Does it make sense to buy a Sigma Art f1.4 for a crop sensor body?

Question

Im currently shooting on a Nikon D5300 with a 35mm f1.8 and I looking for a quality telephoto portraiture lens. I'm interested in the Sigma Art 85mm f1.4 DG HSM. I saw the lens is versatile and my main goal is to shoot portraits with occasional landscapes and wildlife.

When applying the crop factor I get a focal length equivalent to a 127,5mm which should be a good addition to my 35mm f1.8. However, if I understand correctly the aperture need to be multiplied as well, which results in an f2.1 and means I am losing at least an f-stop.

So does it still make sense to buy this 'fast' lens on an aps-c camera to get the great bokeh and background separation it advertises with? I can get the lens new for 830 euro and am estimating if it is great value for money.

Answer 1

I think you're over-thinking this, and with all respect to everyone else trying to help, I think the answers focusing on depth of field equivalence calculations are making things worse. No one is wrong — I just think it's leading in the wrong direction. Let me suggest a different approach.

The crucial thing first: you will absolutely be able to make photographs with this lens on your camera where your subject's nose is in focus but their ears are not. Or more usefully, yes, with this lens and your camera, you can get meaningful separation from your subject and a background, perhaps blurring out a busy background so it does not distract from your subject.

By all accounts, this is a lovely portrait lens. If that's what you are looking for, and the economics work out for you, then it is absolutely "worth it".

But what about this depth of field that could be even more shallow on full frame? Well, it would be even more shallow on medium format. Worrying about that doesn't provide you with any value. What's your alternate? To stick with slow lenses? That would be silly, like, "My car isn't a Formula One racer, so I only drive at 15mph."

Or perhaps you meant, do I need a faster lens? Well, again, not to get great bokeh and background separation. (In fact, you have plenty of room to stop down from f/1.4 and still get that.) If you do, your one alternative is the Mitakon Zhongyi 85mm f/1.2 — no one else makes a faster 85mm lens for Nikon. And that lens has some interesting, positive reviews, but is manual focus and makes a great deal more optical compromise than the Sigma Art lens. So maybe you want that, but — it's not necessary.

In general, there's a lot of mysticism around full-frame on the Internet. Full-frame isn't magic, and isn't the pinnacle of photographic options. It's just a larger sensor size than APS-C — and smaller than medium format, and smaller still than a whole host of historical film formats. It's true that this lens happens to be usable on modern cameras in both APS-C and full-frame formats (DX and FX, in Nikon terms), but that's really just a quirk and shouldn't hold you back.

On this site, a photograph is worth more than a thousand words, so let me present some examples to demonstrate the point. I did a quick search on Flickr and came back with a few.

This one was shot on an APS-C Canon camera (sensor slightly smaller than Nikon APS-C), on a Sigma 85mm f/1.4 lens:

... and that's actually stopped down a tiny bit to f/1.6!

Or here's one on a Pentax K100D (a camera from over a decade ago) — it's a different 85mm f/1.4 lens, but the basics of depth of field are the same:

And here's one on a Nikon D80, again with some other 85mm lens, but, also again, the basic idea is illustrated:

You can find more examples pretty easily. In short, this lens can definitely do what you describe wanting. Of course, whether spending for what you want makes sense is a personal decision no one else can make for you, but my sense is that you won't regret it.

Answer 2

However, if I understand correctly the aperture need to be multiplied as well, which results in an f2.1 and means I am losing at least an f-stop.

In short: No.

If you use a FF-lens with an APS-C sensor, part of the light that is collected by the lens is not hitting the sensor but the amount of light that hits a part of the sensor stays the same (as long as we compare sensors with similar pixel sizes).

So if your only concern is the loss of an f-stop, don't be ;-)

Answer 3

You will never lose any transmission stops (low light ability) using a smaller sensor, unless something behind the camera mount severely constrains what reaches the sensor (unlikely with general purpose still cameras one sensor size apart). Some would say ISO at different sensor sizes is not equivalent: When exposure is discussed, this is nonsense; such comparisons are about noise performance.

The field of view will be that of a 135mm lens, while the depth of field behaviour will be that of a 85mm lens at f1.4 (not a 135mm lens at f1.4). There might be a very slight loss of DoF (which works for you if you want subject isolation) actually due to a smaller circle of confusion being acceptably sharp at smaller pixel pitch.

Answer 4

If an 85/1.4 lens is needed to accomplish a real photographic goal, and you're willing to spend the money, go for it. However, if you're just chasing a large aperture, it isn't worth the extra cost.

An 85/1.4 lens on crop sensor is not "versatile":

• The field of view and working distance limit composition and subject selection. Often framing is too tight with longer lenses and the room simply isn't large enough to back away any more.

• The depth of field at F1.4 is too narrow. I usually have to stop down to F5.6-8 just to get a useful DOF. Even in low light, I would still stop down to F4-5.6 and crank up the ISO. More likely, I'd switch to a wider focal length, which would have wider DOF at larger apertures with similar working distances – 35/2 and 50/1.8 would be reasonable choices.

  Keeping the same F-number and subject size apparently keeps the DOF constant. However, when switching to wider lenses, I maintain similar working distances. I do not push the camera into people's faces to attempt to maintain the same framing.

• Camera shake affects images more with longer lenses. For low light, wider lenses can get away with longer exposure times.

• Lens performance wide open tends to be worse with faster lenses (softer with more aberrations).

• Faster lenses tend to be slightly softer throughout the aperture range than slower equivalents (based on reviews I've seen where lenses with the same focal length, but different max apertures, from the same manufacturer were compared).

In the Adorama article:

• All of the wide-aperture demo images in the "Bokeh Tests" section do not look sharp.
• All of the "Times Square" images were taken at 200mm F4.5 even though the lens is capable of F2.8.

It also seems you're confusing some concepts.

• F/N on APS-C looks like 1.5F/1.5N on full frame in terms of field of view, depth of field, and amount of blur (you've been writing F = 1.5F on APS-C).

• Exposure is calculated based on the unadjusted F-value. You do not lose a stop of light.

• Depth of field and background blur are not the only factors that affect subject-background separation. Other factors to consider include sharpness, bokeh quality, vignetting, and lighting.

Answer 5

You have a lot of good answers already. Technically an 85mm lens is an 85mm lens regardless of camera body. The "crop factor" doesn't really change the focal length per se... it's just that on a crop-body you're only using a 28mm image circle instead of a 43mm image circle (specifically a 3:2 rectangle that can fit inside that circle). In other words, more of the image is spilling off the sides of the sensor on an APS-C body than would spill off the sides on a full-frame camera. But the part of the image that does not spill off... that part is the same.

Exposure doesn't change. e.g. if you shoot at f/1.4 on a full-frame it's still f/1.4 on an APS-C sensor.

But there is something usually does change ... and that's the photographer's behavior. And this does impact the "look" of the final image.

Example:

Suppose you are shooting a half-shot portrait (waist-up) with a full-frame camera. You decide that you need to stand a certain distance from the subject to get a waist-up framing (it's not a 'zoom' lens, so you physically move nearer/farther (zoom-with-your-feet) to achieve the framing you want). Suppose the distance that gives you the framing you want is 8 feet away (giving you a vertical height of just about 3' 4" or about 1 meter). (This isn't a great example because the depth of field would only be 1.7" ... tricky to work with but I'll use the example anyway.)

When you switch to an APS-C size sensor, the field of view (previously 3'4") will drop to about 2'4". To get back to the 3'4" field of view and have similar framing, you would need to step back to about 12' (50% farther away). If you use the same f-stop, the depth of field will naturally increase since the distance increased. The DoF will roughly double. This will have an impact on the amount of background blur. From a DoF perspective (and amount of blur) it's "as-if" you multiplied the crop-factor (1.5x) by the f-stop (1.4 x 1.5 = 2.1) but only for calculating the DoF ... not for calculating exposure (that part does not change).

If you change nothing (don't step back) then the physics of DoF for that exposure, distance, etc. wont change (you'll just get a smaller field of view.)

You can play with a DoF and dimensional field of view calculator to see how this works. Here's a free web-based version I use: http://www.tawbaware.com/maxlyons/calc.htm

Answer 6

Okay, so to boil it down, you're wondering if an 85 f/1.4 would be worth it on an APSC camera because of the crop factor.

Comparatively speaking, your field of view will be equivalent to 127.5mm on a FF camera with DoF equivalent to f/2.1.

So, comparatively speaking, if you were to ask a similar question, "Should I buy a 135mm f/2.0 for a FF camera?" then we could use that answer to aid in answering your question. (I'm using a 135mm f/2.0 because I'm a Canon guy and that's just what I know. I'm sure Nikon has an equivalent)

So, would I suggest you get the 135 f/2.0 for FF? - if you need the focal length, then obviously. You can look for reviews on the focal length but in a nut shell, if you have the space to shoot it, it's a wonderful place to be, especially for portraits. But, the space is the key part - make sure that you have it. If you don't, you may find it a bit tight.

Bringing this back to the 85 f/1.4 on APSC - yes, the focal length may be tight for some, good for others. Honestly, you should rent the lens for a week and see how you feel about it.

But, in looking at just the focal length and just the aperture - I'd say that it's a solid choice, simply because it's FF comparable is also such a solid choice. Again though, that's if you have the space and it fits your style.

Answer 7

I happen to have Canon 85mm f/1.8 (35mm equivalent 136mm) lens for use with my Canon 1.6x crop sensor camera. It's a bit long for being the most used lens, but it's definitely good for low-light conditions where a mild telephoto is needed. Before I had the 85mm f/1.8, I used a 50mm f/1.8 a lot and found many shots from long distances would have benefited from a longer focal length.

In your Nikon, 85mm is equivalent to 128mm. Probably a bit better for general use than 136mm, but less good if low-light telephoto with an emphasis on the telephoto is what you want.

It's a good question if you need the f/1.4 or if f/1.8 would be enough for you. There is a Nikon f/1.8 lens with 57% of the price. The f/1.8 would be 31% of the weight. For my tastes, the Sigma 85mm would be way too heavy, but then again I'm heavily against high-weight equipment. Only you can decide if the high cost and high weight of the Sigma 85mm are tolerable.

If I have time to change to a suitable lens, I prefer primes over zoom lenses. I would probably purchase even a fast 135mm (35mm equivalent 216mm) prime if such a prime was available at a reasonable cost and weight and with an autofocus feature. Canon 135mm f/2 L weighs 750 grams and costs over $1000, being too heavy and expensive for my uses, so if I need 135mm, I pick the 55-250mm f/4-5.6 IS which has f/5 at 135mm. In handheld use, the IS overcomes the small aperture.

Answer 8

You can consider canon 50mm 1.4 instead of sigma version. 50mm 1.4 is one best lens , great value for money. Try not to shoot at 1.4 ,and sweet spot is around F2.0 ...shooting at 1.4 makes the subject smoother.

Canon is the best choice.