Macro Extension Tube HELP

Hi everyone,

I am a new member and also an amateur photographer. I started a few months ago, and I am barely getting "gear up". I wanted to see if any of you could help with a problem I've been having with macro extension tubes. I recently bought a lens 55-250mm IS for canon, and I bought a really cheap macro extension tube, just to try it out. What I do before using the extension tube is, I set up the aperture on the lens to the highest, so I don't get much depth of field. The problem is that I actually do get a lot of depth of field on most of my pictures (happens mostly when I take pictures of flowers). Don't know if it is because is a really cheap extension tube, or I am missing something. Please let me know if there is something I am not mentioning to get help.

Thank you. :)

What focal length are you using on your 55-250mm? If you are on a long focal length and are standing well back from the subject you may well increase your depth of field (which you don't want). On a macro lens, a focal length of 100mm on f/2.8 and positioned close to the subject should produce a very blurred background. Extension tubes should reduce your depth of field as you are effectively getting in closer to the subject.

Quote:

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Originally Posted by BPhotography

What I do before using the extension tube is, I set up the aperture on the lens to the highest, so I don't get much depth of field

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When you say you set the aperture to the highest, what exactly do you mean?

If you mean that you set the aperture to the highest number (ie: f/22) then you are actually setting the aperture for the maximum depth of field. f/22 is the smallest aperture, but the highest number. A lot of people get this confused, and it is oftentimes more confusing to type about. I am assuming that this isn't the case, but figured it was worth mentioning so we didn't get 12 posts in and then realize the error... ;)

What 'really cheap' set of extension tubes did you buy? I haven't seen a set yet that doesn't still control the aperture on the lens, so I am confused by what you're saying about having to set the aperture first.

Additionally (and I'm sure others will correct me if I'm wrong) I believe that in general, Canon lenses do not stop-down the aperture when powered off - which if your extension tubes are not controlling the aperture signals is essentially how the lens is. In fact, I think Canon lenses stay at the widest aperture (I believe f/4-f/5.6 on that lens) at all times unless you're actually making the exposure or using the DoF Preview button. So if your tubes aren't able to pass through the aperture control signals, your lens should be defaulting to the widest aperture (shallowest depth of field) by default.

Hope this helps!

- Bill

There are some really cheap tubes, produced in China I think, which don't have any electrical contacts. This could be the problem here.

I haven't seen these tubes myself but a similar problem was raised on a wildlife forum that I use.

There is a workaround for setting the aperture with "contact-less" tubes.
Mount the lens directly to the camera body and specify the aperture required. Press the DoF preview button and hold it whilst removing the lens. The lens can then be mounted on the tubes and the aperture will remain at the desired setting.

Hope that helps

Bob