Sinar F1 focussing screen

[gwatson]

Hi all. I have a few questions which I hope some of you may be able to help me with. I have just got a used Sinar F1 and the focussing screen just doesn't look right. It consists of a clear sheet of glass with grid etc., attached to the back and then an opaque plastic screen clips into the back (photographer side) on which you focus. I had first thought that the plastic screen was a fresnel, but it does not appear to be.

Does anyone know if Sinar ship the cameras like this? - it looks like it is designed to be there, but looks a bit shoddy. It does not appear to be a particularly bright screen, but since I have not used LF since college, I have no frame of reference. I know these are budget cameras, but I was expecting ground glass, at the least. Also, i am assuming that I am focussing on the image projected on the glass sheet, and not the plastic one. That is right, isn't it?

Should I just get a new ground glass?

Cheers

Geoff

 

[Dave Parker]

Sounds pretty normal for the later sinars, I have seen this type of focusing system in several different brands of cameras in the last few years, if it is just an frosted piece of plastic, I would imagine the viewing screen would be pretty dim, as the optical properties of the plastic would really affect the light transmission of the image.

But again, it is probably a factory set up, based on my experiance.

Dave Parker
Satin Snow Ground Glass

 

[sattler123]

Geoff, I had a Sinar F1 for about a year and what you describe sounds very much like the Fresnel screen that snaps in the frame of the GG. You should see a clear improvement when using the fresnel esp. with wide angle lenses. Remember, GG focusing is much dimmer than what you might be used to from 35mm or Medium Format. Your fresnel might be scratched up - and that's probably why it looks shabby. Sinar cameras are not budget cameras - they are extremely well made precision equipment. I love mine, but ended up selling it because it was just too hard to schlepp it around in the field. To this day I miss the movements and the stability of the Sinar.

 

[gwatson]

Thanks for the replies. You're right, I've just had a look through a loupe and it is a fresnel. However, since there is no gg in the camera, only a clear glass sheet, I assume I am focusing on the fresnel, which I'm not totally convinced is on the film plane. Since I do a lot of close-up/macro stuff, this is fairly critical. Has anyone had problems with this setup, or am I worrying too much?

Geoff

 

[Dave Parker]

As the Sinar cameras are highly regarded world wide, I think you might want to do a couple of test shots to reasure yourself that things are okay with you camera, as it sounds like a factory system, I don't think your going to find any problems.

Dave

 

[gwatson]

Hi Dave. I'm sure you're right. I've only had it a day, so I'll put some film through it today. My only concern was that, since it was a used camera, the previous owner had 'messed' with it a little.

Cheers

Geoff

 

[David H. Bebbington]

I have 2 1/2 Sinar Normas (2 fronts, 3 backs) and a Sinar F1 - in all of them, the screen installation is ground glass first with matt surface facing inward and in contact with the metal frame, and then if available fresnel screen on top of this, with the fresnel (slightly ridged) side in contact with the GG. Screens like the Beattie Intenscreen are supplied with a sheet of clear plate glass, in the case of the Sinar you can either leave the clear glass out or put it on top of the focusing screen to protect it from scratches. There are cameras designed to accept a fresnel screen UNDER the GG (Speed Graphic, etc.), when fitting a Beattie screen in this case, the clear glass would go in first to compensate for the thickness of the fresnel screen which you are no longer using.

 

[Jim McD]

I have had an F1 for 5 years, and it is not a bad question. You seem to be missing the ground glass, but still have the fresnel focusing screen that normally sits over the ground glass.

I focus using the fresnel because it is so much brighter, and have never had an issue with loss of focus versus using the ground glass.

Try some shots focusing on the fresnel and let us know the results. It seems that the fresnel image is the same focus as the ground glass but your results may vary

 

[Trond]

In my newly acquired Sinar Norma 4x5, the ground glass is on top of the fresnel lens. The setup is: Back of camera, ground glass, fresnel lens (with the flat part facing the lens), lens.

Is this how it´s supposed to be?

Trond

 

[Jim Noel]

The Norma should have the GG surface facing the lens. If a fresnel is used, it is snapped on the rear of the GG. The set- up should be just the opposite of what you state.
Jim

 

[jd callow]

The Norma should have the GG surface facing the lens. If a fresnel is used, it is snapped on the rear of the GG. The set- up should be just the opposite of what you state.
Jim

Jim is correct from my exp. I have seen or used a few sinars (2 Norma's, a few f's, an X and a P) all but one went (from lens back) GG (rough toward lens smooth out) then fresnel (ridged to gg smooth out in frame that snapped into place). The only exception was a photog who bought an un framed fresnel and put it mistakenly inside the gg (toward the lens). All his stuff was out of focus, but it still took him a year to figure it out...

He's a paid 'pro' to boot.

 

[Struan Gray]

I have a 5x7 Norma back with a Sinar original Fresnel that fits between the ground glass and the lens. It has small tabs on the side, thinner than the rest of the Fresnel, which move the ground glass back by the required amount to preserve film-plane registration. I have been told that only the 'early' Norma Fresnels were like this, the later ones - like the modern framed ones - going behind the ground glass.

 

[gwatson]

After doing research on this to solve my own problem, I'm amazed to find so many different opinions there are on this. (My problem, I concluded, was that I had two halves of two different focussing systems. I replaced the clear glass with gg, and the sun shines again.Thanks all)

However, it seems to me that the fresnel is a lens that distorts light. Therefore, regardless of where it goes, it will cause anomolies (albeit, sometimes very minor ones) with focussing. If the fresnel goes photographer-side of gg, then you are using the loupe on a distorted image; if it goes lens-side, the image forming on the gg is distorted. Is it not just an aid for composition that should be removed so you can focus on the gg?

Geoff

 

[Struan Gray]

If you put the Fresnel on the lens side of the ground glass it can, in principle, direct more light towards the eye. It is also better protected from scratching. This is why Sinar and Linhof both put their earliest Fresnels on the inside of the camera.

On the outside, it is easier to remove, so you can avoid seeing the grooves when focussing. Also, with wide angle lenses the Fresnel can become counterproductive if you use large shifts or tilts - it darkens the image, and unevenly too - so it's useful to be able to remove it simply and quickly. This is preferred by most photographers, so the Fresnel is usually mounted on the outside these days.

The biggest design problem with a Fresnel on the inside - particularly if you add your own Fresnel lens - is that it introduces a focus shift. More here:

http://largeformatphotography.info/lfforum/topic/501001.html