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04-30-2015, 06:19 AM   #1
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Camera Recommendation for Geometric Morphometrics

Hello all,

I hope I'm posting this is the correct area but I've recently enrolled in a PhD program dealing with marine fish and have recently became interested in doing Geometric Morphometrics work on a fish species we recently raised.

The reason I'm posting here is to ask the community their thoughts/recommendations for camera(s) and or lenses that have a low degree of deformation or distortion. This is very important in this line of work because the process relies on accurate measurements throughout the animal to be used for multivariate statistical analysis.

Geometric Morphometrics Introduction

An example of photography protocol for this process

Doesn't have to be fancy (given this will likely be a personal purchase), just north of 12 MP and low/no distortion if possible.

Thank you all and look forward to discussing this.

04-30-2015, 07:46 AM   #2
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Jobcutter,

Welcome to the Pentax Forums!

If you are looking for a lens with a flat field then take a look at a good macro lens. Pentax makes a few modern with 35mm, 50mm, and 100mm focal lengths. Close down the aperture to f/6.3 - f/8 depending on the lens and you will have an incredibly sharp image. Tamron also has a 90mm macro lens. There are also plenty of used macro lenses available that are also very, very sharp but may lack autofocus, weather seals, modern coatings, etc. None of these are deal breakers in terms of performance. You said you are targeting 12 MP images. A body like the K-30, K-S1, K-2, or K-3 would work very well. Consider the K-01. Downsampling the image from 16, 20, or 24 MP to 12 MP will create very clean images.

Use the camera's built in JPG engine or shoot in raw and process in something like Lightroom, Capture One, etc to suit your taste.

I hope this helps a little bit.
04-30-2015, 07:50 AM   #3
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Well, I clicked on this to see what Geometric Morphometrics was. But all I found out was it was beyond me.

But it appears you are looking to take pictures with as little distortion as possible being introduced by the photographic process. In that case the camera itself is going to have little to no impact on the distortion, assuming we are talking about modern digital DSLR type cameras. What you want to make sure to get is a lens that introduces as little distortion as possible.

On DSLRs the wider the lens the more possibility of distortion, and lenses within the 50 to 100mm range are generally thought to produce images that look close to the actual subject. This is on APS-C cameras, and these focal lengths are often used for portraits to make sure the subject's face is not distorted. However, the size of your subject will determine the focal length that is best for that particular purpose. Also note that a true macro lens, optimized for flat field photography will likely be the best at this.

So I would recommend either a 50mm or 100mm macro lens. The camera itself need not be top of the line and anything from the Pentax k-x on up would work fine.

In short research the lens purchase first, then get a camera to mount it on that fits your budget.

Here are two macro lenses, but there are others. Note the DFA 100mm WR is water resistant, and combined with a WR body such as the k-5, k-5II or k-3 might be a good choice.
SMC Pentax-D FA 50mm F2.8 Macro Reviews - D FA Prime Lenses - Pentax Lens Reviews & Lens Database
SMC Pentax-D FA 100mm F2.8 Macro WR Reviews - D FA Prime Lenses - Pentax Lens Reviews & Lens Database

Another consideration would be lighting. I think this type of application would require good lighting, either flash or constant lights depending on the environment you will be working in. If you are going to be in the field note that the new Pentax flashes are water resistant which might be a plus for you.
04-30-2015, 07:54 AM   #4
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I have a K-3, K-01 and K-7 that I use for technical measurements. When I want minimum lens distortion, I either work with a prime lens or I use lens distortion correction software like PT-Lens.

Generally most prime lenses have low distortion correction.Photozone.de will give you an estimate of the lens distortion.

With a zoom lens, I recommend in-camera PP to remove lens distortion.I use personally PT-Lens and I recommend it strongly.

Hope that the comment may help.

04-30-2015, 08:50 AM   #5
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i had to buy zeiss glass for a project at work, because of their flat field. Was with a highspeedcamera having a nikon mount. I can look up the types of lenes we bought if i rememberright it was 100mm. I can look it up tomorrow.
04-30-2015, 10:30 AM   #6
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A flat field lens is not mandatory, because "flat field" means "uniform sharpness between the center and the corners of the photo".
What you need is a lens with very few optical distorsions: if possible neither barrel nor pincushion distorsion (and no mustache distorsion of course).


Regarding distorsion the Pentax SMC-FA 100mm f/2.8 macro is an excellent choice: -0.019% distorsion
Pentax SMC-D FA 100mm f/2.8 macro is excellent too: -0.027% distorsion
Tamron AF 90mm f/2.8 SP Di macro is not so good: -0.087% distorsion
source: www.photozone.de

I have no data about other lenses distorsion.
04-30-2015, 02:19 PM   #7
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Thank you everyone, this is the exact information I was looking for and all the comments have been helpful.

I'll keep everyone updated with what I go with and how it works moving forward.
07-29-2015, 09:02 PM   #8
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After much research and an attempt to pay for a shutter repair on my brother's K-5IIS (precision cameras quoted $607 for the repair) I decided to go with a new K3 and HD Pentax-DA 35mm F2.8 Limited Macro

Because I'm photographing live (drugged up) specimens on a copystand I plan to live view out via HDMI to a Dell 32" 4K Monitor so I know I'm getting the fine details of the fish into focus. I may also try to FLU Card to my laptop to chose 3 separate points of focus (and thus 3 separate photos) of the fish because of it's depth and stack them in PS for greater detail. See what I mean below.







If I do decide to take this step (assuming 3 photos focused on different spots of the subject doesn't have too much latency) I will test HDMI live viewing to 4K monitor to ensure the 3 points look good before taking the photos. One thing I have been unable to answer is if the K3 can FLU Card out to a device (laptop) and live view at the same time to an external monitor. I'm doubting that it will because the live view on the LCD in the camera is mutually exlusive with live view via FLU Card in a browser. I'll report back with what I find....ideally this would be addressed in a cabled tether...

07-30-2015, 04:04 AM   #9
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In glancing through the the course syllabus it appears that any lens will do. Especially when you consider the images of cameras used, one of them looks like an old Sony diskcam.

For me the real issue is not distortion itself, of the lens, but perspective distortion and having the camera square to the subject. The examples in the syllabus for which a camera could easily be used are all 2D outlines or scaling between specific identifiable characteristic points or features.

To use, for example a pair of callipers as an example for scale, assumes no perspective distortion, and therefore a longer lens, like a medium telephoto (size will be important.

I think what ever program is used to make the scale measurements, the program should be able to automatically adjust for distortion knowing the focal length distance rom lens centre, and distance from subject
07-30-2015, 04:43 PM   #10
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Having a quick look at your PDF, it seems like photographically you're only interested in relatively planar points. As long as you have 3 points in your image which define a plane of known orientation to the subject plane you can use an affine transform to correct for any orientation issues.

Look for "Multiple View Geometry in Computer Vision" by Hartley and Zisserman.
07-31-2015, 05:35 AM   #11
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The macro lenses will do well. I have a Sigma 28mm and when using Lightroom's lens adjustment there's very little change. Pentax's 35mm might be even better.

If you need to square up your lens and subject you're going to want to consider a jig. Whether tripod with camera parallel with your platform, or something like a copypod you'll need to get consistent results every time. Same distance from the subject, and perfectly parallel.
07-31-2015, 06:44 AM   #12
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I'm a little late with this post, but here's my take. The problem you're addressing is similar to mine when photographing fossils for publications: ideally you should have perfect orthographic projection so all linear distances on the image of the specimen are correct (allowing for scale). We always used long focal length lenses as recommended by several people above. The pro-illustrator at the AMNH sometimes photographed large specimens from 12-15 feet away to obtain near-orthographic imaging. On APS, use at least a ~100mm lens, better 200mm.
HOWEVER, there are specialty lenses made for near-orthographic imaging, but as you might suspect they are $$$$$. Try www.edmundoptics.com.

These do not come with usual SLR camera mounts, so you will need one, possible two adapter rings. I suspect such a lens might be attached with a combination of: 1) Pentax K to Pentax S adapter (=42mm screw thread); 2) Pentax S (=42mm screw thread) to "C" video/movie thread. I doubt you can get a direct "C" to Pentax K adapter. Also, I'm not sure how these lenses are set up for focusing. Sometimes specialty lenses are just barrels, no diaphragm, no focusing mechanism. Because you're basically doing close-ups, chances are the lens will focus properly when mounted on a Pentax body, but might not focus to infinity. However, if it cannot focus at the distances required, you might have to purchase a micro 4/3 body, which have much shorter lens flange to sensor distances and have the advantage of a wide range of readily available adapters for mounting almost any kind of lens.

Last edited by WPRESTO; 07-31-2015 at 07:01 AM.
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