What is the difference between the Tamron Autofocus 28-75mm f2.8 XR Di LD Aspherical (IF)

[glen]

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[996GT2]

The 28-75 Di is designed for full frame cameras, so if you mount one on a crop sensor camera like a Canon Digital Rebel it becomes a 44.8 - 120mm lens. The 17-50mm lens is designed with crop sensor cameras in mind.

 

[Zenmervolt]

Originally posted by: 996GT2
The 28-75 Di is designed for full frame cameras, so if you mount one on a crop sensor camera like a Canon Digital Rebel it becomes a 44.8 - 120mm lens. The 17-50mm lens is designed with crop sensor cameras in mind.

Close, but not quite.

Both lenses are affected by field of view crop. The 28-75 offers, on an APS-C camera, a field of view equivalent to a 42-112.5mm lens on a full-frame camera. (Those numbers assume the standard 1.5x crop factor, Canon uses a slightly smaller sensor with a 1.6x crop factor, and your numbers are accurate for Canon.) The 17-50mm lens, when used on an APS-C camera, will offer a field of view equivalent to a 25.5-75mm lens on a full-frame camera (again using a 1.5x crop factor instead of Canon's unique 1.6x).

The difference is in the size of the image circle cast by the lenses. The 28-75 casts an image circle large enough to cover a full-frame sensor, while the 17-50 only casts an image large enough for an APS-C sensor. If you use the 17-50 on a full-frame camera, there will be severe vignetting.

ZV

 

[ghostman]

Zenmervolt is spot on. You always multiply by the crap factor (1.5x for Nikon, 1.6x for Canon). Even the focal lengths of Canon's own EF-S line of lenses, made specifically for the smaller sensors, must be multiplied by 1.6. So an ultrawide Canon EF-S 10-22mm crop camera is actually similar to a Canon EF 16-35mm on a full frame camera. You can also put the Canon EF 16-35mm on the crop camera, but then it would become a ~25-56mm. You can't put a Canon EF-S 10-22mm on a full frame camera though.

To reiterate Zenmervolt's point, the Tamron 28-75mm has a field of view equivalent to a 42-112.5mm. The Tamron 17-50mm has a field of view equivalent to a 25.5-75mm. So the Tamron 17-50mm will still be wider if you mount both lenses onto camera with a small sensor (ie. Rebel XT, XSi, 40D...). The "Di" means digital in Tamron's terminology (it'll still work on film cameras) and the "Di-II" means it's meant for the smaller sensors. If you put the Di-II lens on a full frame camera, you'll see a lot of vignetting.

I have the Tamron 28-75mm for my XTi (with the 1.6x crop factor). It's an excellent lens and is great for portrait shots and filling the frame with the subject. I considered getting the Tamron 17-50mm as well, but then I'd overlap from the 28mm to 50mm range. Besides, my kit lens will satisfy the wide angle for now, but I hope to get an ultrawide angle lens one day.

 

[fuzzybabybunny]

Originally posted by: ghostman
Zenmervolt is spot on. You always multiply by the crap factor (1.5x for Nikon, 1.6x for Canon). Even the focal lengths of Canon's own EF-S line of lenses, made specifically for the smaller sensors, must be multiplied by 1.6. So an ultrawide Canon EF-S 10-22mm crop camera is actually similar to a Canon EF 16-35mm on a full frame camera. You can also put the Canon EF 16-35mm on the crop camera, but then it would become a ~25-56mm. You can't put a Canon EF-S 10-22mm on a full frame camera though.

 

[Muse]

Do these Tamron lenses not have image stabilization? I've been seeing a lot of positive comments about the Tamron lenses in this forum and wonder why. I've also seen it said that at least one of them is somewhat loud. Is image stabilization just not that important?

 

[ElFenix]

Originally posted by: Zenmervolt
If you use the 17-50 on a full-frame camera, there will be severe vignetting.

ZV

but probably only at the wide end.



in addition to the crap factor, depth of field is also affected. because the focal lengths of the lenses don't actually change, you also modify the f-ratio to find out the equivalent f-ratio for depth of field purposes. for a 4/3 camera with a 2x crap factor, add 2 stops, (so olympus's excellent 35-100 f/2 produces images equivalent to a 70-200 f/4 on a 5D). for nikon and sony the factor is about 1 and a quarter stops, for canon it's about 1 and a third stops.

none of that changes the exposure calculation, however.

Originally posted by: Muse
Do these Tamron lenses not have image stabilization? I've been seeing a lot of positive comments about the Tamron lenses in this forum and wonder why. I've also seen it said that at least one of them is somewhat loud. Is image stabilization just not that important?

tamron makes one or two VC lenses. no sonic motors though. then again, my 28-75 was 1/3 the price of canon's equivalent lens.

 

[ivan2]

Originally posted by: ElFenix
in addition to the crap factor, depth of field is also affected. because the focal lengths of the lenses don't actually change, you also modify the f-ratio to find out the equivalent f-ratio for depth of field purposes. for a 4/3 camera with a 2x crap factor, add 2 stops, (so olympus's excellent 35-100 f/2 produces images equivalent to a 70-200 f/4 on a 5D). for nikon and sony the factor is about 1 and a quarter stops, for canon it's about 1 and a third stops.

none of that changes the exposure calculation, however.

Sorry I am losing you, did you reversed the order of the above? I thought 5D is full frame.

 

[ElFenix]

Originally posted by: ivan2

Sorry I am losing you, did you reversed the order of the above? I thought 5D is full frame.

yes, the 5D is 135 format. a 4/3 camera with a 35 mm lens produces an equivalent angle of view (not field of view because of the different aspect ratio) to a 135 camera with a 70 mm lens. a 4/3 camera with a 100 mm lens produces and equivalent angle of view to a 135 camera with a 200 mm lens.

to get equivalent depth of field with a smaller format, you have to open the lens up more to get the same absolute aperture. 70/4 = 35/2. add two stops to the olympus, or subtract two stops from the 135 camera.

on a nikon dx you'd need 47/2.7 and on canon aps-c you'd need 44/2.5. (neither of which is made, btw)

and this is why 4/3 can't really say that the cameras and lenses are lighter and smaller. yes, they can be, but not if you want equivalent images. for example, the D300, D700, 5D, and E-3 are all about the same size.

a D700 with 70-200 f/2.8 (capable of producing much narrower dof than the rest of the combinations), weighs in at about 5.6 lbs.

a D300 with sigma 50-150 f/2.8 (slightly wider dof, but you'd need a chart to see it) is about 3.75 lbs (add about .3 lbs for IS, which this combination does not have)

a 5D with canon 70-200 f/4 IS weighs about 3.7 lbs, though the body isn't sealed and that would probably add some weight.

an E-3 with 35-100 f/2 weighs about 5.4 lbs. that's almost the same as the D700 with a lens that can produce another stop narrower dof. and it's not that much less expensive than the D700 and lens either. if nikon made a 70-200 f/4 VR the nikon kit would be less expensive and weigh less. the canon kit costs just a little more than the olympus lens alone!

want to complement that E-3 with a constant aperture standard zoom? $2200! and it's only f/2, not the f/1.4 you'd need to get the same dof as the $1100 canon 24-70 f/2.8. and there is no option for a 3rd party lens like a tamron or sigma for $350. the closer lens is a 28-70 f/4, but why do that when canon has an excellent 24-105 f/4 (for almost half the price of the olympus and with better range)?

granted, the 4/3 lenses are faster by two stops, but that would only help if a 135 sensor weren't two stops less noisy.

 

[randomlinh]

Originally posted by: Muse
Do these Tamron lenses not have image stabilization? I've been seeing a lot of positive comments about the Tamron lenses in this forum and wonder why. I've also seen it said that at least one of them is somewhat loud. Is image stabilization just not that important?

IS development is expensive. and they probably don't want to do it, given now sony/pentax/olympus have on body IS.

That and yes, it's not THAT important to some. It's definitely nice to have, but I can deal w/o it.

 

[Muse]

Originally posted by: ElFenix

Originally posted by: Muse
Do these Tamron lenses not have image stabilization? I've been seeing a lot of positive comments about the Tamron lenses in this forum and wonder why. I've also seen it said that at least one of them is somewhat loud. Is image stabilization just not that important?

tamron makes one or two VC lenses. no sonic motors though. then again, my 28-75 was 1/3 the price of canon's equivalent lens.

Yes, I just discovered the stickied (I think it's stickied) Canon lenses introduction/etc. thread and read the OP portion pertaining to Tamron lenses. They are there described as a best bang for the buck candidate if not winner. A little loud, not great build quality, but excellent optics, and very much cheaper than top tier lenses, say those by Canon.

Um, pardon my ignorance please, but what's "VC?"

 

[ElFenix]

Originally posted by: Muse
Yes, I just discovered the stickied (I think it's stickied) Canon lenses introduction/etc. thread and read the OP portion pertaining to Tamron lenses. They are there described as a best bang for the buck candidate if not winner. A little loud, not great build quality, but excellent optics, and very much cheaper than top tier lenses, say those by Canon.

Um, pardon my ignorance please, but what's "VC?"

vibration correction.