Camera N00b wrote:.
As an example lets I use Kenko Auto Extension Tube Set DG with Sigma17-70mm f/2.8-4.5 DC Macro. Sigma has minimum focusing distance of20cm (7.9") and maximum magnification of 1:2.3. What will be the newdocusing distance and magnification if I use 12, 20 & 36mm tubes? Howabout if I use all of them at once? What aperture can I use?.
Use any one of those tubes and the focus at infinity will be very close, likely within 12 inches. That seems like a lot, but remember that's at infinity, and measured from the sensor. Working distance will be a few inches..
You get 1:1 when the stack of tubes is equal to the focal length. Go much more than that with tubes and the working distance at infinity focus is somewhere inside your lens..
Finally, I know there are plenty of fake memory cards on ebay so isit safe to purchase tubes from ebay?.
Make sure the tubes have electrical contacts. Cheap ones often don't. Otherwise, as long as they are strong enough to hold the lens you are attaching to it, there's really very little difference..
Seen in a fortune cookie:Fear is the darkroom where negatives are developed..
Make sure the tubes have electrical contacts. Cheap ones oftendon't. Otherwise, as long as they are strong enough to hold the lensyou are attaching to it, there's really very little difference..
I actually meant purchasing Kenko from Ebay. Are there any fake Kenko extension tubes?..
You get 1:1 when the stack of tubes is equal to the focal length. Gomuch more than that with tubes and the working distance at infinityfocus is somewhere inside your lens..
So does this mean if my lens is at 20mm and I am using 20 tube than I will get 1:1? If this is the case what is the benefit in using more than 1 tube?..
Camera N00b wrote:.
You get 1:1 when the stack of tubes is equal to the focal length. Gomuch more than that with tubes and the working distance at infinityfocus is somewhere inside your lens..
So does this mean if my lens is at 20mm and I am using 20 tube than Iwill get 1:1? If this is the case what is the benefit in using morethan 1 tube?.
The reason is so that you can get 1:1 (or yet greater magnification) with longer f-lengths than a very short 20mm. The benefit of that is the increased working distance from the subject which means the subject is NOT inside your lens hood in which position it is very difficult to light !!.
Note 1: The preferred f-length for purpose built macros lenses is around 100mm or 120.... and it's because of the convenience of the longer stand-off resulting..
Note 2: Remember that proper macro type lenses are 'specially computed for their close-working role... so, whilst putting extension rings behind ordinary lenses allows them to focus closer, it does NOT turn them into high performance close up tools... [necessarily]..
Other cheap methods of getting extra macro power from ordinary lenses are.....
I) Supplementary close up lenses. The high grade ones with two elements are pretty good, and even single element ones are not bad by the time the main lens is stopped down to the smaller apertures that are necessary for maximising DoF..
Ii) A *reverse mounted* wide aperture (f/1.4 if you can get it) prime lens of 50mm on the front of a short tele (100mm or thereabouts) also acts as a high-grade high-power supplementary lens. Such 50mm "standard" lenses are still around and sold quite cheaply........ as are the double-screw rings that allow the two lenses to be mated together by their filter threads..
I mention these two methods because, in the absence of a specially designed macro lens, both i) and ii) above can yield better quality close-ups results than an unsuitable design of lens used with extension rings..
Hope this helps. Regards,Baz..
I'll go along with Baz and add that you can easily try it by borrowing a prime lens and holding it carefully (remember: it's your lens you'll damage) in front of the zoom lens..
BTW, people often say "macro" when they mean "close up". Macro means the image is full size on the CCD. To give some idea of the scale, here's a picture of a dead bee beside a dead CCD. The second picture shows the fur on the bee at 1:1 more of less (and slightly OOF)..
Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.
Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.
BTW (2), the fur was taken using a P&S and a microscope. Easily done and mentioned in a thread I posted a while ago to describe it (that was completely ignored)..
Regards, David..
Camera N00b wrote:.
You get 1:1 when the stack of tubes is equal to the focal length. Gomuch more than that with tubes and the working distance at infinityfocus is somewhere inside your lens..
So does this mean if my lens is at 20mm and I am using 20 tube than Iwill get 1:1? If this is the case what is the benefit in using morethan 1 tube?.
Although lens design has improved considerably over the years, a 20mm design, particularly a zoom, is likely to be somewhat lower quality optically than a dedicated macro lens, or even an ordinary lens of longer focal length - perhaps 50 or 100mm..
Of course with these longer focal lengths you would need more extension tubes to achieve the required magnification..
The other point is the lens to subject distance. As the lens is moved further from the camera body, the subject at the same time moves closer to the lens, to maintain focus. This can be very inconvenient, as it may physically obstruct the intended subject, frighten any insects etc., and block out the light source. So it is normally preferred that a macro lens has a longer focal length, to increase the working distance to the subject..
As was mentioned already, with a short focal length, it may be that the subject needs to be so close to the lens that it actually has to be closer than the front surface of the lens, i.e. actually inside the lens.Regards,Peter..
Hi Barrie,.
The reason is so that you can get 1:1 (or yet greater magnification)with longer f-lengths than a very short 20mm. The benefit of that isthe increased working distance from the subject which means thesubject is NOT inside your lens hood in which position it is verydifficult to light !!.
In my last post I typed 20 f length without really thinking. I am fairly certain I will end up purchase Sigma 17-70mm f/2.8-4.5 DC Macro or Tamron 17-50mm f/2.8 Di II LD Aspherical IF SP AF. The Sigma has 0.44 magnification with 20cm / 7.9 in closest focus whilst Tamron has 0.21 magnification with 0.27m / 10.6 in closest focus. Assuming they are at tele end, if I use 25mm extension tube what kind magnification will I get with these two lenses? How about working distance? I would really appreciate if you can answer these questions as it would greatly help me understand extension tubes..
I) Supplementary close up lenses. The high grade ones with twoelements are pretty good, and even single element ones are not bad bythe time the main lens is stopped down to the smaller apertures thatare necessary for maximising DoF..
Can you please provide names/links of good quality (2 elements) close up lenses? What magnification can I get with these?.
Ii) A *reverse mounted* wide aperture (f/1.4 if you can get it) primelens of 50mm on the front of a short tele (100mm or thereabouts) alsoacts as a high-grade high-power supplementary lens. Such 50mm"standard" lenses are still around and sold quite cheaply........ asare the double-screw rings that allow the two lenses to be matedtogether by their filter threads.>.
If I reverse mount Canon EF 50mm f/1.8 II with Sigma or Tamron lens I mentioned above what kind of magnification can I expect? Also, will the image quality be better than using extension tubes? Finally, can you please provide some links for double-screw rings suitable for Canon 400D as I couldn't find any at B&h?.
Hope this helps. .
Yes it was great help, thanks ..
Camera N00b wrote:.
I amfairly certain I will end up purchase Sigma 17-70mm f/2.8-4.5 DCMacro or Tamron 17-50mm f/2.8 Di II LD Aspherical IF SP AF. The Sigmahas 0.44 magnification with 20cm / 7.9 in closest focus whilst Tamronhas 0.21 magnification with 0.27m / 10.6 in closest focus. Assumingthey are at tele end, if I use 25mm extension tube what kindmagnification will I get with these two lenses? How about workingdistance?.
25mm extension on 50mm should give you around 0.66 magnification at infinity, on 70mm about 0.5 at infinity. Infinity focus distance will be around 9 inches (220mm) on 50mm and 12 inches on 70mm (300mm). You'll get a bit more magnification if you have enough working distance to focus a bit short of infinity..
Working distance depends on the depth of the body and the length of the lens. For example, if you are shooting with a Canon DSLR, the body is 44mm deep (sensor to lens mount, aka lens registration), and the lenses you are interested in are:.
Sigma 17-70: 82.5mmTamron 17:50: 81.7mm.
But of course those lengths are minimum. At longest focal length these lenses are longer. How much? Beats me. Let's add 30mm as a guess..
So for working distance we get:.
Sigma 17-70: 300mm - (44mm + 82mm + 30mm) = 144mm (about 6 inches)Tamron 17-50: 220mm - (44mm + 82mm + 30mm) = 64mm (about 2.5 inches).
I) Supplementary close up lenses. The high grade ones with twoelements are pretty good, and even single element ones are not bad bythe time the main lens is stopped down to the smaller apertures thatare necessary for maximising DoF..
Can you please provide names/links of good quality (2 elements) closeup lenses? What magnification can I get with these?.
Canon 250D and 500D. Here's the tables that come with them and Canon extension tubes. It'll give you a good idea of what kind of closeup performance you'll get, just find a lens with similar focal length:.
Http://www.bobatkins.com/photography/eosfaq/closeup.htm.
If I reverse mount Canon EF 50mm f/1.8 II with Sigma or Tamron lens Imentioned above what kind of magnification can I expect? Also, willthe image quality be better than using extension tubes? Finally, canyou please provide some links for double-screw rings suitable forCanon 400D as I couldn't find any at B&h?.
You really should reverse mount a 50/1.4, because 50/1.8 will vignette too much. A good choice is an old Olympus Zuiko 50/1.4, sharp and light. Light is a good thing, since most lenses, and especially consumer zooms, don't appreciate having weight hanging off their front threads. You should be able to find such a lens for around $50..
Reversing rings are available on eBay. Here's one that will work for the Oly lens (49mm), you'll need a step-up ring to bring the other side up to the size of your zoom..
Http://cgi.ebay.com/...3QQcategoryZ79000QQrdZ1QQssPageNameZWD1VQQcmdZViewItem.
50mm or even 70mm is a bit short for mounting the 50mm reversed. You'll start at over 1:1. A longer zoom or prime is a better candidate..
Seen in a fortune cookie:Fear is the darkroom where negatives are developed..
You were more specific than I could be about Canon marque.... I appreciate your stepping in. Regards,Baz..