"Digital" Lenses

[Beyblade]

I have a Sigma 70-200 APO EX f2.8, and it worked wonderfully with my D7, instant focus lock, and very sharp pictures. But now I mount it on my new 7D, the focusing has noticeably deteriorated. Seems to hunt a lot more in "difficult" scenes, and especially in low light ( say indoors ). Why ?

On the other hand I have the KM 28-75 f2.8 D. When used with my 7D, I always thought the lens was really mediocre, and couldn't understand why people were praising it so much. When fitted on to my D7, WOW ! the pics were much more vibrant and sharp, it appears. KM did say that this lens was made to work especially with its DSLRs. But question is - what does it mean, when they say "made to specially work" with its DSLRs ? What is in the lens that makes it work "specially" well with the DSLR ? On the same note, Sigma have lenses tagged DG, for digital cameras, but the non-DG can also work with DSLR. So again, what is in the DG, and how does it make a difference ?

:dunno:

 

[UY79]

I have a Sigma 70-200 APO EX f2.8, and it worked wonderfully with my D7, instant focus lock, and very sharp pictures. But now I mount it on my new 7D, the focusing has noticeably deteriorated. Seems to hunt a lot more in "difficult" scenes, and especially in low light ( say indoors ). Why ?

If you are talking about body only low light focusing, the D7 has a built-in near infrared AF-illuminator which the 7D lacks. Otherwise, with mounted flash, they should be the same in low light.

On the other hand I have the KM 28-75 f2.8 D. When used with my 7D, I always thought the lens was really mediocre, and couldn't understand why people were praising it so much. When fitted on to my D7, WOW ! the pics were much more vibrant and sharp, it appears. KM did say that this lens was made to work especially with its DSLRs. But question is - what does it mean, when they say "made to specially work" with its DSLRs ? What is in the lens that makes it work "specially" well with the DSLR ? On the same note, Sigma have lenses tagged DG, for digital cameras, but the non-DG can also work with DSLR. So again, what is in the DG, and how does it make a difference ?

:dunno:

You are comparing two different mediums here. There'll be slight differences. I still find that skin tones better on film than digital. And I prefer to use Velvia to take landscape over using my 7D.

Sigma's DG and Tamron's Di are examples of digital lenses which have better coatings for use with DSLRs as the CCD or CMOS are more reflective than film and may cause internal reflection. These lenses are with their better coating will improve the quality of image captured on film as well.

 

[UY79]

Forgot to mention that digital lense are designed to make light fall at right angle to the imager. This is to reduce light falloff caused by the digital imager.

http://www.tamron.com/lenses/di/di_slide1_di.asp
http://www.sigmaphoto.com/faq/faq.asp?navigator=3
Scroll down to question 6.

 

[TME]

Also to prevent shadowing from occurring when light hits the CCD at an angle resulting in hazy, less-than-sharp looking shots.

My experience is that the 7D's AF system is weaker than the 7... in terms of motor strength as well as speed and accuracy... so your experience with the Sigma is I think within specs...:think:

 

[Beyblade]

Thanks guys, for the enlightenment . :bigeyes: