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Old Jan 8, 2008, 2:07 PM   #11
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no problem john. i'm thinking iwant the da* 300 too, but will have to see wait and see what it is going to cost. my anticipated tax return is ready to be spent on camera gear and i haven't even got the paperwork to file for it yet.
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Old Jan 8, 2008, 10:23 PM   #12
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Thanks for the pictures of the TCs and the information about the APO Sigma. I've been thinking of sometime getting a TC (when the budget allows). I specifically wanted one to use with the Viv 105 macro, since there are times I want more magnification, but don't want to get any closer. I couldn't figure out from Sigma's website why the APO TC wouldn't work with other lenses, beyond theones they listed. Now I know that the Tamron would be better for my purposes. I wouldn't mind trying it with the A300, but think that might be too long of a combination for me to manage. Not that I can afford to buy anything any time soon - I already spent this year's photo budget.
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Old Jan 10, 2008, 2:40 AM   #13
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Hi al,

What about the effects on image quality, as good as each other, or as bad as each other. I can't see the advantage of spending a large amount on a nice lens and then mounting it on something that might make the images average, yes you can see further, but do you really want to look at what you can see

I'll say now in a big clear voice that I have NO experience with these things, so I'm just asking.:G

as always

thanks

Simon
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Old Jan 10, 2008, 2:42 AM   #14
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Woops that should be hi all,

I'm not so good with a keyboard either !




:O
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Old Jan 10, 2008, 8:11 AM   #15
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It really depends on what you want to do, and what you want to take pictures of. If you want to take pictures of birds, and can't get close enough with your lenses, then adding a TC might be a less expensive way of getting the extra reach to take a decent picture of one (I know about that - I have lots of pictures of bird that are dots). The fact that a TC does compromise the sharpness is something to take into consideration. In my case, both my 300mm and my macro lenses are very sharp, so using a good TC isn't going to make the pictures too bad. Average pictures would be better than no picture at all.

The reason why I'm thinking about a TC is that I've been taking pictures of raindrops on things, and trying to get the reflection inside them. I can't get too close or else I'll knock them off whatever they are on (or in some cases, I can't get any closer). My choices are a TC or replacing the macro lens I have with another one having a longer focal length, something a whole lot more expensive, and probably wouldn't do me that much good anyway, since I'm really trying to go for something that is more than 1:1.

My only experience with a TC in the past was one that my father had bought - an old 2X Pentax. It was terrible as a TC, but makes a reasonable extension tube.
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Old Jan 10, 2008, 3:11 PM   #16
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simowills wrote:
Quote:
Hi al,

What about the effects on image quality, as good as each other, or as bad as each other. I can't see the advantage of spending a large amount on a nice lens and then mounting it on something that might make the images average, yes you can see further, but do you really want to look at what you can see
Hi Simon,

First of all, I haven't owned any Sigma TCs, so I can't give you a first hand comparison, so I'll give you my reasons for choosing the Tamron AF F 1.4x.

1. I remember seeing a comparison test which showed that the Tamron is slightly better optically, but the Sigma is built more robustly -- .

2. The Tamron was considerably less expensive -- IIRC, at the time, it was less than half the cost of the Sigma. The price of the Tamron has since gone up, but it's still a lot less expensive.

3. I decided that I didn't want anything in my bag that could damage one of my lenses if, in a thoughtless moment, I tried to mount it on one of my hard won teles or zooms. The Sigma compatibility chart only covers Sigma lenses -- and I don't own any, so I could never be sure whether their TCs would fit my lenses without doing some possible harm.

As to whether the tradeoff of IQ vs reach, the caveats concerning TC use are:

1. You lose max aperture in directl proportion to the magnification of the TC. In other words, multiply the max aperture of your lens by the mag of the TC and you'll see what your new max aperture with the TC will be. If the combo is effectively f8 or slower, you can expect AF to become iffy at best, if not nonfunctional, in all but the brightest lighting conditions. I consider @f4.5 the slowest useable max aperture for a lens that I want to use with any TC in which AF is a factor. An effective f8 is also pretty much a cutoff for me with MF, as the viewfinder becomes pretty dark, and critical focus gets difficult, even with a split prism VF, since one side usually blacks out at this aperture.

2. A TC will magnify any optical faults of the lens, so the better the lens to begin with, the better your TC results will be. With the best lenses, degradation caused by good 1.4x and 1.7x TCs is very slight, if not unnoticeable -- probably mostly evident in increased Ca and PF, which is easily correctable in PP. With these lenses, the gain in reach easily wins the tradeoff over possible decrease in IQ.
I actually use my 1.4x and 1.7x TCs as the final test to see whether a new tele lens makes the final cut. My standards are pretty high, but not the highest I've seen by any means. If I can get acceptable results with the TCs, then the lens passes, if not, it'll only be a keeper if it uniquely fits a niche that I think is important with its other features.

My most extreme use of TCs is to stack the Tam 140F and the Pentax F 1.7x AFA for a magnification of almost 2.4x. Here's a post with an example of what it can do in the best of circumstances with the SP300/2.8 LD (IF):

http://forums.steves-digicams.com/fo...mp;forum_id=80

Kinda blew away the paradigm that TCs kill IQ! Certainly not typical of my results, but it showed me the ultimate potential of this combo, and knowing this quality is something that is possible, it's something for me to now strive for.

Scott


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Old Jan 10, 2008, 10:37 PM   #17
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i'll try and get out this weekend and take some sample shots with both tele converters for everyone interested. i'll use a couple different lenses with each.
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Old Jan 11, 2008, 4:24 AM   #18
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Thanks Ishino, that would be great if you have the chance.




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Old Jan 11, 2008, 3:28 PM   #19
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Here is one I took today with the AF 1.7 Pentax TC on a 200mm lens using my DS in jpg.



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Old Jan 13, 2008, 11:42 PM   #20
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The older Sigma AF TCs had the recessed element like the Tamron. Prevailing opinion used to be that it was best to use same brand TCs as the lenses as they would be a better match, but lens design has come so far in recent years that that may no longer be true. If the Sigma EF DGs require a TC with a raised element, then the Tamron might not be the best choice for those lenses. It will be interesting to see Ischino'ssample photos.
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