Confused with 50mm 1.4!

[Toby43]

I have bought a Sigma 50mm 1.4 EX DG HSM - having used the Nikon 50mm brand lenses for some years. It lets in just over half a top more light than the Nikon equivalent at the same focal length. ( it is actually equivalent to 45mm FOV compared to my 24-70). My confusion is that the lens seems to let in more bright light. ie the whites are whiter than the Nikon lenses, mid tones and dark tones about the same. My question is - is this a good thing or a bad thing? It means the tonal range is greater but this can make processing more difficult - the highlights are more easily blown. Is it something to with the lens coating? I am no expert in this as can be seen! but any thoughts gratefully received.

 

[Dak on cam]

I have bought a Sigma 50mm 1.4 EX DG HSM - having used the Nikon 50mm brand lenses for some years. It lets in just over half a top more light than the Nikon equivalent at the same focal length. ( it is actually equivalent to 45mm FOV compared to my 24-70). My confusion is that the lens seems to let in more bright light. ie the whites are whiter than the Nikon lenses, mid tones and dark tones about the same. My question is - is this a good thing or a bad thing? It means the tonal range is greater but this can make processing more difficult - the highlights are more easily blown. Is it something to with the lens coating? I am no expert in this as can be seen! but any thoughts gratefully received.

Try setting a fixed white balance: which color channel blows first can depend on what white balance the camera selects based on the tint of the lens. Also what light source are you using?

In the end, the aperture number is specified regarding the visual size of the aperture not regarding the admitted light, so coatings and optical design may affect the admitted light, and the focal length and aperture number are specified at a focus distance of ∞. At closer focus distances, the relations may change.

--
Dak

 

[Michiel953]

Confused. What is the problem?

 

[Toby43]

Confused. What is the problem?

There is more and brighter light at the RH end of the HG. Less in mid and dark, compared to a 24 70 say.

 

[Toby43]

I have bought a Sigma 50mm 1.4 EX DG HSM - having used the Nikon 50mm brand lenses for some years. It lets in just over half a top more light than the Nikon equivalent at the same focal length. ( it is actually equivalent to 45mm FOV compared to my 24-70). My confusion is that the lens seems to let in more bright light. ie the whites are whiter than the Nikon lenses, mid tones and dark tones about the same. My question is - is this a good thing or a bad thing? It means the tonal range is greater but this can make processing more difficult - the highlights are more easily blown. Is it something to with the lens coating? I am no expert in this as can be seen! but any thoughts gratefully received.

Try setting a fixed white balance: which color channel blows first can depend on what white balance the camera selects based on the tint of the lens. Also what light source are you using?

In the end, the aperture number is specified regarding the visual size of the aperture not regarding the admitted light, so coatings and optical design may affect the admitted light, and the focal length and aperture number are specified at a focus distance of ∞. At closer focus distances, the relations may change.

Thanks I'll have a look at the first point and the second is point is well made.

 

[Dak on cam]

Confused. What is the problem?

There is more and brighter light at the RH end of the HG. Less in mid and dark, compared to a 24 70 say.

Inventing your own abbreviations as you go is not likely to help with confusion. I buy "righthand" and "histogram".

At any rate, higher contrast would be a feature, not a bug. And not particularly unlikely for a prime compared to a zoom (more likely than not half the number of lens elements or fewer). The histogram also gets spread out more with a sharp lens since then the brightnesses of pixels bleed over less to their neighbors. That also means that the histogram can change with the focus and depth of field (contrast-based autofocus needs to see a difference, doesn't it?) unless we are talking about uniform unstructured areas that would also confound the autofocus.

 

[Michael Benveniste]

My question is - is this a good thing or a bad thing? It means the tonal range is greater but this can make processing more difficult - the highlights are more easily blown. Is it something to with the lens coating? I am no expert in this as can be seen! but any thoughts gratefully received.

I've never used a Sigma 50mm, but I do own the Sigma 85mm f/1.4 of the same vintage. I haven't experienced that particular issue.

A few possibilities come to mind. With pre "Global Vision" Sigma lenses, the first is always firmware issues, but if the overall exposure the same, then you may be OK there. The second is flare, which could be coating related. Do you see the same behavior when shooting indoors in manual mode, and does using a lens hood help? The third is an increase in overall contrast.

Do you have some controlled samples you can post?

 

[Blufftonian]

Are you comparing the Sigma to your Nikon zoom? (You have a Nikon 50mm f/1.8 in your gear list but nor a Nikon 50mm f/1.4.)

First off the f-number of a lens is purely the ratio of the aperture to the focal length. It serves as a very general indicator of how much light can pass through the lens, but consider that if you take a lens and paint its front element black it will still have the same f number but it won't be transmitting much light at all.

Also consider that your Sigma lens has 8 elements in 6 groups while your Nikon zoom has 15 elements in 11 groups. Every element will degrade transmission to some extent. What we'd really like to know is the T-Stop (transmission) value for the lenses we buy but they are never published, although you do see them for movie lenses where it is much more critical.

https://www.cliftoncameras.co.uk/Blog/understanding-cinelenses-what-is-a-t-stop

I have a Nikon 200-500mm f/5.6 zoom and a Nikon 500mm f/5.6 PF. The prime is faster than the zoom by a little over half a stop.

 

[Toby43]

Confused. What is the problem?

There is more and brighter light at the RH end of the HG. Less in mid and dark, compared to a 24 70 say.

Inventing your own abbreviations as you go is not likely to help with confusion. I buy "righthand" and "histogram".

At any rate, higher contrast would be a feature, not a bug. And not particularly unlikely for a prime compared to a zoom (more likely than not half the number of lens elements or fewer). The histogram also gets spread out more with a sharp lens since then the brightnesses of pixels bleed over less to their neighbors. That also means that the histogram can change with the focus and depth of field (contrast-based autofocus needs to see a difference, doesn't it?) unless we are talking about uniform unstructured areas that would also confound the autofocus.

Just laziness...

thanks for that

 

[Toby43]

My question is - is this a good thing or a bad thing? It means the tonal range is greater but this can make processing more difficult - the highlights are more easily blown. Is it something to with the lens coating? I am no expert in this as can be seen! but any thoughts gratefully received.

I've never used a Sigma 50mm, but I do own the Sigma 85mm f/1.4 of the same vintage. I haven't experienced that particular issue.

A few possibilities come to mind. With pre "Global Vision" Sigma lenses, the first is always firmware issues, but if the overall exposure the same, then you may be OK there. The second is flare, which could be coating related. Do you see the same behavior when shooting indoors in manual mode, and does using a lens hood help? The third is an increase in overall contrast.

Do you have some controlled samples you can post?

I think this lens came out in 2009 and predates firmware. Nothing on the Sigma site now anyway. I will do some control shots. Don't think it's flare or hood as being trying it indoors. Common sense tells me that a 50mm which has a wider field of view than the 50mm 1.8g and a 77mm front end is going to let in more light than the 1.8g. The 24 70 at 45mm has the same FOV as the Sigma 50mm. Of course I expect the zoom impede more light than prime. But it is at the bright end of the histogram that the extra light seems to fall. This make highlight blow out more of an issue. But contrary to that is that I always welcome a lens that lets in more light.

 

[polizonte]

With the 50mm f/1.4 HSM DG version (not EX) on my former D800e, I did not notice what you describe but I have, with some other 3rd party lenses.

 

[Michael Benveniste]

I think this lens came out in 2009 and predates firmware. Nothing on the Sigma site now anyway.

The lens has firmware, but unlike current Sigma lenses it required a trip to their service center to be upgraded.

Common sense tells me that a 50mm which has a wider field of view than the 50mm 1.8g and a 77mm front end is going to let in more light than the 1.8g.

Both should have the same field of view give or take a "fudge factor." Nikon 50mm lenses for example, were traditionally 51.6mm to conform to the Leica "standard."



A 77mm front end will let in more light, but once it passes the iris the amount of light transmitted to sensor is measured by T-stops. While the t-stop varies for different lenses at the same f-stop, it's normally not a huge difference.



I was bored, so here are three shots taken on my back deck. The setup was identical for all three shots using a tripod, so all I did was swap lenses and focus with Live View. Manual mode, f/2.8, ISO 400, sunlight light balance, each used with its OEM lens hood. These are OOC JPGs, so I apologize if the EXIF is munged. NEFs on request.


Tokina 90mm f/2.5 Macro -- This lens has a 55mm filter size. The EXIF shows 86mm because Nikon doesn't let you set 90mm.




Nikon 85mm f/2.8D PC -- This lens accepts 77mm filters, but the front element is recessed. The EXIF shows f/3 because Nikon shows effective aperture with its Micro lenses.


Sigma 85mm f/1.4 EX DG

As you can see, the focal lengths are slightly different. The Tokina may have produced slightly stronger whites, but nothing "pops" out at me as unacceptable or anything I would worry about.

--
Light travels at 2.13085531 × 10^14 smoots per fortnight. Catch some today!

 

[Dak on cam]

Tokina 90mm f/2.5 Macro -- This lens has a 55mm filter size. The EXIF shows 86mm because Nikon doesn't let you set 90mm.

And good riddance for that. The manual states that you should pick the next higher number then, but the next higher one is 100mm.

Still somewhat undecided between 86mm and 100mm here...

 

[GarysInSoCal]

My question is - is this a good thing or a bad thing? It means the tonal range is greater but this can make processing more difficult - the highlights are more easily blown. Is it something to with the lens coating? I am no expert in this as can be seen! but any thoughts gratefully received.

Yeah... blown highlights... not a good thing... and pretty much impossible to recover if they are more than 1 stop over.

Gotta good copy here of a Nikon 50 F1.4... sharp even wide open... BUT... not a very impressive portrait lens on full-frame... a much more impressive on APS-C. The crop factor gets you alittle closer to your subject... ;-)




Andrea (from the Ukraine) at the Select Models Photoshoot... her brother was killed in the war...

 

[Michael Benveniste]

Dak on cam wrote:.
Still somewhat undecided between 86mm and 100mm here...

Since I was shooting in manual mode without flash, it only matters for metadata.

 

[Dak on cam]

Dak on cam wrote:.

Still somewhat undecided between 86mm and 100mm here...

Since I was shooting in manual mode without flash, it only matters for metadata.

It also matters for matrix metering. But actually I am kind of a metadata fetishist and probably will ultimately set up my raw processor to fix up the metadata for my non-CPU lenses. Which means more choices regarding lens ID and lens type. So I should be consistent about it.

Regarding flash coverage it would make more sense to pick the wider setting to avoid the flash narrowing in more than appropriate. However, 3 different flashes with motor zoom reflector I just checked have discrete reflector settings at 85mm and 105mm which would probably not cause a difference between 86mm and 100mm reported by the camera. It's unlikely anyway you'd find a flash that would work fine for 100mm but cause noticeable problems for 90mm.

With regard to matrix metering, scale and absolute brightness are likely figuring into the scene detection from the RGB metering sensor. The brightness should likely be covered by the correct largest aperture setting (assuming a fixed-maximum-aperture lens).