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Author Topic: Focussing On A Ground Glass  (Read 5950 times)
Mort54
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« on: June 30, 2007, 10:23:26 AM »
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Hi All. For those of you using one of the metal plate technical view cameras (Cambo Superwide, Alpa 12 series, Silvestri Bicam, etc), how easy is it to focus using the ground glass? Specifically, I'm interested in how bright the image is on the ground glass compared to what you see thru the viewfinder of a MF system like a Hassy or Mamiya or Contax (assuming the same wide open aperture, of course). Is the image on the ground glass bright enough to achieve tack sharp focussing?

Will a lens with a smaller image circle project a brighter image onto a ground glass than another lens with a larger image circle, assuming the same aperture (for example, will a Rodenstock HR series lens with a 70mm image circle appear brighter than a Schneider with a 110mm image circle, assuming the two lenses are at the same aperture)?

For reasons of brightness on the ground glass, is it worthwhile getting a lens with a maximum aperture of f/4 vs a lens with a maximum aperture of f/5.6?

For focussing, what power loupe do you use? 4X, 8X, 10X? I'd be using this system with a MFDB, if that makes any difference.

I assume you focus wide open, to get the brightest image possible, and then stop down to check depth of field. When stopped down to something like f/16 or smaller, is the image on the ground glass even bright enough to check depth of field?

Are there any other issues with focussing using a ground glass, other than image brightness? I realize the image will be upside down and reversed, but is there anything else?

I know some of your answers will necessarily be subjective, but I don't have ready access to such a system to check it out for myself, so I'm looking for informed opinions.

Thanks,
Mort.
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Roskav
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« Reply #1 on: June 30, 2007, 01:11:48 PM »
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I have used a "ground glass" with rodenstock 35mm and schneider 47mm ... I honestly can't remember off the top of my head what the max aperture on both is .. and I use them every day (architecture photogrpaher!) I didn't invest in a sliding back system but just tried out a hasselblad ground glass back that would have been used for the SWC .. along with a magnifier loupe.  I had gotten the ground glass from a supplier in hong kong via ebay and only discovered to my cost that the glass wasn't hasselblad .. just "for hasselblad" ... so it really isn't the best.  

What I found though was that as usual on ground glass with no fresnel screen you really see the fall off in light from the centrepoint of your view.. just as you would in a large format camera with no fresnel. All the taking off and putting on means that I only really use it if I am capturing with film on this camera (Gottschalt) .... Once you know your lens you can easily set the shot up by "feel" and take one or two shots to fine tune the composition. (digital)

So foccusing is difficult with the maginifier that I use .. 1.5 (I think) .. and you really wouldn't see anything useful at f16 for depth of field analysis .. I would just zoom in on a test image for that.

Ros
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Mort54
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« Reply #2 on: June 30, 2007, 09:10:16 PM »
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.... Once you know your lens you can easily set the shot up by "feel" and take one or two shots to fine tune the composition. (digital)
Hi Ros. Thanks for the feedback. I'm not too worried about the composition side of things. There are several zoomable viewfinders available that can be used for setting up the composition, as an alternative to using a ground glass. It's nailing the focus and depth of field on landscape shots where there is a close foreground in which I want a lot of fine detail that worries me the most. For that I would think I'd need to use the ground glass and a good loupe.

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So foccusing is difficult with the maginifier that I use .. 1.5 (I think)
I would think you'd need much more magnification than 1.5x to reliably achieve dead on focus. I believe I read somewhere that Alain Briot uses an 8x loupe for focusing on his 4x5 view camera. And that's a much bigger projected image than you get using a digital back. So I would think that you'd need an even higher magnification when you're focussing for a digital back.

Obviously there are many cases where focusing by guesstimation or by setting focus at the hyperfocal distance is perfectly good enough. But there are always those special cases, like close foregrounds, that probably need the precision of ground glass focussing.

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.. and you really wouldn't see anything useful at f16 for depth of field analysis .. I would just zoom in on a test image for that.
Given that I currently use a Phase One P45 back, checking focus on the LCD is worthless (the LCD itself is worthless for anything other than examining the histogram). My P45+ should be arriving sometime in the next month or so, and supposedly the LCD on it is much better.
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rainer_v
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« Reply #3 on: July 01, 2007, 05:22:13 PM »
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with the emotion backs i check focus with 100%. on groundglass very diffcult or nearly impossible.
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rainer viertlböck
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Mort54
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« Reply #4 on: July 01, 2007, 05:36:25 PM »
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with the emotion backs i check focus with 100%. on groundglass very diffcult or nearly impossible.
Hi Rainer. That's very discouraging. I'm thinking about getting an Alpa system, to use with my P45, and while I imagine using ground glass would be tedious, I can't imagine having to rely on viewing the image on the back LCD. It seems like it would be very trial-and-error. How do you adjust focus using the back? I assume you take a shot, check focus, adjust if necessary, take another shot, and repeat the process. Isn't that very time consuming?

What is the main cause of the difficulty in using the ground glass? Is it the darkness of the image on the ground glass?

In your case, which camera body are you using?

Regards,
Hans.
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rainer_v
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« Reply #5 on: July 01, 2007, 07:22:16 PM »
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hi hans,
no its not a big deal for me. mostly i shoot at infinity ( architecture ) .... if not i adjust with the meter scale of the optic and check final focus at 100%. i use a gottschalt with sliding back.
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rainer viertlböck
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jklotz
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« Reply #6 on: July 02, 2007, 06:39:35 AM »
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I also shoot architecture with a Cambo WDS with a Phase One P25, but find that, while on my 35mm, infinity seems to indeed be infinity, it is not on the 47mm. I'm told that the entire rig can be sent back to Cambo for calibration, which suposedly fixes this, but there is an extra charge for it plus it will take 4 weeks to get it back. Not a reasonable solution in my mind. So for me, I shoot teathered every time I pull it out of the case. I take a test shot, view on screen at 100%, adjust acordingly, then pop another, etc. until I've nailed it. I've yet to try film with the camera, and doubt I will.

I've tried ground glass at the dealer on thier demo unit, but a) it is only available for hassy mount backs on the WDS (mine is a contax mount), and  was way to dark, especialy in the corners, to be useful even in a reasonably lit interior. Even if I did have a hassy mount, by the time you swap out the back for the glass, compose and focus, replace the back and shoot, it is still faster to shoot teathered. Not to mention the possibility of dust and contamanation on the sesnor with all that swaping around.

I think one of the best investments I've made was a flexable sunshade for viewing my laptop in bright sunlight. Daytime exteriors would be next to impossible without it.
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Mort54
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« Reply #7 on: July 02, 2007, 09:07:59 AM »
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I've tried ground glass at the dealer on thier demo unit, but a) it is only available for hassy mount backs on the WDS (mine is a contax mount), and  was way to dark, especialy in the corners, to be useful even in a reasonably lit interior.
Thanks for the feedback. A couple of quick questions - when you say it's too dark, are you doing your initial focussing with the lens wide open, or with the lens stopped down to it's working aperture? Are you using a dark cloth, or a bellows for your loupe, to keep outside light from interfering with the process?

You're the third responder who had indicated focussing by ground glass is difficult to impossible, which I have to admit was not the answer I was expecting - especially since I see Michael Reichmann using a ground glass with his Linhoff in his video journal. This is forcing me to rethink all my basic assumptions. I really don't want to shoot tethered, since my whole reason for even considering an Alpa 12TC is to put together a small lightweight kit for use on more difficult hikes where my medium format system would just be too bulky and heavy.

Regards,
Mort.
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marcwilson
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« Reply #8 on: July 02, 2007, 09:22:28 AM »
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...since my whole reason for even considering an Alpa 12TC is to put together a small lightweight kit for use on more difficult hikes where my medium format system would just be too bulky and heavy.

Regards,
Mort.
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With a camera like the alpa TC, if using as a small travel kit as opposed to fixed interiors etc, would you not want on most occasion to do your composing with the viewfinder and either guess distance focus or use an optional add on rangefinder..as many would have done with a camera like the hasselblad superwide?

Marc
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Mort54
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« Reply #9 on: July 02, 2007, 09:34:14 AM »
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With a camera like the alpa TC, if using as a small travel kit as opposed to fixed interiors etc, would you not want on most occasion to do your composing with the viewfinder and either guess distance focus or use an optional add on rangefinder..as many would have done with a camera like the hasselblad superwide?
Hi Marc. For composing, I intend to use something like the Linhof zoomable viewfinder. I'm also experimenting with a small pistol site (the ATN Compact Red Dot sight is one example) - it's tiny and weighs next to nothing. However, some compositions with close foreground objects will probably require the ground glass to get the composition just right. It's also these situations - compositions with close foregrounds - that I think will require ground glass focussing to nail the focus. For many other compositions, focussing at either infinity or the hyperfocal distance will work just fine.
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rainer_v
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« Reply #10 on: July 02, 2007, 09:41:53 AM »
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I also shoot architecture with a Cambo WDS with a Phase One P25, but find that, while on my 35mm, infinity seems to indeed be infinity, it is not on the 47mm. I'm told that the entire rig can be sent back to Cambo for calibration, which suposedly fixes this, but there is an extra charge for it plus it will take 4 weeks to get it back. Not a reasonable solution in my mind. So for me, I shoot teathered every time I pull it out of the case. I take a test shot, view on screen at 100%, adjust acordingly, then pop another, etc. until I've nailed it. I've yet to try film with the camera, and doubt I will.

[a href=\"index.php?act=findpost&pid=126042\"][{POST_SNAPBACK}][/a]
i adjusted all my lenses myself. its not diffult, but not one of them was really 100% at infnity after getting them from gottschalt.
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rainer viertlböck
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« Reply #11 on: July 02, 2007, 12:04:47 PM »
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i adjusted all my lenses myself. its not diffult[{POST_SNAPBACK}][/a]
There are directions at Fotoman Camera on adjusting the infinity focus with a helical mount lens:

[a href=\"http://www.fotomancamera.com/download/2006121522239LargeFormatCameras.pdf]http://www.fotomancamera.com/download/2006...rmatCameras.pdf[/url]


I have a Cambo Wide. Focusing and composing on the groundglass is really an approximate art, even with a magnifier.

With an f/8.0 90mm lens mounted (for film), all you can really see clearly is the center portion of the image. The corners are lost in darkness.  And that is outside during full daylight.      

To compose on the groundglass, I note objects near the edges of the frame as landmarks and then turn the camera - so that they are near the center of the frame - so that I can see them clearly.

I also have a 90mm f/4.5 on a different camera that is much brighter and easier to use. Other solutions are to buy a replacement groundglass that is brighter, or a groundglass with fresnal, like a Beattie interscreen.

Instead of using the groundglass for composing, I use a viewfinder that came with the Cambo. You can also buy a viewfinder from Fotoman with the appropriate masks.

The viewfinder is used for composition. Fotoman also sells a rangefinder that can help determine the distance, which you then set using the focusing scale on the lens.  Instead of a rangefinder I have been using a $100 laser measuring device.  It is fairly effective up to about 20 feet outdoors in sunlight. If the distance is longer than that I am usually close to infinity anyway ...  

Good luck!

Best,
Michael
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Mort54
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« Reply #12 on: July 02, 2007, 12:35:27 PM »
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With an f/8.0 90mm lens mounted (for film), all you can really see clearly is the center portion of the image. The corners are lost in darkness.  And that is outside during full daylight.    
Thanks Michael. For the Alpa system, the lenses I'm looking at are either f/4 or f/5.6, so they would be a little brighter than the f/8 you mentioned (in fact, based on all the feedback so far, if I decide to go ahead with this, I'll almost certainly go for the f/4 Rodenstocks just to make sure I get the brightest projected image possible). Also, I'll be using it with a digital back, so only the center portion of the projected image will be used, so hopefully that keeps me away from the darker corners. Finally, the Alpa ground glass does come with a fresnel lens, so hopefully that further helps the situation. Ideally I'd go find one of these and check it out personally, but so far I've been unable to locate a dealer anywhere near me.
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Jost von Allmen
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« Reply #13 on: July 02, 2007, 01:36:39 PM »
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I'm using an ALPA SWA with a P45 (with the P45+ on order) since May and use the original ALPA ground glass with fresnel on a regular base to focus.
I currently use a Nikon 4x loupe which works ok but a Schneider 6x is on order, which will be perfect. 8x might be too high a magnification as you get to see the texture of the ground glass too much.
No problem focussing with my 35mm and 100mm Rodenstock HR's which are f4, light fall off is signficant with the 35mm without the fresnel (unusable).
And focussing works just fine with my 180mm Digitar as well, although it's "only" f5,6.
I never even bothered taking off the fresnell with the 180mm so can't tell the difference it would make.
Although I mostly shoot outdoors, I hardly ever use a dark cloth, the image on the ground glass is bright enough for me, but you'll surely find it easier to frame and focus with it.

All i can say is that critical focussing is a must with the extremely high resolution of the P45 and the lenses mentioned.

Hope that helps!
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Jost von Allmen
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Mort54
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« Reply #14 on: July 02, 2007, 02:04:47 PM »
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I'm using an ALPA SWA with a P45 (with the P45+ on order) since May and use the original ALPA ground glass with fresnel on a regular base to focus.
....
No problem focussing with my 35mm and 100mm Rodenstock HR's which are f4, light fall off is signficant with the 35mm without the fresnel (unusable). And focussing works just fine with my 180mm Digitar as well, although it's "only" f5,6.
Hi Jost. That is music to my ears. Thank you so much for posting. I was beginning to wonder if I was totally on the wrong track in considering the Alpa/ground glass combo.

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All i can say is that critical focussing is a must with the extremely high resolution of the P45 and the lenses mentioned.
My thoughts exactly. My main motivation is to create a lightweight compact kit for traveling and long hikes, but my other motivation was to be able to capture every last bit of detail that the P45 was capable of. Focussing on the ground glass seemed to be the only way (to me at least) to reliably achieve critical focus.

What is your impression of the Rodenstock HR lenses? What kind of camera system were you using before you got the Alpa and the HRs, and how do the HRs compare (in sharpness, contrast, etc) with your previous system?

Also, how much shift are you able to achieve with the HR lenses, since they only have a 70mm image circle? Has that limited the degree to which you can use shift on the SWA?

Regards,
Mort.
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Jost von Allmen
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« Reply #15 on: July 02, 2007, 03:32:39 PM »
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Before purchasing the whole equipment mentioned, I've tested many systems (Hasselblad H2 / Mamiya AFD II / Cambo Wide DS) with Aptus 65 and P45 throughout the last 10 (!) months and got feedback from two professional photographers using P45's with Hasselblad H2 and ALPA XY.
I was looking for a replacement for my whole (analoge..) ARCA SWISS 4"x5".

I ended up with the ALPA SWA, as it is the best possible system for my needs and the way I work (outdoors; slow). I also have no problems with the whole workflow with Capture One.
The HR lenses are outstanding: The 100mm is probably the best lens I've ever used and owned, my new standard!
The Schneider Digitar 180mm was a real surprise: although the image circle is much bigger (find all the data on ALPAs very detailed homepage), the sharpness and contrast match the HR!

With the HR's you get about 10mm shift (at infinity), with the Digitar I can use the full 25mm available with my SWA (although I don't actually use the 180mm shifted).

Lens cast ist clearly visible with the 35mm and also sometimes with the 100mm, but removing it with C1's LCC feature turned out to be absolutely no problem.

Next weekend I'll be testing a Digitar 47mm and the 60mm HR: one of those I'll buy to fill the gap between the 35mm and my 100mm. At the moment I prefer the 47mm for it's ability to shift a large amount ( even more than the 25mm possible), that's the only thing I miss about the 35mm. I do find it's image circle a bit limiting for shifting (when I'm on mountain summits..).
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Jost von Allmen
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rainer_v
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« Reply #16 on: July 02, 2007, 05:46:15 PM »
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i have the 28, 35,60 + 100 hr. the 100 is still not mounted,  i wanted to replace my sinaron 90digital with it. the 60HR allows more shifting than the 28+35HR, it can be shifted 20mm. the 28+35HR  12-15mm ( with dalsa sensor which is 36x48mm). all Hr lenses are great, even if not stopped down.
best lenses i ever owned ..... no CA.
sharp at all apertures.

 i also have the 45 digital sinaron. its good and shifts 25mm ( or more ) , but it wants to be stoppd down,- and it dont match the HR although its still a good uable lens.
the 90 digital sinaron is not my favority, good lense if stopped down,- i expect more from the 100 HR.
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rainer viertlböck
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« Reply #17 on: July 03, 2007, 05:29:31 AM »
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i use th alpa SWA and alpa XY with P45 and A75 DBs. in fact, i found focussing with the alpa groundglass really hard, but then alpa advised me to get the Hasselblad groundglass with slit focusing screen and Hasselblad viewfinder (originllay made for the Hasselblad SWC, i suppose). the framing and focusing improved dramatically with this device. it just gets a bit difficult with extrem shift, but still managable.
all the best, peter
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« Reply #18 on: July 03, 2007, 05:37:52 AM »
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i use th alpa SWA and alpa XY with P45 and A75 DBs. in fact, i found focussing with the alpa groundglass really hard, but then alpa advised me to get the Hasselblad groundglass with slit focusing screen and Hasselblad viewfinder (originllay made for the Hasselblad SWC, i suppose). the framing and focusing improved dramatically with this device. it just gets a bit difficult with extrem shift, but still managable.
all the best, peter
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I use a Flexbody and truewide with groundglass and a RMFX finder (the finder also for the SWC). This works very well, unless you start tilting more than 10degrees (I don't have the tilt correction slides).

The RMFX finder is a true blessing but quite hard to find and not really cheap.

Another solution I saw at a friend is the Sinar (thought it was Sinar) flexfinder which is the same sort of solution as the RMFX but instead of a hard shell it is a sort of leatherette soft shell so you can move the ocular around to check different areas of the ground glass. I am still searching for that thing, I would definitely like to have one of those.
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« Reply #19 on: July 03, 2007, 02:18:06 PM »
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I have found that with the 35 mm, at least when using the Cambo WDS, that the falloff around the edges is pretty extreem, limiting the amount of shift available. I hate to bring up the dreaded center weighted filter discussion, but if you don't mind loosing 2 stops, it gets you another 5mm of shift. Actaully, Schneider recomends the use of the filter with the lens.
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