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Sigma 50-100mm Art Lens


Philh04 Plus
14 2.1k United Kingdom
10 Sep 2018 3:57PM

Quote:Try to understand this Phil. If I attach a full frame 65 to 130mm lens to a full frame 5D and invite the OP to look through and say to him that's the same field of view you will get when you attach that Sigma 50 to 100mm APS-C lens to your 1D Mk 3 that will not be the case.



Of course it will be the case, you cannot change the laws of optics...

In simple terms that everyone should be able to understand....

It is a 50mm to 100mm lens, full stop nothing is going to change that even if it is designed to cover APS-C.

Put that lens on an APS-H camera and the FoV will be equivalent to using a 65mm to 130mm lens on a full frame camera.

No matter how much you argue that very simple fact will not change.

You seem to think that because a lens is designed to cover APS-C it has some special quality, it doesn't. Tests have in fact shown that the lens mentioned will provide sufficient coverage to work on an APS-H sensor, in fact it works extremely well so it will be the equivalent of that 65mm - 130mm. Full stop. there is no argument

Equivalence also works when you increase the sensor/film size from the standard that is accepted as 24 x 36mm or full frame, it simply works the other way round.

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Philh04 Plus
14 2.1k United Kingdom
10 Sep 2018 4:35PM
Put it this way;

Apart from the projected image circle what is the difference between a 50mm lens designed to be used on APS-C, a 50mm lens designed to be used on APS-H, a 50mm designed to be used on a full frame camera or for that matter a 50mm designed to cover medium format (say 6 x 4.5).

Just talking FL equivalents using the Canon crop factors.

APS-C the 50mm will be 80mm equivalent
APS-H the 50mm will be 65mm equivalent
FF the 50mm will be 50mm equivalent
and MF the 50mm will be 31mm equivalent

(645 BTW has a crop factor of 0.62)
Chris_L 6 5.4k United Kingdom
10 Sep 2018 4:36PM
Wow those APS-C lenses are indistinguishable from full frame equivalents.

Where is the crop in your crop factor?

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Philh04 Plus
14 2.1k United Kingdom
10 Sep 2018 4:45PM
Chris I cannot understand why you are trying to attach relevance to the projected image circle... equivalence still applies even if the lens is unable to cover the format... As it happens the lens that the OP was asking about will sufficiently cover an APS-H sensor...

Equivalence is simply a way to express how a particular lens will behave on different formats, it has nothing to do with the coverage of the lens.


Quote:Try to understand this Phil. If I attach a full frame 65 to 130mm lens to a full frame 5D and invite the OP to look through and say to him that's the same field of view you will get when you attach that Sigma 50 to 100mm APS-C lens to your 1D Mk 3 that will not be the case.


This statement, to be quite frank is utter rubbish.
Chris_L 6 5.4k United Kingdom
10 Sep 2018 5:00PM
If I attach a full frame 65 to 130mm lens to a full frame 5D and invite the OP to look through and say to him (according to you Phil) that's the same field of view you will get when you attach that Sigma 50 to 100mm APS-C lens to your 1D Mk 3

That's your claim Phil. It's rubbish. The field of view can NOT be bigger than the image circle

ChrisV 13 2.3k 26 United Kingdom
10 Sep 2018 5:02PM
Isn’t the crop factor actually reversed? I mean if you project the same image circle onto a larger sensor you’re increasing the AoV because you’re going to capture a wider view of the scene (albeit whatever is still retained, vignetted or not).

So if the sensor of that APSH is covered by the image circle it should be divided, not multiplied by 1.3 = 38.5-77mm (rounded). You’re also of course dividing the f stop, so it is effectively slower.
Philh04 Plus
14 2.1k United Kingdom
10 Sep 2018 5:23PM
It is obvious Chris_L that you are simply determined to score points as ever. It does not matter if the lens is not able to cover the sensor, film or whatever, there is still an equivalence, manufacturers wouldn't quote equivalent focal length if the coverage had any relevance...

As it happens the 50mm to 100mm Sigma lens will cover an APS-H sensor, and will cover FF at longer focal lengths and stopped down a little (as expected).

Yes the FoV using a 65 - 130mm lens on FF will be the same as using a 50 - 100mm lens on APS-H, even if it doesn't fully cover the sensor the FoV will be the same... But all academic anyway as the lens covers APS-H.


Quote:So if the sensor of that APSH is covered by the image circle it should be divided, not multiplied by 1.3 = 38.5-77mm (rounded). You’re also of course dividing the f stop, so it is effectively slower.

It is multiplied Chris as is the aperture, the base used for calculations is 24 x 36mm or the so called full frame, so the smaller the sensor the further away you need to be to achieve the same framing...
ChrisV 13 2.3k 26 United Kingdom
10 Sep 2018 8:01PM
Actually the confusion is in the word Ďmultiplierí so itís easy to forget when youíre talking about a lens thatís 50-100 on a Canon APSc you are actually getting an AOV thatís equivalent to 100-200 on canonís APSc sensor. So youíre dividing down from that as a starting point, not 50-100.

I did make that mistake - but I think itís an easy trap to fall into when youíre talking about multiplying. As the lens is made for APSc youíre dividing the AoV you get from that format, so that a lens you think of as starting at moderate telephoto is suddenly significantly wider if it will cover the full sensor (and I take your word for it on APSh albeit with significant vignette wide open.
Philh04 Plus
14 2.1k United Kingdom
10 Sep 2018 8:32PM

Quote:Actually the confusion is in the word ‘multiplier’ so it’s easy to forget when you’re talking about a lens that’s 50-100 on a Canon APSc you are actually getting an AOV that’s equivalent to 100-200 on canon’s APSc sensor. So you’re dividing down from that as a starting point, not 50-100.

Errm no Chris... The starting point is 50 - 100 and I have no idea where you get 100 - 200 from.

The lens is going to be 50 - 100 no matter what size of sensor is behind it so any equivalence calculation starts there, there is no dividing down...

A 50mm lens is just that, a 50mm and will be a 50mm no matter what size the sensor is.

To get the same Angle of View on different size sensors means that you have to move further away if the sensor is smaller than the standardised 24 x 36mm and closer if the sensor is larger, of course this affects DoF so the aperture is also multiplied by the crop factor.

But just taking the focal length equivalence for Canon it simply works out to;

For full frame 50mm = 50mm equivalence

For APS-C (1.6x) 50mm = 80mm equivalence

For APS-H (1.3x) 50mm = 65mm equivalence

Equivalence simply communicates an idea of how a particular lens behaves whilst maintaining identical, or near identical framing on a film or sensor format that differs in size to the 24 x 36 standard.
banehawi Plus
15 2.2k 4069 Canada
10 Sep 2018 10:29PM
What was the question? Wink
Philh04 Plus
14 2.1k United Kingdom
11 Sep 2018 9:08AM

Quote:What was the question? Wink

LoL... The Original question was, can the Sigma 50mm - 100mm f1.8 Art lens be used on a Canon EOS 1D3 and the answer is an unreserved yes, it will work exceptionally well by all accounts.

So apologies to the original poster for the way this thread went.

However some points need to be made clear, equivalence is simply a means to describe how a lens will 'behave' in front of a sensor or film that is smaller, or indeed larger than the base standard of a 24 x 36mm full frame format.

Physical properties of the lens such as the size of the image circle are not taken into account.

To say 'that lens A has an equivalent focal length to xx on a full frame sensor but the image circle may not be large enough to cover that FF sensor is correct.

To say that there is no equivalence because the image circle is insufficient to cover the size of the sensor is utter nonsense, the image circle is not a part of of equivalence.

Now before my first post in this thread, with a little knowledge (i.e coverage problems manifest themselves at the wider end and this lens is just a tad longer than wide) I did a quick bit of research and lo and behold that particular lens looked like it would play with a 1.3 crop sensor so I posted as such with the proviso that there may be a little bit of mild vignetting etc which probably wouldn't matter depending on subject and mentioning the equivalent focal lengths and aperture correctly.

My only error was to type effective instead of equivalent. I was then told that I was wrong.

I did a bit more looking into it and found out that the level of vignetting for this lens when used on a 1.3 crop body is on par for a wide aperture lens at an EV value of -1.7 and improving as the lens is stopped down, as expected....

Still I am told that I am wrong and that there can be no equivalence....

But hey ho... when the OP mounts one on his 1D3 then he will have a full frame equivalent of a 65mm to 130mm f2.34 (lets round that to f2.4, its easier to say and not a huge difference) even though it is still physically a 50mm to 100mm.
Chris_L 6 5.4k United Kingdom
11 Sep 2018 1:50PM

Quote:when the OP mounts one on his 1D3 then he will have a full frame equivalent of a 65mm to 130mm f2.34

No he will not. There will be a huge difference. The angle of view on a real full frame lens would be reduced slightly. The angle of view on the DC lens will not be reduced at all. There won't be any crop factor.

You make it seem that if he was to look through a 50mm lens on a friend's 5D then look through that 50mm Sigma on his 1D III that he will see less, he won't at all! And I think you realise that now!

Philh04 Plus
14 2.1k United Kingdom
11 Sep 2018 2:21PM

Quote:No he will not. There will be a huge difference. The angle of view on a real full frame lens would be reduced slightly. The angle of view on the DC lens will not be reduced at all. There won't be any crop factor.

You make it seem that if he was to look through a 50mm lens on a friend's 5D then look through that 50mm Sigma on his 1D III that he will see less, he won't at all! And I think you realise that now!


It might help if you knew what you were talking about....

Simple facts....

A 50mm lens is a 50mm lens, it cannot be anything else.

A 50mm lens when mounted on a full frame camera will be a 50mm lens.

Mount that same 50mm lens on a 1.3 crop camera and to get the same framing you need to move back to a point where you would need to use a 65mm lens on the full frame camera, hence a 65mm equivalence.

Mount that same lens on a 1.6 crop camera and you have to move back so that you would need an 80mm lens to achieve the same framing, hence an 80mm equivalence.

You are trying to redefine equivalence, perhaps you ought to make a youtube video telling everyone else that they are wrong.

Just because a lens is designed for the smaller format sensor does not give it any special qualities... that 50mm to 100mm when used on an APS-C is still going to have an equivalence of 80mm to 160mm, no matter how you try to justify your ridiculous assertions... even Sigma quote the equivalence (albeit Nikon).

If you use your head... put that lens on an APS-C camera and at 100mm you will have one FoV, put it on a 1.3 crop camera without moving and the FoV will be slightly wider, put is on a full frame camera and the FoV will be wider still.
Philh04 Plus
14 2.1k United Kingdom
11 Sep 2018 3:35PM

Quote:No he will not. There will be a huge difference. The angle of view on a real full frame lens would be reduced slightly. The angle of view on the DC lens will not be reduced at all. There won't be any crop factor.

To continue that statement alone shows complete ignorance on the subject of equivalence... Why do you think that the calculations are based on the 1.6 crop sensor? The crop factor and equivalence are based on the base standard of a 24 x 36mm full frame sensor. Equivalence is simply a theoretical means to describe how a particular lens will 'behave' on a sensor or film format that is smaller than that base standard or indeed larger, yes larger formats also have a crop factor.

To say that the angle of view on the DC lens will not be reduced at all is just plain stupid, when used on a larger sensor then it is quite clear that the angle of view is increased. The lens in question (just using FL equivalence) is an equivalent to an 80mm to 160mm full frame lens when used on an APS-C sensor, it will be equivalent to a 65mm to 130mm full frame lens when used on an APS-H sensor and this is strange, it will be equivalent to a 50mm to 100mm full frame lens when used on a full frame sensor. What part of that can you not understand?
Chris_L 6 5.4k United Kingdom
11 Sep 2018 5:26PM
Try to understand it this way.

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Guess what, the angle of view changes on APS-H but it doesn't get narrower, it gets wider

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