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12-09-2010, 05:34 PM   #1
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manual lens macro focal lenght question

Thanks to this forum, I was able to order and use my first manual lens, a Sears 80-200mm zoom with macro. I won a bid for a Sears 135mm f 2.8 tele lens and the seller was nice enough to include the zoom for free, since no one had bid on it!

My question is what focal lenght do I select when in macro setting?

12-09-2010, 10:25 PM   #2
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I am not familiar with that exact lens but have used the same variety me thinks. The "macro" is not true macro but allows for a closer focus to acheive like a 1:4 ratio (some would say true macro lens can do 1:1 ratio). Typically the zoom lens is set to its maximum zoom, then switched to macro. If you can't figure it out then post a pic showing the rings and markings on the lens. Enjoy the toys!
12-09-2010, 11:03 PM   #3
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That zoom is labeled MACRO because CLOSE-FOCUSING uses too many letters. I have had a few copies of that lens, I have one now right in front of me -- it's one of the few manual zooms that I will keep. Getting into and out of macro mode can be a little tricky. It's best to hold the body of the lens in your strong hand (I'm right-handed, so that's it) and twist the MACRO ring with the fingers of your other hand. Once in macro mode, just experiment. Use whatever focal lengths and focusing distances work for you. In macro, sliding the zoom to change the focal length is what changes the magnification factor. It becomes easy when you've practiced a bit.

Which version of the lens do you have? Is it M42 screwmount, or Pentax bayonet mount? If a bayonet, does the aperture ring have a KR or (A)P or A near the numbers? If it does NOT have an A or (A)P or KR, then you can use it and similar non-A lenses for REAL macro work, just by buying cheap extension tubes. Cheap: under US$10 a set, and it's best to have at least a couple sets.

Have fun!
12-10-2010, 05:49 AM   #4
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Thanks!

Thanks for the quick replies!

I realize the lens is not true macro(1:5 only- 17.7" minimum) and appreciate all the help (so much to learn!) It really is great to have somewhere to go with basic questions.

The lens is "K" mount and the zoom is push-pull and I should be able to use extension tubes for macro (no "A" setting on the lens).

I have no problem using regular zoom mode and setting the
"input focal lenght" on my k-x for when in zoom mode (I just read the scale of that particular focal lenght and input that value ).

My question is how do I determine what value do I input when in "close focusing" macro setting?

12-10-2010, 07:54 AM   #5
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there are a couple of things to note with respect to this setting.

First of all, SR is not wholly reliable at close focus because it cannot compendate for movemet towards and away from the subject, which is a big portion of loss of sharpness.

Second, you need to consider the 1:5 magnification ratio and focusing distance, it appears that your lens achieves the "macro" magnification at minimum focal length of 70mm,. this is not uncommon for zooms to achieve close focus at minimum focal length.

As a starting point, you could set the focal length to 70mm in the camera.
12-10-2010, 10:23 PM   #6
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Lowell is quite right. I'd like to add that the reason I've dumped most of my manual zooms is because of SR ambiguity. For non-macro work, I depend on bright light for a fast shutter, and I leave SR off. For macro work, I use controlled or ambient light and a tripod, and I leave SR off. The only time I use SR with such is if I've put the zoom to a specific focal length and will leave it there for the session.

Always leave SR off when using a tripod or other fixed support (like a wall). As Lowell mentioned, SR is unreliable at close distances anyway. This is stated in your camera manual. Unfortunately, Pentax (at least in my K20D manual) gives no guidelines as to what is "too close", which would vary with focal length anyway. Your best option is: experiment. Try different settings and see what works for you. Be sure to take notes. If you don't write it down, it never happened.
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