lens technicalities

Hi all,

Just upgraded to a D70s (plus 18-70 mm kit lens) and needed some tips and fairly basic questions answered on lenses please.

I am considering buying a macro lens (either Nikon 60 mm or 105 mm). Is there a difference between shooting the 18-70 mm at 60 mm zoom and using a 60 mm macro lens? Is the 18-70 mm lens not 1:1? Further on this, digital cameras have a crop factor (this is the correct phrase?) due to the sensor being smaller than 35 mm. I have heard people say this would make an 18 mm lens around 28 mm with a crop factor of 1.6. Does the crop factor actually affect the focal length i.e. your focal range, or does it just mgnify the image you see? Does this crop factor also mean a 1:1 macro lens is now not a 1:1 but a 1:1.6? And yes....I am more than a little confused...

Any help you can give me would be greatly appreciated

Cheers,

Ash

Hi Ash, welcome to the forum!

To answer your questions:

1) The 18-70 does not go 1:1, the 60 or 105 do, that's why you also want a macro lens.

2) The crop factor does not affect the focal length, it affects the field of view. The crop of the D70 is 1.5 so, a 60mm on a D70 will have the same field of view as a 90mm on a 35mm camera (60x1.5).

3) The magnification does not increase to 1:1.6. The designation of 1:1 simply means that the camera can photograph objects in LIFE SIZE, so, if you photograph a fish that is 20mm long it will be 20mm in the sensor. Now, because the sensor in cropped cameras is smaller you can fill the frame with a 24mm long fish, but to fill the frame on a 35mm camera you would need a 35mm fish. What you CANNOT do with a 1:1 lens is make a 20mm long fish represent an image of 30mm in the sensor, for that you would need a 1:1.5 lens.

This subject of magnification comes up very frequently here, so to be perfectly clear as to what I am talking about, here is a little scheme of what I mean:

As you can see, the lens magnification does not change, it is 1:1 regardless of sensor size (meaning that a 20mm subject will be 20mm in the sensor), you simply crop the field of vision in the smaller sensor.

Luiz

Luiz, with all the crap that gets flung back and forth over this issue, that diagram should be worth a FORTUNE! ;-)

Thanks Luiz,

That was a very helpful explanation. I am deciding whether to buy the 60 mm or the 105 mm macro. I realise they are for different purposes, however I was wondering if it is a waste of time buying the 60 mm when I have the 18-70 mm lens already. With the same subject matter, is the picture you could take with 60 mm macro that much better than one you could take with the 18-70 mm lens? If the answer to the previous sentence is yes, then I guess I would go straight for the 105.

Cheers,

Ash

In VERY general terms, short macro lenses focus on a subject closer to the lens and are preferred by photographers like myself who shoot in murkier temperate waters as they reduce the amount of water through which then lens has to 'look'. Longer macro lenses are used more in clearer tropical waters where they allow for a longer working distance and potentially better lighting. There are many other factors, but, depending on where you dive, this might be a starting point for you to post further questions.

Getting closer is almost always better, macro or wide angle. Getting dramatic shots by getting close is important. Here is one I shot at Catalina Island in California. I was maybe 1.5-2 feet from this torpedo ray.

Thanks guys,

Great info. I'm doing most of my underwater work in Sydney, Australia (temperate, and often frustratingly turbid). Considering your comments on water clarity Paul, I should go for the 60 mm. I may not even see the fish I'm trying to shoot through the murk with the 105 mm!

All the best,

Ash

ps, that is a beautiful shot of the ray Joe!

I have recently started to use the 60mm micro Nikkor. After a Nikonos and then a compact digital the first thing I've had to adjust to is just how long this focal length is compared to what I have been used to.

I've aleays read with interest on wet pixel how many people prefer their 105 Nikkor for fish and macro. As with Paul most of my diving is in green UK water where getting in close is the key to success for me. I am doubtful now if I would get on with anything longer than the 60mm in the UK.