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Carl_Constantine



Joined: 01 Aug 2006
Posts: 304
Location: Victoria, British Columbia, Canada

PostPosted: Fri Aug 18, 2006 12:30 pm    Post subject: camping Reply with quote

I'll be camping for a couple days this weekend. I borrowed my Sister-in-law's 90mm Tamron SP AF Macro 1:2.8. It can do 1:1 quite well. I hope to get some great pics with it in the great outdoors. If I do, pics will definately be going up here ;-)

One of my problems however is overexposure when I use my flash (particularly in daylight). Ideas on how to compensate for that?
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Carl B. Constantine
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Mike B in OKlahoma



Joined: 04 Aug 2006
Posts: 1048
Location: Oklahoma City

PostPosted: Fri Aug 18, 2006 3:03 pm    Post subject: Reply with quote

Is this an external flash, or an internal flash?

I usually don't have overexposure problems with flash outside, except that with reflective creatures in bright daylight (such as some dragonflies) I may have troubles sometimes. I shoot digital, and for me the answer is to chimp. Look at the histogram of your shot afterwards. Use exposure compensation if necessary. If you aren't familiar with histograms and reading 'em, you ought to learn. This is a good start at it:

http://luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

If you're shooting film, then this won't help you a bit of course! :-)
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Mike Broderick
Oklahoma City, OK, USA

Constructive critiques of my pictures, and reposts in this forum for purposes of critique are welcome

"I must obey the inscrutable exhortations of my soul....My mandate includes weird bugs."
--Calvin
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DaveW



Joined: 04 Aug 2006
Posts: 1702
Location: Nottingham, UK

PostPosted: Sat Aug 19, 2006 11:05 am    Post subject: Reply with quote

Carl

Is the overexposure in close-up photography only? If so it may be that your flash is too powerful for close-up if it is not self quenching or under TTL control. Does it switch down to lower power, if so cut down it's power if you are on manual.

Another possibility is that you are using a slow shutter speed plus flash, so are getting a combined exposure from the flash plus daylight. It's hard to tell as I do not know what equipment you are using.

DaveW
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Carl_Constantine



Joined: 01 Aug 2006
Posts: 304
Location: Victoria, British Columbia, Canada

PostPosted: Mon Aug 21, 2006 9:09 am    Post subject: Reply with quote

I have a Sigma Super-DG 500 flash with an omnibounce diffuser (for a canon 580 speedlight I might add). Canon 300D (Rebel) and I'm borrowing my sisters 90mm Tamron AF Macro.

I struggle with focus and such. I see the AF light flash in my viewfinder, but I still don't always get the focus. It drives me nutso (see the two Images I just posted). I don't know how you guys/gals get such great shots (when not stacking). Like the dragon flys many of you posted, had the whole dragon in focus!! (though, I don't know that those are 1:1, but the point is still valid). Me, I get one small point Sad

Much work to do on my technique. I wish one of you lived closer to me, I'd drive by for a weekend of practice and fun.

I had a lot of fun with this lens this weekend. Took some really good shots (non-macro) and a few good macro shots. Tried to get a nice shot of one beatle that had a beautiful maroon color to him but he was extremely fast and uncooperative, so all I get is a purble/maroon blur :-)

Anyway, any help anyone can provide is useful.
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DaveW



Joined: 04 Aug 2006
Posts: 1702
Location: Nottingham, UK

PostPosted: Mon Aug 21, 2006 10:20 am    Post subject: Reply with quote

Switch off autofocus and try manual focus, screen focusing as well as using your depth of field preview, if you have one. Autofocus is not always reliable close-up because the sensor is not always on the subject and may be on features further forward or behind the optimum focus point. In conventional photography the large depth of field usually covers these mistakes.

What sort of apertures are you using anyway?

These articles may help if you are new to insect photography:-

http://azone.clubsnap.org/insectguide/page02.html

http://www.beautifulbugs.com/beautifulbugs/howto.htm

http://www.mplonsky.com/photo/article.htm

DaveW
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rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 18352
Location: Richland, Washington State, USA

PostPosted: Mon Aug 21, 2006 4:20 pm    Post subject: Reply with quote

Carl_Constantine wrote:
I struggle with focus and such. I see the AF light flash in my viewfinder, but I still don't always get the focus. It drives me nutso (see the two Images I just posted). I don't know how you guys/gals get such great shots (when not stacking). Like the dragon flys many of you posted, had the whole dragon in focus!! (though, I don't know that those are 1:1, but the point is still valid). Me, I get one small point Sad

Carl,

About DOF, there has been a lot of very detailed and confusing stuff written. I know -- I've written some of it!

So this time, I'm going to try something different and stick with basic concepts. Everything you really need to know about macro DOF, in a slightly approximate nutshell.

Here goes...
  • DOF is determined entirely by three things: 1) final magnification, 2) optical aperture, and 3) what level of detail you're willing to call "sharp".

  • Optical aperture is adjusted by changing the lens f/stop setting, but optical aperture is not the same as lens f/stop. Dialing in "f/8" on two different setups can give dramatically different DOF.

  • DOF is governed by two competing effects: geometric blur and diffraction. At wide apertures, geometric blur gives you shallow DOF. Stopping down from there gives you more DOF. But at some small aperture, you reach a limit where diffraction makes everything too fuzzy, even the plane of best focus. Smaller yet, and diffraction just gets worse. Optimum DOF is achieved about 1 f/stop wider than the limit imposed by diffraction.
That's it -- three concepts!

Oh, and you'll need some experience.

It's really important to get that experience with your own equipment. The labeled f/stop can be a very misleading number.

Two examples: Jody Melanson and I use similar cameras, but different lens systems. When both of us are set up for 3:1 magnification at the same DOF, Jody's system might say "f/22" when mine says "f/8". Likewise, beetleman and I have different cameras; in some setups my "f/8" would be more like his "f/2", if his camera would even go that wide.

It should be clear that for any of us to blindly use any of the others' favorite f/stop would be inviting disaster.

So... You need to test your own equipment to figure out how it works. The procedure is simple.

Go find some dead bugs, set your camera on a tripod, and shoot some sequences varying f/stop from wide open to as small as it will go. Study the images under the conditions that you care about. (Chances are good that you'll prefer the images at some intermediate f/stop. (Wider apertures will have less DOF, smaller ones will be too fuzzy.)

Write down the lens setup, the magnification, and the f/stop that you like best. Change magnification or lenses, and repeat. After a short while, you'll build up a concise table of best f/stops.

You'll also develop a good feel for how much (how little!) DOF you can get at any particular magnification. If your optimum DOF does occur at some intermediate f/stop, then you can pretty much give up on the idea that you can get more DOF by switching cameras or lenses. Better lenses give sharper images, but that mainly affects wider f/stops where you'll have to settle for less DOF, not more.

Besides using the f/stop that's optimum for your gear, about all you can do is to position the subject to use as little depth as possible. There's a really good reason why the sharpest pictures of damselflies are shot from the side, and dragonflies from above or below -- that's the angle that puts the whole bug in pretty much one plane.

--Rik
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