Guys, I have the deepest respect to every scientific theory. However, as a past scientist I know that if the theory is not backed up by practice it needs to be changed, or at least be modified.
08-14-2010, 08:46 PM
(This post was last modified: 08-14-2010, 08:47 PM by wim.)
[quote name='Yakim' timestamp='1281806738' post='1768']
Guys, I have the deepest respect to every scientific theory. However, as a past scientist I know that if the theory is not backed up by practice it needs to be changed, or at least be modified.
[/quote]
Sorry Yakim, but in this case it isn't just theory, it is fact, which also has been proven in more than 100 years of photography. I know you noticed a difference, but basically something else must be at play. The phenomenon you noticed cannot be caused by the magnification you are using, if they are exactly the same. Same amount of light, same magnification, equals same aperture and shutterspeed, if the EV in both cases is exactly the same, as is the amount of light received per square unit. If it is not the same, which you indicated based on differing shutter speeds or apertures, something else must be affecting this, and that may actually be many things, whether the aperture isn't exactly right, whether the metering system somehow gets fooled, It just has to be something else, there is no other option.
Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
That's what everybody in PN said. That's why I re-tested it. Look at my reply on page #3: "Update: I re-tested and took pictures. You wouldn't be surprised if I told you shutter speeds are the same, right?".
[quote name='Yakim' timestamp='1281854898' post='1782']
That's what everybody in PN said. That's why I re-tested it. Look at my reply on page #3: "Update: I re-tested and took pictures. You wouldn't be surprised if I told you shutter speeds are the same, right?".
[/quote]
You didn't stop down the Canon 100mm lens to see how exposure might be different that with normal electrical communications, the whole idea about your retest.
Anyway, the answers have been there all along, explaining on how the focal length can change differently for each lens, and other factors.
If you want to go about it more scientifically, you will have to measure/calculate the focal lengths for both lenses at the different focus distances, and actually measure the exposure instead of "trusting the camera metering".
As pointed out, the Canon macro and that Mamiya are very different beasts, design wise.
However, we are not discussing those lenses, we were talking about the Canon 90mm TS-E and Nikon 85mm PC. And you, without real reason, "seriously doubt" that you will see the same order of light loss shooting each at 1:2 magnification, because with one you have to put an extension tube on.
However, the one without extension tube DOES extend itself in a similar manner, inside, when focussing closer.
So, you can do two things. Either believe that indeed you will see light loss also with the Nikon (you did note that light loss with both of your very different macro lenses after all, even if your methods were not optimal), or you won't believe it. It will not change the outcome, though.
Good luck with your choices!
[quote name='Yakim' timestamp='1281854898' post='1782']
That's what everybody in PN said. That's why I re-tested it. Look at my reply on page #3: "Update: I re-tested and took pictures. You wouldn't be surprised if I told you shutter speeds are the same, right?".
[/quote]
Some remarks on light loss at magnification ratio 1:1.
With the old macro lens design types close focusing was accomplished by increasing the extension through the built-in helical up to 1:2 and through additional extension tubes between 1:2 and 1:1.
Modern macro lenses which provide continuous focusing up to a magnification ratio of 1:1 without the need of an additional extension tube are in fact zoom lenses because their focal length decreases from infinity towards minimum focus distance. In the older (non-VR) AF-Micro-Nikkor 105/2.8 the lens group behind the fixed back element moves backwards(!) when focusing from infinity to 1:2. But from 1:2 on to 1:1 it reverses its movement.
At 1:1 the focus distance (distance between a focused object and its image) equals four times the nominal focal length. Thus, we can calculate an estimated nominal focal length at 1:1 by dividing the minimal focus distance by four:
minimal focus distance @1:1 - estimated nominal focal length @1:1 - example lenses
350 mm - 87.5 - Sony 100/2.8
310 mm - 77.5 - Canon 100/2.8, Nikon 105/2.8, Nikon 105/2.8 VR, Pentax 100/2.8
300 mm - 75.0 - Canon 100/2.8 IS
286 mm - 71.5 - Nikon 85/3.5
So the loss of 1.5 f-stops that you observed with your Canon 100/2.8 IS corresponds well with a decrease of the focal length to 75% of the focal length @infinity and therefore corresponds with a gain in relative aperture compared to an expected loss of 2 f-stops @1:1 with a traditionally designed macro lens.
My AF Micro-Nikkor 105/2.8 has a calculated aperture diameter of 37.5 mm (= 105 mm / 2.8). Given an effective focal length @1:1 of 155 mm (= twice the estimated nominal focal length @1:1), this lens has a calculated aperture of f/4.1 (= 155 mm / 37.5 mm). But the camera indicates and measures an effective value of f/5.
So this shows that this calculation of the aperture is an over-simplification and that something else is at play. Most likely this is caused by a change of the effective exit pupil while focusing towards 1:1. The role of the pupil magnification is mentioned at http://www.cambridgeincolour.com/tutorials/macro-lenses.htm
Considering the rather extreme light loss of 3.5 f-stops with the Mamiya 120/4: Did you observe this also with an MF body? Maybe the adapter and/or the relative small hight and width of the mirror chamber of the 7D hinder(s) peripheral light from the back lens element to hit the sensor.
Back in the days of slide projectors with mediocre projector lenses I "stepped-down" the projector lens by fitting an aperture ring cut from cardboard directly to the back lens element. This induced vignetting but it also improved the sharpness of the projected image.
HTH, Ralf.
[quote name='Brightcolours' timestamp='1281870027' post='1784']
You didn't stop down the Canon 100mm lens to see how exposure might be different that with normal electrical communications, the whole idea about your retest.
Anyway, the answers have been there all along, explaining on how the focal length can change differently for each lens, and other factors.
If you want to go about it more scientifically, you will have to measure/calculate the focal lengths for both lenses at the different focus distances, and actually measure the exposure instead of "trusting the camera metering".
As pointed out, the Canon macro and that Mamiya are very different beasts, design wise.[/quote]
Stopping down was not relevant in this case as I only compared them wide open. Given the theory and the similarity between the lenses I expected similar results. What surprised me was that the differences were huge, not marginal.
[quote name='Brightcolours' timestamp='1281870027' post='1784']
However, we are not discussing those lenses, we were talking about the Canon 90mm TS-E and Nikon 85mm PC. And you, without real reason, "seriously doubt" that you will see the same order of light loss shooting each at 1:2 magnification, because with one you have to put an extension tube on.
However, the one without extension tube DOES extend itself in a similar manner, inside, when focussing closer.
So, you can do two things. Either believe that indeed you will see light loss also with the Nikon (you did note that light loss with both of your very different macro lenses after all, even if your methods were not optimal), or you won't believe it. It will not change the outcome, though.[/quote]
I searched and could not find a direct comparison between the two. I'd be much more relaxed <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='  ' /> if I see one to corroborate for this.
[quote name='Kodachrome 25' timestamp='1281877401' post='1786']
Considering the rather extreme light loss of 3.5 f-stops with the Mamiya 120/4: Did you observe this also with an MF body? Maybe the adapter and/or the relative small hight and width of the mirror chamber of the 7D hinder(s) peripheral light from the back lens element to hit the sensor.[/quote]
I do not have a MF body. I wanted to get cheap TS on my Canon DSLR. Now that I experienced with it I want to step further. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt=' ' />
[quote name='Yakim' timestamp='1281561927' post='1689']
Both. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt=' ' /> I have a friend who goes to USA for a business trip in about two weeks. He'll return within a month and if all goes well (fingers crossed...) he'll have it with him.[/quote]
Well, so much for superstitions. His trip was postponed. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/sad.gif' class='bbc_emoticon' alt=' ' />
[quote name='Yakim' timestamp='1281941698' post='1798']
Well, so much for superstitions. His trip was postponed. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/sad.gif' class='bbc_emoticon' alt='  ' />
[/quote]
Well, postponed isn't yet aborted...
I'll keep my fngers crossed for it to happen soon anyway, if you don't mind...
Kind regards, WIm
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
ragsnoldiron
Unregistered
[quote name='Yakim' timestamp='1281703336' post='1742']
No need for RAW. JPEG will suffice as I'm only interested in a general impression of what it can do.
Thanks again.
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48 hours only [url="http://cid-d2aa801cea6774c3.office.live.com/browse.aspx/Photozone%20forum%20tse%2024%20II%20request"]here[/url]
Sent a pm explaining a few things. Crap images, but you'll see the difference with the 12mm tube and max focus. Not meant to be art. Only lens movements used in 12mm set, focus left at max, tilt/shift/tilt+shift only. Focus on iso window first set, focus on meter button top second set and left there
Will delete folder in 48hrs.
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