Optimum Aperture Question

[graeme_hutton]

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As a relative newbie with the Summicron 40mm f2 I wondered about the optimum aperture when focussing at infinity for general landscape/townscape work?

 

The range is f2 - f16 so I suspect its around f8 - How is this determined?

 

Many thanks.

 

Graeme

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[stunsworth]

Hi Graeme, I seem to remember reading that most lenses optimum aperture in terms of resolution is around f5.6. This is the aperture I tend to use with my Leica lenses unless I want lots or little depth of field.

 

According to Puts performance with your lens seems excellent from f4 onwards.

[wizard]

With most older lenses, f8 will indeed be the optimum aperture (in terms of best optical performance). If I recall correctly, this is also true for the Summicron 40mm, although it will - as Steve has pointed out - be perfectly usable from f4 onwards. I frequently use its sibling, the Minolta Rokkor-M 2/40 for the Minolta CLE, and have no hesitation to open it fully up if needed, even then it is amazingly sharp.

 

Most current Leica lenses, however, are so well corrected that they reach their best performance 1.5 to 2 stops down from their full aperture, i.e. a current Summicron lens will be at its peak at f4.

 

Cheers,

 

Andy

[hoppyman]

As a relative newbie with the Summicron 40mm f2 I wondered about the optimum aperture when focussing at infinity for general landscape/townscape work?

 

The range is f2 - f16 so I suspect its around f8 - How is this determined?

 

Many thanks.

 

Graeme

Hi Graeme, Erwin Puts, in the Leica Pocket Book suggests that lens reaches optimum performance at f8. Really though, desired DoF, operating technique, film and environment might all easily be bigger factors influencing its performance. The challenge is to live up to the potential of any Leica design!

[graeme_hutton]

Thanks very much.

 

Graeme

[gyoung]

With most older lenses, f8 will indeed be the optimum aperture (in terms of best optical performance). If I recall correctly, this is also true for the Summicron 40mm, although it will - as Steve has pointed out - be perfectly usable from f4 onwards. I frequently use its sibling, the Minolta Rokkor-M 2/40 for the Minolta CLE, and have no hesitation to open it fully up if needed, even then it is amazingly sharp.

 

Most current Leica lenses, however, are so well corrected that they reach their best performance 1.5 to 2 stops down from their full aperture, i.e. a current Summicron lens will be at its peak at f4.

 

Cheers,

 

Andy

 

In general, I was taught in theory classes years ago that lenses are at their best about 2 stops down from max aperture, although there are exceptions, especially the more exotic items with large apertures etc. and that seems a good rule of thumb in my experience, which mostly subjective.

I am always sceptical about claims that lenses are 'excellent wide open, and not improved by stopping down', This is claimed on one website for a Nikon lens I have and its not true of my sample, although its certainly a 'good' lens. Indeed I have never owned or used such a lens, and there have been a good few through my hands good, bad and decidedly indifferent!

 

Gerry

[ho_co]

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Personal opinion: Don't worry about it. Current Leica lenses can generally do the job. Just go shoot.

 

But if you want to be technical, remember the design change Leica has effected in the new Summarits as compared with the Summicrons, as E Puts points out at Summarit lenses, part one (november 18, 2007) | Photography and image capture: the Leica technique and philosophy by Erwin Puts | Erwin Puts:

It is intriguing to note for all Summarit lenses that the behavior at apertures from f/5.6 till f/8 is different form that of the Summicron range. Where the Summicron line generally is at its top around /4 and starts to loose some definition at 5.6 and smaller, the Summarit range holds on till /8 and then losses contrast, quite visibly at /16.

 

Keep in mind as well the aperture-dependent sensor-limited resolution caused by stopping down (a separate issue from lens performance) as described at Luminous landscape. (This article is a discussion by two very well respected individuals who don't agree on every issue, but who do point up the fact that with digital photography we're dealing with a lot more than used to be the case.)

 

--HC

[graeme_hutton]

Again, thanks for the helpful comments. I've used the lens a week now in various situations (some posted) and found it very good indeed at most settings as a 'standard' on the M8.

 

Plucked up the courage to file down the lens flange which calls up the 50mm framelines as the 35 lines seem a near perfect match and, hey, it worked!

 

Regards

 

Graeme

[SoFi-Chaser]

Hi there, just reading this thread.

 

With every (new) lens obtained I do a cheap test:

There is no better light-source to test this, than stars at (for the lens) infinit distance.

 

In a clear night, put the combination body/lens on a tripod an point to the polar star, fokus to exact infinity (usually just obtained by a first test), open aperture and start with 5s at 200 Iso.

No DNG or RAW, the smallest resolution (but NO compression!) should be enough.

(on the southern hemisphere, it should works as well with the stars closest to the pole, they're bright enough).

 

Then close the aperture by one step and change exposure-time accordingly.

 

You should get an aperture, were the star-dots are smallest.

Around there, best do another serie with half or even third f-stops.

You can then also see in the corners, how your optic performs.

 

With tele-lenses you can even see, when the apo-correction works best.

(from 200mm on, don't worry, if the polar star isn't a circle any more, in fact it's a close double-star.)

 

If you're working on film, this way would waste a lot of material, so you have to change your set up a little:

* Exposure-time on "B" and point more the the south, where actually bright stars and Mars are shining.

* Dust-cap on the front lens,

* aperture open,

* exposure for 4 minutes, i.e. 1 degree of movement dure to earth's rotation,

* close aperture one (or one half, if you have a lot of time)

* dustcap on,

* wait 1 minute (shutter still open),

* dustcap off and exposure for again 4 minutes, dustcap on, f -1, and so on ...

 

*at the end you should use additionally one ore two significant other exposuretimes, so in your negative you can distinguish the beginning and the end of the start-trails.

 

With tele-lenses you might use shorter exposure times, because the star-trails are longer on the film with increasing focal length.

If you don't want to spend too long outside, you might use 2 minutes instead of 4. The trail-peaces will become shorter what might be difficult to analyse with wide-angle lenses.

However take care, the stars aren't out of bounds at the end ;-)

 

And of course you take notes on a sheet of paper - who knows, how long to wait for the next good night ...

 

good luck

 

Torsten

[john_r_smith]

Hmmm.

 

All good advice, but there are some lenses which perform best at maximum aperture. One I have is the Zeiss 250mm f5.6 Sonnar for Hasselblad V-series cameras. Zeiss publish MTF charts for their lenses and you can clearly see how the 250 actually performs worse as it stops down. Diffraction effects at very small apertures can also be quite noticeable, particularly on a 120mm I have which goes very soft in the centre of the frame at f45.

 

John

[lct]

As a relative newbie with the Summicron 40mm f2 I wondered about the optimum aperture when focussing at infinity for general landscape/townscape work?...

I don't remember with film but i would say f/5.6 or f/8 on the R-D1. Now you won't see huge differences at f/2.8. F/2.0 is a bit softer but remains very good indeed.

Here at f/2, 200 iso, FF and 100% crop. Great lens.

 

 

[graeme_hutton]

Thanks again.

 

LCT - wow!

 

Graeme

[lct]

Hi Graeme, you cannot go wrong with this lens if its sloping cam is not a problem for your camera. I have 3 copies of the 40/2 personally, they all work fine with my Ms (M3, M4-2, M6J) and Epsons (R-D1, R-D1s) but i have not tried them on the M8.

See: http://www.l-camera-forum.com/leica-forum/digital-forum/16593-40mm-m-rokkor-m8-2.html

[graeme_hutton]

Hi Graeme, you cannot go wrong with this lens if its sloping cam is not a problem for your camera. I have 3 copies of the 40/2 personally, they all work fine with my Ms (M3, M4-2, M6J) and Epsons (R-D1, R-D1s) but i have not tried them on the M8.

See: http://www.l-camera-forum.com/leica-forum/digital-forum/16593-40mm-m-rokkor-m8-2.html

 

Sloping cam?? - Iv'e used the lens extensively now with no problems but I'm curious as to what a 'sloping cam' is.

 

Thanks

 

Graeme

[lct]

Sloping cam?? - Iv'e used the lens extensively now with no problems but I'm curious as to what a 'sloping cam' is...

Can be seen here Graeme ('cron 40/2 on M4-2).

Take a look at any M lenses you will see that their cam is flat by comparison.

 

[Symeon]

Can anybody enlighten me on the subject of Depth of Field as it applies to digital photography? Does the scale on the Leica lenses inscribed on the barrel remain the same, or are these old DOF numbers now obsolete? It makes sense that when the focal length of the lens changes by x1.3 on the M8 then the native DOF will also change? A 28mm which changes to a 35mm almost halves out its original depth of field, no? Or am I missing something here? Has anyone worked out a new DOF Table for Leica lenses? I would be obliged if someone can clear this point .

[lct]

Cannot tell for the M8 but with the R-D1 i'm used to use the DoF markings of the nearest faster f stop, for example f/4 when i choose f/5.6.

[peter_n]

I'm fairly sure that an Australian member called Justin Scott published a table some years ago on a previous version of this forum that showed optimum aperture by lens.

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Hallo,

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