To fresnel or not to fresnel

brianentz

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I have a 5x7 view camera and a lens that really don't throw light out to the edges well when the lens is opened fully up at f8. Makes composition more difficult. I'm sure that when stopped down it shouldn't vignette bad. My understanding is that the fresnel addition would disperse the light more evenly across the glass, but it will be taking the same volume of light and move it across more evenly. This will make the center dimmer, no?
 

Vaughn

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No -- the fresnel takes the light hitting any one spot on its surface at a sharp angle and turns it more perpendicular to the GG so that it arrives straighter towards our eyes.

To better see the image on the GG without a fresnel, put your eye on the same path as the light hitting the spot on the GG you are interested in. The light comes from the center of the lens. So if you want to see what is in the lower right corner, lower you head and look from the corner up towards the center of the lens.

I prefer not to use a fresnel -- don't like the way they 'mess up' the viewing image. Less pleasant to focus.

Note: my preferences are biased due my strong near-sightedness (when I look at the GG w/o my glasses, it is like using a loupe.)

Also, the difficulty you are having seeing the image away from the center most likely will not translate into any vignetting of the image on the film...even wide open (assuming a lens with enough coverage to begin with).
 
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Doremus Scudder

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I have cameras with both Fresnel screens and without. Both are fine for me. The Fresnel screens I have are all factory OEM screens, both Wista and Graphic View. They are quite bright and I can often focus without a dark cloth on bright days and with lenses that are longer and have f/5.6 maximum apertures. The non-Fresnel screens almost always need a dark cloth, but are nice to use because the Fresnel lines are not there to distract and confuse when fine focusing (although I do well with the Fresnel lines too). Some people are disturbed by the lines from a Fresnel screen; some hate the dimness of a regular ground glass. It boils down to personal preference.

FWIW I use a free-held magnifier so I can tilt it to look into the corners easily. It takes a little time to get used to finding the right distance from the ground glass when fine focusing, but after that, a free-held magnifier is much more flexible than those with skirts.

Best,

Doremus
 

abruzzi

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My Arca-Swiss cameras (f-classic 6x9 and f-metric 4x5) have fresnels since that's how they're made--and they're not removable because the sit between the ground glass and the lens--removing them would throw off focus. That does make them noticable brighter and as Doremus notes, frequenlty can be used without a hood. I also have factory fresnels for my sinar norma 4x5 and Technikardan 45 but those I rarely use because the fresnel lines are more apparent. It probably becuase with a fixed focus (toyo) loupe, the Arca Swiss design puts the fresnel further out of the plane of focus and makes them less noticable.
 

Ian Grant

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A better ground glass focus screen can make around 2 stops difference in brightness, adding a fresnel can take that to around 3 stops overall but no brighter at the centre, a composite screen, Beattie etc can take that to 3.5 stops brighter.

How do I know, I quietly sell hundreds of focus screens a year, for field cameras etc, I also make bespoke screens for early SLR and TLR cameras to special order.

More importantly I began making screens because I need them, and want the best, these are for restorations, and also for cameras I use, but then others should have the options for similar screens

Ian
 

MattKing

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Ian Grant said:
How do I know, I quietly sell hundreds of focus screens a year
Click to expand...

That is in comparison to a long ago ex-Apug member, who somewhat vocally sold a bunch of apparently very desirable focus screens, while being quite a bit less "quiet" in discussions in the threads.
And yes, I'm being intentionally cryptic.
 

Vaughn

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I suggest some research into frensnel and focal length of your primary lenses. Just from what I have read (no experience, perhaps others will chime in)...very wide lenses vs. normal/long lenses: they work better with fresnels designed for the focal length of the lens. At least for the extremes.
 

MattKing

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MattKing said:
That is in comparison to a long ago ex-Apug member, who somewhat vocally sold a bunch of apparently very desirable focus screens, while being quite a bit less "quiet" in discussions in the threads.
And yes, I'm being intentionally cryptic.
Click to expand...

My post above wasn't intended to disparage the ex-Apug member - for a long time he was a valuable and much appreciated contributor here - just not as quiet as Ian!
 

Patrick Robert James

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I agree. Personal preference.

If you want to give a fresnel a try you can just cut down a sheet magnifier from the dollar store, or wherever else you can find one. Just slap that over the ground glass. It will give you a rough idea what a fresnel would do.

Another alternative is waxing the ground glass. I wouldn't do it unless the ground glass is plain (might take the lines off if you try to reverse it). A real light coat of wax can really brighten up a ground glass. I did that with my Speed Graphic and it made quite a difference.

It is possible also that your ground glass is just dirty. If you've never cleaned it you might want to try that first.
 

Ian Grant

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Some manufacturers used to offer two different fresnels, these clipped on top of the ground glass screen, one was general purpose the other for wide angle lenses. My experience with my 5x4 cameras is I have no problems with a 75mm wide angle, or longer focal length lenses on my Wista 45DX with the Wista combination screen, or on my Super Graphic. It's harder to use my 65mm wide angle but it's a lens I rarely shoot with so I can cope.

I added a new screen to my Crown Graphic, and when it arrived a fresnel, there is a downside if you use a focus magnifier/lope it isn't as easy, however I never use on as I find the images snap in and out of focus better with a fresnel. I use the Crown Graphic or a Super Graphic for hand held work, so the focus hood and no dark-cloth.

If the OP's 7x5 camera is an older model, then a new screen can definitely make a very significant difference. As it didn't come with a fresnel from new, if one is added it has to be to the rear (eye side) of the focus screen.



This is a fresnel held close to the Crown Graphic ground glass, it gives a rough impression of the potential improvement. I did comparative tests as well as measured tests with a Spotmeter, and the improvements witha fresnel matched.

Ian
 

Philippe-Georges

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I don't want to harm Ian Grant's business, but to the EEC based photographers, I would like to point at the Netherlands based manufacturier of Bosscreen focussing screens: http://www.stabitech.nl/Bosscreen.htm (I am not affiliated with them).
I have one mounted on my Linhof Kardan GT 4"x5", and very happy with it.
These are not grounded, but as a side effect can't stad high temperatures, which isn't a major issue in North-Western Europe...
 
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Terence

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MattKing said:
My post above wasn't intended to disparage the ex-Apug member - for a long time he was a valuable and much appreciated contributor here - just not as quiet as Ian!
Click to expand...

Was it Andrew something? I actually just came across an 8x20 GG someone on APUG made for me sometime around 2008-2009. I only just came back on here after a 10 year film hiatus due to health and family issues. Glad to see so many familiar names still on here.
 

MattKing

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Nope - he is no longer here.
 

Mal Paso

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I have a telephoto that is f19 wide open and a hybrid fresnel makes all the difference. That one doesn't play nice with wide angle but my 65 is f4 now so the standard GG works fine. There are different fresnels for wide angle if you need one. I feels like I've spent weeks focusing my f8 65mm in dark interiors that I lit with flash.
 

Vaughn

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I must say that is what is nice about cut corners on the GG (5x7 and larger). To see what it in the corner, the imaging light coming from the lens is directly entering one's eye...as bright as it can get.
 
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