My lens is not focusing with extension tubes

[Crease123]

I have a Nikon D40 with a Tamron 18-250 lens. Because of the reef hobby, I recently purchased a set of extension tubes from Zeikos (link: http://www.amazon.com/gp/product/B003IVZVDO).

When I try to take a picture with the lens with the extension tubes, the auto-focus does not work properly. I tried to manual focus as well, but it does not work. Any advice here please? I'm dying to take pictures of my hermit crabs.

 

[BlueCorn]

Using extension tubes can be challenging. Achieving focus is often a combination of manually adjusting focus/zoom and the physical distance between you and your subject.

 

[Crease123]

Using extension tubes can be challenging. Achieving focus is often a combination of manually adjusting focus/zoom and the physical distance between you and your subject.

No matter how much the lens try to auto-focus, or me manual-focusing, we do not even come close to achieving a well-focus shot.

 

[BlueCorn]

Using extension tubes can be challenging. Achieving focus is often a combination of manually adjusting focus/zoom and the physical distance between you and your subject.

 

[Misled]

As Doug said,

Achieving focus is often a combination of manually adjusting focus/zoom and the physical distance between you and your subject.

And from what the ad says, they are made for AF, which means you need a motor in the camera body for auto focus, which the D40 doesn't have. The auto focus for your lens has the motor in the lens. Most of what I said is a guess since the link doesn't give much info.

 

[Misled]

Try setting the lens at about 100mm, and get within 4 or 5 inches from the subject. I'm taking for granted you have all three tubes on.

 

[Crease123]

Try setting the lens at about 100mm, and get within 4 or 5 inches from the subject. I'm taking for granted you have all three tubes on.

Im kinda new at photography, what do you mean by setting the lens at 100mm?

I tried moving a wide range of distance from the subject, but the focus is still not right. I'm wondering is it because I'm using a Nikon D40, which do not have AF motors in the body? My lens does have AF on itself though.

 

[swjim]

Look at the numbers on the side of the lens that range between 18-250 and set it to somewhere around 100, that's what Misled meant by setting at 100.

The depth of field will be very thin with tubes and the focus point will be much closer to the lens than you're used to without the tubes. Just to get an idea I would set the camera on a table and look through the viewfinder, you should see a very thin part of the table that is in focus. That is the depth of field you have to work with. Try moving a small object into that area and practice taking some shots. From there you can manually use your focus ring on the lens to move the focus point forward or backward. Moving the focus area closer will reduce your depth of field, moving it further away will increase it. You're shooting digital so don't be scared to experiment, it won't cost you anything.