What a huge difference the Glass makes

Discussion in 'Large Format Cameras and Accessories' started by Ian Grant, Jul 22, 2008.

  1. Ian Grant

    Ian Grant Subscriber

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    Recently I restored a couple of Speed/Crown Graphics, I'd intended to buy new glass but didn't get a chance on my last visit to the UK. I also need new glass for a 10"x8" and 9x12cm camera.

    I have 2 5x4's sat side by side on tripods and was astonished at the differences in screen brightness, I expected a stop or so but instead its well over 3½ stops, and that's with a handicap the camera with the brighter screen had a slower lens.

    The Wista 54DX with the standard Wista screen & fresnel had a 150mm 5.6 Sironar at full aperture and the Crown Graphic a 150mm f4.5 Tessar (coated), and a new ground glass bought via Ebay (2½ years ago), both focussed at infinity.

    Using my Spotmeter & reading from an area of clear blue sky on the screen the Wista gave a reading of 14, while the Graphic was 11.4. I then stopped the Sironar down until both screens had the same approx apparent brightness, that was between 16/22, checking the Tessar on the Wista I had a comparable reading of 14.7 as I'd expect with a faster lens.

    So in fact the difference in screen brightness is equivalent to 4 f-stops, which is highly significant. The dilemma is what glass to use that will get reasonably close to the brightness of the Wista screen on the other cameras.

    The screen on the Crown Graphic came from a reputable US supplier of ground glass screens, it is slightly brighter than the original screen. (Not Satinsnow).

    There seem to be are a number of options:
    1. Beattie or Maxwell screen
    2. Adapt a Wista or Cambo screen & fresnel (to fit).
    3. GVB & Lumigrid
    4. GVB Standard

    The first option is ruled out as too expensive I need up to 5 screens, the 2nd may be the best for one or two cameras but there may be an issue with film plane register adding the fresnel. The 3rd option seems the best for the other screen, maybe with plain GVB glass on the 9x12's.

    Comments on the Shen Hao Glass/Fresnel would be appreciated that option is quite reasonably priced, also sources for reasonably priced fresnels.

    Ian
     
  2. jeroldharter

    jeroldharter Member

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    5 screens is a lot so I understand your reluctance for the Maxwell. I researched this awhile back and decided to get a Maxwell screen for my 4x5 although there is not a huge amount of info out there. I can tell you that is is great and makes a huge difference, especially on the wide angle lenses. So if you have a wide angle setup with a bag bellows or something like that, consider splurging on the Maxwell for that camera. Likewise, if you have a particular setup for low-light photography.
     
  3. Ian Grant

    Ian Grant Subscriber

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    Jerold, I actually have a Beattie screen on a 10x8 so yes I appreciate the difference, but the screens on my Wista & Cambo 5x4's are excellent and I'm happy with that quality.

    My problem is a Beattie or Maxwell screen costs more than the Crown Graphics worth :D

    Ian
     
  4. Paul.

    Paul. Member

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    But what value do you put on your crowngraphic Ian?

    I will spend more on a camera than it is worth to improve my picture takeing pleasure if I can afford it and think it desireable enough, its worth and value are not the same thing in my book. It is a personal thing I do it for me, if someone else benifits after I have finished with it so be it, I regard it as part of the cost of my hobby. But then my youngest camera is over 30 and I drive a 10 year old car so what do I know.

    Regards Paul.
     
  5. Ian Grant

    Ian Grant Subscriber

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    My Crown Graphic isn't my main 5x4 camera, it's not so much the monetary value as its practical value as a hand-held LF camera. It just doesn't warrant buying a new Beattie/Maxwell screen when I'd be more than happy with a screen that was close in brightness to my Wista and Cambo's screens.

    Yes of course you're right to say it's worth improving a camera if possible, and I've changed the lens and now feel it's worth upgrading the screen, purely to make it a more usable camera but at a reasonable cost.

    Ian
     
  6. ic-racer

    ic-racer Member

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    I'm curious as to what the results would be without the fresnel on the Wista. Or if the fresnel were on the Graphic.
     
  7. rob champagne

    rob champagne Member

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    That was my thought too. The fresnel would skew the results significantly so its like comparing apples and oranges except that it shows that a frenel makes things brighter if viewed from the correct angle.

    But brightness does not necessarily equate to ease of focussing. It equates to ease seeing what you are looking at but a screen of sufficient coarsness will snap into focus whereas some of the bright screens are difficult to find the focus point. There is balance between the two which is optimum.

    A while back I removed the boss screen from my camera and put the original linhof screen back on. I was amazed at how much easier it was to focus even though it was not as bright as the boss screen.
     
  8. Ian Grant

    Ian Grant Subscriber

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    As you both asked I thought I'd check. However the Wista doesn't have a separate Screen and fresnel, it's an all in one Super screen plus a protective cover with a grid.

    The Wista screen is very bright and easy to focus, in comparison the screen on the Crown Graphic never produces a particularly sharp crisp visual image.

    Ian
     
  9. rob champagne

    rob champagne Member

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    All in one or not the wistas seem to have a fresnel screen.
    Was the spot you metered in the centre of the screen?
    If not, I would test again using the dead centre of the screen with everything centred at zero on the camera and place the spot meter right on the screen centre so that it is looking from a perfectly perpendicular angle to the centre of the screen. That should give a better indication of relative brightness regardless of fresnel. 4 stops is a huge difference.
     
  10. Ian Grant

    Ian Grant Subscriber

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    The Wista screen has the Fresnel built into it.

    It makes virtuall no difference wheter you read from the dead centre of the screen or not, I just tried it, the Wista does have a non fresnel centre circle of just under an inch diameter, and of course if you view from off centre this area is more directional.

    None of that alters the fact that theres a very definite 4 stops difference between the two screens.

    Ian
     
  11. Robert Budding

    Robert Budding Member

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    Perhaps you should simply focus using the rangefinder. Mine is very accurate, and I've had success using it hand held.
     
  12. Ian Grant

    Ian Grant Subscriber

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    Good thinking, so I just tried :smile:

    The camera came with an early 30's 135mm Tessar, which I've just replace with a 135mm Caltar (Sironar) as the Tessar just wasn't sharp enough. OK I have no Infinity stops (but I have a pair I can use back in the UK) so setting the trackbed & scale at infinity I focussed the lens at inifinity on the screen and locked it inplace. The rangefinder was way out - however . . . .

    I changed the lens, instead fitting a 50's coated 150mm Tessar and did the same, bingo the rangefinder's relatively accurate, so the cam is for a 150mm rather than the 135mm lens that came with the camera.

    So thats fine if I want to use a 150mm lens but I do like the 135mm and also use a 90mm & want to try a 7½" for portraits. In addition I regularly use tilt. A new screen is on it's way.

    Thanks Robert, now I know I can use the Rangefinder, I have another cam off a different Graphic back in the UK so I'll see if that's any different to the one fitted.

    Ian
     
  13. RidingWaves

    RidingWaves Member

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    There was an article in the US Camera Techniques that described making your own GG. I tried it, needed a GG for a 2x3 Graphic, and was very surprised at how easy it was to do. You basically get some fine polishing stuff from a telescope supply, then use a small piece of glass to grind away. I used 2 grit levels, to get a very fine 'tooth' and it is way brighter than the old one, which was original and had a crack. I keep thinking about doing one for my 4x5 Graflex, but leaving the finer grit for just the center so that the coarser one is on the edges, more brighter I think.
    If you need to do 5 and are on a budget, doing it yourself is pretty easy and very cheap.
     
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  15. 2F/2F

    2F/2F Member

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    Unless your Graflex is a fairly late model, it won't have interchangeable cams, so the cam would not be the problem. If you visit Graflex.org, they have the instructions for calibrating the RF to your lens.

    I would not bank on the fact that your RF is calibrated for a 150 lens unless you test is at all distances. (Most I have seen were factory set for a 127mm Ektar lens.) This is because there are three adjustments possible. Any combination of them could be on or off. One is for infinity, one is for 15 feet, and another is for four feet (or perhaps six...my memory fails me).

    Fresnels make a big difference! That's why they were invented. I would like to see the difference when the Graflex has a fresnel installed.
     
  16. Ian Grant

    Ian Grant Subscriber

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    It's a 1961 Crown Graphic, I'd not looked into adjustmentof the Rangefinder, hower "The Hugo Meyer is not a bad Rangefinder, but it has a fixed cam, and each model of the Hugo Meyer is made for and dedicated to a specific focal length of lens. You cannot replace the lens with one of a different focal length and adjust the Hugo Meyer RF internally as you can with the Kalart.. You set infinity with a screw under the narrow model number plate which must be removed. They are built on a square tube inside like the Leica screwmount RF, and are very rugged."

    Obviously when I checked it earlier I tried a variety of distances and the Hugo Meyer rangfinder seemed fairly accuarte with a 150mm lens at all of them. I have to check & set the Rangefinder on my WA Speed Graphic, it's some kind of 3rd party special, the adjusters are visible easily, it's factory set for a lens of somewhere around 90mm.

    Unfortunately just adding a fresnel to the current Graflex screen won't make that much difference, it would make it better by being less directional and greatly aid overall viewing of the whole screen but it won't make an iota of difference to the inherent 4 stops difference of screen brightness measured from the centre of both Wista & Graphic screen.

    I have a Cambo (in the UK) which does have a seperate fresnel and I'll see just how much difference it makes next time I'm in England. I'll try it with the Graphic screen I'm replacing.

    Ian
     
  17. 2F/2F

    2F/2F Member

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    Yep. A 1961 model will have cams! My comments were Re: Kalart side RFs.

    I installed a fresnel on my Sinar and it improved things greatly...however it did it.
     
  18. Ian Grant

    Ian Grant Subscriber

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    Not when it's got a Hugo Meyer side mounted rangefinder :D

    Fresnels work brilliantly and can really help, but unfortunately not with such a poor screen. I know my Cambo screen's not bad without the fresnel and I'd guess significantly brighter than the Graphic. The fresnel makes it far better as it gives more even illumination and apparent brightness towards the edges and corners of the image.

    Ian.
     
  19. ic-racer

    ic-racer Member

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    I guess that answers that. You are saying even when measured from the center of both there was a 4 stop difference. The Graphic's glass has been cleaned on both sides (I guess so, as you said you restored the camera)? It still seems like a huge difference (ie 32 times brighter). But if that is what you measured then it is what it is. If you replace it, let us know how it works.

    I had a Crown for a short period, they are really fantastic!
     
    Last edited by a moderator: Jul 24, 2008
  20. Bob F.

    Bob F. Member

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    Wondering if the built-in Fresnel allowed the use of a finer grinding on the glass. IIRC (debatable) the finer the grain, the brighter the image but the more fall-off you get at the edges; the Fresnel would counter the fall-off. IDK: just guessing!

    Cheers, Bob.
     
  21. argus

    argus Member

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    Hello Bob,
    That is incorrect: finer grain does not cause light fall-off, but increases the hotspot, but this difference might only be linguistic.
    It is possible to have a very finegrained groundglass and keep brightness up in the corners, without Fresnel!


    Geert
     
  22. Paddy

    Paddy Member

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    Hi Ian. Being in the U.K., have you even considered a Bosscreen? http://www.stabitech.nl/Bosscreen.htm#WhyABosscreenGroundglass
    It might be too expensive for your needs. (approx. 94 GBP) I replaced a older Beattie, with a Bosscreen on my Linhof Tech. V 4x5, and it's soooo nice. Due to it's unique design, there's no granularity or hotspots with the image. Very easy to focus too.
     
  23. Ian Grant

    Ian Grant Subscriber

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    Thanks Paddy, I'm going to buy screens from GVB, I'm confident they'll be excellent for most of my needs, and I'll try his Lumigrid type as well.

    Meanwhile I have a "Super Screen" on it's way for the Graphic, I particularly wanted a Fesnel type screen, I'll see what that's like I can always use the fresnel with one of Geert's screens.

    If I didn't already have a Beattie screen on my 10x8, and the excellent screen on my Wista, I'd be interested in a Bosscreen - now in my Bookmarks :D

    Ian
     
  24. Dave Miller

    Dave Miller Member

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    I've recently brought a 5x4 screen from http://sheetfilm.be/ (lumigrid) as a spare for my Shen Hao, it's very good, and I've fitted it as my main screen.
     
  25. Ian Grant

    Ian Grant Subscriber

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    I did ask how good Shen Hao screens were somewhere back in this thread so are you saying they aren't that good Dave ?

    I have heard of others fitting Satin Snow screens instead.

    Ian
     
  26. Ian Grant

    Ian Grant Subscriber

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    Eventually my "Super screen" arrived in the UK just before Christmas after a lot of problems with the supplier, it's a long story, but when I returned to the UK last month & opened it I found I'd been sent a plain Fresnel screen, I cannot recommend buying from Global Matters. There are threads about his business practices on the LFIF and elsewhere, lax US trading laws make it difficult to gain redress from him.

    However adding the screen to my Crown Graphic is going to make a significant difference as can be seen in this very quick snapshot.

    [​IMG]

    I found I already had a spare glass screen I've no idea where it came from but it's brighter than the one fitted at the moment so the two combined should improve brightness and usability further. At the moment the fresnel screen (fitted on the outside) makes a difference of over 1½ stops measured with a Spot-meter and the camera is far easier to focus.

    Ian