Three Macro Coupling Questions

[haltedsisyphus]

I am pleased with the results of coupling a Tamron 17-50mm f/2.8 to a mounted

Canon 70-200 f/4 L with a 67mm-67mm ring. With this setup, I've found that

stopping down the Canon lens reduces the image circle, whereas stopping down the

Tamron does not.

 

In light of this, I have been keeping the Canon lens at f/4 and have been using

the DOF Preview button to set the Tamron lens to f/8 before unmounting it. This

gives full-APS-C coverage from 135mm-200mm with a reasonable depth of field, and

without diffraction taking too much from image sharpness. At 200mm, this setup

also covers a full-frame sensor.

 

Examples here:

http://www.photo.net/photodb/folder?folder_id=720223

 

So, three questions:

 

1. Should I be concerned about the 430-gram Tamron lens hanging by its filter

threads every now and then? For long periods?

 

2. Should I be concerned about leaving the Tamron lens' aperture at f/8 for long

periods of time? Hours, days? (E.g., if I forget to remount the Tamron and

electronically reset the aperture.)

 

3. Any tips from people who have done similar things? From my calculations this

is about 12x magnification; the area covered on the APS-C sensor is about 1.9mm

x 1.3mm; working distance is about 3.5 cm. I'm using a cheap mini halogen

spotlight for strong, focused, constant lighting. Since I don't have tripod

rings or a focusing rail, I've just been setting the camera on a table and

brining subjects to it.

[mikemilton]

First, nice shots...

 

hmmmm.... Well, here is a dumb question. Does the Tamron actually stay at F8 when you

unmount it?

 

I used to use a reversing ring on a FD50F1.2L with quite some success but that, of course,

was a mechanical aperture (Ihad a little plastic gadget that fit on the 'back' of the lens and

actuated the lever. I got better results this way than on the front of my FD70-200F4.

 

Like yourself (I'm guessing) I found using what I had to have a certain elegance

 

Now I just use the MP-E65F2.8 with the MT24 on Manfroto focusing platform

[mark u]

I agree with Mike...the book and quarter are particularly successful.

 

I don't own the Tamron, so I can't comment conclusively on the build quality of that particular lens with regard to the filter threads - however other Tamron lenses I own are very well built and it would give me no cause for concern. I imagine that the 17-50 was anticipated to be used stopped down for several hour star trail exposures, so although I don't think it would be a good idea to keep it permanently at f/8, it won't come to much harm for your use. I would suggest that you exercise the aperture periodically, and check visually that it closes and opens snappily. Use e.g. f/5.6, f/11 and f/22 for the exercise workout.

[brucecyr]

I like your shots too! Half the fun is seeing what things look like at high magnification. I could guess the identities of the LCD monitor and book, but only because I've done those. However, I don't think I would ever have gotten the exact seed type!

 

All of the books and articles I've read recommend stopping down the primary lens and leaving the reversed lens wide open, but why worry about theory if what you're doing works! Not sure, however, exactly how that affects DOF.

 

The vignetting from stopping down the primary may be caused by the possible retro focus design of the reversed Tamron -- see whether its shutter looks noticeably smaller when seen from one end vs. the other. That would also respond to Mr. Milton's query, but I think it should be set at whatever it was when you last put it on the body.

 

While I lack the know how to answer your aperture question (#2), I would guess its no problem -- SFAIK there is no tension or spring involved in keeping the shutter at a specific aperture here.

 

Your magnification estimate, namely:

 

(200/17) ~= (22.2/1.9) ~= 12,

 

is correct. (Where I use the 350D's sensor's width, 22.2)

 

As for question #1, I don't think that leaving the reversed lens in place would be problematic unless, of course, you literally do leave it hanging in space with no other support :-) But I think it wouldn't take much effort to unscrew the two lenses after each session for safer storage.

 

An easy mod is to add one or more additional lights and/or reflectors. You can also try adjustable flashes, like the Vivitar 285 or 283 with the VariPower(?) module, although directing the light onto the target can be a challenge.

[haltedsisyphus]

Thanks all for your kind support.

 

Mike: Yes, the Tamron does stay at f/8 if I hold down the DOF Preview button while unmounting the lens. And you're right - it can be quite satisfying to use what's at hand in new ways.

 

Mark: I'm glad that neglecting to reopen the aperture is unlikely to cause problems, and I'll try to keep the lens fit. If something goes wrong, I will be grateful for Tamron's 6-year warranty.

 

Bruce: I had heard that theory about stopping down the primary lens, and was curious whether there was more to that than a brighter image in the viewfinder. However, as you say, what works, works! I may start playing with different lighting soon; mini-lamps are pretty cheap.

[eosdoc]

For shooting macro subjects, it might be prudent to add a

protection filter at the subject end of the reverse Tamron.

<BR>

E.g. Epoxy a glass filter over a large hole drilled in

a plastic rear lens cap. Otherwise, see:<BR>

<a target=loser href=

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00E539

>http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00E539</a>

<P>

Of course if Nathan is shooting still life, then this is not

an issue.

<P>

There are previous threads about supporting reversed lenses

on a separate tripod mount. See Rob Platt's posts here:<BR>

<a target=loser href=

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=004Hcm

>http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=004Hcm</a>

<P>

Another thread discussed the math about aperture matching:

<BR>

<a target=loser href=

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00JpNe

>http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00JpNe</a>

<P>

To calculate magnification, use a good lens calculator:<BR>

<a target=loser href=

http://eosdoc.com/manuals/?q=jlcalc

>http://eosdoc.com/manuals/?q=jlcalc</a>