Best f-stop for Canon 100mm/f2.8 w extenstion ring

[teddib 0]

<_< OK, I now have the appropriate port extension to allow me to use the Canon 100 mm/f2.8 lens plus the extension ring for macro photography with the 1DsMII. I will be using two Ikelite DS-125 stobes for lighting. As I understand it, increasing the f-stop to a point improves the depth of field while increasing distortion due to diffraction. My question, is what is the ideal setting for this camera/lens/strobe set-up. Maybe I will just need to experiment and with up to 27 dives in the far Northern great barrier reef I should get plenty of chance. I just wondered if someone has optimized some settings to start?

 

Given the magnification, are there any eco sensitive techniques to get a shot (I realize no one will give their sacred secrets away). Just looking for a little advise.

 

Thanks,

Tom

[acroporas 0]

Here is a good link that will explain diffraction and how it effects different digital cameras. There is a tool that will calculate the aperature where diffraction becomes thie liminting factor.

 

http://www.cambridgeincolour.com/tutorials...photography.htm

 

By it's calculator, at F11 resolution is limited by diffraction on a 1DS2 but not at F/8.

 

That said, if there is not sufficient DOF to cover your subjet, or the subject is out of focus because it is very difficult to nail the focus when the DOF is extremely thin the shot is worthless. So if you need more dof do not be affraid to push it past that somewhat. I would not hesitate to use up to F/16.

[teddib 0]

OK. That is very helpful. What impact does the EF25II extension ring have on this equation/calculation?

 

Thanks again,

Tom

[acroporas 0]

Extension should have very little effect. Though I found that it is next to impossible to use a 100mm with a diopter or extension because the focus distance is too close. If you need more magnification I recomend a teleconverter rather than extension on a 100mm lens.

[herbko 0]

OK. That is very helpful. What impact does the EF25II extension ring have on this equation/calculation?

 

Thanks again,

Tom

 

 

Adding the extension ring allow closer focus and higher magnification and really does not change the relationship between the aperture and diffraction. However, for macro the aperture you set is not the real aperture. There's a correction of almost two stop at 1:1 due to the extension of the lens for close focus. That is a setting of F/11 is really an aperture close to F/22 at that magnification. I read that some Nikon bodies and lenses will adjust and give the actually aperture setting, but Canon lenses do not.

[xtremediver 0]

What about using a "Woodys Diopter"; that allows you to get closer and seems easier to use than any of the other options. B)

[teddib 0]

OK. I am on a bit of a short timeline and now have an extension for my port which accomodates the 100 mm plus the EF25II. The focus distance is about six inches. With the port on, this will be more like five inches.

 

I have the Canon Extender EF 2 but it does not work with the 100 mm. What teleconverter would you recommend for the 100 mm? What would the focus distance be with that combination?

 

I investigated the diopter option once before but opted out. What is a typical focus distance with the diopter? How does this impact f-stop?

 

Thanks for all the advise!

Tom

[xtremediver 0]

Here is a pretty good explanation from a rather qualified u/w photographer, read it and see what you think.

 

http://www.stephenfrink.com/sf-tips/200601-macro-techniques/

 

Oh yeah, I use the 12mm extension with my 100 macro and add the 2x teleconverter onto that, it mounts with no problem then.

[teddib 0]

Great article! I will have to take a look at the wet diopter option. It is not clear from this source what that does to the focus distance and f-stop. Do you know?

 

I actually tried your suggestion with the 25 mm extention tube and the Extender EF 2x II. It works! Like I probably would expect, auto focus is hopeless with this magnification so I presume I would be stuck with manual focus. This presents one problem with the Subal housing I have in that the port does not work with manual focus on this lens. I am guessing one might take the lens all the way out and just use distance to the subject to get focus. Than you are pretty much stuck with some pretty close shots.

 

Thanks again for all the help.

 

Tom

[xtremediver 0]

You can "tape" some pins on the extender and this does allow for autofocus, but you will have to do a search on the subject as I don't rmember the site that I saw this on. You will also limit your focal length to less thatn infinity, but that shouldn't matter. If you contact Woody @ Nexus, he will be able to answer your questions better. Good luck! I am using my setup in Mabul/Sipadan latter this week. If I can, I will post an image or two taken with the setup. B)

[teddib 0]

OK, I found that you tape the far left hand three pins in order to block out the signal that the f-stop is out of range making auto focus not work. My symptom yesterday was that AF was working but it was bouncing back and forth and not locking in. This may because of the very narrow depth of field and the low contrast.

 

What I think I am learning is that the extension tube and diopter both require closer focus. The diopter, depending on the quality of optics may introduce so unwanted artifacts. The teleconverter keeps the focal distance but reduces the quality of image and requires more light.

 

Taken from Tackett's Essential guide:

for a 105 mm lens: focal distance is 5 3/4 in, with + 3 diopter is 3 1/2 in, with 2x TC is 5 3/4 in, the combination of +3 diopter and 2x TC is 3 1/2 in.

 

I do not see a major disadvantage to the original solution I had tried, the extension tube, other than I am going to have to get within about six inches to my subject and I will be limited in my options while on any single dive. I have sent an email to Woody and will consider that option if I find a unit that fits the Subal lens.

 

It sounds like given any of this gear this will be operator limited. Shoot a lot of shots and throw all the bads ones away.

 

Keeping my fingers crossed, I should see a lot of good macro subjects near Raine Isand.

 

Regards,

 

Tom

[herbko 0]

If you haven't done this before. Start easy. Shoot with the 100mm only and choose subjects that are a couple of inches across, and work your way to smaller subject once you got that figured out.