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Author Topic: Any Significance in Pentax 645D Megapixel Difference with Rhinocam?  (Read 1620 times)
JimAscher
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« on: June 18, 2013, 06:33:32 PM »
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I am posing this question with some concern for a display of ignorance on my part.

The Pentax 645D has a sensor reportedly of 40 megapixels.  The Rhinocam creates a 645 digital image of up to 128 megapixels through its stitching of eight images of 16 megapixels each.

Does this mean that the Rhinocam image is to that extent “better’ than the Pentax image? 
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MichaelEzra
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« Reply #1 on: June 18, 2013, 07:35:27 PM »
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"Better" has always been a relative term. What is better 8 or 7?.. "Better" for what purpose?

40 megapixels are enough for most purposes.  
Rhinocam will allow to get more resolution via stitching.
Pentax 645D has a wider dynamic range and better color response than Nex sensors.
One can do multi-frame HDR with Nex and use HDR stitching, while also correcting ghosts for any movement in the field of view.
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theguywitha645d
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« Reply #2 on: June 18, 2013, 07:36:16 PM »
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It is true. The Pentax 645D has 40 MP, just like Pentax states in the spec sheet. The difference between 40 and 128 is 88. The is a 79% increase in resolution. Naturally, you can stitch images taken with the Pentax 645D too.
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chrismuc
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« Reply #3 on: June 18, 2013, 07:47:41 PM »
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A few weeks ago, I did a quick comparison with a friend: IQ180 vs. Rhino + NEX 7 w/ HB CF 50FLE.
Theoretically the Rhino can produce very high resolution files, but the cam is that flimsy and slow to use, I mean no wonder, it costs quite nothing compared with other MF equipment. The tripod mount was a little loose and it was impossible to fix it. This means the cam always turned a bit when touching and shifting the shift mechanism with the NEX cam. The shift mechanism has no click stops for the correct positions. Doing eight files takes time, in the meantime clouds and shadow move, so very difficult to stitch the pictures afterwards.
NEX7 = 3.9 um pixel width w/ AA-filter
IQ180 = 5.2 um w/o AA-filter
645D = 6 u w/o AA-filter
That means the MF pics come out sharper if you open the raw files because larger pixel width and no AA-filter.
The NEX7 file "has a lot of pixels" but is softer on pixel level.
I doubt any MF lens would have real 3.9 um "resolution", maybe a Leica S lens.
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Doug Peterson
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« Reply #4 on: June 18, 2013, 09:23:53 PM »
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For most applications the quality of the pixels matters more than the number of pixels.

A 2000mp image composed of soft, abberation filled, noisy pixels with poor color and choppy transitions is worth less in most cases than a razor sharp 6mp image that is free of abberations, smooth in tonality, and has beautiful color.

I'm not saying anything specifically about the rhinocam - I've never used it. I'm just emphasizing that a megapixel spec is, by itself, devoid of any real meaning.

The best answer is always to test the options for yourself and see how they fit your needs/wants.
« Last Edit: June 18, 2013, 09:28:55 PM by Doug Peterson » Logged

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JimAscher
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« Reply #5 on: June 18, 2013, 10:09:20 PM »
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I have recently reported in another thread my experiences to date with the Rhinocam (to which no one so far has added any comment).  http://www.luminous-landscape.com/forum/index.php?topic=79044.0

While I am enjoying it very much, I am still fine-tuning my procedures with it, to make it easier to use.  I find it does produce (for me) some rather stunning pictures.  The ground glass framing is a hassle (with its small, upside down image) but I think i have worked out a solution, which is too bizarre for me to announce in public at this time.   By lubricating the slide, I now have no problem with slippage of alignment when matching up the dots (which I initially also did)  The tripod mount for me is very firm and steady.  Just think "view camera" for procedures, and I think you will be all right.
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Jim Ascher

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ErikKaffehr
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« Reply #6 on: June 18, 2013, 11:41:47 PM »
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Hi,

My guess is that the Rhinocam makes good images when it is properly used, but I don't think it is that easy to make proper use of.

If you have a lot of MF lenses, the Rhinocam could use all the image circle, which an MFD sensor does not. Even the largest ones have a hefty crop factor on a lens made for 6x6 or 6x7.

Regarding DR, I would assume that the NEX has pretty decent DR. We are composing 8 images into one, that would improve DR 1.5 EV. If we look at DxO mark a NEX-6 has a DR of 13.1 (normalized) while the the IQ 180 has 13.56 (normalized). The corresponding figure for the the Rhinocam would be 14.6 (normalized).

But DR is overemphasised in my simple opinion. I have very few pictures among the 65000 or so I have on my hard disk where DR is the limiting factor. Also, DR will always be limited by lens flare.

Best regards
Erik



"Better" has always been a relative term. What is better 8 or 7?.. "Better" for what purpose?

40 megapixels are enough for most purposes.  
Rhinocam will allow to get more resolution via stitching.
Pentax 645D has a wider dynamic range and better color response than Nex sensors.
One can do multi-frame HDR with Nex and use HDR stitching, while also correcting ghosts for any movement in the field of view.
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BartvanderWolf
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« Reply #7 on: June 19, 2013, 03:12:13 AM »
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The difference between 40 and 128 is 88. The is a 79% increase in resolution.

Hi,

When we compare the 645D, with a sensor array size of  44 x 33mm , with the resulting stitch from the RhinoCam, with a virtual array size of 62.4 x 46.8 mm, there is an approx. sampling density increase of +41.8% in each direction. However, sampling an MF lens with the RhinoCam closer to the limits of the image circle doesn't necessarily increase resolution at those edges as much as the sampling density suggests.

So a lot depends on the quality of the MF lens used, and especially its edge/corner performance. On the positive side, the dense sampling will extract the most resolution out of any given lens.

Also, the 645D doesn't use an AA-filter, and AFAIK the e.g. NEX does. I also do not know how well the NEX sensor responds to the more oblique rays at the more shifted positions. One may need to manually assemble a stitched LCC file (because Photoshop won't understand how to handle such light fall-off and Color cast) or perhaps it's easier to do it per tile before stitching. The stitching should be able to handle the adjusted brightness differences between the tiles.

Quote
Naturally, you can stitch images taken with the Pentax 645D too.

Absolutely true and, when using rotational stitching, one always uses the center of the image circle of a given lens.

Cheers,
Bart
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JimAscher
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« Reply #8 on: June 19, 2013, 08:36:26 AM »
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...However, sampling an MF lens with the RhinoCam closer to the limits of the image circle doesn't necessarily increase resolution at those edges as much as the sampling density suggests....  I also do not know how well the NEX sensor responds to the more oblique rays at the more shifted positions.

There has been much discussion in another (NEX) forum of color shift in the Rhinocam due to possibly more oblique angles of the image hitting the NEX sensor among the various medium format lenses used, i.e., the Mamiya and Pentax 645's and the Hasselblads , all of which the Rhinocam currently has lens adapters for.  I have chosen to use Hasselblad lenses (purchased used) as its 6x6 image circle is slightly larger than for the 645 lenses, and its Rhinocam adapter positions the lenses farther out, theoretically reducing the "oblique'"angles hitting the sensor.  In any case, with this lens I do not experience any of the color shifts reported by others using 645 lenses.
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Jim Ascher

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BartvanderWolf
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« Reply #9 on: June 19, 2013, 08:58:08 AM »
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There has been much discussion in another (NEX) forum of color shift in the Rhinocam due to possibly more oblique angles of the image hitting the NEX sensor among the various medium format lenses used, i.e., the Mamiya and Pentax 645's and the Hasselblads , all of which the Rhinocam currently has lens adapters for.  I have chosen to use Hasselblad lenses (purchased used) as its 6x6 image circle is slightly larger than for the 645 lenses, and its Rhinocam adapter positions the lenses farther out, theoretically reducing the "oblique'"angles hitting the sensor.  In any case, with this lens I do not experience any of the color shifts reported by others using 645 lenses.

Hi Jim,

I suppose that in general the more retro-focus optical designs will do better than relatively symmetrical wide angles. Normal and telephoto designs should present fewer issues in general.

Cheers,
Bart
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Ben Rubinstein
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« Reply #10 on: June 19, 2013, 10:25:20 AM »
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How much resolution do these lenses have? The older ones at least show their limitations on a 40 megapixel sensor often, at 128 megapixels and using small pixels at that, they may well show their limitations as far as resolving power. Tonality of course is a different ballgame. I'll never forget my first stitch with a camera fusion adaptor, an old and scratched 90mm Caltar lens with a 100 megapixel stitch using a 5Dc, the tonality was to dream for. We've got a Aptus II-8 which with the schneider 80mm could probably come close to the resolution but resolution is only the start...
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