D FA 21 Limited is one of the three.

sculptormic · 07-01-2020, 08:43 AM

Looks like a nice lens to have. Not to big either. mmmm.

**mattt** · 07-01-2020, 10:30 PM

Originally posted by Serkevan

Not at all. A rough size comparison with recent designs (Tamron 20/2.8, Nikon 20/1.8 and others for example) says that f/2 or whereabouts is perfectly doable, but we won't know until Ricoh tells us.

Thanks for info

redcat · 07-01-2020, 11:32 PM

f2 is a must or it will be a disgrace to the Limited line

angerdan · 07-02-2020, 01:17 AM

Originally posted by mattt

Just checking in to see if we've identified / confirmed aperture speed? There's too much bickering on the forum these days to go through all the posts to find the ansewers. TIA for response.

Originally posted by starjedi

Based on the philosophy of limited lenses, it should neither be bulky (1.4 or even 1.8) nor slow(eg 4). So we can have with prob:
F1.9 --> 15%
F2 ---> 15%
F2.1 --> 10%
F2.2 --> 10%
F2.4 --> 15%
F2.5 --> 15%
F2.8 --> 15%
F3.2 --> 5%

Physically it's limited to f2.8 or smaller. Remember this post:

Originally posted by phoebus

OK! Is that better?

D FA 21 Limited is one of the three. - Page 8 - PentaxForums.com
D FA 21 Limited is one of the three. - Page 8 - PentaxForums.com

**Serkevan** · 07-02-2020, 01:37 AM - **1 Like**

Originally posted by angerdan

Physically it's limited to f2.8 or smaller. Remember this post:

D FA 21 Limited is one of the three. - Page 8 - PentaxForums.com
D FA 21 Limited is one of the three. - Page 8 - PentaxForums.com

The Sony 20mm f/1.8 must be breaking physics, then, because it has a 67mm thread (of which the front element takes about half, it's not even that big), yet it somehow manages more than one stop over the "physical limit".

gazonk · 07-02-2020, 02:10 AM - **2 Likes**

21mm f/2.1 would be about right for a limited lens

**Rondec** · 07-02-2020, 03:51 AM - **1 Like**

I think 21mm f2.8 would be fine if it is solid wide open. I'd rather have a little smaller lens (and maybe a touch cheaper too) than to have an f2 aperture that I really don't need.

Those who need wider aperture will go for the DFA *24 f1.4 which will be excellent, have sharpness across the frame wide open, and have minimal coma.

phoebus · 07-02-2020, 03:53 AM - **1 Like**

Originally posted by Serkevan

The Sony 20mm f/1.8 must be breaking physics, then, because it has a 67mm thread (of which the front element takes about half, it's not even that big), yet it somehow manages more than one stop over the "physical limit".

Maybe the Sony registration distance has an effect - less retro-focal...

**Serkevan** · 07-02-2020, 05:03 AM - **1 Like**

Originally posted by phoebus

Maybe the Sony registration distance has an effect - less retro-focal...

Sure. Let's take the Nikon 20mm f/1.8 - 77mm filter thread but the front element itself has a diameter of 50mm.
Or let's take the ancient, diminutive Nikon 20mm f/2.8 - which has a 62mm thread and a front element of about 40mm.

Clearly, Nikon also learned to break the laws of physics

.

**pres589** · 07-02-2020, 05:06 AM

Originally posted by redcat

f2 is a must or it will be a disgrace to the Limited line

Did you mean Star instead of Limited? Have you looked at the history of Pentax Star lenses and Limited lenses and compared their max apertures? Maybe do that, make a list, and share it with the group. I think it would be educational and a fun way to look back at both lines of lenses.

**travelswsage** · 07-02-2020, 05:52 AM - **1 Like**

Do folks really use a 21mm for wide open aperture? I'm a landscape guy so most shots will be at f5.6 and on. Is the desire for f1.8/2 for astrophotography? Just curious what folks will use the f1.8 of f2 for?

Sandy Hancock · 07-02-2020, 06:01 AM

Originally posted by redcat

f2 is a must or it will be a disgrace to the Limited line

The lenses in the FA Limited line are all sub f/2.0
The DA Limited lenses are all over f/2.0
There is no DFA Limited line yet, so your arbitrary standards do not apply.

**pres589** · 07-02-2020, 06:02 AM - **1 Like**

travels: Yes, indoor shooting would drive me to using a lens like that wide open once in a while. I've had to use my DA 15 wide open at its massive f4 to get large group shots. Glad that ISO 3200 is as viable as it is on modern digital cameras. This 21 would be a clear improvement.

Sandy Hancock · 07-02-2020, 06:03 AM - **3 Likes**

Originally posted by travelswsage

Just curious what folks will use the f1.8 of f2 for?

Low light indoors.
Environmental portraits.
Astrophotography.
Other things.

**pres589** · 07-02-2020, 06:04 AM

Sandy: Don't forget the Ltd zoom which is both slower than f2 max aperture AND the aperture is variable. Horror upon horrors.

That's why I previously mentioned considering star lenses vs limited for max aperture and assuming requirements based on history.

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07-01-2020, 08:43 AM	#616
sculptormic Veteran Member Join Date: Dec 2012 Location: Amsterdam Posts: 469	Looks like a nice lens to have. Not to big either. mmmm.

07-01-2020, 10:30 PM	#617
mattt Site Supporter Join Date: Feb 2011 Location: Niagara Photos: Gallery \| Albums Posts: 3,907	Originally posted by Serkevan Not at all. A rough size comparison with recent designs (Tamron 20/2.8, Nikon 20/1.8 and others for example) says that f/2 or whereabouts is perfectly doable, but we won't know until Ricoh tells us. Thanks for info

07-01-2020, 11:32 PM	#618
redcat Veteran Member Join Date: Jul 2014 Location: Paris Photos: Gallery Posts: 1,939	f2 is a must or it will be a disgrace to the Limited line

07-02-2020, 01:17 AM	#619
angerdan Pentaxian Join Date: Feb 2015 Photos: Gallery \| Albums Posts: 2,639	Originally posted by mattt Just checking in to see if we've identified / confirmed aperture speed? There's too much bickering on the forum these days to go through all the posts to find the ansewers. TIA for response. Originally posted by starjedi Based on the philosophy of limited lenses, it should neither be bulky (1.4 or even 1.8) nor slow(eg 4). So we can have with prob: F1.9 --> 15% F2 ---> 15% F2.1 --> 10% F2.2 --> 10% F2.4 --> 15% F2.5 --> 15% F2.8 --> 15% F3.2 --> 5% Physically it's limited to f2.8 or smaller. Remember this post: Originally posted by phoebus OK! Is that better? D FA 21 Limited is one of the three. - Page 8 - PentaxForums.com D FA 21 Limited is one of the three. - Page 8 - PentaxForums.com

07-02-2020, 01:37 AM - 1 Like	#620
Serkevan Site Supporter Join Date: May 2019 Photos: Albums Posts: 5,976	Originally posted by angerdan Physically it's limited to f2.8 or smaller. Remember this post: D FA 21 Limited is one of the three. - Page 8 - PentaxForums.com D FA 21 Limited is one of the three. - Page 8 - PentaxForums.com The Sony 20mm f/1.8 must be breaking physics, then, because it has a 67mm thread (of which the front element takes about half, it's not even that big), yet it somehow manages more than one stop over the "physical limit".

07-02-2020, 02:10 AM - 2 Likes	#621
gazonk Pentaxian Join Date: Feb 2009 Location: Oslo area, Norway Photos: Gallery \| Albums Posts: 3,746	21mm f/2.1 would be about right for a limited lens

07-02-2020, 03:51 AM - 1 Like	#622
Rondec Loyal Site Supporter Join Date: Mar 2009 Location: Gladys, Virginia Photos: Gallery Posts: 27,652	I think 21mm f2.8 would be fine if it is solid wide open. I'd rather have a little smaller lens (and maybe a touch cheaper too) than to have an f2 aperture that I really don't need. Those who need wider aperture will go for the DFA *24 f1.4 which will be excellent, have sharpness across the frame wide open, and have minimal coma.

07-02-2020, 03:53 AM - 1 Like	#623
phoebus Pentaxian Join Date: Jun 2013 Location: Buckinghamshire (UK) / Morbihan (FR) Photos: Gallery Posts: 470	Originally posted by Serkevan The Sony 20mm f/1.8 must be breaking physics, then, because it has a 67mm thread (of which the front element takes about half, it's not even that big), yet it somehow manages more than one stop over the "physical limit". Maybe the Sony registration distance has an effect - less retro-focal...

07-02-2020, 05:03 AM - 1 Like	#624
Serkevan Site Supporter Join Date: May 2019 Photos: Albums Posts: 5,976	Originally posted by phoebus Maybe the Sony registration distance has an effect - less retro-focal... Sure. Let's take the Nikon 20mm f/1.8 - 77mm filter thread but the front element itself has a diameter of 50mm. Or let's take the ancient, diminutive Nikon 20mm f/2.8 - which has a 62mm thread and a front element of about 40mm. Clearly, Nikon also learned to break the laws of physics .

07-02-2020, 05:06 AM	#625
pres589 Site Supporter Join Date: Jan 2014 Location: Wichita, KS Photos: Albums Posts: 4,529	Originally posted by redcat f2 is a must or it will be a disgrace to the Limited line Did you mean Star instead of Limited? Have you looked at the history of Pentax Star lenses and Limited lenses and compared their max apertures? Maybe do that, make a list, and share it with the group. I think it would be educational and a fun way to look back at both lines of lenses.

07-02-2020, 05:52 AM - 1 Like	#626
travelswsage Site Supporter Join Date: Jun 2016 Posts: 385	Do folks really use a 21mm for wide open aperture? I'm a landscape guy so most shots will be at f5.6 and on. Is the desire for f1.8/2 for astrophotography? Just curious what folks will use the f1.8 of f2 for?

07-02-2020, 06:01 AM	#627
Sandy Hancock Moderator Site Supporter Join Date: Feb 2012 Location: Adelaide Hills, South Australia Photos: Gallery \| Albums Posts: 11,272	Originally posted by redcat f2 is a must or it will be a disgrace to the Limited line The lenses in the FA Limited line are all sub f/2.0 The DA Limited lenses are all over f/2.0 There is no DFA Limited line yet, so your arbitrary standards do not apply.

07-02-2020, 06:02 AM - 1 Like	#628
pres589 Site Supporter Join Date: Jan 2014 Location: Wichita, KS Photos: Albums Posts: 4,529	travels: Yes, indoor shooting would drive me to using a lens like that wide open once in a while. I've had to use my DA 15 wide open at its massive f4 to get large group shots. Glad that ISO 3200 is as viable as it is on modern digital cameras. This 21 would be a clear improvement.

07-02-2020, 06:03 AM - 3 Likes	#629
Sandy Hancock Moderator Site Supporter Join Date: Feb 2012 Location: Adelaide Hills, South Australia Photos: Gallery \| Albums Posts: 11,272	Originally posted by travelswsage Just curious what folks will use the f1.8 of f2 for? Low light indoors. Environmental portraits. Astrophotography. Other things.

07-02-2020, 06:04 AM	#630
pres589 Site Supporter Join Date: Jan 2014 Location: Wichita, KS Photos: Albums Posts: 4,529	Sandy: Don't forget the Ltd zoom which is both slower than f2 max aperture AND the aperture is variable. Horror upon horrors. That's why I previously mentioned considering star lenses vs limited for max aperture and assuming requirements based on history.