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Forum: Pentax SLR Lens Discussion 02-24-2019, 05:29 AM  
MTF Mapper
Posted By whojammyflip
Replies: 10
Views: 622
Nope, I have just beenevaluating lenses against each other. The next possible test is to mount some enlarger lenses and profile them...could give Ctein a run for his money. One thing is clear, there is a good reason for the "f8 and be there" phrase. Except for the Pentax M 85mm....that lens peaks in certain respects at f4.

The most controversial result I have had is for the Tamron 278D at 135mm f8 to f16. Wide open its a bit of a stinker though and the extremes are not good.

I have just posted this in the lens review section:

Tamron 278D at 135mm f8, MTF25 resolution


Tamron 278D at 135mm f8, contrast at 20, 40, 80lpmm


---------- Post added 24th Feb 2019 at 12:49 ----------



This is my kind of expertise. I work in analytics and this is fun for me.

The next step would be to just do the MTF calculation on the MTF Mapper targets, and get an aggregate reading for contrast at say 40lpmm, across the frame, in order to be able to rank lenses on a single metric. I think 100lpmm might make more sense as this is the around the limit for the sensor/film resolution. The trouble is that most lenses score zero at this spatial frequency. That Tamron is exceptional.
Forum: Pentax SLR Lens Discussion 02-23-2019, 05:56 AM  
MTF Mapper
Posted By whojammyflip
Replies: 10
Views: 622
Some MTF curves for primes at f4, interesting to see little or no difference between the M 50 1.7 and 1.4. Using MTF Mapper on an A1 grid, as PEF files.

Pentax M 50 f4 at f4


Pentax M 50 f1.7 at f4


Pentax M 50 f1.4 at f4


Pentax A 50 f2 at f4
Forum: Pentax SLR Lens Discussion 02-22-2019, 08:58 AM  
MTF Mapper
Posted By whojammyflip
Replies: 10
Views: 622
Here is a comparison of the Pentax M 28 2.8 at f4 vs the Pentax M 28 3.5 *wide open*

Pentax 28 2.8 at f4:


Pentax 28 3.5 *wide open*


I've literally just shot around 200 shots, so I am not going to post the lot. I also have the Pentax M 50 f4 and the Pentax A 50 f2 which I am going to compare with the M 50 1.4 and M 50 1.7.

This train is leaving the station! I have been meaning to get around to quantifying the performance of the Pentax lenses for a while, using MTF testing. So here it comes, watch this space.
Forum: Pentax SLR Lens Discussion 02-22-2019, 01:54 AM  
MTF Mapper
Posted By whojammyflip
Replies: 10
Views: 622
Hi, I have got up and running with MTF Mapper, printed a grid target and am performing some MTF testing. It generates MTF curves, ie contrast at chosen resolutions 10, 20 and 40lpmm. I am running through testing of 31 lenses at the moment, at each marked f stop. My most interesting results have been:

- Pentax M 85mm, sharp wide open, and hits peak average sharpness at f5.6, with contrast across the frame of over 63% at 40lpmm
- Vivitar Series 1 v1 70-210mm, sharpest lens at 210mm at any aperture with average contrast of 50% at 40lpm at f5.6
- Tamron 278D 80-210mm, sharpest lens at 135mm at f11 with average contrast of 64% at 40lpmm

I particularly like the slanted edge MTF testing on a grid, as its a quick way to profile a lens across the image plane.

Here is the result for the M 85mm at f5.6:


Here is a list of lenses I have for testing (cannot mount the Vivitar S1 35-85 at the moment as its rear flange hits the K7 body):
Pentax DA 18-55 AL
Pentax M 75-150
Pentax M 80-200 v1
Vivitar S1 V1 70-210
Vivitar S1 V2 70-210
Vivitar S1 V3 70-210
Tamron SP 70-210 19ah
Tamron SP 70-210 52a
Tamron SP 60-300 23a
Kiron 80-200 f4
Kiron 75-150
Vivitar S1 35-85
Vivitar S1 28-90
Tamron 28-105 179D
Tamron 80-210 278D
Pentax F 80-200
Tamron SP 28-135
Tamron SP 28-80
Tamron SP 24-48
Pentax M 24-50
Pentax FA 28-70
Tamron 28-80 77D
Sigma 21-35
Pentax M 135
Pentax M 85
Pentax M 50 1.4
Pentax M 50 1.7
Pentax M 28 3.5
Pentax M 28 2.8
Tamron SP 90 2.5
Pentax M 200
Forum: General Photography 08-29-2018, 12:03 AM  
How fast is your PC - and should I upgrade mine now Ihave a K3-ii?
Posted By whojammyflip
Replies: 29
Views: 1,420
I would buy an entire desktop on ebay, in a box. Thats the best way to get a decent PC in my opinion. Anything faster than 50% of the top CPU Benchmark score is a waste of money, unless you are either gaming or someone else is paying. I'd stick to something from generation 6 or more recent. Watch out for 'socket' compatibility if you want to be able to upgrade, and stick to DDR4 ram.

I recently sold a i7 970 based pc on ebay for something like 150 pounds (could have been 170 - but the guy got a great deal), with 16gb of ddr3 ram, and a SSD drive. I think the buyer was pretty chuffed. It was in an Antec box, which makes a big difference. I wasn't miffed about this as I picked up a i7 6600 with 32gb of ddr4 ram and asus board in a fractal design case, with a Samsung m2 500gb drive for 500 pounds.

I think the motherboard is important, and I stick to Asus boards. There may be some brand snobbery, but there is little point in saving a tenner on the framework of the computer, which limits the speed of transfer of data between components. I dont muck about with fancy cooling systems or fans and lights.

One way to make your computer go further is to switch to Ubuntu, which uses less RAM than something Windows based.
Forum: Film Processing, Scanning, and Darkroom 12-16-2016, 02:07 PM  
Can anyone recommend a good scanner-(convert film to digital)?
Posted By whojammyflip
Replies: 33
Views: 4,370
I have a Canoscan 9000f and in comparison to a shot with a DSLR such as the Samsung gx20 of a negative in a LPL metal carrier, the Canoscan is terrible....the advantage of the Canoscan is that I can do around 200 images in an evening whilst doing other things at the same time....so for high resolution, a shot on the lightbox is prefered, but for speed the Canoscan wins handsdown. Both solutions are cheap.

you can have quick, cheap, good....pick 2
Forum: Film Processing, Scanning, and Darkroom 12-16-2016, 02:04 PM  
Scanning Pentax 645 film
Posted By whojammyflip
Replies: 37
Views: 4,691
may be possible to be able to take several shots of the same negative using a digital body, and then average the results to get a higher resolution, imagine if you could shift the negative relative to the body half a pixel along....you could double the resolution
Forum: Pentax SLR Lens Discussion 12-16-2016, 01:45 PM  
Lens Reviews A28 vs F28
Posted By whojammyflip
Replies: 28
Views: 1,709
side by side comparisons are easier to evaluate as you are not looking at an absolute measurement, rather a relative judgement is being made

in this respect, the 28mm f3.5 m series lens is miles sharper than the 28mm f2.8 m series v1 lens, as I have tested these two on tmx film on a tripod, with an Edmund resolution target, and then looked at it through a nikkor 50 2.8N and a 25x scope, achieveing 250x magnification

under these circumstances, I think its fair to say an objective measurement was taken and the 28mm 2.8 literally had about 60% of the resolution of the 28mm 3.5
Forum: Pentax SLR Lens Discussion 04-20-2016, 02:26 PM  
FA 31mm f/1.8 Limited price jump since K1 announcement
Posted By whojammyflip
Replies: 13
Views: 2,171
Contrary to the optimism about prices, I picked up a mint 85mm f2 prior to Christmas for less than GBP 100, when they used to go for 1.5x or 2x that price.

Looking at the Pentax primes for cropped sensors, I think its possible that Pentax will provide new lenses for the full frame camera. If they dont, then maybe companies like Zeiss and Sigma will.
Forum: Pentax SLR Lens Discussion 04-17-2016, 07:02 AM  
Pentax-A SMC 50mm F/1:2 vs 1.2 (K Mount)
Posted By whojammyflip
Replies: 10
Views: 1,646
I've got the 50mm M series 1.4 now and got rid of the M 1.7. I also have an A series 1.7 and A series f2. Practically, they are all sufficiently sharp for general usage.

However, the 1.4 is noticeably sharper than the 1.7, between say f2 and f5.6. I've compared the M series 1.4 and 1.7 on Edmund res test charts, and the 1.4 was measurably sharper. I've seen similar differences between the 35mm 2.8 and f2 lenses (with the f2 being sharper) and the 28mm 2.8 and 3.5, with the 3.5 being sharper.
Forum: Pentax SLR Lens Discussion 03-21-2016, 03:25 PM  
SMC Pentax 1:2/28: the poor man's Distagon?
Posted By whojammyflip
Replies: 108
Views: 37,551
I keep track of lens prices, in case I should ever find a GBP 400 note down the back of the sofa, and happen to see a rare Pentax lens. I have seen the Pentax 15mm and 18mm lenses hover around GBP 400. It would seem reasonable to expect the Pentax 28 f2 to do the same, but I have seen it go for about GBP 350. At the moment, this is equivalent to something like USD 600 or USD 700. Its really quite expensive when you consider a Zeiss 85 f1.4 or 18/4 for the CY mount is around GBP 400.
Forum: Pentax SLR Lens Discussion 03-21-2016, 03:14 PM  
Resolution is not the same as IQ, not even close.
Posted By whojammyflip
Replies: 54
Views: 4,069
Pentaxforums has stepped up a gear. I note that the original poster is on my ignore list, having logged in.

Something piqued my interest here, its a real flame war thread I think.

My two penneth worth would be that the factors you have mentioned such as light and composition are being conflated with the difference in resolution. If a shot has been taken hand held at close range, neither lens will be limited by resolution thanks to camera shake, which impacts shots even at 1/500.
Forum: Pentax SLR Lens Discussion 02-25-2016, 11:33 AM  
Pentax M 20 f4 on Full Frame
Posted By whojammyflip
Replies: 21
Views: 2,336
Its the 24/2.8 which I tested: I was testing this using TMAX film in a Pentax MX, and got over 100lp/mm, based on an Edmunds optics resolution target and central resolution only. I was using a focus scope under and enlarger with the head wound all the way up and then reading the groupings off and backing out the resolution. Its not necessarily the most accurate, but it does give you a good relative measurement vs other lenses. I've not done this for ages. I need to get round to putting a script together in some software to share so that people can do MTF testing for free.
Forum: Pentax SLR Lens Discussion 02-23-2016, 01:54 PM  
Pentax M 20 f4 on Full Frame
Posted By whojammyflip
Replies: 21
Views: 2,336
The median price of a M 20mm on an ebay auction has been 180 pounds including postage, over the past few years. EUR 350 therefore looks steep. EUR 260 may be more reasonable/realistic/fair. You have to figure, this is a very wide perspective. I have used the 24mm K series prime and its the sharpest lens I have tested, in the centre, sharper than the M 28 3.5.
Forum: Pentax SLR Lens Discussion 02-23-2016, 01:46 PM  
Pentax K 28mm f2 or Carl Zeiss Distagon T* ZK 28mm f/2 lens for Pentax K
Posted By whojammyflip
Replies: 100
Views: 18,331
I think this price rise has possibly been priced in. This fabled full frame body has been speculated about on Pentaxforums for quite a while. Lenses like the 85mm M series are now cheaper than they were a couple of years back (I just picked up my second copy of this for 100 pounds, when I bought the first for 150 pounds about 5 years ago), and thats after the full frame has been announced.

Its interesting to look at the lenses of the dead mounts like Konica, and to see the 15mm wide angle going for about a third of the Pentax equivalent. Pentax lenses have already risen pretty high.

I think most people want autofocus lenses, and if Pentax release some autofocus primes, the cost of the better manual primes may actually fall. It would suit me, I rather regret having sold a M 28 f2. I've got the 35, 50 and 85 in the fast versions. Its just a shame that Pentax didnt release as part of the M series a fast 135, with a bigger ring like the 200.
Forum: Pentax SLR Lens Discussion 02-20-2016, 05:57 AM  
Pentax K 28mm f2 or Carl Zeiss Distagon T* ZK 28mm f/2 lens for Pentax K
Posted By whojammyflip
Replies: 100
Views: 18,331
for anyone interested, I've just seen a K 28 2.0 "hollywood" on ebay:
Pentax K SMC 28mm F2 / F2.0 Very Rare Prime | eBay

its beyond my budget/wife's threshold for acceptable purchases, so I am not buying it...I've had the M 28/2.0 before, and decided that the lowly 28/3.5 was sufficiently sharp (a lens which is really sharp is the k 24/2.8)

i've got nothing to do with the sale, I just thought it might be nice to give the heads up to people on Pentaxforums
Forum: Pentax SLR Lens Discussion 12-07-2015, 02:12 PM  
35mm vs 50mm usage
Posted By whojammyflip
Replies: 14
Views: 2,128
on digital, 50 will behave like a 85mm lens on film...quite a nice perspective for portraits

for general shots, some might say something shorter than 35mm might be more useful as you can get more in
Forum: Pentax SLR Lens Discussion 12-07-2015, 02:01 PM  
Macro: 50 or 100? Best "General?"
Posted By whojammyflip
Replies: 25
Views: 1,785
for what its worth, I've got a book on classic lens design from Neblette, and the Apo Skopar has an identical layout to the Pentax M 100 f4
Forum: Pentax SLR Lens Discussion 10-24-2015, 06:45 AM  
rare lens alert 1000mm
Posted By whojammyflip
Replies: 7
Views: 1,207
Just seen there is a rare 1000mm f8 Pentax lens up for grabs on Ebay. I've got nothing to do with the auction, but its a rare one I thought I'd give everyone the heads up on.
Forum: Pentax Camera and Field Accessories 01-02-2015, 12:31 PM  
B+W lens hoods
Posted By whojammyflip
Replies: 1
Views: 873
Anyone know where to get hold of B+W/Schneider metal lens hoods in the UK, please? I am looking out for some 58mm ones for my Pentax 645.
Forum: Film Processing, Scanning, and Darkroom 03-03-2014, 04:01 AM  
DSLR scanning
Posted By whojammyflip
Replies: 24
Views: 4,588
interferometry involves taking two rays of light and superimposing them, simultaneously, when they're exactly in phase, they add together, and when out of phase, they cancel out...this is wavelength dependent, so that some wavelengths cancel and others don't due to differences in multiples of wavelength involved...examples would be the mutli coating reflection having a colour to it, or coloured bubbles

alternatively, you can measure distances using a laser which is being modulated at a known frequency (so that the carrier wave has a much longer wavelength than the actual light) etc

there is one example of superposition of waves where the waves don't have to occur at the same time...this is when a single photon of light can be shot out through young's slits and you still get double slit diffraction patterns which would occur from the interference of two beams of light, but we know there is only one photon which has been sent, so it should result in single slit patterns....an argument for parallel universes

I don't think Pentax cameras will be doing this any time soon...

---------- Post added 3rd Mar 2014 at 11:02 ----------

Double-slit experiment - Wikipedia, the free encyclopedia
Forum: Pentax SLR Lens Discussion 02-28-2014, 12:54 PM  
Fast Portrait Prime
Posted By whojammyflip
Replies: 40
Views: 3,328
wow, just wow, I forgive you buddy and draw a line in the sand
Forum: Pentax SLR Lens Discussion 02-28-2014, 03:58 AM  
Fast Portrait Prime
Posted By whojammyflip
Replies: 40
Views: 3,328
you cannot create what is not in the original as the saying goes...the point spread functions of the lens are just completely different to a normal lens...if you could do this, then no one would buy fast lenses...they'd just replicate bokeh effects digitally
Forum: Film Processing, Scanning, and Darkroom 02-27-2014, 01:25 PM  
DSLR scanning
Posted By whojammyflip
Replies: 24
Views: 4,588
I have to stress that I dont think its worth anyone's time to go mad like the bloke I'd linked to, with masses of photos being stitched together...the major advantage of this process is that its quick, significantly faster than the scanning I did with a v300.
Forum: Pentax SLR Lens Discussion 02-27-2014, 01:19 PM  
Significance of innaccuracy of focus in lens testing
Posted By whojammyflip
Replies: 7
Views: 1,214
I have a split screen from focusingscreen, on a KM. The KM is not the best viewfinder, but a split screen is pin point accurate. You have to verify its shimmed correctly by shooting a ruler at a 45 degree angle, running away from you, and confirm that the visual focus corresponds to the "chemical focus"...this is an issue from the darkroom too, where light our eyes are sensitive to is not the same as light the camera is looking at. I dont think the KM does live view. I dont use it for anything other than digitizing negatives and lens testing :)

We have vision which peaks in the yellow/green area. If you want to do this all really accurately, you would use a beautiful old MX with a great big viewfinder, a yellow green Hoya X0 filter on the lens, and ADOX film with resolution which is higher than the lens. A yellow green filter ensures the film is being exposed to what your eye is sensitive to. You could do the filter on digital too, but it would muck around with the demosaicing, I think.

---------- Post added 27th Feb 2014 at 20:31 ----------



I can post a link later when I have made a new and improved slant edge...rather than using black paper, I am going to use a light trap, so that there is no possibility of a shadow affecting the sharpness of the image edge. The idea is that a slant edge on a gradient gradually transitions across pixels on the sensor, as you move down the images beneath, the slight angle of the image means that the high contrast edge moves slightly relative to the grid of the pixels. The processing finds the gradient, rotates the image so that it is vertical, and then finds the average change in pixel value in the transition from left to right on the image. This is a digital equivalent to calculating the accutance. If the lens does not attenuate the sharpness of the original object, then the gradient would be completely flat until the transition where it would peak, and then it would be completely flat again. Practically, the gradient is kind of wave like. From the wave that is formed, a calculation is performed which works out what the lens can see in terms of sharpness...what frequencies have to be present in that wave, and how strong the frequencies are. The sharper the gradient, seen in the image, the greater the presence of the highest frequency waves...ie the higher the resolution capabilities of the lenses. Again, whats nice about this is that its not really distance related (a line looks like a line wherever you are standing, whereas a pair of lines doesn't), and thus does away with Edmund resolution targets. On the flip side, it involves a bunch of software and is less intuitive. I hope the explanation above is not too much like voodoo.

Its literally a simple question of generating images like these:

Pentax M 135 3.5 at 3.5



Pentax M 135 3.5 at 5.6


In the first image, its clear to see the colour fringing. The second image at f5.6 is sharper. Quick MTF said that for the 30% contrast level, the resolution was 1650LPH, in photozone.de speak...and this is with a dodgy test target....if I get a guillotine to ensure that the edge is dead straight, its possible this will be even higher. However, if you download the images and run QuickMTF now, you wont get the same results, as I have cropped the images. However, you will get .335 cycles per pixel...there are 172 pixels per mm, so this means 58lp/mm. This highlights the benefits of something like an Edmund test chart, in that you can see the bars with your eyes, and read off the resolution from a conversion chart. I guess this is work in progress. Aside from absolute lens resolution measurement, its useful just to go through the process comparing lenses to understand that the difference between good lenses is probably less than the variation in my ability to take a sharp shot, even when I am trying hard.

Software:
http://www.quickmtf.com/
http://mtfmapper.blogspot.co.uk/
http://sourceforge.net/projects/mtfcalculator/

MTF calculator is the quickest, but you can only use it for relative measurement. MTF mapper looks interesting but I have not had it working yet. Quick MTF is probably the most refined thing I have found, but its pretty expensive in comparison to other software...its quite tempting for me to actually write something myself. There is some shareware called imagej, and I might try taking the code into R.

PS, I am pretty sure my neighbours are wondering what the hell I am doing taking photos of black and white wedges!
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