Low light issues

[photoflyer]

I don't really want a prime lens, a zoom is better for what I need.

Don't discount primes too quickly. They can be the cheapest way to acquire speed which is what you want. The 35 and 50 mm variety at f 1.8 are small and inexpensive. I too like the flexibly of a zoom and I have several very good ones but sometimes to get "the shot" the little $100 prime comes out out the bag.

 

[petrochemist]

Thanks for the replies

I don't really want a prime lens, a zoom is better for what I need.

From what you have said, and due to the camera limitations I think that it may be worth getting the Sigma lens. Even a small improvement would be an improvement on how things are at the moment.

However, as was mentioned, the circumstances I outlined would probably not occur that often, so the question is would the Sigma lens be as good, or better than the Nikon kit lens in general use ?

If tripods & flash are not allowed, I'd say the zoom is USELESS for what you need! You need much more light gathering. The reframing ability of a zoom is nice but it's easy to crop the image from a prime to give a narrower FOV...
For the cost of the 17-70 you could probably get a 50/1.8, & a 10/2.8 while still having money left over (quite possibly enough for a body 5 years newer than your d5000)

 

[ac12]

I don't really want a prime lens, a zoom is better for what I need.

It does not matter what YOU want, it matters what the situation calls for, and what compromise can be made.

Standard ISO guideline is, raise the ISO level to whatever you need to get an image. You either have ISO noise or a blurred image from too slow shutter speed. Your 1.5-2 sec shutter speed is WAY TOO SLOW for hand holding, and only doable on a tripod.
The newer cameras are better at high ISO than the older cameras.

FAST glass almost always wins, in a low light situation.
There is only so high you can raise your ISO, and there is only so low that you can lower your shutter speed.
While I would love to use a short zoom to shoot indoor basketball, an expensive pro f/2.8 zoom is still 1 stop slower than my f/1.8 prime, and consumer zooms are even slower.
So while I would be at 1/500 sec f/2 ISO 3200, you would be at 1/500 sec f/5.6 ISO 25600.

 

[Gary Evans]

Yeah, I think that I'll keep my kit zoom lens and get this:

Nikon DX 35mm f/1.8G AF-S

 

[TCampbell]

A tripod would, of course, be ideal (if you can bring one).

What lens was the "other guy" using? I think a 35mm focal length may be a bit too long (on an APS-C body, that's slightly longer than "normal" focal length. Normal for APS-C is roughly 28mm ... give or take a tiny bit).

Using a very low focal ratio will thin the depth of field ... so you may find that you don't have very much of the scene in acceptable focus.

BUT... you can counter that by using a short focal-length (wide-angle) lens ... which increases the depth of field. Another advantage of the short focal-length is that it stretches the sense of depth and makes the chamber in the cave seem larger. ALSO... the shorter the focal length, the easier it is to hold it steady. Hand-held for 2 seconds isn't going to work no matter how short the focal length is. But anything you can rest the camera on can be a big help.

I've not done any photography in caves ... but my inclination would be to use something in the 14-20mm range.

To give a few examples...

A 14mm @ f/2 (Sigma makes a 14mm f/1.8) focused to about 10 feet... as an 18' DoF (everything from 6-24' is in acceptable focus). At f/2.8 it has a 54' DoF. That's one of the wonderful things about these very low focal ratio lenses is that you get the stretched sense of size and depth, a massive depth of field, *and* you can use a low focal ratio at the same time.

Play with the numbers at a website like this one: http://www.tawbaware.com/maxlyons/calc.htm
or this one: Online Depth of Field Calculator