Magnification, sharpness, diffraction, aperture and the MPE 65mm macro

[Overread]

Just a little test done with the MPE to see what apertures were usable at different magnifications.

Setup:
Camera and lens:
Canon 400D
Remote cable release
Canon MPE65mm macro
Teleconverter used for last tests - Sigma 2*teleconverter
Hoodman anglefinder - set to 2.5* magnification to aid focusing

Lighting:
Canon 580EX2
Offcamera flash cord
Lumiquest softbox

Support:
Manfrotto 055XPROB tripod
Manfrotto Junior geared head
Ebay focusing rail (single section) (note apparently also the same as the Adorama focusing rail)

Subject setup:
Single 2 pence UK coin
Single LED bulb torch with flexi arm

Camera settings used for each shot:
1/200sec shutter speed
ISO 100
Aperture (varies)
Manual flash power output (varies)



The full setup:

Camera and lens mounted using the lenses tripod collar (sold with the lens) onto the focusing rail; the rail being attached to the quick release plate of the geared head and the whole setup mounted on the tripod. The geared head was set to an angle (as shown on its head markings) of just over 45 degrees - this tilted angle was delibate as I wished to know the performance of the focusing rail whilst at a tilted angle with the whole setup. In addition a tilted angle lets the varying depths of field be displayed on the coins. Due to limitations in gear the flash had to be handheld by the photographer.

Each shot was focused by using the LED torch as a point of bright light, the light shining onto the coin surface. This proved to be essential at the greater magnifications as the image through the viewfinder would become very dark, coupled with a very small depth of field this further increases the difficulty of accurate focusing. The 2.5* setting on the Hoodman angle finder proved to be very beneficial for the aid of focusing at such fine magnifiations - though those with liveview can use up to 10* magnifcation on the preview image for even further fine focusing.
Focusing for each setting was achived by moving the focsing rail and not adjusting the focus on the camera, for this purpose in the tests. In this the focusing rail performed very well, allowing easy movement of the rail whilst the pressure screw was applied and not requiring any tightening further once the hand is removed from the rail controls. In the field further finer focusing could be done by adjusting the focus on the lens itself, unless preserving a fixed magnification was needed.
Test shots were taken and the flash power adjusted accordingly based on the output of the camera histogram - note that this along with the handholding of the flash itself did lead to some inconsistant results - especailly where the angle of the flash changed between shots. AT this small distances even small changes in the flash distance and angle could lead to larger changes in the resulting image. To counter this a better test would be to have the flash mounted on a fixed stand

Once each series of shots was taken the magnification was adjusted to the next level (as written on the lens barrel) and the focusing rail repositioned to aquire the new focus.

Test shots were then uploaded to the computer and the RAWs were processed - however only the white balance was adjusted for these shots (and the brightness on a very few). Even when output as JPEGs the sharpness, contrast and other settings have not been adjusted from the cameras base settings. This results in a softer image than would be possible by using tools such as the clarity slider in RAW processing and the unsharpen mask in the final stages of image editing = however it gives a level field that all the shots can be viewed on, rather than show up slight differences in the amount of sharpening applied (since whilst the amounts could be fixed each shot would have required different amounts in normal processing). In addition the major dustspots were also removed (least I think I got most of the major ones). More minor dustspots which would normally be removed from proper images were left in.

Link to the image set on flickr - the title of each image denotes the aperture used and the magnification factor of the shot. Note that fullsized versions of each shot are availible for review

Test results - after a quick review of the presented images at fullsize (you know its quicker to view them on flickr than it is to wait for windows image viewer....)
1:1

Here we can see that f8 is clearly the sharpest aperture to use of those tested. However results from both f10 and f13 show little difference between each other and would still be very usable when sharpened in editing. The results from f16 however are showing a far more noticable effect of diffraction (espeacially when compared to the f8 results)

2:1

Here we can see that things have got harder still, f13 is now more comparable to that of f16 from before. F10 is fairly usable still however, whilst f8 remains the sharpest aperture from those displayed.

3:1

f16 is now becoming a very soft aperture to use indeed and f13 is quickly following it. f10 would be the highest suitable aperture at this magnification now. Also note how dustspots are becoming far more of a problem in these shots (remember only major spots were removed the rest remain)

4:1

f10 might just be usable, but its really softened a lot since the smaller magnifications. In all honestly f8 would be the new ideal aperture to use for this magnifcation.

5:1

The first thing to notice is that f5.6 has appeared on the scale now, this is in responce to the constant softening of results and whereby f8 might no longer remain the most suitable aperture to use. Secondly looking at the results its clear that whilst f16 gives a massive depth of field for this range the results are very soft indeed. Even opening all the way up to f8 we still have a very noticably soft image - f5.6 might be the most desirable aperture for this magnification - even though it makes things a lot harder with its far finer depth of field.

10:1

Ok not as strict a test here since lower apertures are missing, but still at this high magnification one might be more forced to pick the smaller f8 over f5.6 just because of the improvement in depth of field that the aperture brings.


Test improvements:
select a single point on the coin to be the point of focus for all the shots.A left and bottom line on the image would also allow easier compartive results in the difference of subject area shown at each different magnification. Further a fixed flash position would have allowed for more consistant results with the flash head to have been recorded - lessening differences in sharpness due to contrast changes.

[daft_biker]

Have you noticed that f/16 looks worse the more diffuse the flash?

I do sometimes use it at 1:1 but stay below f/11 most of the time. Have you seen the bokeh wide open? That's nice and useable too

f/5.6 is still pretty wee at 5x....I quite often use it and smaller if I don't mind a little compromise but f/4 seems to be sharper for pixel peeping.

Have you campared 1:1 on your 150mm to the MP-E at 1:1?

[Overread]

The more diffuse the flash light is probably resulting in the softer contrast in the overall image - playing around with blackness, contrast and clarity sliders in RAW editing might creep back some of that apparent lost sharpness. It was a weakness in the test that I could not fix the flash position perfectly for each shot though it was quite revealing to see that even small distance changes could give quite a big different in the amount of light that was cast on the subject.

The aperture and bokeh parts are always going to rely on the subject I suspect - if I get a nice cold/sleepy bee or moth shooting nearer wide open and focus stacking will likley be the order of the day whilst a more awake subject (or a quick keeper shot from a sleepy insect before taking stacked shots) will likley see me reaching for those smaller apertures.

As for the 1:1 test, I've the 70mm macro, 150mm macro and now the MPE all to test against each other. I might even test the 150mm and 70mm properly at 1:2 macro as well. And that is the test for today. (and heck if I find time I might even compare my raynox DCR 250+1.4telceonverter against the MPE results)

[daft_biker]

The aperture and bokeh parts are always going to rely on the subject I suspect - if I get a nice cold/sleepy bee or moth shooting nearer wide open and focus stacking will likley be the order of the day whilst a more awake subject (or a quick keeper shot from a sleepy insect before taking stacked shots) will likley see me reaching for those smaller apertures.

Aye, I just pick an aperture I feel like using for the shot

I don't mind the odd bit of stacking but I don't bother stacking to still end up with only a wee bit of the subject in focus. I prefer using a tripod and rail so I can get the whole subject sharp but the opportunities to do that on live subjects seem few and far between (especially when you need something like 20 shots per mm at 5x!).

Anyhoo, have you seen this?

[Overread]

Yes the stopshot website is one I came across a while ago (I belive through the profile on flickr of the guy who uses a fair few of their laser trips for insect captures). I have to say though a motorized focusing rail linked up to automatic camera shooting is a dream come true - though chances are I might end up going for their laser trips and such first!

As for focus stacking don't forget that even if you only get a small part of the insect in focus through a few frames, the resulting stacked image is often a lot sharper than a single image can achive. I also find that the more frames there are the more chance there is for a right headache in trying to get it to work

[daft_biker]

I have to say though a motorized focusing rail linked up to automatic camera shooting is a dream come true - though chances are I might end up going for their laser trips and such first!

Same here

I also find that the more frames there are the more chance there is for a right headache in trying to get it to work

I've seen a lot of stacks with bits of focus missing between frames....even on the cover of magazines It's just not my cup of tea all the time.....




I can't be bothered with the extra PP work for something like that but I quite like doing stacks like this where there's significantly more DoF (23 shots). I do want to get better at those but I find I need the tripod and rail for them.

[Overread]

Gah that is way way too much spider for my liking! But yes I do agree getting a fantastic and very revealing series of shots to stack like that is fantastic! Even better is that we don't have to do it by hand (I did that once or twice with flowers when I first found out about the method - took ages and that was just 2 or 3 frames and they were pretty sharp to start with - stacking by hand a 23 series of shots taken at 4,5 timesl life size - gah way too many hours to od by hand

[Overread]

Just reading on stopshots website in their future products section and came across this

Distance Dependant Sensors

Cross beam sensors work very well for many applications but sometimes you want a sensor that is smaller and doesn't require arms to hold out sensor elements. The arms can get in the way and also be triggered by objects in the periphery. This is where distance dependant sensors come in. We are working on designing a forward looking sensor that will be able to detect a small object at a given distance from the sensor. This will be especially useful for photographing insects amongst flowers, trees or other plants.

Now that is a dream come true! A single sensor mounted onto the camera set to the exact distance needed and then just go forth and shoot! Heck if its good enough it could quite easily redefine macro shooting (just walk and focus and as soon as the subject comes into focus - click - shot captured with no shake problems from pressing the shutter button)

[daft_biker]

Just reading on stopshots website in their future products section and came across this

Distance Dependant Sensors

Cross beam sensors work very well for many applications but sometimes you want a sensor that is smaller and doesn't require arms to hold out sensor elements. The arms can get in the way and also be triggered by objects in the periphery. This is where distance dependant sensors come in. We are working on designing a forward looking sensor that will be able to detect a small object at a given distance from the sensor. This will be especially useful for photographing insects amongst flowers, trees or other plants.

Now that is a dream come true! A single sensor mounted onto the camera set to the exact distance needed and then just go forth and shoot! Heck if its good enough it could quite easily redefine macro shooting (just walk and focus and as soon as the subject comes into focus - click - shot captured with no shake problems from pressing the shutter button)

Use the AF system in the camera? Bit like using single shot AF but in manual focus....press the shutter all the way and the shutter fires when the AF says something is in focus. Can't see any reason why it would take any more than a firmware tweak to the camera. Doing it with the shutter open and an external flash trigger would be more accurate though.

[AlexMonro]

Use the AF system in the camera? Bit like using single shot AF but in manual focus....press the shutter all the way and the shutter fires when the AF says something is in focus. Can't see any reason why it would take any more than a firmware tweak to the camera.

I believe most Pentax DSLRs have this feature - I think they call it Catch-in Focus.