MPE-65 aperture optimum at high Magnification

[LordV]

Thought I'd noticed that MPE-65 shots at high magnification were suprisingly soft. I normally use F11 at all magnifications but did a quick test at 4:1 at F11, F8 and F6.3 of a piece of rubbish on a leaf (it didn't move). Shots were taken using my normal technique of resting the lens on a hard surface- processed from RAW with my normal settings and then just cropped in PS (no post processing). The images were not resized after cropping apart from the DPI being dropped from 300 to 180.
Is it my imagination or do they seem to get sharper going down from F11 to F6.3 ?.

Brian V.



http://static.flickr.com/62/225907457_c5441e820b_o.jpg

[dpastern]

I agree, f6.3 seems MUCH sharper. Is this with the 350D or 20D Brian? Can you replicate this on both cameras? RM, can you duplicate this as well? If this is the case, it really does limit how good the mpe-65 is for macros at the higher magnifcations. I would really like to see Sigma do a 1-2x macro lens, that'd be really cool.

Dave

[LordV]

I agree, f6.3 seems MUCH sharper. Is this with the 350D or 20D Brian? Can you replicate this on both cameras? RM, can you duplicate this as well? If this is the case, it really does limit how good the mpe-65 is for macros at the higher magnifcations. I would really like to see Sigma do a 1-2x macro lens, that'd be really cool.

Dave
It was with the 20D. Remember I'm being extremely picky here- that bit of rubbish is 1.96mm long- It may just mean that when going for high mag shots of small objects you do need to drop the aperture. I can live with the F6.3 when shooting V small bugs. I'm just wondering if there is something odd about the optics of the MPE-65 such that at high magnification the effective aperture is smaller than set- did wonder why the min aperture on the lens is only F16.
Ah- amazing what you find when you look- just found this quote in a thread on the MPE-65 "The MPE-65 has an effective aperture of ~f16 (when set at f2.8 ) at 5X magnification"
Mind you I did ask in another forum about the effect of adding ext tubes to a normal macro lens and the 2 stop loss of light giving an effective aperture smaller than set- the anser then was - yes this darkens the pic but does not affect DOF or diffraction calculations.
Brian V.

[AeroSmith]

According to the MP-E owner's manual:

Effective f-number=f-number x (Magnification+1). I assume this is the case for any high magnification lens, not just Canon's.

At 4x magnification:

f/2.8 on the camera is really f/14.
f/4.0 on the camera is really f/20.
f/5.6 on the camera is really f/28.
And so forth.
At 4x showing f/16 on the camera the effective f-stop is f/80!

Your f/6.3 is really f/31.5 at 4x. And f/11 is really f/55. My guess is at such high effective f-stops that diffraction is substantial.

[LordV]

According to the MP-E owner's manual:

Effective f-number=f-number x (Magnification+1). I assume this is the case for any high magnification lens, not just Canon's.

At 4x magnification:

f/2.8 on the camera is really f/14.
f/4.0 on the camera is really f/20.
f/5.6 on the camera is really f/28.
And so forth.
At 4x showing f/16 on the camera the effective f-stop is f/80!

Your f/6.3 is really f/31.5 at 4x. And f/11 is really f/55. My guess is at such high effective f-stops that diffraction is substantial.

OMG the manual :)
I'll have to read that sometime :)-
Thanks for pointing that out- however I had been told on another forum with a query about ext tubes and apparent aperture that "apparent aperture" caused by the lens lenghtening did not affect diffraction softening. Is this wrong (apparently it is) ?
Brian V.

[AeroSmith]

I had been told on another forum with a query about ext tubes and apparent aperture that "apparent aperture" caused by the lens lenghtening did not affect diffraction softening. Is this wrong (apparently it is) ?
Brian V.

Hmmm, I'm affraid I don't have a definative answer for that one. Though your images do seem to indicate that diffraction softening is substantial at these very high effective f-stops. So I'm guessing the information from the other forum may be incorrect.

I know one thing, I will be shooting at very low indicated apertures with my MP-E for a while to see if that improves my images (though it's tough to find the time with work and kids and all to get setup with the beast).

And, btw, thanks for getting me to finally read the manual. :)

[Lester Wareham]

Absoloutly, nice test.

See my reply to your question in the EF lens section. At 4:1 I estimate f4.5 gives the same softening as f11 at life size, much more effect due to magnification than I expected if valid.

This works out to be the same as the light loss effective aperture f-stopX(M/P+1) if you assume the pupilary magnification P is 1. It is difficult to measure P for the MP-E 65mm due to the internal light stop but it will not be much less than 1 so the order of magnitude should be the same.

[LordV]

Thanks Lester and aerosmith :)
The effect you are describing Lester is far less than the "effective aperture" given in the manual. Wonder if another way of looking at it would be to consider the actual focal length of the lens at higher magnification- I bet it changes and hence the f/value at fixed aperture diameter would also change. Whatever the effect is it looks like I'll need to drop the aperture as I up the magnification . Means even more focus stacking :)
Brian V.

[PhotosbyKev]

I wish you guys would arrive at the right answer. My MP-E65 arrives on Thursday and I'd like to use the correct aperture for max resolution :) :)

[Lester Wareham]

Thanks Lester and aerosmith :)
The effect you are describing Lester is far less than the "effective aperture" given in the manual. Wonder if another way of looking at it would be to consider the actual focal length of the lens at higher magnification- I bet it changes and hence the f/value at fixed aperture diameter would also change. Whatever the effect is it looks like I'll need to drop the aperture as I up the magnification . Means even more focus stacking :)
Brian V.

Brian, It should work out about the same as the effective aperture although they two phenomon have differing physical processes. The manual values for EA neglect the pupilary magnifiction which is probably not 1 as that would imply but this will be a second order effect.

[LordV]

I wish you guys would arrive at the right answer. My MP-E65 arrives on Thursday and I'd like to use the correct aperture for max resolution :) :)
There's no correct aperture- it's always a balance between DOF and diffraction softening. Certainly between 1:1 and 2:1 I get sharp shots at F11 but it looks as if I should start dropping the aperture when shooting at 3:1 and above.
{EDIT}- this is the table that Lester worked out.
Edit: Working out based on simple assumptions I get the following table for APS-C
Magnification ________ Diffraction Limit APS-C
____________________ Approx Set f-stop
0 (infinity focus d=f) __________ f22
1 (d=2.f) ___________________ f11
2 (d=3.f) ___________________ f7
3 (d=4.f) ___________________ f5.6
4 (d=5.f) ___________________ f4.5
5 (d=6.f) ___________________ f4


Brian V.

[bandit 1]

Hiya Brian,

Well I can't help with all this Techno stuff but that F6.3 looks way sharper on my monitor.

Ever thought about a Raynox 250 :lol: :lol: :lol:

Cheers for now
Mark

[racketman]

I wish you guys would arrive at the right answer. My MP-E65 arrives on Thursday and I'd like to use the correct aperture for max resolution :) :)

agonizing wait; I read f8 is the best aperture for detail with this lens. LordV uses f11 most of the time and his images are all razor sharp. You'll love the lens but remember it cant manage less than 1:1 so can be a limiting if you are chasing larger insects or want to show more enviroment.

[Lester Wareham]

agonizing wait; I read f8 is the best aperture for detail with this lens. LordV uses f11 most of the time and his images are all razor sharp. You'll love the lens but remember it cant manage less than 1:1 so can be a limiting if you are chasing larger insects or want to show more enviroment.

True, guess the MP-E comes into its own even more on the 5D though.

[TimNYC]

It's just an optical illusion. The main subject is all that is really in focus, as opposed to the fg and bg also being in focus at f/11.

[LordV]

It's just an optical illusion. The main subject is all that is really in focus, as opposed to the fg and bg also being in focus at f/11.
Don't think that's quite correct- there is sharper detail inside the lump of dirt at F6.3 although agree the DOF is much narrower.
Brian V.

[Lester Wareham]

I just thought I would cross reference (http://photography-on-the.net/forum/showthread.php?t=209004)the threads on this subject.

[LordV]

Thanks Lester- just to add another cross reference http://photography-on-the.net/forum/showthread.php?t=209465 how do you do that in one word Lester?

Brian V.

[PhotosbyKev]

agonizing wait; I read f8 is the best aperture for detail with this lens. LordV uses f11 most of the time and his images are all razor sharp. You'll love the lens but remember it cant manage less than 1:1 so can be a limiting if you are chasing larger insects or want to show more enviroment. I'm currently planning to use a 1D MkII N with the MP-E65 and have a 20D fitted with the Sigma 150mm macro lens and tubes to cover the larger subjects. I think the 1D will be better on the MP-E65 because of the improved viewfinder brightness but I may change my mind :)

[Lester Wareham]

Thanks Lester- just to add another cross reference http://photography-on-the.net/forum/showthread.php?t=209465 how do you do that in one word Lester?

Brian V.

Type the word you want and select it, Click the hyperlink icon and type/paste in the link in the popup and OK, add a suitable colour and underline using the format icons.

This creates all the necessary HTML.

[Lester Wareham]

I'm currently planning to use a 1D MkII N with the MP-E65 and have a 20D fitted with the Sigma 150mm macro lens and tubes to cover the larger subjects. I think the 1D will be better on the MP-E65 because of the improved viewfinder brightness but I may change my mind :)

I think so too, also the 1:1 min mag limit will be less restricting. On the downside you will need more magnification to fill the frame with smaller critters.

Good luck!

[halfmoonray]

Thanks LordV! At higher magnifications, I thought that it was just my inability to focus well. I will try lower apertures.

[macro junkie]

BUMP...good thread

[lance v]

I have to agree with the 'i must read the manual some time' coment:p

[macro junkie]

I have to agree with the 'i must read the manual some time' coment:p
only time i read it is when somone asked me how far i was from the subject..its all in there..;)

[lance v]

only time i read it is when somone asked me how far i was from the subject..its all in there..;)

OOOOOOOO thats right, mine didnt come in a box, and didnt have a manual....thatd b y iv never read it lol wooops

[GaryT]

Brian--this is an excellent thread. I am thinking (and have been) for some time now about getting one of these. F6.3 is defineitely the sharpest, with some loss of DOF. I wonder if this applies to any other macro lenses as you approach thier higher magnifications. I will have to experiment with my 100m/tube set-up to see. Thanks for sharing this info with us.

[LordV]

Brian--this is an excellent thread. I am thinking (and have been) for some time now about getting one of these. F6.3 is defineitely the sharpest, with some loss of DOF. I wonder if this applies to any other macro lenses as you approach thier higher magnifications. I will have to experiment with my 100m/tube set-up to see. Thanks for sharing this info with us.

Thanks Gary
Diffraction effects can affect any lens macro or not but I think it is more pronounced with macro as any method of magnification tends to make the "apparent aperture" smaller.

Brian V.