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Thread: Tech cameras and IQ.

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    Re: Tech cameras and IQ.

    Yes, TC = Tech Camera. Sorry about that...
    Bob

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    Re: Tech cameras and IQ.

    Quote Originally Posted by TEBnewyork View Post
    Precisely why both exist and freedom of choice is a good thing!
    That we knew. The original poster asked for opinions on the pros and cons of tech cameras v. MF DSLRs. He had only heard from those who love tech cameras. I was offering up the alternative view.

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    Re: Tech cameras and IQ.

    Actually no ones view is ever wrong here either. It has benefits and it has downsides. Totally get the different reactions we all have towards them. maybe why so damn confusing sometimes to decide. I know this has been on my brain for about 3 years. Nice thing I get to use them often and see what they can do and not do. I'm just in this 3 year circling pattern on it. Been playing with the Arca RM3DI and Cambo WRS the last couple days and they both have good points and not so good points. Than there is Alpa so besides to jump in or not than its which one as well. LOL

    I think this discussion would never have a ending either. LOL Which is great really , love hearing folks views.
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    Re: Tech cameras and IQ.

    having shot Nikon, olympus, my path led to 2-1/4 once i saw the image in the ground glass, then to 4x5 for even more of that luscious view plus all the movements. It was all about the view, not to mention image quality

    MFD and a tech camera can offer the controls and the IQ, but compromise the view completely. I started with the Rollei X-act 2, GG adapter, then Horseman, used shifts, GG adapter, and the optical viewfinder, but swapping back for GG adapter was a pain, plus the 36 x 38mm image was too tiny, losing the lucsiousness, and the telescopic viewfinder was not so hot. Tried a magnifier, but the GG grain was an issue. went to the H-blad, nice viewfinder, not quite GG though, no movements, too many features for my style, etc.

    Now using the Cambo WRS,with shift both ways; lenses have tilt and swing and I have developed my own accurate I-phone holder to work as a viewfinder, so I can really PRE-view and frame the shot.
    When the IQ back shows up, the just-shot preview will be primarily used to confirm focus and exposure, confirm application of tilt, shift

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    Re: Tech cameras and IQ.

    I have used both technical cameras and SLR type MF systems--unfortunately, the sensors are very different and can not really show a one-to-one comparison (P25+ and Pentax 645D). I would say there is not a big difference in IQ. The way the camera works and what it can do is a far greater influence over the quality of the resulting image. I would base a choice over camera type by the way I work or the features I need rather then some perceived difference in IQ.

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    Re: Tech cameras and IQ.

    Re: Tech cameras, IQ, & Travel Tripods: I have learned a lot from the Tech camera threads, and hope to be pullinng the trigger soon on a Tech camera for my IQ180. Meanwhile, I wonder what tripods are being used by those who have Tech cameras? It seems to me that someone traveling with a Tech camera kit may not require as much tripod "muscle" as other medium format setups. What do those of you who use Tech cameras & travel by plane use for a tripod? My current GT3541LS is a beast at 3.8lbs and with the Cube (which I may use with a tech camera) there seems to be no good way to transport the tripod in limited space. How are the folks who use Tech cameras a lot dealing with tripod/travel?
    Last edited by cs750; 18th June 2011 at 04:57. Reason: typo correction

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    Re: Tech cameras and IQ.

    I think a 2 series Gitzo is just fine for these tech cams. I also have the big 3 series and it is overkill. I would probably still use my Z1 ballhead. But the 2 series in my mind has plenty of muscle and easier to pack.
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    Re: Tech cameras and IQ.

    I have 2 different tripods that I use:
    Gitzo Traveller with P0 head
    Gitzo 2 series with a cube

    The traveller works just fine in terms of weight but it isn't my first choice for windy conditions and if I will need height. When driving around I almost always opt for the 2 series but have both in the car. I will take the traveler on planes when keeping the kit light and the 2 series when going on a dedicated photo trip or workshop.

    There is probably a really good solution between the two.

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    Re: Tech cameras and IQ.

    I use a long 3541L and the Giant 5 series when working from the car, and a 1541 series for travel. The 1541 is fine, but I do not normally extend the last legs set with MF -- though I have and find no loss of sharpness. I did fabricate a hook under the platform to hang my bag from which I believe adds to total system stability.

    I am tall at 6'-6" (198cm), and never found a 2 series that made solid travel sense for me. The 1541 is few inches longer than the 2541 fully extended without the center column, and yet is enough smaller collapsed it will fit easily in a 22" roller. The 15 series is rated to around 18 pounds, and the 25 series about 26 pounds --- not a huge difference given my tech cam weighs like 6 max with all the goodies and heavy HR-W lens on it.

    What's weird about the weight ratings too, is that seems to apply only for stuff ABOVE the platform -- hanging my bag below the platform definitely adds stability and the tripod suffers no ill effects when I do that.
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    Re: Tech cameras and IQ.

    I just picked up a Really Right Stuff TVC-24 tripod. These new RRS tripods are really well-thought out and engineered. This is going to be my "lightweight small travel tripod" option---when I don't feel like lugging my Gitzo 5541LS around!

    For bigger applications the TVC-3 series has Gitzo 5 series specs but substantially lighter.

    The RRS tripod is easily a "Gitzo alternative" but also has that Gitzo price.

    ken

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    Re: Tech cameras and IQ.

    I've got 2-different tripods both Gitzo. The main is a GT5540LS with a Cube attached and use this over 90% of the time. The other is a older GT2540 with a RRS BH40 I use when I know I'll be hiking over a mile or when I'm feeling lazy.
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    Re: Tech cameras and IQ.

    Carrying ANY tripod when flying: Thanks Terry, Guy, Jack, Don & Ken for the info on your Tech camera tripod. My experience is any tripod eats up a suitcase; I have wondered about checking the tripod on a flight in a light weight tripod case...but some concerns. The other possibility is to Check a larger bag with warm clothes and tripod. When traveling by plane to a region where warm clothes may be needed for sudden weather changes my tripod seems to be the biggest problem. I can carry my electronics gear onboard, but have little room for anything else. What works for you? Thanks, Charles.
    Last edited by cs750; 18th June 2011 at 06:54. Reason: typo correction

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    Re: Tech cameras and IQ.

    I'll check a tripod (3541LS) in a dedicated padded tripod bag. I will wrap the legs in bubble wrap and remove the head which I put in the camera bag. On my way home I'll replace the bubble wrap or stuff the bag with dirty laundry

    When I'm working from my car I use a 5541SGT with Cube. This is simply THE best tripod I've ever owned albeit at the expense of being somewhat beefy and so not something I take on plane trips.
    Last edited by GrahamWelland; 18th June 2011 at 08:35.
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    Re: Tech cameras and IQ.

    Quote Originally Posted by cs750 View Post
    Carrying ANY tripod when flying: Thanks Terry, Guy, Jack, Don & Ken for the info on your Tech camera tripod. My experience is any tripod eats up a suitcase; I have wondered about checking the tripod on a flight in a light weight tripod case...but some concerns. The other possibility is to Check a larger bag with warm clothes and tripod. When traveling by plane to a region where warm clothes may be needed for sudden weather changes my tripod seems to be the biggest problem. I can carry my electronics gear onboard, but have little room for anything else. What works for you? Thanks, Charles.
    My 2 series fits diagonally in a mid sized rolling suitcase - it is a little too big to carryon that bag.
    My traveler can go anywhere in almost any bag and really takes up very little room.
    When traveling with photo gear (except a small m4/3 kit) I almost always have to check a bag because my cameras and tech I always carry on.

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    Re: Tech cameras and IQ.

    Large roller duffle and take the head off and throw legs in bag. Put between cloths. Unless I am traveling with my lights and that bag will fit a human in it. Lol
    Photography is all about experimentation and without it you will never learn art.

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    Re: Tech cameras and IQ.

    Actually been thinking of a new roller bag this morning. Yea bags are a disease for me.
    Photography is all about experimentation and without it you will never learn art.

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    Re: Tech cameras and IQ.

    I'm using a Gitzo 2541L with a GH2780 ball-head for my Alpa TC. I've removed the center column which I never used anyway, and put a Kirk FP-200 plate on it. This add a nice hook for my bag and makes the tripod more stable. When traveling, I take the ball-head off, the tripod then fits diagonally in a standard 22 inch roller-bag.

    Cheers, -Peter

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    Re: Tech cameras and IQ.

    When I travel via airplane, I like Terry, also travel with a Gitzo Traveler. It fits inside my ThinkTank Airport Ultralight backpack with my D700 kit and then the bag fits inside a Pelican 1510 wheeled case that is stowed in an overhead bin. I remove the RRS BH-40 head and place it inside the backpack with the legs. My Alpa Max kit is packed in another Airport Ultralight backpack that I wear as carry on.

    In windy conditions, I hang the backpack from the hook of the Traveler and it remains stable. I tried this setup in Iceland last summer and it served me well. The most important thing I care about when I travel is security since I tend to travel alone. This is the reason I came up with my system of both kits getting in the airplane and within my view. It is not hard for me to change planes with one backpack on and the other secured in the wheeled 1510, plus I can switch backpacks out of the hard case in a flash if I need to.

    I also use two other tripods when I work out of the studio. One is my trusty Gitzo 1325 and the other is a Gitzo GT3531s. I am petite at 5'3" so the 's' was a good 'used' buy through eBay. Both tripods have RRS BH-55 heads attached. One head is a real beater that I bought from a forum member for dirt cheap, but it works flawlessly and I use it when I shoot in the wetlands close to my home. I shoot with a tripod 100% of the time and would never leave home without the best I can afford.

    Have fun setting up your kit!
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    Re: Tech cameras and IQ.

    On tripods, it depends how I'm traveling and what I'm shooting. If I'm shooting with a tech camera and will have a car close by my cube permits much quicker and more precise setup than anything else that I've ever tried, and the cube really requires a 3 series. Mine is on a Gitzo 3541LS with a Gitzo leveling base.


    If weight matters I use an Arca monoball P1 on a Gitzo GT 2541EX - I've used the Gitzo all over the world in a huge variety of situations.

    Either way for air travel I take the head off and put it and the legs in checked luggage.

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    Re: Tech cameras and IQ.

    mine is the Gitzo 1327 cubed. I prefer the three sections, not four, at the expense of more compressed length and i like the elevating center column (slides), much easier for small ht adjustments (at the minor expense of some stability loss). and i use the hook to suspend my bag

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    Re: Tech cameras and IQ.

    Quote Originally Posted by Woody Campbell View Post
    On tripods, it depends how I'm traveling and what I'm shooting. If I'm shooting with a tech camera and will have a car close by my cube permits much quicker and more precise setup than anything else that I've ever tried, and the cube really requires a 3 series. Mine is on a Gitzo 3541LS with a Gitzo leveling base.


    If weight matters I use an Arca monoball P1 on a Gitzo GT 2541EX - I've used the Gitzo all over the world in a huge variety of situations.

    Either way for air travel I take the head off and put it and the legs in checked luggage.
    Woody,
    No issues with the cube on a 2 series. I haven't tried it on others.

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    Re: Tech cameras and IQ.

    Quote Originally Posted by TEBnewyork View Post
    Woody,
    No issues with the cube on a 2 series. I haven't tried it on others.
    Hmmm . . Interesting - I'll try it. The head weighs about as much as the legs, but who says that can't work.

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    Re: Tech cameras and IQ.

    Quote Originally Posted by TEBnewyork View Post
    No issues with the cube on a 2 series. I haven't tried it on others.
    I find that the Cube is very top heavy on my 2531 but that does have a center column. If it were mounted on a flat top plate then I'm sure that you could probably get away without it feeling like a club stick.
    Remember: adventure before dementia!

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    Re: Tech cameras and IQ.

    I just got back from 7 days of hiking in the Eastern Sierras with an Alpa STC, 80mm and 35mm lenses and P45+ back. I used the Gitzo 0541 (1.75lbs) (load capacity 11.2 lbs) and Acratech GPs ballhead (0.9lbs) (load capacity > 25lbs).

    Worked perfectly. Also, with the Acratech GPs, panos going further than the shifting abilities of the STC are easily done.

    Just my experience...
    Bob

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    Re: Tech cameras and IQ.

    Just a quick note, with examples forthcoming over the next week, probably in a dedicated thread. My RM3D and 40 HR-W arrived yesterday afternoon. I got off a few quick test frames -- nothing worth posting -- but have to say WOW! The 40 HR-W is a freaking laser, clearly out-resolving the IQ180 sensor across the full zeroed frame. So sharp, I had to increase my Focus Mask setting on my IQ180 to *75* to get a thin enough "green" zone to ascertain precise focus zone! Even shifted (horiz) the full 15mm, the lens remains usable to almost the full corner -- I say almost because the lens physically vignettes just before the 15mm mark, call it 12.5 of total usable horizontal shift. From about 11 or 12mm out, the lens remains very sharp, but exhibits significant curvature, so subject matter in the primary plane goes soft with the extreme shift.

    LCC cast is notably less than the with the 43SK as we knew, and corrects easily. Even though the 40HR distorts more than the 43SK, it is still very low relative to most of my Phase D lenses. Architectural or large product shooters will definitely want to correct however, and would likely correct the 43SK as well. As indicated in the earlier posts, the Alpa lens corrector does a fantastic job of linearizing the image -- kudos to Alpa for this incredible tool!

    That's all for now, more to follow soon!
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    Re: Tech cameras and IQ.

    Quote Originally Posted by Jack Flesher View Post
    ...As indicated in the earlier posts, the Alpa lens corrector does a fantastic job of linearizing the image -- kudos to Alpa for this incredible tool!
    Hi Jack,
    Do you use the Alpa corrector in place of or in conjunction with LCC in C1?
    Thanks,
    Bob

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    Re: Tech cameras and IQ.

    The Alpa tool has nothing to do with LCC files. It is just there to correct distortion.

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    Re: Tech cameras and IQ.

    Quote Originally Posted by Jack Flesher View Post
    I got off a few quick test frames -- nothing worth posting -- but have to say WOW! The 40 HR-W is a freaking laser, clearly out-resolving the IQ180 sensor across the full zeroed frame. So sharp, I had to increase my Focus Mask setting on my IQ180 to *75* to get a thin enough "green" zone to ascertain precise focus zone! Even shifted (horiz) the full 15mm, the lens remains usable to almost the full corner -- I say almost because the lens physically vignettes just before the 15mm mark, call it 12.5 of total usable horizontal shift. From about 11 or 12mm out, the lens remains very sharp, but exhibits significant curvature, so subject matter in the primary plane goes soft with the extreme shift.
    Told you so ;-)

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    Re: Tech cameras and IQ.

    Quote Originally Posted by rga View Post
    Hi Jack,
    Do you use the Alpa corrector in place of or in conjunction with LCC in C1?
    Thanks,
    Bob
    Here is the workflow: Run the LCC and process the file as you normally would in C1. Then you take the output tiff to a 32 bit version of CS -- I use CS4 since it's on my machine. Now run the Alpa corrector on the tiff, and save it as a corrected version. You could do your final editing in the 32 bit CS if you wanted, but I then take that tiff to 64 bit CS, and do all of your normal post editing.

    Cheers,
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    Re: Tech cameras and IQ.

    Quote Originally Posted by Christopher View Post
    Told you so ;-)
    Yes you certainly did! But it was hard to know just how good it was until I had the entire file in front of me to scroll through at 100% -- wear safety glasses to avoid cuts on your eyeballs!
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    Re: Tech cameras and IQ.

    Thank you!

    Quote Originally Posted by Jack Flesher View Post
    Here is the workflow: Run the LCC and process the file as you normally would in C1. Then you take the output tiff to a 32 bit version of CS -- I use CS4 since it's on my machine. Now run the Alpa corrector on the tiff, and save it as a corrected version. You could do your final editing in the 32 bit CS if you wanted, but I then take that tiff to 64 bit CS, and do all of your normal post editing.

    Cheers,

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    Re: Tech cameras and IQ.

    Yes, the 40-HR is so good. I ended up using only the HR lenses for my linhof techno.

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    Re: Tech cameras and IQ.

    I have to stop reading the 43/40 threads. Makes me second guess my decision to stick with the 43XL.

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    Re: Tech cameras and IQ.

    Quote Originally Posted by TEBnewyork View Post
    I have to stop reading the 43/40 threads. Makes me second guess my decision to stick with the 43XL.
    They are both great lenses, each with a different set of strengths. And the upside is there is no bad choice. These are great times for photographers for sure.
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    Re: Tech cameras and IQ.

    Jack:

    what is your opinion on lens shimming to set infinity focus for tech cameras? alpa makes a point of it and I know the cambo has the ability to tweak the body side lens mount.
    As I see it, you set focus on the infinity stop and take a series of shots, adding or subtracting shims (for the alpa) to adjust lens to sensor distance, until distant objects come into best focus.

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    Re: Tech cameras and IQ.

    Question to those of you who work with the DIGARON-W 40mm .

    There is a CF available but it does not say anywhere that you need to use a CF .
    Looking at the ALPA pages .

    Do you use a CF and if so , what is your experience ?
    Is a CF required more when using a FF sensor in comparison to a 37x49 sensor ?
    Regards . Jürgen .
    -----------------------------------------------------------------------------------

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    Re: Tech cameras and IQ.

    Quote Originally Posted by jlm View Post
    Jack:

    what is your opinion on lens shimming to set infinity focus for tech cameras? alpa makes a point of it and I know the cambo has the ability to tweak the body side lens mount.
    As I see it, you set focus on the infinity stop and take a series of shots, adding or subtracting shims (for the alpa) to adjust lens to sensor distance, until distant objects come into best focus.
    Good question John, and the answer is maybe :

    I think if you have an Alpa or Cambo, you definitely want to shim for infinity accuracy, and you need to make sure any tech cam/lens combo can achieve infinity focus. However with the Arca having it's helical as part of the body, and with that helical having such a huge range (4 full turns), shimming is basically "built-in" to the camera via that helical, so all you really need to do is calibrate to each specific lens.

    For those unaware, the Arca helical is about 4" in diameter, has 32 distinct points with 4 hash-marks between each main graduation around the perimeter -- and you can easily interpolate half-way between each hash -- for a total of 320 distinct reference points per turn, and you have 4 full turns. Thus you can simply mark any lens for it's true infinity number on the helical, and you're done.

    HOWEVER! With the new Phase IQ back technology, as long as your lens hits infinity the numbers on the scale only need to get you close. From there, you can use the Focus Mask feature in the IQ back and "see" the PoF in the image review as it pops up. So *my* current mode of operation is: 1) Compose (I estimate it with wides), focus by estimation, estimate exposure, shoot; 2) Review frame's composition, histo and FM (Focus Mask); 3) adjust exposure if necessary, move focus point in or out as needed and adjust composition as necessary; 4) shoot frame 2, repeat steps 2 and 3 as required; 5) once I have my final "perfected" composition, exposure and focus all set where I want them, I wait for the light/moment I want and take final frame, then take the LCC immediately afterward. I'm set.

    In practice, this may mean I take as many as 6 or 8 "set-up" shots to get composition and exposure all perfected with shifts and tilt, but those 6 or 8 frames take maybe 2 or 3 minutes total. Then I wait for the light as needed and take my final capture. By taking the LCC frame after my final, when I'm reviewing my images in my C1 session, I know exactly where in the chain my "perfected" composition was. However, since the last few frames are all usually very minor tweaks, the single LCC is generally adequate for them too if for some reason I decide I like the one or two before the final better.
    Jack
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    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  38. #88
    Sr. Administrator Jack's Avatar
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    Re: Tech cameras and IQ.

    Edit post just to finish the above discussion point: I finally got out yesterday for some infinity testing with my Arca RM3D and Rodie 40HR-W. I was able to confirm infinity focus -- a series of high-tension towers at about 300, 600 and 900 meters spacing and then trees and rocks on a ridge about 5 Km distant behind them on a relatively clear Sierra morning. Result was this: 300m tower and 5Km trees all came into crisp focus at the same spot.

    Point one. Interestingly, there were three of the hash points on my Arca ring that all appeared equal i sharpness, but then the hash's outside those were showing slightly softer. (Each hash mark is 1/170th of a turn on the ring, and equal roughly 14 microns of lens extension delta.) This was at f7. Anyway, I inferred the mid-point has as true infinity, and suspect that the lens is resolving enough higher than the sensor pixel pitch that the hash-marks to either side of that while less sharp, are still out-resolving the sensor. Impressive for sure.

    Next point is that 100m was 3 hash marks (~45 microns) in from that, and 30m was another 3 in from that. I take from this that extremely fine shifts on the focus ring to make relatively significant alterations to focus points that all fall within a traditional definition of photographic infinity. Stopping down would not improve DoF enough to make these irrelevant at 100% pixel view. Print resolution and normal print viewing distances however would -- IOW being a little off is probably close enough for most critical work even for larger prints. But it's nice to know we can get pretty extreme focus criticality here.

    Final point is I noted no back-lash issues, at least within one single hash-mark on the Arca ring, and at least to what the IQ180 can resolve -- to me this is impressive. Clearly there is some back-lash or we would not be able to turn the ring. I've read that Arca claims 10u precision here and I have no reason to doubt that after viewing my empirical results.

    I'll probably start a new thread on my experience with eh RM3D as I gather a few post-worthy images!
    Jack
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    Re: Tech cameras and IQ.

    Hi Jack,
    Did you by any chance play with the focus mask parameters on the IQ to determine the optimal setting for you point of focus? If so did it vary from lens to lens?
    Thanks,
    Bob

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    Re: Tech cameras and IQ.

    Quote Originally Posted by rga View Post
    Hi Jack,
    Did you by any chance play with the focus mask parameters on the IQ to determine the optimal setting for you point of focus? If so did it vary from lens to lens?
    Thanks,
    Bob
    Yes I did and yes it does. On my Phase with my Schneider LS lenses, I comfortably use a setting of 40 - 45. With the 40 HR-W, I need to crank that up to 65 - 70 to get the level of discrimination I want. I believe we will find that generally speaking our sharper, higher-contrast lenses are going to need higher FM settings to render a similar mask zone to that of our less sharp, lower contrast lenses.
    Jack
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  41. #91
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    Re: Tech cameras and IQ.

    Quote Originally Posted by Jack Flesher View Post
    Edit post just to finish the above discussion point: I finally got out yesterday for some infinity testing with my Arca RM3D and Rodie 40HR-W. I was able to confirm infinity focus -- a series of high-tension towers at about 300, 600 and 900 meters spacing and then trees and rocks on a ridge about 5 Km distant behind them on a relatively clear Sierra morning. Result was this: 300m tower and 5Km trees all came into crisp focus at the same spot.

    Point one. Interestingly, there were three of the hash points on my Arca ring that all appeared equal i sharpness, but then the hash's outside those were showing slightly softer. (Each hash mark is 1/170th of a turn on the ring, and equal roughly 14 microns of lens extension delta.) This was at f7. Anyway, I inferred the mid-point has as true infinity, and suspect that the lens is resolving enough higher than the sensor pixel pitch that the hash-marks to either side of that while less sharp, are still out-resolving the sensor. Impressive for sure.

    Next point is that 100m was 3 hash marks (~45 microns) in from that, and 30m was another 3 in from that. I take from this that extremely fine shifts on the focus ring to make relatively significant alterations to focus points that all fall within a traditional definition of photographic infinity. Stopping down would not improve DoF enough to make these irrelevant at 100% pixel view. Print resolution and normal print viewing distances however would -- IOW being a little off is probably close enough for most critical work even for larger prints. But it's nice to know we can get pretty extreme focus criticality here.

    Final point is I noted no back-lash issues, at least within one single hash-mark on the Arca ring, and at least to what the IQ180 can resolve -- to me this is impressive. Clearly there is some back-lash or we would not be able to turn the ring. I've read that Arca claims 10u precision here and I have no reason to doubt that after viewing my empirical results.

    I'll probably start a new thread on my experience with eh RM3D as I gather a few post-worthy images!
    Your getting geeky bud. ROTFLMAO
    Photography is all about experimentation and without it you will never learn art.

    www.guymancusophotography.com

  42. #92
    Gardenerbob
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    Question Re: Tech cameras and IQ.

    I hate to be a 'Silly Billy'
    but, what does 'DF', stand for.
    Bob

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    Re: Tech cameras and IQ.

    Quote Originally Posted by Gardenerbob View Post
    I hate to be a 'Silly Billy'
    but, what does 'DF', stand for.
    Phase One DF body.

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    Re: Tech cameras and IQ.

    brain wandered while i was running a machine...came up with this comparison to jack's findings. I am using Cambo lenses on I assume, Cambo helical focusing mounts

    43mm lens: closest focus is 400mm with lens-to sensor calculating to 48.17mm. focus barrel rotates about 110 degrees. that works out to .047 mm (47 microns) per degree of rotation

    70mm lens: closest focus is 800mm with lens-to sensor calculating to 76.7mm. focus barrel rotates about 270 degrees. that works out to .025 mm (25 microns) per degree of rotation

    120mm lens: closest focus is 2,600mm with lens-to sensor calculating to 125.8mm. focus barrel rotates about 250 degrees. that works out to .023 mm (23 microns) per degree of rotation

    looking at what jack posted, he was getting 170 ticks per full revolution, so each tick is about 2.11 degrees. His result of 14 microns per tick is then 7 microns per degree

    so the arca is 7 microns per degree for all lenses
    the cambos (and probably the alpa's) are from 47 to 23 microns of lens movement per degree of barrel rotation.

    a bit more data: comparing lens movement between focusing at 10 meters and 10.5 meters for the different lenses above:

    43mm: 10M vs 10.5M = 9 microns half a tick, or one degree, for the arca, about 1/5 degree for the cambo

    70mm: 10M vs 10.5M = 23 microns 1.5 ticks for the arca, about 1 degree for the cambo

    120mm: 10M vs 10.5M = 70 microns five ticks for the arca, about 3 degrees for the cambo

    last thing: the cambo lens barrel dia gives about 1/2mm per degree on the circumference

    all arithmetic subject to error, of course

  45. #95
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    Re: Tech cameras and IQ.

    Quote Originally Posted by jlm View Post
    so the arca is 7 microns per degree for all lenses
    the cambos (and probably the alpa's) are from 47 to 23 microns of lens movement per degree of barrel rotation.
    According to the Alpa distance tables, Schneider lenses are 27.8 microns per degree; Rodenstocks are 33.3. This is for the lenses listed to fit the HPF rings.

    Dave
    Last edited by dchew; 2nd July 2011 at 13:46. Reason: had my numbers reversed!

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    Re: Tech cameras and IQ.

    Quote Originally Posted by jlm View Post

    last thing: the cambo lens barrel dia gives about 1/2mm per degree on the circumference
    Interesting comparative data John! A FWIW to add to your info, each tic on my Arca barrel is about 2mm wide, so about 1mm of travel per degree.
    Jack
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    Re: Tech cameras and IQ.

    Perhaps a new thread: Tech cameras and GQ, as in Geek Quotient.

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    Re: Tech cameras and IQ.

    Quote Originally Posted by stephengilbert View Post
    Perhaps a new thread: Tech cameras and GQ, as in Geek Quotient.
    As they say, if the shoe fits...
    Jack
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    Re: Tech cameras and IQ.

    Speaking of GQ, I posted the following on Lulu earlier today --

    The Arca R focus helix is approximately 110mm in diameter, has 172 tick marks (numbered every 5 ticks, from 0 to 34), and moves the lens in or out 2.5mm per revolution -- i.e., 2500/360 = 6.94 microns/degree, or 2500/172 = 14.53 microns/tick mark. Lacking a vernier scale, about the best that could be achieved in terms of repeatability is 1/2 a tick mark, or 7.27 microns. Arca claims 10 micron repeatability for the Rm3di <http://www.rodklukas.com/resources/Arca-Swiss_NewProducts_2010.pdf>, which coincides with the minimum shim increment from Alpa.

    The scale that Arca uses appears to be based on the circumference of the focusing mount: 110 x pi = 345.6, which, when truncated to an even integer, yields 172 ticks and a final diameter of 109.50mm.


    This afternoon I worked out the theoretical extension table (in Arca units) for the SK 43XL. Plugging in Schneider's published focal length for this lens: 44.6mm, I can almost but not quite duplicate the table that Arca sent with my lens. At distances beyond 10 ft, the differences are 1/2 tick or less. At closer distances, the differences increase, but are still less than one tick up to 6 ft. However, if I use 44.95mm as the focal length, I can precisely duplicate the Arca-Swiss table.

    So, in my case, has Arca-Swiss measured the actual focal length of my lens and used that to generate the table? What else do they take into account in generating focus tables?

    On a related point, infinity focus is stipulated as an extension of 0mm. What if the sensor is a little farther back? How does one compensate?

    Dave.

    [As I noted on Lulu, I'm still lacking a mount for my back, so I'm reduced to admiring Arca-Swiss engineering as opposed to using the camera.]

  50. #100
    Porpoise
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    Re: Tech cameras and IQ.

    With these experiments, Jack proves physics is right. Traditionally, like for the markings on most lenses, DoF calculations are done with a CoC value of .030mm. Discussions are mostly ended with the statement that your acceptable CoC is subjective. Meaning that you decide which resolution you need. But if .030mm is enough, why did I buy the IQ180 that was just delivered? Fmor DR and color tonality, the IQ140 won't be far behind. For maximum resolution, it makes more sense to me to start with the pixel size as the CoC value. We don't want to confuse all those pixels! For the IQ180 that means .0052mm.

    A 40mm lens at f/4 then has a hyperfocal point at 77m, meaning that even with a perfect lens, you won't achieve better than pixel resolution nearer than 36.5m. But beyond that point, all the way to infinity, a good lens outresolves the IQ180. If perfectly focused at 900m, the nearest point where your lens still outresolves the IQ180 is 70.9m.

    A better way to calibrate the focus, might be to determine the point at which you don't get maximum resolution when focused on "infinity". If you want resolution at 300m or anywhere else beyond 70.9m to be less than resolution at infinity, you should in fact focus beyond infinity. Your camera would be a bit farsighted, as the minimum point of focus will suffer.

    On the other hand if you want a maximum range of maximum resolution, your "infinity" focus could in fact be the hyperfocal point at 77m. Any nearer focusing would start to degrade resolution at infinity. A bit of nearsightedness might be a good thing.

    So we have reached a point where calibrating the focus doesn't mean to look for resolution at infinity, but rather to decide on the range where maximum resolution can be reached.

    Hans (who isn't a geek at all) ;-)

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