Quick Question: Kenko EOS extension tubes

I'm gonna be getting a set of these tonight. I was just wondering what

magnifications it will give on my 1.6x sensor camera for various lenses I own.

I remember there was one of these online calculator things that will give the

answer but I can't find it on google. Anyone can provide a link please?

 

Quick Question:

 

With the extension tubes on, does the closest focusing distance become closer or

does the image received by the sensor just get bigger with the same focus distance?

Though it's a bit out of date (doesn't have recent lenses), this page might be of use - http://www.bobatkins.com/photography/eosfaq/closeup.htm

 

It gives magnification ranges with 12 and 25mm tubes along with working and focusing distances. For newer lenses in the same focal length range the numbers will be similar.

Try Julian Loke's calculator here: http://eosdoc.com/jlcalc/

To answer your 'Quick Question' - The closest focusing distance becomes closer (and so does the most distant - so you generally lose infinity focus). When you refer to 'the image received by the sensor just getting bigger with the same focus distance' - this is the action of a teleconverter, rather than an extension tube. The only exception is that there are some devices that do both (such as the Life Size Converter intended for use with the EF 50mm f2.5 CM)...

You focus closer AND your image gets bigger at the same time. Consider an extreme and impossible example with, say, a 50mm lens at a distance of 50mm from the subject. The image would focus on your focal plane at a distance of infinity (i.e. with an infinitely long extension tube. Magnification would be infinite. Considered another way, consider a slide to be the subject, a projector's lens to be a camera lens, and the projection screen to be the camera's focal plane. Get the idea? A 1:1 relationship exists between subject size and image size when the lens is twice the focal length from the focal plane and also twice the focal length from the subject. Not a quick answer, but I hope a helpful one.

can anybody weigh in on Canon versus Kenko, now in 2008. The old discussion threads for

this debate are VERY old...I am buying a 70-200 L USM. The salesperson is trying to convince

me that the Canon is not worth the extra 50$...any thoughts would be greatly appreciated.

So long as the extension tubes have all the electrical connections required, then, as far as I am concerned, it matters not which you buy. I got the cheapest available and they are just fine.<div></div>

Just bought the 3-piece Kenko set and I am quite happy with them.

 

Unlike teleconverters, there is no glass in these, so save the 50 bucks, I say.

 

--Jon

oh...i guess i am showing my ignorance.I didn't realize that I was asking about extension

tubes...i really wanted to know about the 1.5 tele extender..with glass. I guess I will search a

discussion group on that. Sorry guys, my apologies.

Thanks for all the feedback on the extension tubes. I got the set and seems pretty cool. One thing i noticed is that with the 12, 20, and 36mm all mounted together, it's really easy to put the focal plane inside the lens! What was cool was that with the 70-200 mounted, at 200mm, the closest focus is a few cm infront of the lens, but at 70mm, it's well behind the front element hehe.

 

Axel >> I seem to remember a discussion on there a few months back regarding Kenko teleconverters compared to the canon ones and that thread linked to tests shots that clearly showed that the Kenko produced slightly sharper images....and it's cheaper!

Thanks Weiyang...i will give it a try...it's only 150 dollars after all.

<I>So long as the extension tubes have all the electrical connections required, then, as far

as I am concerned, it matters not which you buy. </I><P>

 

Well.... maybe. I tried a set of cheap tubes, and when used in a stack with a heavy camera

there was enough flexing to interrupt the electrical contacts and generate numerous

ERR99 events. I could see them bend at the joints between tubes... not reassuring. This

happens to a much smaller extent with Canon tubes, and I've never had an electrical

problem with the latter.<P>

 

Also, the locking pin arrangement looked less secure than on the Brand C tubes. I didn't

have a problem, but one frequent poster here... I think Lester Wareham... mentioned that

he nearly dropped a 300/4 due to loose attachments in Kenko tubes. <P>

 

So yes, the Canon tubes are more expensive, but I think you do get what you pay for.