Sony A7III: 85mm lens by itself or 55mm 1.8 in a crop mode on fly to "simulate" 85mm?

Question

I'm a casual & amateur street photographer.

OK, so recently I sold my entire Canon gear (6D and 24-105 + extras) and I switched to Sony for the first time ever. The main reason was to be ultra portable while still remain in a full frame world hence the choice. The only lens I bought was deliberately small Carl Zeiss 35mm 2.8. This combo is lightweight and I like it.

However while 35mm is classic for street I can forget about subject isolation due to the focal length. I fight hard to keep the background tidy but it's not that easy.

I would like to try something longer. Ideally 85, but I came up with a nasty idea. You already see the title.

Since A7III offers crop mode that I assigned to my C3 button, I can quickly turn it on or off. I know that the downside of crop is less megapixels due to the crop factor.

Question: would you rather go with Zeiss 55mm / 1.8 and enable crop to get something around ~85 on fly or would you directly go to Sony 85mm / 1.8?

Getting 55 and switching to crop on fly looks a way to get virtually 3rd lens for free. I know that 24 mega pixels will be reduced in the final image but this is still acceptable. What would you recommend?

Thanks, Matt

Answer 1

Zeiss 55 1.8 is a very expensive lens.

I believe you could get two used Sigma Art 1.4 lenses to roughly the same price.

If you want to get the shallow depth of field then cropping is not what you want to do.
That translates to a higher aperture value, and makes more in focus.

I have no experience of the Zeiss, but I have two Sigma Art and prior to my last Art purchase I read and looked at lots of reviews on all the focal lengths and they all perform very well as far as I can see from reviews.
The two I got are fantastic in my opinion.

Having two lenses will be bulkier but give you a better aperture value.
Perhaps a good f2 zoom is a good medium way.

But regarding the subject.
I would not crop in camera.
Save it to post where you can crop to what you want and not be "limited" to two crop modes.

Answer 2

The first few paragraphs of juhist's answer can be confusing, so stated a bit differently: A 55/1.8 lens in crop mode will produce an image that looks like one made with an 83/2.7 lens (but exposure will still be calculated with F1.8). If the reduced aperture look (F2.7) and the reduced resolution (10.6mp), are acceptable to you, crop mode may work out fine.

• I use focal reducers to do something similar to what you're planning. A 50/1.8 lens with focal reducer is converted into a 36/1.3 lens (with exposure calculated at F1.3). A 200/4.5 lens is converted into a 147/3.7 lens. I've found that many lenses work better in one mode or the other. Also, focal reducers are a bit of a hassle to change. So despite being able to use lenses for dual purposes, they tend to be used for only one.

• Consider choosing the secondary function (crop mode) based on the focal length you expect to be less useful. For instance, if you expect to shoot much more at 85 than 50, it would make more sense to get the 85/1.8, which can double as a 127/2.7 lens. You can then let the 35/2.8 double as a 52/4.2 lens. You could also skip the 85 to go for a 135/2.8, which could double as 202/4.2 lens.

I'd consider something like Tamron 28-75/2.8 + 135/2.8 prime. Crop mode would extend the zoom to 112/4.2, and the prime to 202/4.2. That would more or less cover the 28-200 range with two lenses. For faster apertures in low light, I'd consider adding a 50/1.8.

• But not 50/1.4 because the 50/1.4 lenses I have need to be stopped down to F2.8 for sharpness, while the majority of my 50/1.8 and 50/2 lenses are sharp wide open.

• And probably not 85/1.8 because 50mm is generally more versatile and you can get similar framing with crop mode.

Answer 3

The plan seems to be good (with crop mode, you see the cropped result in viewfinder, if Sony works like EOS RP works, as an answer to the comment by Andreas), with one caveat.

Do note the 55mm / 1.8 = 30.555 mm aperture opening in 55mm lens, whereas 85mm / 1.8 = 47.222 mm aperture opening is in 85mm lens.

The 55mm / 1.8 and 85mm / 1.8 lenses are not equivalent. To get equivalence, you would need either 55mm / 1.2 + 85mm / 1.8 or 55mm / 1.8 + 85mm / 2.8.

Since background blur depends on the aperture opening, you won't get equivalent background blur with 55mm / 1.8 cropped and 85mm / 1.8 full frame. The 55mm / 1.8 cropped is more like 85mm / 2.8 full frame.

Only you can know if a simulated 85mm / 2.8 is enough or if you really need the 85mm / 1.8.

I'd say 55mm is so close to 35mm that I would select the 85mm, and then use 35mm with crop to obtain the 55mm. Then you have one lens with good subject isolation (85mm / 1.8) and the 35mm / 2.8 that can simulate 55mm / 4.4. The 55mm / 4.4 would be similar to Canon 24-105 at this focal length (f/4.4 vs f/4 only a small difference), so you should know what to get from 55mm / 4.4.

Furthermore, you can crop the 85mm / 1.8 to obtain effectively what is 135mm / 2.8. If the two lenses you have are distinct from each other, you have 4 lenses effectively with crop mode. If the two lenses you have are similar to each other, you have 3 lenses effectively with crop mode.