G & M focusing screen identification in a850 & a900

[XKAES]

Does anyone know of a way to determine if an a850 or a900 camera has a G or an M focusing screen without removing the focusing screen from the camera?  With the L screen it is easy because you can see the grid.

[SnappyMilt]

I don't know about the G screen (is that the screen that comes with the camera?), but I have an M screen (FDA-FM1AM), and it has no markings whatsoever. It is a fully unmarked "ground glass" type focusing screen. I assume you want to know how to set the focusing screen type in the tool menu, <tool3> -> <Focusing Screen> ? Otherwise, if you assume that option is set correctly, you can just look there!

[XKAES]

Thanks, but I'm not trying to figure out how to set the screen type in the menu.

The G screen is the standard screen.  The M screen makes it easier to check "peak focus" (whatever that means) with faster f-stop lenses (ex. f1.4, f2.8) according to the manual.

I'm trying to figure out what screen I have without having to take out the screen.  I know I don't have the L screen because that has a visible grid.

If the G and M screens look exactly the same in the viewfinder, them I'll have to take out the screen to see.

I'm hoping that there is some minor difference that can be seen in the viewfinder, but I have no idea what that is??????

[michelb]

There is very little info on these even in the books i looked at.

 

See attached a picture of the instructions sheet that came with my FDA-FM1AM and as you can see it shows both the FM1AM and FL1AM and if you look closely, you will notice there are tabs all around and the ones on the right side are a different shape. I don't have a picture of the G screen but my guess is the G screen will have a differently shaped tab on its right side also giving it its differentiation.

My M screen has that tab shaped exactly like on the drawing

trouble is to see that, you need to remove the original screen from the camera as it is hidden behind the frame that holds it down

 

Let us know if you see a difference

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Edited October 15, 2021 by michelb

[SnappyMilt]

I just swapped out the G screen for the M screen in my a900. Unfortunately, there is no visible difference between the two in the viewfinder. There is a difference in exposure, however, if you don't have the correct screen selected. The exposure for my test scene with the G screen was 1/40 at f/5.6. If I changed the menu to indicate the M screen instead, the exposure changed to 1/60 at f/5.6. With the M screen installed and M selected in the menu, the exposure returned to 1/40 at f/5.6. For what it's worth, I have attached two images of the two screens below -- G screen on top and M screen on the bottom. The first image clearly shows the difference in the upper tab on the right. The second image shows the difference in the reflection of my work light. The reflection in the G screen is more focused and shows a definite interference pattern. The reflection in the M screen is more diffuse and the interference pattern is much less distinct. 

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[SnappyMilt]

FYI, the bulb being reflected in the second photo is a clear bare incandescent bulb.

[SnappyMilt]

Quote

There is very little info on these even in the books i looked at.

Gary Friedman devotes three whole pages to explaining the three different focusing screens (concentrating on the M screen), explaining the history behind the M screen, and explaining how best to use it. See pages 57-60 in Chapter 2 of Gary Friedman's excellent book, "The Complete Guide to Sony's Alpha 850 & 900". Mr. Friedman has excellent books on all of Sony's still cameras. 

[SnappyMilt]

If you are interested, here is the link to Gary Friedman's web site:

https://www.friedmanarchives.com/Alpha900/

 

[SnappyMilt]

So, to find out which focusing screen is installed without removing the screen, take a photo of an 18% gray card with a camera you trust. Then photograph the gray card with your a900 set to G screen and with it set to M screen. The photo whose exposure matches the photo taken with the camera you trust will be the one set to the screen you have installed.

[XKAES]

Thanks very much.  I have not heard of Gary's book, but I will definitely check it out.

As to the screen, you have confirmed my suspicion.  Since the screens are not difficult to remove, I'll just take it out and check it visually.

It sounds like the M screen is the better screen even if you don't have "fast" lenses.  I had assumed it should only be used if your have fast lenses.

[SnappyMilt]

According to Gary's book, the M screen is not as bright as the G screen. Do you have the special tool for removing and inserting the screens?

Edited October 15, 2021 by SnappyMilt
Added a question.

[XKAES]

Thanks for that tip.  Screen brightness is something to consider -- especially since most of my lenses are not "fast".

As to the special tool, I don't need it.  The screen is pretty easy to remove with a small screwdriver and a pair of tweezers -- I've done it before.  It's much easier than with the older Minolta screens, but it is important to be careful, of course.

[XKAES]

Just a follow-up to my original post.

I checked out the focusing screen that I have, and it's a G-screen, as I suspected.  I bought the camera used, and the screen type was set to M, not G in the menu.  I thought that odd because the camera only has about 12,000 exposures -- and that some people probably think that by changing the screen setting in the MENU provides you with the benefits of the actual screen.

I've reset it to G-screen in the menu, so I'm all set.  The screen does have a few minor scratches on it -- so someone had "messed" with it -- but I can live with it until I find a replacement -- apparently not easy to find at a decent price.