Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
12-25-2010, 07:22 PM   #1
New Member




Join Date: Dec 2010
Location: Canada
Posts: 19
converting a 1:2 100mm F4 pentax macro lens to 1:1?

Hello, I am new to this forum and to macro photography in general. I just recently purchased a used pentax 100mm f/4 SMC-M lens for use on my k-x body and I have a quick question regarding getting its magnification from 1:2 to 1:1. I picked up this lens used at a local camera shop rather than buying a newer more expensive 1:1 macro lens as I am on a limited budget.

First off I would like to state that my main macro interests revolve around photographing insects, arachnids other small arthropods and perhaps even small reptiles, I would therefore prefer to be able to shoot without using a tripod constantly as I have heard it can be cumbersome. I would also like to shoot small plants, flowers and fungi.

I should also mention that I am going on a biodiversity monitoring internship to borneo, and will be shooting in the rainforest under a dense canopy where light conditions will not be optimal, and good lighting will be at a premium.

I have read that there are a few ways of getting my magnification to 1:1. It can be done using a 50mm set of extension tubes, which will not affect the quality of the lens, but will reduce the amount of light by 2 full stops as well as reducing my working distance(not sure by how much?). For the insect photography I would like to keep my 100mm working distance if possible. Next I could use a teleconverter (possibly a vivitar 2x), but this may negatively affect the quality of my lens and will also reduce available light by 2 stops, although it will effectively double my working distance as well(possibly requiring a tripod to reduce shake). Lastly I was wondering if it would be possible to use a good achromatic close up filter/lens such as a marumi to get to 1:1 without reducing my available light. What diopter would work for this (+3,+5)? and how would this affect the working distance of my lens?

I am not quite sure which option will work the best, 1:2 macro might even be good enough for shooting insects. What I want to do might not be capable of doing with this lens. I found a 105mm F2.8 lester dine 1:1 macro for twice the price, but this discovery was too late, as I had already purchased this lens (somewhat hastily). I would appreciate any suggestions from someone with more experience shooting macro. Thank you for your time, and my apologies for the long winded post.

Cheers


Last edited by Rice; 12-25-2010 at 08:50 PM. Reason: made significant mistake in the title
12-25-2010, 08:46 PM   #2
Senior Member
stover98074's Avatar

Join Date: Apr 2010
Location: Seattle
Photos: Gallery
Posts: 153
Put some distance between the lens and the camera body. M42 tubes with M42 to Pentax K adapter will do the job. Bellows will work better.

A set of M42 tubes run about $15. The adapter is about $20 if you splurge.

You have a wonderful lens - and at 1:1 or greater you may want to utilize a tripod and a macro focusing rail.

This is a brief article on inexpensive macro - it explains how extensions help with magnification.

https://sites.google.com/site/inexpensivemacrophotography/

This was taken with a 105mm length lens on a bellows.

12-25-2010, 09:04 PM   #3
Loyal Site Supporter
Canada_Rockies's Avatar

Join Date: Nov 2007
Location: Sparwood, BC, Canada
Photos: Gallery | Albums
Posts: 9,545
The 50 mm tube will give the lens the range from 1:2 through 1:1, which is what I do when I absolutely have to have 1:1 on the sensor.

What you will need in the rain forest is a good macro flash, rather than a change of lenses. The Lester Dine is a fine lens, but so is your Pentax M. The flash should allow you to vary the lighting to give either the full frontal no shadow or to reduce the power on one side or the other to give you shape shading.

You will never set the lens to f/4 and take a good macro shot. The depth of field is negligible at these distances. You will find that you are fighting to get to f/11 or f/16 so that you can get at least some depth of field. The better high ISO in your K-X compared to my K10 will definitely help.
12-26-2010, 12:08 AM   #4
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
Let's see if I have this right: You need 1:1 macro of high quality, shot in dim light in a rainforest without a tripod, and you currently own a SMC-M lens. That is tricky. Shooting macro with a small aperture for tolerable DOF, without supplemental light, WILL require a tripod. Shooting macro hand-held using flash and a manual-aperture lens is bothersome because you can't control exposures automatically. And shooting with extension (tubes and/or bellows) in a rainforest can be hazardous to the equipment.

So, my suggestions for handheld:

1) Best would be a weather-resistant auto-aperture 100mm macro lens with a ringflash -- but that may be beyond your budget.
2) An auto-aperture standard 135mm prime lens or good 80-200mm zoom with a corrected macro adapter (like a Raynox DCR-150 or -250) and a ringflash would cost much less -- but that would have somewhat lower image quality, maybe not enough to rule it out.
3) Other options -- bellows and/or tubes, reverse-stacking, etc -- will also have lighting and control problems. And reverse-stacking means working VERY close.

For macro shooting, autofocus and wide apertures are unneeded. For handheld macro shooting in dim light, auto-aperture and flash ARE needed. That M100/4 is a great lens but not for this application. I wish I could come up with other suggestions. Good luck.

12-26-2010, 01:55 AM   #5
New Member




Join Date: Dec 2010
Location: Canada
Posts: 19
Original Poster
Thank you everyone for the advice thus far. I will definitely be getting a tripod in order to deal with the low light on the forest floor for photographing fungi and plant life. I had just wanted to know if it was possible to shoot the macro without it in some situations involving skittish insects and still get decent results. For many insects the 1:2 magnification of my current lens may be sufficient enough to suit my needs.

I have a 55-300mm zoom lens, would this work well with a close up macro adaptor such as marumi or raynox? or would I be better off sticking with the macro lens I have and a flash? On that note, what would be a good ring flash to check out which is reasonably priced? I might be able to tough it out and figure the exposures out manually while using the flash on my current lens, as I will be gone for approximately 6 months and will have plenty of spare time for experimentation.

Also, does the concern regarding extension tubes being hazardous to the equipment have to do with exposing the internal components of the camera to moisture. If so I intend to get around this issue when changing lenses etc. by doing so within the enclosed field research station and as infrequently as possible.

I also would welcome any suggestions for waterproof cases/bags to protect my equipment during the frequent periods of rainfall I will undoubtedly face. I have been considering the lowepro dryzone rover as I will need a protective case for my camera as well as a field backpack for work. however I have been unable to examine one of these in person to evaluate its quality, and will likely end up having to order one online(any opinions from someone who has seen/heard of/or used this type of bag would be appreciated). Also plenty of silica gel packets in my storage bag to keep moisture build-up down, as well as subsequent mold growth. Any other suggestions for preventing/minimzing moisture damage to camera equipment while shooting in the tropics? I have been scouring similar topics on this forum, but I may have missed something, and every bit of information helps.

regards
12-26-2010, 02:49 AM   #6
Veteran Member
xjjohnno's Avatar

Join Date: Jan 2009
Location: Melbourne Australia
Photos: Gallery
Posts: 2,115
LED ring light might be another option for the lighting department along with the macro tube or diopter option. Whatever you use including illumination options will require a stready base so bellows, macro rails + tripod are going to be a must. 1.1 macro is no easy task hand held, even with high ISO and shutter speeds.
12-26-2010, 06:24 AM   #7
Veteran Member
jolepp's Avatar

Join Date: Oct 2010
Location: Finland
Photos: Albums
Posts: 3,196
How does this work, really? I mean one could think that tubes or an achromat cause two stop loss when going from 1:2 to 1:1 as the dimensions are multiplied by 2 and hence the area on which the light is spread is 2^2=4 times larger. However, if the working distance also gets smaller at the same time, the intensity (photons/area) of light entering from the front element is also increased in a similar fashion, that is, half the distance, four times the intensity (ignoring the loss from the gear/shooter possibly blocking some of the light that would be reflected from the target)?
12-26-2010, 06:38 AM   #8
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
The Raynox DCR 150 (208mm, 4.8 diopters) will increase your magnification range to just over 1:1 with good image quality for insects, etc.

A 50mm extension tube will be a little more difficult to use in the forest, but macros using it will be good at the edges unlike those taken with the Raynox (the lack of edge sharpness with a Raynox or other diopter lens macro is much less of a practical problem than one might think because natural subjects aren't normally flat enough for the edges to be in focus.)

I agree with everyone else that lighting will be your biggest problem. It would be nice if you could find an A type lens so your camera's auto-flash feature will work. It is possible to fool your camera into thinking all lenses are A type, so that might be an option for you.

You might try an LED ring light - it should be a big help.

12-26-2010, 06:44 AM   #9
Site Supporter
Rense's Avatar

Join Date: Dec 2008
Location: Zetten - The Netherlands
Photos: Gallery | Albums
Posts: 8,822
Rice, may I bring this group to your attention? Macro Photography - PentaxForums.com It's a group completely dedicated to macro photography. You're welcome to join!

Concerning the light question: I find the DIY macro flash diffuser of Grzhoofr (see for his photos here very helpful and very cheap. You can find a sort of tutorial how to make one on my blog here. This tube improved my own macro work dramatically...... (as well as a f/2.8 macro lens did, by the way...)
12-26-2010, 07:08 AM   #10
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
You need to consider all the options

Along with a tripod I would get a macro focusing rail

For extension tubes you can get a set with aperture couplings for about $70

Also look into a good close up lens with no more than 1-2 zippered because you can add this to the front in a hurry when in the field

As for light loss this will always be an issue at high magnification. Flash is very important. As a minimum look for one that can tip down slightly. Off camera is better perhaps with a bracket
12-26-2010, 07:15 AM   #11
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
QuoteOriginally posted by jolepp Quote
How does this work, really? I mean one could think that tubes or an achromat cause two stop loss when going from 1:2 to 1:1 as the dimensions are multiplied by 2 and hence the area on which the light is spread is 2^2=4 times larger. However, if the working distance also gets smaller at the same time, the intensity (photons/area) of light entering from the front element is also increased in a similar fashion, that is, half the distance, four times the intensity (ignoring the loss from the gear/shooter possibly blocking some of the light that would be reflected from the target)?
Tubes cause a light intensity loss at the sensor because they move the lens further from the sensor; the effective f-number is increased by a factor of:

(1+Magnification) = (1+Extension/Focal_Length).

Large diameter diopter lenses added to a primary lens do not increase the distance from the lens to the sensor, hence do not affect the light intensity on the sensor (the effect of the diopter lens is to decrease the focal length of the primary lens.)

One advantage of using a diopter close-up adapter rather than extension is that the viewfinder stays bright which helps with focusing.

Dave
12-26-2010, 09:30 AM   #12
Veteran Member
jolepp's Avatar

Join Date: Oct 2010
Location: Finland
Photos: Albums
Posts: 3,196
QuoteOriginally posted by newarts Quote
...
Large diameter diopter lenses added to a primary lens do not increase the distance from the lens to the sensor, hence do not affect the light intensity on the sensor (the effect of the diopter lens is to decrease the focal length of the primary lens.)
...
But they do scretch the image on the sensor plane and would not seem to result in more incoming light (number of photons). It would seem that scrething the image dimensions to 2x would scretch the total area to 4x and hence reduce the intensity of the light making it to the sensor surface to 1/4, the rest have their path bent so that they now (hopefully) get absorbed at other places than the sensor surface?
12-26-2010, 01:11 PM   #13
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
A suggestion: My bible for macro and field photography is an old book that apparently has not been improved upon. It is Field Photography: Beginning and Advanced Techniques by Alfred A. Blaker -- a Scientific American book. It is from the film era but is quite relevant to digital work.
12-26-2010, 02:00 PM   #14
Site Supporter
Rense's Avatar

Join Date: Dec 2008
Location: Zetten - The Netherlands
Photos: Gallery | Albums
Posts: 8,822
QuoteOriginally posted by RioRico Quote
A suggestion: My bible for macro and field photography is an old book that apparently has not been improved upon. It is Field Photography: Beginning and Advanced Techniques by Alfred A. Blaker -- a Scientific American book. It is from the film era but is quite relevant to digital work.
Don't know this work...will look for it. I hope it's still available second hand?
12-26-2010, 04:20 PM - 1 Like   #15
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
QuoteOriginally posted by jolepp Quote
But they do scretch the image on the sensor plane and would not seem to result in more incoming light (number of photons). It would seem that scrething the image dimensions to 2x would scretch the total area to 4x and hence reduce the intensity of the light making it to the sensor surface to 1/4, the rest have their path bent so that they now (hopefully) get absorbed at other places than the sensor surface?
First remember that when a lens with F-Number N is extended so it has a magnification of M, it has an effective F-Number of N(1+M).....we will use this later.

Now consider a 100:4 lens wide open (physical aperture= 100mm/4=25mm), focused at infinity (it is 100mm from the sensor).

Remove it from the camera & screw on a 100mm focal length "close-up lens"; this creates a "new" lens with focal length f:

1/f=1/100+1/100 or f=100*100/(100+100) = 50mm

The F-Number of this new lens is its focal length divided by its physical aperture, 25mm, or:

N = 50mm/25mm = 2

The "new" lens' decrease in focal length is accompanied by a corresponding increase in speed!

Now put it back on the camera; it is a 50mm lens, 100mm from the sensor, so it has a magnification ratio of 1:1. Its effective F-Number is N(1+m)=2(1+1)=4 so the image brightness has not changed.

In terms of your description, the stretch of the image which would decrease the brightness was accompanied by an exactly compensating increase in F-Number.

Dave

PS One gets the same general result if the specific numbers I used for the illustration are replaced by appropriate letters standing for focal lengths, etc.

The above assumes the original physical aperture is the smallest in the optical chain. If the "close-up lens" is a distance, d, from the primary lens, the new focal length is:

f=f'f"/(f'+f"-d).
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
100mm, affect, distance, insects, k-mount, lens, light, macro, macro lens, pentax lens, photography, quality, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Options for macro(or near macro) photography dinneenp Pentax SLR Lens Discussion 4 05-09-2010 01:26 PM
What are my macro options? paolojackson Pentax SLR Lens Discussion 10 09-07-2008 11:55 PM
Lens options for wildlife and Macro hrishi Pentax SLR Lens Discussion 1 08-29-2008 06:29 AM
Macro Options blip Pentax SLR Lens Discussion 5 06-24-2008 06:41 PM
Macro options.. hrishi Pentax SLR Lens Discussion 12 06-14-2008 07:04 PM



All times are GMT -7. The time now is 10:19 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top