CLPEX Chat Board

Hi all forensic photographers
I am looking to purchase a DSLR, the camera is not a problem it has to be a Canon as they are the Police provider, my problem is which lens should be purchased, again this needs to be Canon. At this stage the 18mp 600D camera is at the top of the list, price v features. This camera has a cropping of x1.6, this I understand from what I have read, but the stuff I have read relates to everything but close-up work. If I take a photo with a 100mm macro on the 600D it's like using a 160mm lens so I would need to be a mile down the road to photograph a house and about an 18inches from the subject if photographing a fingerprint, clearly this would not be suitable, though this is the lens most are recommending. Even the 50mm lens I need to be across the road from the house to take the shot. Have I got this wrong or am I on the right track?

I have been told I need the 18mm-55mm lens that comes standard with the camera and a 50mm macro for close up and the reason for having macro is the flat lens inside the 50mm do not distort the image on close up in the same way that the curved lens in the 18-55mm does. Am I still on track?

So why can't I buy an 18mm-55mm macro to do it all? And if I could would it be cheaper than the camera.

Look forward to lots of response.
Thanks
Neville

I am not familiar enough with Canon equipment to comment specifically on the lenses you mention, but can give some general information about lenses.

Many macro zoom lenses will focus at the macro setting only at the widest angle. And, wide angle lenses can have significant barrel distortion if used too close to the subject. Additionally, macro zoom lenses generally do not focus as closely as macro prime lenses - so you may not get as much resolution as you would if you filled your frame using a dedicated macro lens. And, a macro zoom lens is less likely to be a flat field lens, but a prime macro lens will be - meaning that the lens is designed to provide maximum sharpness across a flat subject area, which is what we're usually photographing when doing close-up photography.

As such, I would recommend using two lenses in your scenario - one for general use, and one for macro photography.

George

Hi George
Thanks very helpful. Most likely go for the 50mm macro and the standard 18-55mm, unless someone has something else to add.
What is the normal lenses used by SOCO on DSLR?

Neville,

I used a Canon 60D at work that came with an 18-135mm lens and we purchased a 100mm macro lens for all close-up work. You can use the macro lens for telephoto work but I wouldn't recommend it. As far as close-up work is concerned, I absolutely don't have to be 18" away from my prints to image them. The lens is fixed at 100mm and the the focus is all internal. I can fill the frame with a fingerprint and have a working distance of 4-6" normally. If it's a curved surface, I'll back out a bit and let my depth of field take over but cranking up the f-stop as high as it'll go (I believe f/32 on the 100mm Canon I have) and do a 2-3sec. exposure.

I don't think you'll ever be able to get very close to a latent prints with the 18-55mm lens to be suitable for comparisons. You're print will be less than 1/4 of the sensor size and you'll be losing the potential to fill your frame with the print. The 50mm macro is also a good choice but you'll end up working closer to your work if you want to still fill the frame. If you want, IM me your email address and I'll send you a couple of pictures of what I'm talking about with the camera that I use for case work.

If I'm not mistaken, there is a difference between a normal 50mm lens and a 50mm (or any) macro lens...George, perhaps you can clarify? That's why for any close-up work, we'll use the macro lens over the normal lens.

Hi Josher
Thank you for the responce, The 4-6 inches sounds fine, considering cost would you advise the 100mm or the 50mm.

I have been told that the difference between the macro and other lenses is the macro has flat glass lense which means nil distortion on close up but the trade off is a short depth of field. Other lenses have curved surfaces which gives good depth of field but on closeup the destorted fisheye effect.

For true 1 to 1 macro photos, you will need a 100mm. If i recall correctly, the canon 50mm macro can only do 1:2, or half the size of true 1:1. You can fix that by adding a doubling lense extension, but that's another expense and another set of lenses the image has to pass through so a greater chance of distortions.

Hi RM
Thanks, this may well be the case I have no idea, but at the end of the day how relevant is it, my thumb print would not fit on the CCD of the 600D, the CCD would need to be 35mmx20mm to fit my thumb plain impression with out falling off the edges and the CCD of the 600D is only 22.2 x 14.8mm that would only allow my little finger plain impression to be capture at 1:1. We can't print at 1:1 (contact) as our printers are incapable of that, so from what you are saying the 50mm would be the better option. I have to say my knowledge on lenses needs some filling in the last time I purchased macros was for the 350D and as I was on a very short time frame I purchased the 50mm macro I was sold by the salesman. I had no idea if was the right thing or not at the time, but it worked.
Neville

If you are not planning on doing true 1:1 photographs, then it doesn't really matter what lens you get. Since you will have to do some adjustments to the image to scale it, having a 50mm over the 100mm will not be a big deal. Plus the 50mm is almost half the price of a 100mm. I suggest you go to a local camera shop, not Best Buy, and talk to the staff there. Bring a sample print and the camera body so you can try out the different lenses right there.

The camera to subject distance may be an issue with the 100mm lens for footwear, blood spatter, etc. You could add extension tubes to a 50mm lens, giving it close focusing capabilities when needed for fingerprints and other very small subjects, then use it without the extension tubes for the subjects that allow for a greater distance. Extension tubes are like lenses with no glass that pare placed between the camera body and the lens, which enables a lens to focus more closely - they are relatively inexpensive, and are generally considered to be less ideal than a macro lens, but a better choice than using close-up filters (which are technically lenses that attach to the front of a lens, just as a filter does, and they enable one to focus more closely). Close-up filters are not a bad choice - just the third choice between using a macro lens, extension tubes (or bellows), and close-up filters.

This isn't an important issue, but the term you want to use regarding macro lenses is "flat field" not "flat glass." Macro lenses are designed so that they keep maximum sharpness on a flat plane or flat field - but the glass isn't flat.

Finally, the suggestion to compare the different solutions at a camera store is an excellent one. A good camera store may let you bring a memory card so that you can take some practice shots in the store for later comparison. Bring some sample fingerprints, palmprints, and footwear lifts so that you compare the sharpness, ease of use, and focusing distance for these different sized subjects. I would suggest that you call them first to set up an appointment.

George

I tried to visit the 3 local camera stores but two of the better ones did not have a 600D in stock and the other one a parallel importer was so busy we had to leave before being served; I didn't make an appointment though.
I have to admit being a bit confused about the flat lenses statement so thanks for clearing that up for me.
I have put the order in so will report back with the results if we get approval.