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seawolf66
18-Mar-2012, 09:24
Does a Fresnel lens really improve focusing for you?

rdenney
18-Mar-2012, 09:50
No, that's not its purpose. A Fresnel gather light and points it back to your eye, so that you can see the whole image from edge to edge with enough brightness to compose the photograph. If anything, most Fresnels make focusing using a loupe more difficult, because the Fresnel pattern is a distraction when magnified. Many camera manufacturers made the Fresnel easily removable for focusing, e.g. Sinar.

With short, slow lenses, one might require a Fresnel to see enough of the image to even be able to see the edges, but then the Fresnel has to be designed for such short lenses to be completely effective. Lenses much too short for the Fresnel will cause ghosting and other artifacts in the Fresnel that actually undermine its use.

Rick "noting the Fresnels that one can focus through easily are expensive" Denney

BrianShaw
18-Mar-2012, 10:00
When using a loupe, no.

When not using a loupe, yes.

IanG
18-Mar-2012, 10:13
Yes a fresnel lens in combination with a good ground glass screen can help enormously with focussing by increasing the brightness substantially.

About 4 yeras ago I realised that my Crown Graphic was substantially harder to focus than my Wista putting the two side by side there was over 3 stops difference in overall brightness despite the fact that the Crown had an f4.5 lens and the Wista f5.6 (both 150mm at full aperture). The Wista has a combination screen'fresnel.

I measured the differences in brightness (using a Spotmeter) and also stopped the Wista's lens down until they matched in brightness (the differences matched) and it was 3 and 1/3 stops, admiottedly the Crown had it's original screen.

Changing the Crown's screen for a Steve Hopf one increased brightness by about a stop, adding a fresnel took it closer to the Wista's combination screen/fresnel and about 2 stops brighter than it had been. That improvement means it's new very much easier to focus particularly when used hand held, the focus hood is fine on it's own.

Since then I've fitted new screens to all my other LF cameras, it made the a big difference to my German pre-WWII 9x12 cameras (Orion Werks, Rodenstock, KW Patent Etui's etc) these can now be focussed easily even in quite low light. If I could find the right fresnels I'd fit then as well).

Ian

TheDeardorffGuy
18-Mar-2012, 17:53
Fresnel lens..........I hate them. Really truely hate them. You really need different ones for different FL lenses. A really nice fine grind ground glass with the corners cut works just fine. In 40 years of doing this I've seen so many Fresnel lens come and go on the market.....If there was one perfect one it would still be there and this question would not be asked. (I do not blame you at asking it at all, It needs to be asked!!)

seawolf66
18-Mar-2012, 18:38
7048570486Basically my eye's are getting older , Just was wondering if the Fresnel lens would help me out in focusing I use a lope but some
times it a hit or miss with me for being on the money with sharpness : thanks all you folks for your answers
below are two just in last few day as you see one is good the is close but no cigar.

TheDeardorffGuy
18-Mar-2012, 19:08
You need a loupe that is adjustable to your eyes. The other day I found all my Agfa style loupes that I modified to focus for my eyes. I machine a bit off the bottom edge. Now I need to add a bit!! I finally got a Schneider loupe and love it. I drew a + on the GG and focus on it. Thats it.

Bob Salomon - HP Marketing
19-Mar-2012, 03:39
I hope you are drawing that + on the grain side of the gg and not the non-imaging forming side of the gg.

IanG
19-Mar-2012, 07:30
]Basically my eye's are getting older , Just was wondering if the Fresnel lens would help me out in focusing I use a lope but some
times it a hit or miss with me for being on the money with sharpness : thanks all you folks for your answers
below are two just in last few day as you see one is good the is close but no cigar.

You need to try one and see. There is some variation in fresnels and some people swear by the more expensive Maxwell or Beattie screens.

While I can see where Ken's coming from not liking Fresnels there's a good reasons for using them as well which is why many cameras are sold with them fitted. Many of us find they make focussing very much easier and I very rarely need to use a loupe.

Ian

E. von Hoegh
19-Mar-2012, 07:48
Does a Fresnel lens really improve focusing for you?

No.

seawolf66
19-Mar-2012, 09:20
No.

short answer LOL

seawolf66
19-Mar-2012, 09:27
I thank all of you for your responses here in this matter , you each have presented a good view point in this matter
now its up to me to decide, I first will recheck the Lope and make sure Its focusing properly , If that is fine then
I need not go further other wise I'll look at Fresnel lens : Thanks to all of you for your time on this subject matter: Lauren

rdenney
20-Mar-2012, 07:11
Fresnel lens..........I hate them. Really truely hate them. You really need different ones for different FL lenses. A really nice fine grind ground glass with the corners cut works just fine. In 40 years of doing this I've seen so many Fresnel lens come and go on the market.....If there was one perfect one it would still be there and this question would not be asked. (I do not blame you at asking it at all, It needs to be asked!!)

Have you tried a Maxwell screen? These defy convention. I can focus through mine using a 10x loupe and can hardly see the Fresnel pattern. But I can also see to compose a 65mm lens without a hood in sunny conditions. It works fine for a 300mm lens (my longest), too.

The only downside to the Maxwell is cost. If they were as cheap as plain ground glass screens, everyone would have them except people who believe they need to suffer to produce good art.

Rick "a non-masochist with poor vision" Denney

bravo_
20-Mar-2012, 10:27
Hello,
I have a question , and i think this place is best for the solution of mine problem,
I wana change lens of mine camera,so i wana know which lens is best?

Lynn Jones
20-Mar-2012, 10:33
it certainly brightens the periphery of the ground glass image especially in the case of WA lenses. However some superb technical scientists are against the GG fresnels. With a good magnifier it is possible to focus on either the GG, the front or the back of the fresnel. I haven't had that problem personally but the literature has been out these.

Lynn

BrianShaw
20-Mar-2012, 10:35
Hello,
I have a question , and i think this place is best for the solution of mine problem,
I wana change lens of mine camera,so i wana know which lens is best?

Maxwell

Noah B
20-Mar-2012, 10:44
I personally like fresnel screens. I use a 305mm G-Claron f/9 lens, and on my original Deardorff GG the image was too dark for me to compose most of the time. I then purchased a fresnel screen off ebay from the seller ecbuyonline. He's located in China, but makes quality fresnel inserts for MF cameras up to LF.

TheDeardorffGuy
21-Mar-2012, 18:12
Thanks Rick. I had not even heard of them. I fine tuned the GG on the 3 cameras I shoot with 20+ years ago I have not looked since. If you remember 20 years ago there was a fresnel battle going on. Since most shooters tend to use one lens most of the time the Mfgrs tended to make screens for the 300mm lens on 8x10 and a 150 or so for 4x5. I found none of them great at all. Some of the Mfgrs sent me samples to test. I think I had around 15 at one point. The funny thing is no one had correct instructions to install them correctly ala Graflex.
()lens()-------Smooth side - Frensel side against Ground side-Smooth side of glass. this requires the gg frame to be machined down the thickness of the fresnel to maintain correct focal plane. You do not put them on the back of the glass and expect to focus through them and the ground surface...


Have you tried a Maxwell screen? These defy convention. I can focus through mine using a 10x loupe and can hardly see the Fresnel pattern. But I can also see to compose a 65mm lens without a hood in sunny conditions. It works fine for a 300mm lens (my longest), too.

The only downside to the Maxwell is cost. If they were as cheap as plain ground glass screens, everyone would have them except people who believe they need to suffer to produce good art.

Rick "a non-masochist with poor vision" Denney

IanG
22-Mar-2012, 08:39
You do not put them on the back of the glass and expect to focus through them and the ground surface...

Actually you do with some camera backs with a fresnel, particularly when the back has had an fresnel added later, but sometimes fron new as well. My Cambo had a fresnel fitted to the back of the glass from new and when I added a fresnel to my Crown Graphic that was how it had to be fitted or the register would have been wrong.

I used my Super Graphic with the Graflok back from my Cambo for a year before finally finding a good Super Graphic back (focus frame), the Cambo had the fresnel on the back, the Super Graphic lens side of the grownd glass and in all honesty both are easy to use and focus.

Your point about the correct focal plane is important and I've been surprised when buying 2 Graflex focus panels (around Christams) to find the fresnels incorrectly fitted on frames designed to have them inside next to the ground glass. It doesn't helf that the Graflex castings have no identification to tell you whether they are machined for a fresnel or not :D

Ian