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Old Jan 10, 2007, 9:01 AM   #1
JMJ
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Okay, first post.....here it goes

I have been searching and searching the forums and havenot been able to get a good solid hit on what I am looking for. Maybe my search terms are flawed, because given the size of these forums I'm sure this has been answered, I just can't find it

I'm trying to find the advantages of using a digital SLR lense instead of a film lense on a Rebel XTi. I understand how the lens multiplier effects the focal length of a lense and I know what it will do to my images, but I just can't seem to find anything in regards to the digital SLR lenses. I am definitely not against reading, so if you are someone who has posted something on this, if you could provide a link I would REALLY appreciate it

Thanks!
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Old Jan 10, 2007, 9:37 AM   #2
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'Digital' lenses have a newer optical coating to reduce the reflection off the sensor (which is much more reflective than film). This reflection would bounce up to the rear lens element and then back down to the sensor resulting in a magenta *spot* in the image.

Some lenses have also been redesigned to yield a more perpendicular path of the light rays exiting the lens (mainly wide angles, I think). Some lenses exhibited some degree of vignetting and this redesign minimized that.

However in practical terms, most *old* film lenses work just fine on a digital SLR, but some lenses are also known to be particularily problematic.

I have about 8 lenses, only one of which is a newer *digital* design. All of my lenses are problem free.
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Old Jan 10, 2007, 10:03 AM   #3
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Also on top of what Amazingthiland said a lot of the digital lenses like the Canon EF-s, Sigma DC, Tamron DI-ii can only be used on small aps-c sensor cameras like the drebel/30D.
They have been "optimized" to only produce an image circle large enough for these small sensors. This makes them physically much smaller and lighter in weight:!:

The standard lenses work on both aps-c and full frame sensor cameras, with the benifit on the aps-c of them only using the center (the sweet spot) of the image circle so they actually tend to perform better on them than on the full frame camras:idea:


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Old Jan 10, 2007, 10:04 AM   #4
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amazingthailand wrote:
Quote:
'Digital' lenses have a newer optical coating to reduce the reflection off the sensor (which is much more reflective than film). This reflection would bounce up to the rear lens element and then back down to the sensor resulting in a magenta *spot* in the image.

Some lenses have also been redesigned to yield a more perpendicular path of the light rays exiting the lens (mainly wide angles, I think). Some lenses exhibited some degree of vignetting and this redesign minimized that.

However in practical terms, most *old* film lenses work just fine on a digital SLR, but some lenses are also known to be particularily problematic.

I have about 8 lenses, only one of which is a newer *digital* design. All of my lenses are problem free.
Excellent, thanks for the reply!
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Old Jan 10, 2007, 10:08 AM   #5
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PeterP wrote:
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Also on top of what Amazingthiland said a lot of the digital lenses like the Canon EF-s, Sigma DC, Tamron DI-ii can only be used on small aps-c sensor cameras like the drebel/30D.
They have been "optimized" to only produce an image circle large enough for these small sensors. This makes them physically much smaller and lighter in weight:!:

The standard lenses work on both aps-c and full frame sensor cameras, with the benifit on the aps-c of them only using the center (the sweet spot) of the image circle so they actually tend to perform better on them than on the full frame camras:idea:

Thank you. I think I'll get the camera and go to a shop and try different lenses. Download the imagesto my computer and check them out. At least that will give me a good idea of any problems I might encounter.
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Old Jan 10, 2007, 2:27 PM   #6
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Also keep in mind that in general new lens designs from about the mid 1990's have been done with significant computing power input into the design.

They just tend to be optically better. And of course all the digital lenses are very new in their design.

It just so happens that most of the new lenses being designed today are digital lenses.

Comparing the MTF charts for the humble and much-maligned kit lenses (Yes even the Canon 18-55!) against the older film lenses is quite interesting. Even though they may be relatively cheap and nasty they still are often significantly sharper than many of the older designs which were well thought of in their day.
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Old Jan 10, 2007, 3:21 PM   #7
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Yes very true.

I guess you really have 3 lens types to look at:
The old film based FF lenses.
The new FF lenses optimized for digital.
and the digitally optimized aps-c lenses.


Tamron designation is DI for FF digital, and DI-ii for aps-c digital.
Sygma is DG for FF digital , and DC for the aps-c.

Not actually sure what Canon uses. They have EF for FF and EF-S
for aps-c. But nothing I can see to indicate a FF is digitally optimized.
Their DO lens is interesting, but that stands for diffractive optics I believe :-)

:? :? :? TOo many acronyms :?:? :?
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Old Jan 11, 2007, 9:47 AM   #8
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PeterP wrote:
Quote:
Yes very true.

I guess you really have 3 lens types to look at:
The old film based FF lenses.
The new FF lenses optimized for digital.
and the digitally optimized aps-c lenses.


Tamron designation is DI for FF digital, and DI-ii for aps-c digital.
Sygma is DG for FF digital , and DC for the aps-c.

Not actually sure what Canon uses. They have EF for FF and EF-S
for aps-c. But nothing I can see to indicate a FF is digitally optimized.
Their DO lens is interesting, but that stands for diffractive optics I believe :-)

:? :? :? TOo many acronyms :?:? :?
Too many acronyms is an UNDERSTATEMENT! :lol:

I'm going to read this several times and let it soak in. I'm still not quite sure what lense I really need......A guy in a store recommended one to me (Tamron 18-200 mm AF F/3.5-6.3 XR Di II)as a good overall lense, i'm going to have to keep poking around the forums here......tons of good info and not enough time to absorb it all!

Thanks again for all your input everyone.
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Old Jan 11, 2007, 10:50 AM   #9
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one other thing to add:

this may or may not be important to you, but I also like to consider build quality when I buy a lens. One of the things that bugs me about Canon right now is they are creating a number of EF-S lenses (designed for aps-c sized sensors) but I believe they are all still plastic lenses. There is something to be said for the durability of a metal lens.

A year and a half ago, my Canon 100-400 lens was knocked off a bench onto cement. The lens is a very nice metal constructed lens which now has a slight dent. The lens still functions perfectly - no problems. I would be concerned that a similar lens made from plastic may not have survived. And, at least with Canon, they aren't making their EF-S lenses cheap - you pay an arm and a leg for them. Third party lenses dessigned for APS-C are less expensive, but if I'm paying $800 or $1000 for a lens I would prefer a good build quality to it. Hopefully the APS-C style lenses will eventually get good build quality to go with the good optics - but right now,I think they're all still plastic.

Just another thing to consider. Again it may not be important to you.
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Old Jan 11, 2007, 12:16 PM   #10
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JMJ wrote:
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A guy in a store recommended one to me (Tamron 18-200 mm AF F/3.5-6.3 XR Di II)as a good overall lense
I think the most popular starter lens for Canon shooters is the Canon 17-85 IS USM, but honestly, I would probably go with this Tamron 18-200 or its Sigma counter part. Sigma also is planning to release an 18-200 with their version of IS.






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