Fits 7artisans 50mm F1.1 on Bessa R2M

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BossesBilder

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There is a lens named "7artisans 50mm F1.1" with Leica bayonet but it looks a bit deep, so I wanna know if anyone have tried this lens on Bessa R2M.
 
I would be worried about focus accuracy of such a fast lens with the Bessas' short RF base.

Cheers
Dez
 
Anything over 100% is iffy, anything under is good.

Click on the OK/NOT OK button for a quicker result
 
splitimageview said:
Only the R4 is a problem with 50/1.1

Here is a link to the RF accuracy chart

https://docs.google.com/spreadsheets/d/1BWB8ZaryAV8Q6UlBGFs6I5wwj-MdxeaSkLP_kiZVQgY
Click to expand...


That chart shows errors for the MP
EBLs for the MP:

.58 39.7
.72 49.3
.85 + 1.2 magnifier 59.2
MP (.72?) + 1.5 magnifier 74

Problem is .85 + 1.2 magnifier, the result of 59.2 is incorrect. That would be the result of the .72 + 1.2 magnifier.

So, kinda discounting what I am seeing here. There's a whole lot of numbers, some which may or may not be correct, that results in a whole lot of nothing.

All that matters is :
1. That your camera's rf is correctly calibrated
and once that has been achieved
b. the EBL.
 
Huss said:
That chart shows errors for the MP
EBLs for the MP:

.58 39.7
.72 49.3
.85 + 1.2 magnifier 59.2
MP (.72?) + 1.5 magnifier 74

Problem is .85 + 1.2 magnifier, the result of 59.2 is incorrect. That would be the result of the .72 + 1.2 magnifier.

So, kinda discounting what I am seeing here. There's a whole lot of numbers, some which may or may not be correct, that results in a whole lot of nothing.

All that matters is :
1. That your camera's rf is correctly calibrated
and once that has been achieved
b. the EBL.
Click to expand...

I read that as 0.85 viewfinder OR 1.2 magnifier on the standard 0.72 viewfinder, not plus.

Even the Go/No Go part is odd since the 135mm f/2.8 lens doesn't seem to be a GO with any camera on the list. I wonder why Leica built one then?

Could easily be wrong though since that is one of the few things I think I understand with this chart.

EDIT - I guess we are getting a bit off topic here since the issue is the 7Artisans lens, not this chart. :D
 
Pioneer said:
I read that as 0.85 viewfinder OR 1.2 magnifier on the standard 0.72 viewfinder, not plus.
Click to expand...

Down to it's simplest terms, a .72 viewfinder with a 1.2 magnifier has a magnification of .72 * 1.2 = .864. Which is more than .85. So for a chart w/ lots of numbers and stuff, that still is obviously wrong.

;)

But you're right, this is about the Bessa. The lens will fit, but accuracy really is down to rf alignment primarily, then everything else.
 
This RF accuracy chart was originally a spreadsheet created by Roland (ferider) in this thread.

If there are errors, please point them out and I'll update the sheet.

In the 9+ years this has been extant, no one has pointed out any errors before, but that doesn't mean they don't exist. :)

The formula is shown on the spreadsheet:

b' = (e * f^2) / (k * z) where b' is the effective base length of the rangefinder, e the visual acuity (0.0003 at approx. 1 arcmin), f the focal length, k the aperture and z the circle of confusion (0.020mm for APS-C, 0.030mm for film)
 
Huss said:
That chart shows errors for the MP
EBLs for the MP:

.58 39.7
.72 49.3
.85 + 1.2 magnifier 59.2
MP (.72?) + 1.5 magnifier 74

Problem is .85 + 1.2 magnifier, the result of 59.2 is incorrect. That would be the result of the .72 + 1.2 magnifier.

So, kinda discounting what I am seeing here. There's a whole lot of numbers, some which may or may not be correct, that results in a whole lot of nothing.

All that matters is :
1. That your camera's rf is correctly calibrated
and once that has been achieved
b. the EBL.
Click to expand...

There are multiple MP models listed:

0.58x MP with an EBL of 39.7, column O
0.72x MP with an EBL of 49.3, column P
0.85x MP with 1.2x magnifier, EBL 69.9, column Q (this originally showed a 0.72x with a 1.2x magnifier but has been updated to correctly show 0.85x)
0.72x MP with 1.5x magnifier, EBL 74.0, column R

The effective base length is determined by the RF baselength (in this case 68.5mm) multiplied by the magnification, so for example the standard 0.72 MP would be 68.5 x 0.72 which would be 49.3.

When using a viewfinder magnifier the equation would then be the RF base times the viewfinder magnification times the viewfinder magnifier magnification.

Note that the 135/2.8 has goggles (i.e., a viewfinder magnifier.) The sheet needs to be updated to reflect this, although I'm not sure what the magnification factor is on this lens. EDIT: since updated to reflect 1.5x.
 
splitimageview said:
There are multiple MP models listed:

0.58x MP with an EBL of 39.7, column O
0.72x MP with an EBL of 49.3, column P
0.85x MP with 1.2x magnifier, EBL 69.9, column Q (this originally showed a 0.72x with a 1.2x magnifier but has been updated to correctly show 0.85x)
0.72x MP with 1.5x magnifier, EBL 74.0, column R

The effective base length is determined by the RF baselength (in this case 68.5mm) multiplied by the magnification, so for example the standard 0.72 MP would be 68.5 x 0.72 which would be 49.3.

When using a viewfinder magnifier the equation would then be the RF base times the viewfinder magnification times the viewfinder magnifier magnification.

Note that the 135/2.8 has goggles (i.e., a viewfinder magnifier.) The sheet needs to be updated to reflect this, although I'm not sure what the magnification factor is on this lens. EDIT: since updated to reflect 1.5x.
Click to expand...

Thanks for your help trying to explain this. This certainly takes rangefinder focus accuracy to a new level of complexity from my perspective. I will have to take some time with the calculations to get more comfortable with this. A quick comparison of the numbers between camera and rangefinder base lengths seems to show some unexpected results, but that certainly doesn't mean they are wrong, just unexpected.
 
Which ones are unexpected?

There are only two cameras that can have problems with the 50/1.1, one of which would likely have a blocked viewfinder anyway (CL) and the other is more of a specialty wide angle body (R4.)
 
splitimageview said:
Which ones are unexpected?

There are only two cameras that can have problems with the 50/1.1, one of which would likely have a blocked viewfinder anyway (CL) and the other is more of a specialty wide angle body (R4.)
Click to expand...

Relax. The chart is fine. It is just a lot for me to absorb quickly, especially when I am really supposed to be putting up Xmas decorations, not cruising the interweb and reviewing camera spreadsheets. :)

From what I can tell it really doesn't give a lot more useful information then the EBL numbers do, it just applies it to each lens. The EBL is still the determining factor. A longer effective base length means you can more accurately focus faster or longer lenses.

The unexpected part is when I look at the results for the MP with the 0.58 finder. I find it a bit confusing that this rangefinder can be expected to accurately focus a 50mm f/1 (or 1.1 since there is not a lot of difference) yet is not expected to accurately focus a 75mm f/ 1.4 lens. Even the CLE, with an EBL of 28.8 is supposed to be OK with a 50mm f/1 lens, but not OK with a 60mm f/1.2.

To me these results seem a bit odd and indicate that the calculations are more influenced by focal length than aperture. I don't doubt that the calculations are correct I just find the assumptions behind the calculations to be contrary to my own expectations.

Like I said, your spreadsheet is fine. It is more a function of my own expectations of focus accuracy between cameras with different effective base lengths. I just would not have expected to see that much difference between a 60/1.2 lens and a 50/1 lens.

EDIT - Of course when you factor in a half blind old Grandpa like me then your entire chart could be suspect. I have trouble focusing a 50/1.4 lens wide open with an M3. :D
 
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