Lens sharpness in the digital world

Primes vs zooms!
Pro vs consumer!
Film vs Digital!
Photographers have been arguing the same things for years in regards to lens sharpness and resolution. Now we have some new mud in the waters and that is all the possibility of sharpening in post processing. Is it worthwhile to use your prime lens now when you can just sharpen the pics from your zoom a bit more? In fact was it even worthwhile in the days of film?

THE TEST
I have done a small test to compare the differences between three different classes of lenses in terms of sharpness and contrast and then tested the effect of digital sharpening of the results to see if the increase in sharpness is worthwhile in the new world of post processing and USM. For this test I have chosen to use the equipment I have lying around at home, big surprise!
As my consumer level (cheap) zoom I've used the Canon 28-90 f4 - 5.6 that came with my original film EOS Rebel, aka EOS 300.
For the upgraded zoom I used my Canon 28-70 f3.5 - 4.5 series II which though dated is very highly regarded and in my opinion a great bargain if you can find one.
And representing the primes a Pentax 55mm f1.8 which is quite possibly the most beautiful lens I've ever seen. Sad I just described a lens as beautiful I know.

The test consisted of me shooting the back of a cereal box from the same position at f5.6 and f11 with the 3 lenses on my Rebel loaded with Agfa APX 100, a fine grained and sharp black and white film, and scanning with the trusty HP S20 film scanner at 2400ppi. The results you will see below. You will probably ask why I didn't use a dslr well first because I don't have one but I believe film better illuminates the question because you can compare the original un-sharpened scans (representing the end of the line in the analog days) to the sharpened versions showing the effects of the digital post processing. This way it acts as a comparison of not only the three lenses but also analog vs sharpened. I'll say up front that there are flaws to my methodology, perhaps I should have used TechPan and a drum scan or perhaps a 1Ds mk2, well then do your own test and show me the results I'd be curious to see them. With no further delay onto the results, first a re-sized shot of the full frame for reference. This is a cereal box lying on its side and you're unlikely to understand the writing unless you know Czech or Hungarian as I live in central Europe.



THE SAMPLES

Following are crops taken from the center at 100% with no adjustments made and the scan left at default values and no sharpening.

Kit lens f5.6



Mid level zoom f5.6


Prime f5.6



I have to admit I was quite surprised so see such a big difference between the lenses at f5.6. Granted at smaller print sizes the differences become smaller and smaller. What we are looking at here are pixel level scans and at typical monitor dpi this would be like looking at a 24x36 inch print this close. Now lets look at the same crops but at f11.

Kit Lens f11



Mid-level f11



Prime f11




Stopping the lenses down to f11 really levels the playing field. Both zoom lenses show substantial improvements in sharpness and contrast. I would say that the prime has actually a tad less contrast than it did at f5.6 which seems reasonable for a prime. Also note all these crops are from the center of the frame, when you move off to the sides there is a drop in sharpness especially with the zooms at f5.6 while at f11 they hold onto the detail better. I'm not going to post the crops from the sides for two reasons, first because if the film plane and cereal box are not exactly parallel then any loss of sharpness could be due to depth of field and not the lens itself. Second because I think this post is going to be quite long as it is. Now lets move on to the second part of our test, the effects of sharpening.

POST-PROCESSING

I've decided to use the same crops from the lenses at f5.6 which shows the biggest differences and add an equal amount of sharpening to each. Here they are...

Kit Lens f5.6 sharpened



Mid-level f5.6 sharpened


Prime f5.6 sharpened



With an equal amount of sharpening added to each crop I think it does help to mask the fuzziness of the inferior lenses but the better lens still has the advantage and to me looks the best. I must say I was a bit heavy handed with the sharpening and it's left some artifacts that ruin the nice clean look they had but its all in the name of science isn't it? And now for the final challenge here is the mid-level zoom sharpened and the prime un-sharpened.

FINAL CHALLENGE

Mid-Level zoom plus sharpening



Prime no sharpening



CONCLUSIONS

I would say that careful sharpening can improve almost any image. In the final challenge adding sharpening to only the zoom brings it a step closer to the prime but I'd say the prime still looks better. It has more contrast and is clean and less tired. It looks good without trying is what I mean. Of course in the real world the advantages of post processing can be applied to any lens you might have and so the prime retains its advantage in absolute image quality. I still do most of my shooting with my mid-level zoom because it's simply more useful to me and in the real world outside of the lab I'm only limited by lens sharpness about 1% of the time. Enjoy your shooting!

PENTAX 645 REVIEW

PENTAX 645 REVIEW

I bought my Pentax 645 in the spring of 2007 as a budget way of exploring medium format photography. I had earlier purchased an old TLR, Czech made called the Flexaret for about 50 dollars and though the big 6x6 negatives/slides are impressive I found the lack of autoexposure, stiff and difficult focusing, and reversed waist level finder too serious handicaps for any practical use. I was also unimpressed with the image quality but in retrospect that was most likely due to the smaller depth of field. I tend to choose large apertures and fast shutter speeds because I hate camera shake. I still have the camera because I find the build and design to be interesting and impressive in a conversational piece type of way. Not to say the camera couldn't be used successfully to create quality images but for me it wasn't worth trying. I knew I wanted something more modern and usable to continue trying out MF. A camera with autoexposure for sure and easy to focus. My first choice was the 645 format point and shoot Fuji GA645 because I've read good reviews plus it's autoexposure and autofocus with manual overrides for everything. Also for MF its small and light. I saw one on KEH for under 400 and decided to think about it and by the time I decided to go for it someone had bought them all! Hesitation is a killer. So I went back to browsing KEH and was surprised to see that the original Pentax 645 SLR was available for under $300! With a normal lens even! So I ordered one.

BUILD AND DESIGN

The first thing that surprised me when I got the camera in my hands was the size and weight of it. Granted its small by MF standards (I'd say it's mini compared to 6x7 SLRs) but in today's world of pocket digicams this is a camera that people will notice because of it's size. My other cameras are a digicam Fuji E550 and plastic 35mm SLR Canon 300(Rebel) and its substantially larger than them but not much larger than a pro 35mm SLR and you're getting that big piece of film with it. If you are a pro or want to look like one this is no problem because people will give you respect when you pull a camera of this size and all black but I prefer to be candid so it's not ideal in that sense. The build is top notch, everything is black alloy and functions well. In use though the camera is great, I really love the big viewfinder, show it to anyone with a dslr and there jaw will drop because this is niceeee! The choice of using push buttons instead of dials for changing values I don't like but it works fine. This is a SLR which is my favorite style of camera and it's manual focus and the big clear viewfinder with microprism together with the smooth focusing lenses is a joy to use. Honestly it's a camera that I just enjoy to pick up and focus with as a way to view the world. The lens it came with was the standard 75mm (~45mm equiv) f2.8 which I then added a 55mm (~33mm equiv) f2.8 as a wider and therefore more usable carry around lens for scenery and landscape. Both lenses are built beautifully with smooth focusing that is perfectly spaced, you never have to spin the lens too far to focus but it's still easy to make precise adjustments. Fully loaded camera plus lens probably weighs around 3lbs so I wouldn't want to keep it around my neck all day. In reality that is the main problem I have with this camera and the reason I use it rarely is that I don't feel the quality improvement is worth the increase in size, weight, and film expense. Granted I like to shoot classic b&w film and to see some grain!

IMAGE QUALITY

I've only shot less than ten rolls so far with the camera so perhaps it's premature to pass judgment but here is how I see things now. I have shot color negative film either Fuji Superia 100 or Kodak Portra 400 VC and have made prints sized 12x18in. With this camera making sharp grainless enlargements is a snap, it's positively easy! The 400 speed film had just a hint of grain at close inspection and the 100 smooth as silk, nothing. The quality of the images is great the only thing to watch for is that dof (depth of field) is smaller than what 35mm or dig gives you so of course only the in focus areas will be sharp. This of course can be used to advantage as portrait shooters most certainly know. When I compare the pictures I've made at this relatively small size to the others I've made with 35mm and digital I can see that it is slightly better quality but the difference to me is small, it's subtle. In other words I'm not convinced it's worth it. Perhaps this will change when I run some rolls of b&w through it and make some prints. Another disclaimer is that I'm not comparing prints of the same subject, just prints of the same size of different things that I've decided were worth printing out, hardly a proper test of image quality I know but in a sense maybe a test of real world usability? I'm doubtful that even b&w will make a worthwhile advantage because using a sharp modern film, TMAX 100 springs to mind, with a sharp lens I've made satisfyingly sharp prints at this size with the fine grain just becoming noticeable. In other words it looks great at 12x18 which is the largest size I usually print to because it's the largest size the new minilabs can do. I feel that anything that looks sharp at this size will look sharp at any size because as it gets bigger you will have no choice but to stand farther away to see the whole print together. You can always rub your nose against it later looking for grain but only us photo-geeks do that :) To summarize the image quality is great but I'm not convinced that the jump is worth the limitations such as extra size and weight, more expensive, etc. Perhaps the days of MF have come and gone with modern sharp and low grain films and of course digital. Although it is comforting to know that at least today in 2007 there is no digital camera that can out resolve the 645 (using one exposure) for under $7000 approx.

CONCLUSION

Today I'm left scratching my head wondering if the returns outweigh the costs at least for me and my style of shooting. The jury is undecided on this one so stay tuned for updates... I can recommend the camera without hesitation to anyone who thinks that it would suit their use. I hope my experiences will help people make an informed decision.

UPDATE January 2008

It seems that my earlier conclusion that the image quality improvement wasn't enough to make the camera worthwhile has been proven false after I finally scanned some negatives. I did this by sacrificing a few poor negatives so they would fit in my 35mm dedicated scanner, the old but functional HP S20. At it's maximum resolution of 2400 ppi when I examine the scans at pixel level the Pentax results are every bit as sharp as my 35mm stuff. What I conclude from this is that the linear increase of the negative size is the same as the increase in quality. For 645 that is about 1.7x meaning that you could print at 1.7x the size of 35mm and get the same quality. So if you are happy with your results at 11x14 with your choice of film, then the same film on 645 will look the same at 18x24. At the small prints I have made though (12x18) there isn't much difference between the formats I shoot, MF, 35mm, digicam. The difference however would be clear if I wanted to print large. I would like to have some higher res scans done but in reality there won't be much difference unless the negative is critically sharp. Most of my shots aren't even sharp at 2400 when you look at 100%, granted that's the equivalent of printing at 24x36 inches.