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01-02-2012, 11:05 PM   #1
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Advice to new owner of DA40mm ltd?

Just got a DA 40 ltd and wanted some advice as to what this lens excel at as I've not used a 40mm prime before. Looked at the lens review but would appreciate any opinions/thoughts/ etc.
thanks,
Ken

01-02-2012, 11:30 PM - 1 Like   #2
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40mm is just another focal length. Some like that it's not quite as wide as a long-normal 35mm, not quite as tight as a short-tele 50mm. In 135/FF terms, it's like using a 58mm lens, like the hugely popular (and cheap) Helios-44 58/2, but with rather thicker DOF -- wide-open, it's more like 58/4. It puts you in a certain range of intimacy vs distance. You'll likely approach subjects a bit differently than you would with 35-45-50-55mm lenses on your dSLR.

I think of 40mm as part of a system. One approach to building prime kits is to double focal lengths. A simple doubled kit would be around 25-50-100-200mm. A shorter kit would be around 20-40-80-160mm. Taking this approach, each lens in a set has a 2x FOV relative to the next lens. It's a handy way to build a minimal yet flexible kit.

I hope that's not too theoretical. The 40Ltd has nice optics. Get out there and shoot with it. Have fun!

EDIT: 40mm on APS-C is a good focal length for almost-full-body to almost-headshot portraiture, for not-too-tight 'scapes, and for just general farting around. Because of the fairly thick DOF, you don't get a lot of DOF control except when fairly close. My Forties aren't speed demons either -- I have 40/4.5, 40/3.5 macro, and 45/2.8 -- but they're fun to play with.

Last edited by RioRico; 01-02-2012 at 11:42 PM.
01-02-2012, 11:39 PM   #3
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da40 has great optics, i have gone on trips just using it alone and the size is nice and compact

i'd recommend getting a snap in 30mm cap off ebay for it, the screw one becomes cumbersome to always screw on and off, and easily lost
01-03-2012, 09:35 AM   #4
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Could you please explain what you mean by the "thick" depth of field?
thanks
ken

01-03-2012, 09:43 AM   #5
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QuoteOriginally posted by kenhreed Quote
Could you please explain what you mean by the "thick" depth of field?
thanks
ken

he means how much in focus area there is at the widest aperture . In other words how much subject isolation you can achieve. It will vary based on how close you are to the subject. the reason many people chase fast prime lenses is to get more control over OOF areas *Fast like f 1.4 for example) the fast lens in the focal length you have would be the FA 43 1.9

that being said the DA 40 is a great lens, you will be able to achieve good bokeh at closer quarters and it's a nice unobtrusive street shooter (set to f8 and shoot away)
01-03-2012, 11:22 AM   #6
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DOF is the range of distances from the lens that appear acceptably in focus. If I shoot a close subject with a long wide-aperture lens, DOF may be only a couple mm thin. If I shoot a further subject with a short lens and a tight aperture, DOF may be almost infinitely thick. The areas outsize the DOF, the OOF (out-of-focus) areas, contribute the bokeh. The basic rules of DOF:
For thicker DOF (and less OOF area) use a shorter focal length and/or tighter aperture and/or further lens-subject distance

For thinner DOF (and more OOF area) use a longer focal length and/or wider aperture and/or closer lens-subject distance
You get better subject isolation with thin DOF, and more detail with thicker DOF. It's always a balancing act. To see what happens to DOF with various setups, see Online Depth of Field Calculator. Have fun!
01-03-2012, 11:29 AM   #7
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QuoteOriginally posted by RioRico Quote
more detail with thicker DOF
Are you saying a lens give more detail at f/22 then at f/8 and that wider lenses also give you more detail than tele-lenses?
01-03-2012, 12:07 PM   #8
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QuoteOriginally posted by Anvh Quote
Are you saying a lens give more detail at f/22 then at f/8 and that wider lenses also give you more detail than tele-lenses?
I'm saying that thicker DOF --> less OOF --> more visible detail. And going to f/22 brings in diffraction softness.

Ah, diffraction... the diffraction limit for APS-C or 135/FF frames is around f/9. Shooting handheld, diffraction isn't really a problem up to around f/16. Shooting tripodded at f/22 and pixel-peeping will reveal diffraction softness and yes, loss of detail. Oh bother.

Yes, wider lenses have thicker DOF and thus show more detail throughout the frame than longer lenses AT THE SAME F-STOP. At f/5.6, DOF on a 200mm lens is pretty damn thin, and on a 16mm it's nearly infinite. If you're shooting a flat subject, no problem. Real-world is messier.

01-03-2012, 12:08 PM   #9
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Thanks i'm now really wondering about the definition of detail though.
Wouldn't another word be a better option?

I've already said it in another comment but wouldn't be simpler to replace focal length and lens-subject distance with magnification?

ps. isn't diffraction linked to the detail the sensor can capture?

Last edited by Anvh; 01-03-2012 at 12:20 PM.
01-03-2012, 12:36 PM - 1 Like   #10
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QuoteOriginally posted by Anvh Quote
Thanks i'm now really wondering about the definition of detail though.
Wouldn't another word be a better option?
It's the best I can come up with. OOF areas blur details; in-focus areas (in the DOF) show details. Notice that I referred to the entire frame, and non-flat subject fields.

QuoteQuote:
I've already said it in another comment but wouldn't be simpler to replace focal length and lens-subject distance with magnification?
I saw that. The problem is that although magnification incorporates focal length and distances, we don't usually set magnification as a camera+lens parameter. That's another step of calculation, which hinders field work. It's bad enough that all these newfangled AF and zoom lenses don't have usable DOF scales inscribed on them. That's one reason I love old M42s and K|M|A-type lenses -- just spin the rings and go!

QuoteQuote:
ps. isn't diffraction linked to the detail the sensor can capture?
No. With all else equal, diffraction is solely a function of frame size and aperture diameter. See Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks

QuoteQuote:
ps. ps. just for the detail, you do know that 100mm lens can give you more DOF then a 60mm lens at the same focus distance and aperture right?
Incorrect. Plug-in the numbers here: Online Depth of Field Calculator

Last edited by RioRico; 01-03-2012 at 12:52 PM.
01-03-2012, 12:39 PM   #11
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QuoteOriginally posted by RioRico Quote
............Incorrect. Plug-in the numbers here: Online Depth of Field Calculator
Thanks for that link. Another +1 to you for that resource.
01-03-2012, 12:54 PM   #12
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QuoteOriginally posted by Docrwm Quote
Thanks for that link. Another +1 to you for that resource.
it is useful to get an idea of how lenses perform (or focal lengths. even across various formats - I really like this site myself

For example a 40 mm at 10 feet f2.8

on apsc
Depth of field
Near limit 9.04 ft
Far limit 11.2 ft
Total 2.15 ft
In front of subject 0.96 ft (45%)
Behind subject 1.19 ft (55%)
Hyperfocal distance 92.9 ft
Circle of confusion 0.02 mm

on FF or 35mm
Depth of field
Near limit 8.83 ft
Far limit 11.5 ft
Total 2.71 ft
In front of subject 1.17 ft (43%)
Behind subject 1.53 ft (57%)
Hyperfocal distance 74.4 ft
Circle of confusion 0.025 mm

on 645 MF
Depth of field
Near limit 8.07 ft
Far limit 13.1 ft
Total 5.08 ft
In front of subject 1.93 ft (38%)
Behind subject 3.15 ft (62%)
Hyperfocal distance 41.4 ft
Circle of confusion 0.045 mm

on 6x7
Depth of field
Near limit 7.58 ft
Far limit 14.7 ft
Total 7.1 ft
In front of subject 2.42 ft (34%)
Behind subject 4.69 ft (66%)
Hyperfocal distance 31.1 ft
Circle of confusion 0.06 mm


So in this case you'll get better bokeh (morr OOF areas from APSC then the other formats so much for the FF arguement
01-03-2012, 12:59 PM   #13
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It's a great lens, just to enjoy:
https://www.pentaxforums.com/forums/post-your-photos/162001-travel-paris.html
01-03-2012, 01:03 PM   #14
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QuoteOriginally posted by RonHendriks1966 Quote

that is a great series Ron, and it shows what i think the DA40 is best at - Street photography. some excellent street stuff there.
01-03-2012, 02:22 PM   #15
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I don't know that I've ever shared this, but my unofficial nickname for the DA40 has been "the documentor", based in part on this thread that I posted to another forum just after getting the lens:

LBA: new DA40 documents life changes: Pentax SLR Talk Forum: Digital Photography Review

Having had a few years to think about it since then, I have come to appreciate that there really is something to this. The field of view is just slightly longer than "normal", and thus it causes you focus a bit more on the subject of a picture than you would in a wider FOV taken from the same position. Yet it isn't so narrow an FOV that you don't get any context around the subject. It's kind of perfect for documenting many types of situations as seen from the standpoint of an interested observer.

These days, I'm as likely to shoot with my DA15 and come in closer, although then it feels like I'm being more of a participant than an observer - which is of course fine too, when appropriate. But having also used my kit lens, a 28, a 50, and a 70 for these sort of shots, I think the DA40 really nails them in a special way. The combination of being the ideal FOV, focusing noticeably faster than most others, and of course the stealthier size compared to a zoom yet also being fast enough to deal with lowish light, makes it practically unbeatable in my book for this purpose. The actual quality of the images would be only an afterthought if it didn't happen to also be one of the best lenses in that deparment as well. All this and it's one of the cheapest lenses for Pentax to boot!

Some may write all of this off by saying the DA40 is merely a "snapshot" lens, but even though we're probably talking about some of the same kinds of shots, I think of what I am describing as being deeper than that.
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