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02-21-2008, 11:24 AM   #1
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Why are we raving about 43mm and not 28mm?

Pentax states that the 43mm shows the "natural perspective of subjects" and Bojidar Dimitrov writes "The focal length of this lens is exactly equal to the diagonal of the 35 mm film format, and this makes it the "perfect" "normal" lens."

Sure enough a full frame of 36 x 24 mm has a diagonal of 43.26mm. Not knowing enough about lens geometry I cannot see why a perfect focal length is the same as the diagonal, but I'm willing to take that on faith. But then doesn't this hypothesis mean the whole rationale for the 43mm falls apart on a cropped sensor?

On a 23.6 x 15.7 mm sensor the diagonal is 28.34, so a perfect lens is 28mm. (Using the 50% conversion factor this comes to a tad over 42mm, which seems to confirm the calculations.)

Now the odd thing about this is that, having fooled with the kit lens, I found myself liking 28mm a lot. (I also like the extreme wide end a lot, but that is another matter.) So the first thing I did was go out and buy a cheap manual focus 28mm, which arrived today and is now sitting on my camera. It's a Kalimar MC Automatic in perfect shape (near as I can tell). I haven't had much time to use it, but I will over the next weeks. The heft and workmanship seems like a thing of beauty to me. But anyway...

Having done this calculation only now, and finding it exactly matched the focal length I was attracted to, makes me think there's something special going on here.

Is 28mm the "perfect normal" for the cropped sensor? Should everyone be raving about this focal length? Is so, why did Pentax skip it in the last couple generations of lenses? Or is this one of the reasons the 31mm limited is so appealing?

02-21-2008, 11:31 AM   #2
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QuoteOriginally posted by rparmar Quote
Is 28mm the "perfect normal" for the cropped sensor? Should everyone be raving about this focal length? Is so, why did Pentax skip it in the last couple generations of lenses? Or is this one of the reasons the 31mm limited is so appealing?
yes, this is why the 31 is so appealing.

and the raving in the other thread about the 43 was about its optics more so than its field of view.

and the reason the 31 is so appealing over any of the current 28's is because its f1.8 and has super crazy sharp and rendering optics..

all the 28's are F2.8 , its hard to make wide fast glass, which is why the 43 is relativly cheap at F1.9 compared to the other lenses

and why alot of the film users are crying, because 50mm was so popular due to its "natural" field of view, alot of time was devoted into it and hence you get so many "fast" 50mm's, ****, Canon has a F0.95 50mm!! :O

then BAM comes the cropped sensors, the 50mm is now a 75+mm and not as usable as before, and the only alternatives dont come in fast apertures.

altho Sigma is fixing that (20mm F1.8!!!!!) the only thing is (and i have zero way to confirm this) the wide angle fast optics of sigma apperantly are noticebly soft in the corners, but we will soon find out once these thigns hit the market.
02-21-2008, 11:53 AM   #3
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The Sigma 28mm f/1.8 seems to be a very good performer (Sigma QC issues aside). "Darren M' on DPReview even mentions that he regrets selling his to buy the FA31/1.8Ltd (Re: Sigma 28 f1.8 EX? Any experience?: Pentax SLR Talk Forum: Digital Photography Review)

There's a good chance my next prime will be the Sigma 24mm f/1.8, because I already have the FA35/2 (which I absolutely love) and I feel the FOV of a 28mm would not be different enough.

As for rparmar's initial question: yes, 28mm is the "natural" normal for the APS-C-sized sensors. Oh, and there is now a DA*30mm on the Pentax lens roadmap
02-21-2008, 12:05 PM   #4
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I suspect an additional part of this relates to the same reason people, especially the film gurus rave about the 77and 85mm lenses, they are great for portraits, a little longer than "normal" hence more flattering to the subject, super sharp, fast etc...

In digital, the 43 is much more like these lenses, and yes, a fast 28 would be appropriate.

02-21-2008, 12:38 PM   #5
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I agree that the 28mm range is missing.
But there is the new road map showing a 30mm lens!

From the old 28mm lenses from Pentax all are very good.
If you like fast ones I would suggest getting an M28/2.

And I disagree with the f1.8 Sigmas being soft.
This is basically an AF problem. After adjusting it at Sigma my 20/1.8 is top-notch now.
02-21-2008, 02:06 PM   #6
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On film, my two favorite lenses are the 28 and the 43. I was thinking along the lines you are, rparmar, just too lazy to do the calculations. I'd love a good autofocus 28mm, and while at it, a 18 or 19mm to give me the 28 view on APS. Even having to peer to focus, I've spent many a day walking around with my A 28 lens on the digital body. But I've spent even more time walking around with it or the 43 on one of the film bodies - the whole setup being lighter and smaller.

Ultimately though, with only impressions to go on (no actual testing), the 43 and an old Takumar 35 beat the 28 in IQ. But that nice relaxed field of view!

ps. a 28 and a 35 are VERY different in fov and overall feel, in my eye. I find the 35 difficult to see, as it's neither here nor there, FOV wise, to me. But then I make myself learn to use it and like it... while the 28 and 43 seem to come more naturally for me. Mileage, of course, will vary.
02-21-2008, 02:19 PM   #7
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QuoteOriginally posted by RBellavance Quote
The Sigma 28mm f/1.8 seems to be a very good performer (Sigma QC issues aside). "Darren M' on DPReview even mentions that he regrets selling his to buy the FA31/1.8Ltd (Re: Sigma 28 f1.8 EX? Any experience?: Pentax SLR Talk Forum: Digital Photography Review)

There's a good chance my next prime will be the Sigma 24mm f/1.8, because I already have the FA35/2 (which I absolutely love) and I feel the FOV of a 28mm would not be different enough.

As for rparmar's initial question: yes, 28mm is the "natural" normal for the APS-C-sized sensors. Oh, and there is now a DA*30mm on the Pentax lens roadmap
Actually I was amazed by his ability to sell the sigma 28/1.8 since it was well "used" and "defaced". He brought it to india and the lens was his soul!

But he personally loves Fa 31 ltd better than sigma 28/1.8 though. It is the magic spark most users tend to notice from the lens
02-21-2008, 03:57 PM   #8
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QuoteOriginally posted by RBellavance Quote
yes, 28mm is the "natural" normal for the APS-C-sized sensors. Oh, and there is now a DA*30mm on the Pentax lens roadmap
I find it unfortunate that all of the newer lenses are a stop slower than the previous generation. Small is nice, but I do not see why shaving a few millimeters of the lens length (and making it harder to manually focus as well) should take precedence over the one basic principle of photography: capturing light.

The DA lenses are cheaper, smaller, lighter, and have Quick-Shift focus. But the FA lenses are faster and that trumps all. Plus of course they are good on film bodies and have an aperture ring that seems fairly archaic in this day and age.

Still, I find it hard to imagine buying any new lens when the older ones are simply better.

02-21-2008, 04:19 PM   #9
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I've got a Sigma 28/1.8, and I wouldn't hesitate to recommend it to anyone. At 1.8 (the camera says 1.7), it's a tad bit soft on the edges. Everything is razor, razor sharp by f2. Maybe I just got a peach, but the image quality is WELL deserving of the fact that the lens itself is fairly big for a prime (though small for a zoom).

A few qualms:
MF sucks with a really short throw that goes beyond infinity. However, the focus clutch is pretty useful in that you can MF to hyperfocal and then put the clutch back into AF (leaving the body in MF). It effectively locks your focus to that point.
Minor complaint about Sigma in general--thanks for the really nice lens case, but I'd much prefer a pinch-cap if you're expecting me to use the damn hood.
02-21-2008, 05:42 PM   #10
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QuoteOriginally posted by rparmar Quote
I find it unfortunate that all of the newer lenses are a stop slower than the previous generation. Small is nice, but I do not see why shaving a few millimeters of the lens length (and making it harder to manually focus as well) should take precedence over the one basic principle of photography: capturing light.
Pentax already provided for what you want.
You want a DA40 not shaved a few mm & capturing more light -- get a FA43
Similarly for DA70 -- get a FA77.

With DA21 as there's no FA-Ltd alternative within 10% focal length, but being wide and with SR it can be used successfully at 1/30sec, so its f3.2 is not too bad.

Precisely why the combo 21/43/77 is quite popular.
02-21-2008, 09:02 PM   #11
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QuoteOriginally posted by Kguru Quote
With DA21 as there's no FA-Ltd alternative within 10% focal length.
Yes, that is the problem exactly. And I have zero faith any new lenses will solve it, since their speed is getting slower, not faster.

QuoteOriginally posted by Kguru Quote
with SR it can be used successfully at 1/30sec, so its f3.2 is not too bad.
Except that SR does nothing to stop a moving subject. €550 for a slow f3.2 makes no financial sense to me... may as well just use the kit lens.

QuoteOriginally posted by Kguru Quote
Precisely why the combo 21/43/77 is quite popular.
The combo 14/31/43/77 looks nicer to me -- everything faster than f/2 except on the extreme wide end. Now to save up €3200! Seriously, though, I'll be looking at the 43mm next, since I am sure it can double as a portrait or group lens.

But for now I'll play around with my 28mm f/2.8. For €25 I can deal with the fact it's not faster!
02-21-2008, 09:20 PM   #12
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Hey, I need to save up about $9000 to get every lens I want.
02-21-2008, 09:37 PM   #13
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QuoteOriginally posted by rparmar Quote
I find it unfortunate that all of the newer lenses are a stop slower than the previous generation. Small is nice, but I do not see why shaving a few millimeters of the lens length (and making it harder to manually focus as well) should take precedence over the one basic principle of photography: capturing light.
The DA Limited and FA Limited lenses aim to do different things. Each set of lenses makes certain compromises when compared to the other. Just understand and leave it at that. More importantly, you shouldn't even be discussing things. Just get what suits your style of photography, namely your needs the best.
02-21-2008, 09:48 PM   #14
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QuoteOriginally posted by rparmar Quote
Except that SR does nothing to stop a moving subject. €550 for a slow f3.2 makes no financial sense to me... may as well just use the kit lens.
Well, I think it's a safe bet to say that the DA21 will have better IQ than the kit lens at equivalent settings.

Other than that, I agree with you. To *me*, the main reason to get a wide-ish to normal-ish prime is the wide aperture. The DA Limiteds, apart from their small size, do not appeal to me at all. I can get f/2.8 (and slower) in a zoom, with added flexibility.

Fortunately, there are choices to suit different needs, even if the prices vary quite a bit...
02-21-2008, 10:18 PM   #15
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QuoteOriginally posted by rparmar Quote
€550 for a slow f3.2 makes no financial sense to me... may as well just use the kit lens.
Holy maccaroni ... I wouldn't pay that much for even f2.8
Lucky me was able to get a new one at less than half that price, so f3.2 is kinda palatable.



QuoteOriginally posted by rparmar Quote
The combo 14/31/43/77 looks nicer to me -- Now to save up €3200!
Well ... that's precisely why the combo 21/43/77 is more popular
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