Graphic focus question.

[ulysses19]

I have a Crown Graphic with a 150mm Xenar. When I bought the camera the ground glass was broken, so I bought a replacement panel on ebay. I feel like my images are not as sharp as they should be upon enlargement. I was reading on Graflex.org that some Graphics originally came with a fresnel and that replacing the ground glass without a fresnel would change the plane of focus by roughly 1mm. Is this really enough to throw off critical focus at infinity, lets say, while shooting landscape stuff? Or is it more likely that this old Xenar is just not all that sharp (especially at the corners)? There definitely was not a fresnel on the camera when I bought it, but obviously I can't say anything about the previous four decades of its existence. Any help would be greatly appreciated including suggestions for affordable but sharp modern 150mm's or 90mm's that I could replace the Xenar with. Thanks.

 

[Nick Zentena]

Xenar if stopped down and not using too much movements should be fine. Is the centre off? Or the corners?

Is the camera true? The front standards not bent etc?

How are you focussing? Do you check after you stop down?

 

[ulysses19]

focus

I shot at f/32 (as far down as the lens goes). The camera appears to be in good all around condition, but obviously any Crown Graphic has seen some miles. I would say the corners are not as sharp as I want them to be. My previous experience with large format is with new lenses and cameras, so maybe I am just expecting way too much from older equipment.

<todd>

 

[Nick Zentena]

No the Xenar and camera if in good state should focus just fine.

Won't have all the coverage of the latest greatest lens. Won't have the latest coatings. But it should be sharp enough.

http://www.hevanet.com/cperez/testing.html#100mm_thru_163mm

There is a 150mm Xenar in those tests. Some of those lenses are likely older then yours and do fine for sharpness.

 

[ulysses19]

focus

Sorry, just took a look at my Xenar. It is acutally a 135mm/4.7. The Xenar that came with the camera was a 150, but i replaced it with this lens. The front standard looks true and the lens is clean and clear. Perhaps I just suck at focusing my camera. It has a four bladed pop out hood so using a loupe is out of the question. Guess I'll shoot some more film and see how it looks. Thanks for the info and help.

<todd>

 

[Jim Jones]

Todd -- If your Crown has the common Graflok back, the pop out hood can be removed by depressing one of the catches on either side of the hood.

 

[Dan Fromm]

Todd, if the center is sharp then you don't have a focusing problem. The 135/4.7 Xenar doesn't quite cover 4x5 and will give you soft corners. CHECK CENTRAL SHARPNESS.

 

[David H. Bebbington]

One more thing to check - installation sequence (looking at camera from rear) is fresnel screen FIRST (underneath) with patterned side facing back and the ground glass on top. Ground glass installed alone will be approx. 2 mm too close to the lens.

Regards,

David

 

[Dan Fromm]

David, todd, Pacemaker Graphic focusing panels were delivered without and with fresnels. Same castings, same casting numbers. Those with have the bosses on which the ground glass sits machined down, those without don't.

It isn't safe to assume that because there's no fresnel there used to be one.

The OP should sacrifice a sheet of film to find out whether what seems to be in focus at the center of his camera's GG is also in focus on film. If I were doing it, I'd take the test shot at f/8.

 

[razzledog]

Ground glass position

I have noticed that many Graflok backs have fresnels fitted but some do not. The difference of 1mm will throw your focus to the wind, (0.02mm is probably too much) so you may as well shoot pinhole! Measure the depth from the contact pads of the focusing panel to the glass, remembering that the screen faces rough side toward the lens.

It should measure within a bee's dick of 5mm. The fresnels I've had are usually between 1-1.5mm thick and if installed, must have their rough side facing the glass....so they are assembled rough facing rough. The exact positioning of the ground glass is imperative if you want razor sharp negs. The fitting of a fresnel doesn't affect the focus plane, only helps to spread the light from the image.

The Graflok focusing panels are machined out to suit either fresnel or not.

Hope that helps.

 

[Ole]

I shot at f/32 (as far down as the lens goes).
...
I would say the corners are not as sharp as I want them to be. ...

Try at f:16 or f:22 - at f:32 you're in "diffraction land".

The corners won't be as sharp as the center with a 135mm tessar-type lens, but at least you'll be able to see if the center is sharp!

 

[Les Newcomer]

If the ground glass frame was designed for a fresnel, then the ground glass alone would rattle horribly and you might find filler stuff (cardboard shims) either under the fingers at each side or between the glass and the frame.

conversely, if the frame was not designed for fresnel and it had one, those fingers would be bulging and straining.

 

[Dave Miller]

Since this camera/lens combination was designed to feed the newsprint trade are you perhaps expecting too much by way of definition?

 

[Ian Grant]

I use a Crown Graphic and 1937 135mm Tessar, with a plain screen and the images are as sharp as those from my Wista and modern Rodenstock Sironar N.

Ian

 

[ulysses19]

dumb

After reading through responses to my query I decided to take a closer look at the ground glass. Lo and behold, the GG was in backwards (rough side facing out, smooth facing the lens). Not sure if that would really affect focusing, but I will shoot some test shots with the GG as it should be and see what comes out. Thanks.