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Author Topic: Gigapixel Lens A7r  (Read 6839 times)

David Mills

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Gigapixel Lens A7r
« on: August 02, 2015, 11:41:03 pm »

I didn't really know how to title this topic. The question is - If one is attempting to produce super sharp huge prints (6X18 feet) through the process of a multi-row stitched (landscape) panorama and HDR, what lens would you recommend for the A7r to accomplish this? I'm not talking GigaPan. GigaPan is not an option. Thanks.
« Last Edit: August 02, 2015, 11:43:33 pm by BAPP »
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Bart_van_der_Wolf

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Re: Gigapixel Lens A7r
« Reply #1 on: August 03, 2015, 04:10:57 am »

I didn't really know how to title this topic. The question is - If one is attempting to produce super sharp huge prints (6X18 feet) through the process of a multi-row stitched (landscape) panorama and HDR, what lens would you recommend for the A7r to accomplish this? I'm not talking GigaPan. GigaPan is not an option. Thanks.

Hi,

In general, one needs a lens that has very good center performance, because some of the edge/corner detail of each tile can be cropped/blended out by using a larger overlap between the tiles (which will of course require to take more images). But more important is to use an appropriately longer focal length that produces a larger on-sensor magnification (= resolution) while at the same time balancing with the diffraction effects of the narrower aperture required to maintain a certain Depth of Field. Maybe even focusstacking needs to be used for some of the tiles..

So basically you need to calculate backwards from the required number of pixels for the intended output size and viewing distance, to the required number of pixels in the stitched image. Then divide that number of pixels by the number of tiles (with overlap) that is required, and build in a margin for resampling losses (so rather down-sample than up-sample). Angle of view and possible use of different projections also plays a role.

The scene content may also add a few limitations that may need to be factored in, like DOF, subject movement, changing light, etc., but starting with the technical calculation will present the physical shooting requirements which may need to be relaxed a bit if the practical shooting conditions require it.

Cheers,
Bart
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NancyP

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Re: Gigapixel Lens A7r
« Reply #2 on: August 03, 2015, 11:41:01 am »

Figure out what your total angle of view will be, horizontal and vertical. You want a good 1/3 overlap on each side. You might also want a little "extra" on the edges of the image. So:

3 x Total Angle of View
__________________   =    # shots per row (or column)
Lens Angle of View

So if you wanted a total horizontal angle of view of 120 degrees, and had a good 85mm lens on hand plus your FF camera (lens vertical AOV  16 degrees, assuming you shoot in portrait mode), you would need 23 shots per row.

If you then wanted a total vertical angle of view of 40 degrees, with the same 85 mm lens and FF camera (lens horizontal AOV 24 degrees), you would need 5 shots per column.  That's 115 shots total for entire image. There's generous cropping room at the edges.

This explains the appeal of the Gigapan automated system and of the indexed rotators for these gigapixel images. Even shooting one row manually/by eye takes some time.
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David Mills

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Re: Gigapixel Lens A7r
« Reply #3 on: August 03, 2015, 12:47:43 pm »

Thanks. All great information on the "how to". Any specific suggestions on a lens for the A7r. I do some extreme backcountry locations that require multi-day backpacks so the GigaPan is not a practical option for this application unless I pack it in via horseback. Thanks and thanks again.
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Bart_van_der_Wolf

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Re: Gigapixel Lens A7r
« Reply #4 on: August 03, 2015, 02:23:53 pm »

Thanks. All great information on the "how to". Any specific suggestions on a lens for the A7r. I do some extreme backcountry locations that require multi-day backpacks so the GigaPan is not a practical option for this application unless I pack it in via horseback. Thanks and thanks again.

Hi,

The required focal length depends on the required file resolution for output. The required output resolution is determined by the viewing distance of the print.

Example, an 18 feet wide print would probably be viewed from some 6 to 18 feet distance. If it must retain high resolution with shorter viewing distances, everything scales proportionally. Let's assume 10 feet viewing distance, easy to calculate with, then for someone with 20/20 visual acuity, the output must be printed from a 29 PPI source image (which would be upsampled to 360 PPI for printing with good output sharpening).

The 29 PPI image means that the print file before upsampling to native printer resolution would be 29 PPI x 216 inches = 6264 pixels wide. That's easy enough with most lenses that offer enough Field Of View for your scene, 2 or 3 stitched images would already allow to that. Those 2 or 3 images would need to cover the angle of view you want to shoot. If the angle of view is extreme enough to compromise the available lens quality, a longer focal length and more stitched images will be required.

However, if you need the same viewing quality at 1 foot (1/10 of the example) viewing distance, then you'd perhaps need 10x as many pixels, or something like 15-16 images with 30% overlap taken with a much longer focal length, per required Row (maybe 5 rows will suffice). If cylindrical projecton is acceptable, then not much (if any) additional resolution is required. For Rectilinear projection it would depend on the actual angle of view to cover.

So you need to determine the print viewing conditions, and the scene angle of view to cover, the rest can be calculated. Maybe a good 24mm, or 35mm, or perhaps a lightweight 50mm lens is all you need, but to determine that more info is needed.

As far as traveling lightweight, I can still recommend a click-stop indexer if you indeed need to stitch many images for the field of view you have in mind, and you could even use that instead of a ballhead or other head if you need to shave of as much weight as possible. But then a very lightweight (but with significant load capacity) Easy Leveler II will allow to do the final leveling and composing, to finish what you started with the tripod legs. I use one mounted directly on the tripod base plate, and a Manfrotto click-stop indexer on top of that with an Arca Swiss clamp on top of that for my No Parallax Point (NPP) bar (a RRS MPR-CL II) . Multi-Row setups may require more components.

Cheers,
Bart
« Last Edit: August 03, 2015, 02:42:56 pm by BartvanderWolf »
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David Mills

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Re: Gigapixel Lens A7r
« Reply #5 on: August 05, 2015, 11:58:34 am »

BartVanderWolf: Again, much appreciate the input. As somewhat newer to the world of photography and discovering quickly that what I’m trying to accomplish is rather complicated, let me rephrase the intended conclusion. Disregarding for now (and this maybe a moronic way to phrase it) much of the stuff about viewing distance and such, the question when you boil it down might be better framed, is it possible and if so how, does one produce a 7X21 foot print at 300dpi?
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Bart_van_der_Wolf

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Re: Gigapixel Lens A7r
« Reply #6 on: August 06, 2015, 04:49:17 am »

BartVanderWolf: Again, much appreciate the input. As somewhat newer to the world of photography and discovering quickly that what I’m trying to accomplish is rather complicated, let me rephrase the intended conclusion. Disregarding for now (and this maybe a moronic way to phrase it) much of the stuff about viewing distance and such, the question when you boil it down might be better framed, is it possible and if so how, does one produce a 7X21 foot print at 300dpi?

Hi,

A 7 x 21 foot print, 84 x 252 inch, at 300 PPI = 25200 x 75600 pixels (1.9 Gigapixels). Divide that by the number of pixels that the camera produces and multiply that by 1.4 for an approx. 30% overlap of the image tiles. That should give you an idea of the number of image tiles you need, and whether landscape orientation or portrait orientation of the camera is more efficient. Those image tiles would have a high enough resolution to also allow closer viewing conditions, but it would be overkill for larger viewing distances, and would require more (multirow pano) equipment to shoot.

You then need to look at which focal length lens produces the partial Field of View for the individual image tiles that adds up to the total Field of View that needs to be captured. You then need to determine if the Depth of Field from such a lens can be achieved without having to use excessively narrow apertures for the camera that will be used, since that would cost resolution. That might lead to the conclusion that the use of Focus Stacking, or a Tilt/Shift lens, is needed.

Do note that this is a very crude approximation, not really what you initially asked. That's because several different Panorama projections other than e.g. Cylindrical can require additional shots to be taken, or the use of longer focal lengths and more rows. There may also be a need to create the original stitched panorama at a somewhat oversized dimension, to allow for down-sampling to achieve better lens resolution.

Producing/printing such output is something you should plan together with a Lab that can handle such sizes, and mount it for a transportable/re-usable setup.

Cheers,
Bart
« Last Edit: August 06, 2015, 10:29:27 am by BartvanderWolf »
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NancyP

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Re: Gigapixel Lens A7r
« Reply #7 on: August 06, 2015, 11:11:26 am »

I am finding it hard to imagine someone closely examining (1 foot distance) a 7' x 21' print. Billboards are 20 ppi or something? Surely 100 ppi would be way more than enough?
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Bart_van_der_Wolf

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Re: Gigapixel Lens A7r
« Reply #8 on: August 06, 2015, 11:53:51 am »

I am finding it hard to imagine someone closely examining (1 foot distance) a 7' x 21' print. Billboards are 20 ppi or something? Surely 100 ppi would be way more than enough?

Hi,

I agree that 300 PPI Capture resolution is probably(?) over-stressing the requirements, and that was why I asked what the viewing distance requirements are. That will make a lot of difference.

Cheers,
Bart

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BradSmith

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Re: Gigapixel Lens A7r
« Reply #9 on: August 06, 2015, 08:43:02 pm »

BAPP said: ...........how does one produce a 7X21 foot print at 300dpi?

Bart answered your question in detail and correctly.  You seem to want a simpler answer.   Here it is......

Take a LOT of images.   

OK, OK!!!    I know.    How many?  With the pixel dimension of the a7r you asked about, using the calculation method described by Bart, it would take 5 rows of 21 images/row with the camera in the vertical, portrait orientation. 

Then I suppose the question becomes......but my computer chokes to death on 105 36Mp images!  How do I photomerge them???

Start another topic for that question
« Last Edit: August 06, 2015, 08:57:01 pm by BradSmith »
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elf

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Re: Gigapixel Lens A7r
« Reply #10 on: August 07, 2015, 01:37:21 am »

I think your technique is going to be more important than the number of images.  I've done up to 65 frames handheld, so if you practice a fair amount, you should be able to do a hundred frames.  It's really just a matter of knowing where the entrance pupil is and how to consistently rotate the camera around it.  The nice thing is, you can just go out in your backyard and practice until you're good enough to do it in the field.

Choose the lens by how much detail you want to capture, not by the number of images needed to fill an arbitrary size.
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Bart_van_der_Wolf

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Re: Gigapixel Lens A7r
« Reply #11 on: August 07, 2015, 03:26:17 am »

Then I suppose the question becomes......but my computer chokes to death on 105 36Mp images!  How do I photomerge them???

Start another topic for that question

Hi Brad,

Luckily there are dedicated stitching applications that understand that not all images need to be in RAM memory at the same time. They read and write to disk when necessary, and many calculations are only based on the control-points that link the image tile features anyway. Some procedures can also be performed just as well on (temporary) JPEG versions of the 16-b/ch input TIFFs, which the program only generates when needed. Then there is also GPU acceleration and parallel processing going on, keeping all CPU / GPU cores busy.

PTGUI should be able to do the job with relative ease. Photoshop may choke on the task though.

Cheers,
Bart
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BradSmith

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Re: Gigapixel Lens A7r
« Reply #12 on: August 07, 2015, 02:25:31 pm »

Bart,
Thanks.  I wasn't aware that the specialized programs such as PTGui handled the task in a different manner than Photoshop which is all I've used.  Billboard sized tasks such as being discussed here would be good reason for purchasing the specialized software.

And by the way, thank you for the expertise, time and effort you put into your posts on LULA.  When I see a post from you, I know there is serious CONTENT coming my way.
Brad
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Misirlou

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Re: Gigapixel Lens A7r
« Reply #13 on: August 07, 2015, 03:13:51 pm »

Are you certain a Gigapan would be too much? They came in three sizes. I was able to attach a Sigma DP2 Merrill to the smallest size one, and that rig works great. The A7R is a pretty small camera, and might fit on the medium one. The small size Gigapan is really not very heavy or bulky, and could easily be tied to a backpack or something. Presumably the medium size one is more to deal with, but it takes so much trouble out of the process.
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David Mills

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Re: Gigapixel Lens A7r
« Reply #14 on: August 09, 2015, 07:51:03 am »

Thanks everyone for the great input on this topic. Much of this for now anyway is over my head, but I’m learning. The specific application is the creation of large (as I have mentioned already) as clear as possible prints. What I haven’t mentioned is that these prints are then part of a presentation I give to hospitals, senior citizens, the disabled, inner city schools, and more. Essentially bringing the beauty and grandeur of the outdoors to individuals that lack the ability or opportunity to experience it for themselves. So, I am trying to replicate as best I can the experience of being there. For an individual to wheelchair up to these free standing sharp-as-a-tack prints and get the feeling of standing on the rim of the Grand Canyon for example, is what I’m striving for. I’m getting there, and mostly through trial and error and not much actual photographic knowledge. Here’s a photo example, my first stitched pano, 28 photos, taken about 3 years ago as my wife and I were completing a 5 day rim-to-rim backpack across the Grand Canyon. I look back on this pic and chuckle thinking how it turned out pretty good considering at the time I had both inferior knowledge and equipment. Sometimes you just get lucky I guess! Needless to say I’m continually working on technique and equipment related to this project, and greatly appreciate input on both.
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David Mills

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Re: Gigapixel Lens A7r
« Reply #15 on: August 11, 2015, 06:49:44 am »

Any thoughts on tilt/shift lenses with regard to multi-row panos?
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Bart_van_der_Wolf

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Re: Gigapixel Lens A7r
« Reply #16 on: August 11, 2015, 09:22:58 am »

Any thoughts on tilt/shift lenses with regard to multi-row panos?

Hi,

If the Depth of Field for a given lens, at a given aperture (F-number), is too shallow to cover everything from foreground to background with adequate sharpness, then a lens with Tilt capability may help. This is in particular the case with longer focal lengths, and buy/close foregrounds. But it also depends on how the scene is exactly laid-out (best for focus is roughly in a flattish plane or wedge of optimal focus), and if everything should really be equally sharp, although the latter is usually the case for Gigapixel projects.

Focusing at the hyperfocal distance, or a bit closer, is common procedure with Gigapixel projects. DoF will be from half the hyperfocal distance to infinity. The area in front of that will be visibly slightly less focused, but not in a total blur, the transition is gradual.

For the A7R, the hyperfocal distances for a few common focal lengths could be assumed (with a CoC=1.5x sensel pitch) to be:
35mm, at f/11, 48 feet
35mm, at f/16, 34 feet
50mm, at f/11, 99 feet
50mm, at f/16, 70 feet
70mm, at f/11, 194 feet
70mm, at f/16, 138 feet
85mm, at f/11, 287 feet
85mm, at f/16, 202 feet

So no big issue for somewhat distant vistas, but more tricky when a closer foreground is also present and needs to be in equally crisp focus. Then focus stacking or tilt lenses may be of help.

The Shift capability is perhaps less important for what you are planning, but it allows to have a certain control over how perspective is rendered. However, you already have that with a decent pano stitching application like PTGUI, and shifted images need additional (offset-)settings for a successful stitch. Photoshop often fails at those (maybe recent versions are a bit better?), but memory management of large pano stich projects is not what Photoshop is very good at anyway.

Cheers,
Bart
« Last Edit: August 11, 2015, 09:48:03 am by BartvanderWolf »
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David Mills

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Re: Gigapixel Lens A7r
« Reply #17 on: August 11, 2015, 05:00:51 pm »

With regard to the process, I have done many single row stitched HDR panos with pretty good results (see attached). And even though they print fairly large, they are not as large as I need, consequently I’m pushing the envelope and redeveloping my technique and workflow. As of this moment my technical solution would be – 3 row HDR (5 brackets) focus-stacked pano (one row foreground, one row mid, and one row background) with appropriate overlap. Gear is my A7r (soon to be A7rII) and Nodal Ninja or Really Right Stuff pano solutions. Now, back to the original question of this thread – lenses? I am considering the following lenses. Please bear in mind that I am considering the following lenses only from the standpoint of “practicing the technique” and once I’m sufficiently practiced at the technique I’ll spend the money necessary for better glass.   

Samyang (or Rokinon) 85mm f/1.4 Aspherical IF Lens
Samyang (or Rokinon) 100mm f/2.8 Macro Lens
Samyang (or Rokinon) 135mm f/2.0 ED UMC Lens

General comments on these lenses for my application are appreciated and I’m particularly interested in what one might feel is most appropriate the 85mm, 100mm, or 135mm, and why?

I understand these lens manufactures are interchangeable, so whether it’s Samyang or Rokino doesn’t really matter.
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NancyP

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Re: Gigapixel Lens A7r
« Reply #18 on: August 11, 2015, 07:00:33 pm »

Yep, Samyang is the parent manufacturer, they sell the lenses under their own name and to wholesalers who use the names Rokinon, Bower, Pro-Optic, and a few others. The question of  focal length depends on your use and how many frames you want to take per pano. The Samyang 135 is apparently sensational, so if you like manual focus, and have $549.00, you can get a lens that has optical quality similar to the big brands costing 2 to 4 times as much. The 85 is meh, it's an older design, but for an experiment, you can't beat $250.00 for a lens. the 100 hasn't gotten reviewed much.
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elf

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Re: Gigapixel Lens A7r
« Reply #19 on: August 11, 2015, 10:31:29 pm »

Search for writings by Harold Merklinger.  He can answer the question of which lens is best for the images you want to create.   It all depends on the amount of detail you desire and the time it takes to get it. 
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