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Old Nov 5, 2004, 7:34 PM   #1
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1. Do you need 2.8 aperature lens to get narrow DOF? I tried briefly with the kit lens to narrow the DOF using program mode and didn't really have much luck. Is that because of the 4.5 aperature minimum of the kit lens? Soon I'm going to add a 70-300mm lens if I can make due with a 4.5 min aperature, but I may wait if I'm going to be too limited due to aperature, speed, etc.

2. Can you take decent macro shots with a lens that is, say 70-300mm? I like shooting wildlife and such (hence the need for something in the 70-300 range), landscapes/sunsets (I'll make due with the kit lens for now), and good macro shots. It would be great if I could get both macro and the 300mm range out of one lense. Maybe it's not possible or practical? I guess the bottom line is I don't really know what you need to take good macro shots. I think I know that there are some lenses with much narrower "zoom" ranges that are probably better for macros, but I'm trying to cover my bases in a reasonable way given that after about one more lense purchase I may be not be able to add any lenses for a while.

Thanks, once again, for the great help around here.


PS: I'm feeling like a forum leech, so I pared down the questions but forgot to change the title!
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Old Nov 5, 2004, 9:20 PM   #2
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There's 3 ways to get narrow DOF:
1 - Open up the aperture
2 - Get closer
3 - Move the zoom to the Tele position
You can plot DOF curves by varying the above parameters: http://www.dof.pcraft.com/dof-frames.cgi


As to macro you need to look at the minimum distance... Zoom lenses are usually at their worst at the closest position. There's way to get around this like extension tubes and close-up attachments, but the best is usually a dedicated macro lens which is designed to work at short distances...
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Old Nov 5, 2004, 10:14 PM   #3
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Thanks NHL.

That's basically what I was figuring. I didn't really think about the physical distance you are from your subject effecting the DOF, though. In retrospect, I probably should have.

I'm still not exactly sure what the practical effect of having a lens with a lowest aperture of say 4.5 vs 2.8 is. I know that eliminates some ability to use aperture to narrow the DOF. I'm just not sure how limiting it is at this point. I guess that's something to just experiment around with a little more.

Anyway, thanks again. The help I've received on this site has been fantastic. I hope to be able to give some back one day.
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Old Nov 6, 2004, 4:59 AM   #4
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Wannabe wrote:
Quote:
I'm still not exactly sure what the practical effect of having a lens with a lowest aperture of say 4.5 vs 2.8 is. I know that eliminates some ability to use aperture to narrow the DOF. I'm just not sure how limiting it is at this point...
FYI http://www.dofmaster.com/dofjs.html

Pick D70 -> Enter 200mm for focal lenght -> f/2.8 for aperture -> 10 ft: DOF = .08 ft

Pick D70 -> Enter 200mm for focal lenght -> f/4.5 for aperture -> 10 ft: DOF = 0.13 ft ft (ie almost twice the depth)


... try with different distances and focal lenghts as well!
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Old Nov 6, 2004, 6:08 AM   #5
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Thanks for the link! That's awesome.

Don't have that much time to mess around with it this morning, but with just a couple input data groups I at least have a lot better feel for the differences.

Thanks so much!
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