focusing 90mm with .58 finder?

[crane17]

I am a glasses wearer so I chose a 0.58 finder to see the 35 & 28 lines on my M7. Recently i have considered adding a 90mm lens but the finder lines seem so small. Is it possible to accurately focus with such a set up? or do I need to purchase a 1.25X eyepeice magnifier? (they cost several hundred so I have even considered adding an M3 as abck up and to use with the 90)

Also, anyone have any experience with the HK 1.25x eyepeice magnifier I have seen on ebay?- much cheaper at ~$50

Any advice is much appreciated!
Still new to this,
Crane 17

 

[aizan]

.58x leicas have an ebl of 40.16mm.
http://cameraquest.com/leica.htm

here are the minimum requirements from erwin puts:

75 1.4 40.2 mm
90 2.8 28.9 mm
90 2.0 40.5 mm

http://www.imx.nl/photosite/leica/technics/rfaccuracy.html

 

[StuartR]

I think you will be fine, but it depends on your eyesight. When I had a Hexar RF (.6x finder), I confidently used the 75/1.4 and 135/4 without too much trouble. The framelines are small for the 135, but if you are a bit flexible with your framing, the focus is certainly capable.

 

[JNewell]

Also depends on aperture in use. A 90/4 focuses fine on a CL, but a 90/2 or a 75/1.4 is if-fy at max apertures. Also, ANY lens at ANY aperture will focus "accurately" at infinity or near that - so there are several variables to consider.