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Author Topic: Cross-polarized light setup for photographing artwork  (Read 25701 times)
adpix
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« Reply #20 on: February 27, 2014, 04:47:52 PM »
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Let me hedge my response by saying that you will not sacrifice polarization by shooting through an umbrella or free standing scrim. What's significant here is that the light goes directly through one simple layer of cloth. But it's in the nature of soft boxes that light bounces around within them before exiting the front scrim. So polarization may be lost under that circumstance.

As a brief aside, let me say that I have found free standing scrims to be the most convenient means of lighting big canvases because I can aim the strobe where I want it as well as vary the light's intensity from soft to semi-hard by moving the strobe closer or farther from the scrim.
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« Reply #21 on: February 27, 2014, 05:18:58 PM »
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OK, that makes sense (the bouncing). Maybe not softbox, just a single layer then. Be interesting to try anyway.
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« Reply #22 on: February 27, 2014, 06:18:27 PM »
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One reason not to cover your soft box with a polarizing filter is simple cost. A smaller filter over the reflector is much less expensive. That is especially revelant to my practice of shooting through two six by six foot scrims.

The fact that polarization is not lost through scrims is easily demonstrated. Set up your lights as usual, turn on the modeling lights on the strobes and kill the room lights. Then take a bottle of colored glass and invert it on a light stand in front of your art. Look through the lens and will see two reflections on the bottle. If your polarizing filters on the lights and camera are properly aligned, you will see the two reflections disappear as you rotate the polarizing filter on your lens. I use this method all the time to establish the desired degree of polarization.

I can't speak to Profotos, but most studio strobes that I've used have a variance in Kelvin temp from head to head. You need a color meter to detect it and correct with gels. Plus I have found that keeping the over all color temp in the 5000-5500 range gives me a better image, as opposed shooting too warm or cold, and then correcting in post processing.

I get my polarizing film for about $18/linear foot so 8 feet (2 x 4ft soft boxes) of it doesn't cost that much. It is also very quick to clip the film to the front of the soft box or have permanent tabs of velcro glued on so as to velcro the film to the outer velcro of the soft box already there for modifiers, etc. I get my polarizing film from polarization.com.

Your method of determining the desired amount of polarization is interesting. Gonna try that one. I'm currently using Robin Myers' (rmimaging.com) Polarizer Adjustment Card. I can hang it right in front of the art. It is a great little and cheap tool that allows me to guarantee full polarization. I can also decide to back off a bit if I want.

My Profotos provide a consistent 5600K (+/- 30K) so pretty accurate. Do you use gels to correct for this amount or is there a threshold where you won't bother using gels?
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Jason DiMichele
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« Reply #23 on: February 27, 2014, 06:22:26 PM »
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As a brief aside, let me say that I have found free standing scrims to be the most convenient means of lighting big canvases because I can aim the strobe where I want it as well as vary the light's intensity from soft to semi-hard by moving the strobe closer or farther from the scrim.

How large are your large canvases? Are you using 2 or 4 lights and what power are they? Aren't you losing a lot of light efficiency when shooting through the scrim as the light coming out of the flash isn't contained or directed as much as an umbrella or soft box?
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Jason DiMichele
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« Reply #24 on: February 27, 2014, 07:43:40 PM »
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In a couple of days I'll shoot a triptych that measures 14-ft by 5-ft. The basic lighting will be two of Buff's biggest monoblocs.  I'll shoot through two scrims and adjust things until I have less than 1/10 stop of variance. Sure, there is loss of light in my set-up, but the Nikon D800 handles multi pops very successfully.

The art incorporates metal foil, which goes dead after I have used double polarizing to kills specular highlights in the paint. So, employing the rule that angle of incidence equals angle of reflection, I point four to six additional monoblocs so that the light hits the metal fail and bounces back into the lens. These strobes are clustered around the camera and do not go through the big scrims situated to right and left. They would ruin the shot, except that they are turned very, very low so that all they do is give specular reflections, without affecting the base exposure which is two or three stops higher. Or affecting the color temperature of the shot. It's an iterative process requiring a lot of test shots to get the balance just right, so I shoot tethered to an Apple MacBook Pro.

One tip on adjusting color temps with Roscp gels. If the steps between gels is bigger than you need, then it's time for surgery. Cut away part of the gel (strips or holes) and light mixing will provide you with the correct color temp at the art, as measured by your color meter.

Finally,  I have found that the Brush tool in Lightroom does wonders in adjusting local color and density.


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« Reply #25 on: March 06, 2014, 12:24:51 PM »
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It took me a while to get to test this (diffuser in front of the polarizer). But I'm not convinced.

Attached are three examples. One is a "straight" setup, polarizer attached to the strobe reflectors. The second is identical, but with umbrellas in front. The third is umbrellas only; no polarizer. Judge for yourself.
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« Reply #26 on: March 06, 2014, 12:47:05 PM »
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Definitely number one. Adding diffusion after the polarization scrambles the light again. It's physics and the whole point of a diffusion source to begin with. The quality of polarization can't be as good post diffused as light straight through the polarization film. With the film over my soft boxes I get the best of both worlds. Sure I need more lighting power (as I don't want to do multiple pops) but I continually get fantastic results.
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« Reply #27 on: March 06, 2014, 12:55:28 PM »
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Yup. No contest.

The other way isn't as easy to test. I need to get more film, but I have two strip soft boxes that should work once I get it.

This is a bit like finding the holy grail of shooting art. I want to get rid of the specular highlights, but at the same time I also want to get rid of the harsh shadows that inevitably result from using point light sources. Strip soft boxes could well be the compromise that will work.
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« Reply #28 on: March 06, 2014, 01:38:58 PM »
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I'd love to see some pictures of some of the softbox arrangements all of you are using. Photographing oil paintings is something I do regularly.

Minimizing time in Photoshop repairing glints would be very welcomed here.

Thanks

jim
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« Reply #29 on: March 06, 2014, 02:44:30 PM »
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The other way isn't as easy to test. I need to get more film, but I have two strip soft boxes that should work once I get it.

This is a bit like finding the holy grail of shooting art. I want to get rid of the specular highlights, but at the same time I also want to get rid of the harsh shadows that inevitably result from using point light sources. Strip soft boxes could well be the compromise that will work.

This is the film I'm using:

http://polarization.com/polarshop/

It's $15 a linear foot and 17" wide. I just use big clips to attach it to the soft box so that I can easily take it on and off and roll it away safely in a tube. My current art repro soft boxes are 1x4'. I found it beneficial to put a little mark at the top of the film when I've go them oriented properly so that the film on both soft boxes is attached correctly (they have to have the same alignment to be properly polarized).

With proper polarization you will always get more contrast and saturation, easily (as you know) tweaked in post processing. My shadows are totally fine. Never had any issues there.

Cheers,
Jay
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« Reply #30 on: March 06, 2014, 02:59:23 PM »
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$15/linear foot is a good price.  The cheapest I can find Rosco Cinegel for is $21/linear foot (also 17" wide), but only in 10 foot quantities.  The 17"x20" sheet usually goes for $44. 
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« Reply #31 on: March 06, 2014, 03:00:51 PM »
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I'd love to see some pictures of some of the softbox arrangements all of you are using. Photographing oil paintings is something I do regularly.

Minimizing time in Photoshop repairing glints would be very welcomed here.

Thanks

jim

Hi Jim,


What is your current setup for art reproduction?

With regard to photos of soft box setups, there's nothing really fancy. It's just two soft boxes on a 45 degree angle to the art. The fancy part is a strip of polarizing film (in my previous post) that's attached to the front of the soft box to polarize the light coming out. Plus a polarizing filter on the camera lens.

I've used cheap and now really good lighting and soft boxes and have had good results with both. My better equipment is more reliable and consistent and is definitely more enjoyable to use. But high quality art repros can be done on the cheap.

Since I want to reproduce the art only once (more beneficial for myself and artist) I typically (unless I know for sure that it will only ever need to be reproduced at a small size) digitally stitch with my spherical panoramic head I made. I also just built an adapter to attach my 35mm bodies to my large format cameras (4x5 and 8x10) and going to see how that works out. That will allow me to orthographically stitch which will alleviate me from having to tweak any distortion from the digital stitching.. I'm digressing now sorry. Wink

Other than that just make sure the exposure corner to corner is proper. This is one situation that I don't use the histogram to check for even illumination. And I would suggest using one of the polarization cards from rmimaging.com or put a piece of shiny metal in the scene so you know when you've gotten max polarization. However, you may also want to dial back the polarization a bit if you want to keep some more of the texture depending on the painting you are reproducing. 

Cheers!
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« Reply #32 on: March 06, 2014, 03:03:19 PM »
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$15/linear foot is a good price.  The cheapest I can find Rosco Cinegel for is $21/linear foot (also 17" wide), but only in 10 foot quantities.  The 17"x20" sheet usually goes for $44.

This is the only stuff I've used. The results are excellent. Since I've never compared it with another product I can't say if there's a quality difference but I would doubt it. Have you tried various polarization film brands? If so I would love to hear what your findings are.

Cheers!
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« Reply #33 on: March 06, 2014, 05:05:09 PM »
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We use two SB800 flashes shot into 3ft white reflector umbrellas. We do a lot of shooting on each piece to get the uniformity we want and are still left with unwanted glints on most units which require photoshopping to remove. Each piece has its own particular quirks that need accommodating.

The artist (my daughter) makes all the calls on when a shot result is adequate in real time. She does the vast majority of the PS work and I'd like to reduce that as much as possible to give her more time on easel.

We shoot these with her D300 live to her laptop using liveview and the Nikon app (don't remember the name.) Liveview shooting has made a big improvement in the process. I'd just like to get the lighting more uniform and with less specular highlighting.

Money isn't really the issue here it's reducing the time away from the easel. If I can buy something that works I'll do it. I'd prefer if it worked with the Nikon lighting systems.

BTW, we don't do any stitching as her works are 4ftx6ft max and she shoots a lot of detail shots in addition to the full work ones. Resolution for the intended purpose of documenting the work is fine at this time. Perhaps we might go to a higher resolution camera or stitching in the future but likely a higher resolution camera first to avoid more fiddling with stitched images.

Where would you suggest I look for lightboxes similar to yours?

Thanks!

Jim
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« Reply #34 on: March 06, 2014, 06:55:21 PM »
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We use two SB800 flashes shot into 3ft white reflector umbrellas. We do a lot of shooting on each piece to get the uniformity we want and are still left with unwanted glints on most units which require photoshopping to remove. Each piece has its own particular quirks that need accommodating.

The artist (my daughter) makes all the calls on when a shot result is adequate in real time. She does the vast majority of the PS work and I'd like to reduce that as much as possible to give her more time on easel.

We shoot these with her D300 live to her laptop using liveview and the Nikon app (don't remember the name.) Liveview shooting has made a big improvement in the process. I'd just like to get the lighting more uniform and with less specular highlighting.

Money isn't really the issue here it's reducing the time away from the easel. If I can buy something that works I'll do it. I'd prefer if it worked with the Nikon lighting systems.

BTW, we don't do any stitching as her works are 4ftx6ft max and she shoots a lot of detail shots in addition to the full work ones. Resolution for the intended purpose of documenting the work is fine at this time. Perhaps we might go to a higher resolution camera or stitching in the future but likely a higher resolution camera first to avoid more fiddling with stitched images.

Where would you suggest I look for lightboxes similar to yours?

Thanks!

Jim

Hi Jim,

With all honesty (and respect) I believe that your lighting setup is not particularly adequate for art reproduction. First up are your SB800's. They pack about 100WS max which isn't really powerful enough, especially if you're shooting through diffusion and then (ideally) polarized film. Between the diffusion and the polarized film you'll lose about 4 stops of light.  The umbrellas are not ideal as their light source is more directional. You want as soft and diffused light as you can get. If you're using umbrellas you're going to want to get them as close as possible to the art to make a larger light source and that may get in the way of your lens. For your lens you'll want to use a longer lens and stand further back for two reasons. First reason is less distortion with a longer lens and the second reason is that you don't want to be in the path of the light reflecting off the painting which can cause reflections back onto the lens. With the SB800's I'm assuming you're shooting a fairly wide aperture with high ISO. The lower ISO the better for fine detail. Please give me more information about your camera settings while shooting. You should just use a light meter and meter all 4 corners and center of the painting to ensure you have even illumination. It's a lot quicker than shooting a number of evaluation test shots and analyzing them.

I completely agree with reducing the amount of post processing time. Using the soft boxes with polarizing film on the outside you can completely remove any glare or reflection. You can even control how much you want to curb with the polarizing filter on the camera lens. However, there will always be some level of post processing required, even if you make a custom camera profile. For example, when a photo is taken with polarization, there will almost always be more contrast and saturation. This is easily fixed. However, the majority of the post processing will come when tweaking colour and tonal separation. Depending on the painting and the colours involved, the post processing can take a few minutes or hours. But you will never have to do any glare removal. The other problem is that if you are removing glare, that means you're also not capturing the true colour of the piece since the glare is reducing contrast, saturation and possibly shifting the hue. I think it's fantastic that you and your daughter are working together on this. Smiley

If money isn't too much of a concern then you can probably get a nice lighting setup for about $1000-1700CA (including a light meter) so I'm not sure what that is in US dollars right now.. perhaps pocket change. LOL. And you might want to seriously consider stitching or upgrading the camera as I'll get to in a moment. I would upgrade to the D800 if I were you, especially since you're doing single shot captures.

Now to the camera. As long as you are sure that you're not going to want to print these captures you are taking now, your current camera will be fine. It's a great camera. However.. with the D300 being 12 megapixels, you would, even printing at the more or less minimum (for a reasonable viewing distance) 180ppi, you would only get about a 16x24" print. That's assuming you used 100% of the sensor and didn't require any cropping. That's not a bad print size but it's nowhere near your original of 48x72" you are reproducing. If there was a chance you wanted to print a piece of your daughters art at full size you would ideally require approximately 111 megapixels. That's just technical information though. Realistically for the detail in paintings and with the quality of today's sensors you can interpolate an image quite a bit and get good results. However, a D800 at 36 megapixels or image stitching will get you a lot closer. That's why I stitch my 22 megapixel images. I can get to 100+ megapixels quite easily.  If you are going to upgrade the camera anyway you might as well capture the art once.

I use Profoto lighting and modifiers. However, there are a lot of great companies out there selling lights and modifiers (soft boxes, umbrellas, etc). For the art repro you ideally want strip soft boxes no more than 17" wide so the polarizing film will cover the width. The soft boxes will run you about $2-300 each, the polarizing film $15/ft so no more than about $60 per soft box. For the monolights I would recommend at least 500WS. Two of them will be enough. If you can spring for the 1000WS lights having the extra headroom will give you a touch more flexibility but may not be worth the cost difference.

You're very welcome! Smiley

Cheers,
Jay
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« Reply #35 on: March 06, 2014, 07:45:01 PM »
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Jay

I realize we don't have the optimum setup by any stretch but that's why I was asking for info! This is really for documenting her work hence the tons of detail shots. We've discussed stitching and just doing an X by Y of the whole piece but that's not likely just yet.

All you supplied is great! I'll be doing some serious research on the lighting ideas you provided.

We actually shoot about f/5 with ISO 200. Focal length varies but usually for full size it's around the middle of the 24-70mm zoom range more or less. The two SB800 are right at their limits with these settings when bounced into the umbrellas. Lack of glare is always the first acceptance criteria for the shot. We try to reduce specular specs as well at the same time but if there's a tradeoff we always go in the direction of lack of areal glare. She is extremely critical about accuracy.

Full size reproductions don't concern her now. Perhaps in the future. But I'd gladly take her D300 as a hand-me-down!

A quick glance at B&H shows a 1.5'x4' unit: http://www.bhphotovideo.com/c/product/808728-REG/Profoto_100483_Heat_Resistant_Softbox_RF_1_5x4.html

I think I'd be happier with a full length unit but a 6' unit shown there is only 1' wide.

Which would you chose?

I'd need two of course...

The Profoto Pro-B Plus is only $200 more for the 1200WS version over the 600WS Profoto AcuteB. I don't think I'd mess with the 600 for that difference.

Pricey drivers!! D4=$$

Need to look at rings also. Suggestions welcome!

Thanks!!

jim (happy studio slave)
« Last Edit: March 06, 2014, 08:39:31 PM by jtmiller » Logged
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« Reply #36 on: March 06, 2014, 09:24:17 PM »
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Apparently physics differs from one studio to the next. But, like medicine, product photography is both art and science. On my current shoot of a set of panels that measures about 8-ft long, I have incorporated polarized lighting that shoots through fabric diffusers (very successfully) and polarizers with Rosco gels clipped  to reflectors that do not shoot through scrims,  the latter arrangement because I wanted harder light in a couple of spots. These reflector-mounted gels I then canted slightly so their degree of polarization differs from those behind the 6x6 diffusers.

As to multi-pops, the process does require a studio that can go dark. And a high-end camera.  I have not noticed any significant build-up of noise in my images. Or complaints from editors in whose catalogs the images appear.
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« Reply #37 on: March 06, 2014, 09:50:20 PM »
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Apparently physics differs from one studio to the next. But, like medicine, product photography is both art and science. On my current shoot of a set of panels that measures about 8-ft long, I have incorporated polarized photography that shoots through fabric diffusers (very successfully) and polarizers with Rosco gels clipped  to reflectors that do not shoot through scrims,  the latter arrangement because I wanted harder light in a couple of spots. These reflector-mounted gels I then canted slightly so their degree of polarization differs from those behind the 6x6 diffusers.

As to multi-pops, the process does require a studio that can go dark. And a high-end camera.  I have not noticed any significant build-up of noise in my images. Or complaints from editors in whose catalogs the images appear.

Physics or not, the eyes judge the results. During my testing the results have never been better than having the polarizing film the last material the light goes through. That doesn't necessarily mean that I've completely and thoroughly exhausted all testing scenarios I suppose. You must be using quite a bit of light. Doubt that you are evenly illuminating that whole 8ft panel in one go with just two lights.

Not sure how you define a "high-end camera" (mfdb?) but a "high-end camera" is not required for multi-pops. I was using multi-pops with my large format camera and film over a decade ago. You can multi-pop with any camera on bulb.

I'm glad to hear that you've been so successful with all the catalogs you're published in and create many a happy editor. Smiley

Cheers,
Jay

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« Reply #38 on: March 06, 2014, 10:07:31 PM »
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Jay

I realize we don't have the optimum setup by any stretch but that's why I was asking for info! This is really for documenting her work hence the tons of detail shots. We've discussed stitching and just doing an X by Y of the whole piece but that's not likely just yet.

All you supplied is great! I'll be doing some serious research on the lighting ideas you provided.

We actually shoot about f/5 with ISO 200. Focal length varies but usually for full size it's around the middle of the 24-70mm zoom range more or less. The two SB800 are right at their limits with these settings when bounced into the umbrellas. Lack of glare is always the first acceptance criteria for the shot. We try to reduce specular specs as well at the same time but if there's a tradeoff we always go in the direction of lack of areal glare. She is extremely critical about accuracy.

Full size reproductions don't concern her now. Perhaps in the future. But I'd gladly take her D300 as a hand-me-down!

A quick glance at B&H shows a 1.5'x4' unit: http://www.bhphotovideo.com/c/product/808728-REG/Profoto_100483_Heat_Resistant_Softbox_RF_1_5x4.html

I think I'd be happier with a full length unit but a 6' unit shown there is only 1' wide.

Which would you chose?

I'd need two of course...

The Profoto Pro-B Plus is only $200 more for the 1200WS version over the 600WS Profoto AcuteB. I don't think I'd mess with the 600 for that difference.

Pricey drivers!! D4=$$

Need to look at rings also. Suggestions welcome!

Thanks!!

jim (happy studio slave)

Jim,

I have 2 x Profoto 1x4' mainly because the polarization film is only 17" wide so I'm completely covered with the 1' wide soft box. If you go with the 1.5' box you'll have a bunch of light spilling out from around the polarizing film. I bought these soft boxes specifically for art repro and product photography. I have larger soft boxes and umbrellas for different styles of photography. You can also look at the regular, non-HR soft boxes as they are just as good. Can't really imagine a non-all day shooter requiring the HR unless you're pushing serious light around in that thing all day long.

With regards to the lights, you may want to consider the following. Not only are they a lot cheaper but they are awesome lights. There is a large discussion to be had with regard to battery packs / heads vs monolights (my suggestion below) but I'm going to say that for your needs you're probably spending more than you'll get out of the D4 / heads. Great that you have flexibility with your budget but might as well keep it for the next upgrade (like the camera <nudge> <nudge> lol). So my suggestion is:
http://www.bhphotovideo.com/c/product/605754-REG/Profoto_901054_D1_Air_1000_W_S.html

By rings I'm assuming you mean the speed rings. The following standard Profoto speed ring is what I'm using:
http://www.bhphotovideo.com/c/product/900688-REG/Profoto_100501_Speed_Ring_Adapter.html

Hopefully this will help you out. Definitely feel free to ask me for any additional advice / suggestions!

Cheers,
Jay

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« Reply #39 on: March 06, 2014, 10:21:11 PM »
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Hi Jay

Good info all! After sending that last one I also discovered the D1 1K units. They look like they are more in our price range.

I was wondering about hotspotting with the strip boxes. I was looking more seriously at the 1x6 based on your polarizer width concerns. Will the D1 adequately fill a box this long?

I've done some more reading tonight on lighting in general and this system looks like one which will serve our needs.

Where have you been getting your polarizer material? EDIT: Nevermind, found it in your previous posts.

Thanks

Feel free to email me as I think I've enabled that option.

Jim
« Last Edit: March 07, 2014, 08:09:50 AM by jtmiller » Logged
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