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Old Jan 2, 2010, 4:26 PM   #21
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bigdawg, Very nice pic's. Thats something I Haven't been doing because of the worry about defraction and my little 6 MP sensor (I've been stayin at about f/8-11 on my K100 Super). I'll try some at f/16-22 just to see what happens. I might have been over-estimateing the defraction damage to the picture as I haven't done any real testing to see what would happen at higher settings. I tried to check out the Exif on your butterfly (?) shot but didn't get any useful info from it. What lens did you use in those pic's ?
The moth was shot with this lens.......
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Old Jan 2, 2010, 4:30 PM   #22
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It does a pretty good job on closeups at a 1:4 macro as well as this at the 200mm end...
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Old Jan 2, 2010, 4:53 PM   #23
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I'm no expert, but from what I've read, depth of field is based on optical characteristics of the camera and focal length of the lens. In other words, two 50 mm lenses, focused at the same distance on the same camera with the same aperture set, will give you the same depth of field. I could be wrong about that, but that's my understanding.
All things being equal, this is correct.

What extension tubes do is to effectively bring the lens and subject closer together by shifting the focal range closer to the camera - in other words, you gain magnification and close focus, but lose depth of field at the near end, and lose infinity focus at the far end. You also lose up to 3 stops from the maximum aperture value, depending on the length of the tube. Telextenders increase the effective focal length - i.e. a 100 mm lens with a 2x extender becomes a 200mm lens, but decreases the effective aperture, costing about 2 stops while narrowing the field of view and depth of field to that of a prime lens of that focal length. Supplementary ("plus") lenses have no light loss penalty, and all but the highest quality ones may degrade the image somewhat. All this is why people pay more for lenses that do not require those band-aid solutions.
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Old Jan 3, 2010, 12:08 AM   #24
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mtngal, "On the other hand, a teleconverter (i.e., something with optics, such as a 1.4 TC) does increase the focal length of a lens. From what I understand, they don't change the focus distance." Ur right on that as that was one of the things that I tried to see if I could get some more distance tween my lens and the subject, It made NO differance at all in that , But it did seem to add magnafication. At 1:1 lens setting of my Sigma 50mm the image was bigger on the lcd screen with my Kenko 1.5x TC attached, versus with just the lens and no TC. Focus was even touchier with the TC added, and of course with the same camera settings the viewfinder was a bit darker also due to the loss of about a stop of light.

First pic is 1:1 with Sigma 50 2.8 EX DG at 2" from front of lens @ f/8, about 15 seconds Exposure without Kenko SHQ 1.5x TC. Second pic is with TC attached (All else same as first pic) and same 2" from front of lens. It does seem to have been magnefied with the TC attached.
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Old Jan 3, 2010, 2:17 AM   #25
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bigdawg, That is a nice lens, but then again just about all the shots I've seen on here with a Vivitar lens were good. I wasn't expecting a 28-200 with a 1:4 Macro ability, After looking at ur pic's I thought it was a pure Macro lens u took them with, then again all the shots of urs I've seen were good ones. Your a pretty good photographer and I've enjoyed your pic's. Thanks for replying to my post.
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Old Jan 3, 2010, 7:31 AM   #26
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First pic is 1:1 with Sigma 50 2.8 EX DG at 2" from front of lens @ f/8, about 15 seconds Exposure without Kenko SHQ 1.5x TC. Second pic is with TC attached (All else same as first pic) and same 2" from front of lens. It does seem to have been magnefied with the TC attached.
While a teleconverter changes the focal length of a lens, it doesn't change the minimum focus distance by more than the length of the teleconverter.
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Old Jan 3, 2010, 12:52 PM   #27
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TCav, "While a teleconverter changes the focal length of a lens, it doesn't change the minimum focus distance by more than the length of the teleconverter." Before I ran that test I reasoned that it would change it, so much for my reasoning I quess. The appearent magnification also suprised me. The whole experiment was a suprise, to be truthful. Thanks, and have a good one TCav.
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Old Jan 3, 2010, 2:08 PM   #28
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Originally Posted by AZK6er View Post
mtngal, "On the other hand, a teleconverter (i.e., something with optics, such as a 1.4 TC) does increase the focal length of a lens. From what I understand, they don't change the focus distance." Ur right on that as that was one of the things that I tried to see if I could get some more distance tween my lens and the subject, It made NO differance at all in that , But it did seem to add magnafication. At 1:1 lens setting of my Sigma 50mm the image was bigger on the lcd screen with my Kenko 1.5x TC attached, versus with just the lens and no TC. Focus was even touchier with the TC added, and of course with the same camera settings the viewfinder was a bit darker also due to the loss of about a stop of light.

First pic is 1:1 with Sigma 50 2.8 EX DG at 2" from front of lens @ f/8, about 15 seconds Exposure without Kenko SHQ 1.5x TC. Second pic is with TC attached (All else same as first pic) and same 2" from front of lens. It does seem to have been magnefied with the TC attached.
Hi AZK6er,

In your test, you kept the wrong thing constant, the focusing distance. . . If you keep the magnification constant (same image size in the viewfinder), then you can get the added working distance that was your original goal. Using the TC will give you 1:1 with a bit more separation between the lens and the subject. . . or, as your test shows, more magnification at the same distance from the lens.

Scott

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Old Jan 3, 2010, 4:36 PM   #29
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Scott - Great explanation.

AzK6er - Thanks for the demonstration - I'd like to be capable of doing exactly what you demonstrated: get additional magnification without changing the focus distance. I've tried using my home-made extension tube (works, but decreases the focus distance significantly) and reversing a 50mm in front of my macro lens (works quite well, but also decreases focus distance and can be a bother to focus). Now to convince myself (and my other half) to spend the money to buy the one I've been eyeing (it's really expensive).
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Old Jan 3, 2010, 8:45 PM   #30
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snostorm, "If you keep the magnification constant (same image size in the viewfinder), then you can get the added working distance that was your original goal". Ah-ha, Good point that I didn't think of. I'd have to adjust the magnification b4 I mount the TC onto the Sigma 50 as when I try to adjust magnification/focus the lens has this grinding sound as I move the focus ring, it does it with both the Kenko 1.5x's I have, it's like nails on a chalk board. They and the Sigma 50 were bought new so I think that I might have to get a Sigma TC and use it with this lens instead. I got 2 Kenko TC's since I was reading of a few that were stacking their TC's and it sounded like a fun thing to do. It worked out OK but alot of PP afterwards, plus, only works on bright sunny days (I was testing this out with my DA 50-200 @200), even then NO AF, just Manual. Sorry, I degress. Thanks snostorm and mtngal, Ya'll have a good one.

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