Focal range

[Ken]

Hi,

I currently own a D5600 and the following lenses:

Sigma 10-20mm F3.5
35mm F1.8
18-55mm kit lens
55-200mm

I shoot mainly landscapes, street, cities and nightscapes and will be travelling to Hong Kong soon where I'll be shooting the skyline, streets, bridges and skyscrapers.
I'm looking to buy either the Sigma 24-70mm F2.8 or Sigma 70-200mm F2.8. The 24-70mm I feel will be more versatile but the 70-200mm has the reach. I'm not concerned about the weight of the latter too. I do see myself eventually buying both but can only afford one right now and wondering which one will benefit me more in Hong Kong and for the subject matter I mainly shoot in general. Thoughts on this?

Also In the midst of my research I've found my confused over full frame lenses on crop sensors and ultimately found an article that made the most sense to me. An article that basically said to stop referencing a sensor format (full frame) that I'm not even using.

So another question is if I was to buy the Sigma 24-70mm, focal range wise am I correct in saying I'm only 4mm out relative to the Sigma 10-20mm and I don't need to worry about the 24-70mm being 36-105mm which would make it 16mm away from the Sigma 10-20mm?

I essentially want the 24-70mm and 70-200mm to replace my 18-55 and 55-200mm thereby covering the 10-200mm focal range as follows...

10-20mm <4mm not covered by the lenses> 24-70mm <> 70-200mm

Finally as for the f2.8 aperture on the 2 lenses I'm looking to buy, is that actually going to be f4.2 on a crop sensor even if the LCD states f2.8?

Thanks!

 

[Raymond Lin]

24-70 on a cropped sensor is like 35mm on the wide end, i mean I've been to HK so many times and I find 35mm comfortable but that may not be for you.

F/2.8 would stay the same, a crop sensor is essentially a digital crop in camera.

 

[Snapshot]

I think that article has got you thoroughly confused. What is written on the lenses is always the physical focal length so if you consider that the 24-70mm is equivalent to 36-105mm when used on your D5600 then you must also consider that the 10-20mm is equivalent to 15-30mm. Or you drop equivalence and just think about 24-70mm and 10-20mm.
Aperture is also a physical measurement and the exposure is not affected by the size of the sensor. But don't start a conversation about aperture equivalence as things will get contentious and confusing......

 

[Drollic]

For crop sensor and a mixture of shooting in hk, the kit lens focal range is ideal. The second hand market out there is amazing for lenses if you know where to look although sadly the exchange rate is now terrible. Maybe trade the 35mm and kit lens for something like the 18-35mm 1.8 sigma. I wouldn't want 24-70 for landscape on crop. The 18-24 you give up is far more useful than the extra reach. You can get really nice results on crop at 1.8 and around 35mm for people as a bonus. There's so much to see and take in there, ideally you don't want to be messing around swapping out lenses.