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Ground Glass Brightness

 
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DHF845



Joined: 20 Jul 2008
Posts: 93
Location: Hudson Valley Area, Upstate NY

PostPosted: Thu Jan 01, 2009 10:43 pm    Post subject: Ground Glass Brightness Reply with quote

Did Graflex use a special type of mirror or ground glass on the Series D?
I just got my first Series D Graflex, an RB Series D [3-1/4 x 4-1/4 in.] (s.n.173062, I think that makes it circa 1931).
I first realized the difference when shooting indoors by available light. Since then, I've done side-by-side comparisons. The Series D has a brighter, clearer viewing screen. Its ground glass image looks 2 stops brighter (to me) than my other Graflexes, even a post-war RB Series B [2-1/4 x 3-1/4 in.] with Ektalite view screen (all have similar f-4.5 standard lenses).
Did interchangeable lens-board models get better mirrors and ground glass? Can I make my Series B's viewfinder image as bright as my Series D's?
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sevo



Joined: 18 Oct 2008
Posts: 34
Location: Germany

PostPosted: Fri Jan 02, 2009 2:17 pm    Post subject: Reply with quote

Not that I am aware of. Going by old reviews and ads (one of them referenced in an old posting here), later (post mid thirties) Graflexes had front surface coated mirrors, but yours would seem to be older than that, and in any case, few people have seen a Graflex with old front coated mirror in the wild - most of them presumably dulled and got replaced by a rear coated mirror ages ago.

Many, if not most old LF reflexes (with front mirror) have dulled mirrors - the only still perfect LF reflex front surface mirrors I've ever seen were on cameras from the Zeiss Ikon group, and may have been made by the Zeiss telescope branch (who had mirror technologies way beyond any other camera maker). And rear coat mirrors sometimes are in a bad shape as well.

The ground glass on Graflexes is not dark, provided that it is clean - indeed, it is bright compared to modern view camera ground glass, as that tends to be optimized for wide angles and large movements, which both need wide scattering rather than narrow angle brightness. It might be that the ground glass on your B was replaced with a view camera glass at some time.

In any case, it might just be a matter of dirt - before you do anything else, clean the dull cameras ground glass and mirror (unless you have a front coated mirror).


Last edited by sevo on Sat Jan 03, 2009 6:11 pm; edited 1 time in total
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DHF845



Joined: 20 Jul 2008
Posts: 93
Location: Hudson Valley Area, Upstate NY

PostPosted: Sat Jan 03, 2009 9:22 am    Post subject: Mirrors and Ground Glass Reply with quote

I have 3 Graflexes that I use as primary photo equipment-the 3 x 4 Series D, the late-model 2 x 3 Series B, and a National Graflex Series II. They're all near mint, I got them that way. They've all been carefully cleaned and serviced, all have scratch-free mirrors.
The ground glass on all 3 seems like the fine grain type. No indication that any of them were ever repaired or retrofitted. They were unmolested, little-used specimens I was lucky to find. The Series D just has a much brighter screen image. Its mirror does seems like it's optical or telescope quality, but I'm pretty sure it's the original mirror.
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sevo



Joined: 18 Oct 2008
Posts: 34
Location: Germany

PostPosted: Sat Jan 03, 2009 7:23 pm    Post subject: Reply with quote

It is easy to see whether it is a front or rear coated mirror - on a front coated one, there is no gap between anything held to the mirror and its reflection.

Going by another thread (http://www.graflex.org/helpboard/viewtopic.php?t=3754), yours would be some years too early for a front surface mirror - it might have been optional back then, or may have been installed during some repair.

One other thing you may have to take into account is the focal length - longer lenses with the same aperture will deliver a subjectively brighter ground glass image, as more light is on axis towards the eye.

Sevo
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DHF845



Joined: 20 Jul 2008
Posts: 93
Location: Hudson Valley Area, Upstate NY

PostPosted: Sun Jan 04, 2009 1:41 am    Post subject: Reply with quote

I read that thread some time ago. Goes to show how we disagree when interpreting Graflex history. Re: The light-gathering effects of longer lenses, I can recall studying that in optical theory in art school, but I forgot that part of the lesson.
I found this: http://photo.net/large-format-photography-forum, "Graflex RB series D how to replace MIRROR". Lots of detailed info.
I probably have the date wrong on my Series D (Help, Gandolf!). I don't know how much batch orders caused different model cameras to be built out of numerical sequence vis-a-vis total production. Finally, a factory mirror replacement would leave little or no trace.
The bottom line is my 'new' Series D was an expensive pro-grade camera. It had an easy life. My 2x3 Series B's and National Graflex were less expensive, marketed to amatuers, and not maintained. This affects the quality of the mirror I see today. If I want a brighter image in my 2x3 RB Series B and National Graflex, I'll need to replace the mirrors.
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