www.ukbutterflies.co.uk

I recently got a 100-300 F4 Sigma for my Sony A700 and I would like to get some extension tubes to use with it for butterflies. I've been looking at the Kenko auto set but I'm not quite sure if they're very strong, bearing in mind that the Sigma is about 1kg in weight. I know that most of the time attached tube(s) would be taking the weight of the camera rather than the lens but I don't want the things to fall apart should I need to temporarily hold the camera, to change lenses for instance. Has anyone got these, and are they any good?
Thanks.

Mike
I have used the Kenco set (they make nice coffee too!!) on my Sigma 500 f4.5, and that weighs 3.15Kgs (7 odd pounds in old money).
The way I look at it is that I always carry by the lens, or support on a mon/tripod.
In that circumstance, it is the weight of the body that matters - not the lens.
I hate having a camera with a lens any heavier than a 50mm prime on a neckstrap - I am sure the weight of the lens on it's mount isn't healthy.
HTH (a little)
Roger

I also have a set of the Kenko tubes and would say that they are reasonably strong (probably stronger than the mount of the Sigma lens?).

If you were really worried about the weight of the lens and the body, you could use a Manfrotto 293 lens support - I've tried this with a D300+300mm F4 and a 30mm extension tube, and it feels a lot more secure. Bit of a weight though.....

Chris

I have a monopod that I attach to the lens, but for extra reach I also have a 1.4x teleconverter. To add the TC while out taking pictures, I have been detaching the monopod, temporarily let the lens hang down on the camera while removing the end caps from the TC, separate the camera and lens, then reattach with TC inserted. Mounting an extension tube would involve a similar process. I think I should work on a better technique that doesn't stress the mount but it's awkward with only two hands. Anyway, thanks for the comments. I shall save up my pocket money for some tubes before the butterfly season. In the meantime that Sony AF 500mm reflex looks tempting....

At the UKB Workshop, Roger Harding seemed quite happy with his Kenko tubes so I got a set by mail order from LCE for £99 plus postage. This was the cheapest price I found by a UK seller, although you can probably get a better price by buying from Hong Kong via ebay and taking a chance on getting stung for import duty + VAT.

They arrived today and I've had a little play with them. They seem quite well made although maybe a little tight on the mount. Autofocus works ok within the limits of aperture and closeness and there is full coupling for ADI flash and auto-aperture. There are three tubes of 12mm, 20mm and 36mm thickness. The smaller two tubes have AF drive as a simple direct 1:1 transfer, with the 36mm tube geared down by 1:2. The latter obviously means slower autofocus but it's likely to be more acccurate.

I've tried them so far with the Sony 500mm mirror, Sony 55-200mm zoom, and the Minolta 70-210 beercan.

The mirror just doesn't cut it for autofocus. At F8 maximum aperture, any additional cut in light gathering power by adding extension tubes has it hunting far too much to be useful.

The beercan works fine, with the 20mm probably being the most useful, although there is some red/cyan chromatic aberration. It gives a nice range at full zoom from about 2 feet to 8 feet with around 1:2 magnification at 2 feet away. Slightly odd to get used to is that if you need to get closer than 2 feet, to avoid some obstruction for instance, you can zoom back a little to bring the closest focus point closer. This is because the extension tube has a higher effect with shorter focal lengths.

The real eye opener was with the 55-200. I need to try both this lens and the beercan out in the field, but photographing a coin as a test subject, this cheap lens gave better close-up results than the beercan with a bigger focussing range and lower levels of CA.

This coin was shot with the 55-200mm Sony zoom and is uncropped.

I've tried various combinations of these tubes out in the field over the last two days with my Sony 55-200mm and Minolta 70-210 "beercan" zooms. With these two lenses at least the close up lens solution works better, i.e. the Canon 500D +2 dioptre achromatic. The 55-200 used yesterday with the 20mm tube had one or two that were real crackers - you'd think they were taken with a macro lens - but too many were soft, probably from camera shake. I think what happens is that using the extension tube screws up the in-camera image stabilisation. With the beercan it is compounded by rather uncertain autofocus.
Today, using the beercan I swapped out the tubes and put the close up lens back on and immediately AF was snapping into focus pretty much every time.
So it looks like Gary's experience with zoom lenses and extension tubes are repeated with mine, and that tubes are best used with prime lenses.
I have yet to try the tubes with my Sigma 105mm Macro, but I expect them to work rather better with that lens and be useful for very close work, although with a very narrow DOF they will probably be usable with a tripod only.

When I started doing digital macro I was disappointed as they were not as good as my old slides. I didn't realise then that the sharpest pictures are when you are not using the two extremes of apertures. nowadays for macro I am only going up (or is it down ) to F16 normally whereas I was previously going up to F22 and beyond to get greater depth of field.

Yes I agree. This is because most modern DSLRs are cropped format with very high resolution sensors, and defraction starts to have a significant effect at apertures smaller than F11. When using full frame DSLRs then the same criteria as 35mm film applies, but when you have the newer 20+MP sensors, resolution exceeds that of 35mm film, and defraction again starts to become noticeable at relatively large apertures.
The problem with extension tubes with many lenses however, is nothing to do with defraction but a question of optics, in particular, zoom lenses. Prime lenses are tuned to give maximum resolution at a single focal length and at a range of distances from infinity down to a relatively close distance. Their optics are simpler than with zooms so less 'peaking' is necessary to obtain good results between the focussing range. This means that any tail off in resolution beyond the near focus limit when adding tubes is likely to be gradual, and resolution will hold up well. Even more so when the prime lens is a macro. Zooms are tweaked to a high level to obtain relatively decent resolution, but only within their focussing ranges. Beyond that range they tail off very quickly and are much less sharp when using tubes. This problem is compounded with Sony Alpha mount cameras because the image stabilisation is thrown when the focal point is beyond what a lens can produce.
Close up lenses do not suffer from these latter two problems as the main lens is operating within its normal focussing range. As a result, my 70-210 beercan is just as snappy and accurate in focussing on butterflies using the close-up lens as with normal subjects without it.
Where close up lenses can suffer is with chromatic aberration, particularly with single element designs, which is why I don't have one.
The Canon 500D close up lens is a relatively simple design, consisting of only two glass elements, but the elements are very well matched, and optical quality is very good, keeping CA to a minimum. The main limitation is focussing depth when attached. Only a relatively small focus range is possible. Constructive use of the zoom range is required to get magnifications greater or less than the viewing distance. But within that range, very good results can be obtained.
With my beercan and 500D, fieldcraft is important as I need to get within the focussing range before I can begin to start shooting, but once I reach that point, I can stay put and vary the zoom focal length to get different image magnification. I can fire off shot affter shot with AF snapping into focus quickly and accurately.

chitin wrote:..... nowadays for macro I am only going up (or is it down ) to F16 normally whereas I was previously going up to F22 and beyond to get greater depth of field.

At the photo workshop, it was amply demonstrated how F-stop and sharpness are related. (Worth going to for that alone!)
I used to shoot up to f16+ sometimes in bright conditions; now I keep between f-8 and f-11 and understop routinely by at least 1/3; for d-o-f, the trick for me seems to be to find that point for your set-up and style where you step-back by 6"-15" (and crop later) to try to find those few mm's where all is sharp!
(It ain't half difficult tho' )
N
BTW - I have used extension tubes on my 90mm macro and concur with Eccles; loose a bit of image quality, v. little d-o-f but fantastic detail where it IS sharp!
Candidate for a macro slide and photo-stacking software to build a composite sharp image from the bits, if you have the patience or ...you could get a life, I suppose