[UserAccessDenied]

Ok, I'm trying to calculate magnification and have found posts and threads in regards to two separate equations... Now can I just add these together? See below for details:

I'm using extension tubes with a macro lens and a reversed lens at the end...

These equations are not my own derivative -

Magnification1 = Total extension of tubes / Focal length of lens + intrinsic extension of lens

Magnification2 = Focal length of lens / focal length of reversed lens

So, I'm going to calculate Mag1 first, then add Mag2?

Mag1 = 49mm (tube entensions) / 105mm (lens) + 1 (intrinsic extension of 1:1 macro lens) = 1.46 (this is now my intrinsic extension value...)
Mag2 = 105mm / 50mm (reversed prime) = 2.1

Mag1 + Mag2 = 3.56

So according to these calculations, I'll achieve 3.56:1 with this setup.



I just want to know if algorithmically this makes sense. I know about the loss of light and stability and paper thin DOF and distance to subject... I just want to know if I can use these equations in the future.
Ideally, I'll throw on a subject, take a picture of a metric ruler and calculate the true magnification based on the size of my sensor. But when it comes to purchasing or acquiring tubes and rings and lenses prior to being able to test them, an equation to roughly estimate is definitely helpful!


Let me know if you guys have suggestions or have been able to confirm the equations above.

Thanks!!

[dms]

You cannot add a reversed lens to the 105mm on extension--you will only get the center of the image. Simply reverse a wider angle lens on the 105 mm. Or as a start (not as good optically) add more extension to the 50mm lens. BTW if it is a fast 50mm (f/1.4 or f/1.2) it will not do as well optically and will need to be closed down more.

On second thought I am not sure if the 105mm on 49 mm extension will work--it may. Added to that the extension of the 105 mm lens--I think even more likely to cause vignetting. But I have never tried it nor do I recall seeing this done in this way. However, the equations seem OK. I guess my point is w/ reversed lens the magnification is likely OK but the results may not work w/ a shorter FL main lens (105 mm in your case is already pretty short--but likely OK for a 1.5x cropped sensor) or w/ the main lens on significant extension.

On third thought! (Sorry.) More extension is less reason for vignetting so long as the image can be focused, so your approach may be fine.

[UserAccessDenied]

You cannot add a reversed lens to the 105mm on extension--you will only get the center of the image. Simply reverse a wider angle lens on the 105 mm. Or as a start (not as good optically) add more extension to the 50mm lens. BTW if it is a fast 50mm (f/1.4 or f/1.2) it will not do as well optically and will need to be closed down more.

On second thought I am not sure if the 105mm on 49 mm extension will work--it may. Added to that the extension of the 105 mm lens--I think even more likely to cause vignetting. But I have never tried it nor do I recall seeing this done in this way. However, the equations seem OK. I guess my point is w/ reversed lens the magnification is likely OK but the results may not work w/ a shorter FL main lens (105 mm in your case is already pretty short--but likely OK for a 1.5x cropped sensor) or w/ the main lens on significant extension.

On third thought! (Sorry.) More extension is less reason for vignetting so long as the image can be focused, so your approach may be fine.

Thanks for the response dms,

The 50mm I'm using is an old manual F1.7, but the aperture ring is there so I do stop it down to F11 or F16.

I'd love to find a cheap 24mm to use with this setup, but budget is tight right now and I just haven't found one yet...
Even if it's not K mount! I really only need one with a clean filter threading so I can reverse it!

I might even try to MacGyver an old m42 lens so the exposed threading while reversed can still hold my DX-8R ring flash.
So if I can find an old m42 24mm lens with aperture ring for under 50$, I'm in! hahaha


Thanks for the tips!

[Glorfindelrb]

Simple tip to check your calculations if you already have your setup: shot a ruler and just use 'sensor size'/'visible ruler size'.

[dms]

At very high magnification resolution will suffer due to diffraction. Probably best to use f/4 to f/5.6 on the reversed lens. The 50 mm f/1.7 does well in macro--even pretty wide open.

I suggest Lefkowitz, "The Manual of Close-Up Photography" (Amphoto 1979) as a reference. He discusses every approach and often gives comparison pictures.

[UserAccessDenied]

Apparently reversing a 24mm prime to a 105mm macro would produce 5.375:1 magnification when considering the intrinsic extension of the macro lens...

That's INSANE!

with just the 50mm reversed I'm achieving 3.1:1
That's still pretty tough to focus in the field...
EDIT: Just breathing can knock the subject out of focus, not to mention the subject itself moving or the wind blowing.

Seems to me that 3:1 magnification is my threshold for handheld field work. If I can setup a tripod and get the lighting just right, maybe 5:1 or greater can be achieved, but for now I'm still learning the basics.

One of my friends said at 6:1 he could see his subject coming in and out of focus to the rhythm of his heart beat. That's something to think about when your DOF is literally paper-thin.

I can't wait to get the adapter in the mail so I can actually get to practicing techniques at these magnifications!

Maybe I'll just buy a 24mm prime anyways, wouldn't hurt to have such a focal length in the bag.

[baro-nite]

In my experience, meaningful 6:1 magnification isn't possible with ordinary camera lenses, because of the diffraction problem (or, in the case of larger formats, because of the problems of projecting a large enough image circle). Yes, you can put, say, a 24mm lens reversed onto a 150, but you aren't going to capture more detail than you would with a good 3:1 or maybe 4:1 setup. dms has it right, once you get to these magnifications if you want maximum detail you need to keep aperture ring settings pretty wide. At 3:1 you can get away with f/8, and at 4:1 you'd better keep it to f/5.6 or below. Of course that means very thin DOF, which is where focus stacking comes into play. Also, as dms points out, vignetting can be a problem with certain combinations of lenses and/or extension. Best way to find out is simply to try different combinations.

5:1 is possible with a specialized lens. Beyond that the best bet is microscope objectives, which can be sharp at very low f-numbers, at the cost of very short working distance and reduced image circle. But there are some that work well for DSLR photomacrography.

Back to your question about calculating magnification, adding a supplementary lens (such as a reversed lens) effectively shortens the focal length of the entire system as compared to the primary lens, so you'd need to calculate that to figure the effect of the extra extension. Sorry, I don't know the formula. I have often used Glorfindelrb's method of photographing a ruler.

One of the best lenses for reversal is the "K series" 28/3.5, and it's also an excellent lens used normally. However, I've found that humbler lenses do just about as well for stacking Edit: for stacking lenses, that is.

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Last edited by baro-nite; 03-26-2015 at 07:31 AM. Reason: clarification

[UserAccessDenied]

I reversed my 50 to my 105 last night with a rubberband just to get a feel for how it will look.

wow! Magnification is 3:1 easily. DOF is paper thin and I had to hand-hold my ringflash; but I'm very excited to play around with this setup.


Baro-nite: do you know of any good focus stacking software for Mac? preferably free?
I use GIMP right now, but I don't think there is a focus stacking feature. Atleast not that I know of.


Thanks!

[baro-nite]

I use Zerene Stacker. I run it on Mac OS; it's a Java app. I do enough stacking that I've found it well worth the money. There's a student edition if you happen to fit that category. There's a 30-day free trial. There's a fairly hefty learning curve, so if you decide to try it out, stick with it for a while. The main thing is learning to use the retouching tool efficiently -- this is essential for getting the best output with just about any stack.

The developer is the guy who runs photomacrography.net and its associated forum, the place to be if you want more information about extreme macro and focus stacking.

[UserAccessDenied]

I use Zerene Stacker. I run it on Mac OS; it's a Java app. I do enough stacking that I've found it well worth the money. There's a student edition if you happen to fit that category. There's a 30-day free trial. There's a fairly hefty learning curve, so if you decide to try it out, stick with it for a while. The main thing is learning to use the retouching tool efficiently -- this is essential for getting the best output with just about any stack.

The developer is the guy who runs photomacrography.net and its associated forum, the place to be if you want more information about extreme macro and focus stacking.

I'll have to check that out..
I was really hoping to find some open-source software, but seems like that just doesn't exist right now (for Mac OS at least)


I've heard great things about Zerene Stacker. Just gotta justify the subscription!
I'll download the trial and give it a run once I have a decent amount of stacks to test out!

Thanks again!

[Nass]

Zerene is the one I use as well, it's the class leader for focus stacking. There are some free stacking softwares here, but I can't say I've had much success with them myself. If you get any working on a mac could you ping me a mail so I can update the page? This thread actually inspired me to get my butt in gear and finally create some macro calculator tools that I've been meaning to add to my site for some time - I'll be adding more in time, and where appropriate, with a Pentax slant too (ie sensor size, lenses). Please do note that the equations are all a tad approximate, this is a bit unavoidable because we don't necessarily know such things as the optical centre of a lens or its exit pupil.

[UserAccessDenied]

Zerene is the one I use as well, it's the class leader for focus stacking. There are some free stacking softwares here, but I can't say I've had much success with them myself. If you get any working on a mac could you ping me a mail so I can update the page? This thread actually inspired me to get my butt in gear and finally create some macro calculator tools that I've been meaning to add to my site for some time - I'll be adding more in time, and where appropriate, with a Pentax slant too (ie sensor size, lenses). Please do note that the equations are all a tad approximate, this is a bit unavoidable because we don't necessarily know such things as the optical centre of a lens or its exit pupil.

Your site is great!
Lots of information there and I can't wait to try Zerene out... I heard there is a learning curve so I'm waiting until I have a nice repository of photos to stack, then I can sit down and spend a few hours on it...
I strive through trial and error... Especially in this digital world; I envy the photographers of the film era!
Today I can setup my tripod and test out a plethora of settings and after 1000's of shots, pick through to find 5 or 6 decent results... We're spoiled now...