Nikon and Sigma like Canon

Ever since I got my Sigma 150mm macro lens, James has been bugging me to get a Canon 500D dioptre for it. A supplimentary lens that really transforms it in his opinion - and he's right.

Anyway I finally gave in and got the Canon 500D as well as 62-72mm step-up ring so I could also fit it onto my Nikon 105mm VR macro lens too. Can you tell I am going to Indonesia soon?! Anyway I am pleased to report that the Canon lens works very well on both the Sigma and Nikon macro lenses on a Nikon camera body.

No surprise, really. But worth mentioning given the fact that Nikon UK say that Nikon has discontinued their 5T and 6T dual element dioptres. And these dioptres are rarely available over the counter to try and often have to be ordered.

In conclusion the Canon 500D seems awesome after initial tests (on land admittedly). It is bloody expensive - a similar price to Canon's EF 75-300mm MkIII USM (which probably tells you something about the quality of each!). Also if you plan to use it in a housing it adds another 1.5cm to the length of the lens - which may cause issues with ports.

Alex

any ideas on the new reproduction ratio with this fitted, Alex?

and roughly what's your working distance on the 150 with and without it fitted?

cheers

Steve

Hi Alex

If I remember correctly, the 500D is designed for tele lenses. I have one of these and have tried it on wide lenses where it does not work well underwater. I am sure that it will operate well on a tele lens (as this is what it was designed for), but its worth mentioning that it may not (depending on you set-up) help if you try it on a wide.

Yep, it is designed for lenses between 70 and 200mm I think. It is not that strong a dioptre and I would guesstimate that is approximately halves the working distance and doubles the repro-ratio (or maybe just slightly more than that).

Alex

The 500D is (I believe) an equivalent +2 diopter, and limits infinity focus to ~19" from the sensor plane.

Topside, the 100mm+1.4xTC+500D diopter magnifies around 2:1, but with only a one stop loss of light. I'll try to check the closest focus distances for both setups (100+1.4x+500D and 100+500D) tomorrow. I've yet to try to measure how either the magnfication or focus distances changes underwater, if they do.

Am I correct that the 250D is even more powerful?

has anyone used that?

Steve

The 250D is made for different focal lengths - shorter I think.

The Nikon 4T, 5T & 6T are also made for longer lenses - the same range as the Canon 500D I think.

Alex

Magnification calculations are being based on the 22.5mm horizontal sensor size of the Canon 20D. Text follows images.

Standard 100mm lens. Maximum magnification is 1:1. Focus distance at 1:1 is approximately 5.5" from front of lens.

100mm lens with Canon 500D. Maximum magnification is ~1.32:1. Focus distance at maximum magnification is approximately 4" from front of assembly.

100mm lens with 1.4x TC. Maximum magnification is 1.4:1. Focus distance at maximum magnification is approximately 5.5" (same as lens alone, standard property of TCs) from front of assembly.

100mm lens with Canon 500D and 1.4x TC. Maximum magnification is ~1.88:1. Focus distance at maximum magnification is approximately 4" from front of assembly. The determined magnification does seem to show that the diopter magnification and teleconverter magnification are associative (~1.32:1 * 1.4:1 = ~1.85:1).

What would be more interesting is performing this same exercise underwater to determine what changes - magnification or focus distances. Hope this helps slightly.

matt, thanks for that !!

i'll try and add to that this week as i was going to be trying under water the following combo (on a 1d mkii):

100mm + 1.4TC + 500D and i was going to add the Seacam wetdiopter 2 to see how it adds to this.

i guess i'll have to bring a couple of rulers down with me to see the effects

if the weather holds here i hope to be able to post some results on sunday...

/paul

nice one Matt, that's really useful

Thanks!

While these measurements are useful comparatively - it is helpful to know that one setup is more powerful than another - I am not sure that the absolute maganification is that important.

I couldn't really tell you how many mm a particular subject is - especially as things look 33% bigger underwater anyway.

Alex

Just to (maybe) clear up the optics terminology, the Canon number (in xxxD) is the focal length in mm of the close up lens, i.e. the working distance when the main lens is set at infiniti.

In other words, the 500D gives you a long focus distance (set at infiniti) of 50cm and the 250D takes that down to 25cm.

Dioptres or diopters are the reciprocal of that focal length, measured in metres. So a 500D is a +2 dioptre lens. It brings parallel rays of light into focus at 1/2m. The 250D is a +4.

Then you have the Nikon numbers:

3T (52mm thread) = 5T (62mm thread) = +1.6 dioptre

4T (52mm thread) = 6T (62mm thread) = +3 dioptre

Capiche?

If not, don't worry, you're in good company, you'll see these lenses listed as all sorts of wrong dioptres. e.g. the 250D is found listed as a 3 or 4 dioptre lens, depending on where you look. Joy!

Martyn

Excellent Info Martyn.

Now if someone could also post the dioptre strengths of the common external dioptres used underwater this would be an awesome resource.

Alex

What???

But worth mentioning given the fact that Nikon UK say that Nikon has discontinued their 5T and 6T dual element dioptres.

A quick check of B&H and Adorama seems that you are correct. But why?

I was getting ready to pull the trigger on the new 105mm VR and that takes 62mm diopters. I already have the 52mm Nikon 4T for the old 105mm--so I was plannning to get a 6T.

With a new macro lens just out that takes 62mm thread why is Nikon now discontinuing their compatable close-up lens? The Canon at ~$120 is about twice as much, and since I'd need a 72mm thread with a step-up ring maybe it won't fit in my Ikelite port?

Is the Canon somehow better for twice the price?

What should I do? Look for a leftover 6T? But where? Or should I just bite the bullet and get a 77mm 500D and standardize with all my other filters and hope it fits the ports?

Now if someone could also post the dioptre strengths of the common external dioptres used underwater this would be an awesome resource.

 

Alex

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You can measure it yourself. Take a parallel beam of light, the sun will do just fine (well maybe not in the UK ) and lift it up from the surface until it is in focus. Measure the distance to get the focal length (F) of the close-up lens. Take 1000/F to get the diopter value.

As Martyn said, the working distance with the lens focused at infinity is aproximately 500mm (1000/dioptervalue). To get the more commonly listed distance between subject and sensor, just add the focal length. So 500+150 for the Sigma 150mm + 500D diopter. The magnification at infinity focus with diopter is the lens focal length/diopterF, so 150/500 or 0.3 for this combo at 65cm distance. The calculation for magnification factor at closest focus is too tricky to remember by heart and includes some fudge factors. There is a neat webpage explaining a lot of stuff that I can try to find again when I get home tonight.

Has anyone tried this with pure telelenses. I've just been going over this for the Canon 200mm f2.8L which normally focuses down to 1.5m. With the 500D that is reduced to ~40cm with a 0.57 magnification factor. An extra 1.4 TC gives you a 280mm F4 lens that still focusses at ~40cm with a 0.8x magnification factor. It should all just fit in the 7.5" Ikelite port. In some sense I think it is even more interesting to see what can be done with the lens at infinity focus, 500+200=70cm, this would give a still respectable 0.64x magnification). I know, this is cheating and a real man can touch even the most shy creature with the tip of his port without chasing it away. However, a real man also powertools.

Bart

Please disregard my 200mm telelens blurp. I thought the 500D/200mm combination would give a 200mm lens that can focus relatively close but the 500D will actually reduce the effective focal length in the process. It can be done by adding extension tubes but in the end you're just trying to force a non-macro lens to behave as a real one. OK if you already have the telelens and need a cheap way to get some macro-ability but otherwise its better to do it right and get a 150mm or 180mm macro lens that has been designed for the job.

Bart