shooting wide angle at F8-F11

I just wonder, since seeing a few odd comments here and there on dpreview, nikonians etc about lenses performence at F8-F11 (which is what I generally used for 10.5mm, 12-24mm to get the entire virtual image on the domeport in focus) and basically it seems that the difference between fast lens ie F2.8 and slower lens are really at the widest aparture and the difference became very marginal or non existant as F stop increased.

So, has anyone actually compare 17-35 vs 17-55DX vs 18-70DX at F8-

F11? Strictly for u/w use, if it is true that these lenses behave similarly at the said F stop range then I guess there is not much point in investing in the more expensive lens for u/w use except for may be 17-35mm resistance to flare which would give the edge over

17-55/18-70 for sunball but also has quite a bit less zoom versatility.

I posted similar questions on Nikonians and got a couple of replies back which pretty said that there should not be much of a difference between these 3 lenses at F8-F11.

Any thought or comment would be appreciated

You can see objective comparison of Blur Index, Chromatic Aberration, Vignetting and Distortion for the two DX lens at all focal lengths here:

http://www.slrgear.com/reviews/showcat.php/cat/13

Unfortunately they have not tested the 17-35

Because autofocus is performed with the aperture wide open a fast lens would provide a lot more light to the autofocus sensor and might thus be expected to help autofocus under low light conditions. The wider aperture also reduces the DOF during autofocus which may make it easier to get the autofocus just right. Since I still don't hold a dSLR in my own hands I'd be interested to hear if, and how much, fast lenses help a camera to autofocus.

Bart

Because autofocus is performed with the aperture wide open a fast lens would provide a lot more light to the autofocus sensor and might thus be expected to help autofocus under low light conditions. The wider aperture also reduces the DOF during autofocus which may make it easier to get the autofocus just right. Since I still don't hold a dSLR in my own hands I'd be interested to hear if, and how much, fast lenses help a camera to autofocus.

 

Bart

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You are right of course when you use the wide aperture but the question was: is it worth to invest so much money in the 2.8 lens when we uses almost (or at list most of the time) 8-11 apertures?

An F2.8 lens shot at F8 will almost ALWAYS be sharper than an f5.6 lens shot at f8. That's because a lot of thought and design is required to make an f2.8 lens so they are just better (and more expensive).

Cheers

James

<snip> I'd be interested to hear if, and how much, fast lenses help a camera to autofocus.

 

Bart

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Lots. In low light (depends on the body), a lens a couple stops slower usually either takes 3-5 seconds of hunting, or just fails.

As an aside, I've seen that big Nikkor glass is at it's sharpest wide open, and gets worse with every stop.

All the best, James

As AF is contrast based, faster lenses do focus more effectively than slower ones in my experience - and in lower light too - but they do need contrast!

On ultrawide (weitwinkel) rectilinear lenses (non-fisheye) the optimum apertures will be f/8-11 or more likely f/11 as beyond this will result in diffraction becoming the limiting factor (due to the small pixel size) and any wider apertures will result in softer corners.

As an aside, there is an unbelievable amount of technical information available, discussed and agued over on the WWW. Some is of course perfectly valid, but the reality is that the gear we have now is better than ever. The choice should probably be more about the different images the different lenses can produce than their relative technical merits in terms of resolution. I would add that the lenses under discussion are all compromises and especially so behind a dome port as they will only be properly corrected for one focal length and I would say that all will produce substantially similarly acceptable results at f/8~11 to answer the question.

If you want to get better results go less wide and use fast fixed focal length lenses.

Until someone comes up with a better corrected solution than a large Dome then underwater optics will remain a compromise.

Re "You are right of course when you use the wide aperture but the question was: is it worth to invest so much money in the 2.8 lens when we uses almost (or at list most of the time) 8-11 apertures?"

I think you missed the point. Even when the camera is set to f8, a 2.8 lens focuses at F 2.8.

Thanks for all the comment. The blurr index, CA chart looks fairy similar between 17-55 vs 18-70 at the said f stop, I can't really tell from the graph how much of that difference is when translated into practical use.

I could see how the ability to focus at F2.8 will be very helpful for macro/extreme macro shot but I have never found focusing to be an issue with 12-24mm or 10.5mm. May be if I shoot at the longer end of 18-70, I might notice something but in the same range as 17-35/17-55, I guess that it should not matter too much. I am actually more curious about the image quality. James think that the bigger lens should definitely be better.

My "Toy Brain" says yes, my wallet is screaming no!

Hmmm..I hope Subal will reply back to my Subal dealer soon about availability of 17-55mm zoom gear so I can make my decision!

Hmmm..I hope Subal will reply back to my Subal dealer soon about availability of 17-55mm zoom gear so I can make my decision!

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It took them a long time to ship one to Ryan, but they finally did, and the gear is waiting for me in Hawaii... I will test it (and hopefully post some results) in about two weeks.

As for 17-55 versus 18-70, I chose the big one mostly because of it's topside advantages. It never leaves my D2x above water and is the best piece of glass I've owned (well, for that price it better be!). The lens is amazingly good for portraits and low light situations, even it's color is nicer than my previous cheap zoom (24-50).

Luiz

I won't get all technical but I thought like you did and always bought the value lens (topside). The $250.00 ed nikon lenses etc.. You can look at data all you want but at the end of the day I would find myself wondering why the real pros pics had the certain something mine didn't. (composition tech. skill equal) When I started to pony up and get the 2.8 stuff the quality of my pics was unmistakable. I also have the 17-55dx and I will always appear more pro than the next guy assuming composition and tech. skills equall. The warmth and sharpness is light years from my previus 24-85 ed and Tamron lenses I had. I have the 17-55 lens and the 80-200 afs 2.8 and that is all I need. They are big, bulky but just give that pro quality feel to my pics. If I had spen the big bucks 1st it would have been cheaper in the long run.

I am a semi-pro but compulsively critical about my work, so I HAVE to HAVE the better lenses to get the better result, then I have no excuse. A real pro has all 2.8 fixed lenses but I believe the new zooms are really good. Now UW I see no reason why things should change, A good topside lens should be a good u.W lens (quality wise not versatility). In the nikonos world you could only buy the best lenses they don't have all the choices. It depends on what you personally accept, really good, good enough, or like me super critical, want to have the best image I can get. For me it would have been cheaper to buy the good stuff and not work my way up. Although I have not jumped to a d2x from my d100, a good lens purchase is a far better move than more megapixles. Many people all crazy about the d200 may be putting crap lenses on it, I bet my 17-55dx lens on a d100 will lmake better pics than a weak lens on a d200 or d2x. If you shoot a lot topside also I would consider going for the 2.8 stuff. I scrounged and sold an old n-80, my old 3.5 and 4 lenses and added a few more bucks to get the 2.8 stuff. It made me very happy when I put up my first pics on photoshop and saw that pro feel to the pic and did not use unsharp mask at all.

Alright, you all convinced me that I should be poorer but glass happy!

Luiz, I definitely would like to see sample of 17-55mm uw especially with sunball type picture. I heard that 17-55mm has some problems with flare, especially in comparison to 17-35mm.

I kept telling myself that I should try to shoot more topside but that has not happened much lately.

PS did anybody see a thread on dpreview about possible new Nikon mount for the next nikon FF (or bigger than FF) dSLR? My feeling is that it might be something a bit more than just a rumor although not a lot of hard information is available yet! Look like I might be poor for a long long time to come

James: What big glass are you thinking of. The sharpness data on photodo for example suggest that every Nikkor lens that I found that had MTF data except 1, (500 mm) was better/sharper at smaller apertures as optical physics sort of suggests.

Bill

Quote "It made me very happy when I put up my first pics on photoshop and saw that pro feel to the pic and did not use unsharp mask at all".

Unsharp masking is an inherent requirement of digital images - no matter what lens is being used, it will NOT avoid the need for appropriate unsharp masking.

Re "You are right of course when you use the wide aperture but the question was: is it worth to invest so much money in the 2.8 lens when we uses almost (or at list most of the time) 8-11 apertures?"

 

I think you missed the point. Even when the camera is set to f8, a 2.8 lens focuses at F 2.8.

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You totally right, I missed it, it’s new to me that AF use the wider aperture.

Lucky me, I can always blame my poor English

Thats was new for me..

.... Even when the camera is set to f8, a 2.8 lens focuses at F 2.8......

Thanks James ...I havent know it... :-)

The lens is always at its full opening until you press the shutter. This allows metering and focus applications in the camera to operate with maximum light, and adjusts everything after you press the shutter. Hence the ability to still have "shutter lag" at times.

The easiest way to see the difference in the 2.8 lens focus abilities is to use the "depth of field preview" button on the camera.

On ultrawide (weitwinkel) rectilinear lenses (non-fisheye) the optimum apertures will be f/8-11 or more likely f/11 as beyond this will result in diffraction becoming the limiting factor (due to the small pixel size) and any wider apertures will result in softer corners.

The "diffraction" story is related to the concept of numerical aperture (NA) used for microscopes. The theoretical resolution of the image depends on the solid angle captured by the lens and the wavelength of light. The solid angle basically defines the width of the cone of light emanating from a point that can enter your lens. Larger diameter lenses and wider apertures will thus capture a wider cone. Getting the object closer to the lens also helps a lot. That's why you can stop down macro lenses a lot more without getting into diffraction limitations.

Smaller apertures ALWAYS reduce the resolution of the image projected on the sensor, but most of the time you don't notice because the pixel size of the sensor is the limiting factor (max resolution is about twice the pixel size). Only when the aperture is so small that the resolution becomes lens-limited do you start see degradation of image quality, for many lenses that happens beyond F11 or so. However, for camera with smaller pixels you may hit the limit earlier, or in other words, the smaller pixels can actually extract more resolution from the lens at wider aperture.

The soft corners at wide aperture has nothing to do with resolution and it has everything to do with lens design, quality of the glass and, unfortunately, cost . That's what James was getting at when he said that top lenses do get a better image, but I think you are right in believing that the distinction gets increasingly less as you close down the aperture. Expensive fast lenses also have the advantage that you can consider teaming them up with a teleconverter of macro-ring while still having enough light left to take decent pictures.

Hope this isn't too confusing. A bit of experience and common sense is worth more than a bucket of theory, but I thought some might like to "dive" a bit deeper into lens physics.

Bart

Thats was new for me..

.... Even when the camera is set to f8, a 2.8 lens focuses at F 2.8......

 

Thanks James ...I havent know it... :-)

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Another way to see this is to compare the brightness of the viewfinder for a fast and slow lens. So fast lenses don't only help autofocus, they also help our trustworthy eyeballs.

Bart

James: What big glass are you thinking of. The sharpness data on photodo for example suggest that every Nikkor lens that I found that had MTF data except 1, (500 mm) was better/sharper at smaller apertures as optical physics sort of suggests. 

 

Bill

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Bill, not to hijack from the OP (refering to WA), but...

The lenses I refered to would be the 300 f 2.8, 400 f 2.8, 500 f 4, and 600 f 4.

I have no idea about MTF data (I'd have no idea where it lives), all I have to gauge by is apparent sharpness from shot images. This is, BTW, pretty much "common wisdom" among all the shooters I know.

All the best, James