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06-01-2011, 10:09 PM   #1
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Which reverse ring?

I want to be able to reverse my lens for some macro/closeup photography. Which reversal ring should I buy? I want something that is quality made. Which coupling ring should I get?

And any extension tube recommendations would be a appreciated as well

06-01-2011, 10:38 PM   #2
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I have a basic 49mm reversing ring that I use to put an old Super Tak 28mm f3.5 in front of a Super Tak 55mm f2.0 with a 2x Teleconverter to get right in close.. but if I need more light I put a 43 Ltd in front of the 55mm and have had pretty good results.
I haven't had a chance to pick up any extension tubes, but I sure would like to!

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06-01-2011, 10:44 PM   #3
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You'll need a 52mm reversal ring if you're planning on using your K55mm 1.8 lens.
06-01-2011, 10:49 PM   #4
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Does it matter how much space is between the lens and body or between 2 lenses? Can I use step up and step down rings to adapt whatever lens?

06-02-2011, 01:04 AM   #5
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I would use a decent quality reverse ring. I have both a Pentax 49mm and a 52mm one. Both were picked up quite cheaply on "that" place.

I would not use step rings as you would be using then between the lens and camera. To maintain quality, you need to make sure the lens is correctly aligned to the light path. This is not that important to filters and certainly not for hoods. There is always a "cheap" way to do things and great fun for trying ideas out but quite often "cheap" = degradation in quality

Kim

QuoteOriginally posted by geekette Quote
Does it matter how much space is between the lens and body or between 2 lenses? Can I use step up and step down rings to adapt whatever lens?
06-02-2011, 10:17 AM   #6
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QuoteOriginally posted by geekette Quote
I want something that is quality made.
While you search for something that's "quality made" you may want to try removing the glass from two cheap filters and epoxying them together. 49-49, 49-52, 49-55mm, etc.

I've got a drawer full of DIY reverse rings made that way. Some have lasted for over twenty years so I suppose the quality's OK and the price is certainly right. That's about all many of the old film-era filters are good for today other than stacking 'em to make custom hoods.

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06-02-2011, 11:14 AM   #7
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The only quality parameter I'm aware of is the material the rings are made of. Aluminum is most common and has an unfortunate tendency for the threads to seize making it difficult to unscrew rings once mounted. This can be avoided by applying a bit of solid wax to the ring's threads. Brass is best.

Unfortunately the construction material is not often specified.

In my limited experience almost any inexpensive tubes will do as will any reversing ring (with the caveat of thread lubrication in mind).

I know of little practical degradation of optics due to stacking filter rings to adapt from one diameter to another when reverse stacking lenses. While it is true that lens misalignment would be detrimental, it is hard to imagine a way to make crooked or off center adapter rings.

The separation of two stacked lenses has a small effect on the effective focal length of the stack but it is of little practical consequence (the greater the separation distance the greater the combined focal length). Vignetting is usually a bigger threat.

The stacked lens focal length formula is:

F=F'F"/(F'+F"-d) where d is the spacing between lenses of focal length F' & F"

The formula for the nominal magnification for stacked lenses is changed to:

m = (F'-d)/F" where F' is the primary lens focal length.
06-02-2011, 01:36 PM   #8
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Well thanks all for your help. I guess I am going to order the fotodiox 52mm reversal ring and fotodioc 52mm coupling ring. I'll try lubricating them with wax, this might help keep paint particles from getting on the lens as well.

newarts, thanks for that formula--I'll play with it once I get the adapters

06-02-2011, 02:36 PM   #9
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QuoteOriginally posted by geekette Quote
newarts, thanks for that formula--I'll play with it once I get the adapters
When you try them you'll find not much exciting. Plus they are approximations.... like exactly how do you measure lens separation distance? I think their value is in indicating how things change; they are less useful for absolute predictions.
06-02-2011, 02:56 PM   #10
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QuoteOriginally posted by geekette Quote
newarts, thanks for that formula--I'll play with it once I get the adapters
When you try them you'll find not much exciting. Plus they are approximations.... like exactly how do you measure lens separation distance? I think their value is in indicating how things change; they are less useful for absolute predictions.
06-02-2011, 08:45 PM   #11
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There are two totally different types of reversal rings, used quite differently.

1) Mount-reversal: These are threaded on one side and have a simple PK mount on the other. Screw the ring into the lens' front thread, then flip the lens around for close work. For a prime lens, working distance will be ~45mm, under 2in. So you'll work close -- but magnification comes from extension, not mere reversal. You get a little extension if the lens front is inset somewhat. For more magnification, add cheap PK macro tubes between the camera and the reversed lens.

Working distances vary when you reverse a zoom. I have a cheap A35-80, arguably one of the worst lenses Pentax ever sold. But reversed, it is quite sharp. On my K20D, at 35mm, mag= ~2x at a working distance of ~5cm. At 80mm, mag= ~0.5x at ~15cm, and it will focus past infinity for non-macro shooting. Shorter zooms like the F35-70 won't reach infinity when reversed on my K20D. Longer zooms (like a 70-200) can be reversed for greater working distance.

2) Thread reversal: These have male threads on both sides, and are used to reverse-stack a shorter (secondary) lens onto a longer (primary) lens. I typically use a 49-49mm ring to stack 28-35-50mm Takumars onto 100-105-135 lenses (mostly Taks). Magnification is given a simple ratio: primary / secondary. So a 35mm reverse-stacked on a 105mm gives 105/35= 3x. Keep the primary aperture wide-open and keep the lens fronts as close as possible, to avoid vignetting. Control the exposure with the manual aperture ring on the secondary. Working distance is still ~45mm.

The traditional field method of reverse-stacking doesn't even need a ring; just use gaffer's tape (NOT black electrical tape!) to hold the primary and secondary together. Cheap and easy, eh? As mentioned, if you use rings, rub a little candle wax on the threads to avoid binding. I use various ultra-cheap thread- and mount-reversal rings with no problems.
06-02-2011, 10:34 PM   #12
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So I am about to order the following Fotodiox accessories from Amazon:

Extension tube set for Pentax:
Amazon.com: Fotodiox Pentax K (PK) Macro Extension Tube Set Kit for Extreme Close-up, fits Pentax K-5, K-r, K-x, K-7, K-m, x70, X90, K200d, K20d, K100D Super, K10D, K110D,K100D, *ist DL2, *ist DS2, *ist DL, *ist DS, K1000, K2000, K-M: Camera & Photo

52mm to PK mount reverse ring
52mm to 52mm coupler

I received the Fotodiox step up ring set and am pretty impressed with the quality so far.
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