PetaPixel review of the HD DFA 100mm 2.8

jgnfld · 05-04-2023, 06:28 AM

Originally posted by simon_199

For sure. Between max aperture and size/weight of camera lenses there is clear correlation. But still, 1/3 of a stop is very little, within the wiggle room of small alterations of a basic design. Maybe they could have made it 5% bigger and gain back that 1/3 stop and decided against it for wathever reason. It would still be a compact lens with a much more modern design than the original screw driven. The factors at play are many in determining size and weight, data suggest that presence or absence of in-lens motor is by far one of the least relevant, given the ample availability of silent focusing lenses in point of the size/weight/cost/focal length envelope.

With the modern sensors Pentax uses, 1/3 of a stop is never an issue in my experience anyway. Hard to imagine the marginal situation where it would.

But Uncle V makes a valid point about that observation which I've wondered myself.

simon_199 · 05-04-2023, 06:44 AM

Originally posted by jgnfld

With the modern sensors Pentax uses, 1/3 of a stop is never an issue in my experience anyway. Hard to imagine the marginal situation where it would.

But Uncle V makes a valid point about that observation which I've wondered myself.

To sacrifice 1/3 of a stop was surely dependent on some tradeoff. Even if "to sacrifice" is not fair because it's a completely different design (even retractable, maybe that's the culprit, who knows) and not a mere refresh of the previous lens with the same optical formula. So it's impossible to attribute the loss of one stop to one factor or another. What we can conclude is only the factual information: the lens has the same range and very similar speed within 1/3 of a stop, it costs the same, it is smaller or similar in size, and has a fantastic in-lens motor. So no, screw drive AF is not a necessary condition for light, small and cheap.

**Rondec** · 05-04-2023, 06:45 AM

Originally posted by UncleVanya

It’s easy to forget that the PLM also lost 1/3 of a stop of light. That may have influenced the design permitting the size.

My guess was that the focus by wire mechanism was the difference. PLM motors are pretty tiny and only having to move a very small focus group is helpful in keeping lens size down. Beyond which, telephoto zooms have more space in which to hide focus motors. The issue is more difficult with a lens like the DA 40 limited or most of the other DA limiteds, where the whole lens size if pretty tiny and so adding a focus motor would have to increase the size at least a little bit.

I don't know how the Canon EF 40mm f2.8 compared with the Pentax DA 40mm in terms of performance, but the DA is 88 grams versus 130 grams for the Canon. Interestingly, the Canon 40 didn't seem to come with a hood -- there was an insubstantial one sold separately for 25 dollars.

Wheatfield · 05-04-2023, 06:58 AM - **1 Like**

Originally posted by Mistral75

The HD Pentax-D FA Macro 100mm f/2.8 ED AW is only one of many exceptions, so many that their number contradicts your statement:

Dating back to the 1990s doesn't mean from the 1990s.

Just sayin.

Reading the rest of the thread, it has become obvious that we are in circular firing squad territory.
I'm afraid this one has run it's course.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Pentax 100mm comparison, DFA 100mm f2.8 vs M 100mm f2.8	house	Pentax SLR Lens Discussion	18	03-08-2022 06:50 AM
PetaPixel K-3 Mark III Review	Kobie	Pentax K-3 III	44	08-09-2021 02:44 PM
Petapixel K-3 Mark III Review	bladerunner6	Pentax News and Rumors	2	07-26-2021 11:35 AM
Macro DFA 100mm/2.8 vs DFA 100mm/2.8 WR	tcom	Post Your Photos!	9	01-11-2010 02:10 PM

05-04-2023, 06:28 AM	#46
jgnfld Moderator Loyal Site Supporter Join Date: Feb 2015 Location: Avalon Peninsula, Newfoundland Photos: Gallery \| Albums Posts: 1,789	Originally posted by simon_199 For sure. Between max aperture and size/weight of camera lenses there is clear correlation. But still, 1/3 of a stop is very little, within the wiggle room of small alterations of a basic design. Maybe they could have made it 5% bigger and gain back that 1/3 stop and decided against it for wathever reason. It would still be a compact lens with a much more modern design than the original screw driven. The factors at play are many in determining size and weight, data suggest that presence or absence of in-lens motor is by far one of the least relevant, given the ample availability of silent focusing lenses in point of the size/weight/cost/focal length envelope. With the modern sensors Pentax uses, 1/3 of a stop is never an issue in my experience anyway. Hard to imagine the marginal situation where it would. But Uncle V makes a valid point about that observation which I've wondered myself.

05-04-2023, 06:44 AM	#47
simon_199 Pentaxian Join Date: Oct 2014 Posts: 613	Originally posted by jgnfld With the modern sensors Pentax uses, 1/3 of a stop is never an issue in my experience anyway. Hard to imagine the marginal situation where it would. But Uncle V makes a valid point about that observation which I've wondered myself. To sacrifice 1/3 of a stop was surely dependent on some tradeoff. Even if "to sacrifice" is not fair because it's a completely different design (even retractable, maybe that's the culprit, who knows) and not a mere refresh of the previous lens with the same optical formula. So it's impossible to attribute the loss of one stop to one factor or another. What we can conclude is only the factual information: the lens has the same range and very similar speed within 1/3 of a stop, it costs the same, it is smaller or similar in size, and has a fantastic in-lens motor. So no, screw drive AF is not a necessary condition for light, small and cheap.

05-04-2023, 06:45 AM	#48
Rondec Loyal Site Supporter Join Date: Mar 2009 Location: Gladys, Virginia Photos: Gallery Posts: 27,653	Originally posted by UncleVanya It’s easy to forget that the PLM also lost 1/3 of a stop of light. That may have influenced the design permitting the size. My guess was that the focus by wire mechanism was the difference. PLM motors are pretty tiny and only having to move a very small focus group is helpful in keeping lens size down. Beyond which, telephoto zooms have more space in which to hide focus motors. The issue is more difficult with a lens like the DA 40 limited or most of the other DA limiteds, where the whole lens size if pretty tiny and so adding a focus motor would have to increase the size at least a little bit. I don't know how the Canon EF 40mm f2.8 compared with the Pentax DA 40mm in terms of performance, but the DA is 88 grams versus 130 grams for the Canon. Interestingly, the Canon 40 didn't seem to come with a hood -- there was an insubstantial one sold separately for 25 dollars.

05-04-2023, 06:58 AM - 1 Like	#49
Wheatfield Moderator Join Date: Apr 2008 Location: The wheatfields of Canada Posts: 15,981	Originally posted by Mistral75 The HD Pentax-D FA Macro 100mm f/2.8 ED AW is only one of many exceptions, so many that their number contradicts your statement: Dating back to the 1990s doesn't mean from the 1990s. Just sayin. Reading the rest of the thread, it has become obvious that we are in circular firing squad territory. I'm afraid this one has run it's course.