lens extension tubes

yooperdooper

i am cosidering buying extension tubes for my lenses.i have a canon10-20mm usm efs 3.5-4.5 and a sigma 18-50 3.5-5.6 dc i woul like to shoot flowers closeup and i do not understand the other ways an extension tube would help.thanks john i have a 30d

ziggy53

yooperdooper wrote:

i am cosidering buying extension tubes for my lenses.i have a canon10-20mm usm efs 3.5-4.5 and a sigma 18-50 3.5-5.6 dc i woul like to shoot flowers closeup and i do not understand the other ways an extension tube would help.thanks john i have a 30d

As a very general rule zoom lenses do not work as well as prime lenses and extension tubes. I can recommend, for example, the Canon 50mm, f1.8 "plastic fantastic" as a fairly good lens to use with extension tubes.

It has to do with "convergence" and that is the property of a lens to converge the different wavelengths of light at the same point. Zoom lenses tend to have best convergence at a single distance from the back of the lens to the film plane. Zoom lenses also tend to have "image curvature" problems with different "back focus" distances.

Diopter accessory lenses, 2 element coated diopter lenses especially, are what I recommend for zoom use as a rule. The Canon 500D and 250D are very high quality accessory diopters with the 500D more appropriate for longer focal lengths and the 250D more appropriate for short focal lengths.

I personally use a 3.3 diopter Sony CU lens with the Canon 50mm, f1.4 and get pretty good close up results in my travel kit. For more magnification I add a Tamron F series 1.4x teleconverter and get approximately 1/2 life size.

I do not recommend the EF-S 10-22mm for macro/CU work because of the focal lengths and resulting magnifications (just not worth it.) You might try, however, reversing the 10-22mm zoom in front of the 18-50mm zoom and, if you like the preliminary results, purchase a reversing adapter to better couple those 2 lenses. Do be careful not to touch the fronts of the 2 lenses together.

The major redeeming feature about extension tubes is that they work with almost any lens made for your system. How well they work is another matter entirely.

Bob Atkins has a wonderful discussion here on macro and close-up (Canon related):

http://www.bobatkins.com/photography/eosfaq/closeup2.htm

yooperdooper

1+ 2+ 4+ 10+
today i purchased the 1+ 2+ 4+ 10+ set the extension tubes and the 250d and 500d were not in stock anywhere i checked.any insight into these?thanks john

ziggy53

yooperdooper wrote:

... the 250d and 500d were not in stock anywhere i checked.any insight into these?thanks john

B&H appears to have 3 of the 4 thread sizes available for the 500D:

http://www.bhphotovideo.com/bnh/controller/home?ci=0&sb=ps&pn=1&sq=desc&InitialSearch=yes&O=jsp%2Fworkaround.jsp&A=search&Q=*&bhs=t&shs=canon+500d&sb=ps&pn=1&sq=desc&InitialSearch=yes&O=jsp%2Fworkaround.jsp&A=search&Q=*&bhs=t&Go.x=0&Go.y=0&Go=submit

... and 2 of the 250D sizes:

http://www.bhphotovideo.com/bnh/controller/home?ci=0&sb=ps&pn=1&sq=desc&InitialSearch=yes&O=jsp%2Fworkaround.jsp&A=search&Q=*&bhs=t&shs=canon+250d&sb=ps&pn=1&sq=desc&InitialSearch=yes&O=jsp%2Fworkaround.jsp&A=search&Q=*&bhs=t&Go.x=0&Go.y=0&Go=submit

yooperdooper

thanks
thanks for ALL your help

yooperdooper

testing closeup lens set
yesterday i "experimented wit closeup lens set.i took about 75 pictures using all4.about 50% of the pictures were in focus. i think the ones that were in focus were taken from 6-inches. does this seem right?a few of the pictures came out very nic.i shot flowers.thank you john ps i used a 18-50mm f3.5-5.6 lensand a uv lens filter

ziggy53

yooperdooper wrote:

yesterday i "experimented wit closeup lens set.i took about 75 pictures using all4.about 50% of the pictures were in focus. i think the ones that were in focus were taken from 6-inches. does this seem right?a few of the pictures came out very nic.i shot flowers.thank you john ps i used a 18-50mm f3.5-5.6 lensand a uv lens filter

Close focus accessory lenses are designed to shift the infinity focus of the host lens to a closer focus distance. The diopter lens is really a lens in its own right and the Canon 250D is really a 2 element, 250mm lens. Likewise the Canon 500D is a 2 element 500mm lens.

Reverse mounting a photographic lens in front of another photographic lens can be a very high quality alternative.

To calculate the effective focal length, and the effective field-of-view, of a lens plus diopter combination it is probably easiest to add the diopter equivalents.

A +2 diopter lens added to a 50mm lens (where 50mm is 1000/50 or +20 diopters), is +22 diopters or 1000/22= about 45mm. More importantly, a +2 diopter is 500mm/19.7 inches, so the combination is equivalent to a 45mm lens which can focus to 19.7 inches.

If you want to deal with focal lengths the formula is 1/host-focal-length + 1/diopter-focal-length = 1/equivalent-focal-length. In the case of the Canon 500D on a 50mm lens that would be:

1/500 + 1/50 = .002 + .02 =.022

Inverting that (1/.022) yields 45.4545~mm or the same as the diopter based calculation (which is comforting.)

Adding the diopters 1+2+4+10 yields 17 diopters, so I would expect a close focus distance (with the host lens set at infinity) of 1000/17 or about 59mm/2.3 inches, however zoom lenses complicate the matter so 6 inches is possible.

Adding all of the diopters is also adding a considerable number of additional elements and potential distortion. If these are very high quality 2 element diopter sets then the quality may be OK, but probably not optimal. If these are inexpensive 1 element diopter lenses, you will probably see color fringing and some distortion increasing towards the edges of the image.

yooperdooper

thanks
thanks