Home

Please support mflenses.com if you need any graphic related work order it from us, click on above banner to order!
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

My truth about some Minolta MD and Canon fifties
Post new topic   Reply to topic
Home   Manual Focus Lenses
View previous topic :: View next topic  


PostPosted: Wed Mar 29, 2023 10:33 am    Post subject: My truth about some Minolta MD and Canon fifties Reply with quote
Take the following with a grain of salt.

Canon nifty fifty is a lier, despite the fact I love it very much.

On a tripod with constant illumination set up you Canon FD 1,8 at max aperture and record the speed. Next, same thing with Minolta MD 50 2,0. Same speed. Record the difference between f2,0 and f2,8 on the MD, you will loose half the speed. so F2,0 is "correct" on the Minolta.

F1,8 is not correct on the Canon and, up to 3,5, all f stops are somewhat optimistic.

I already noted that with another setup. Put the camera on a tripod and focus on a near object and observe the size of the bokeh balls on the background wide open with the Canon and let us say the Minolta MD 50 1,7. The size of the bokeh balls on the Minolta is noticeably bigger evidencing a wider aperture despite the 0,1 f stop difference.

I consider that we are discussing aperture issues, not transmission, since all glasses are clean and the number of elements is sufficiently low to avoid taking them into consideration.

This is confirmed by the bokeh balls test that is not related to transmission.

So now I did compare at infinity the sharpness of the Canon FD 1,8 and the Minolta MD 1,7, 2,0 and 1,4 at f2,0, 2,8 and 4,0 and the differences are so subtle that there is no point posting images that would be too similar.

On a side note, MD 50 1,7 is rather week wide open, at true 1,7. It is a little bit difficult to select f2,0 due to the lack of stop on the aperture ring so you have to start from f2,8 and locate the point on the aperture ring that will provide you with twice the speed, surprisingly physically close from the f2,8 stop.

So now you have true f2,0 on the MD 1,7 and you can compare with the famous 50 2,0 MDIII considered the best full open. Same results.

So the 1,7 is not the lesser lens, it just provides you with a weaker wider aperture you are free to use.

Happy pics to all.


PostPosted: Wed Mar 29, 2023 11:33 am    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
lumens pixel wrote:
...The size of the bokeh balls on the Minolta is noticeably bigger evidencing a wider aperture despite the 0,1 f stop difference.

I consider that we are discussing aperture issues, not transmission, since all glasses are clean and the number of elements is sufficiently low to avoid taking them into consideration.

This is confirmed by the bokeh balls test that is not related to transmission.
...
Happy pics to all.


My tests show bokeh ball size is related to focus distance. Certainly the difference in shutter speed is indeed due to different transmission.


PostPosted: Wed Mar 29, 2023 11:44 am    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
visualopsins wrote:
lumens pixel wrote:
...The size of the bokeh balls on the Minolta is noticeably bigger evidencing a wider aperture despite the 0,1 f stop difference.

I consider that we are discussing aperture issues, not transmission, since all glasses are clean and the number of elements is sufficiently low to avoid taking them into consideration.

This is confirmed by the bokeh balls test that is not related to transmission.
...
Happy pics to all.


My tests show bokeh ball size is related to focus distance. Certainly the difference in shutter speed is indeed due to different transmission.


In this case focus distance was exactly the same. Camera on a tripod I focused on a near fixed object and observed the bokeh ball in the distance. I changed the lens without moving the camera, refocused on same object and observed the same bokeh balls. So distance here cannot be the problem.


PostPosted: Wed Mar 29, 2023 11:54 am    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
lumens pixel wrote:
Take the following with a grain of salt.

Canon nifty fifty is a lier, despite the fact I love it very much.

On a tripod with constant illumination set up you Canon FD 1,8 at max aperture and record the speed. Next, same thing with Minolta MD 50 2,0. Same speed. Record the difference between f2,0 and f2,8 on the MD, you will loose half the speed. so F2,0 is "correct" on the Minolta.

F1,8 is not correct on the Canon and, up to 3,5, all f stops are somewhat optimistic.

I already noted that with another setup. Put the camera on a tripod and focus on a near object and observe the size of the bokeh balls on the background wide open with the Canon and let us say the Minolta MD 50 1,7. The size of the bokeh balls on the Minolta is noticeably bigger evidencing a wider aperture despite the 0,1 f stop difference.

I consider that we are discussing aperture issues, not transmission, since all glasses are clean and the number of elements is sufficiently low to avoid taking them into consideration.

This is confirmed by the bokeh balls test that is not related to transmission.

So now I did compare at infinity the sharpness of the Canon FD 1,8 and the Minolta MD 1,7, 2,0 and 1,4 at f2,0, 2,8 and 4,0 and the differences are so subtle that there is no point posting images that would be too similar.

On a side note, MD 50 1,7 is rather week wide open, at true 1,7. It is a little bit difficult to select f2,0 due to the lack of stop on the aperture ring so you have to start from f2,8 and locate the point on the aperture ring that will provide you with twice the speed, surprisingly physically close from the f2,8 stop.

So now you have true f2,0 on the MD 1,7 and you can compare with the famous 50 2,0 MDIII considered the best full open. Same results.

So the 1,7 is not the lesser lens, it just provides you with a weaker wider aperture you are free to use.

Happy pics to all.



Hello,

i've been quite intrigued by your findings and I wanted to reproduce your results wide open with the MD III 50 mm f/2, the nFD 50 mm f/2 and the nFD 50 mm f/1,8 (I didn't bother with the FD 50 mm f/1,8 SSC and the MD III 50 mm f/1,7 because they are packed away in boxes...).

So I've put my Sony A7 II on a solid tripod, the exposure mode on Manual (M) and the mesure on Spot.

1. with the Canon nFD 50 mm f/2 wide open, I've recorded an exposure at f/2 at 1/250s and 100 ISO.


2. with the Minolta MD III 50 mm f/2 wide open, I've recorded an exposure at f/2 at 1/250s and 100 ISO.

3. with the Canon nFD 50 mm f/1,8 wide open, I've recorded an exposure at f/1,8 at 1/320s and 100 ISO.

4. with the Canon nFD 50 mm f/1,8 slightly closed down, I've recorded an exposure at approximately f/2 at 1/250s and 100 ISO.

So, for my lenses at least, everything is like it should be. The trick is to measure the exposure in Spot mode, since all lenses suffer from vignetting wide open and the vignetting pattern varies from one lens to another. The heavier the vignetting, the more the meter in Average or Multizone mode tends to compensate by over exposing (thus, the T value seems to be lower than it is in reality...).


#1


Canon nFD 50 mm f/2 wide open


#2


Minolta MD III 50 mm f/2 wide open


#3


Canon nFD 50 mm f/1,8 wide open

#4


Canon nFD 50 mm f/1,8 slightly closed down to about f/2.

So, the Canon nFD 50 mm f/1,8 is not a fraud and I agree with you that it is a usually much undervalued lens.

Best regards


[/img]


PostPosted: Wed Mar 29, 2023 12:14 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
Alsatian2017 wrote:
lumens pixel wrote:
Take the following with a grain of salt.

Canon nifty fifty is a lier, despite the fact I love it very much.

On a tripod with constant illumination set up you Canon FD 1,8 at max aperture and record the speed. Next, same thing with Minolta MD 50 2,0. Same speed. Record the difference between f2,0 and f2,8 on the MD, you will loose half the speed. so F2,0 is "correct" on the Minolta.

F1,8 is not correct on the Canon and, up to 3,5, all f stops are somewhat optimistic.

I already noted that with another setup. Put the camera on a tripod and focus on a near object and observe the size of the bokeh balls on the background wide open with the Canon and let us say the Minolta MD 50 1,7. The size of the bokeh balls on the Minolta is noticeably bigger evidencing a wider aperture despite the 0,1 f stop difference.

I consider that we are discussing aperture issues, not transmission, since all glasses are clean and the number of elements is sufficiently low to avoid taking them into consideration.

This is confirmed by the bokeh balls test that is not related to transmission.

So now I did compare at infinity the sharpness of the Canon FD 1,8 and the Minolta MD 1,7, 2,0 and 1,4 at f2,0, 2,8 and 4,0 and the differences are so subtle that there is no point posting images that would be too similar.

On a side note, MD 50 1,7 is rather week wide open, at true 1,7. It is a little bit difficult to select f2,0 due to the lack of stop on the aperture ring so you have to start from f2,8 and locate the point on the aperture ring that will provide you with twice the speed, surprisingly physically close from the f2,8 stop.

So now you have true f2,0 on the MD 1,7 and you can compare with the famous 50 2,0 MDIII considered the best full open. Same results.

So the 1,7 is not the lesser lens, it just provides you with a weaker wider aperture you are free to use.

Happy pics to all.



Hello,

i've been quite intrigued by your findings and I wanted to reproduce your results wide open with the MD III 50 mm f/2, the nFD 50 mm f/2 and the nFD 50 mm f/1,8 (I didn't bother with the FD 50 mm f/1,8 SSC and the MD III 50 mm f/1,7 because they are packed away in boxes...).

So I've put my Sony A7 II on a solid tripod, the exposure mode on Manual (M) and the mesure on Spot.

1. with the Canon nFD 50 mm f/2 wide open, I've recorded an exposure at f/2 at 1/250s and 100 ISO.


2. with the Minolta MD III 50 mm f/2 wide open, I've recorded an exposure at f/2 at 1/250s and 100 ISO.

3. with the Canon nFD 50 mm f/1,8 wide open, I've recorded an exposure at f/1,8 at 1/320s and 100 ISO.

4. with the Canon nFD 50 mm f/1,8 slightly closed down, I've recorded an exposure at approximately f/2 at 1/250s and 100 ISO.

So, for my lenses at least, everything is like it should be. The trick is to measure the exposure in Spot mode, since all lenses suffer from vignetting wide open and the vignetting pattern varies from one lens to another. The heavier the vignetting, the more the meter in Average or Multizone mode tends to compensate by over exposing (thus, the T value seems to be lower than it is in reality...).


#1


Canon nFD 50 mm f/2 wide open


#2


Minolta MD III 50 mm f/2 wide open


#3


Canon nFD 50 mm f/1,8 wide open

#4


Canon nFD 50 mm f/1,8 slightly closed down to about f/2.

So, the Canon nFD 50 mm f/1,8 is not a fraud and I agree with you that it is a usually much undervalued lens.

Best regards


[/img]


Interesting Volker and I have to check again. Nevertheless that would not solve the bokeh ball difference.

I am not sure if spot metering is the best approach. Let us consider that FD 1,8 is indeed f2,0 but suffers from more vigneting than MD 1,7, spot metering in the center would be the same while there would be an aperture difference. So maybe your test is not conclusive. I would suggest you test the bokeh balls size and tell us your findings.


PostPosted: Wed Mar 29, 2023 12:18 pm    Post subject: Reply with quote
Naught, naughty Canon! Wink

A few points to take into account.

Caveat to what I am saying below: I only have experience with servicing and adjusting apertures of Minolta manual focus lenses.

Old-style apertures of preset-era lenses were much more accurate. Not only more blades, but also the mechanical geometry ensured they were much more accurate. The two pins setting the blade location in preset-era lenses are set far apart at opposing ends of the blade, i.e. each blade is an arc-shape that is pulled across the open aperture.

The modern aperture blade geometry has the two blade location pins set relatively close to each other at the same end of the aperture blade. These blades are finger-shaped and are pushed into the open aperture.

The modern construction has less friction, is faster, and is hence more suited to automatic aperture mechanisms BUT: they are less accurate. Adjustment/calibration is far more finicky on these, and minute adjustments of the adjustment mechanism results in rather large differences in apertures.

The modern apertures should be properly calibrated when fresh out of the factory, but any service afterwards is likely to result them being a bit off unless the service centre (or DIY enthusiast) takes appropriate care and recalibrates. On some later Minolta (MF) lenses, merely loosening (not removing) the 4 mount screws a bit and immediately tightening them back up again can take the aperture settings out of calibration. Just so you know.

Open aperture should be well defined, provided that at that setting the aperture blades are designed to be fully retracted.

Finally, it is a minor matter, but f/# stops (not N.A. numerical apertures), are defined as the ratio of the effective focal length of the lens to the diameter of the ENTRANCE pupil, not the diameter of the EXIT pupil (or physical aperture stop diameter for that matter). Counterintuitive I know, but that's the way it is. Depending on lens design/construction that does therefore mean that two lenses of equal focal length with equal f/# stops do not necessarily have exactly the same bokeh-ball size.

Of course with your Canon lens they still may have been bit optimistic with their aperture spec...

Last edited by RokkorDoctor on Wed Mar 29, 2023 1:04 pm; edited 2 times in total


PostPosted: Wed Mar 29, 2023 12:44 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
lumens pixel wrote:


Interesting Volker and I have to check again. Nevertheless that would not solve the bokeh ball difference.

I am not sure if spot metering is the best approach. Let us consider that FD 1,8 is indeed f2,0 but suffers from more vigneting than MD 1,7, spot metering in the center would be the same while there would be an aperture difference. So maybe your test is not conclusive. I would suggest you test the bokeh balls size and tell us your findings.


Spot metering is the one and only approach since you want to exclude the influence of vignetting on exposure Smile

The exposure difference in Average or Multizone metering mode is the direct result of the stronger vignetting in the Canon lens. Have you seen my pictures - there are no differences in luminance in all four pictures which is consistent with my findings. Chasseur d'images tested the following vignetting values wide open : nFD 50 mm f/2 (0,5 IL), nFD 50 mm f/1,8 (same lens but without light reduction ring in front of the aperture, 0,7 IL), Minolta MD III 50 mm f/2 (0,6 IL) and MD III 50 mm f/1, 7 (0,7 IL). What's important for exposure evaluation by the cameras lightmeter, is not only the absolute amount of vignetting in the extreme corners, but its distribution pattern throughout the frame. Fall-off might be faster with the Canon lenses and slower, smoother with the Minoltas.

Greetings
Volker

Last edited by Alsatian2017 on Wed Mar 29, 2023 12:53 pm; edited 1 time in total


PostPosted: Wed Mar 29, 2023 12:47 pm    Post subject: Reply with quote
RokkorDoctor wrote:


Finally, it is a minor matter, but f/# stops (not N.A. numerical apertures), are defined as the ratio of the effective the focal length of the lens to the diameter of the ENTRANCE pupil, not the diameter of the EXIT pupil (or physical aperture stop diameter for that matter). Counterintuitive I know, but that's the way it is. Depending on lens design/construction that does therefore mean that two lenses of equal focal length with equal f/# stops do not necessarily have exactly the same bokeh-ball size. Two lenses with equal N.A. (numerical aperture) do have the same bokeh ball sizes.

Of course with your Canon lens they still may have been bit optimistic with their aperture spec...


Very good analysis, thanks Like 1 Like 1


PostPosted: Wed Mar 29, 2023 12:59 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
Alsatian2017 wrote:
lumens pixel wrote:


Interesting Volker and I have to check again. Nevertheless that would not solve the bokeh ball difference.

I am not sure if spot metering is the best approach. Let us consider that FD 1,8 is indeed f2,0 but suffers from more vigneting than MD 1,7, spot metering in the center would be the same while there would be an aperture difference. So maybe your test is not conclusive. I would suggest you test the bokeh balls size and tell us your findings.


Spot metering is the one and only approach since you want to exclude the influence of vignetting on exposure Smile

The exposure difference in Average or Multizone metering mode is the direct result of the stronger vignetting in the Canon lens. Have you seen my pictures - there are no differences in luminance in all four pictures which is consistent with my findings. Chasseur d'images tested the follwing vignetting values wide open : nFD 50 mm f/2 (0,5 IL), nFD 50 mm f/1,8 (same lens but without light reduction ring in front of the aperture, 0,7 IL), Minolta MD III 50 mm f/2 (0,6 IL) and MD III 50 mm f/1, 7 (0,7 IL). What's important for exposure evaluation by the cameras lightmeter, is not only the absolute amount of vignetting in the extreme corners, but its distribution pattern throughout the frame. Fall-off might be faster with the Canon lenses and slower, smoother with the Minoltas.

Greetings
Volker


Well, yes and no;

f/# stops are related to light transmission, but not measurable by light transmission. Those would be T-stops you are talking about.

f/# stops are purely determined by physical dimensional parameters: (effective focal length) / (entrance pupil diameter). If you want to check the accuracy of an f/# stop you need to measure the diameter of the entrance pupil (assuming the quoted FL is accurate); no other way of doing it.

If you use a light meter (I agree spot would be best) you are looking at comparing T-stops, not f-stops.

https://en.wikipedia.org/wiki/F-number#Notation

https://en.wikipedia.org/wiki/F-number#T-stop


PostPosted: Wed Mar 29, 2023 1:03 pm    Post subject: Reply with quote
Interesting all, thank you. I guess we could at least exclude the aperture blade mechanism from the equation wide open knowing that all blades are retracted. There is still a difference in speed with similar vignetting according to Chasseur d'images tests and in bokeh balls size. But I need to check all again.


PostPosted: Wed Mar 29, 2023 2:00 pm    Post subject: Reply with quote
lumens pixel wrote:
There is still a difference in speed with similar vignetting according to Chasseur d'images tests and in bokeh balls size. But I need to check all again.


Yes, but the vignetting pattern might play a role here... If you check again, it might be worth it to do it with Spot and Average/Multipattern metering.


PostPosted: Wed Mar 29, 2023 2:02 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
RokkorDoctor wrote:


Well, yes and no;

f/# stops are related to light transmission, but not measurable by light transmission. Those would be T-stops you are talking about.

f/# stops are purely determined by physical dimensional parameters: (effective focal length) / (entrance pupil diameter). If you want to check the accuracy of an f/# stop you need to measure the diameter of the entrance pupil (assuming the quoted FL is accurate); no other way of doing it.

If you use a light meter (I agree spot would be best) you are looking at comparing T-stops, not f-stops.

https://en.wikipedia.org/wiki/F-number#Notation

https://en.wikipedia.org/wiki/F-number#T-stop


Thanks for clarifying Like 1 Like 1


PostPosted: Wed Mar 29, 2023 2:02 pm    Post subject: Reply with quote
That is what I like about the old PP and MP magazine tests: Next to the resolution numbers a measured focal length is reported, a measured F stop and a measured T stop + related transmission percentage. Vignetting usually expresses itself in the transmission percentage.

Though I do not have the MD and nFD test results here, the MC and FD results for that lens type I have.




The Olympus OM 50mm 1.4 is my favorite vintage standard lens, the resolution numbers are fine in the test result I have but the numbers like transmission show that it may not be a fair result if everything is counted in competition with other lenses. The excuse could be the small volume of the OM lenses but nevertheless.
Where the measured F and T stop really count is in the vintage standard 1.2 lenses. People buy them for their speed expressed in F and T stop and the measured results are not so nice. On the other hand with slower lenses, Macro lenses for example, the T stop can be better than the F stop number.


PostPosted: Wed Mar 29, 2023 2:44 pm    Post subject: Reply with quote
Ernst Dinkla wrote:
That is what I like about the old PP and MP magazine tests: Next to the resolution numbers a measured focal length is reported, a measured F stop and a measured T stop + related transmission percentage. Vignetting usually expresses itself in the transmission percentage.

Though I do not have the MD and nFD test results here, the MC and FD results for that lens type I have.




The Olympus OM 50mm 1.4 is my favorite vintage standard lens, the resolution numbers are fine in the test result I have but the numbers like transmission show that it may not be a fair result if everything is counted in competition with other lenses. The excuse could be the small volume of the OM lenses but nevertheless.
Where the measured F and T stop really count is in the vintage standard 1.2 lenses. People buy them for their speed expressed in F and T stop and the measured results are not so nice. On the other hand with slower lenses, Macro lenses for example, the T stop can be better than the F stop number.


Thank you Ernst. Like you I am very much found of old test magazines. I curse the day when my delicious wife threw all my old documentation. If someone would ever centralise all the relevant data on the net that would ba a fantastic resource.


PostPosted: Wed Mar 29, 2023 3:28 pm    Post subject: Reply with quote
From what I've seen f2 cine lenses are usually T2.2. A small loss in transmission.


PostPosted: Wed Mar 29, 2023 4:41 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
lumens pixel wrote:
visualopsins wrote:
lumens pixel wrote:
...The size of the bokeh balls on the Minolta is noticeably bigger evidencing a wider aperture despite the 0,1 f stop difference.

I consider that we are discussing aperture issues, not transmission, since all glasses are clean and the number of elements is sufficiently low to avoid taking them into consideration.

This is confirmed by the bokeh balls test that is not related to transmission.
...
Happy pics to all.


My tests show bokeh ball size is related to focus distance. Certainly the difference in shutter speed is indeed due to different transmission.


In this case focus distance was exactly the same. Camera on a tripod I focused on a near fixed object and observed the bokeh ball in the distance. I changed the lens without moving the camera, refocused on same object and observed the same bokeh balls. So distance here cannot be the problem.


Simply adjusting the focus changes the size of bokeh balls, regardless of focus distance.

In the test, both lenses are focused at the same distance, however the bokeh balls are different sizes. Focus of one of the lenses can be adjusted so bokeh balls are the same size.

Since in the test the bokeh balls are different sizes when lenses are focused to same distance, DOF, and therefore aperture sizes must be different.

I.e. bokeh ball size difference indicates different size apertures.

BTW, "bokeh balls" are more properly "out-of-focus" highlights.


PostPosted: Wed Mar 29, 2023 5:02 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
visualopsins wrote:
lumens pixel wrote:
visualopsins wrote:
lumens pixel wrote:
...The size of the bokeh balls on the Minolta is noticeably bigger evidencing a wider aperture despite the 0,1 f stop difference.

I consider that we are discussing aperture issues, not transmission, since all glasses are clean and the number of elements is sufficiently low to avoid taking them into consideration.

This is confirmed by the bokeh balls test that is not related to transmission.
...
Happy pics to all.


My tests show bokeh ball size is related to focus distance. Certainly the difference in shutter speed is indeed due to different transmission.


In this case focus distance was exactly the same. Camera on a tripod I focused on a near fixed object and observed the bokeh ball in the distance. I changed the lens without moving the camera, refocused on same object and observed the same bokeh balls. So distance here cannot be the problem.


Simply adjusting the focus changes the size of bokeh balls, regardless of focus distance.

In the test, both lenses are focused at the same distance, however the bokeh balls are different sizes. Focus of one of the lenses can be adjusted so bokeh balls are the same size.

Since in the test the bokeh balls are different sizes when lenses are focused to same distance, DOF, and therefore aperture sizes must be different.

I.e. bokeh ball size difference indicates different size apertures.



Exactly my point.


PostPosted: Wed Mar 29, 2023 5:22 pm    Post subject: Reply with quote
Ernst, thanks for this info! nFD and FD are the same optics on both occasions - the 1.8 and the 1.4
Btw, do you happen to have the 50/1.4 data?

I tested all nFD 50s when I had them lying around during covid, and their separation (bokeh balls / blur) is stunningly different - the 1.2L shows at least half a stop more "blur" than the 1.4 at an identical f/1.4. I also compared a Leica Noctilux f/1, and the nFD 1.4 showed at least one stop LESS separation at an identical f/1.4 and f/2. I guess it comes down to optical construction.

photonstophotos.com suggests that canon primes (outside the extremes of speed or focal length) are what they claim to be (quite as opposed to zooms). so a 1.8 lens is actually a 1.76 or a 1.84, but usually not a 1.96.
just sharing my experience; I have no attachment to either canon nor minolta.


PostPosted: Wed Mar 29, 2023 6:49 pm    Post subject: Reply with quote
kathala wrote:
Ernst, thanks for this info! nFD and FD are the same optics on both occasions - the 1.8 and the 1.4
Btw, do you happen to have the 50/1.4 data?

I tested all nFD 50s when I had them lying around during covid, and their separation (bokeh balls / blur) is stunningly different - the 1.2L shows at least half a stop more "blur" than the 1.4 at an identical f/1.4. I also compared a Leica Noctilux f/1, and the nFD 1.4 showed at least one stop LESS separation at an identical f/1.4 and f/2. I guess it comes down to optical construction.

photonstophotos.com suggests that canon primes (outside the extremes of speed or focal length) are what they claim to be (quite as opposed to zooms). so a 1.8 lens is actually a 1.76 or a 1.84, but usually not a 1.96.
just sharing my experience; I have no attachment to either canon nor minolta.





PostPosted: Wed Mar 29, 2023 7:32 pm    Post subject: Reply with quote
Assuming two different lenses do indeed have the same focal length, then comparing whether their f/# stops are genuinely the same when set the same on both lenses is easily done by observing both frontally side-by-side from a reasonable distance (say > 20 x FL): if the entrance pupils appear to have the same diameter as seen from the front, the two f/# stops are the same, regardless of what bokeh balls may be suggesting.

(May be difficult to do with lenses that you can't control the f/# stop of when detached from the camera)


PostPosted: Wed Mar 29, 2023 7:55 pm    Post subject: Reply with quote
Yes, bokeh ball size does vary with focal length due to change in magnification.

For same focal length and same size physical entrance pupils bokeh balls should be same size.


PostPosted: Wed Mar 29, 2023 11:55 pm    Post subject: Re: My truth about some Minolta MD and Canon fifties Reply with quote
Alsatian2017 wrote:


So, the Canon nFD 50 mm f/1,8 is not a fraud and I agree with you that it is a usually much undervalued lens.



http://forum.mflenses.com/canon-fd-50-1-7-and-olympus-pen-e-pl1-t84402.html


PostPosted: Thu Mar 30, 2023 9:05 am    Post subject: Reply with quote
Front lens diameters as just measured:

30,8 Canon FD 50 1,8 so 51,3/30,8=1,67
31,7 Minolta MD 50 1,7 so 51,2/31,7=1,61

Certainly imperfect.

How does it work for retrofocus lenses? My FD 28mm 2,8 front lens measures 32,5mm so 28/32,5=0,86 which is irrelevant.


PostPosted: Thu Mar 30, 2023 10:02 am    Post subject: Reply with quote
lumens pixel wrote:
Front lens diameters as just measured:

30,8 Canon FD 50 1,8 so 51,3/30,8=1,67
31,7 Minolta MD 50 1,7 so 51,2/31,7=1,61

Certainly imperfect.

How does it work for retrofocus lenses? My FD 28mm 2,8 front lens measures 32,5mm so 28/32,5=0,86 which is irrelevant.


No, the entrance pupil of the lens is not the same as the front lens diameter. The entrance pupil will be smaller, substantially so for wide angle lenses.

The entrance pupil is the virtual image of the aperture, as rendered by the front optics (assuming no other stops inside the lens).

Therefore the entrance pupil of a lens is the illuminated area (disc) you see when holding the lens up to the light and observe it from the front. The front lens diameter will almost always be somewhat larger diameter than the entrance pupil, otherwise excessive vignetting would occur.

For retrofocus wide angle lenses the front lens diameter is significantly larger diameter than the entrance pupil, up to several times in fact. So. e.g. for a wide angle lens, the front lens may have a diameter of e.g. 50mm, but the entrance pupil may only be e.g. 10mm diameter. In general, the longer the focal length of the lens, the closer the diameter of the entrance pupil will be to the diameter of the front lens.

For the Minolta MDIII 50/1.7 the front lens diameter is approx. 31.7mm, but looking at my sample the entrance pupil I estimate to be closer to somewhere between 29 and 30mm, implying an f/# stop of approx. 51.2/29.5=1.74

For my Minolta MDIII 28/2.8 the front lens diameter is approx. 30mm, the entrance pupil is only approx. 10mm, implying indeed a maximum f/# stop of 28mm/10mm=2.8


PostPosted: Thu Mar 30, 2023 10:39 am    Post subject: Reply with quote
RokkorDoctor wrote:
lumens pixel wrote:
Front lens diameters as just measured:

30,8 Canon FD 50 1,8 so 51,3/30,8=1,67
31,7 Minolta MD 50 1,7 so 51,2/31,7=1,61

Certainly imperfect.

How does it work for retrofocus lenses? My FD 28mm 2,8 front lens measures 32,5mm so 28/32,5=0,86 which is irrelevant.


No, the entrance pupil of the lens is not the same as the front lens diameter. The entrance pupil will be smaller, substantially so for wide angle lenses.

The entrance pupil is the virtual image of the aperture, as rendered by the front optics (assuming no other stops inside the lens).

Therefore the entrance pupil of a lens is the illuminated area (disc) you see when holding the lens up to the light and observe it from the front. The front lens diameter will almost always be somewhat larger diameter than the entrance pupil, otherwise excessive vignetting would occur.


For retrofocus wide angle lenses the front lens diameter is significantly larger diameter than the entrance pupil, up to several times in fact. So. e.g. for a wide angle lens, the front lens may have a diameter of e.g. 50mm, but the entrance pupil may only be e.g. 10mm diameter. In general, the longer the focal length of the lens, the closer the diameter of the entrance pupil will be to the diameter of the front lens.

For the Minolta MDIII 50/1.7 the front lens diameter is approx. 31.7mm, but looking at my sample the entrance pupil I estimate to be closer to somewhere between 29 and 30mm, implying an f/# stop of approx. 51.2/29.5=1.74

For my Minolta MDIII 28/2.8 the front lens diameter is approx. 30mm, the entrance pupil is only approx. 10mm, implying indeed a maximum f/# stop of 28mm/10mm=2.8



You learn every day. Thanks RokkorDoctor.
Post new topic   Reply to topic
Home   Manual Focus Lenses
Goto page 1, 2  Next
Page 1 of 2