Reverse mounting ?

[Terapixel]

Help from you Pundits out there please:

*Why do you reverse mount a lens ?
*How do you reverse mount a lens? (have any pics of reverse mounted lenses?)
*Know of any reverse mountable lenses for a Canon Powershot A40?

Much appreciated!

[shene]

Originally Posted by Terapixel

*Why do you reverse mount a lens ?

This is because reverse mounting can yield very high magnification. If the reverse-mounted lens has focal length X and the on-camera lens has focal length Y (in actual number rather than its 35mm equivalent), the magnification is Y/X. Or, if you prefer to use diopter, the reverse mounted lens has a diopter of 1000/X. Thus, a 50mm SLR lens is a +20 diopter close-up lens.

Originally Posted by Terapixel

*How do you reverse mount a lens? (have any pics of reverse mounted lenses?)

There are pages in my 4500 user guide explaining how to do it: the "TC-E2 for Close-Up" in the Odd Stuffs section and the "It All Starts with Thread Size and Rings" page in the Filters section. There are other actual unedited and tested shots that are searchable at DPreview's site www.dpreview.com So, search the Nikon Talk Forum and you should be able to find them.

Originally Posted by Terapixel

*Know of any reverse mountable lenses for a Canon Powershot A40?

Any good normal and wide angle lens with flat field can be reversed. It does not have be a Canon. Choose the one whose front glass can go very close to the front glass of the on-camera lens when it is zoomed all the way in. The quality, in general, depends on your on-camera lens.

CK
http://www.cs.mtu.edu/~shene/DigiCam
Nikon Coolpix 950/990/995/2500/4500 User Guide

[Terapixel]

Thanks shene, much appreciated. I could not find a photo of what a camera lools like with a reverse mounted lens on it though. Can you reverse mount a lens to make a telephoto lens or is it just for macro photography?

[shene]

Originally Posted by Terapixel

I could not find a photo of what a camera lools like with a reverse mounted lens on it though. Can you reverse mount a lens to make a telephoto lens or is it just for macro photography?

In fact, the "TC-E2 for Close-Up" page does have a number of photos of reverse-mounting a Nikon 55mm on a TC-E2 teleconverter, which is than mounted on a Nikon Coolpix 990.
Here is a more recent example. The following shows the result of mounting a Nikon AFD 50mm F1.8 on a Nikon Coolpix 5700. To do so, we need a macro coupler. A macro coupler has two male threads, one for the camera lens and the other for the reverse-mounting lens. Since I use a AFD Nikon 50mm F1.8, which has a 52mm thread, the macro coupler shown has one end of 52mm. The Nikon Coolpix 5700 requires an adapter for using converters. The following shows the Nextphoto 5700 Coolfix adapter http://members.rogers.com/nextphoto/coolfix5700.htm This adapter has a 62mm thread size, and, hence, a 62-52mm step-down ring is needed. Choose your macro coupler and step rings to fit your camera and the SLR lens.


Now, screw the macro coupler on to the SLR lens thread, followed by the step ring:


If an adapter is needed, screw the adapter to the step ring as shown below:


Finally, put the whole thing on to your camera, and the result is


There are a couple of points to be made. FIRST, use the longest focal length to yield maximum magnification. SECOND, use the largest aperture of the SLR lens. It is F1.8 as shown in the above images. This will provide more light for the camera to focus. If your SLR lens has a lock, release it so that you can turn the aperture ring to get the maximum aperture. THIRD, set the SLR lens to infinity or minimum focusing distance and use the camera to focus. Yes, you can use the focusing ring of the SLR lens to focus; but, it would give you much difference. Move the camera to frame and focus approximately. Then, allow the camera's AF system to do the remaining.

Hope this helps and happy shooting.

CK
http://www.cs.mtu.edu/~shene/DigiCam
Nikon Coolpix 950/990/995/2500/4500 User Guide

[djb]

am i safe to assume that it is better to have a lens used to reverse with the same or larger thread size than the camera's fixed lens?
also is there any place to buy these male-male stepdown rings?

dennis

[shene]

Originally Posted by djb

am i safe to assume that it is better to have a lens used to reverse with the same or larger thread size than the camera's fixed lens?

The answer is YES and NO. In other words, thread size is not the keep issue. The key issue is the angle of view of each lens. Some lenses may have a small front glass and yet its thread size is quite large. The Nikon AFD 50mm F1.8 is a good example. The reason is that companies usually prefer to standardize the thread size of their lenses. So, the question is if one can move the on-camera lens very close to the reversed lens. If we could, the image quality is better, light loss is less significant, and vignetting is unlikely. Since digital cameras usually have odd size lenses, it would be much better doing some tests before commit to this reverse mounting technique.

Originally Posted by djb

also is there any place to buy these male-male stepdown rings?

There are many places one can find macro couplers. For example B&H http://www.bhphotovideo.com/bnh/cont....x=5&image.y=4

CK
http://www.cs.mtu.edu/~shene/DigiCam
Nikon Coolpix 950/990/995/2500/4500

[djb]

shene, you're absolutely correct. i forgot about angle of view. i have all sorts of lenses to try. i know i have an old canon 50mm f/1.4 at home as well as a 24mm f/2.8. i can't remember the filter size. i'll check out the urls you indicated. thanx!!

dennis

[Terapixel]

Thanks shene, much appreciated - specially the photos. Gonna go get my lens now !

[richardh]

This is about what to expect as far as magnification from the a40. these were taken with an a70 but the lens system uses the same size elements and same sensor size. This is a 50mm lens by the way.
http://www.pbase.com/richardh/slr_macro
Two were taken with the a70 at 3x zoom. The other two were taken with the reversed 50mm slr and with the camera at 3x zoom. I was just starting out with macros so they are a little fuzzy but the magnification is accurate to what you will get.
Corection:
The a40 cannot focus as close as the a70 (it has been a while since I used it). I just took a couple of pics with the a40. I cannot explain it but without the slr lens the a40 could not focus as close as athe a70, which is expected, but with the slr lens, the a40 did focus as close as the a70?
Here are quick sample pics with the a40 and a reversed 50mm slr lens (the same lens used on the above a70 pics).
http://www.pbase.com/richardh/a40slrmacro
I am uploading them now so they should be there in about half an hour (dial up).

[shene]

Here are some examples of using reverse mounting SLR lens. The measurement is not exact; but, they should be very close to the true value. The following image is taken with a 5700 at its minimum focusing distance and longest "macro" focal length (i.e., yellow flower). Its width is about 30mm.


This one is taken with a Nikon 50mm F1.8 reversed. Its width is about 8.5mm, which is 3.5X larger than that of the 5700.


The CCD of the 5700 is 2/3" with width and height 8.8mm and 6.6mm, respectively. Thus, the magnification of the 5700 shown above is 8.8/30=0.29=0.3X of life size, and the reverse mounting one is 8.8/8.5=1X about life size.

The next one is taken with 5700 in macro mode.


And, this one is taken with 5700 and a reverse mounted Nikon 50mm F1.8. As you see from this and the previous one, corner sharpness is not so great. This is due to a number of reasons. FIRST, the 50mm F1.8 used F1.8. Stop it down a little will definitely improve sharpness. SECOND, to use higher shutter speed, the 5700 also used larger aperture (F3.x?). Close it down will improve sharpness. The upper edge is not sharp because the camera was not leveled. (I only wanted to show magnification rather than sharpness, and the latter can be judged quite easily.)



Raynox has a very reasonable macro lens, MSN-500, designed for Nikon Coolpix 9xx and 4500 series. But, it can also be used on a 5700 without vignetting. See below.


Here is the result. Unfortunately, the 5700 magnifies the deficiency of the MSN-500 too much, and the image quality is simply not good.


CK
http://www.cs.mtu.edu/~shene/DigiCam
Nikon Coolpix 950/990/995/2500/4500 User Guide