Flash recommendation

[mohds]

Hello all,

 

I am new to RTI, does anyone have a recommendation on a flash attachment (cordless/mobile) for use in a museum setting with objects of various sizes? We have a Canon ultrasonic EOS Rebel T3i.

 

Thank you!

Maria

 

 

[cdschroer]

Welcome Maria!

 

The first thing I recommend is reading the section on Lighting equipment and Flash options in the Guide to Highlight Image Capture starting on page 18.  This will give you some ideas on setups and triggering.

 

At CHI we use Speedlite flash units for a lot of our work, for areas up to about 3ft by 2 ft. That is with the full size ones (not the small ones sometimes sold for the rebel line of cameras) These have the advantage of being battery powered and light weight enough to move around.  For larger subjects, or if working outdoors we will go for a larger mono-block, but you want one that is lightweight enough to attach to a monopod and move to the different light positions.  We have been happy with an Einstein from Paul C. Buff.

 

There are various triggering options.  We have been happy with the Pocket Wizard TT1 and TT5 combination, but they are pricey. There are lower cost options, and I'll let others speak about their experience.  The least expensive way to trigger your flash is with a long sync cable.  There isn't a sync port on the Rebel cameras so you have to use a hot shoe adapter.  This also becomes a cable you have to manage.  We always carry a sync cable as a backup, even when we use the radio triggers.

 

Hope this helps, and I also hope others will chime in with their advice.

 

Carla

[janelle.batkin]

Hi Carla,

 

I will be doing RTI photography of low-relief graffiti on stone columns at an archaeological site in Africa.  We plan on using our Canon G16 for the job, which has manual settings including manual focus.  Do you foresee any issues with using a point-and-shoot camera for RTI?  Also, is there a flash unit you recommend that can be used with both Canon and Nikon cameras?  Our budget is $200.

 

Best,

Janelle

[marlin]

hi Janelle,

 

Using a point a shoot, well, its a trade off right? If thats what you have, and thats the gear you've got for RTI, than you can make it work. It all depends on what expectations you have, and how you are going to use (or say/write about the final data).

 

A point and shoot can work. Manual is good. Make sure that the manual settings are locked down. Yes, including the focus, Manual Mode, etc etc. It sounds like you've read the capture PDF. Good on you.

 

You also might want to look into the Flash Synch Speed of the G16 --- and do some test. I cant recall if its a digital sync ... but just dont let the the curtain interfere with the image and start to clip (big dark areas on the image). You might be in the clear, but in general for any camera check that setting you might have to lower your shutter speed to let the light get in.

 

There are numerous flashes that could / should work with both Nikon and Canon. I cant recommend a product, bc, honestly, I havent used many of them. Other Users? Can you guys chime in on this?

 

A generic flash unit might be ok, but, be sure to dive into the flash setting on your camera, I'm pretty sure that there is a 'force flash' setting, which basically sends a signal to the hot shoe and fires what ever is in the hot shoe. Previously, i had the G12 --- and I needed to have that setting On to get my pocket wizard to actually trigger. I hope that this makes sense.

 

Be sure so set up and 'faux' test capture and run thru the gear and the steps b4 you get on location and you should be able to work it all out.

 

happy F stop

Marlin. 

[cdschroer]

I'll add to Marlin's notes with a few of my own.  We haven't found a reliable flash unit in your price range.  That doesn't mean it doesn't exist, just that that is a very small budget.  You need something that can illuminate a large enough area, from the proper standoff of the subject.  If you will be in daylight, then you also need to block the ambient light with neutral density filters, and that will require a more powerful light to get a good exposure, back through the neutral density filters.  How large of an area are you planning to shoot?

 

In your budget you also need to think about batteries and chargers, and a way to trigger the flash.  The cheapest way is with a sync cable - but that means you need a way to talk to the sync cable from your camera (probably through a hot shoe attachment) and it has to be able to fire the flash unit.

 

A note about batteries - there are things to think about there too - see the write up on rechargeable AA batteries here:

http://forums.culturalheritageimaging.org/index.php?/topic/257-rechargeable-batteries-—-aas-and-a-bit-more/?hl=batteries

 

The illumination is an important part of getting a high quality result, and so you will need to do some research to see what you can find that might work at a very low cost.  I know that the triggering mechanism for Nikon and Canon via the hot shoe are different and many products are specific to one or the other.  However, using a PC sync cable could get around this - but it will depend on the products you use. You will need to read specs and/or or try it out.

 

And, since it has a zoom lens, you will want to tape it so that it doesn't drift to other focal lengths.  The biggest drawback of a point and shoot camera is that the built in zoom lenses all have distortion effects, much more than a 50mm or 100mm prime lens, like we routinely use and recommend.  That isn't the end of the world, and the software will still process your images into a result.  You just need to be aware that your data will have barrel distortion.  You may want to add distortion correction as part of your processing pipeline (this is available in Adobe Camera RAW in Photoshop - and there are a variety of software tools for this)  To be clear, this isn't required, and the software will create RTI's from the images you take with this camera.  My point is that the optics on a point and shoot (even a good one like the Canon G16) will have more distortion than the recommended lenses.

 

I'll also note that you should be shooting RAW in addition to all the manual settings.  This is discussed in this thread:

http://forums.culturalheritageimaging.org/index.php?/topic/248-jpeg-v-jpeg/?hl=%2Bjpeg+%2Braw  Scroll down a ways to see my explanation of why we strongly recommend a RAW workflow, even though RTIBuilder uses JPEGs.

 

Carla

[leszekp]

I own two fairly recent Canon point-and-shoot models, and both digitally process images to compensate for most of the lens distortion at different zoom levels. One of them also shoots raw, and Lightroom has a profile that corrects for the distortion as well. But both also have a problem with lens creep, where the image shifts as you take successive photos, even though the lens is stable. I have to shoot about 20 dummy shots to eliminate this effect, but then the image is stable unless the lens zoom is changed again.

[Taylor]

You can find Canon 580EX flashes for around $200 or less on e-bay that are good for working indoors.  They're probably not powerful enough for shooting RTIs outdoors except perhaps in shady conditions.  Since you're not going to put the flash on the camera's hot-shoe for RTI, these flashes can work with a range of different cameras, provided you get the right remote shutter and flash triggers (you'll need to check which ones will work with your camera and flash; there are lots of after-market options you can explore).  I use the 580EX with a Panasonic GH2 and some inexpensive wireless remotes, for example.  For even less money, you could get a Canon 199a flash or an old Vivitar flash like a 285HV, but again, you'd need the right triggers to use these with your camera.

 

Owners of some Canon point-and-shoot models might be able to make use of the CHDK firmware to allow their cameras to shoot in RAW format.  I didn't see the EOS Rebel T3i on the CHDK Wiki list, however.  CHDK adds other useful features to certain point-and-shoot Canon cameras as well.  There's also Magic Lantern firmware for certain other Canon cameras, which I haven't tried but might provide some useful features.  Maybe one of these provides a firmware update that could help with the lens creep problem, but I'm not sure.

[leszekp]

I use CHDK with my dome RTI system to automatically fire the shutter via the USB connector. Unfortunately, it does nothing for the lens creep issue. I've tried the RAW option in CHDK, but it doesn't use the built-in lens distortion correction capabilities of the camera, and the result is so heavily geometrically flawed that it's pretty much unusable/uncorrectable. Photoshop/Lightroom don't support RAW from CHDK.

[Taylor]

Hi leszekp,

 

If you can take an additional set of CHDK Raw calibration images for your camera's aperture and focus settings for the project at hand, you might be able to remove the distortion from your CHDK Raw images by aligning the images and exporting the calibration from Photoscan, if it's worth the extra trouble.  Then you could correct the distortion in any set of CHDK Raw images captured with the same camera aperture and focus settings simply by loading them into Photoscan and importing the calibration file.  See macsurveyr's comment here.  You probably can't reproduce the exact aperture and focus settings for past projects, but I just thought I'd mention it in case it's useful in the future.

[Jon]

The EOS T3i is a DSLR, and doesn't support CHDK, but then it, like the PowerShot G16, both shoot RAW out of the box. You might consider, for RTI, using a manual-only flash like the Vivitar 385HV which is under $100 and very close to the output of Canon's Speedlite 600RT. You'd need either a long sync cord or a remote trigger to go with it though.