Lens and extension tube question.

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I've been looking into long and somewhat fast lenses for various reasons. I cam upon this lens 100-300mm F4 EX DG APO HSM made by Sigma. From what i have read it is pretty good and for the price tag of only 1k I think it fits the bill. Anyone have any idea if this is a good lens?


Also do extension tubes degrade quality and slow the f stop? Thanks.. Also what are good extension tubes as I dont really see much of a difference.. Thanks all.

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[Dwig]

...Also do extension tubes degrade quality and slow the f stop? ...

Using an extension tube will alter the effective f/stop. The greater the extension, relative to the lens' focal length, the greater the change.

There are a lot of factors that comprise "image quality". Using extension tube will cause a change in a few of these. How much change occurs varies a great deal from lens to lens. Some lens designs suffer very little while some suffer substantially.

The primary factor that changes is the flatness of field. Lenses are designed so that when you focus at some distance in the center, the edges of the image are in focus at the same distance. When you use an extension tube you are using the lens at distances that it wasn't designed for and this balance of both center and edges being focused at the same distance is disturbed. If you are doing copy work the degradation of this aspect of IQ is very, very serious. If you are doing "macro landscape & wildlife" (e.g. bugs and flowers) it is of little concern as the subject isn't the same distance from the lens across the field of view.

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[Derrel]

I briefly discussed my Sigma 100-300 f/4 in this thread a few days ago here on TPF http://www.thephotoforum.com/forum/p...anon-zoom.html I will say this about the Sigma--it balances well on a bigger Nikon and although it is rather bulky compared to say an 80-400 Nikon, it "feels light" in action....it just feels and swings and points like it's not even there when it's on the front of a D1 or D2 weight camera...is not nose-heavy and arm-tiring. Igt's a nice length for baseball and track and field and outdoor portraiture. Having the 100mm from 200 to 300mm allows you a lot of background control and a lot of framing options, all with f/4 speed. It's good at f/4.5 and f/5.6 apertures. It is not as sharp as a 300mm prime lens at 300, but it's quite good. It's super-handy, but mine doesn't focus as reliably as I would like, but mine is old. Maybe it need to be re-chipped. I bought it used for $550 in 2004 as I recall.

I would generally agree with Dwig's comments about extension tube use; you can usually get by on 3-D objects by adding an extension tube, especially on APS-C d-slrs, since the majority of the image is made using only the very central part of the lens's image circle, and the edges are simply not imaged by the sensor. On flat, 3-D subjects where edge-to-edge sharpness is paramount, using an extension tube on a general-purpose,ordinary lens is sometimes going to produce bad images--but using a tube on a flat-field macro lens, here will probably be no problems at all. This varies from lens design to lens design; some lenses have a lot of field curvature, and others do not.

Some lenses are not very good with telephoto converters, but are good with extension tubes, like Nikon's old 300mm f/4.5 ED-IF, which John Shaw used to do many,many of the beautiful close-up nature shots in his numerous guidebooks. tHis old manual focus era lens is pretty decent with extension tubes.

[djacobox372]

I would recommend a 80-200mm f2.8 af nikkor instead, they sell used in mint condition for $600 or less.

[Live_free]

I would recommend a 80-200mm f2.8 af nikkor instead, they sell used in mint condition for $600 or less.

This lens focuses faster and reaches farther for a few hundred less. 2.8 is cool but as a lens I will probably just stick a 1.4 teleconverter on making its affective length around 600mm (With a DX camera) I would be mainly using this for wildlife.