Need a lense advice:))!!! please.

Hello guys/gals, i currently have a Nikon D40
and my lense is 70-300mm Nikkor lense without an autofocus...
while the zoom is great, you have no idea how many pictures have to be deleted because they are simply out of focus!!!
My question to you is, do you know if these two lenses are any good? will they work and autofocus with my D40???, and whats the main difference between them:

Sigma 70-300mm f/4-5.6 DG Macro Telephoto Zoom Lens for Nikon SLR Cameras
Price:$99.95

and

Sigma 70-300mm f/4-5.6 DG APO Macro Telephoto Zoom Lens for Nikon SLR Cameras
Price: $170

Whats the APO??? lol and why is it priced higher because of it???
DO I EVEN NEED IT????

Thank you.

Quote:

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Originally Posted by RussK19

Whats the APO??? lol and why is it priced higher because of it???
DO I EVEN NEED IT????

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APO, short for apochromatic, gives better color correction, and reduced chromatic aberration.

From Sigma's website:

Quote:

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In order to attain the highest quality images, the APO lens has been made using special low-dispersion (SLD) glass and is designed to minimize color aberration.

SIGMA's APO zoom lenses minimize color aberration. As the refractive index of glass depends on the wavelength of light, color aberration occurs when different colors form images at different points. This problem often occurs with telephoto lenses, but the Special Low-Dispersion (SLD) glass and

Extraordinary Low Dispersion (ELD) used in SIGMA's APO lenses helps to compensate for color aberration, thereby allowing them to produce of sharp images.

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A thing to keep in mind with the Nikon D40 is that there is no on board autofocus motor (as you experienced with your Nikkor Lens). One thing I tell all my D40 friends is to make sure the lens youre buying has an autofocus motor!

Looking at the two Sigma lenses you mentioned, the Sigma 70-300mm does not seem to have an on-board focus motor, so you will have no autofocus. Check this link out on Sigma's site to give you an idea what to look for. The list on that site is somewhat expensive, but it does explain what to look for in Sigma's lineup.

Hope this helps!

Wanted to address the "are these lenses any good" part of your post. These lenses are consumer lenses which are fine but to get the highest image quality you need to shoot at a relatively high stop f/8 or higher.

Most lens don't perform well wide open and these lenses are more susceptible to this phenomenon.

I have a Canon 75-300 in the same price range and I couldn't figure out why my photos were so crappy until I started shooting at a deeper stop. Thankfully, our photography happens during the daytime outside!