extension tubes? and macro ring flash for d90

[n00g33]

Hi APers!

I'm getting into more dental photography at work. Right now I've got a 17-55mm 2.8 with an on camera flash that I've been using. I need to crop all my photos but it is sufficient for now.

I'm thinking of getting some extension tubes to let me get in closer. Anybody know how much it will crop the photo when I add a set of kenko tubes at 50mm? I'd rather not get another lens if I can help it. Was thinking something cheaper like a sigma 70mm if that was the case.

I also need a ring flash. I'd like an actual ring so I can use it for portrait fill - not just one of those 'close up' photography ones. Suggestions and user reviews needed please.

Thanks

[arthurking83]

I would seriously reconsider the rather not get another lens attitude firstly.

Having a proper macro lens shouldn't be underestimated to begin with.

Extension tubes on a lens don't always go well together, and this could be due to the limitations of the lens's ability. Not all lenses have an ability to focus closely AND produce quality results, but a well known high quality macro lens usually does!

If it's a D90, then there are many high quality lens options to go with for reasonable money(less than $500) and they'll all give you very high quality results in a more consistent manner!

The use of Nikon branded extension tubes will not allow AF or metering, so you have to shoot more frames to get less usable images.

Kenko make sets of extension tubes that at least allow for metering, not sure if they allow AF tho.

[Speedway]

I have these (http://stores.ebay.com.au/LinkDelight-Photography-Aus-Shop/Macro-Tube-/_i.html?_fsub=7870251&_sid=348023981&_trksid=p4634.c0.m322) both the AF and non AF for my canon (Nikon mount listed). The AF ones although dearer are the ones to get as they allow full AF, IS and aperture control and are less than 1/2 the price of the kenko ones. These (http://stores.ebay.com.au/LinkDelight-Photography-Aus-Shop/Others-/_i.html?_fsub=7870252&_sid=348023981&_trksid=p4634.c0.m322) are also available from the same site and although not a true flash give good results for very little outlay.
Keith.