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Forum: Pentax Medium Format 10-22-2011, 11:35 PM  
Nikon Right Angle Viewfinder on a Pnetax 67II
Posted By ARCASIA
Replies: 11
Views: 6,301
Yes, still very happy. In fact, I almost always use the right angle finder because of the improved focussing, even though it may be inconvenient to do so.

Best, Alan
Forum: Pentax Medium Format 10-22-2011, 11:28 PM  
Nikon Right Angle Viewfinder on a Pnetax 67II
Posted By ARCASIA
Replies: 11
Views: 6,301
Hi,

Patience my dear fellow. No need to be hasty. The only thing that must be modified is the DK-18 adapter - not the DR-5 , the Pentax 67II nor any other camera you may use it with. I thought I explained it well in my post but I will elaborate further. Without the adapter, the thread diameter on the DR-5 is too small for the 67II. However, the DK-18 has just the right thread diameter. The problem is that the receiving threads on the 67II are recessed, and the diameter of the recess is not big enough to accept the unthreaded part of the DK-18. Thus the threads on the DK-18 are prevented from reaching the receiving threads on the 67II. The unthreaded part of the DK-18 is meant for grip - this is the part of it that must be milled down to a diameter smaller than that of the viewfinder recess diameter on the 67II. When finished and installed on the DR-5, it looks as shown in Figure 3 above. Once turned down sufficiently, the modified DK-18 should fit into the 67II recess with a little room to spare.

The DR-5 with the modified DK-18 installed can then be used on either the 67II or on the Pro series Nikon cameras (D3, D700, etc.). Removal of the modified DK-18 from the DR-5 is now a little more tricky, since the grip has been machined off - I use a small pipe wrench gripped onto the machined surface of the DK-18, though with some care, a vise grip may be equally effective.

I brought the use of the DR-5 on the 67II to the attention of this forum because accurate focussing is always critical and this is by far the best solution I have ever used. If you can get it to work, I am sure that you will be very happy also.

Best, Alan
Forum: Pentax Medium Format 07-26-2011, 06:49 AM  
Which combination of tripod and head do you use with your MF camera?
Posted By ARCASIA
Replies: 39
Views: 13,750
Thank you for making this point so vividly, Luc. It is very important for people to understand that what is critical or vital for telephoto photography is not terribly relevant to wide angle photography - one really can get by nicely with much less, thankfully.

Best, Alan
Forum: Pentax Medium Format 07-26-2011, 12:02 AM  
Nikon Right Angle Viewfinder on a Pnetax 67II
Posted By ARCASIA
Replies: 11
Views: 6,301
I have alternately used the Pentax right angle viewfinder and the 2X eyepiece on the Pentax 67II for some time now, but I have never really been happy with either. One can use one or the other, but not both at the same time. Also, the 2X eyepiece has a lot of geometric distortion and is floppy on the camera, whereas the right angle viewfinder is not as sharp as I would like, and the focussing barrel could use a little more turning resistance.

However, there is a very nice solution! The Nikon DR-5 right angle viewfinder can be fitted onto the Pentax 67II, as shown in the first two photos below. It has a very nice toggle to switch between 1X and 2X, is very sharp in both positions, and has much less geometric distortion, as well as greater turning resistance in the focussing barrel, than the Pentax 2X eyepiece. In 1X mode, the entire picture is visible, as well as the technical information displayed in the viewfinder.

The DR-5 is mounted onto the P67II prism using the Nikon DK-18 thread adapter, which comes with the DR-5, or can be purchased separately. Unfortunately, the unthreaded part of the DK-18 has too great a diameter and will not fit into the eyepiece socket on the P67II, preventing engagement of the threads. This problem is easily solved by turning down the diameter in a lathe, or grinding it off by hand - you can mount it on a drill bit and turn it against a metel file. In either case, be careful not to remove so much material that you damage the outer threads. The DR-5 with the modified DK-18 adapter ring is shown in the 3rd photo below. Note that the lathed part of the DK-18 is shiny. Note also that in modified form, it can still be used on the Nikon D3 series and the D700.

When setting it up. one must first adjust the diopter on the prism of the P67II. Then install the right angle viewer and adjust the focus on the viewer by turning the barrel. This assures that focus is simultaneously achieved in both the 1X and 2X modes.

This DR-5 is the best right angle eyepiece I have ever used and it is a dream come true on the P67II.

Best, Alan
Forum: Pentax Medium Format 07-24-2011, 12:16 AM  
Which combination of tripod and head do you use with your MF camera?
Posted By ARCASIA
Replies: 39
Views: 13,750
I agree with your point of view and experience. I have found that it is very difficult to get sharpe photos using MF gear and lenses with focal length greater than or equal to 300mm. One must use both the right equipment and the right techniques.

I use an aluminium Gitzo G1500 tripod together with a matching systematic 5 hydrostatic head with quick release. It is shown in the first photo below supporting a P67 plus Takumar 400mm telephoto. The top tubes are 37.5mm dia with 2mm thick walls. They join into the top mounting ring with separation of about 125mm, so very good at resisting axial torsion. and can carry very heavy weight.

The head, shown in close up in the second photo, is seamlessly bolted into the tripod, has a very thick neck, and short vertical distance from the tripod mount to the quick release plate - all factors contributing to the overall stiffness of the mount. There is only one ring beneath the mounting plate that needs be turned in order to change the orientation of the camera.

I always now use with long lenses a mounting rail as a quick release plate so that I can bolt both the lens and the camera to it - the subsequent reduction in vibration, compared against a single point mount to the lens only, is obvious even in the viewfinder. This of course makes portrait orientation difficult because the orientation of the lens and camera can no longer be individually changed, but there are always compromises to be dealt with. I manufactured a steel L-bracket with 7mm x 50mm cross-section that I leave permanently attached to a quick release plate, so to go to portrait mode, I simply attach the L-bracket/mounting plate to the head, and bolt the rail of the camera assemblage yo the L-bracket, as shown in the 3rd and 4th photos.

If all that is not enough, additional practices are necessary for ultimate sharpness: 1) I never use the tripod with legs extended any further than is shown in the 1st photo - and this is true for any tripod, not just mine; 2) even though the tripod/head/camera/lens weighs in at about 9kg, I hang an additional 5-10 kg from the hook under the head - this assures that the tripod feet are securely set on the ground; 3) I drape a further additional 8kg diver's weight belt over the lens to add mass to the camera system - good for reducing the effect of the shutter release; 4) I always use MLU; 5) when I take the shot, I rest my left hand atop the lens above the mount and I hold the camera with my right hand, in order to add damping; and 6) I squeeze the shutter firmly and slowly, holding my breath, like one fires a gun.

Some of you may consider this extreme overkill, but I have examined all aspects mentioned above over many years, and am left with no doubt that it is all necessary - necessary that is, if you want to achieve the most sharpness possible out of a telephoto lens/MF camera combination. Now, if you are willing to tolerate a little less sharpness, well, that is another matter...

Best, Alan
Forum: Pentax Medium Format 06-01-2011, 01:40 AM  
Pentax Medium Format Resources: Pentax 645: Third party lenses via adapter
Posted By ARCASIA
Replies: 73
Views: 40,349
Very nice summary. I have been shooting with CZJ Pentacon 6 lenses on a Pentax 645 and 645NII cameras for a number of years now with very satisfying results. I should caution that it was quite difficult finding an adapter with parallel mounting surfaces, and went through several East European and Chinese samples before I found a good one. It is amazing how far off some of them were. Also, one must accept stop down operation.

If you really want to use Pentacon 6 lenses, I would suggest getting a Kiev 88 CM or Arax CM, which is actually a Kiev 88 CM that has been improved through various modifications. With the Arax CM, you can get a through the lens metered prism (spot and weighted), 6x6 size, rather than 6x4.5, and automatic aperture operation.

Another course of action is to adapt Pentacon 6 lenses to the Pentax 67 by rebuilding the mount end of the lens. I have adapted the Carl Zeiss Jena 120/2.8 Biometar, and the 180/2.8 & 300/4 Sonars to the 67 mount. All 3 lenses have large enough image circles for the 67 format. Like the 645, it is stop down metering, but the film size is 67, rather than 645, to me, well worth the effort. The adaptations are reversible for the 120/2.8 and the 300/4, meaning you can recover the P6 mounting if you wish, but with the 180/2.8, the alteration is irreversible, as structural parts of the original 180 lens must be altered.

Best, Alan
Forum: Pentax Medium Format 05-14-2011, 08:44 PM  
FA 35mm F3.5 test with 645d
Posted By ARCASIA
Replies: 39
Views: 12,051
Here are a few examples of the wide aperture type of photography that I practice. None taken stopped down past f/5.6 and none would have worked if the rules of landscape photography were to be applied. Whether a lens is sharp to the corners is not of any real significance here, but out of focus rendition means the world - rare is the lens that provides such desirable rendering. Beyond the lens, the technical and compositional problems of wide aperture photography are every bit as challenging as those confronted in landscape work.

Alan

1) Lotus: 645 NII + CZJ 180mm Sonnar at f/4;
2) Lillies: 67II + CZJ 180mm Sonnar at f/2.8;
3) Girl: 67II + CZJ Sonnar at f/5.6;
4) Bubble: 645 NII + CZJ 50mm Flektogon at f/5.6; and
5) Hip Hop dancer: 645 NII + Pentax FA 35mm at f/3.5.
Forum: Pentax Medium Format 05-10-2011, 04:53 PM  
From This List, Which 4 Pentax-A 645 Lenses Would You Choose
Posted By ARCASIA
Replies: 16
Views: 4,103
I'd keep the following:
35mm - when you want it wide;
55mm - when you want it not quite so wide;
120mm macro - a very good macro lens;
80-160mm - a great all round, single lens kit;
300 ED - don't sell this one. As someone else said, more contrast and deeper colours than the others, great for isolating subject matter and close cropped portraits; and the
1.4 converter when you need a little more reach.

That leaves you with the 75, 150, 200 and the 2X converter to sell - hope that is enough money!

Alan
Forum: Pentax Medium Format 03-14-2011, 12:13 PM  
Want to buy, or Where to Buy - Arsat 30mm Fisheye
Posted By ARCASIA
Replies: 19
Views: 8,397
Gevorg Vartanyan has run Arax for years and is well respected among collectors and users of Russian camera equipment. There is nothing to fear here. He sells both the 30mm fisheye and the adapter. If you want these pieces, just send Arax a response and tell them what you want to buy to start the process. Don't worry, they will respond.

Best, Alan
Forum: Pentax Medium Format 02-06-2011, 05:48 PM  
FA 35mm F3.5 test with 645d
Posted By ARCASIA
Replies: 39
Views: 12,051
Hi Sergio,

Thanks so much for your presentation of evidence regarding this lens. And no, your post is not too long. It is really great how your photos so vividly show the effect of no anti-aliasing filter. It is not often that we get such a persuasive post - there has been too much impulsive impuning of Pentax lenses lately based on unscientific comparison of a few quick photos or reference to the opinions of others.

True, your evidence can be easily dismissed by alluding to product variation. It is odd though, I have owned nearly 20 Pentax 67 and 645 lenses over many years, including the FA 35/3.5, and not one exhibited the negative characteristics so often referred since the availability of the 645D. And many were bought used. But of course, what do I know, I just use film!

If only the naysayers could present real evidence as you have to implicate all of these poorly designed lenses manufactured without any QA to speak of, then it would be finally confirmed that I have been shooting with junk lenses for all of these years, and I could rest easily knowing that the short comings apparent in my photos could be attributed to faulty equipment!

Best, Alan
Forum: Pentax Medium Format 01-09-2011, 02:00 AM  
Large Lens Support
Posted By ARCASIA
Replies: 6
Views: 8,130
Early on, I started to use a rail mount, or two point mount, as you call it, attaching both the lens mount and the camera to it, as shown in the photo betow. It was at first to compensate for the flimsy lens mounts on Carl Zeiss Jena lenses that I adapted to the 67, but eventually I have come to use it for all my long lenses.

I use a Series 5 Gitzo hydrostatic head that mounts into my Gitzo G1500 three section tripod. The head has two advantages: the vertical distance from the top of the tripod to the mounting plate is small, and the central shaft is thick steel, both of which reduce the amplitude of torsional vibrations. The tripod itself is made of aluminium and weighs just short of 5kg, with main tube diameter of 37mm. This tripod is very stiff torsionally, but even so, I rarely extend the second tubes more than 250mm, and I almost never extend the third tubes.

I have found that it is simply not sufficient to just hang mass from the hook beneath the head. Such mass mounting does not help at all to resist torsion within the system as it is mounted on-axis, although it does help to prevent the tripod falling over if mass is to be added elsewhere. As I do - I take a divers weight belt with about 14 kg of lead shot in it and drape it over the lens - this puts mass on the lens where it is most needed.

Finally, I hold the tripod firmly just below the head with one hand to dampen torsion in the tripod and hold the camera with the other hand to dampen torsion at the camera/lens level.

If I do all of these things, I can get very sharp shots using my 400 Takumar and a 2X converter."

Best, Alan
Forum: Pentax Medium Format 01-07-2011, 07:09 PM  
Combined effect of defraction, lens defocus and sensor/film size on resolution
Posted By ARCASIA
Replies: 8
Views: 3,970
Hi Leping,

Thank you for your comments. I too struggled over the issue of how many pixels are required to resolve a line pair to MTF50 with a digital sensor. Many people routinely use 2 pixels per line pair and ignore the issue of alignment. But as you point out, depending on alignment, this results in the MTF ranging from 0 (no contrast) to 1 (perfect contrast). However, a statistical average would result in an average MTF of 50%.

With 3 pixel resolution, the lp/mm count is about 59 lp/mm for the three sensors considered, not taking into account aliasing. Depending on alignment, the resulting MTF would range from 33% to 66%, with the statistical average again at an MTF of 50%. One would think that the results of MTF tests would show much less variance in the results if 3 pixels per lp was the more accurate assumption.

As for the effect of aliasing, I have seen photo comparisons between sensors with and without a low pass filter installed to remove the effect of aliasing. The photos shown without the filter installed were indeed sharper, but in some photos, Moire patterns were evident. But strictly speaking, application of alias filtering in accordance with the Nyquist criteria would reduce the resolution of the sensor by 1/2. Perhaps implimentation of low pass filters on modern sensors is not so strict and some compromise is accepted, but I do not have this type of information.

For comparison, I recalculated some results given below assuming 3 pixels per lp, but not taking into account anti aliasing. These assumptions correspond to a digital resolution round about 59 lp/mm at MTF50, as you have suggested.

RESULTS FOR MAXIMUM COLOUR PHOTO SIZE - 3 pixel per lp digital resolution

Results are given at f/8, 1m setback, and limit of visual acuity, rounded to the nearest inch:
12.3 MP DX sensor: 12in x 18in;
35mm film: 17in x 25in;
25.4 MP FX sensor: 18in x 27in;
40 MP MF sensor: 23in x 30in;
645 film: 27in x 37in; and
67 film: 37in x 45in.

My problem with these results is that they indicate that modern 25MP FX digital sensors resolve to about that of 35mm film, and that the 645D has significantly less resolution than the 645 film camera. I believe that these results run against the preponderance of current opinion.

As for lens defocussing, most of the resolution tests performed that I have seen test the lens together with the camera, so one gets the combined resolution of the sensor/film and lens. If we assume such a test yields 34lp/mm for MF film, and 54lp/mm for modern digital, common values, we can back out what would be the lens only resolution, which with my initial assumptions (but ignoring diffraction) would correspond to a 105lp/mm MF lens and a 150lp/mm 35mm lens.

Best, Alan
Forum: Pentax Medium Format 01-07-2011, 02:45 AM  
Combined effect of defraction, lens defocus and sensor/film size on resolution
Posted By ARCASIA
Replies: 8
Views: 3,970
Hi Mike,

Welcome to the Pentax MF Forum and thank you for your kind remarks. I will try to answer your three questions:

1) Yes, the MTF50 equation for defraction I used, which is based on the Rayleigh diffraction limit, gives the lp/mm resolution as a function of the f-number, which if you recall. is the ratio of the lens focal length divided by the exit pupil diameter. So the focal length is taken into account'

2) Yes, but more precisely, when viewed at 1m setback, a print with 24in horizontal dimension will have the same resolution if the picture were to be taken with the 645D set at f/20 or with the 645 film camera set to f/25. There may be a difference in appearance between the two photos due to other factors.

3) A very good question. The pixels of digital sensors are located at the bottom of structural wells. If light leaves the lens parallel to the optical axis, as in a telecentric lens design, the well structure will not affect the (vertical) incidence of light onto the pixels. Modern lenses made for use with digital sensors are designed as practicable to achieve this. If however, the light from the lens is not vertically incident, the light will hit the corner of the well and be diffracted towrds the pxel, causing distortions, often in the form of chromatic aberration. The extent to which this may be a problem depends on the particulars of the sensor and lens design. I have not taken this into account in my analysis.

Best, Alan
Forum: Pentax Medium Format 01-07-2011, 12:34 AM  
Combined effect of defraction, lens defocus and sensor/film size on resolution
Posted By ARCASIA
Replies: 8
Views: 3,970
I was inspired by comments in another post entitled 645N II vs. 67 II, in particular those by Luc Ibanec, to perform an analysis of resolution, taking into account the combined effects of diffraction, lens defocus and sensor type (film/digital) & size. I tried to use as realistic assumptions as practicable, though some of you may have differing opinions about what is appropriate. Please post whatever constructive comments as you wish, but please, no flaming - I have given this my best effort but do not claim to have any special knowledge of the truth so I would appreciate only responses in kind.

This analysis only looks at the issue of resolution. One may prefer digital over film or vice versa because of other issues such as the extent of micro-contrast, the type and quality of grain/noise, or the rendition of colour - but these issues are not addressed here.

The analysis is applied to nine different sensor/film and lens combinations and has two objectives: 1) to determine the maximum dimensions of a photo for each combination; and 2) to determine the maximum f-number that each combination is capable of when producing a photo of fixed 24in horizontal dimension and similar resolution. In all cases, the photos are assumed to be viewed at the limit of visual perception for 1m setback where details are resolved to MTF50. Below I list the assumptions and then the results.

FILM/SENSOR

I considered three digital sensor configurations and three film sizes assuming two different types of film:

DIGITAL:
Nikon D300: 12.3 MP, DX 15.8mm x 24.6mm, MTF50: 90.8 lp/mm;
Nikon D3x: 25.4 MP, FX 24mm x 35.5mm; MTF50: 84.8 lp/mm;
Pentax 645D 40 MP, MF 33mm x 44mm; MTF50: 83 lp/mm;

FILM - MTF50: 1) Velvia 100 - 50 lp/mm; and 2) B&W - 100 lp/mm
35mm: 24mm x 36mm;
Pentax 645: 41.5mm x 56mm; and
Pentax 67: 56mm x 69mm.

The MTF50's for film are taken from manufacturer's data; for digital from pixel density, assuming 2 pixels per line pair to resolve to MTF50 with no account of aliasing. Thus, the MTF50's may be optimistic for digital on both accounts, but my experience leads me to believe that state-of-the-art digital sensors are currently out resolving the best colour films at the pixel density/film grain level so the assumption stands.

LENS DEFOCUS

By lens defocus, I mean blurriness caused by aberrations, but not diffraction. I assume and MTF50 of 150 lp/mm for the 35mm and smaller sensors/film and 105 lp/mm for medium format. These MTF's correspond to the very best lenses of each type used at optimum f-stops in the range of f/5.6 to f/8. The effect of increased aberrations at lower f-numbers is not accounted for, and the effect of diffraction is taken account separately.

LENS DIFFRACTION

The Rayleigh diffraction limit given in lp/mm by 1/(1.22*N*lambda), where N is the f-number and lambda is the wavelength of light, assumes an MTF of zero. At MTF50, I have used lp/mm = 0.38/(N*lambda), and assume lambda = 0.5 microns, which is the wave length of daylight.

OVERALL RESOLUTION AT MTF50

I have assumed the overall serial model:

1/lp/mm(overall) = 1/lp/mm(film/semsor) + 1/lp/mm(lens) + 1/lp/mm(diffraction)

This is a common model for the combined effect of the sensor and the lens. One can determine with greater accuracy the combined effect of lens defocus and diffraction by numerical integration, but I have found that the serial model above provides a pretty good approximation, good enough to resolve trends, which is really the objective of this study.

VISUAL ACUITY

I have assumed a visual acuity of 300 ppi at 25cm setback. This corresponds to 1.15 arcminutes, which is a little lower than 1 arcminute (350 ppi at 25cm) for 20/20 vision. Some say that the ultimate limit for humans is about 0.6 to 0.8 arcminutes for centre vision, but since most people who view photos in galleries and most people who use these cameras are not 18 year olds with perfect vision, the 300 ppi limit seems appropriate to me.

OVERALL METHOD

Use the visual acuity assumption of 1.15 arcminutes to determine pixel density for viewing at 1m setback, convert to lp/mm (assuming 2 pixels per line pair), and match with the lp/mm(overall) for each sensor/lens combination at a given f-number. Repeat for all combinations and f-numbers.

RESULTS FOR MAXIMUM COLOUR PHOTO SIZE

Results are given at f/8, 1m setback, and limit of visual acuity, rounded to the nearest inch:
12.3 MP DX sensor: 15in x 22in;
35mm film: 17in x 25in;
25.4 MP FX sensor: 22in x 32in;
40 MP MF sensor: 27in x 36in;
645 film: 27in x 37in; and
67 film: 37in x 45in.

Conclusions: In terms of resolution, 35mm film is slightly better than that of the 12.3 MP DX sensor, but not as good as the 25.4 MP FX sensor, which is capable of producing a large size print at 22in x 32in. The 645D and the 645 film cameras produce almost the same size photo, which leads one to wonder if this was the intention of the Pentax designers. At 27in by 36in, the 645D photo is larger than that produced by the FX sensor, but not so much larger that one could not consider using the two camers interchangeably in many instances. The 67 still reigns as the camera capable of producing the largest photo by a significant margin.

RESULTS FOR MAXIMUM B&W PHOTO SIZE

Results are given at f/8, 1m setback, and limit of visual acuity, rounded to the nearest inch:
12.3 MP DX sensor: 15in x 22in;
25.4 MP FX sensor: 22in x 32in;
35mm film: 23in x 35in;
40 MP MF sensor: 27in x 36in;
645 film: 39in x 49in; and
67 film: 49in x 60in.

Conclusions: In terms of resolution, B&W film still rules the day. The 35mm film produces a photo size about the same as the 25.4 MP FX sensor. The 645 film produces a photo significantly larger than that of the 645D, and the 67 produces a huge 49in x 60in print.

RESULTS FOR MAXIMUM f-NUMBER ASSUMING FIXED COLOUR PHOTO DIMENSION

Results are given for a colour print with 24in horizontal dimension viewed at 1m setback for the largest f-number possible satisfying the same limit of visual acuity:

12.3 MP DX sensor: f/5.6;
35mm film: f/10;
25.4 MP FX sensor: f/16;
40 MP MF sensor: f/20;
645 film: f/25; and
67 film: f/35.

Conclusions: The results do indeed show that the effect of diffraction on resolution is predominantly dependent on both the diffraction limit of the lens and the size of the sensor/film. In this regard, the new 645D demonstrates better performance than the FX sensor, but not as good as the 645 or 67 film cameras, with significantly bigger film/sensor areas.
Forum: Pentax Medium Format 01-02-2011, 03:36 PM  
645N II Vs 67 II
Posted By ARCASIA
Replies: 32
Views: 14,647
Three comments:

1) If you want to print big, or want to use high power telephoto setups on MF, and insist on high resolution, you MUST carefully consider camera support. No question, no doubt. If you do not print big, my suggestion is to go back to 35mm film or digital as medium format systems by comparison are very limited, heavy and cumbersome.

2) If it is a windy day, wait for another day - to me, that is the essense of MF film photography: you cannot always get what you want when you want it; many times you must wait patiently for the right shot to avail itself. If that doesn't work for you, and you must have the shot, don't try to force it - use a different camera system. If you wait and the right conditions avail themselves, then you are still left confronting a large number of technical considerations to be overcome, including those related to image stabilisation.

3) As for mule packing and using monster wooden surveyer's tripods, don't knock it until you've tried it. A good friend of mine packed in 67 equipment on mules along the old silk route from Chengdu in southwestern China to Lhasa in Tibet for six months and came back with some of the most stunning landscape and cultural photos I've ever seen.

Alan
Forum: Pentax Medium Format 01-01-2011, 07:43 PM  
645N II Vs 67 II
Posted By ARCASIA
Replies: 32
Views: 14,647
Hi Leping,

Thank you for taking the time to post in this forum - it is not often that we are able to learn from one who routinely pushes the 67 to the limit by printing such large photos - this is really what the 67 is made for, and you are right to imply that mastering technique is essential in obtaining satisfying large format prints. I have also been to your website a number of times in the past - very fine work indeed.

I wanted to add a little to your statements about controlling shutter vibrations. I have spent a great amount of time trying to minimise such vibrations and agree that to really have a positive impact, one must pay attention to all details of the mounting.

Early on, I started to use a rail mount attaching both the lens mount and the camera to it, as shown in the attached photo. It was at first to compensate for the flimsy lens mounts on Carl Zeiss Jena lenses that I adapted to the 67, but eventually I have come to use it for all my long lenses. Being able to slide the camera lens back and forth, I thought, would allow me to find the spot where thecamera/lens is perfectly balanced, allowing easy movement on the head. However, as you point out, long overhang of the camera back will increase the effect of shutter vibration through torsion because of the long moment arm between the shutter and the central vertical axis of the tripod. Now, I move the camera/lens forward in the mount from the balanced point. This allows the shutter to be placed close to the tripod axis, thus reducing the magnitude of the torsional vibration. Additionally, out of balance mass from the lens acts to reduce torsional vibration. The rail mount allows one to do this without the worry of large lens overhang damaging the lens mount.

I use a Series 5 Gitzo hydrostatic head that mounts into my Gitzo G1500 three section tripod. The head has two advantages: the vertical distance from the top of the tripod to the mounting plate is small, and the central shaft is thick steel, both of which reduce the amplitude of torsional vibrations. The tripod itself is made of aluminium and weighs just short of 5kg, with main tube diameter of 37mm. This tripod is very stiff torsionally, but even so, I rarely extend the second tubes more than 250mm, and I almost never extend the third tubes.

I have found that it is simply not sufficient to just hang mass from the hook beneath the head. Such mass mounting does not help at all to resist torsion within the system as it is mounted on-axis, although it does help to prevent the tripod falling over if mass is to be added elsewhere. As I do - I take a divers weight belt with about 14 kg of lead shot in it and drape it over the lens - this puts mass on the lens where it is most needed.

Finally, I hold the tripod firmly just below the head with one hand to dampen torsion in the tripod and hold the camera with the other hand to dampen torsion at the camera/lens level.

If I do all of these things, I can get very sharp shots using my 400 Takumar and a 2X converter.

Best, Alan
Forum: Pentax Medium Format 01-01-2011, 03:37 AM  
645N II Vs 67 II
Posted By ARCASIA
Replies: 32
Views: 14,647
By my calculation, the 645 has 2.7 times the area of 35mm film, whilst the 67 has 4.5 times the area.

Both the 645NII and the 67II offer spot, centre weighted and matrix TTL metering. The min sync speed for flash is 1/60 s and 1/30 s for the 645NII and the 67II, respectively.

The 645NII has AF and the 67II is manual focussing only but with an automatic diaphragm.

The 67II takes 10 shots with 120 film and 20 shots with 220 film. The 645NII can take 16 shots with 120 film and 33 shots with 220 film. Neither can be changed easily at mid roll.

Both offer mirror lock up. The shutter and mirror lift mechanisms in the 645NII are very smooth with almost no vibration; in the 67II, the vibrations levels are higher and can sometimes be a problem, but MLU helps a lot.

A number of lenses manufactured by different companies (Carl Zeiss Jena, Schneider, Arsat, and others) can be fitted to the 645NII via inexpensive comercially available adapters. The 67II takes only Pentax 67 lenses.

For serious shooting, I'll almost always choose the 67II over the 645NII - that big negative size is really hard to beat.

Best, Alan
Forum: Pentax Medium Format 12-30-2010, 11:01 PM  
645D vs 645N comparison
Posted By ARCASIA
Replies: 21
Views: 7,363
If my film shots looked like the ones shown, I would have fled from film long ago (assuming top digital and bottom film). I agree with Tuco that the 645N is much more capable than that shown here. I would go on to say that the photos shown in this post can be very misleading to many who have not had much experience with film, and provide unearned fodder for the cause of those who champion digital over film without really having much of an understanding of either.

Alan
Forum: Pentax Medium Format 12-22-2010, 07:06 PM  
It this a true statement on lens for the 645D
Posted By ARCASIA
Replies: 36
Views: 8,408
Hi Steven,

There is no doubt that AF has its place, and is indispensible for certain types of photography, such as at sporting events, or when subjects cannot or do not have the patience to stay still, or in other cases where there is not much time to go thru the ritual of manual focussing. But many modern photographers seem to believe that AF is or should inherently be a superior focussing system. Perhaps this view originated in attempts to manually focus using the viewfinders found on digital cameras with reduced sensor size, together with commercial grade focus confirmation lights.

In those instances where the subject is stationary and there is sufficient time and light, I almost always manual focus, without bracketing, and have enjoyed a very high success rate. Now, I shoot off a tripod, in part to eliminate photographer wobble, and usually confirm using a 2X eyepiece. Through long experience and careful comparisons I have come to believe that AF cannot do better than MF in these instances, and often does worse, especially when shooting faces at close range and wide aperture, where artistic judgement is required regarding what exactly to focus on.

With the now common use of low dispersion glass, aspherical elements and computer aided design, lens technology on the average is getting better. But modern lens design has its drawbacks too. Design to production time has been drastically reduced to in some cases a matter of months, and designs tend to be developed by teams relying more on numerical optimisations rather than on long experience and prototype field testing. By comparison, the Nikkor 135/2 AIS MF lens was seven years in development having multiple prototypes, and the optical expert in charge had over 20 years previous experience in designing outstanding lenses for Nikon.

There are many older MF lenses whose optical designs and executions are legendary, and it would seem a real shame if the ones that can be mounted on the 645D were to be ignored simply over an issue of MF vs. AF capability. I have now sold all of my 645 FA lenses, because in practice, I rarely used them. The only 645 A lens that I currently own and use is the 120/4 macro. Instead, I use a selection of Pentax 67 and Carl Zeiss Jena (CZJ) lenses on my 645 systems, when I am not using my 67's. I have never felt remorse over selling the FA's, apart from that induced by a Collector's hording instinct, as I closely considered each sale and concluded that I had in my remaining inventory MF lenses whose optics were at least as good as what each sold FA lens had to offer.

I would suggest that before anyone categorically rules out MF lenses, they tryout on the 645D a Pentax 67 55/4, 75/4.5, 100/4 macro, or a 300/4 M*, and maybe a CZJ 50/4 Flektogon or a 180/2.8 Sonnar. I suspect that you will be very pleasantly surprised at the results, and your pocketbook will also be very happy!

Best, Alan
Forum: Pentax Medium Format 12-13-2010, 04:01 AM  
I'd like to adapt a Nikon lens TO the Pentax 6x7...possible??
Posted By ARCASIA
Replies: 6
Views: 4,285
The mounting flange to register (film) distance on the Pentax 67 is 84.95mm, whilst it is 46.5mm for the F-mount. That is about a 40mm difference that you will lose in focussing range, leaving the lens to be only useful for very close-up work, which is what I presume you intend to do with it.

I'd suggest using a 67 mount taken from an inner extension tube - the mount can be removed from the rest of the tube by unscrewing three small screws and three tiny dowels. Try not to strip the dowel head with the screw driver as you will then have to drill it out in order to remove it.

Then remove the F-mount from the Nikkor. At that point, you can machine (use aluminium) a short connecting cylinder than can be attached to the Nikkor lens sans F-mount, following the bolting configuration of the F-mount and adapting the cylinder accordingly. Then drill and thread three mounting holes at 180 degrees in the outside top of the cylinder to accept the 67 mount - 2mm threading will do. Drill three corresponding 2.5mm dia holes in the face plate of the 67 mount taken from the extension ring and attach it to the cylinder - I'd use 5mm length screws with hex heads.

I would suggest finding a local machine shop to help you with the fabrication of the aluminium cylinder. If this is too difficult for you, contact me privately, as I have been adapting various lenses to the 67 using this methodology for a while now, though not any F-mounts, and my machinist has learned all the ins and outs of it.

I am a bit suprised that the area of illumination of the Nikkor is sufficient for the 67, but maybe you will be lucky. I had been told it was insufficient for several of the lenses that I adapted, but they all worked out fine.

Best, Alan
Forum: Pentax Medium Format 11-29-2010, 05:47 PM  
Nick Devlin 645D follow-up review on Luminous Landscape
Posted By ARCASIA
Replies: 45
Views: 10,925
Hi Nick,

This point about tolerances cannot be over emphasized, and it is equally true for film. I recently adapted 120, 180 and 300 Carl Zeiss Jena lenses for my Pentax 67II, which in all cases requires the manufacture of spacers to fit between the lenses and the new 67 mounts. A friend recommended a tolerance of 0.010mm or 10 microns in the thickness of the spacer over its entire (mounting) surface. At first, I doubted this requirement, but prototype manufacture and testing indicated it was indeed true. This requirement turned the fabrication of the spacers into a rather formidible task, requiring multiple repetition of the surface finishing step with excessive measurement of thickness using very precise measurement tools.

So yes, for "perfect" picture quality, the lens, the mount and the sensor must all be aligned within tolerance. The fact that "the 75mm lens did just fine" tends to implicate the lens, rather than the mount or the sensor, but only after one could verify with absolute certainty that the camera and the wall were correctly aligned.

Best, Alan
Forum: Pentax Medium Format 11-12-2010, 11:22 PM  
Price for 67 body and lens
Posted By ARCASIA
Replies: 2
Views: 1,743
Hi,

There is a 67 with TTL prism and late SMC 105 lens in BGN condition now at KEH. The price is USD 533. BGN condition from KEH means it is in pretty good shape.

Best, Alan
Forum: Pentax Medium Format 11-04-2010, 07:04 PM  
Kerrick James and the 645D in Boston!
Posted By ARCASIA
Replies: 14
Views: 4,060
Hi Kerrick,

I don't suppose that the Philippines is on your regular circuit? Oh well. Thanks for posting here and keep us informed about your experiences with the 645D, especially as regards whether or to what extent it might have changed your commitment to MF film photography.

Best, Alan
Forum: Pentax Medium Format 11-04-2010, 06:52 PM  
645D Lens choices
Posted By ARCASIA
Replies: 6
Views: 4,682
Hi Steven,

I am sure that most of the 645 and 67 lenses will do well on the 645D. In particular, I would expect the following 67 lenses to be stellar performers: 55/4, 75/4.5, 55-100/4.5, 100/4 macro, 300/4 M* and 400/4 M*. For 645 lenses, I should think the 35/3.5, 75/2.8, 120/4 macro, 150/2.8 and 300/4 EDIF. You might also want to try with an adapter the Carl Zeiss Jena 180/2.8 Sonnar for portraits and flowers - wonderful out of focus rendition and very sharp to the corners at f/2.8, nothing quite like it in the Pentax line up.


Best, Alan
Forum: Pentax Medium Format 10-20-2010, 04:48 AM  
Fullsize 645d sample from this morning..
Posted By ARCASIA
Replies: 19
Views: 8,070
Hi,

Many other people have posted photos taken by the 645D in this forum or links to such photos. We even have a long running post in this forum of photos taken by Pentax MF film cameras. It is very useful for people like me who are only interested in MF photography and who don't want to wade through all of the Photos posted in the Post Your Photos section.

I should add that the introduction of the 645D presents the first real MF digital alternative to us Pentax users, many of whom have been scanning MF film for years. The possibility of having MF capability in a digital format is very enticing indeed, especially with real time feedback on shots taken, and the elimination of scanning film. But it comes at a hefty price - money that can be used on so much other gear, if it is to be spent that way. Personally, I am delighted to see so all of these 645D photos showing up in this forum. It provides a chance to see the results of the camera in action taking "real-life" photos. The more the better, as it is only by examining many shots taken in many situations that one can get a true understanding of a camera's capability.

Best, Alan
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