Need help understanding "Subject Framing Distance"

[bob williams]

When I first looked at this I thought it was pretty self explanatory. I thought this was the distance you need to be away from the target to get a full frame shot at the specified dimensions (47.25"x31.5")---This made perfect sense when I looked at the 10-22, But when I looked at the 135 F2L, this is what I got:



<table align="center" width="625" cellpadding="3" cellspacing="0" class="SpecsTable"]
<tbody>
<tr>
<td valign="top" class="SpecsTableCell"]<span style="font-size: 8pt;"]47.25" x 31.5" Subject Framing Distance</td>
<td valign="top" class="SpecsTableCell"]


135mm = 15.42'
189mm = 20.82'
270mm = 30.17'
</td>
</tr>
</tbody>
</table>



I first thought that the 3 different values were for different crop factors, FF, 1.3 and 1.6, but the math didn't work---So I am confused---I would really appreciate it if someonecould shed some light on this Spec:


Thanks,


Bob

[neuroanatomist]

I thought this was the distance you need to be away from the target to get a full frame shot at the specified dimensions (47.25"x31.5")

That's correct, although it might be better to say 'frame-filling shot' instead of 'full frame shot' since the latter implies a sensor format (i.e. crop vs. FF; Bryan states where distances are for APS-C vs. FF on some EF lenses, and obviously EF-S lenses must be framing distances for a crop sensor).


The three numbers are the subject framing distances for the native lens (135mm), lens + 1.4x Extender (189mm) and lens + 2x Extender (270mm).

[bob williams]

The three numbers are the subject framing distances for the native lens (135mm), lens + 1.4x Extender (189mm) and lens + 2x Extender (270mm).

That makes sense---Duhhhh


Thanks, One more question: For a 1.6 crop body and this Lens, would you simply multiply the distance by 1.6 to get subject framing distance for that combination?


Thanks again,


Bob

[neuroanatomist]

For a 1.6 crop body and this Lens, would you simply multiply the distance by 1.6 to get subject framing distance for that combination?

In theory, yes. There might be slight differences (for one thing, Bryan mentions in his reviews that some camera models have LCDs which are a pixel or two shy of showing the full image, so that leads to tiny variation in framing the test shots.

[bob williams]

In theory, yes. There might be slight differences (for one thing, Bryan mentions in his reviews that some camera models have LCDs which are a pixel or two shy of showing the full image, so that leads to tiny variation in framing the test shots.

Close enough for my needs: For Me, this is a very useful stat for lenses. As a thumb rule---this is slightly larger than awaist up portrait, so when determining if a lens would suit my needs I look at the distanceI would have to be away from the subject to achieve a waist up portrait. So, on a 7d with a 135 F2l, I need at least 24 feet (15.42x1.6) to get this approximate framing, Less if I am doing a head shot.


Is my logic correct?





Thanks

[Jon Ruyle]

For a 1.6 crop body and this Lens, would you simply multiply the distance by 1.6 to get subject framing distance for that combination?

In theory, yes. There might be slight differences (for one thing, Bryan mentions in his reviews that some camera models have LCDs which are a pixel or two shy of showing the full image, so that leads to tiny variation in framing the test shots.

Furthermore, it is definitely *not* true at very close distances.

[bob williams]

Furthermore, it is definitely *not* true at very close distances.

I am not talking "close" distances, I am talking about the distances specified----Jon, Please explain your comment, I am tryng to understand this. It could make a differnce on whether or not I spend my next $1000 dollars on a lens.


Thanks


Bob

[neuroanatomist]

Furthermore, it is definitely *not* true at very close distances.

I am not talking "close" distances,

Agreed - I assumed we were discussing the Subject Framing Distances as now included in Bryan's specifications data, which have relevance for portrait framing too, as Bob points out. Granted - 'very close distances' do apply to those specifications for some lenses, e.g. the EF-S 10-22mm or the EF 14mm f/2.8L II.


But, Bob is probably not planning to frame an upper body portrait with a UWA lens...unless maybe he's shooting a project for a medical practice that is trying to promote cosmetic surgical procedures... [:O]

[bob williams]

But, Bob is probably not planning to frame an upper body portrait with a UWA lens...unless maybe he's shooting a project for a medical practice that is trying to promote cosmetic surgical procedures... [img]/emoticons/emotion-3.gif[/img]

True Statement, I am afraid I would get hit really hard if I tried to do a waist up frame with my 10-22[:#], Of course with the right subject, It might be worth the pain.

[Jon Ruyle]

Furthermore, it is definitely *not* true at very close distances.

I am not talking "close" distances, I am talking about the distances specified----Jon, Please explain your comment, I am tryng to understand this. It could make a differnce on whether or not I spend my next $1000 dollars on a lens.


Thanks


Bob

Sorry- I was just being a bit pedantic. Your statement is not exactly correct at any distance, but at your example distance for the 135mm, it is very close (within a few inches- if that's close enough for you, don't worry)


At macro distances, it isn't close at all.