zoom vs. prime

I have what may be a dumb question but here goes. I have a Sigma 70-

200 2.8 lense and recently purchased an old Nikon 105 2.8. I've had

some trouble with camera shake on my balcony ambient light wedding

shots (could be due to a cheap tripod- I recently got a better one-

or mirror slap? I was using a cable release) Now, does my 105 2.8

let in more light or help me prevent camera shake more than, say, my

70-200 set at 105? Or is 2.8 just 2.8 on whatever lense is used?

Will the weight of the lense make a difference? Any suggestions

would be appreciated. I figured if anyone would know the answer to

this question it would be you guys.

Good question! Years ago, before zooms, movie cameras often had a three or four lens turret on the front. A quick twist allowed you to change focal lengths. The movie people noticed that not all lenses transmitted the same amount of light. Turning that turret might cause the next scene to come out a bit darker or lighter, even at the same f-stop. Several factors affect the brightness. No glass is 100% transparent and internal reflections being the two main ones. The movie folk started to get their lenses callibrated for actual light transmission, but used the f-stop scale progression, hence the name "T-stop". Your 105/2.8 might check out at about T-3.2 while that zoom, being a more complicated design with many more elements, might only measure T-3.9 or less! There are companies that will T-stop your lenses but it ain't cheap. Through the lens light metering pretty much does away with the need anyway.

Perhaps I should have added that yes, the camera will tell you to shoot (or pick a speed on auto) that is faster with the brighter 105 prime than with the dimmer image from the zoom set on 105.

The optical chareteristics (f-stop/amount of light passing throught the lens) between a zoom and a prime, at the same f-stop, have no bearing on motion blur, because the shutter speed will be the same.

 

The mecahnical differences between a given camera, lens, tripod head, leg set and environment (stability of what the tripod is sitting on and things like wind) will make a difference. In principal, attaching a heavier mass (big zoom lens) to the camera body, will produce less amplitude in vibrations due to the mirror and shutter movement. However, the whole camera, lens, tripod is not a perfectly rigid structure, and there is flex in a number of areas. For a bunch of reasons (technical term), it's easier to get higher amplitude, low frequency oscilations with a big heavy lens.

 

Bottom line: with a big/long heavy lens you need a more solid tripod/head than with a shorter lighter lens, even if they have the same focal length and aperture.

This isnt a lens question,but rather a shutter/film speed one.On a tripod in a church with available light and a normal lens,I never shoot people below 1/60th second.A longer lens,magnifies camera shake,so I would think that 1/125 or 1/250th would become necessary.This means ISO 800 or faster films.

Ok, if what Al said is correct then I have another question. For the sake of argument/understanding: If I take a handheld meter reading at the alter before the ceremony and then set both lenses/cameras side-by-side to the same settings, will the two lenses give slightly different exposures at the same settings, say 1/60 2.8?

With the two lenses set to the same f stop and the same shutter speed, the two exposures may be different. It will be a fraction of a stop, and you will not see it with print film. Exposure is much more critial for movies. A single scene can be made up of multiple takes and small changes in exposure will be noticeable.

You could wind up with differing exposures, but unless you're shooting digital or chromes,

you'll more than likely not see the difference.

 

It would be helpfull to know what shutter speed range you're in. Mirror slap tends to at it's

worse in the 1/10th to 1/30th range, but with a 200mm, this shouldn't be that much of an

issue unless your tripod was really nasty. Does your camera have mirror lock-up? Usually

for a ceremony, things move slow enough in the middle to be able to use mirror lock-up

with out a problem.

 

A dumb question, but did you use the tripod collar on the 70-200 or where you mounting

the camera? A 70-200 hanging off a tripod mounted camera is going to cause problems

even on a sturdy tripod.

There are a whole bunch of entries on T-stops. But essentially lenses don't all transmit the same amount of light at the same f-stop. The f-stop is just the relationship between the focal length and the diameter of the diaphragm opening. A 100mm lens with a diameter of 25mm is f/4. A 50mm lens with the same 25mm opening is f/2.

 

The air to glass surfaces of old (mostly pre WW-II) uncoated lenses can each reflect as much as 5% or so of the light hitting them. Thus complicated designs weren't practical. With coating, and then multi-coating, ever higher percentages of light got transmitted rather than reflected. To some extent lens designers took advantage of this with ever more complex lens designs, zooms for instance, so we still just get a percentage of the light getting through to the film. Also, glass is not 100% transparent. Some lenses might have well over an inch of glass between the subject and the film!

 

Then all lenses vignette a bit, with darker edges and corners than the center of the photo. This is most pronounced with wide angles, and stopping down the lens usually helps too. But the makers will tell you that it's an f/2.8 lens even if the edges are a stop or more darker wide open, and may even fudge the figures a bit, saying 2.8 when it's really 2.9, especially with off brand optics.

 

I just did a google search and came up with this: http://www.uemforums.com/2pop/ubbthreads/showflat.php?Cat=&Number=18649&Main=18298

I'm learning alot today. Thanks for all the help!

My last attempt at a balcony shot was at 200mm 2.8 1/30 and 1/60. I did have the tripod collar. I don't have a mirror lockup, unfortunatelty. But, now have a sturdier tripod and I might try the lighter fixed 105 lens. Maybe it won't magnify the camera movement so dramaticly.

Even if it isn't practical to worry about t-stops (so thats what its called!) with print film I feel alot better knowing its effect than not knowing.

Then there's the bean bag! You put the bean bag on the balcony rail, snug the lens barrel down into it, and shoot. I'm not pulling your leg on this one. It works! Make a nice big thick one, but don't stuff it too full. Light weight, easy to pack, and if business gets really bad, some molasses, a pot of boiling water...LOL. Seriously, they used to suggest this in the photo mags years ago for bracing a telephoto.

<i>Bruce Rubenstein , aug 06, 2004; 09:44 a.m.

 

 

With the two lenses set to the same f stop and the same shutter speed, the two

exposures may be different. It will be a fraction of a stop, and you will not see it with

print film. Exposure is much more critial for movies. A single scene can be made up

of multiple takes and small changes in exposure will be noticeable</i><p>

 

Bruce, movies are shot on color negative film with a similar exposure latitude to still

films. Color and density shifts between shots are corrected, shot by shot, when

printing. The one difference is that the "work print" or "dailies" (the print off the

camera negative that is used for editing/next day review) is not corrected shot by

shot. When millions of dollars are spent on the photography, the

cinematographer does not want to see much variation in the dailies. His/her job is at

stake!<p>

 

That said, the only really accuarte f-stop or t-stop on the lens is when it is wide

open. Once the iris ring is turned, the stops can vary by +- 1/3 stop and still be

considered "in spec".<p>

 

That said, I shot some footage with an old Canon FD 14mm lens with only f-stops

marked and the decrease in exposure was very obvious.<p>

 

Al is correct about the t-stops technically, but I'm not sure turrets had anything to do

with it. My guess is that it was the invention of the SLR movie camera that pushed the

lens away from the film plane and mandated more complicated lens designs. Or

perhaps it was the adoption of the zoom lens, which has a very noticeable light

transmition loss.<p>

 

-bruce

Here's a quote from over on the Leica Forum today:

 

>>>Ronald Moravec , aug 06, 2004; 01:08 p.m.

I keep thinking about a nice 350 4.8 as I like my 250 4.0 of similar design, but then the 400 6.8 is so nice to work with and goes on a visoflex too.

Glad you are happy. You will find it is 1/3-1/2 stop faster than indicated due to good light transmission.<<<

 

The 400mm f/6.8 consists of only one pair of elements cemented together! Bright and contrasty!

BG - Thanks for explaining the actual process in shooting a movie on film. I did not know that final matching was done in post production.