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Forum: Pentax Medium Format 1 Day Ago  
Pentax 645N only in TTL mode for Strobe
Posted By kaseki
Replies: 4
Views: 206
Heh. Thanks. I completely forgot about the historical approach (which isn't actually pre-history for me, but that may be why I forgot).
Forum: Pentax Medium Format 1 Day Ago  
Pentax 645N only in TTL mode for Strobe
Posted By kaseki
Replies: 4
Views: 206
Not having ever tried non-TTL on my N, I delved into the operating manual to find no mention of using any flash other than particular Pentax flashes. It seems it is bulb mode or bust. Here is a snippet from the specifications page:
Forum: Pentax Medium Format 2 Days Ago  
DA25mm 645 lens Internal Filter options?
Posted By kaseki
Replies: 21
Views: 1,772
Update: It has been a week since I chatted with B&H. Other than sending me a copy of the chat log, there has been no response to my request.
Forum: Pentax Medium Format 2 Days Ago  
Dirty focusing screen
Posted By kaseki
Replies: 5
Views: 324
I don't have the directions handy at present, and haven't yet changed any screens myself, but the kits that Pentax sold had a pair of tweezers that were used to grab a tab on the screen to pull it out and insert a replacement. The directions are probably on the Internet somewhere.

Seemingly needless to say, but I will anyway, there is risk of damage working in that area, so extreme care is needed.
Forum: Pentax Medium Format 4 Days Ago  
Behind the Scenes of "Post your medium format photos!"
Posted By kaseki
Replies: 44
Views: 1,923
Looks like a possible application space for that poorly publicized photographic accessory, the midnight chainsaw.
Forum: Pentax Medium Format 5 Days Ago  
Behind the Scenes of "Post your medium format photos!"
Posted By kaseki
Replies: 44
Views: 1,923
Looks like he sensed he was being watched.
Forum: Pentax Medium Format 6 Days Ago  
Post your medium format photos!
Posted By kaseki
Replies: 16,045
Views: 2,646,229
1.5+ meters :cool::cool::cool:
Forum: Pentax Medium Format 02-22-2021, 01:34 PM  
DA25mm 645 lens Internal Filter options?
Posted By kaseki
Replies: 21
Views: 1,772
While I don't know the latest in precision of 3D parts, I think the thread precision could be good enough to screw in a step-down ring once, and then use the inner step-down ring thread for filter changes. It is also possible to have a not quite interference fit between a cylindrical wall and the outer part of the step-down ring, and a bit of epoxy for retention. Or drill and tap a set screw hole half way into the frame and half way into the step-down ring. Or tap the 3D assembly with an outer step-down ring thread form tap. A mechanical designer could come up with several options of varying cost.

I would want a few of these holder frames for the few filters that I could conceive of using so that I could minimize time and lens guts exposure. In such a case, there wouldn't need to be a lot of action on the filter threads. Assume brass ring filters to minimize grab on the step-down ring or whatever thread material is used.
Forum: Pentax Medium Format 02-22-2021, 11:07 AM  
DA25mm 645 lens Internal Filter options?
Posted By kaseki
Replies: 21
Views: 1,772
While awaiting a response from B&H, it occurred to me that if the "filter holder frames" needed for fast swapping of filters prove to be unobtainable, or restricted to repair/replacement, fabrication of a suitable alternative could be a project for 3D printing. Significant simplification could be applied assuming that each potential user already has a filter holder with rotation capability -- only needed for the circular polarizer.

The 3D-printed units could dispense with filter rotation, eliminating the knurled control, three gears, and whatever spindles and such lurk inside the plastic. A solid frame could be used with a 40.5-mm inside thread. Alternatively, one or more step-down rings could be obtained and locked down to get a metal 40.5-mm thread. For the 645DFA 25-mm lens, the filter axial position may be moderately important, so care would be needed to get the provided mating thread in the correct position. The DA 650mm may be more forgiving in that respect, as the filter is behind all the curved glass.

A means of attachment to the lens body would still be needed. I'm not sure much simplification is possible there, but the basic parts appear straightforward. Variation to avoid patent infringement, if applicable, should be possible.

---------- Post added 22nd Feb 2021 at 13:12 ----------

With respect to @mikeSF's comments hereinbefore, what are the advantages of using an ND filter over operating the camera in the multi-exposure composite mode?
Forum: Pentax Medium Format 02-21-2021, 11:02 PM  
Pentax 67II + AF500 FTZ
Posted By kaseki
Replies: 3
Views: 295
There are only three components of control, ISO, exposure (or flash duration in this case) and aperture. TTL operates by quenching the flash when the camera detects there is enough light reflected off the film. It is only necessary that the shutter speed ensure the shutter is open when the flash is fired. No camera control of aperture can be made during the flash duration. So, in flash mode, the aperture is whatever the user has set (manually), the exposure is whatever goes with the flash timing (making it effectively manual) and the ISO is whatever is set into the camera (also manual).

In P-TTL (645D and Z) there are two flashes, and the camera uses the measured detection of the first to estimate target range and reflectivity allowing the camera to set flash total energy (power and quenching time).
Forum: Pentax Medium Format 02-20-2021, 09:34 AM  
Sony has discontinued the 50MP MF sensor
Posted By kaseki
Replies: 50
Views: 2,024
"I would argue that higher than the resolution needed for natural viewing distance is deemed necessary [by photographers] because we [photographers] are pixel peepers at heart." Photographers was the intended meaning of "we." Sorry for any confusion.

If I had written as edited above, perhaps it would be obvious that I was in agreement with your: " ... The weird fascination of photographers with resolution is not shared by the general public."
Forum: Pentax Medium Format 02-20-2021, 09:19 AM  
Is my 645nii really a 645n?
Posted By kaseki
Replies: 8
Views: 609
Both the N and NII Operating Guides are available on the WWW for download. (If you can't find them perhaps this site allows me to attach files to messages.) I would suggest reviewing both guides for differences and then mapping the results to your camera.
Forum: Pentax Medium Format 02-19-2021, 01:07 PM  
DA25mm 645 lens Internal Filter options?
Posted By kaseki
Replies: 21
Views: 1,772
...

"Ricoh Imaging accessories for both PENTAX and RICOH products can be purchased from any Authorized Ricoh Imaging Dealer."
[list of dealers ~ 100]
"Please Note: With regards to accessories and products that are not typically carried as in-stock inventory. These items can be ordered from any of our Ricoh Imaging Authorized Dealers."
...

I guess this means those of you hanging onto the underside of the earth will have to deal with your own nation's authorized dealers, although something could be worked out if a 'Merkin dealer cooperates and Oz dealers don't.

It also reminds me that a list of all possible accessories should be available. The possibilities might approach endless if we had one.

I'll call B&H when they reopen and see if they will place an order and I'll keep this thread posted with saga updates.

Sunday update: B&H Chat will contact their buyer when he is in on Monday to determine filter holder availability. The plan is to email me with a result.

Also, https://pentax.com.au/accessories/filters shows the filter holder to be in stock @ 172. AUD (presumably). Even pricier than the 80. BPS price.

(((Noticed while searching: two (one demo) DFA645 25mm lenses for sale in Norway: http://fovi.no/objektiv/pentax-645-fatning)))
Forum: Pentax Medium Format 02-19-2021, 11:22 AM  
Sony has discontinued the 50MP MF sensor
Posted By kaseki
Replies: 50
Views: 2,024
I believe the reason why the camera taking an image to be printed for human viewing doesn't have to have the resolution implied by the number of dots on a print is that natural scenes have power spectral densities that are logarithmically dropping with spatial frequency. (See example below.) Humans have a limited eye resolution that degrades with contrast reduction, so when the scene is 7 orders of magnitude lower in power per cycle (over 20 stops) the contrast is way below the number of shades of gray that most can detect. Color only changes this argument in value, not in principle.

In this representative PSD of an image the abscissa is the log base 10 of the spatial cycles across the image. "2" represents 100 cycles. For a 30 inch image, this is only 1.5 inches. So fine detail is way off to the right. The ordinate is the relative power in each spatial frequency. Human eye resolution varies from half an arc minute at high contrast, to half a degree at very low contrast. So if one is viewing an image of the scene from a "natural" distance, one will not resolve the low contrast high spatial frequency content.

I would argue that higher than the resolution needed for natural viewing distance is deemed necessary because we all are pixel peepers at heart. :lol:

First example I came across in a quick search: Image Evolution Using 2D Power Spectra
Forum: Pentax Medium Format 02-19-2021, 07:44 AM  
Behind the Scenes of "Post your medium format photos!"
Posted By kaseki
Replies: 44
Views: 1,923
@TDvN57: Thanks for improving my knowledge base, and thence, if Fortuna smiles on me, my insight.
Forum: Pentax Medium Format 02-19-2021, 12:00 AM  
Behind the Scenes of "Post your medium format photos!"
Posted By kaseki
Replies: 44
Views: 1,923
Sorry if my reaction seemed sincere. I did appreciate the absurdity, including the previous stopping the world. I just couldn't resist commenting on it with all the apparent seriousness that it was presented with. Unfortunately, text communication is even worse than masked communication; first all the facial language is removed, and then voice tonality is removed.

And thanks for clarifying the 405 seconds value was software provided; I had thought that you had hacked the EXIF directly. The modified EXIF in this form is potentially misleading; single shot exposure and number of frames would be more useful for clarity.
Forum: Pentax Medium Format 02-18-2021, 07:58 PM  
DA25mm 645 lens Internal Filter options?
Posted By kaseki
Replies: 21
Views: 1,772
I have sent a message to Ricoh-Imaging in the USA using their contact form. I await their answer with bated breath.
Forum: Pentax Medium Format 02-18-2021, 07:21 PM  
DA25mm 645 lens Internal Filter options?
Posted By kaseki
Replies: 21
Views: 1,772
Perhaps they might answer the telephone if the UK lock-down hasn't chased them out of the office. Perhaps of the myriad dialects in the UK not conforming to std. rcvd. English, I will understand what I hear. An email might also work; didn't look at that. Spelling is close enough. :D

I noticed for EU shipping by UPS that they listed 30 pounds sterling. Seems pretty high for a couple of ounces. I also don't know what the shipping conditions are UK to USA. Japan has to use DHL for camera stuff at present. It was very easy previously. The Japan Post had a deal with the USPS and one could declare and mail a package that quickly got to its destination. DHL has to deal more deeply with Customs, so there can be delays. Also, one's telephone number seems to not get passed along in the process, so when no package arrives, one has to call and find it, and maybe pay a Customs inspection fee.

Correction: the website is an English version with UK denominated currency, but the actual business location is in France. I'll try their contact system.

Tilt! That form only allows messages from listed EU countries. I'll think further about "pain" vs. reward.
Forum: Pentax Medium Format 02-18-2021, 06:30 PM  
DA25mm 645 lens Internal Filter options?
Posted By kaseki
Replies: 21
Views: 1,772
If I could get one I could tell you how it turns out. At this writing it seems to be vaporware in the USA.

Note: previous message had various edits over time that might have been missed.
Forum: Pentax Medium Format 02-18-2021, 05:38 PM  
DA25mm 645 lens Internal Filter options?
Posted By kaseki
Replies: 21
Views: 1,772
That filter holder must be a state secret outside of Europe. I couldn't find it as an available part in any USA Ricoh-Imaging literature. B&H doesn't list it. The image of the filter holder (see below) appears with Amazon's web page for the lens, but no separate purchase information is listed. And Ricoh Imaging UK doesn't sell into the USA, at least via their web site link above.

Except for the color, in the orientation seen in the attached image the 645 DFA 25mm filter holder appears identical as @angerdan noted.

Flipped over, one finds that the externally exposed knurl for circular polarizer rotation has a small (~7mm) metal gear on its shaft. This mates to a second metal intermediate idler gear (~8mm), which drives a fine tooth (~47mm) plastic ring gear on the outside of the filter adapter ring.

References I found by @angerdan: Pentax Normal 40.5mm Filter (for rear filter holder of DA 560mm and 645 DA 25mm) - Page 2 - PentaxForums.com

And a note: Previously reported testing by me of the 25mm confirmed my suspicion based on optics behavior in general, there must be glass in the filter, for example a CP filter or a clear filter or an ND filter. Otherwise, the optical prescription deteriorates.
Forum: Pentax Medium Format 02-18-2021, 09:31 AM  
Behind the Scenes of "Post your medium format photos!"
Posted By kaseki
Replies: 44
Views: 1,923
Aligned to the projected angle subsumed by a single pixel? Let me check my birth certificate to affirm that I wasn't born yesterday.
Forum: Pentax Medium Format 02-17-2021, 08:27 AM  
645z vs K1 sensor. How to explain?
Posted By kaseki
Replies: 15
Views: 923
I only bought mine for the exercise. :lol:
Forum: Pentax Medium Format 02-17-2021, 08:15 AM  
Behind the Scenes of "Post your medium format photos!"
Posted By kaseki
Replies: 44
Views: 1,923
Ah! Winter mosquitoes. Fortunately here in S. NH (21F at writing), ours are limited to the other seasons. :asleep:

P.S. Thanks for the EXIF. I'm surprised that a single shot for 405 seconds seems to be free of star trails.
Forum: Pentax Medium Format 02-16-2021, 07:44 AM  
Image circle?
Posted By kaseki
Replies: 13
Views: 759
At present, I don't know of a method for direct aperture control such as one might want for B mode. I don't know enough about non-reciprocity of available 120 film stock to guess how well astronomical photography might work. If the aperture stays full open on B, then at least one has some compatibility with generally low ISO value film. Depth of field for star fields and distant terrain might be OK full open. Still, 25-mm no-aperture-ring WR DFA compatibility with FA based cameras may not be as complete as one might wish.

While I can imagine using long exposures on water to fuzz up water motion, I am completely unfamiliar with the principles and purposes of Bulb vs. ND terrain photography so I have no answer there. I guess a slightly longer 645 or 67 lens that has an aperture ring will have to do.

While film vs. focal plane array in portraiture might be a subject for debate, I am reasonably certain that our Z cameras are better for star trails than their film predecessors. Think of all the negative development and scanning needed to make a zillion images for summation (that I think you have reported). And every 12 shots the camera gets disturbed by a film change. And the cost of the film needed. Yikes!
Forum: Pentax Medium Format 02-15-2021, 10:12 PM  
Image circle?
Posted By kaseki
Replies: 13
Views: 759
My guess, pending testing, is that given an ISO setting, the aperture will follow the AE programming (+/- exposure offset) as a function of scene light and the chosen shutter timing. So a static scene that has a particular need for a specific aperture for, say, depth of field, could get that aperture (approximately) by changing shutter speed until the view-finder displayed f/no was close to the desired f/no.

Note to self: Taking notes is advised to compare with the data on the film edge when developed.

Now to think of an appropriate scene to blow a roll of film, and environmental conditions I can stand. I think for easiest camera auto exposure estimation, I need to wait for the snow to melt.
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