Ground Glass for 4x5.

<p>Can I use a different Ground Glass and fresnel lens on my Sinar? On my Sinar the Fresnel fits on top on the Ground Glass, I hate that because you end up scratching up your fresnel. could I use a different brand GG and Fresnel on the Sinar? is the thickness of the Glass an issue? thanks.<br>

Any thoughs where I could get a 3rd party GG and Fresnel other then ebay?</p>

<p>Art, </p>

<p>Anything that moves the ground glass out of its current position (for example, placing a fresnel on the lens side) will throw your focus off.<br>

The only thing I can suggest is to be careful with the Sinar fresnel. Mine is quite old and still not too scratched up. Besides, it's nice to be able to remove it when you want. It also makes adding masks when shooting other formats extremely easy.<br>

You might contact S. K. Grimes and see if they have any suggestions.<br>

You might also post your query on the Large Format Forum if you haven't already.<br>

Joe D.</p>

<p>I'm not too sure what you wan tto accomplish, Art - get rid of the scratches on your fresnel or get rid of the fresnel in exchange for a brighter GG. Sure, you can replace both the GG and fresnel without upseting the focus but it might not do too much more for you than what you already have.</p>

<p>Scratches never bothered me, but if htey bother you why not just get rid of your fresnel. You can always replace it later if you want.</p>

<p>Thickness isn't much of an issue, but size is critical. Measure your current GG before buying!</p>

<p>There are some GGs out there that advertize to be brighter - I think both are available on ebay. I bought one from a company that isnow out-of-business, and antoehr from one of those ebay guys. I think they are indeed slightly brighter but not so much that I really noticed. In my case, both were very helpful because I fumbled my back (twice) and broke my GG.</p>

<p>You can remove the fresnel, but you can't move it in front of the ground glass without adjusting the spacing to account for the new arrangement. I don't know if this is easy or not on your Sinar.</p>

<p>You can replace your ground glass, but even the "bright" ones are not really much better in my experience. The thickness doesn't matter since the image is formed on the front edge (the ground part). The thickness may matter for the clips that hold it to your camera.</p>

<p>I cover my fresnel with a piece of mylar, and replace that when it gets scratched up. A cheap and easy solution.</p>

<p>Although I have used Sinar cameras, I don't own one or ever have I tried changing out the ground glass. But I would be sure to measure the ground glass before purchasing a new one to replace it with, unless the new one specifies that it will fit your camera camera. I do have several different brands of view cameras, field, technical and monorail, and the ground glass from one to the next do not always fit the other camera. Some work while others are too large or too small.</p>

<p>And you do not want to move the position of your ground glass, as mentioned above, it will change your focus and your film will not be sharp.</p>

<p>The ground glass on the Sinar F1 I owned was shimmed in place.</p>

<p>Graflex Corp. mounted their ground glass so that it was 1/2 the thickness of the Ektalite Field Screen used back from no Ektalite Field Screen or the optical center of the Ektalite/ground glass combination.</p>

<p>Check the ground glass frame opening where the ground glass sits. If it is wider than the ground glass-Fresnel combination then the Fresnel can be mounted in front of the ground glass and adjusted for correct focus, if not then the frame will need to be milled to accommodate the pair.</p>

<p>If you're going to put a Fresnel on the lens side of a GG screen, then the position of the GG needs to be adjusted for the thickness of the Fresnel by decreasing the distance of the GG/Fresnel combination from the lens. In other words the seating of the GG needs to be made slightly thinner in some way - e.g. milling, filing, scraping or removal of shims. The thickness of the GG itself shouldn't matter, since the ground-focusing side pushes toward the lens and against the Fresnel, but obviously any retaining clips need to have enough "give" to accommodate the extra thickness of a Fresnel screen.</p>

<p>The formula for the amount of seating adjustment is: Thickness of Fresnel divided by Refractive Index of Fresnel material. For most common optical plastics, the R.I. is about 1.5, therefore the reduction needs to be around 2/3rds of the physical thickness of the Fresnel screen, and not half as stated above. For example; if the Fresnel is 2mm thick, then the GG seating needs to be reduced by (2mm/1.5) = 1.33mm. An error of +/- 0.1mm is probably acceptable here, since cut film won't sit in a standard plastic DDS to anything much closer than this accuracy. </p>

<p>Your answer is simple....just get yourself a Maxwell screen (optical resin with incorporated fresnel) and put a protective cover glass (plain or gridded) over this. ....amazing brightness/sharpness/contrast!</p>

<p>ps...is Bill Maxwell still in business? I'd like to have him make me screens in 5X7 and 8X10 if possible.</p>

<p>Try maxwellprecisionoptics@yahoo.com (Maxwell Precision Optics, P.O. 33146, Decatur, GA 30033-0146).<br>

I bougth one of his Hi-Lux Brillant Matte screens and found it to be superior to my existing (very good) Ebony screen.<br>

His screens are expensive but in my opinion worth every cent.<br>

Another source for ground glass is www.hopfglass.com. I don't know if he makes fresnel screens, but I've heard his screens are very bright.</p>

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