In the wait of the Sigma Art 135mm

ericktessier

I will probably buy the Art 135mm as soon as it's available but in the wait, I was playing with the numbers Sigma gives about this lens and I hope I'm wrong in my calculation. This is supposed to be a fantastic lens but...

Am I right or the 1:5 magnification and the 87.5cm minimum focusing distance gives 122mm as focal length? There'll be a lot of focus breathing since the angle of view (which should be when focusing at infinity?) is 18.2 deg giving 135mm focal length at infinity...

In comparison :

The Nikkor 105mm 1.4 would vary from 103mm to 106mm which is way more acceptable.

The Art 85mm would give 82mm to 85mm.

Please tell me I'm wrong for the Art 135mm.

snakebunk

I think that the 135 and 1:5 may not be exact numbers.

How did you do the calculation?

ericktessier

Using multiple online tools to calculate magnification ratio on a full frame sensor.

Maybe Sigma didn't gave the exact magnification ratio but to have 135mm this would lead to 1:4.2 which is far from 1:5. The Art 50 and Art 85, on their technical datas all have precise magnification ratio (1:5.6 and 1:8.5). Why wouldn't they have given precision for the Art 135mm?

snakebunk

Ok, it was just a guess. I have read that long tele lenses are often a lot shorter than what the spec says, a 500 mm lens may actually be something like 480 mm.

ericktessier

Seen on the B&H website : Preorders start 12am Fri Mar 17

heartyfisher

I am not exactly sure how you did your calculations... but...

1) It is likely that the 135 is indeed shorter at closer distances due to focus breathing that is in most lenses.

2) Your calculations may be off a bit because of tele lense designs (opposite of retrofocus wide angle designs), which makes a tele lense physically shorter than its focal length. This plays a part in the actual distance to object(MFD). In a telephoto lense, the image which is focused on the sensor should have been be a few cm behind the sensor. ie for your calculations the MFD could possible be over 90-92 cm.

ericktessier

Then why would Sigma state 0.875m as minimum focus distance? Ok assuming the behind the sensor thing I do get it.

But that means that for a 500mm lens, the minimum focus distance given by the manufacturer would be way off if the relation is linear with the focal length.

heartyfisher

The MFD quoted is the actual physical distance that the lens focuses to from the sensor.

In a 500mm lense the focus plane should be 500mm from the front element. But the nice lense designers have reduced the physical length of the lense. The nikkor 500mm is 387mm in length. If you add the f-mount flange distance of 46.5 the length equals to 433.5 a saving of at least 66.5 mm in physical distance. However, the image is still "virtually" (sorry dont know what word to use LOL) at 500mm.. if you look through the front element it looks deeper than the physical lense..(A bit like the tardis LOL)... just like in the retrofocus wide angle lenses if you look through the front element it looks shallower then the physical lens.

ericktessier

And that's my point. To have a MFD of 0.875 and a magnification ratio of 1:5 on a full frame sensor you have a focal length of 122mm.

I don't really care about focus breathing but considering I already have the Nikkor 105mm 1.4 I'm not sure if I'll see a big difference with the Art 135mm if it's only a 122mm (ok this value is only at MFD which makes a real difference because of the higher magnification ratio (1:5 compared to 1:7.69)).

FreezeAction

Has anyone actually purchased and used this lens? I have an interest in this focal length for making multiple row landscape panoramas. There is no DXO data to look at currently.

WestEndFoto

It is common for lenses to have shorter focus lengths at close focus. The old 70-200 2.8G was notorious for this and even the E has not licked it, though it is no longer a serious issue.

Seriously? You are worried about 122 instead of 135? I

I would not worry about it unless you are capturing nose hairs.