|
Forum: Pentax SLR Lens Discussion
03-14-2024, 07:05 AM
|
| |
Diffraction measured right at the aperture only depends on aperture diameter obviously. So, for the same f-number, longer focal lengths have larger aperture and therefore less diffraction. However, there's glass behind the aperture. For longer focal lengths, the airy disks get magnified and therefore become larger on sensor.
Turns out both effects cancel each other out.
Diffraction is therefore (in theory) independent of focal length and only depends on f-number.
|
|
Forum: Troubleshooting and Beginner Help
07-20-2023, 03:24 AM
|
| |
Don't do it.
Reasons:
If you use a cleaning device without suspended basket, the filter will be damaged by touching the basin.
If your retention ring is not screwed in tightly, the filter glass will vibrate and the coatings wil come off.
Use warm water and soap, rinse with de-ionized water and dry with either optical paper or shreds of old newspaper.
Buy a lint-free filter case (genuine leather or plasitc are good),
|
|
Forum: Pentax SLR Lens Discussion
06-07-2023, 05:06 AM
|
| |
It's called an "airy disk" and happens stopped down in high-contrast situations. In astrophotography, you go to great lengths to reproduce this effect since it can be used to gauge the quality of your optics (a pronounced, circular disk with a set number of rings usually means you have good optics).
There may be copies of this lens around that don't produce the effect, but that won't automatically mean they are of higher quality.
Can you easily reproduce the effect even at lower f-numbers? If so, try another copy of the lens.
|
|
Forum: Photographic Industry and Professionals
06-07-2023, 05:17 AM
|
| |
That was bound to happen - not much money to be made with ILC lenses compared to their other ventures. Also, current lenses can't really be improved much more - most of them are diffraction limited. That's why others like Laowa release a bunch of weird contraptions as lenses - it's just a way of fracking the oldschool photographers' wallets some more before the market finally dries up.
|
|
Forum: Photographic Technique
06-02-2023, 11:05 AM
|
| |
When placing my order, I added a nice message about being anal about focus and needing enough shims.
|
|
Forum: Photographic Technique
05-31-2023, 03:49 AM
|
| |
You can swap out the focussing screen for one with a split prism. It will need some calibration work using different shim sizes, but that rarely takes longer than an hour.
I use one and I'm spot on even with the 50mm 1.2 .
If your image is too soft even in the OVF, you need to stop down slightly or use a sharper lens. If that's still not enough, give it some structure by using an additional lightsource for focussing - either a video light or some structured lightsource like a crossline laser.
|
|
Forum: Pentax DSLR Discussion
05-10-2023, 07:08 AM
|
| |
If you want that in a DSLR, it's all just a matter of how you make your bayer filter. You can make pixels for R, G,B, near IR, far IR, UV - just that your resolution decreases the more different wavelengths you observe. In theory possible,but won't sell enough to justify the production costs.
If you want a multispectral camera that takes PK lenses, you can build your own no problem as long as exposure time and manual focus isn't an issue for you:
Buy a full-frame astro cam and a motorized filter wheel, slot in as many bandpass filters as you want and add a T2/PK adapter to the front. You have to take one exposure for each wavelength but with a motorized filter wheel this happens quickly.
|
|
Forum: Pentax News and Rumors
06-22-2022, 08:12 AM
|
| |
The original wording can be read as "even" (...でも安心して), but this is no problem in Japan - people are pretty happy with their own gender-specific safespace, so to say. If it was an Ikebana event, you would read "...even men...".
It's also a matter of language - they use honorific language which sometimes requires phrases like that.
|
|
Forum: General Photography
03-28-2022, 01:13 AM
|
| |
Yodobashi Camera do sell Pentax gear, I even bought a 2x-L rear converter from them. It's maybe easiest to find and I guess most likely to have english speaking staff.
|
|
Forum: Pentax DSLR Discussion
01-20-2022, 04:48 AM
|
| |
This may be an unpopular opinion, but I'd go with the K5II (I own both, btw).
K3 sometime has mirror runaway. It's said to be fixed by firmware, but for me it still happens, especially when using long exposures or interval shooting.
K5II images look better without noise reduction. K3 has lots of chroma noise and I found myself dialing up NR in post more than i would've liked.
AF in K3 isn't head and shoulders above. Same for metering.
Dual card slot also isn't that much a advantage because buffer is small on both.
|
|
Forum: Pentax DSLR Discussion
12-08-2021, 08:42 AM
|
| |
Phase detection AF knows which way to go according to the direction of phase shift (same way as you would do manually with a split prism).
If you are way out of focus, the PDAF can't correlate both images and it has to slowly crank through the whole focus range.
CDAF never knows which way to go, it has to guess based on some heuristics and then reverse direction if the guess was wrong.
|
|
Forum: Pentax SLR Lens Discussion
10-27-2021, 08:17 AM
|
| |
* Shake it so you can hear any loose parts.
* Check it for dents and dings, especially around the filter rings. Don't use a filter if the threads are even slightly bent as you may run nto a situation where the filter gets stuck and can't be removed without damage.
* If it has an aperture lever, actuate that and see how quickly it jumps back to closed position. If it doesn't jump back instantly, see why (hint: there may be oil on the blades).
* Have a look at the aperture blades, they should look pristine without any stains.
In case your aperture blades are even slightly oily, you need to clean them and change the grease.
* If it has an aperture ring, check whether that is snappy and actually changes the aperture.
* While you're playing with the aperture, make sure it's open all the way and take a look through the lens. Check for dust/fungus, scratches and balsam separation.
* Check the focusing mechanism, it has to run smoothly without slack. If it's not smooth, you may need to re-lube. If there's slack, the mechanism may be worn out.
* Same as above for the zoom ring.
* If the lens extends while focussing or zooming, check whether there's any wobble in the barrel.
* Put it on the body and check for slack (mount could be bent or worn out, happens a lot with Tamron Adaptall or plastic mounts).
* If the lens has electrical contacts, check for oxidation and apply contact cleaner if necessary.
* Some older lenses have the whole bayonet blackened which insulates it from the electric contacts. Those lenses may not be detected by newer digital cameras. If that's the case, just remove the paint around the area where the contact springs should land.
* Check any rubberized parts for brittleness.
After that, you can start checking the optical properties. You may want to try it out on a flat surface or even better a lens chart to calibrate the AF and check for decentering, metering and focus shift.
You should now have found any flaws that would prevent you from using it, so you can finally take it outside for test shots.
|
|
Forum: Photographic Technique
07-26-2021, 12:06 PM
|
| |
As far as lenses go, fewer/thinner elements is better. Glass is somewhat opaque to UV light.
As lightsource you can buy UV leds, they come in different wavelengths (UV-A, UV-B or UV-C). If you want to be on the save side, only use UV-A lightsources. It's also a good idea to use a weak light source and compensate with exposure time.
There are also UV-flashguns for forensic purposes showing up on ebay from time to time, but they are rare and expensive.
In some cases, blocking out the visible light may be counter productive as you may want to catch the fluorescent light (looks cool with minerals).
If you use anything "harder" than UV-A you don't really see the light anymore, so you can't tell whether the lightsource is turned on until you get a headache (but then it's too late, you will already have conjunctivitis and possibly a damaged retina). Please also remember UV doesn't trigger the pupillary light reflex, so it is very dangerous if used in the dark.
UV goggles should of course match the wavelength of your lightsource. Try wearing a freshly washed, white shirt. If you see it light up, that's a strong hint your lightsource is still on. Make sure to cover your skin if you use shorter wavelengths and/or use sunblock.
|
|
Forum: Pentax SLR Lens Discussion
04-22-2021, 03:55 AM
|
| |
I wouldn't point my finger at any lens I own simply because there's a chance that I just got a bad copy.
That being said, there's one lens that is objectively bad: the SMC 85mm F2.2 Soft
In a typical "soft" lens (such as the F 85mm F2.8 Soft), you have reasonably sharp optics (so you can achieve focus) and the ability to offset one optical group along the axis, putting the lens in "soft" mode.
With the SMC 85 2.2 Soft they just trolled their customer base . That lens doesn't have a "sharp" mode because it's just a plain simple doublet in a barrel, literally on par with the methaphorical "bottom of a coke bottle". The softness isn't a carefully engineered optical design property, it's just the result of having only a single, uncorrected lens group.
Didn't keep them from charging more than for most 5-6 element lenses in their lineup. It's a "soft" lens, afterall, so it just has to be more expensive than the regular ones, right?
|
|
Forum: Pentax SLR Lens Discussion
04-16-2021, 03:31 PM
|
| |
No, totally disagree. And I'm usually the first person to rave about the character of vintage lenses.
Would have agreed if you'd put up the 43 against, say, the FA50 or the DA* 55mm. But the DFA 50? Nope.
43mm is quite soft wide open and improves to around f4.
50mm on the other hand doesn't improve as you stop it down, since it already reached maximum sharpness at f1.4. And we're talking crazy levels of sharpness, it's on par with the Zeiss Otus. It freaking out-resolves the K1 wide open, the only lens that makes me turn on moire filtering.
43mm has plenty of purple fringing on digital, while the 50mm has very few PF wide open and zero purple fringing as you stop it down.
43mm has nice subject isolation (microcontrast) from f2.8, while the 50mm has Zeiss-levels of 3D pop all through the aperture range.
43mm has a pleasant bokeh while the 50mm has super buttery smooth bokeh.
43mm is noisy screw drive with the usual slack in the geartrain while 50mm has super fast, latest generation SDM with Quickshift.
Now, I totally get why people like the 43mm. I own it myself. Character goes a long way.
Heck, my favorite Pentax lens of all time is the SMC A 28mm 2.8.
But in this case - no matter how much I like your Toyota Celica, if there's a Bugatti Chiron next to it, I don't think twice.
|
|
Forum: Pentax SLR Lens Discussion
03-01-2016, 02:41 AM
|
| |
Rear mounted teleconverters usually decrease the f-number of your lens, as they effectively increase focal length without making the image brighter. (or, using your words: they magnify the image on the sensor so that the same amount of light is spread over a bigger area, hence you loose light).
Rear mounted teleconverters (speedboster) on the other hand make your lens faster because they collect more light on the sensor - but they only work if your sensor is smaller han your original image circle - otherwise you will get vignetting.
Front mounted stuff can be anything, mostly:
* Wide angle converters
* Macro lenses
* Effect filters
Unlike the rear mounted stuff that can't change the entry pupil size, the front mounted converters can (or, to keep the above paradigm: they don't magnify the image but rather increase/decrease the angle of reception of your lens). Most front mounted wide angle converters are funnel-shaped and effectively increase the entry pupil size which gives you a faster lens.
Front mounted macro lenses mostly decrease the minimal focus distance. This comes with the side effect that infinity focus is lost. They also come with all sorts of abberations and most of them will make your lens slower (they increase focal length without changing the entry pupil size). This is especially true for the single element screw in ones.
What you have here is a front mounted teleconverter. It looks like a quality one, and those are designed to not only increase focal length, but also entry pupil size. It will probably not change the lens speed while increasing the focal length when mounted on the lens that it was intended for.
You should keep in mind that in an optical system, not only the distance of lens elements matters, but also their orientation - elements which are added to the "curved" side of other elements potentially increase abberations dispropotionally and need to be carefully designed. As the front mounted converters are added to the (usually heavily bulged) front element af a lens, the designer had to have a certain curvature in mind that he optimized the converter for. This also means that most front mounted converters are designed to work well only with a certain lens (in your case, an olympus zoom lens). If you put them on a different lens, you may add a heavy amount of abberations.
|
|
Forum: Pentax SLR Lens Discussion
09-25-2015, 08:23 AM
|
| |
No, it's because because digital sensors are more sensitive to UV and IR. Film era lenses were never corrected outside the visible spectrum. If you use them on digital the uncorrected UV/IR image becomes visible as fringe. If the fringe is mostly purple, it's the uncorrected UV image. If it's mostly red, there's also some IR in it. You can mitigate it by agressively using UV/IR cut filters on your lens. That's also the best way to tame the 43mm ltd.
|
|
Forum: General Photography
09-03-2015, 05:35 AM
|
| |
You just got me started. I made the exactly same experience.
In past days, not everyone had a camera. It was something special to have both the gear and the knowledge to be able to take pictures and therefore, people were grateful. I really miss those times where you took a picture with your SLR, later gave it to someone and people were crazily happy about it and put it on the wall and kept it there forever.
Nowadays, everyone has at least a smartphone and most people have point&shoot cameras. Taking pictures is no longer anything that's considered "work" or "art" especially since 99% of people use auto exposure. Pictures aren't kept as memories, they are gathered.
Average Joe thinks that the effort for you was in pressing a button. He isn't aware that you actually had to know your shit and select a decent composition and exposure and also invest some time in PP. He thinks the only reason that his pictures suck compared to yours is that you shelled out more money for an expensive camera.
My experience is that people with no knowledge about photography usually are not grateful at all. They more or less expect you to give them pictures for free. If you take some time for PP they will sometimes even be pissed because it "can't take so long to download those from your camera". I even had one case where I was on vacation with someone and took some HDRs and later got scolded because I "copy&pasted some other sky". In other cases I was accused of using a "shitty camera" because the "background is blurry". Yeah, and what's always happening is that you get shafted because the pictures you took are "too large".
People that know at least the basics of photography are a totally different story, though.
Anyways, my strategy is the following: Whenever there is a chance some "bystander" wants to have a copy of some image, I quickly take a few jpeg shots in green mode - no composition, subject centered in frame, maximum DOF, no PP, lowest resolution. That's for them and it exactly meets their expectations.
|
|
Forum: Pentax Medium Format
07-30-2015, 03:53 PM
|
| |
I think that's a dangerous, thing to say. Of course, total light doesn't factor in when it comes to exposure. But this is photography 101, whoever doesn't know that already just isn't ready for medium format, period.
However, in a controlled (studio) environment, where you are not constrained by exposure times and/or aperture or where you can crank up your flashguns all the way you like, total light is the *only* thing that matters. Total light is the signal you're getting from your sensor. The more energy it contains, the better the S/N ratio. For a given print size, the amount of energy your sensor absorbed dictates your S/N ratio. Not even the pixel sizes play a role here, a 10x15 print will have the same noise no matter how many megapixels you divided your sensor into.
In other, more constrained environments, like sports or wildlife, the situation is different. In that cases total light doesn't matter because a certain scene only gives you a fixed amount of photons to work with. If you record more than that, you blur your scene in the time and/or the spatial domain. In this case, it doesn't matter much how big the sensor is that captures that predefined set of photons.
|
|
Forum: Pentax SLR Lens Discussion
07-30-2015, 10:33 AM
|
| |
It depends on your expectations. The adapter optics are not designed for your lens, it's probably a generic gauss double that adds all kinds of abberations. Also, compare the adapter's lens diameter to the diameter of your rear element and draw your own conclusions.
I don't know enough about the Komura's strong points, but things like sharpness, aperture, longitudinal and lateral CA and possibly field curvature will degrade.
Color rendition and contrast will probably stay in the same ballpark.
|
|
Forum: Pentax SLR Lens Discussion
02-02-2015, 06:47 AM
|
| |
Is this your first DSLR? If not, just skip the rest of my post.
If it is, you're walking right into the trap of buying the latest body and cheap lenses with it.
In reality, lenses are always more important. Picture quality is mostly limited by lens abberations and to a lesser extent by the body/sensor.
An expensive body with a bad lens will give you sub-optimal pictures. A cheap body with a good lens takes great pictures. An expensive body with an good lens takes great pictures and has more features.
Whether a lens is bad or good does not solely depend on the price (the plastic fantastic 35mm 2.4 and 50mm 1.8 are cheap and great). However, especially in the area of high magnification zooms you may easily get into a situation where your (expensive) DSLR outresolves the cheaper super-zoom. This is where you wasted money on the camera that you could have invested in a better lens.
Short version:
The K-3 is probably overkill if you really plan on using those zoom lenses, as the sensor outresolves the lenses.
Try to go for a K5 II or even a K-50, they give you the same image quality.
You can upgrade the body later (that's what you will end up doing anyways).
The saved money can be invested in better glass.
For landscape, the SMC-DA 12-24mm would be good.
As a normal lens I highly recommend the 20-40mm limited.
For macro, the 100mm DFA is probably best.
If you really need long zoom ranges, have a look at the DA* line of lenses and/or wait for the new HD superzoom(s).
Just to make sure I'm not misunderstood: Of course there's nothing wrong with buying those zoom lenses you mentioned, but they should never be the only lenses in your bag. If you buy the megapixels, then you need to buy some glass to feed them.
|
|
Forum: Pentax DSLR Discussion
01-22-2015, 06:14 AM
|
| |
Well, I think that is probably a very subjective thing. The problem I had with opti-brite is that the added brightness is not where I need it (center is bright enough with splitprism) and it visually increases DOF and makes it less "snappy" and therefore makes it harder to assess the amount of out-of-focus blur.
|
|
Forum: Pentax DSLR Discussion
01-21-2015, 12:10 PM
|
| |
I had both. First I used a Katzeye on my K-5, then I switched to ee-S, then back to Katzeye. My K-3 now also has a Katzeye.
I didn't like the ee-S so much since I found the split prism to be much more accurate.
Yes, metering is less consistent, but that's only a problem if you shoot JPG (I never do that).
After a few days, you know by instinct how to compensate for exposure.
The split prism/micropsirm combo with rule of thirds grid and circle is perfect for composition. I can't see how this could ever impair me, in fact, my composition became better with the KatzEye.
I use it together with the O-ME53 viewfinder and I can focus spot-on with my 1.4 lenses through the viewfinder.
As for the problem with using slow manual glass with a KatzEye: don't do that. You bought the thing to focus fast lenses spot on. Slow manual lenses are not a usecase for split-prisms.
You won't need opti-brite, it's not worth the extra money.
Most importantly;
* Make sure to shim the screen correctly.
* Seriously, make sure you put the correct shim
* Double and triple check for focus accuracy with your fastest and longest lens. Don't be afraid to try out many shims
Installing the focus screen needs a dust-free environment. Go to your bathroom, turn on the shower so it washes all the dust out of the air.
Use gloves. Never ever touch the screen with your bare fingers.
Use pliers to extract the old screen. Don't scratch the screen. Every scratch will be prominently visible in your viewfinder.
If you find dust, use a blower. In very severe cases, use isopropyl alcohol and optical paper.
Use your thickest shim, insert new screen, do a focus check.
If you're not spot on, rinse and repeat with the next smaller shim.
Once you have the correct shim, it's a joy to focus manually. Actually, MF with split-prism can be more accurate than AF with some very fast lenses. You also notice easily when the AF missed - if you have quickshift, you can correct focus in the last split-second, which is cool.
|
|
Forum: General Photography
11-17-2014, 05:59 AM
|
| |
I for one was happy about every gift related to photography I got, but it made me stick with low quality gear longer than I felt comfortable with, since I didn't want to offend the donor.
So, if you spend 100 bucks, spend it on something that's worth the money.
As you already bought a tripod, I hope it's not a very cheap one. The cheap ones tend to be either overly bulky or unstable.
The only "cheap" tripod that I can recommend is the Velbon Ultra MAX-i M. If it's one of those things for 40 bucks, don't be offended if he swaps it for a more sturdy one on a year or so.
Other things coming to mind:
Do you know what kind of things he likes to shoot?
If he enjoys landscape:
* Remote! (this *really* made a difference for me)
* Polarizer (choose correct diameter for his lens!), this depends on how experienced your brother is, beginners probably don't have much use for it
* I know beginners enjoy HDR very much, so a book on HDR photography or a HDR software would be cool
* Beginner's filter kit (Cokin should do, again, mind the lens diameter)
Sports/wildlife:
* Camera strap (maybe a sniper strap would be good)
All around:
* Good quality cleaning kit (Zeiss et al)
* Beanbag
* Camera bag (make sure it has a sling for the tripod and that the tripod fits)
In case he got a K-3 (which would be overkill), you could think about a Pentax Flucard (make sure it's the original Pentax one labelled O-FC1)
|
