Help with multiple strobe hit calculations

[aphexafx]

^ What it comes down to is, I need more experience with this format, and I need to think 4x5 while I am designing my shots, etc... Well, I am determined at least, so that's good I hope. lol. Thanks, again.

[aphexafx]

I got my test sheets processed today and it looks like things worked out pretty damn well! In fact, I'm elated; I just don't know how to make that come across in text. I shot four sheets, and all of them were pretty well exposed with just minor issues that are probably related more to my metering and lighting technique - this is better than I had hoped for. I now trust the math! A huge stride for me, haha.

This shot was made with my Nikkor-W 180mm at roughly f/45 and 3/10, which required 16 hits of the strobe. This scan shows an over-exposed neck on the bottle (there is more detail there in the actual chrome...). However what is important to me is the overall exposure with the 16 hits of light, and this confirms everything for me. Yay. If this were a real shot I would mask the light to adjust the neck because the rest of the exposure is pretty good.




The next shot was made with my Nikkor-W 210mm at f/64, which required 24 hits from two strobes. This exposure is pretty much dead on - well ok it is just slightly hot. The chrome shows slightly more saturation on a light box, but this is a decent scan of it.




So, I have a LONG LONG way to go from these quick shots, but I am nips about getting these multi-strobe exposures to kind of ring in on my first try. The other two sheets were of an identical scene shot with both lenses so that I could compare thier aperture accuracy and the exposures are identical, I cannot find a single thing that is different between them regarding tonality. So, in short, SWEEEEEEET.

Also, the DOF is deeper than I had anticipated - using the DOF calculator on my camera with my lens wide open, I guess, gave me the impression that it would be shallower than it is, so this is something I have to get used to, and really good to find.

Thanks for all the help.

[Frank Petronio]

The Wine Glasses are a nice idea for what is too often a really cliched shot in a lot of portfolios. Bravo.

How come the cards are aligned and straight-edged in your DX shot but not -- sort of curving -- in the 4x5? Is it the distance between the "lens" of the wine glass and the background? Or did you have to do Photoshop work on your digital example?

The Sinar numbers are conservative, the background probably isn't in critical focus but it's acceptable.

If you can shoot like that in DX, then moving to 4x5 will be fun and easy for you. However, you might want to learn to use the inherent qualities of large format to your advantage, to differentiate your film work from your small format digital (exploit them both for what they are best at.) What qualities might those be? The very things you are fighting against, i.e. depth of field and the clearer, larger ground glass that expands the detail of still life compositions.

[Struan Gray]

How come the cards are aligned and straight-edged in your DX shot but not -- sort of curving -- in the 4x5? Is it the distance between the "lens" of the wine glass and the background? Or did you have to do Photoshop work on your digital example?

One of the glasses is closer to the lens than the other in the 4x5 shot. You'd have to back off and use a long lens to get the angles right and make the edges of the cards straight again. Doing so is (I am told) a classic look in product photography - think McDonalds drinks seen in curiously exact academic perpspective.

One other thing I have been told is that once you get above about five or six pops of the flash you have to worry about the intermittency effect, a cousin of reciprocity failure. Because the flash is relatively short, the film has time to 'heal' between pops, and the combined exposure is less than if you had no re-charge time on your strobes. How much you have to compensate will depend on your strobes (particularly the on time) and the film you are using. Typically you add a few pops extra for every ten or so, but if you want to be accurate to 1/10 of stop or have precise control of where the highlights go on slide film you will have to test for yourself.

[Drew Bedo]

"I would REALLY like to get this scene (or equivalent) onto a 4x5 chrome, there has to be a way to do it!"

If "equivalent" is acceptable:
Try forcing the perspective by using larger glasses (MUCH larger). I have sometimes seen over large stemware at interior decor shops. In Houston TX this would be Michsael's or Hobby Lobby.

By using oversized props, the shot is no longer in the macro range and all the macro related problems go away; DOF and extension compensation...etc. What do you think? Will that work for you?

Please post the new images wgen you re-shoot and tell us what you did!

[aphexafx]

Thanks, Frank. It is a "set" that I have worked with a few times and yes I would love to perfect it for my portfolio. As to the differences between this version and the DX version, I shot the DX version with an 85mm (ends up being 127mm) lens, however the main difference is that I simply spent more time with the digital shot lining up the glasses with the background. A slight movement either way of center (to the camera lens) and things start bending all over the place. Also, those are old (and/or cheap) glasses and they are not perfectly formed, so with the digital shot I spent time rotating them to find their best sides, above I did not. Yes I did some clean up in the digital version, but I did not have to clean many edges - time was the real difference.

Your advice is good, I am excited about doing more with the 4x5!

Struan, your reference to the McDonald's product work has me laughing all day. I know exactly what you are referring to without even looking them up. It is a great example. I am saving for a 300mm Nikkor-W to complete my kit and look forward to playing with a longer lens for tabletop type work. However, like Frank is pressing, I am equally excited to start learning what I can really do with my 180mm and 210mm.

I am so far unaware of intermittency failure, and so far unaffected in my five shots (lol) but now I know and I will keep that in mind. Thank you, if I ever come across this I will not be in the dark. Your few words could be worth a gold mine.

Drew, what a fantastic idea! Seriously, it is a fantastic solution. And here I've just studied some great examples of false perspective in this kind of photography! Great idea, and it sounds like fun as well - I do want to solve this shot with normal glasses, but, hell, I can already imagine a surveying trip to the craft stores to see what they might have...

[Drew Bedo]

aphexafx:
I appreciate your desire to shoot this set-up with regular sized stem ware.

I have used a focusing target to help with DOF issues since I became visually impaired. Place a conveniently sized bar-code from some purchased item (Jello box works) into the set-up where you want the sharpest focus. It will really snap in and out when wide open. Then move this target around to the front and back of the composition and check DOF stopped down. This is not a lighting check, so you can really blast the scene with strong, direct spots of any color temp...you just need to see the card at the shooting extension and aperture.

Remember to Shoot-n-Show...

[Ralph Barker]

aphexafx:
. . . Place a conveniently sized bar-code from some purchased item (Jello box works) into the set-up where you want the sharpest focus. . . .

Interesting thought, using a Jello box to see how much wiggle one has, DOF-wise.

[Drew Bedo]

Jello...wiggle...giggle: Got it!
For clarity, just cut out the bar-code from the box. It’s a small piece of cardboard and can be put anywhere. Jello is just a convenient example. If a larger target is needed, try a sheet of graph paper on card stock. Edmund Optical has all kinds of targets, but I don’t have a research grant, so...no.

[Brian K]

Relax somewhat. Even on Ektachrome a third of a stop difference is barely noticeable.
While you're at multiple flashes, you might a well do plenty of them and stop down a bit more (but do it in the dark without shutter vibrations). You can't go wrong over 16 'pops' but you can go wrong in the 4 'pops' area.

I have to take issue with a 1/3 stop difference in exposure being barely noticeable with Ektachrome. When I shot Ektachrome my brackets or processing were in 1/8 stop increments and even that difference was noticeable. When you're doing studio work the only acceptable exposure is being dead on.

I do agree though that after 16 pops the difference of a pop or two is small, 1/16 of a stop per pop. But you can also start getting a reciprocity like failure when so many pops are required as well as weird color tinges added by the afterglow of the flash tubes. Try to keep the pops less than 8 if at all possible.

Also if you are working in the studio it's better to darken the studio, open the shutter and block the lens in between pops with a black card versus setting the shutter to 1/60 and cocking and firing it multiple times as there is always a possibility of getting frozen ghost images if the camera moves or shakes at all during the pops or as a result of re-cocking the shutter each time. The typical procedure is set the shutter to "B" or "T", cover the lens with the black card (but do not touch the camera or lens with it) wait for the camera to settle after the shutter is opened, move the black card out of the way, pop, cover the lens with the black card while the strobes recycle, uncover the lens and pop, etc. Obviously the studio is darkened and the modeling lights are off and also stand perfectly still as you do this as floor vibrations will cause ghosts..