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jaapv

M8-Focus on focussing

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The formula is quite simple, focal length/aperture x focal length/eyepiece magnification. However, on an SLR screen the focussing aids etc. are laid out for a virtual aperture of between 4.0 and 5.6 to avoid blocking, so for aperture the value of 45 should be inserted. For a completely matte screen other formulas apply, but the net resultaat is similar.

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next time i go to see Arsenal play i will definitely watch out for those m8/7/9 shooters who verify your theory. and i shall search for M and birds and dolphins and running dogs meanwhile.

incidentally, the (nikon and hasselblad) AF worked very well in the rice paddies, since the sensors are small enough (so that they do not see too much of the periodic structure).

peter

I'll save you the trouble. Dolphin: Summilux 75, Dogs, Summicron 90 AA, Gull TE 135 Now start working on your technique instead of your empty sarcasm.

Edited by jaapv

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The formula is quite simple, focal length/aperture x focal length/eyepiece magnification....

Which makes 6,328mm for a 135mm lens at f/4 and a 0.72x magnification? I suspect i'm missing something here.

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I'll save you the trouble. Dolphin: Summilux 75, Dogs, Summicron 90 AA, Gull TE 135 Now start working on your technique instead of your empty sarcasm.

 

why don't you show 100% crops of files, taken with wide open f stop? it is completely pointless to show f11 highly reduced files.

peter

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Don't use the Allen key - I've been told off pretty severely by Will van Manen for that. It may correct a misalignment on infinity, but it upsets the two other checkpoints for focus. Better to get a qualified technician to do the adjusting. It is a skilled job and one really needs a reference lens and a collimator.

 

Oh, dear! Thanks Jaap. I will have to remember that.

 

I did adjust my M8s which now focusses fine for all of my lenses except the 90f2.8 but it might mean a trip to Solms for the whole lot. What do you suggest?

 

I have the 75 summarit, 50 Summicron and the WATE which are not really focus critical I think.

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Sorry my mistake, focal length of eyepiece !

OK Jaap so what eyepiece focal length values did you take for your calculation?

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OK Jaap so what eyepiece focal length values did you take for your calculation?

 

Using Jaap's formula backwards on the numbers in his first post in this thread, the value is not constant across focal lengths. All figures are millimetres:

 

f B' EyepieceFL

21 1.63 60.09

35 4.43 61.45

50 9.82 56.57

90 29.20 61.64

135 65.70 61.64

Given the light path through the eyepiece and pentaprism a value of about 6cm seems reasonable, and differences in the third or fourth significant figure can be attributed to rounding errors ... but I'm extremely suspicious of the 50mm figure. Jaap, can you explain it? Is there perhaps a typo in your original "9.82"? (9.02 would fit much better.)

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Jaap,

we may be talking about different types of work here. Your outdoor shots would not present any difficulty for focus to me either.

 

Here's a sample of what is to me a more demanding situation with no chance of a second frame and where there's no opportunity to shoot the live action again.

 

Low light with zero daylight, 800 iso, f2.8, 1/80 second.

 

I can shoot this shot with an RF, but I need a moment longer and my hit rate drops. If I shoot tis with my 75mm Summilux at f1.4, I might get a 'nicer' image, but risk of error is too high and I'm paid to deliver.

 

Pleased this thread has stayed civil.

 

2nd shot at 640 ISO, f2.0, 1/80s. This is a shot I would happily do on my M's and have done many of this sort and expect a high hit rate, but I like to get near to 100% with a over 800 shots in a day.

Edited by Rolo

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Granted immediately, Rolo. The response was to the suggestion that for moving subjects rangefinderfocussing would be impossible to inaccurate. Btw- as opposed to the sneer all three images were at 5.6...

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Using Jaap's formula backwards on the numbers in his first post in this thread, the value is not constant across focal lengths. All figures are millimetres:

 

f B' EyepieceFL

21 1.63 60.09

35 4.43 61.45

50 9.82 56.57

90 29.20 61.64

135 65.70 61.64

Given the light path through the eyepiece and pentaprism a value of about 6cm seems reasonable, and differences in the third or fourth significant figure can be attributed to rounding errors ... but I'm extremely suspicious of the 50mm figure. Jaap, can you explain it? Is there perhaps a typo in your original "9.82"? (9.02 would fit much better.)

 

52/45 x 52/61.53 Summicron on universal focussing screen of an R camera. Not my figures, though, Gunther's

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Thank you Giordano but i still don't understand sorry.

I don't see any formula in Jaap's first post, just a series of numbers. The formula of his post # 41 above is "focal length/aperture x focal length/eyepiece magnification".

He explained that "focal length/eyepiece magnification" means "eyepiece focal length/eyepiece magnification" and you're suggesting that the eyepiece focal length value could be around 60mm.

I haven't heard of such a value before but again i'm not a techie at all. Just a poor lawyer trying to understand the arcanes of DoF and all that sort of things.

Now, i'm trying to apply this formula and it leads to a strange 2812mm value for a 135mm lens at f/4 and 0.72x magnification.

With a 0.95x magnification, i've got a result of 2131mm.

I must do mistakes somewhere but so far i can't seem to understand the meaning of those figures nor can i see in what they can be compared to the effective or mimimum base length of a rangefinder.

Thanks for your help.

 

______________

 

Using Jaap's formula backwards on the numbers in his first post in this thread, the value is not constant across focal lengths. All figures are millimetres:

 

f B' EyepieceFL

21 1.63 60.09

35 4.43 61.45

50 9.82 56.57

90 29.20 61.64

135 65.70 61.64

 

Given the light path through the eyepiece and pentaprism a value of about 6cm seems reasonable, and differences in the third or fourth significant figure can be attributed to rounding errors ... but I'm extremely suspicious of the 50mm figure. Jaap, can you explain it? Is there perhaps a typo in your original "9.82"? (9.02 would fit much better.)

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Thank you Giordano but i still don't understand sorry.

I don't see any formula in Jaap's first post, just a series of numbers. The formula of his post # 41 above is "focal length/aperture x focal length/eyepiece magnification".

He explained that "focal length/eyepiece magnification" means "eyepiece focal length/eyepiece magnification" and you're suggesting that the eyepiece focal length value could be around 60mm.

I haven't heard of such a value before but again i'm not a techie at all. Just a poor lawyer trying to understand the arcanes of DoF and all that sort of things.

Now, i'm trying to apply this formula and it leads to a strange 2812mm value for a 135mm lens at f/4 and 0.72x magnification.

With a 0.95x magnification, i've got a result of 2131mm.

I must do mistakes somewhere but so far i can't seem to understand the meaning of those figures nor can i see in what they can be compared to the effective or mimimum base length of a rangefinder.

Thanks for your help.

 

______________

 

All I did was take Jaap's formula from post #41 as corrected in post #44, which can be presented as an equation:

 

measuring base = focal length/aperture x focal length/eyepiece focal length

 

I then substituted in each pair of values (focal length and measuring base) from post #1, assumed an aperture of f/4.5 (#41), and then solved each time for eyepiece focal length - getting that series of values around 6cm.

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The word magnification is wrong, the formula is: focal length/aperture* x focal length/focal length of viewfinder. That will give you the measuring base of an SLR camera.

 

* For technical reasons on anR camera with the universal focussing screen this value is 45.

 

I would suggest we accept the values as given. It is extremely unlikely that Günther Osterloh, Jonathan Eastland and Erwin Puts are all wrong, as they arrive at the same numbers.

 

Btw, I just found another thread on the subject:

http://www.l-camera-forum.com/leica-forum/leica-m8-forum/26329-real-men-use-manual-af-birds.html

Edited by jaapv

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Thank you Giordano but this way the SLR values are very close to those of the M8. And this does not change the fact that long lenses are difficult to focus with the latter for the simple reason that whatever CoC value one chooses reasonably (0.026mm and 0.0188mm below), the effective base length of its rangefinder (47.09mm) remains smaller that the requested one (53.87mm & 64.64mm for a 135mm lens at f/4.5 below). Right?

 

All I did was take Jaap's formula from post #41 as corrected in post #44, which can be presented as an equation:

 

measuring base = focal length/aperture x focal length/eyepiece focal length

 

I then substituted in each pair of values (focal length and measuring base) from post #1, assumed an aperture of f/4.5 (#41), and then solved each time for eyepiece focal length - getting that series of values around 6cm.

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...For technical reasons on anR camera with the universal focussing screen this value is 45...

You mean f/4.5 i guess?

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You mean f/4.5 i guess?
The experts seem to transpose that to 45. But yes, it is based on 4.5 I suppose.. It depends if you use Cm or Mm in the original aperture calculation, I guess.

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Jaap,

we may be talking about different types of work here. Your outdoor shots would not present any difficulty for focus to me either.

 

Here's a sample of what is to me a more demanding situation with no chance of a second frame and where there's no opportunity to shoot the live action again.

 

Low light with zero daylight, 800 iso, f2.8, 1/80 second.

 

I can shoot this shot with an RF, but I need a moment longer and my hit rate drops. If I shoot tis with my 75mm Summilux at f1.4, I might get a 'nicer' image, but risk of error is too high and I'm paid to deliver.

 

Pleased this thread has stayed civil.

 

2nd shot at 640 ISO, f2.0, 1/80s. This is a shot I would happily do on my M's and have done many of this sort and expect a high hit rate, but I like to get near to 100% with a over 800 shots in a day.

 

Nice images, Rolo. And you are right.

 

Nicer image vs missing the critical shot, I'd pick the safer route myself and used a DSLR myself. Used my M8 at my sis-in-law's wedding and not having the pressure to deliver

 

50mm Zeiss C Sonnar at f1.4

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Jaap,

we may be talking about different types of work here. Your outdoor shots would not present any difficulty for focus to me either.

 

Here's a sample of what is to me a more demanding situation with no chance of a second frame and where there's no opportunity to shoot the live action again.

 

Low light with zero daylight, 800 iso, f2.8, 1/80 second.

 

I can shoot this shot with an RF, but I need a moment longer and my hit rate drops. If I shoot tis with my 75mm Summilux at f1.4, I might get a 'nicer' image, but risk of error is too high and I'm paid to deliver.

 

Pleased this thread has stayed civil.

 

2nd shot at 640 ISO, f2.0, 1/80s. This is a shot I would happily do on my M's and have done many of this sort and expect a high hit rate, but I like to get near to 100% with a over 800 shots in a day.

Indeed we are talking different things here. If professional, I would not chance missing those shots either, even if it were my fault and not the camera's Even as an amateur I would opt for certainty.

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Oh, dear! Thanks Jaap. I will have to remember that.

 

I did adjust my M8s which now focusses fine for all of my lenses except the 90f2.8 but it might mean a trip to Solms for the whole lot. What do you suggest?

 

I have the 75 summarit, 50 Summicron and the WATE which are not really focus critical I think.

I would send the lot to Will. Faster and cheaper and as least as good.

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