Field Camera ground glass design

[Mike1234]

I just received my +6 reading glasses and gave them a try on my Toyo 810G GG. They work GREAT!! I'll never use another loupe of any sort including the tilting type. I can move my head around freely to few all corners with ease and both my hands are free. Plus I can view with both eyes for greater resolution. My eyes are +1.5 in error myopically so this compares to +4.5 to others without this issue. That said, I could use +8 or +10 for ultra-fine focus. I'm going to buy a +4 set for corse viewing and stack the +6 to slide on top for fine focusing. To HECK with loupes!!

[bobwysiwyg]

Mike,

Where did you find them? Not much selection where I am.

[wclavey]

I am going to bungle the words here, so please forgive me that... I know this in advance.

Back on the question and response about putting a fresnel between the lens and the GG, it was my understanding that a fresnel lens transmitted the light at a rate that was equivalent to only 67% of the equivalent amount of air... in other words, if you inserted a 2mm thick fresnel into the light path, that was the equivalent of moving the GG forward by 0.66mm (2.0 - (.67 * 2.0))mm.

Perhaps that is not true. But if it is, then inserting a screen that is fresnel on 1 side and GG equivalent on the other so that the GG surface is in the same place as a plain GG would have been is the equivalent of shifting the GG surface forward (toward the lens) by 33% of the thickness of the viewing screen, isn't it?

Again, my apologies for the brutally layman description of what I'm trying to say - - but I'm sure you who know what you are talking about will understand.

[Peter K]

Back on the question and response about putting a fresnel between the lens and the GG, it was my understanding that a fresnel lens transmitted the light at a rate that was equivalent to only 67% of the equivalent amount of air... in other words, if you inserted a 2mm thick fresnel into the light path, that was the equivalent of moving the GG forward by 0.66mm (2.0 - (.67 * 2.0))mm.

This will only work with a fresnel-lens with infinte focal-length, a clear plate.

But a fresnel-lens is at first a lens with the focal-lengt of e.g. 150mm that works together with the taking-lens as I've described here #36. So if you won't to calculate the compensating factor for not only every lens you're using but also for all different bellows-extentions, put the fresnel-lens behind the gg. It's easier.

[Mike1234]

Mike,

Where did you find them? Not much selection where I am.

I bought these on-line. I couldn't find anything stronger than +2.75 locally OTC here either.

http://www.speert.com/closeup.cfm?ID...1373&keywords=

[bobwysiwyg]

Thanks, Mike.