[Tom777]

If you want to get a good idea on the image quality of these lenses, then go to photozone.de and read up on them there. According to the test results, both 17-50s are very close in terms of sharpness, with the Tamron edging out the Sigma by a small margin. You'll notice how the sharpness on the Tamron is doesn't fall off at the edges nearly as bad as the Sigma does. However, there's a lot more to a lens than just an MTF chart. The lenses were tested with Nikons APS-C cameras, but since they were both tested with the same camera, the results are still valid.

If you're going to be photographing insects a lot, then a 100mm is your best option with the Pentax mount since I don't know of anyone making a longer macro lens for the Pentax mount. The difference between macros of various focal lengths boils down to the minimum focusing distance. Keep in mind that although a 50mm has a closer focusing distance than a 100mm, this doesn't mean that it'll give you tighter shots. If you were to photograph a dictionary with any true 1:1 macro lens, the words and letters in the viewfinder would be identical, with the focusing distance being the only difference. Since an 100mm macro at 1:1 allows you to be further away from your subject than with a 50mm macro at 1:1, you are much less likely to scare off your subjects - we all know how skittish insects are. Additionally, since you're further away, you're less likely to be casting shadows onto your subject.

To avoid having your insect friends fly away, it's best to try photographing them in the early morning when their bodies haven't warmed up enough for them to take flight. You'll have the added benefit of being in better light in the early morning hours and in certain conditions the dew would not have evaporated either. A quick search on 500PX.com for "dragon fly" will give you an idea on what others are using.

Thanks FrankC and others for the advice


I will look at photozone.de and read up on them there now I'm back to the Tamron 17-50


Tom G

[TER-OR]

Do what you can with the 17-50 but if you're into insects, get a Pentax 100mm macro. That's really what you want. Go to the Marketplace here and put '100mm' into the watchlist, you'll get emails letting you know when someone is selling one, keep an eye on prices to figure out what your budget is - I'd slot $400 into this purchase, and count it a bargain if you find one at $350.

Have a look at my Flickr stream - all my shots are in the field, not in controlled studio conditions. The K5 + FA100 is great. I'd probably get the DA100 WR now, but this FA will be good if Pentax ever releases a FF camera...IF... Being able to flick the camera back into manual focus when autofocus doesn't work is invaluable. I never have to take my eye from the viewfinder, just a quick flick on the physical switch. Autofocus will get confused in the field, with green plants in front of other green plants. Now I'm doing a scientific survey of pollinators (primary interest is bumble bees) so I have the GPS module attached, too. This kit is supremely powerful for research photographs.

[Tom777]

Just won this on fleabay Pentax SMC M 50mm f/1.7 K mount lens


it gets a good review so look forward to trying it out for £27.99 can't be bad two days to go on the macro lens yet


Tom G

[Just1MoreDave]

... Is there one that would be best IQ, or are they all about the same. I think the 70mm may be to short but it gets a raving review??

Dedicated macro lenses are all really close in IQ, even the old ones. It is almost not worth worrying about. At least, pick all the other stuff like magnification, AF or other features first, then if you still have two lenses to compare, think about IQ. It'll probably be too close to call.

Focal length is secondary to magnification ratio for macro lenses. You are used to going from say 18mm to 55mm and seeing the details get larger in the viewfinder. But imagine you have three macro lenses that can do 1:1 maximum magnification. One is 50mm, the second is 100mm, the third is 200mm. You take a photo of the same subject with each lens at its maximum magnification. The photos all show the same size subject. Mostly the photos will be identical, with some difference in depth of field. The biggest difference is working distance. With 200mm, you are much further away from a subject than with 50mm. Your subjects suggest a good working distance compromise. Some people like to use their macro lenses for portraits or whatever, shots at normal distances. In that case, focal length works like your initial idea of focal length: 50mm has more stuff in the frame, 70mm less, 100mm even less.