Focal Length?

[DSJohnson]

I just bought my first Prime lens the other day, mainly for portraits. I realized that I have a DX camera so I need to pay attention to the focal lengths to get exactly what I wanted. Since I wanted a 50mm focal length I purchased a 35mm lens.

Well my next purchase in the upcoming months will be a wide angle lens for architecture/interiors/cityscapes/landscapes. I have my eye on the Sigma 10-20mm but it just occurred to me that yet again I have to take into account that multiplier factor.

So if I get the 10-20mm that will really be getting me about 15mm on the wide end correct?

That kinda sucks if that's correct. I have an 18-55mm already and I do realize that 15mm is definitely a significant difference... Is there anything I can do at all to make that 15mm closer to 10mm... I doubt it, just checking.

[dcclark]

Yes, you're right. With the 1.5x crop factor, your field of view will be equivalent to a 15-30mm lens on a full-frame camera.

But, 10mm is the widest that any rectilinear lens gets on crop bodies (you can get wider fisheyes, but those are... well, fisheyes!). Believe me, the difference between 10mm and 18mm is enormous, even on a crop body. At those focal lengths, every millimeter adds much more onto your field of view than it does at, say, 100mm or 200mm.

Remember, the widest "full frame" lens Nikon ever made (and I think the widest of any ultrawides) was "only" 13mm, and that was a $10,000 ulta-specialized beast!

[Sterling]

You're a little mixed up regarding focal lengths. Lens focal lengths are all measured in mm. There aren't different mms for DX bodies and FX bodies. The view with each body will be different but the lens will have the same focal length. For example, your 18-55 would be equivalent to a 27-82 on an FX body. And like you say, a 10-20 would be equivalent to a 15-30 on an FX body. So in summary, the 10-20mm would make a great wide angle companion to your 18-55, overlapping only from 18-20mm and giving you a total range of 10-55.

[beatryder]

I've got the 10-20 Sigma and the 18-105 Nikkor and believe me when I say this: The 10-20 is much much wider than the 18-105. There is little difference between 18 and 20, so don't worry too much about duplicating your focal lengths.

The 10-20 is a super fun lens, and with a larger flash can be great for tight spaces.

What' the others are saying is correct, for the most part, don't even worry about DX vs FX as I doubt that anyone will try and sell you and FX lens for your DX body (even though it would work, but you'd have different results).

[OsmosisStudios]

As dcclark alluded, a 10-20 lens will be multiplied by 1.5. But so will your 18-55. So you end up with 35mm equivalent lenses of 15-30 and 27-90. You're really only overlapping 3mm, and that between 27 and 30.

[DSJohnson]

Thanks guys for the help. I'm definitely going to get the lens. Can't wait to take some great landscape/cityscape shots with it.