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Imitating an MP-E using a reversed zoom
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johan



Joined: 06 Sep 2011
Posts: 961

PostPosted: Wed Sep 26, 2012 6:48 am    Post subject: Imitating an MP-E using a reversed zoom Reply with quote

(Admin edit: This thread was originally started as a reply in "Taming the MP-E". At johan's request and because the change makes eminent sense, I have split it off to form a separate thread here.)

I'm... a bit hesitant about putting up this link because it's an incomplete project of mine... but what the heck, maybe it's time to open this up for constructive improvement suggestions anyway. Please have a look at http://www.flickr.com/photos/jingleslenobel/sets/72157630726382944/ - it's an 'almost' mp-e 65 that I made. It might help some people in a similar situation to me, who don't fly the Canon flag but would like something like the mp-e 65. Which costs very little. And means you can see what you're doing.

Construction is dead simple and costs peanuts. It goes: my Pentax camera body => full contact extension tube (34mm) => a deglassed Pentax SMC f/1.7 => 49mm male-male => reversed Pentax 35-80FA f/4-5.6

The interesting bit is the deglassed Pentax SMC f/1.7. This was the kit lens, the nifty 50 of its day, there are a few squillion around on ebay for peanuts. But the point is, by deglassing it, you're left with a working aperture mechanism that is controlled in the body. Use this to control the light from the reversed zoom and you don't need to stop the zoom itself down. So you can see what you're doing which is always somewhat splendid. Please note the extension tube obviously has to be full contact, ie communicate aperture information body <==> 50. Otherwise it won't work =)

The next interesting point is, since all you're after is the aperture mechanism, you can use the cheapest cruddiest optic for the 50mm component as long as the aperture communicates with the body. You're going to remove the lenses anyway so quality of glass is irrellevant (ie low cost of purchase)

And the last interesting point is that it means you can factually do this with prettymuch any brand of body... just swap my 50mm deglassed Pentax lens (which I need because I use Pentax bodies) with some body-communicating old 50mm lens of your brand. (50 because it gives you a good fast aperture, 35s, 28s and pancakes are thinner but slower). Removing all the glass from a 50 isn't rocket science, even I can manage it.

So on the plus side, it gets me 1:2 to about 3:1, one ring controls zoom factor, it's lightweight, sturdy, has a nice working distance (30 cm to about 10 cm), no need to stop down, acceptible IQ... not too shabby for a bodge job. Enough that if you're like me and can't be doing with trying to look through dark stopped down reversed lenses, it's a way forward. The photos on the set look ok to me. No, it's not a JML, but it's way better than nothing.

On the not so plus side, this is not a very forgiving construct (3:1 handheld is damm hard!), abberations can appear when stopping down and unless you're careful over your choice of subject matter and settings, you'll get vignetting. I for example get most joy when the zoom is at f/5.6 rather than wide open f/4. Another challenge is nice light with a flash. The diffuser I use when at 1:2 is big and reaches 25cm forward. But in the field this gets in the way when you zoom to 3:1 because the working distance becomes 10cm. I'm working on it. I would very much welcome your input on this thread about suggestions how to solve these various issues!

This is the zoom: http://www.pentaxforums.com/lensreviews/SMC-Pentax-FA-35-80mm-F4-5.6-Zoom-Lens.html - please note that I've bought 5 other zooms in this range in the last 3 months for this project and this is by far the most convenient one, as it has a seperate focus and zoom ring.

Samples:

1:2


3:1
(apologies for the cruddy stack, my wife was on my case about something so done in a hurry)

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Last edited by johan on Wed Sep 26, 2012 9:11 am; edited 1 time in total
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Pau
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PostPosted: Wed Sep 26, 2012 8:57 am    Post subject: Reply with quote

Johan,
your mpe-64 project will merit a more detailed post in the tecnichal forum!
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ChrisR
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PostPosted: Wed Sep 26, 2012 10:21 am    Post subject: Reply with quote

Very clever Johan - Yes it deserves a thread of its own!
I expect we'll come up with other applications for your auto diaphragm!

Immediate thoughts -
i) What happened with the other zoom lenses you tried?
I suppose one with a good macro capability would be a contender because your sensor is still close to the lens.
Have you tried anything like an enlarger lens on the front of the 50?
Fixed focal length but possibly sharper? A 50mm f/2.8 and an 80f/4 would make an interesting set.

ii) the aperture is in the "Wrong place" of course, there must be some downside to that. Strange bokeh?

iii) Flash - strap it to the front lens body perhaps, so its distance to subject doesn't move as much.. I remember someone doing that with a Canon 270EX ( tippy-ended thing) on the other MP-E.

iv) I suppose you could remove more stuff from in front of the diaphragm on the 50 lens, to get it closer to the zoom...

v) Perhaps you could use something like an old 70 - 200f/4 zoom, remove whatever's in front of the diaphragm, and fix a short lens on, so "zooming" the deglassed zoom would give you a range of extensions. (I once had trouble removing glass from a lens, so I used a blowamp and an ice cube)


Last edited by ChrisR on Wed Sep 26, 2012 10:52 am; edited 1 time in total
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Harold Gough



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PostPosted: Wed Sep 26, 2012 10:24 am    Post subject: Reply with quote

Very impressive results, Johan. I'm struggling with visualising the mechanics. I seem to be with you for the deglassing but after that you lose me.

Harold
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ChrisR
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PostPosted: Wed Sep 26, 2012 10:56 am    Post subject: Reply with quote

Harold try holding a "macro focusing" zoom reversed, up to your camera.
Then think, coupling ring between the glassless one and the zoom.
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Harold Gough



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PostPosted: Wed Sep 26, 2012 11:34 am    Post subject: Reply with quote

Johan,

Thanks for the inspiration.

Chris,

Thanks for the clarification.

I was getting tird up over the body links, contacts, etc, which I don't need.

I have to confess to neglecting reversed lenses until very recently and reversed zooms until a few minute ago.

I have just tried reverse-mounting my Carl Zeiss Jenazoom-2 35-70mm macro * on 42mm and 65mm extensions. Essentially, my x2 crop sensor covers 8-20mm on 42mm extension and 3.5-10mm on 65mm, the 35mm FL getting the maximum magnification at the closest focus. For the latter range the working distance is approximately 40-50mm, respectively.

At the moment the aperture is not controlled. I just need to temporarily lodge the stop-down lever, normally actuated by the camera, to then be able to use the aperture ring to select them fully manually via the selector ring. Something to try out tomorrow.

* Test image (mounted normally, not reversed) here:

http://www.photomacrography.net/forum/viewtopic.php?p=80338&highlight=jenazoom#80338

Harold
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rjlittlefield
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PostPosted: Wed Sep 26, 2012 12:10 pm    Post subject: Reply with quote

johan wrote:
abberations can appear when stopping down

ChrisR wrote:
ii) the aperture is in the "Wrong place" of course, there must be some downside to that. Strange bokeh?

That's where the aberrations are coming from. The built-in aperture is positioned to minimize aberrations by cutting off the most aberrated parts of each bundle of light rays. With the built-in aperture opened and the added aperture closed, off-center parts of the image get formed by relatively more of the aberrated rays. Partly closing the built-in aperture can eliminate some of those and improve the image quality away from center, but at the cost of darkening those areas too. The improvement in image quality and the onset of vignetting go hand-in-hand in this case.

--Rik
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johan



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PostPosted: Wed Sep 26, 2012 2:45 pm    Post subject: Reply with quote

Thank you very much for moving this Rik.

I have some other notes & observations to add to this but it's getting late here so I'll add them tomorrow!
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ChrisR
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PostPosted: Wed Sep 26, 2012 3:43 pm    Post subject: Reply with quote

Harold wrote:
body links, contacts, etc, which I don't need.

Nor do most of us for macro Harold! The point about the mismatch of makes, is just the Auto diaphragm.
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elf



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PostPosted: Wed Sep 26, 2012 5:35 pm    Post subject: Reply with quote

Here's another technique for creating an MPE-64: http://www.microsofttranslator.com/bv.aspx?ref=Internal&from=ja&to=en&a=http://dc.watch.impress.co.jp/docs/review/labo/20090528_170176.html

One of these days when my soldering skills improve, I may even try it Smile
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ChrisR
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PostPosted: Wed Sep 26, 2012 8:13 pm    Post subject: Reply with quote

That looks a lot of effort for a mediocre result!
One could smash up an old zoom and glue a JML in the front. I have a spare one..
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Harold Gough



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PostPosted: Thu Sep 27, 2012 12:13 am    Post subject: Reply with quote

Regarding the position of the aperture (but not the budget aspect!):

One of theses old shutters (just used as a diaphragm) might be better:

http://www.largeformatphotography.info/shutters.html

Harold
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Harold Gough



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PostPosted: Thu Sep 27, 2012 4:11 am    Post subject: Reply with quote

Harold Gough wrote:
I have just tried reverse-mounting my Carl Zeiss Jenazoom-2 35-70mm macro * on 42mm and 65mm extensions. Essentially, my x2 crop sensor covers 8-20mm on 42mm extension and 3.5-10mm on 65mm, the 35mm FL getting the maximum magnification at the closest focus. For the latter range the working distance is approximately 40-50mm, respectively.

At the moment the aperture is not controlled. I just need to temporarily lodge the stop-down lever, normally actuated by the camera, to then be able to use the aperture ring to select them fully manually via the selector ring. Something to try out tomorrow.


My initial results are here:

http://www.photomacrography.net/forum/viewtopic.php?p=115818#115818

after modifying the lens:

http://www.photomacrography.net/forum/viewtopic.php?t=18243

Harold
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johan



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PostPosted: Thu Sep 27, 2012 6:22 am    Post subject: Reply with quote

Some observations to add to this. First of all I need to dampen expectation - although it works it is a bit hit and miss. This is why I didn't want to make a big deal out of it over on Flickr... it's a classic case of "in the land of the blind, the one eyed man is king"!

Terminology:
"Auto diaphragm" - a deglassed lens that communicates with and can be controlled fully by the camera.
"ET" - extension tube

Lenses
------

I've tried various mid-range zooms for this project and although they all work to a certain degree, some just seem to work better than others. I'm not entirely sure why and what the factors are and this is partially why I posted here to see if maybe some of the older and wiser heads in the community might contribute a comment or two. I believe the factors are the following though

1. Lens construction type
2. Difference entrance/exit pupil
3. Max aperture of lens
4. Distance diaphragm <==> back element

To test #3 I went and bought a Tamron Tamron 35-80mm F2.8-3.8, hoping that it's unusually wide aperture might mean I'd get decent IQ. Quite the opposite; very soft. I think more of the rays go through the rubbish bits of the lenses on a wider aperture maybe.

Distance zoom <==> auto diaphragm
---------------------------------
The amount of abberation and vignetting increases as the distance between the reversed lens and the auto diaphragm increases. Ideally you want the auto diaphragm as close as possible to the reversed zoom optics. This is why I have both the reversed zoom and the auto diaphragm focused at infinity and taped fixed at that position -- it minimises this distance.

The ramification of this btw is that you can also increase the magnification by having both lenses focused at their closest points rather than infinity. So for example my little plastic Pentax is perfectly capable of doing 1x-5x if I do that but I choose not to. 1:2 to 3:1 just happens to be more useful to me personally.

There are various paths for possible improvement here that I'd like to pursue, namely:

- using a very flat pancake lens for the auto diaphragm (shorter distance, but downside is they're typically too slow)
- finding a crappy old zoom which itself has a diaphragm that moves as you zoom, and cutting the end off to make the moving diaphragm bit as close as possible to the reversed zoom. I don't know if such a thing exists. but this would be the ideal for using reversed primes as well.
- seeing what happens if I replaced the shutter blades in the auto diaphragm with semi translucent ones (to combat vignetting)

Note, distance zoom <==> cam is pretty important. If your reversed zoom is too close to your cam you'll always have vignetting, you need to move it out a bit using ETs and/or an auto auto diaphragm to eliminate this.

f/stop
------

With the Pentax zoom wide open at f/4 I use the auto diaphragm up to f/16 without vignetting at 1:2. At 3:1 I use the auto diaphragm up to f/2.8 without vignetting. This is a matter for individual experimentation. I find that I do get a nicer picture with the zoom 1 stop down though, ie at f/5.6, and using that I restrict myself to f/12 at 1:2.

Hood
----
A soft plastic lenscap with a hole cut in makes a very easy hood =)

Light
-----
Last but definitely not least. As I mentioned one challenge is that the great big bling homemade flash diffuser that gives you gorgeous and just enough light at 1:2 gets in the way at 3:1. This is because the working distance goes from 30cm to 10cm. In a sense this is part of the mp-e's beauty because they complement that lens with twin flashes that can be set at a position that a) don't get in the way and b) gives you nice light whatever magnification you choose to use.

Fwiw, the options I've been looking at are:
- 2 x Sunpak PF20XD on a Chinese ring bracket thing from ebay, slaves controlled by the onboard
- Pentax ringflash
- Metz 15 MS-1 wireless ringflash

Realistically, the bug season is rapidly coming to an end in England so I don't expect to progress with this until Spring.

What I'll say though is this, light makes a massive, massive difference. So much so that for all the tinkering I do with f stops and distance zoom <==> auto diaphragm, placing some flashes roundabout the subjects controlled wirelessly makes far more difference to IQ than the rest combined. Which is why this is the main avenue I expect to pursue.
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Harold Gough



Joined: 09 Mar 2008
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PostPosted: Thu Sep 27, 2012 6:44 am    Post subject: Reply with quote

johan wrote:
To test #3 I went and bought a Tamron Tamron 35-80mm F2.8-3.8, hoping that it's unusually wide aperture might mean I'd get decent IQ. Quite the opposite; very soft. I think more of the rays go through the rubbish bits of the lenses on a wider aperture maybe.

Interesting. That is one of the best of the Tamrons for macro (highest magnification at 80mm FL). Mine is at least as good as my 90mm. I have not tried it reversed.

I have to say that trying to get subjects framed and in focus in outdoor conditions has given me great respect for those who get regular good results with the MPE-65.

Harold
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