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Old Sep 22, 2006, 8:39 PM   #1
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I have a K100D. I'm planning on getting the sigma 70-300 apo macro lens. What type of extension tubes do you recommend and how much do they cost?
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Old Sep 23, 2006, 8:15 AM   #2
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hey doc,
basically there are 3 types.

full manual, these have no mechanlcal coupling (MC) to stop down the aperture. when you are setting up the shot you have to view at the stopped down setting. prob is that you need to do macros at f11+ to get enough DOF and at f11 and above the view finder gets pretty dim. i would not pay more than $11usd for a set. even if i did i doubt i'd use them much.

auto aperture, these (like mine) have a lever to stop down the aperture. you view with the lens wide open and hit the AE-L button to get an exposure setting. got mine for $15.50usd delivered. i've seen them sell for as much as $50usd however. that's way too much..

full auto, these work just like an 'A' lens. you view wide open and the exposure is automatically figured out by the camera and lens no matter what you have set the aperture to. i'm not sure if auto focus is maintained as the motor is in the camera body on pentax cams.(please chime in w/more detail here). cost for a 3 ring set is $75-150usd.

the 70-300 lens will already do 1:2 macros. you may be perfectly happy with that. to give you an idea-- at 1:2 mag, you can NOT get a full size dragonfly in the image. also i'm not sure how much more mag you would get with all 3 rings on the lens because with a 50mm lens it requires about 50mm extention to attain 1:1 mag. i'd say get the lens and play with it before you order the ext tubes. they are mainly designed for using with prime lenses.

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Old Sep 23, 2006, 9:02 AM   #3
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hi,

i have the sigma 70-300 (non apo) and use the auto aperture tubes (real pentax) like what roy mentioned. manual exposure and focusing but i find with closeups i'm working slowly enough that it's not an issue. i got mine (3 ring set) on e'bay for around 25 bucks and latergot a matched 50mm tube for i think about $19. real happy with them.

auto focus/auto exposuretubes would be nice but for me not worth the extra cost. the only thing i miss is having the exif info (my tubes can't relay that to the camera)

all the best, eric
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Old Sep 23, 2006, 10:06 AM   #4
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you have to be careful with the ones that support auto aperture. I bougt mine off ebay, they have all couplings and electrical connections but they don't work. mechanical coupling for stopping down when pressing shutter works but no auto aperture. I don't know why, everything is clean it looks like all connections work fine when mounted on lens or body but they just don't work. but since I use manual external flash it doesn't bother me, I have to shoot in M mode anyway. it's that I could buy manual tubes for half the price I paid for those.

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Old Sep 23, 2006, 11:20 AM   #5
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I have these:

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7532447505

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Old Sep 23, 2006, 1:05 PM   #6
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those look like they do not shut down the aperture. am i right??

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