An interesting comparison test I just made!

Cyclops · Post by **Cyclops** » Fri Aug 28, 2009 1:11 pm

Before I got the macro lens one way of getting close ups was to use my 75-300 zoom with a +4D close up lens attached.
However I havent used that method in a long time, and not very often and now I know why!
Recently the topic came up on another site and I said that using a 75-300 at 300mm would have the advantage of a bigger working distance. However one result from this test is that thats not true at all! The lens was just as close to the subject as it would be if using the 100mm macro!
But thats not the biggest disadvantage by far, as you will see in the enclosed pics!

First up the 75-300 and +4D

same shot with the 100mm

Next subject, can you tell which lens is which?

and a link to a shot with the 75-300 at closest focus-its not good!
http://img.photobucket.com/albums/v11/D ... 300_4D.jpg

The thing is, I'm trying to figure out what magnification I should get when using the 300mm focal length with a +4D.
My calculations give me 1.2X, but that shot in the link looks higher than that.
Could this be because the 300mm with a smaller sensor gives a focal length of 480mm due to the crop factor?(It doesnt give an increased focal length but you know what I mean)

So a 480mm lens with a +4D lens would give....1.92X
Hmmm.
Either way it aint a viable alternative method of getting good macro shots!!

ChrisR · Post by **ChrisR** » Fri Aug 28, 2009 1:43 pm

It's useful to record just how ghastly things can be, eh?!
The 4D is 250mm of course, but cost a fraction of the zoom's price, so we shouldn't expect too much.
There's another thread - bound to be delved into by Rik, about how you don't tend to get what you expect physically when you combine lenses.
A 300 + a 250 "should" give you (300+250)/4 = 137.5mm. You could work out what the extension of the zoom "must" be for a given distance marking , apply that to a 137.5mm lens, and work out what the mag should be. When I've tried it, it's always been a mile out. Much of the reason is that the sums are for "thin" lenses of course.

I have a 3D close-up, and that's pretty awful too, but a 1D on a 400mm lens is very effective and not toooo bad.
NB the Nikon T close-ups are doublet lenses as is the Canon 500D. they're all of the order of a couple of D, and the stronger Raynox close-ups are 4 element lenses, with a price to match.

Cyclops · Post by **Cyclops** » Fri Aug 28, 2009 2:10 pm

Well how I worked it out was:
1/4=0.25
0.25*1000=250
300/250=1.2X (1.2:1)

or allowing for the sensor crop factor
480/250=1.97X (1.97:1)

As a side note, the shot of the rose with the macro lens was actually not bad and I uploaed it as a full size image here:
(OK to post a link I hope)
http://stumm47.deviantart.com/art/Mini-Rose-135074898

rjlittlefield · Post by **rjlittlefield** » Fri Aug 28, 2009 2:10 pm

As predicted by ChrisR, here's a bit of analysis that takes a different tack from his.

A +4D closeup lens has focal length of 1/4 m = 250 mm.

If the subject is exactly 250 mm from the closeup lens (and the lens is accurately spec'd!), then the rear lens will see the subject at infinity. In that case, if the rear lens is set at 300 mm, then the magnification should be 300/250 = 1.2X, and it shouldn't matter how the lenses are designed.

If the subject is any farther than 250 mm from the closeup lens, then it is effectively "beyond infinity" for the rear lens, and you won't be able to focus on it.

The case that's hard to analyze is when the rear lens is focused closer than infinity and the subject is correspondingly closer than 250 mm from the closeup lens. In fact it's so hard to analyze that I don't even try. I used to, but after much frustration I gave up and switched to just photographing a ruler.

You mention that the photo at the link "looks higher than that", which I presume means higher than 1.2X. If I'm reading correctly, you also say that the shot at the link is with the 75-300 is at closest focus. Yes, that will give more magnification, though how much more, I'm not going to hazard a guess. In any case, if you really care about magnification, I suggest photographing a ruler and dividing field width by the sensor size. Impressions are highly unreliable -- at least mine are -- and simply dividing field width by sensor size gets rid of all that "crop factor" confusion.

The ghastly CA and fuzzy edges you're experiencing is typical of inexpensive closeup lenses. I have a small collection of these from many years ago that now gather dust for exactly the reasons you've so clearly documented.

--Rik

Cyclops · Post by **Cyclops** » Fri Aug 28, 2009 2:17 pm

rjlittlefield wrote:

The ghastly CA and fuzzy edges you're experiencing is typical of inexpensive closeup lenses. I have a small collection of these from many years ago that now gather dust for exactly the reasons you've so clearly documented.

--Rik

Yes and an interesting result for me is that even if I had a quality close up lens to use with the zoom I still get no greater working distance than if I used the 100mm!
So in other words, and to sum up, theres no benefit!

ChrisR · Post by **ChrisR** » Fri Aug 28, 2009 2:28 pm

So in other words, theres no benefit!

Well you've made yourself a 137mm, or something, lens, so it would behave like a 100, ish.

Whereas if you use a drainpipe of extension tubes behind the 300, you'd get a good working distance, probably at f twenty-something at 1:1 wide open.

Cyclops · Post by **Cyclops** » Fri Aug 28, 2009 3:05 pm

One other difference between the two lenses,aperture. The 75-300 goes down to f45 at 300mm! Mind you its awful dark when you press the stop down button,and these shots were 30 second exposures!

rjlittlefield · Post by **rjlittlefield** » Fri Aug 28, 2009 3:35 pm

ChrisR wrote:Whereas if you use a drainpipe of extension tubes behind the 300, you'd get a good working distance, probably at f twenty-something at 1:1 wide open.

Cyclops wrote:The 75-300 goes down to f45 at 300mm!

Ah, now there's a combination. Nominal f/45, plus a drainpipe of extension tubes for 1:1, throw in a pupillary magnification factor of 0.7 or so for the zoom, and you too can have a lens system at effective f/109.

I tried effective f/90 once on my 300D. [ref] The images would have been fuzzy even printed at postcard size.

--Rik

Wayne Baker · Post by **Wayne Baker** » Fri Aug 28, 2009 8:37 pm

I tried a magnifying glass from the $2 shop once - was about the same quality result as the $200 Hoya set I purchased - what a waste of cash that was....

Cyclops · Post by **Cyclops** » Sat Aug 29, 2009 11:53 am

Well one more thing for me to try,and inspired by Rodrigo (ironman_br) the next thing to try is reversing a 50mm onto the 75-300mm. At 300 that would give me 6x!

ChrisR · Post by **ChrisR** » Sat Aug 29, 2009 1:15 pm

I tried a 20 on a 400. The result was so forgettable I've forgotten what happened.

Cyclops · Post by **Cyclops** » Sun Aug 30, 2009 4:34 am

ChrisR wrote:I tried a 20 on a 400. The result was so forgettable I've forgotten what happened.

Crikey,thats 20x! With a telephoto. No wonder it was forgettable! It must have been dark in the viewfinder,probably lots of vignetting too!

Cyclops · Post by **Cyclops** » Wed Sep 02, 2009 8:05 am

rjlittlefield wrote:
I tried effective f/90 once on my 300D. [ref] The images would have been fuzzy even printed at postcard size.

--Rik

That was interesting to see Rik. EDOF looks good!

PaulFurman · Post by **PaulFurman** » Sat Oct 31, 2009 4:07 pm

ChrisR wrote: Whereas if you use a drainpipe of extension tubes behind the 300, you'd get a good working distance, probably at f twenty-something at 1:1 wide open.

I tried a 20 on a 400. The result was so forgettable I've forgotten what happened.

This got me tinkering... I have a 300mm f/4 medium format CZ Jena lens without the focusing helix, just the glass & metal that holds it... which is still pretty big. I know it's not very good at close focus from experience (pretty good at infinity though) so I thought, hmm, maybe reversed? So I put it on a bellows reversed and I could not get it to form a focused image at all. At about 20 feet I can barely make out rough shapes. Mounted normally with 200mm extension it focuses to about 5 feet. I don't know what's going on.

ChrisR · Post by **ChrisR** » Sat Oct 31, 2009 4:29 pm

Mounted normally with 200mm extension it focuses to about 5 feet

You wouldn't expect too much from it reversed.

What you've giiven us above means that roughly if it were on 5 feet (1500mm) of bellows, it would focus on a subject 200mm in from of it.
Magnification would be approx 1500/200 (can't be accurate without knowing the dimensions etc of what you have) and the effective max aperture f 30 something. (f4 x (M+1))
That's a heck of a Working Distance, but probably not a particularly useful setup for many subjects! A little unwieldy to focus, given that the depth of field would be very small.

If you could arrange it with enough extension that it would be focussed at infinity, and used say a reversed 50mm lens on the front, you'd have a 6x combo with a Working Distance about 40mm from the 50mm lens's flange, depending on what it were deigned to fit. (ie, where the film/sensor would normally be)

I suspect my dismal results might have been due to the wide-angle lens's Curvature of Field; a 50mm should be a lot better.