[UncleVanya]

6x7cm format divide by 2 to get the 24x36mm format equivalent: 105 / 2 = 52mm fullframe ergo 52*1.5 = 78mm in Apsc.
6x7cm format divide by 2 to get the 24x36mm format equivalent: 165 / 2 = 82mm fullframe ergo 82*1.5 = 122mm in Apsc.

You should divide by 1.5 not multiply... 52mm on full frame is more like 35mm.

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105mm on 6x7 is around 35 APSC.
165 on 6x7 is around 50mm in APSC.

[carabez]

105mm on 6x7 is around 35 APSC.

From the link you posted:

"As an example a 50 mm [full frame] lens on APS-C has an "equivalent" focal length of 75mm." ergo 50mm fullframe lens * 1.5 = 75mm apsc lens

[UncleVanya]

From the link you posted:

"As an example a 50 mm [full frame] lens on APS-C has an "equivalent" focal length of 75mm." ergo 50mm fullframe lens * 1.5 = 75mm apsc lens

That is correct, but you are misunderstanding what it means. Look at the chart. And simply think about it this way. The DA* 50-135 is the APSC equivalent of the DFA 70-200. The DA* 16-50 is the equivalent of the DFA 24-70, Full frame gives a wider angle of view. You don't calculate the full frame lens then multiply it by 1.5 and mount that, you do the opposite.

An example, of I want a 50mm lens field of view on the K-3 and K-1 I can use either one as my standard reference point. Assuming I like the way it looks on the K-3, I need a lens close 75mm on the K-1 to be similar in angle of view etc. If I prefer the look of a 50 on the K-1, then I need a 35mm (roughly) on my K-3 to get the same angle of view and framing. Your example reversed this math.

[kernos]

Angle of view is not the only consideration. A 50mm lens is still going to render like a 50mm lens on a crop sensor. You don't get a 75mm lens, just a smaller version of a 50mm image. More of the image will be in sharp focus at portrait length at the same fstop, You will not get the same results for blur unless you go with a wider aperture, which explains why m4/3 lenses often have really wide max apertures. For portrait work (in general) on APS-C it is better to use a portrait length lens and just back up, at least for head and shoulders shots.

[UncleVanya]

Angle of view is not the only consideration. A 50mm lens is still going to render like a 50mm lens on a crop sensor. You don't get a 75mm lens, just a smaller version of a 50mm image. More of the image will be in sharp focus at portrait length at the same fstop, You will not get the same results for blur unless you go with a wider aperture, which explains why m4/3 lenses often have really wide max apertures. For portrait work (in general) on APS-C it is better to use a portrait length lens and just back up, at least for head and shoulders shots.

I disagree in practice despite the theory saying you are right. I have many shots that don't fit that model but work well. Post some shots with APSC 50 and longer and illustrate your concerts.

[carabez]

You will not get the same results for blur unless you go with a wider aperture

That correct!

If a 100mm lens set to f/2.4 on a 6x7 camera (which has a crop factor of 1.0) gives the same field of view and depth of field that a 50mm lens set to f/1.2 would on a Fullframe camera (which has a crop factor of 2.0)

Sensor size perspective and depth of field

Now, what's field of view and depth of field do I have with a 6x7 100mm f2.4 on a apsc camera?

[UncleVanya]

That correct!

If a 100mm lens set to f/2.4 on a 6x7 camera (which has a crop factor of 1.0) gives the same field of view and depth of field that a 50mm lens set to f/1.2 would on a Fullframe camera (which has a crop factor of 2.0)

Sensor size perspective and depth of field

Now, what's field of view and depth of field do I have with a 6x7 100mm f2.4 on a apsc camera?

30-35mm around f1.0 if you insist on trying to get depth of field and angle of view the same. However that ignores the format ratio differences which aren't the same so angle of view is far from easy to compare.

[carabez]

However that ignores the format ratio differences which aren't the same so angle of view is far from easy to compare

Yup, it's not easy to compare, in fact is a waste of time.

I have a Fullframe format 55mm f1.2 lens
I have a 6x7 105mm f2.4 lens
I have the apsc Pentax 55-300mm
I have the K-3

Let's go testing

[UncleVanya]

Yup, it's not easy to compare, in fact is a waste of time.

I have a Fullframe format 55mm f1.2 lens
I have a 6x7 105mm f2.4 lens
I have the apsc Pentax 55-300mm
I have the K-3

Let's go testing

That 55-300 is far from similar. Too narrow and slow to be similar. My FA 31 f1.8 would be closer but not identical.

[kernos]

I disagree in practice despite the theory saying you are right. I have many shots that don't fit that model but work well. Post some shots with APSC 50 and longer and illustrate your concerts.

Ok this is going to be hard to prove from my own work, but I will give it a try imperfect as the comparison is going to be. All shots are of my friend Jesse. Comparison is with the Canon FL 55mm 1.2 which is generally agreed to be a good portrait lens on full frame and the FA77 which everyone agrees is a good portrait lens on APS-C or full frame.


First shot K5iis Canon FL 55mm 1.2 I am guessing this is either 1.2 or 1.4 simply because the ISO is 100 and the shutter speed is 1/40 indoors with some natural light and overhead illumination.




I like the photo well enough, but the facial lines are stronger than what I'd like in a portrait.

Second shot K5iis FA77 f2.5 ISO 100 1/125 mostly diffused natural light with some overhead. Even closed down more than the Canon, the facial lines are less pronounced.



Third from a headscarf series I did with near ideal natural light. FA77 f2.8 ISO 100 1/100




This of course proves nothing. I even like the first photo although Jesse did not because it highlighted facial lines. But objectively, the longer lens, even stopped down a bit, gives a more classic portrait look. If you are going for character and grit, then its true that a the shorter focal length will work fine and may even be preferable. But that's not typically why someone buys a portrait lens, which was the OP's goal.

[UncleVanya]

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Focal length and format are a part of the equation. I think we can agree to disagree.

---------- Post added 09-03-18 at 11:58 AM ----------

Just to add one more thing. I endorse getting whatever focal length works for you. The op likes longer lenses, great there are dozens of mf 135's that fit his desired needs. The person who talked about 6x7 lenses however had their math backwards I'm not here to debate in this thread the methods of long vs short I'm however compelled to clarify that 75mm on apsc is not equivalent to 50mm full frame that is what needed correction... everything about equivalent focal lengths is heuristic formats have differing characteristics that equivalence only scratches the surface with.

[kernos]

Focal length and format are a part of the equation. I think we can agree to disagree.

For sure, although there really is not a disagreement. I like your photos and they fit your artistic purpose and situation. There are folks who manage to get headshots out of 50mm lenses that work beautifully too. I love this shot and it is a perfectly valid and lovely portrait, but part of the photographers vision is highlighting the particulars of skin texture and freckles. So, the harshness fits what she's trying to achieve.

Alexandra Bockhareva, Canon 4ti, Helios 77M 50mm 1.8

[Andrea K]

On FF without AF ? I found that the Tokina ATX-Pro 60-120mm f/2,8 gives me the best results.. seems a sort of STF lens

[kernos]

On FF without AF ? I found that the Tokina ATX-Pro 60-120mm f/2,8 gives me the best results.. seems a sort of STF lens

It would be great to see some examples. The lens review examples are not terribly good.

[UncleVanya]

For sure, although there really is not a disagreement. I like your photos and they fit your artistic purpose and situation. There are folks who manage to get headshots out of 50mm lenses that work beautifully too. I love this shot and it is a perfectly valid and lovely portrait, but part of the photographers vision is highlighting the particulars of skin texture and freckles. So, the harshness fits what she's trying to achieve.

Alexandra Bockhareva, Canon 4ti, Helios 77M 50mm 1.8

Excellent work And I agree.