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Home: Video University Forums: Digital Photography for Videographers:
constant lenses

Shadow
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Oct 4, 2006, 11:39 AM

Post #1 of 7 (588 views)
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constant lenses	Can't Post

I realize that constant lenses are superior to the variable ones.
I am wondering what the main difference is with using the two. For example, the Sigma 50 - 200mm lens f4 - 5.6. What in the photo is going to be different with the variable lens? Obviously it isn't good in low light but is there a noticable difference throughout the picture if the lens is not constant?

Thanks
Heidi

Jenn M
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Oct 4, 2006, 11:42 AM

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Re: [Shadow] constant lenses [In reply to]	Can't Post

Hi Shadow,

My understanding is that with lenses like that - the apeture changes depending on the focal length. At 50mm, you can go down to f4, but at 200mm you can only go down to 5.6; thereby lessening your opportunity to get better DOF and not as good in low light.

Shadow
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Oct 4, 2006, 11:56 AM

Post #3 of 7 (583 views)
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Re: [Jenn M] constant lenses [In reply to]	Can't Post

Thanks Jenn
That makes sense. My friend has a lens that is 4-5.6 and we didn't know why sometimes we could get a lower fstop than others, I didn't realize that the zoom was what determined it. For some reason I had thought the photo would be somewhat off in some spots.

Thanks Jenn

:)
H

Postal Boy
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Oct 4, 2006, 2:14 PM

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Re: [Shadow] constant lenses [In reply to]	Can't Post

Clarity is the biggest thing. A zoom lense has a lot more glass in it to compensate for the varying zoom lengths (lense groups). A fixed lense has very precise lenses, and a lot fewer pieces of glass to cause distortion. In other words, it is "cleaner" and "more crisp" and allows more light through.

-Postal

WLR
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Oct 8, 2006, 11:53 PM

Post #5 of 7 (530 views)
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Re: [Shadow] constant lenses [In reply to]	Can't Post

In Reply To

What in the photo is going to be different with the variable lens? ANS: The size of the subject youre shooting. Also your shutter speed, which will change steplessly as you zoom the lens if you have it in automatice exposure. Obviously it isn't good in low light but is there a noticable difference throughout the picture if the lens is not constant? They are ok in low light. If you are worried about shutter speed, just temporarilly use a higher iso like 1600 or 3200.

Thanks
Heidi

Friends don't let friends shoot jpeg.

DarrenS
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Oct 9, 2006, 6:14 AM

Post #6 of 7 (525 views)
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Re: [Jenn M] constant lenses [In reply to]	Can't Post

Hi Jenn. That's true with less-expensive zooms but the higher-end ones offer a constant aperture at all focal lengths (ie. doesn't change as you zoom in or out).

Zooms are great for lower resolution cameras. You can't see a big enough difference in the images to warrant spending the hundreds (or thousands) more for a good prime. The convenience far outweights the sharpness/distortion/contrast factors in most cases. But higher-end cameras can capture the sharpness & contrast a good prime can provide. I have a 10mp Nikon D200 which has an amazing image processor (same as the D2X) and I'm certain even it can't record all the beauty one of my primes provides. The Nikkor 200mm f2 lens is very, very sharp and I'm pretty sure you'd need 16mp and a darn good image processor to even start surpassing the glass. But lenses stick around longer than bodies so this is a good thing. Like buying your kids clothes a bit big so they can grow into them :)

DarrenS
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Oct 9, 2006, 6:37 AM

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Re: [Shadow] constant lenses [In reply to]	Can't Post

Hi Heidi...I'm baaaack. Long time no talk. What's it been, two whole days now? :)

With a good prime you're going to get better contrast and color saturation as well as more sharpness and, as you said, more speed (usually). Also less distortion...or at least -more uniform- distortion (as opposed to the 'complex' distortion of many zooms). Complex distortion is almost impossible to fix. Well, at least I don't have the patience for it (it's not impossible, just impossible for me). It's kinda like a mixture of pincushion and barrel distortion in the same picture, in various places in the scene. I don't think photoshop can even do it to be honest, but I'm no expert. I think you need another software package to do it. Uniform distortion can be fixed pretty easily in photoshop. If you're shooting animals or people this usually doesn't matter as much as buildings or anything with straight lines. But I've seen some zooms make people look bad too, even when shot at an appropriate focal length (ie. approx 70mm on a nikon dslr). Nothing can beat a good prime. The only zoom I own is the cheapo nikon 18-70mm that came with my camera, but I have to admit it's one amazing little lens and I'm keeping it. Probaby the sharpest zoom with the best color/contrast I've ever used and it's only like 300 bucks! The zoom really bites, it 'bunches up' at the widest settings...but at that price who cares as long as the pictures are nice. It's small, very light and very handy for family functions.

Darren