Extension Tubes... - DPChallenge Forums

06/18/2005 09:14:38 AM · #1

Thought I'd just share...

I've just recieved a set of Kenko Extension tubes. I got them cheap in an online auction, to keep me happy till I can afford a propper macro lens. I had a bellows for my old film SLR, and miss macro shooting.

So.. The Tubes look like:

With the 50 F/1.8 on the end of all three tubes. Gives roughly 1.8:1 magnification.

And you get:

For your efforts. That's full height in the frame, but cropped square...

A 100% crop. Check out the 'Fujitsu' naming.

The text of 'Fujitsu' is roughly .04mm high (.0016 inch). The specs and haze are probably from the quartz glass window over the chip. I'll have to find the old Pentium 166 I've got without it's metal cap, it'll be more photogenic!

And for something that most of you will be able to relate to, here's a full-frame shot of a US dollar bill, just scaled to give you an idea of the coverage..

I actually went hunting for a spider in the garage, but couldn't find any... Plenty of webs but nothing photogenic with more legs than me. :-).

Extension tubes are a great way to get into macro photography, and nowhere near as expensive as a macro lens. The down side is poor or no AF, and very, very, very small DOF to work with.

Cheers, Me.

Prof_Fate

06/18/2005 10:44:43 AM · #2

I got some really cheap extension tubes, so cheap they can't sue EOS lenses...so i got an M45 adapter and an old M45 Pentax 135mm F2.8 lens and m45-eos body adapter. All manual everyhting..but it works. I miss a prism to accurately focus (one can be had for the Rebel, but then you lose the pretty red lights when AF works...and for $200...perhaps when it is my backup body)

How do you get the math for the magnification? My cheapo tubes have 4 pieces and can be mixed and matched...

Your use of the 50mm 1.8 helps - nice lens!

here are some shots i took when i first got the bits (total investment about $60)

06/18/2005 07:23:55 PM · #3

Hi-ho,

I got the 1.8:1 from the wee manual with the Kenko tubes, as the example lens they have is a 50mm prime. Not sure how accurate it is.. Please hold.

If you wanna know acurately, take a photo or a ruler at your closest focus with a particular lens/tube setup. (Dramatic pause while I go take a pic)

You can see from this that I'm getting about 15.2mm across the frame (Metric steel ruler).

The sensor size is 22.5mm across, so the magnification is 22.5/15.2 or 1.48:1.

Comparing it to a FF sensor, it's effectively the same as 2.36:1 (36/15.2) which in anyones book is cool, and much higher than the documentation suggested.

To take this a little further, the per-pixel dimension in the image is 15.2/3504 (width/pixels) = 4.3379um. The text on the chip was 11 pixels high, which makes it 0.0477mm high on the chip, which wasn't far out from my original guestimate. :-)

Jacko posted a link to a site ages ago that actually had forumlae for working out magnifications etc, I thought I'd book marked it but can't find it now.

I'm just going to just make up a small table using the 'take a ruler photo' method, and keep a laminated copy in my camera bag along with the DOF & hyperfocal distance tables I use for landscapes.

Cheers, Me.

06/18/2005 07:27:08 PM · #4

Originally posted by Prof_Fate:

here are some shots i took when i first got the bits (total investment about $60)

Nice train shot... What scale? HO? I'll be mighty impressed if it's Z. :-).

The big problem with model train shots is the working distance, as you often can't get the angle you want as there are buildings scenery etc in the way. My Dad is a train nut, and I've seen the pain he will go to for a shot on his layout...

Cheers, Me.

Canon EF-S 15-85mm IS USM

06/19/2005 04:51:33 AM · #5

Hmmm, posting to my own thread again, that might just be sad..

Anyway, I got out into the great outdoors this afternoon, and only found one photogenic subject before the light gave out on me. Posted it to another thread:

//www.dpchallenge.com/forum.php?action=read&FORUM_THREAD_ID=226916

Cheers, Me.

LN13

Canon EOS-60D

06/19/2005 07:40:11 AM · #6

What's the difference between extension tubes and close-up filters. I know one goes behind the lens and the other in front. I'm asking about the functional differnces.

Would they be used in different situations? Trade-offs?

Jacko

Canon EOS-20D

Canon EF 24-70mm f/2.8L USM

06/19/2005 08:09:57 AM · #7

I have to get extension tubes for macro work, but also to use with my 17-40L. I saw some pretty funky shots taken with a wide angle lens and extension tubes. It lets you get closer to the foreground objects in a landscape shot. Very interesting look.

doctornick

Apple iPhone 13 Pro

06/19/2005 10:06:21 AM · #8

Originally posted by larryslights:

Close-up filters degrade the quality of the piicture since they are pieces of glass in front of your lens, extension tubes do not degrade the quality.

Three Kenko Extension tubes and the Canon 100mm f/2.8 Macro