**Weekly Pentax Forum Photo Thread July 26 - August 1**

Started 2 months ago | Discussions thread
OP flektogon Veteran Member • Posts: 5,202
Re: **Weekly Pentax Forum Photo Thread July 26 - August 1**

Richard Smals wrote:

flektogon wrote:

Nice pictures Richard. Regarding a different exposure at the same settings (at different cameras), I think that main culprit is the ISO "interpretation". But I found differences among Pentax lenses mount to the same camera, and differences among Pentax cameras even using the same lens. That difference I estimate to be something like +/- 2/3 EV

Thanks flektogon. I'm going to investigate this further, i've seen these ISO interpretation also but never this extreme though. The 55-300 PLM seems to have a very bad lens transmittance value (T-stop).

O.K. As I have got this lens as well, I can confirm that it gives me exactly a right "brightness" (in the P mode and regardless of a JPEG or RAW output) in comparison to, for example, my DA 35/2.8 macro Ltd. The latter one requires around -0.66 EV compensation to obtain the same (optimal) brightness. So, yes, the transmittance of DA 55-300 is definitely lower, but on my KP it performs optimally. Now, the DA 35 gives me optimal brightness when mounted on my K-x. So, if I mounted there the DA 55-300, for sure the results would be too dark. But I am not going to experiment with it .

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