Death of a spider

[LordV]

Just to celebrate my normal macro-lenses return from sigma UK. Taken with my 105mm EX on a 31mm Jessops extension ring- giving 1.5:1
Brian V.

http://static.flickr.com/27/52091355_6d2795a20d_o.jpg

[kallousa]

Man you have a real artist eye.
amazing shot for an extraordinary chance you had. Thanx for sharing

Regards

[Bald Eagle]

A most unique shot, very well done. great work.:D :D

[BigAl-SA]

That is an amazing shot Brian...

[BigAl-SA]

BTW, did you get feedback on what they did to the 105?

[RockOne]

Real interesting shot.

[pxl8]

Lovely shot, esp. the magnified leg inside the drop.

Quick question, how does 31mm of extension on a 105mm 1:1 lens give a 1.5:1 ratio?

The way I understood the maths it's something like (105+31)/105 = 1.295 at min. focus, what am I missing?

[lmele]

You do it every time Brian, keep them coming man.:)

[LordV]

Man you have a real artist eye.
amazing shot for an extraordinary chance you had. Thanx for sharing

Regards
Thanks Lallousa- comments always appreciated- esp nice ones:D
Brian V.

[LordV]

A most unique shot, very well done. great work.:D :D
Thanks BE- just lucky- I actually just thought the drop was rather interesting- didn't find out why until I converted the RAW. ;)
Brian V.

[LordV]

BTW, did you get feedback on what they did to the 105?
Thanks for the comment Al,
They repaired the iris actuator- lens seems to be behaving now.
Brian V.

[LordV]

Real interesting shot.
Thanks RockOne. Did turn out rather unusual.
BrianV.

[LordV]

Lovely shot, esp. the magnified leg inside the drop.

Quick question, how does 31mm of extension on a 105mm 1:1 lens give a 1.5:1 ratio?

The way I understood the maths it's something like (105+31)/105 = 1.295 at min. focus, what am I missing?

Thanks pxl8-
Re- magnification- Real answer is I don't know- You are correct with the above formula but not sure if it gets modified if you are using a macro lens in the first place. My emergency lens seems to follow the above- using 7.5cms of rings with a 50mm lens I got 1.5:1.
With the macro 105mm lens set at 1:1 and then adding rings I got the following using a ruler as a subject= these are the full width readings in cms. The sensor is about 2.2cms wide.

Ring length magnification factor
13mm 1.22:1
21mm 1.33:1
31mm 1.47:1
52mm 1.83:1
65mm 2:1

Brian V.

[LordV]

You do it every time Brian, keep them coming man.:)
Thanks for the encouragement Len.
Brian V.

[pxl8]

Ring length magnification factor
13mm 1.22:1
21mm 1.33:1
31mm 1.47:1
52mm 1.83:1
65mm 2:1


Thinking about it some more, it appears the crop factor of DSLR needs to be taken into account when calculating the magnification as follows:

(Focal Length + (extension * 1.6))/Focal Length = magnification

105/1.6 = 65 which gives the same results you found with your tests.

105+(21*1.6)/105 = 1.32
105+(31*1.6)/105 = 1.47
105+(52*1.6)/105 = 1.8
105+(65*1.6)/105= 1.99

It would be interesting to see if this holds true for other macro lenses or it's unique to the Sigma and the 1.6 scalar being the same as the crop factor is just coincidence...

[LordV]

Thinking about it some more, it appears the crop factor of DSLR needs to be taken into account when calculating the magnification as follows:

(Focal Length + (extension * 1.6))/Focal Length = magnification

105/1.6 = 65 which gives the same results you found with your tests.

105+(21*1.6)/105 = 1.32
105+(31*1.6)/105 = 1.47
105+(52*1.6)/105 = 1.8
105+(65*1.6)/105= 1.99

It would be interesting to see if this holds true for other macro lenses or it's unique to the Sigma and the 1.6 scalar being the same as the crop factor is just coincidence...

Yes that's interesting- why does the formula seem to work for my 50mm lens on the same camera without the crop factor. I actually wonder if when a macro lens goes macro it effectively reduces it's apparent focal length and the 1.6 X factor is a very big coincidence.
Just to show you what an idiot I can be- when I first tested the lens when I got it back from sigma with the rings etc, I could only just get it to 1.5:1 with all the rings and a 1.4X extender thrown in- I hadn't noticed they must have switched the focus limiter which stops the lens at about 1:3 max :o .

As you say would be interesting to get some data for diff focal length macros and extension rings.
Brian V.

[LordV]

It appears that focal length of a lens is based on when it is focused on infinity- it changes slightly at minimum focus- the longer the focal length the more it changes. For macro lenses it appears to be even worse at 1:1 where the focal length of canon 100mm macro lenses is about 75mm and my lens calculates as being 78mm (apparently its the MFD/4 for macro lenses at 1:1). That explains some of the extra magnification but not all (it appears to behave as a 63mm lens).
Brian V

[Guitartists]

While extremely odd and morbid.... that is amazing how the legs wrap around that beautiful droplet of water! Fantastic eye!!! :D

[LordV]

Thanks for the comments Guitartist. You could almost imagine it as a gothic piece of jewellery pearl in a gold spider clasp :)
Brian V.

[dod]

nice, very unusual :)

[mecdave]

Cool shot! Anybody notice the joker's face in the stem just above the sack?

[chemicalbro]

Lovely shot, esp. the magnified leg inside the drop.

Quick question, how does 31mm of extension on a 105mm 1:1 lens give a 1.5:1 ratio?

The way I understood the maths it's something like (105+31)/105 = 1.295 at min. focus, what am I missing?

the way i understand it is that if the lens is set at 1:1 then any extension is simply added on......... giving 1:1.31x.... (i remember Leorooster telling me that one some time ago...)

its a fantastic shot whatever the magnification.....(does it really matter :))

[LordV]

Thanks Mecdave and Chemicalbro for the comments and looking.
Brian V.

[chemicalbro]

after thinking about this for a while I now think pixl8 is right in his calculations.......

say you wanted 2:1 .you would need 105mm of extensions......... if you wanted 1.5:1 you'd need 52mm... if you wanted 1.25:1 you'd need 26mm.... so adding 31mm....... indeed gives 1.295

[LordV]

after thinking about this for a while I now think pixl8 is right in his calculations.......

say you wanted 2:1 .you would need 105mm of extensions......... if you wanted 1.5:1 you'd need 52mm... if you wanted 1.25:1 you'd need 26mm.... so adding 31mm....... indeed gives 1.295
Agreed that's what the calculation tells you. I didn't calculate it, I measured it. Without the extender my 105mm ex gives me 2.2 cms width in the viewfinder- ie same width as the sensor. With the 31mm extender it gives me just under 1.5cms, this is exactly the same as I saw with my 50mm lens with 7.5cms of extender rings. 2.2/1.5 = 1.47. A partial explanation is as I mentioned earlier. Apparently at 1:1 the focal length of the lens is actually about 78.5 mm not 105mm. Not sure where the rest comes from though :D .
Brian V.

[chemicalbro]

lol.......... manufacturers always quote numbers to make stuff sound better.............. like they say that the working distance of the 105 is 31cm........... what they don't tell you is, that measurement is from the sensor to the subject...not from the end of the lens :)

[marie]

Thanks for the comments Guitartist. You could almost imagine it as a gothic piece of jewellery pearl in a gold spider clasp :)
Brian V.
:shock:
it's such an unusual sight and capture.
terrific
congratulations

[pxl8]

Brian,

If you checked visually in the viewfinder then that probably explains the small difference in values between the maths and what you saw. The viewfinder is cropped slightly compared to the image on the sensor.

[LordV]

:shock:
it's such an unusual sight and capture.
terrific
congratulations
Thanks Marie :D
Brian V

[LordV]

Brian,

If you checked visually in the viewfinder then that probably explains the small difference in values between the maths and what you saw. The viewfinder is cropped slightly compared to the image on the sensor.

Yes I thought there was a small difference, but it doesn't really explain it.
I have to use a dioptre setting on the eyepiece which also affects it.
But when I use the 105mm at 1:1 I see and get (in a pic) 2.2 cms of ruler which is approx correct for the sensor width. With my 50mm lens and 7.5 cms of tubes I see 1.5 cms which is what would be expected (ie 1.5:1). I get exactly the same with the 105mm and 31mm of tubes .
When I get time I'll take pics of all the various magnifications to check it out.
;)
Brian V.

[Leorooster]

Amazing shot. Very artistic and colorful. I think it's an empty shell/skin though. Excellent work!

[CyberDyneSystems]

That's a stunning shot!

[LordV]

Amazing shot. Very artistic and colorfuly. I think it's an empty shell/skin though. Excellent work!
Thanks Leorooster. Think you may be right about the shed skin.
Brian V.

[LordV]

That's a stunning shot!
CyberDyneSystems Thanks for looking and commenting.
Brian V.