Sigma 105mm working distance on Nikon D5300?

I want a macro lens and I came across the Sigma 105mm EX DG OS HSM… This lens is designed for a full frame camera, but I'm using the Nikon D5300(crop sensor). Can anyone tell me what minimum working distance would I have. By working distance, I mean the distance from the object to the front of the lens.
Thanks…
http://www.sigma-imaging-uk.com/lens/macro-lens/macro-105mm-f28-ex-dg-os-hsm

If it is the current lens, Sigma says 12.3" for a 1:1 macro ratio.

What you have to realize though is that the minimum focus distance is not the issue, the ability to focus to 1:1 is.

For example, 1:1 means life size, so a 1/2" bug would cover 1/2" on the sensor, as if it were placed directly on the sensor.

A 40mm macro lens (Nikon AF-S 40mm) with a 1:1 ratio might have a close focus distance of say 6", with that 6" providing the 1:1 ratio.

So the Sigma 105m lens having a close focus distance of 12.3" to produce a 1:1 image will look exactly the same size as the 40mm lens.

So… This means the 105mm lens is better for bugs as you don't have to get as close to obtain the photo (or perhaps scare off the bug), and indeed, the 105mm lens is preferred for bugs over the shorter focal lengths precisely due to the longer distance.

But that also carries a penalty… DoF. DoF at macro ranges is wafer-thin, and with a 105mm lens, you typically have to use apertures of f/11 or smaller to obtain a suitable depth of field (in-focus area). And in fact, lenses such as the Tokina 100mm macro (which I have), you can go all the way down to f/64 in macro mode.

This presents a problem… You will need a macro flash when going with that small of an aperture - even in the direct noon day sunlight.

Since the DoF is wider at the shorter focal lengths, lenses such as the 40mm macro not only do not usually need a flash, they can often be hand-held.

But with a 105mm lens, you all but need a tripod and flash to obtain sufficient DoF.

A cropped camera will allow you to back up more for the same 1:1 photo, which means that the DoF will be a bit more favorable with a cropped camera, so you might get away without having to use a macro flash.

You can also use focus stacking as indicated above if you use a tripod and are not photographing moving objects such as bugs. But if you are doing bugs - at least those not on display with a pin through them - you can't usually use focus stacking as bugs do not stay put for several photos.

If you are just getting into macro and don't care about bugs, then I would recommend something like a Nikon 40mm f/2.8 micro (which I own), But if bugs is your goal, then the Tokina 100mm f/2.8, Sigma 105mm f/2.8, Nikon 105mm f/2.8, and so on is your best choice… Along with needing a tripod and macro flash (at least eventually).

Also certain techniques are in order. You will want to use a remote shutter, and if your camera supports it, use MUP mode (Mirror Up). Just the mirror slapping during the photo can blur the photo from vibration.

Lens review:

http://www.althephoto.com/lenses/bigtok.php

What do the specifications say on the Sigma website. All APS-C sensors have a 1.5x crop factor but for Canon. It has a 1.6x crop factor

The other factor you need to know is that when you set a macro lens to a specific image to subject ratio like 1:2 or 1:1, the focusing becomes a function of you moving the whole camera an lens combination toward or a way from the subject. If you try and "auto-focus", the image to subject ratio will change

I use a special 4-way rail camera mount attached to my tripod. Once my lens is set to the exact image to subject ratio I need, I then use the rail mount to move the focus along the subject. Then using the depth of field preview, determine the proper lens aperture. If parts of the subject are still out of focus, I use a technique called 'focus stacking'

EDIT: The longer the macro lenses focal length, the shallower the depth of field at any given lens aperture. This is why those photographers who specialize in macro photography, usually own at least two macro lenses. One of my colleagues is a Medical Media photographer she owns five macro lenses, from 40 mm out to 200 mm

I simply looked up the specs on the Sigma website and came up with this gem:
"Minimum Focusing Distance31.2 cm / 12.3 in"

Now, that's the distance from the subject to the camera's digital sensor, so you'll need to subract about 5", as that's the length of the Sigma lens, plus about another inch for the depth of the camera body. That would leave you with about 6.3" from the front element of the lens to your chosen subject.

http://www.sigmaphoto.com/...-hsm-macro