[gmans]

Pretty sure you do not need a true Macro lens, the depth of field would be very thin and stopping down would increase ISO or diminish shutter speed. the 18-55 is pretty sharp at close focus. Check all the review of the various lenses.

[raider]

Shooting frogs....hmm...I remember Leopold on this forum and DPR also do the same...I think he uses the DA14 as well....have a look at his photos if you like. HTH.

[fretlessdavis]

Pretty sure you do not need a true Macro lens, the depth of field would be very thin and stopping down would increase ISO or diminish shutter speed. the 18-55 is pretty sharp at close focus. Check all the review of the various lenses.

DOF isn't different with macro vs normal lenses... It's the same at the same focal length and aperture. Macro lenses, however, are designed to be good at close range-- less distortion and better sharpness. Zoom lenses hardly stack up to primes in this regard.

Also using a 100mm vs 50mm vs zoom lens-- you won't have much working distance with something in the 35-50 range.. At the magnification you're looking at, you'll have working distances in the 8-12" range, which can be a big pain with anything that's alive. a 90mm or 100mm macro lens gives you about double the working distance.

It's easy to do a simple flash setup for Macro, that eliminates the need to bump up ISO, and gives you a handy 1/180 of a second at all times

[gmans]

Also using a 100mm vs 50mm vs zoom lens-- you won't have much working distance with something in the 35-50 range.. At the magnification you're looking at, you'll have working distances in the 8-12" range, which can be a big pain with anything that's alive. a 90mm or 100mm macro lens gives you about double the working distance.

The OP asked for a cheap lens to take photo s of Frogs, up to 75 mm long, this still is my recommendation. the higher the magnification the thinner the depth of field. Read the OP post.

[baro-nite]

the higher the magnification the thinner the depth of field

This is true but irrelevant given that the OP wants to shoot at a given magnification, whether using the 18-55 or something else. OP wants low distortion and lots of detail, which ideally calls for a macro lens. So it's a question of whether or not the 18-55 is good enough for the purpose.

[gmans]

This is true but irrelevant given that the OP wants to shoot at a given magnification, whether using the 18-55 or something else. OP wants low distortion and lots of detail, which ideally calls for a macro lens. So it's a question of whether or not the 18-55 is good enough for the purpose.

A frog of 75mm would more than likely have a depth of 25mm or so. The previously stated his magnification less than 1.3 so somebody do the math. The OP wants a cheap Lens.

If he can get a True macro with WR and cheap so be it.

[fretlessdavis]

The OP asked for a cheap lens to take photo s of Frogs, up to 75 mm long, this still is my recommendation. the higher the magnification the thinner the depth of field. Read the OP post.

I did read the OP. If he's going 1:3 on a zoom vs on a macro lens, DOF will be the SAME. A macro lens is desgined for this, and will give better results.

$120 is cheap for a lens. The 50 f/4 macros are even cheaper. These will have less distortion, too, which he mentioned in the OP. Did *you* read the OP?

Edit: I reread-- he said subjects between 25-75. A 25mm long subject will need a true macro, as that's getting pretty damn close to 1:1. The compromise would be cropping quite a bit, extension tubes, or a macro lens (best option).

[gmans]

I did read the OP. If he's going 1:3 on a zoom vs on a macro lens, DOF will be the SAME. A macro lens is desgined for this, and will give better results.

$120 is cheap for a lens. The 50 f/4 macros are even cheaper. These will have less distortion, too, which he mentioned in the OP. Did *you* read the OP?

Edit: I reread-- he said subjects between 25-75. A 25mm long subject will need a true macro, as that's getting pretty damn close to 1:1. The compromise would be cropping quite a bit, extension tubes, or a macro lens (best option).

My apology about reading the OP, did not mean to sound harsh. I have the 50mm F4 macro very nice little lens, it is I believe a flat field copy lens designed for copy work. the distortion would possibly be greater given the frog is not flat and the depth field that is required? Anyhow interesting debate. Comparsion between the 50mm or 100mm Macro versus the 18-55. Anyone?

[DeadJohn]

Right now I'm thinking that the DA 18-55mm WR might be exactly what I need. With a maximum magnification of 0.34x, a 75mm long subject will just about barely fit on the sensor, which is perfect. Since I want to take all my photos at the same magnification, I don't need to go larger for the smaller frogs. And I don't need (or want) extreme close up; these are frogs I'm photographing, not insects! The fact that it's a WR lens is attractive as well since I'm going to be using this out in the field where conditions aren't always clean and dry. (Part of the reason I went with Pentax in the first place, since nobody else makes a weather-sealed camera in my price range.)

Does that make sense to y'all? I'm never sure if I'm getting the magnification conversions right, there are always so many factors to worry about. In any case I don't think I need a true macro lens – if I made the image of the frog the same size as the sensor or larger, it wouldn't fit! But a close-up filter might still do the trick, and it would be easier to carry (and cheaper!) than a second lens. What do y'all think about that option? Are there any good close-up filters (or lenses, whatever you want to call them) for the K5?

The 18-55 looks like a good option. Zoom to 55, manually focus to minimum range, then move the camera to focus. If the zoom and focus settings remain constant all of your photos will have the same scale. Take some test photos of graph paper to see how much distortion you get.

The 18-135 with a Raynox adapter or other closeup adapter might magnify too much. You can't reliably zoom to anything other than the 18 or 135 extremes. Maybe there's a Raynox or similar adapter that gives roughly x0.33 magnification with the 18-135? There's a mathematical formula in an old thread for how to calculate the magnification for any lens/Raynox combo. I'll hunt for it later.

[baro-nite]

If he can get a True macro with WR and cheap so be it.

Obvious won't happen. Only the OP can know whether WR is more important than the higher resolution of a macro lens. Compromises, compromises.

[fretlessdavis]

My apology about reading the OP, did not mean to sound harsh. I have the 50mm F4 macro very nice little lens, it is I believe a flat field copy lens designed for copy work. the distortion would possibly be greater given the frog is not flat and the depth field that is required? Anyhow interesting debate. Comparsion between the 50mm or 100mm Macro versus the 18-55. Anyone?

No worries-- I wasn't actually aware that the 50mm f/4 Macro was a flat-field type lens, either. I had a 55mm Micro-Nikkor in my Nikon days, but found that short of a macro to be pretty much useless in the field. the 100mm f/4 macro seems quite suited to field work from what I've seen and used. If you need more DOF, stop down and use flash.

Also consider the OP will be using in the field to take pictures of living things. For example, something in the middle of his size range (50mm) would give him a 4-6" working range @ 55mm. Getting a big lens that close to something alive will be challenging.

Another thing to consider, is that since you're on APS-C, close-up filters work quite well. With a +3 Hoya Close-up on an SMC-M 50mm f/1.7, this is what I got straight out of camera:



Sharp corner to corner. Since the close-up filters are worst at the edges, it isn't a problem with larger image circles-- and if you rack out an APS-C lens for zoom and focus, most will do OK. They seem to preserve working distance, too.

I've got an extra set of the Hoyas over in the marketplace if you're interested in playing with them. $5, so no risk really, vs. the $40 new Hoya is charging these days.

[gmans]

The depth of field is the biggest concern, interesting to have play with Depth of Field Calculator @ Online Depth of Field Calculator

The Focal length versus depth of field. FL55 mm is good compromise working distance 250mm to400mm versus FL100mm working distance 600 or 700mm

[fretlessdavis]

The depth of field is the biggest concern, interesting to have play with Depth of Field Calculator @ Online Depth of Field Calculator

The Focal length versus depth of field. FL55 mm is good compromise working distance 250mm to400mm versus FL100mm working distance 600 or 700mm

@50mm working distance will be at MOST about 8" for a 75mm frog filling the frame. With his smaller subjects that is going to be even less. @ a 400mm working distance will get about a 7" horizontal area into the frame.

[gmans]

My point is that to fill the frame and depth of field of approximately 25mm you working distance has to be greater. It has to be compromise. Should have explained myself. You can not have both, the way I see it.
Camera, film format, or circle of confusion


Focal length (mm)55
Selected f-stop 16
Subject distance


Calculate
Subject distance 35 cm

Depth of field
Near limit 33.9 cm
Far limit 36.1 cm
Total 2.19 cm

In front of subject 1.06 cm (48%)
Behind subject 1.13 cm (52%)

Hyperfocal distance 950.8 cm
Circle of confusion 0.02 mm

[fretlessdavis]

My point is that to fill the frame and depth of field of approximately 25mm you working distance has to be greater. It has to be compromise. Should have explained myself.

Oh, got it, sorry. Everything seems pretty tricky with this set up, though. If they'll sit still, it may be worth focus stacking. Since the photos are for measurement purposes, does the entire frog need to me 100% in focus?