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Forum: Pentax Medium Format
12-19-2013, 06:31 AM
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I just checked and saw the link to Don Groom's work had gone dead. It's still floating though. The PDF about cosmic rays in astroimaging is now hosted here:
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Forum: Pentax Medium Format
12-19-2013, 06:12 AM
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Yes, I believe it affects all imaging sensors, both CCD and CMOS. I believe the main reason I see more of it with the 645D is the sheer size of the sensor. If I'm correct, a full-format 35mm system should be affected to a degree somewhere between APS-C and 645D.
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Forum: Pentax Medium Format
12-18-2013, 02:13 PM
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Hi Scoot,
I've made some observations on long exposures with the 645D compared to the Pentax K-5, and made the same observations as others did with a Canon that the 645D seems more prone to noise. In my experience, however, it's not really the noise from the 645D CCD cirquit itself that is the main problem. What frustrates me more is the random, and sometimes very conspicuous, spurious noise caused by Compton scattering. I was completely baffled by it first time I saw it and wrote a lengthy post in my blog about it. It may be of interest to you. The images I refer to in the lengthy post are here.
Since that experience, I've come to think that the only real option is to combine a number of shorter exposures in post.
On a recent trip to California and Nevada I saw less to the spurious noise problem than back home in Norway. There are some examples in the November archive. I have no idea if the problem actually does increase with latitude, though.
Another trick I applied in the USA was to do multiple exposures of 30 seconds. The shot of the Desert Highway in Zion Canyon is made that way. I have examined the raw file and found no spurious noise at all. The algorithm that combine parts of a multiexposure must be a bit different from the darkframing, I think.
Hope this can be of some help to you.
Best,
Jostein
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Forum: Pentax Medium Format
04-10-2013, 12:53 AM
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Welcome to the forum, uintaangler. :-)
The focus confirmation in the 645D viewfinder is threefold. One is a brief, red blink emanating from the sensor point that lock on. The other is a hexagon that lits up at the bottom of the viewfinder, beside the tech info about aperture, shutter speed and ISO. In addition there is an optional beep that sounds when focus locks on. I would assume this is very much in line with what you have on your current camera.
In manual focus, both with AF and manual focus lenses, all three indicators will still operate with the same reliability. If you use manual focus lenses, however, only the centrepoint sensor works.
As to reliability, and I assume you also think of accuracy, I am a very happy camper regarding the 645D performance. I have used it outdoors in temperatures between +25°C and -25°C with no hassle. Many of the older lenses have barrels made of metal that contracts in cold climates, but focus remains spot on.
I agree with you that the selection of current (in-production) lenses for the system is somewhat limited and expensive. Personally I do not own any of them. But I do have a decent set of focal lengths in AF anyway (from 35mm to 400mm). The film-era lenses for this system are all up to the task of dealing with digital, so as long as you buy from a reputable dealer you can safely buy second hand. That goes for the older manual focus lenses as well. Some of them are even outstanding, like the 645-A 120mm f/4 macro, for example. And with an adapter, you can also use optics from the Pentax 67 system. The adapter propagates aperture control.
As one of the early adopters of the 645D system, I have been monitoring the release of new lenses for the system with some concern as to whether Hoya, and then Ricoh, would develop it further. Since the release of the 90mm macro I feel reassured it is a system that will continue for a long time. So hopefully the price of optics will come down somewhat in the future.
As a final note, you should not expect to find much negative comments from 645D owners in this forum. If nothing else, people here will fiercly defend their investments... :-)
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Forum: Pentax Medium Format
01-11-2013, 01:12 AM
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Forum: Pentax Medium Format
01-11-2013, 12:20 AM
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That campstove looks very interesting in its own right. Especially for me who live at a latitude where solar power is almost absent for half the year.
But I'm not sure you can charge D-Li90 on it. From the specs it seems the only output voltage is standard USB 5.5 volts. Our batteries run at 7.2 volts, so you will at least need a transformer between the stove and the battery.
I have never seen any transformer like that, but id' really love to have one. :)
In my experience, the most convenient off-grid power sources provide 12V. If a DC charger for D-Li90 exists, it will most likely fit a 12V socket. If you can't find a DC charger, you can buy a small inverter going from 12V DC to 230V AC, and use your regular charger. There are inverters available the size of a beer can.
The power source itself is more of a challenge. As was said, the solar panel you need is the size of a windscreen. But I know there are alternatives made from multiple small panels mounted on canvas. Then at least you can wrap it up and transport it. But it's still a lot of hassle.
The cost of a solar panel solution will cost you a lot more than a couple of extra batteries. :-)
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Forum: Pentax Medium Format
01-09-2013, 01:52 PM
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Thanks for commenting, JinDesu. I forgot to post the technical details; it's shot handheld at 1/1600s, f/11 and ISO 800.
Here's a crop of the two crystals in the centre. As you can see, the depth of field is paper thin. It's hard to see which parts are actually in focus, but some crystal faces here and there are good.:)
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Forum: Pentax Medium Format
01-08-2013, 07:44 AM
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Hi,
Just wanted to share a shot I took with the 645D at somewhere between 4X and 5X.
These are hoarfrost crystals that I found on my car window a few days ago.
The optical setup was, counting from camera: 645D || set of 3 extension tubes || FA*300/4 || reversing adaptor || FA 75/2.8. It looked like this:
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Forum: Pentax Medium Format
09-03-2012, 11:38 PM
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No, there isn't. I asked the same thing to Pentax Norway (when it still existed), and they demonstrated very convincingly that the lens tube is not constructed to take the load. The metal will bend.
Maybe you could solve the problem by replacing the tilt-head on the Manfrotto with this:
Manfrotto 234 Swivel/Tilt Monopod Head - Supports 5.5 lbs 234
It's the same thing as the 293 comes with, but sans the proprietary QR.
You will need an Arca-Swiss type of QR on top of that, with threads in the hole. Not sure if RRS has one, but IIRC there's one from Wimberley, and maybe one from Benro.
HTH,
Jostein
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Forum: Pentax News and Rumors
07-12-2012, 02:53 AM
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There was something towards the end of the text about banks and long-term investments.
Maybe something is lost in translation, but when statements containing both references to investors and restructuring of a company I always suspect the stock market to be the ultimate receiver of the "news", and that it might not mean an awful lot to the rest of us.
WRT stepping up efforts, he specifically mentions countries of growing markets like Russia and China. I hope they succeed there even if I can't see change coming to my own corner of the world. :)
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Forum: Pentax Medium Format
07-11-2012, 06:36 AM
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Not at all, Gryphen.
It's kinda weird for us ordinary mortals, though...
Turns out this is a phenomenon well known among astrophotographers. They call it "Spurious noise", and is actually caused by backscattering and decay products from occasional cosmic rays slipping through the atmosphere.
I wrote something about it over at my own blog soapbox, but I'll save you the drivel. :)
Here's a link to a scientific paper in PDF describing the issue very accurately, written by astronomer Don Groom at Lawrence Berkeley National Laboratory, USA.
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Forum: Pentax Medium Format
06-20-2012, 12:32 AM
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Glad to hear it, Newmoon!
Very interesting also that there are so many ways to use ExifTool.
Yours is probably one that will suit many more users than my tinkering... :)
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Forum: Pentax Medium Format
06-15-2012, 10:18 AM
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I realise that point was not well written. I meant that yo drag-and-drop the image file onto the exiftool icon. This prompts exiftool to open and work on the files you dropped onto it. Do not paste a copy of your image file into the Exiftool folder. If you succed at updating the metadata, it will apply to that copy only; instead of the original that Lightroom is aware of.
Fingers crossed you make it work, Newmoon. Please keep asking if you still wrestle after the weekend.
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Forum: Pentax Medium Format
06-14-2012, 03:47 AM
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Newmoon,
Here's how I do it. Hope it can be of help:- Put the exiftool.exe in a folder on your desktop
- make a text file in the same folder and call it something like "645A35mm.txt". You may call it what you like, of course...:) -Personally I need self-explanatory filenames to help my memory. Copy the below lines into the text file. It will cover your most basic needs for the lens in question:
-ExifIFD:LensMake = Pentax
-ExifIFD:LensModel = smc Pentax 645-A 35mm f/3.5
-XMP-aux:Lens = smc Pentax 645-A 35mm f/3.5
-XMP-aux:LensInfo = 35mm f/3.5
-overwrite_original Be sure you keep the leading dashes.
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- rename the ExifTool program file like this:
exiftool(-@ 645A35mm.txt -n -k).exe This tells ExifTool to take the text file you just created as input parameters.
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- I prefer to update the lens info after importing to Lightroom:
- In Lightroom, right-click the image you want to update and select "show in explorer"
- Click and drag your image file onto the renamed ExifTool.exe file.
A command-line window opens as ExifTool performs its magic.
You can select multiple files at once. On my system, ExifTool can handle 30-40 files at a time before throwing a cryptic error message.
- Back in Lightroom, go to the Library module. Select all the files you have modified, right-click and select metadata -> update metadata from file.
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- That's all.
If you have other manual focus lenses, you can make copies of the ExifTool.exe and rename them to take different text files for input. If you follow the outline above, you can just replace one lens name with another.
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Forum: Pentax Medium Format
05-12-2012, 09:00 AM
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One more; Thanks jwjohnson. :)
Dunno what it is about his own camera that Bigvern doesn't trust... :p
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Forum: Pentax Medium Format
05-05-2012, 09:38 AM
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I can confirm that my camera does the same thing. In "B" mode, the camera will do a dark-frame after every shot no matter what.
I think the workaround is to take multiple 30-second shots and stack them in the computer afterwards, using astrophoto software. Some plugins for Lightroom or Photoshop may also do the job, I think.
I have tried to use multi-exposure too, but the camera is not as good as computer software at separating true detail from noise.
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Forum: Pentax Medium Format
05-02-2012, 08:46 AM
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The effect is cumulative, and In my experience it got annoying with exposures at 8 minutes and longer. But I suppose the amount of spurious noise accumulated will depend on many things. At my latitude there are sometimes auroras. It seemed to me that the spurious noise became more abundant then, but it may have been a coincidence.
Hope for your sake that you continue to be un-annoyed. Apart from the spurious noise, the image quality is certainly soothing. :)
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Forum: Pentax Medium Format
05-01-2012, 02:25 AM
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Ryan,
I experimented with really long exposures this winter, and found that the 645D sensor is sensitive to what the astronomers call "spurious noise". The most noticeable artefacts look like curved or curled streaks, and are indirectly caused by cosmic radiation, no less, hitting the sensor. When rays hit during exposure, you get bright streaks. When rays hit during the dark-framing in "B" mode, you get dark streaks.
There's a science research paper describing spurious noise in CCD telescopes here (PDF). Or if you take my word for it and can bear with my drivel, I wrote a blogpost on my find here. :-)
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Forum: Pentax Medium Format
03-16-2012, 01:54 AM
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I too have the 645A*300/4, and queried a 645-qualified Pentax rep about options. He recommended strongly against putting a collar on the lens, because the construction of the lens tube would not sustain the weight of both lens and camera. I bought instead the Manfrotto solution mentioned above, and it works very well. If your system is Arca-Swiss based, consider instead the solution from RRS called "long lens support package". It's filed under "multi-purpose bars and rails" on their webside. With any luck this link takes you there:
Really Right Stuff - Item Listing
Notice that both solutions basically consist of a monopod head connected to an L-shaped stabiliser for the lens. If you already have a monopod head you might have half a solution. :-)
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Forum: Post Your Photos!
01-28-2012, 07:37 AM
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Forum: Pentax Medium Format
12-07-2011, 03:29 AM
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I believe the weather sealing of the 645D is done in the same spirit as is the K-7 and K-5.
My K-7 with a DA*60-250/4 shrugged off sleet and gale at South Georgia in 2009. I wouldn't do the same with the 645D, but that's mostly because I don't have any of the new optics for it. I don't think the weatherproofing is very good with the older 645FA and 645A lenses.
- Just my 2 ¢ worth... :)
Best,
Jostein
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Forum: Pentax Medium Format
12-03-2011, 02:05 AM
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It is not "pretty slow in general". It is handling large amounts of data in particular. :p
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Forum: Pentax Medium Format
12-03-2011, 02:03 AM
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My current cards are 16GB Sandisk Extreme Pro, labeled 45 MB/s.
I don't have exact timings, but it looks like just under 4 seconds in total with these cards. The time between the shutter closing and image stored is divided 50-50 between camera processing and file saving.
How does that align with your write times, jackinkc?
best,
Jostein
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Forum: Pentax Medium Format
11-20-2011, 07:18 AM
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Thanks Yamanobori!
The first thing this phenomenon made me think of was a scientific image I once saw, of how cosmic rays could be detected in a fog chamber... :p
Today I did some 15 min. exposures at ISO 200 with the lens cap on. The number of hot pixels are roughly the same in consecutive exposures, but it's never the same pixels. I guess that's why the dark-framing doesn't catch it in the first place. No pixels are permanently stuck.
I also did the same with the K-5. There are a few hot pixels here too, but a lot fewer per megapixel than with the 645D.
I will indeed try to play with some astrophotography stacking program.
Thanks again.
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Forum: Pentax Medium Format
11-17-2011, 02:29 AM
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Here are two images showing what I'm concerned about, overview and detail. The detail show a number of bright spots. For the second image, I also have a version exposed for 30 seconds at ISO 1600, and while the general noise level is higher, there are fewer bright spots on high ISO. Any suggestions for rational explanation will be much appreciated...
The first is a 487s (8 min, 7 s) exposure at ISO 200:
Attachment 109280
Detail shows a number of bright spots, but also what looks like luminescent dust. Beats me how this emerge...
Attachment 109281
Second image is a 916 seconds (15 min, 16 s) exposure at ISO 200:
Attachment 109282
In which the same phenomenon occurs:
Attachment 109283 |
