FA* 85 vs A* 85

KX-Digital · 02-19-2019, 05:46 AM

Originally posted by Digitalis

when using the standard focus screen there really isn't much difference in brightness between an f/2.8 lens and an f/1.2 so saying there is a difference in brightness between f/1.4 and f/1.8 is complete BS

That depends entirely on the focusing screen. However adamyau mentions he uses the LX a lot and on that focusing screen, assuming he has the standard SC-21 installed, it makes quite a difference and with an SA-23, SE-60, SG-60 or MX SA-3 even more. If he happens to have an SA-26, SC-26 or SC-69 it will probably not make such a difference but those are not well suitable for a short and fast lens.

Partially you are right though as fact is the focusing screens of all Pentax AF-slr's and D-SLR's* do suck. These screens are have optimised brightness for the small-aperture autofocus lenses Pentax was making at the time and as stated by Pentax then, can not be used to accurately (manual-)focus fast primes. Even the AF-system is not accurate enough to be used with lenses faster than 2.8 although they work fine if closed to 2.8 or smaller so focussing inaccuracy falls inside the depth of field. It is the reason i mounted an MX screen SC-1 and later an LX screen SA-23 in my Z-1 (the SC-21 however doesn't fit), mounted a cut down Canon Ec-L in my K200d and will buy a Canon Ec-A for my next Pentax D-SLR.

The screen of the Minolta 300si is, however bright, very suitable for manual focussing.

*(i have not seen a manualfocus d-slr yet, neither from Pentax or from any other manufacturer). With those it doesn't make a difference because the screen is not brighter and is those screens are specifically said by Pentax to be not suitable for fast

02-19-2019, 05:46 AM	#16
KX-Digital Junior Member Join Date: Jul 2009 Location: Europe, Benelux, Zeeuwsch-Vlaanderen, Terneuzen Posts: 26	2.8 vs 1.4 (or 1.2) Originally posted by Digitalis when using the standard focus screen there really isn't much difference in brightness between an f/2.8 lens and an f/1.2 so saying there is a difference in brightness between f/1.4 and f/1.8 is complete BS That depends entirely on the focusing screen. However adamyau mentions he uses the LX a lot and on that focusing screen, assuming he has the standard SC-21 installed, it makes quite a difference and with an SA-23, SE-60, SG-60 or MX SA-3 even more. If he happens to have an SA-26, SC-26 or SC-69 it will probably not make such a difference but those are not well suitable for a short and fast lens. Partially you are right though as fact is the focusing screens of all Pentax AF-slr's and D-SLR's* do suck. These screens are have optimised brightness for the small-aperture autofocus lenses Pentax was making at the time and as stated by Pentax then, can not be used to accurately (manual-)focus fast primes. Even the AF-system is not accurate enough to be used with lenses faster than 2.8 although they work fine if closed to 2.8 or smaller so focussing inaccuracy falls inside the depth of field. It is the reason i mounted an MX screen SC-1 and later an LX screen SA-23 in my Z-1 (the SC-21 however doesn't fit), mounted a cut down Canon Ec-L in my K200d and will buy a Canon Ec-A for my next Pentax D-SLR. The screen of the Minolta 300si is, however bright, very suitable for manual focussing. *(i have not seen a manualfocus d-slr yet, neither from Pentax or from any other manufacturer). With those it doesn't make a difference because the screen is not brighter and is those screens are specifically said by Pentax to be not suitable for fast