Beating the Venus 25mm F2.8 2.5x-5x Super Macro

Started May 17, 2018 | Discussions thread
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MightyMike Forum Pro • Posts: 38,917
Beating the Venus 25mm F2.8 2.5x-5x Super Macro

A few months ago Venus Optics introduces a new macro lens that is wide, covers the FF image circle and offers 2x to 5x magnification.

More information here...

Now my initial reaction was "Ooooohhh!" as any time there is offered a new macro solution it is interesting. The price looked good too at $400 USD which would come to approx. $600 CAD at the time. However a closer look revealed a preset aperture (no "A" position), no easy way to connect my Death Ray lighting system, no filter threads and the MTF values were IMO weak. Then I realized I have macro systems that don't have the "A" position, I could probably come up with a way to connect my Death Ray lighting system, I suppose I don't need filter threads and that is the MTF at F2.8, its probably better stopped down. However The price point though decent bothered me as I just had my Samyang 135mm F2.0 stolen.

***Light Bulb***

I have all the MTF charts and technical details for the Rodenstock enlarging lenses, I can buy helicoid extension tubes, adapters and stepping rings and make my own at less than half the price (for the lens system that is, it cost more for the new lighting rig.)

I zeroed in on the Rodenstock Rodagon-WA 40mm F4.0 Enlarging lens, one of the best they made and sure enough the MTF charts were definitely better. I found ideal helicoid extension tubes for focusing, got the adapters and stepping rings I needed. I also came up with a way to mount the lights also on a helicoid extension tube to be able to move them back and forth. I had someone machine me 2 mount plates for the lights in different configurations and machine me a way to lock them in place too.

The lens adapters and stepping rings (some of which I already had) cost me $254 CAD, most certainly less than half the price of the Venus 25mm F2.8. The lighting rig on the other hand cost me another $237 CAD however it could have cost that or more and have less functionality on top of the Venus 25mm cost so its a win too. There was another $150 or so in stuff I bought but ended up not using in this project, but then thats just the cost of prototyping.

So what is my lens capable of (magnification range)?

Well lets call it the MightyMike 40mm F4.0 2x to 5.5x Modular Super Macro. Now thats a little misleading as although it can shoot at 2x if you remove one of the focusing helicoids in normal use its a 2.7x to 5.5x.

As for size it fits right inbetween these 2 options

So how do the lenses compare?

- 40mm F4.0 vs 25mm F2.8 (Venus win for F2.8)
- Minimum Aperture F22 vs. F16
- 2x-5.5x vs 2.5x-5x (MightyMike win for more range)
- 6 elements in 4 groups vs 8 elements in 4 groups
- 5 blade aperture vs 8 blade aperture (Venus win)
- Length (without lighting rig) 121mm vs 82mm @ 2.7x and 2.5x respectively
- Length (with lighting rig) add 12mm
- Width (without lighting rig) 60mm vs 65mm
- Width with lighting rig (bigger regardless)
- Weight (lets say similar)
- MightyMike 40mm Min Focus Distance at 2.7x = 34mm with lighting rig
- MightyMike 40mm Min Focus Distance at 2.7x = 46mm without lighting rig
- Venus 25mm Min Focus Distance at 2.5x = 45mm without lighting rig
- MightyMike 40mm Min Focus Distance at 5.5x = 26mm with lighting rig
- MightyMike 40mm Min Focus Distance at 5.5x = 38mm without lighting rig
- Venus 25mm Min Focus Distance at 5x = 40mm without lighting rig

I may redesign the Death Ray rig to offer more working distance, however I'll have to be creative when coming up with a way to access the aperture if I do this.

- The MightyMike 40mm has 2 focus rings, the Venus 25 has 1 focus ring
- The Venus 25mm is also nicely packaged however the MightyMike 40mm can be taken apart and changed for whatever purpose I desire. I even should be able to hook up the 25 degree tilt device I made for the original death ray project (the magnification range will change by doing so)

- Now for the MTFs (Venus 25 on top, MightyMike 40 on the bottom) It may not be a perfect direct comparison but its pretty clear The Rodenstock Rodagon-WA 40mm F4.0 should out contrast, out sharp and probably out resolve the Venus 25 at when the Venus is at F2.8. I'm sure the Venus 25 performs better stopped down.

Now before I get to the show part of the show and tell here are a few things I learned during this process (some before as well)

1) The aperture = the existing aperture * (magnification + 1)... So at F11 and 2.7x magnification you're effectively at F40.7, at F11 and 5.5x magnification you're effectively at F71.5. However this doesn't mean that you're deep in diffraction or that you've got great pinhole type DOF. what this tells us is that the amount of light reaching the sensor plane is similar to that of F40.7 or F71.5 or whatever you calculate but as far as DOF and diffraction go you're still at F11 (by this example) you just need more light.

2) My death ray can emit as much as 700x the amount of light of the sun at a short distance with all 8 lights, however when I considered putting all 8 lights into a semi-circle so that I could get lower to the ground I found that I'd have to move them further from the subject and I'd ultimately have less light on the target then the original full circle design. That said I recalculated for 5 then 3 lights and found 3 of the lights crammed together tightly produces the same amount of light on the target as 8 in a circle further apart. This means I can use fewer lights, less power, have a longer battery life and still have the same amount of light on the subject. Of course so long as the subject is small enough to fit in between the lights.

3) 700 times the brightness of the sun emitted doesn't mean 700 times the brightness of the sun making it to the sensor. Not all the light hits the subject and the subject is not likely to be 100% reflective. To put things into a different perspective 700 times is just about 9.5 stops. In practice I seem to be getting somewhere in the ballpark of 2-4 stops brighter than sunlight back to the sensor. Clearly there is a lot of wasted light and no easy work around.

Finally here are the photos of the MightyMike 40mm F4.0 2x-5.5x Modular Super Macro Lens. You may notice the enlarging lens is in reverse, that is actually how its used in practice and therefore will likely offer the best results. Photos from the lens will be in the following replies.

Configured for 2x magnification

Configured for 2.7x magnfication

Configured for 5.5x magnification (magnification scale in 0.5x increments)

A reversed M42 extension tube works as a hood and the attachment for the lighting rig, removing this will offer 12mm more working distance however the lighting rig would cover the aperture ring (not impossible to fix, the fix may come later)

Configured for 2.7x magnification on a K10D with the new Death Ray configuration and the lights pointed perpendicular to the subject

Configured for 5.5x magnification on a K10D with the new Death Ray configuration and the lights pointed perpendicular to the subject

In this case we're at 2.7x magnification but I've moved the lights back as they're on their own helicoid extension tube to allow for more room for the subject, I should be able to go beyond this position as well

Just the lens and the lighting rig

from the back

Both mount plates, 1 for 3 lights, 1 for 4 lights. however the difference one should get for adding a 4th light is just 1/3rd of a stop.

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Mike from Canada
"I am not a great photographer! God is a great creator! All I do is capture His creation with the tools He has provided me."
'I like to think so far outside the box that it would require a telephoto lens just to see the box!' ~ 'My Quote :)'

Pentax K10D
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