[Michael Piziak]

Reverse lens adapter on a macro lens - what happens ?

I'm just curious what happens - I have these 2 manual lens, the Asahi Pentax 50mm M macro (f4) and the Asahi Pentax 100mm M macro (f4)

The only other lens I have are the 18-55mm kit lens, 55-300mm lens, & a manual Asahi Pentax F1.7 M prime lens. I'm assuming the kit lens or F1.7 lens is what one should really try reverse lens adapters on.

Last question. Is there any advantage of buying a reverse ring for a particular lens if one already has my 2 macro lens (and I have the Asahi Pentax set of 3 extension tubes)...

---

Last edited by Michael Piziak; 01-11-2023 at 09:18 PM.

[lxdude]

No advantage. Macros are optimized for close distance, highly corrected, with high resolution and flatness of field. Reversing it will not improve it.

When all I had was a 55mm 1.8 lens (decades ago) I got many very good close-up and macro shots with a reversing ring, with tubes for getting even closer. When I got a 55mm 3.5 macro, I tried it reversed and found no benefit, except the deeper front element to filter ring distance gave a bit more magnification. That wasn't worth the loss of auto diaphragm, and the uncertainty of possible loss of optical quality.

A lens optimized for infinity will give better results reversed than not, at macro range. The reason is that the proper light path is restored, or nearly so. That is, normally the distance from lens to subject is much larger than the distance from lens to film. In or near the macro range with a reversed lens of normal or shorter focal length, the distance to the subject is much shorter, approximating the distance from lens to film, so the light follows the approximate path light normally does, only in the opposite direction. That is, it enters the rear (mount side) of the reversed lens at or near the same angle it normally exits the lens.
With the addition of tubes or bellows the distance from lens to film is increased, and the light even more closely follows the path through the reversed lens as it does through the unreversed lens set at closest focus.

I just tried gaining better magnification by attaching the 100mm macro normally, racked out to 1:2, then reverse attaching the 50mm macro to its front, as a highly corrected front diopter. It increased the magnification to around 4:1, but left almost no working distance and vignetted. The deep recess of the elements kept it further from the front element and made it less effective. Then I tried the f/2 50mm on the front instead and got about the same magnification, much less vignetting, and about 1 inch working distance.

I tried reversing the 100mm/f4 macro, and couldn't get it to focus without adding extension tubes and it reduced magnification by about a factor of 2, compared to normally mounted on the same tubes and set to infinity. I'm guessing that the 100 being a telephoto, reversing it is like looking through the opposite end of a telescope, minimizing instead of magnifying.

Overall, I think tubes or bellows are better with macro lenses, with the lenses unreversed.

[MossyRocks]

I am not sure how a reverse mounted 50mm macro would perform but a regular 50mm would likely get close to a 1:1 macro so reversing a 50mm macro likely wouldn't provide any benefit. I don't' have the M 100mm F/4 macro but for S&Gs a couple of years ago I reverse mounted my D FA 100/2.8 WR Macro. I also had a helicoid in the mix. With that setup I was still basically able to focus to infinity and it would get into the macro range as well. I am unsure how close to 1:1 I could get but it was fairly close from what I can guess. With that setup it was mostly to see what happens after seeing some shots with the Auto 110 70mm F/2.8 reverse mounted on a K-1. Basically the Auto 110 70/2.8 has some massive but fun field curvature so I wondered if other lenses would give that effect. With what I had I did find that the 77ltd and the D FA 100/2.8 WR macro will produce some big field curvature away from the center of the frame. It is a fun effect and I will use it from time to time. For some reason I can't find the thread I started for doing dumb things like that where I have a shot showing the effect with the D FA 100/2.8 WR macro but it was named something like "you're using it wrong".

[MarkJerling]

Reverse lens adapter on a macro lens - what happens ?

I'm just curious what happens - I have these 2 manual lens, the Asahi Pentax 50mm M macro (f4) and the Asahi Pentax 100mm M macro (f4)

The only other lens I have are the 18-55mm kit lens, 55-300mm lens, & a manual Asahi Pentax F1.7 M prime lens. I'm assuming the kit lens or F1.7 lens is what one should really try reverse lens adapters on.

Last question. Is there any advantage of buying a reverse ring for a particular lens if one already has my 2 macro lens (and I have the Asahi Pentax set of 3 extension tubes)...

Reverse mounting and/or extension tubes gets you super close to your subject. This was, of memory, using a very ordinary 50mm manual lens, reversed.





In short, reversing a macro lens will get you much closer to your subject than the "right way round".

---

Last edited by MarkJerling; 01-12-2023 at 04:04 PM. Reason: Added information.

[MossyRocks]

In short, reversing a macro lens will get you much closer to your subject than the "right way round".

Now I kind of want to be dumb and do this with the DA 35/2.8 macro just to see.