already had for their 35mm SLR's on the new digital SLR's.

 

 

All lenses designed for 35mm cameras project an image circle onto the film that covers the 24x36mm rectangle. The 35mm camera records the portion of that image circle that is defined by the opening behind the shutter for the film (24x36mm in size). A digital SLR with an APS-C sized sensor only records the smaller area (approximately 15x22mm) of the image circle projected by the lens.

 

 

When you put a 100mm lens on a 35mm camera and take a photograph, then put the same lens on a DSLR such as the Rebel XTi and take the same photograph - same subject, same position for the camera - with the same lens, and then enlarge both photographs to the same size print (4x6 inches, for example), it will appear as though the photo from the Rebel XTi was taken with a longer lens. That is because the image recorded by the Rebel XTi was of a SMALLER PORTION of the image circle projected by the lens - cropped, if you will - compared to the image recorded by the 35mm camera.

 

 

The special lenses for the Rebel XTi (and other Canon APS-C cameras) are called the EF-S series. These project a smaller image circle, making the lenses less expensive to design and produce in wide-angle and extreme wide-angle formats. However, an EF-S lens set to 20mm will produce the exact same image as an EF lens set to 20mm. Focal length is focal length, period.

 

 

Now to the primary point that I want to make: A lens NEVER CHANGES ANYTHING when you put it on different format cameras. Focal length never changes. Aperture range never changes. The only thing that would change is the apparent field of view, and that change is not a function of the lens but it is a function of the size of the sensor or film that will record the image.

 

 

The "crop factor" has only one valid use. Here's an example: Joe took a photo of Mount Rushmore with a 35mm camera from a particular place using a 200mm lens. You want to replicate that photo with your Rebel XTi. What focal length do you need to do that from the same location that he took his photo? Divide the 200mm by 1.6 and you get the answer - 125mm. The "crop factor" is a REFERENCE between the two formats that lets you compare the field of view of particular focal lengths between the two formats. The "crop factor" is always given assuming that the 35mm format (24x36mm) is the reference master.

 

This link:

 

http://photography-on-the.net/forum/showthread.php?t=45388

 

will take you to an area of another forum that has many discussions of the Crop Factor issues. There are some excellent visual aids which will help you understand as well.

>>>>by Walang PangalanL Strange: these "canned air" products are used to clean electronics without any noticeable problem. Is your statement backed up with a plausible physical mechanism or actual evidence? Nevertheless, it is important to follow the directions on the can, which usually read "never shake or invert prior to use". It's also a good idea to allow a second or so of flow to clean out any residue before directing the jet into intended use.<<<<

 

I have seen cans marked with messages that the fluid in "canned air" products can and will damage things like the mirror surfacing and other delicate items inside cameras if you get the liquid on those surfaces. The fact is that the stuff is not safe for delicate plastics and I would not trust it around lens coatings.

 

Rather than screwing around with the "canned air" products, it is much safer to just use a decent squeeze-bulb blower to clean cameras.

You can NOT use a Speedlite flash in automatic exposure mode and any other flash units at the same time. The reason is that the combination of camera and Speedlite calculate the exposure based on the Speedlite's pre-flash, then the Speedlite is triggered for a duration based on the calculation. If you have another flash source going off at the same time as the main Speedlite flash, the result will be overexposure.

 

If a Speedlite and a flash connected to a PC terminal (such as on a 20D) do in fact trigger in sync, the Speedlite and the camera MUST be set to fully manual mode.

First off - NEVER EVER USED "CANNED AIR" around cameras. The stuff in those cans is NOT AIR. If you managed to get droplets of the liquid on certain parts of the camera, you can have permanent damage.

 

Here's the age-old method to clean lenses:

 

Quality lens tissue (such as that sold by Kodak), a good lens cleaning fluid, and PROPER TECHNIQUE is the way that I have cleaned my lenses for decades. What is "proper technique"?

 

First - the goal is to clean the lens (or filter - I would use the very same process) without grinding any dirt/debris into the lens. To me, this absolutely dictates single-use surfaces for anything that touches the lens. That's why I use lens tissues instead of a washable cloth or - particularly - something like a lens pen.

 

Here are the steps that I use to clean a lens:

 

1. Use a squeeze-bulb blower to blow any loose dust off the lens. 90% of the time, step #1 is all that is necessary.

 

2. Take a lens tissue out of the pack. Fold it once, holding only what was the ends of the tissue. You want to be extremely careful to NEVER TOUCH the areas of the lens tissue that will be touching the lens. This will avoid transferring oils from your fingers to the lens.

 

3. Moisten the folded portion of the lens tissue with a little lens cleaner. You don't want the tissue dripping wet, but it must be damp.

 

CAUTION: NEVER apply lens cleaner directly to the lens (though it won?t hurt a filter, you don?t want liquid leaking into the lens? innards).

 

4. Wipe LIGHTLY across the lens ONCE with the damp tissue. Then either turn it over or fold it so that you can wipe again, but with an unused surface. You can do this as often as needed, as long as you never wipe the lens twice with any surface of the tissue. This prevents scratches. Again, make sure you never touch an area of the tissue that will touch the lens.

 

5. Ensuring that the lens is actually clean, use a dry tissue, handled the same way as above, to wipe the lens dry. Since you have already removed the dirt, there's no risk of scratching the lens with the dry tissue.

 

6. Dispose of the used lens tissues in a proper trash receptacle.

 

That's it in a nutshell. Simple and effective. I've been cleaning my lenses this way for over 40 years, and all of them have pristine glass (and none have ever worn "protective" filters).

You could support the cable ABOVE you and the equipment. Depending on your situation, you could suspend strings from the ceiling, use something like lighting stands, or many other ways to support the cable above the camera and computer. Of course, a very simple way would be to have the camera and computer mounted on a single roll-around fixture in the studio.

Additional thoughts:

 

Use fully MANUAL exposure control in the camera. No camera exposure automation at all will work with studio flash lighting. No special camera functions or settings will do anything for you. Set the shutter speed at 1/250 or a little slower (you've already done the experimentation there). Changing the shutter speed any further (to slower values, that is) will have NO effect on the flash exposure.

 

Turn ambient lighting in the area down so that the flash sources provide the only effective lighting.

 

Like Chris said, turn your ISO setting down to the lowest possible setting.

 

Beau's comments about light quality (softness, etc.) vs distance between lights and subject are very true.

You cannot use any studio flash with shutter speeds faster than the "max sync speed" that the camera is designed for. At shutter speeds faster than the "max sync speed", the second shutter curtain/blade starts covering the film/sensor before the first one has travelled all the way across (uncovering the film/sensor).

 

There's no way around this issue with focal plane shutters.

 

Essentially, changing shutter speeds to any value slower than the "max sync speed" has no effect on the flash exposure. That's because the duration of the flash pulse is extremely short compared to the shutter speeds. Very slow shutter speeds may allow ambient light to have an effect on the exposure, but they will not change the flash exposure.

 

If you want to use wider apertures with your flash units, turn the flash output down. If you cannot do that, move the flash units further from the subject or use softboxes or some other diffusing panels to further reduce the light.

For an APS-C camera, the ideal starting lens for portrait work would be the EF 50mm f/1.4 lens. It provides the same field of view as an 80mm lens mounted to a 35mm film camera, and the 80mm lens has been a classic recommendation on a 35mm film camera for conventional waist-up portraits for decades.

All of the digital Rebel series use mirrors in the viewfinder optics rather than the much better pentaprisms used in the 20D/30D/5D series.

 

The Rebel bodies are far different from a construction point of view and the controls when compared to the 20D/30D/5D series.

 

The 5D is essentially similar to the 30D except for the size of the sensor (and the mirror/focusing screen, of course), but is radically different from the Rebel series.

 

Even the 5D, though, is a far cry from the 1-series cameras when it comes to the construction.

>>>I gather from previous posts that when a lense is mounted on an xti there is a multplyer of about 1.6 added to the effective lense length. Is this correct? Is this a function of all digital cameras or only the ones with the smaller sensors? Is this true for all lenses, the EFS and the EF lenses. I recently purchased an ef 70-200 f2.8L usm lense and a 2x extender. Does this mean that at full zoom with the extender I have an effective zoom of >600 mm?<<<

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Mike, the "crop factor" is a VERY misunderstood thing by a great many folks who are new to photography. If you have no experience with 35mm film cameras, you can virtually forget that it exists.

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The actual focal length of any lens is ALWAYS what is printed on the front ring of the lens (within tolerance limits for the manufacturers, that is) and it never changes based on what camera you fasten the lens to.

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Focal length does not change with different designs of lenses either. By that, I mean that a 50mm EF lens and an EF-S zoom set to 50mm will provide the same image in the same camera.

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The ONLY purpose for the "crop factor" is to compare the FIELD OF VIEW between various camera formats. A camera's format is the size of the film frame or the size of the digital sensor in the camera.

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Click on <a href="http://photography-on-the.net/forum/showthread.php?t=45388">this link</a> for a decent explanation of "crop factor" with some graphic illustrations, etc.

>>I guess I'll light the background with my incandescent Floods<<

 

That's not a good idea because of the very different color of the light - unless you want the yellow/orange color on the background.

The problem is that the lights change both intensity and color at a rate of 120 times per second (in the U.S. where power frequency is at 60Hz).

 

The solution is simple. Shoot at very specific shutter speeds - 1/120, 1/60, 1/30, 1/15, etc. Each of these shutter speeds will allow the frame to be exposed for at least one half-cycle of the power or multiples of a half-cycle. Then you will get uniform light intensity and color from shot to shot.

 

The only other solution is to use flash lighting sources that are powerful enough to over-ride the lighting in the facility.

Bugger - WHEN WILL WE BE ABLE TO EDIT POSTS?

 

I meant Robin above, not Ron.

Ron was probably confusing folks talking about field of view when I believe he was talking about how LARGE the image in the viewfinder seems. Nothing would change the field of view in the viewfinder (except changing lenses, of course), but optics in the viewfinder can make the image that you see with the eye be any size the designer wanted it to be.

 

With the smaller sensor and thus the corresponding smaller focusing screen, there's only so much light available in the image seen by the viewfinder. If you make the viewfinder image larger, it will be dimmer. The Rebel series of SLR's use mirrors instead of a prism which further reduces the light to the viewfinder. This is why the images through the viewfinder are intentionally smaller than what we used to have in our film cameras.

 

That said, the viewfinder in my 20D is quite acceptable.

>>>From what I understand to this point, a 1.6 crop sensor (such as is on my Rebel XT) effectively lengthens your lens. So (correct me if I'm wrong), a 100mm lens becomes a 160mm on the XT and a 10mm would become a 16mm. (good to this point?) If you put those lenses on a 5D or other full frame, you would get what the lens says--either 100mm or 10mm.<<<

 

Tyler, the focal length of a lens NEVER CHANGES when you put it on various cameras with different film/sensor formats (sizes). NOTHING about a lens changes. The only thing that changes is the field of view, and that is a function of the camera's format combined with the focal length of the lens.

 

In other words, a 100mm lens DOES NOT BECOME 160mm when you put it on an XT. This cannot be stressed enough.

 

Many people have been confused enough that they believe that the focal length of Canon EF lenses magically change to some other focal length (published focal length times the "crop factor") while EF-S lenses, which are designed for the APS-C cameras like the XT, do not change. This is absolutely wrong, of course. Again, focal length is focal length and that never changes. Apertures (or aperture ranges for zoom lenses) never change either. The characteristics of a particular lens are permanent for that lens.

 

This is a properly worded statement that defines what does happen regarding the "crop factor": A 100mm lens on an XT has the same field of view as a 160mm lens on a 35mm film (or "full-frame" DSLR) camera.

You should check the trigger voltage before using the flash unit. Turn on the flash and measure from the center pin on its hotshoe mount referenced to the contacts at the side.

 

I think the switching circuitry in the 30D is rated for 250 volts, but you want to be absolutely sure before using the flash if it has a trigger voltage much over 6 volts.