[Thagomizer]

Hi all;

Let's say I'm trying to get to 2:1 reproduction ratio. This could be achieved several ways: 24mm reversed on a 50mm (more than 2:1, I know), 35mm reversed on a 70mm, 50mm reversed on 100mm, etc. Obviously there are going to be differences in the total length of the resulting set-ups and some might work better due to the actual quality of the lenses involved or their particular design (a slower f2 or f1.7 50mm, for example, is supposed to work better as a reversed lens than a 1.4 or 1.2). Given that each of these combinations would result in 2:1, is there any other reason, apart from those noted above, to go with one pairing over another? Are they going to give the same working distance? Will the angle of view correspond to the focal length of the primary lens mounted to the camera? I haven't got around to actually trying many of these for a semi-rigorous comparison, but I'm curious as to what I might expect.

[ChristianRock]

If I may ask, why not just reverse the lens without using a 2nd lens? I have done it a few times with 24mm, 28mm, 35mm and 50mm lenses, and I've been happy with the results most of the time. Adding a 2nd lens only adds even more glass elements to the setup, which I'm sure won't help optically. I have found out that flat field lenses (such as my M 50 f4 macro or my M 50 1.7) work better than lenses that have a bit more field curvature (like most 50 1.4 designs). The M 28 3.5 also works very well, as do most 24 2.8 designs.

[pathdoc]

Because double-ended reversing rings are cheaper than reversing adapters that go into the mount, and keeping a right-way lens on the mount enables you to have active all those snazzy features that come with full aperture, distance and data communication, e.g. PTTL.

On the flipside, the direct-mounted reverser does enable you to do insane things like putting a D-A or D-FA lens on an M42 film camera that is potentially older than most of the DA lenses' designers. Which gives you bragging rights, I guess, but I don't know what else.

[baro-nite]

The idea that a lens reversed on extension gives a higher-quality result than reversing onto a second lens is incorrect in my experience. I've tested quite a lot of both. You can get excellent results either way, but stacked lenses tend to do better in the edges and corners of the image. Just give it a try and see how you like the results.

[Thagomizer]

Thanks all. I suppose I'm bound to find out these answers myself as I've got lots of toys to work with. I've got extension, (M42, dumb PK and deglassed TC PK-A), Vivitar Macro focusing 2X TC (in both PK and PK-A versions), M42 bellows, reverse adapters for PK and M42, and lens stacking adapters (mostly DIY from step up/down rings). For actual 1:1 macro lenses I've got Sigma the 50mm f2.8 EX DG and the Sigma 70mm f2.8 EX DG; at 1:2 I've got a Super Takumar 50mm, SMC Takumar 100, Tamron 90mm f2.5 52BB. I've used Pentax A and M 50mm f1.7s and a Vivitar 28mm f2.8 reversed, as well. A reversed KInotel 1.5" f1.9 8mm movie lens on extension gives great results, too. The "Shanahan solution" of reversed normal to short prime on a TC also works well.

I've played with most of these, in various configurations, but haven't done a close scientific-ish comparison between them. The ease of use (automatic diaphragm, auto aperture, of a true 1:1 PK-A mount macro lens is hard to beat, but I like being able to push beyond 1:1, hence my interest in reverse stacked lenses.

At this point I'm more interested in single shot, hand-held field work as opposed to focus stacking techniques. Not that I won't pursue stacking in the future, but my interests at the moment are of a more in-camera rather than post-production mode. I'm still learning. Hanging out here helps a lot. I know a lot of the people here have done more of this for far longer and drawing on their/your expertise is very helpful. As I do more of my own experimentation and testing over the winter, I'll post my results on the Forum. That's the plan,anyhow....

[tryphon4]

Why don't you try a good (achromatic) closeup lens?

I guess you ignore the main macro principle: Macro ratio is only a question of :
- distance between the lens back and the film/sensor
- lens focal length.

A closeup lens is a very simple lens, so using a closeup or a reversed lens is practically the same. You have to keep in mind that a closeup or a reversed lens decreases the resultant focal length.

The focal length choice is very important because :
- retrofocus lenses are not well suited for macro1
- the distance between the lens back and the film/sensor, for a given macro ratio, is proportional to the lens focal length
- the working distance is proportional to the lens focal length2

1If you reverse a retrofocus lens, due to its optical formula, the working distance could be less than 0mm. Most of 24x36 wide angle lenses are retrofocus. On another hand, a wide angle lens is like a very powerful closeup (35mm= about 29diopters, 20mm=50 diopters) so a (reversed3) wide angle lens, combined with another lens, can be useful.

2i.e, a 50mm4 lens, at 1:1 and up (even at 10:1) will give a working distance of about 50mm. A 100mm lens, at 1:1 and up (even at 10:1) will give a working distance of about 100mm. It is quite easy to measure it.

3 In the macro world, reversing a lens is very common but the explanation is a bit complex.

4 Here we speak in terms of resultant focal length (take into account the closeup/reversed lens effect!)

So if you need a huge working distance, you need a huge focal length.
For most of my recent macro shots I use a 2:1 60mm, it gives a nearly 60mm working distance but if I need more, I use a 90mm or even a 105mm (assuming that I am able to manage a very long extension tube).

[Doundounba]

If you just want to get to 2:1, then my choice for that is a Raynox DCR-250 on a 100mm macro. It's just much more convenient than shooting anything reversed (coupled or not), where you need to stop down the reversed lens and it can become very hard to see anything... (Some people shooting reversed lenses even add bracket-mounted flashlights to their setups to aid with focusing.)

But, for your question - which combo precisely if/when shooting coupled reverse lenses - I'd opt for: 0) A prime for the primary (non-reversed) lens; 1) those lenses you have which you think are the sharpest when used normally; and 2) lenses that give you a combo that is the proper length to have good diffusion. I'm not kidding about that last point - good light is super important, IMHO. Whatever you best diffusion setup is - jerry-rigged DIY or store-bought - it will be appropriate for a certain length of setup. For me, for example, I'm setup to shoot with horizontal flash, so using a physically longer lens combo works better for me. If I wanted to shoot something very short (say a reversed 28mm by itself), it would mess-up my light, and I'd need to make a new diffusion setup. (So, for example, to get 4:1, I would choose to couple a 200mm and a 50mm rather than a 100mm and a 24mm.)

For lenses, in practice, we're blessed in Pentax land with a bunch of pretty good old primes to choose from. You can get an M-series lens in 85mm, 100mm, 135mm, 150mm and 200mm. For best optical results, probably get them all to use as primaries, get an old 28mm and an old 50mm for the reversed lens, then pick your exact combo based on the magnification you want.

On the other hand, for flexibility, I like to use a reversed zoom as a secondary, which allows one to change magnification on the fly based on the subjects one encounters. (It's better to use a zoom as a secondary, not a primary.) I've tended to use an M 135mm F/3.5 with a reversed 24 or 28 to 70mm zoom as a kind of poor man's MP-E - giving a workable range of 2:1 to about 5:1. (Be aware that at high magnification, diffraction can really hurt your shots though... ) I've been known to carry that pre-assembled in my bag, with the 100mm macro plus Raynox DCR-250 on the camera. That gives me fairly easy access to infinity to 5:1, with 0.8:1 to 2:1 as the main working magnification range (the range of the 100mm plus Raynox combo).

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Last edited by Doundounba; 12-16-2017 at 01:04 PM.

[photoptimist]

Hi all;

Let's say I'm trying to get to 2:1 reproduction ratio. This could be achieved several ways: 24mm reversed on a 50mm (more than 2:1, I know), 35mm reversed on a 70mm, 50mm reversed on 100mm, etc. Obviously there are going to be differences in the total length of the resulting set-ups and some might work better due to the actual quality of the lenses involved or their particular design (a slower f2 or f1.7 50mm, for example, is supposed to work better as a reversed lens than a 1.4 or 1.2). Given that each of these combinations would result in 2:1, is there any other reason, apart from those noted above, to go with one pairing over another? Are they going to give the same working distance? Will the angle of view correspond to the focal length of the primary lens mounted to the camera? I haven't got around to actually trying many of these for a semi-rigorous comparison, but I'm curious as to what I might expect.

Assuming all the lenses are set at infinity focus:

1. The best pairing will depend on the quality of the two lenses. I'd pick the pair in which the rear lens has the best corner-to-corner sharpness at the planned operating aperture as long as the respective front lens does not totally suck in the center. Also some pairs (probably the wider-angle pairs) might have more vignetting than others.

2. The working distance (from the front lens to the subject) would be the same 45.46 mm Pentax flange focal distance for all pairs. If you play with the focus or add extension, then working distances will vary.

3. the angle of view will depend on the internal design of the front lens. In particular, what matters is the location of that lens' rear exit pupil. For simple normal and telephoto lenses, it will tend to be proportional to focal length. But for wide angle lenses and zooms it could be anything.


P.S. A reversed lens is an achromatic close-up lens of diopter +1000/f.

[tryphon4]

P.S. A reversed lens is an achromatic close-up lens of diopter +1000/f.

P.S. A reversed achromatic lens is an achromatic close-up lens of diopter +1000/f.

[photoptimist]

P.S. A reversed achromatic lens is an achromatic close-up lens of diopter +1000/f.

Quite true!

Yet virtually every SLR camera lens is achromatic. Achromatic implies designing a lens with at least two elements and optimizing it to bring two wavelengths of light (usually blue & red) into focus at the same place. The subtle green and magenta fringes in out-of-focus areas are often found in achromatic lenses.

What is rarer are apochromatic designs which require at least three elements and designing the lens to focus at least three wavelengths in the same place.

Cheap close-up lenses tend to have a single element so they are not achromatic.

Better close-up lenses have at least two elements so they may be achromatic.

I don't know if any close up lenses are truly apochromatic although a quick internet search suggests that some achromatic lenses have been misidentified as apochromatic.

[Thagomizer]

Thanks everyone for the great information.

tryphon4 and Doundounba: A Raynox of some flavour is definitely on my "To get (at some point) list." a longer 1:1 macro (90-105mm range) is on that same list.

The 2:1 ratio was mostly a theoretical example as the math is easy and I've got a number of ways to get there. I was just wondering if there were any factors I was overlooking (like lighting diffusion, thank you Doundounba!) that might favour one combination over another.

I've got a K 135 f3.5 to use as a primary. I've also got some older zooms with aperture rings (F 35-70, a couple of other film era kit lenses) that I've yet to try as a DIY MP-E65. I'd only thought of using it reversed on extension (as per Johan's suggestion) , but never thought of reversing it on a primary (thanks Doundounba).

photoptimist: I'd suspected that working distance would equal flange focal distance (with everything at infinity); it was good to hear this confirmed.

Lots of great information and ideas. Thank you for sharing: I shall do likewise as I learn.