[aurele]

Yeah, I'm now wondering what the T-stops are for the rest of my lenses, too. Where can one find this information, or measure it in lenses one might already have?

The best "guesstimate" i've done so far is using the known T-stop of my modern lenses.

Some website, like DxO can provide a T-stop value. DxO is not the only one. The maker of the lens can give it too (like Samyang - look the cine version that has speed express as T-stop. The 85mm if T-1,5. The 14mm is T-3,2, etc ....)

I do use the DA*55 as a base lens : it has a T-stop around 1,7 wide open (and is marketed as F1,4).

You take a picture with the DA*55 of a controled area (at the same F-stop than your other lens).

You take the same picture of the same thing, with your other lens.

The difference in exposure value, gives you a guesstimate of the t-stop.

The DA 35/2,4 has a T-stop between 2,2 and 2,4 i think.

The A 50, 1,7 has a T-stop of maybe 2,2 - 2,4.

The DA 40 has a T-Stop of 3.

the M 75-150 is around 5.

the Vivitar S1 70-210 f3,5 is probably around T-4,5 - 5.


The newer the lens, the closer the T-stop value may be to the F-stop, than the older one.

But that's just a mere guess.

[baro-nite]

I don't know if this is a reasonable method for testing this, but I just made exposures of a blank wall, first with no lens, then with the M and K 35/2 wide open (focused at infinity). I then opened the files in my usual raw developer and tried to match the exposures. Here's what I found:

With the M version, an adjustment of +2 EV got me about the same mean exposure value. With the K, this needed +2.08 EV. The K is a touch yellower and that might explain some of the difference.

Seems unlikely that the M has a t-stop of 2, but that's what this test seems to tell me.

[aurele]

I don't know if this is a reasonable method for testing this, but I just made exposures of a blank wall, first with no lens, then with the M and K 35/2 wide open (focused at infinity). I then opened the files in my usual raw developer and tried to match the exposures. Here's what I found:

With the M version, an adjustment of +2 EV got me about the same mean exposure value. With the K, this needed +2.08 EV. The K is a touch yellower and that might explain some of the difference.

Seems unlikely that the M has a t-stop of 2, but that's what this test seems to tell me.

Adjusting WB before exposure wil help you getting a good leveled measure.

Because adjusting WB do have an influence of the lumination levels, in PP.

[Green&White]

Sony A7 & Super-Multi-Coated Takumar 1.8 85, ƒ4

[pinholecam]

Yeah ! I found it

The thread is really good, and the comparaison did help me a lot !

The DA35/2.4 is really a step above the M version. and despite being f2.4 vs f2, my guess is that the DA have a better T-stop than the M one.

My real only complain about the DA is the ultra short focus throw ! If only i could make it longer

My own findings are that the FA35/2 is already a superb lens.
Very little that it can't do even vs the FA31ltd.
This is especially so on apsc where the full FOV of the 31ltd is not utilized (part of the reason for the high cost is that its a wider than 35mm with f1.8)

The 31ltd does have an edge with about 0.3-0.5ev exposure difference (ie. t-stop difference), smoother bokeh and less obvious hex shaped OOF highlights.

[chti]

Northern Laos
Pentax-K 35/2

[chti]

Pentax-K 35/2

Attached Images

View Picture EXIF

File Date

 

[Green&White]

Sony A7 6 smc Pentax-FA 2.8 100 macro, ƒ5.6

[chti]

Sony A7 & SMC-Pentax M85/2 wide open.

[elpolodiablo]

X post from M club

M 50 f1.4 on Sony A7
















And this one with M 75-150 f4

[pinholecam]

X post from M club

M 50 f1.4 on Sony A7

And this one with M 75-150 f4

Nice!

[ranchy]

Sunrise in Bagan, Burma.
Pentax M85/2

Wow nice shot with the M85!

[jlstrawman]

Sony A7 II + SMC Pentax-m 20mm f/4

[pinholecam]

The day has finally arrived.
The long wait is over.


M85/2




K1+K28/3.5

[debakarma]

Thanks pinholecam, for testing out the K & F series on the K1. Looking forward to more of your tests. Looks like the old glass is holding up just as well with the new DFAs. Lots of us will continue to hold our old glasses just for that alone.

---------- Post added 05-02-16 at 08:55 AM ----------

I do use the DA*55 as a base lens : it has a T-stop around 1,7 wide open (and is marketed as F1,4).
You take a picture with the DA*55 of a controled area (at the same F-stop than your other lens).
You take the same picture of the same thing, with your other lens.
The difference in exposure value, gives you a guesstimate of the t-stop.

Aurele, thank you so much for this great info. I have the DA*55, so when time permits I might post a few guess-estimates.