Ad
Ad
Ad
Pages: « 1 2 3 [4]   Bottom of Page
Print
Author Topic: Beyond 400mm  (Read 18467 times)
Romy Ocon
Newbie
*
Offline Offline

Posts: 9



« Reply #60 on: April 16, 2009, 01:07:38 PM »
ReplyReply

Quote from: samirkharusi
Yes. And for static subjects you can still use stacking to get rid of it. I have an image of Saturn, taken with a standard Canon 600mm/4.0L IS using the video stack technique, and a 1.4x extender coupled to a 5x extender to yield a focal length of 4200mm, through 27 lens elements! I used a $100 webcam with its lens (and UV/IR blocker) removed. It is possible that one could do better using an IR blocker, but I simply forgot to use one; force of habit since I normally use the C14 mirror scope for planetary videos and that yields better images with IR included (allowing faster frame rates and possibly more steady seeing in IR):
http://www.samirkharusi.net/televue_canon.html
These days with the video-capable new DSLRs, such exercises would be simpler to try out. And the DSLR sensors are way better than in a 5-year old webcam...


Hi Samir,

Which DSLR will you recommend to video planetary objects, with high enough pixel density? The soon-to-come-out 500D has a video pixel density of only 1080p on an APS-C sensor (albeit 20 fps only). The 5D2 has even sparser pixel density - 1080p on a 24x36 mm sensor.

Romy
Logged

Philippine Wild Birds in HD video - http://exposureroom.com/members/RomyOcon.aspx/videos/
samirkharusi
Full Member
***
Offline Offline

Posts: 196


WWW
« Reply #61 on: April 17, 2009, 01:26:48 AM »
ReplyReply

Quote from: Romy Ocon
Hi Samir,

Which DSLR will you recommend to video planetary objects, with high enough pixel density? The soon-to-come-out 500D has a video pixel density of only 1080p on an APS-C sensor (albeit 20 fps only). The 5D2 has even sparser pixel density - 1080p on a 24x36 mm sensor.

Romy
Hi, the pixel size does not matter all that much provided you know what it is effectively and you use sufficient magnification. Not having played with one of these HD-capable DSLRs as yet, I am still unclear as to what "effective pixel size" would mean in this context. Eg when one is shooting 1080 HD (2 megapixel screen size), is the Field of View (FoV) that of the full frame of the camera? be it APS-C or full 35mm format, or is it a 2 megapixel crop of the stills FoV? A full stills-frame FoV would imply that the pixels are binned in the firmware and that the effective pixel size is much larger than the native pixel pitch of the sensor. There is also another way of extracting video captures from DSLRs that have LiveView but no HD output, eg Canon 40D. The astro software ImagesPlus enables capturing the magnified LiveView as a video capture that can be processed very well for planetary imaging. In this context the effective pixel size, I suspect, is equal to the native pixel pitch. So, for successful planetary capture you need to know what is the effective pixel size, something trivially easy to do once you start playing with the actual camera body. Just compare the FoV using your chosen video capture (HD or from magnified LiveView) to the stills FoV.

Next you need some kind of tele-extender that will make your lens or telescope have a focal length that corresponds to a focal-ratio (f-number) that is at least 4x the effective pixel size in microns. Let us say that you have determined that the effective pixel size of your video captures is 4.7microns (this happens to be the native pixel pitch of a 50D but I could have picked any other number if the camera bins the pixels). 4*4.7 yields a desirable focal ratio of 19. If your lens wide open is f4 you will need a tele-extender that multiplies that 5x to get to f20. So, eg a TeleVue 5x Powermate will do the job, but a 1.4x + a 2x will be insufficient magnification (makes it an f4*1.4*2 = f11) for Nyquist Critical Sampling. If you are using an f10 SC Telescope, a 2x tele-extender already gets you to f20. I have a write-up that explains why you need that magical 4*(pixel pitch) as an f-ratio for Nyquist Critical Sampling here:
http://www.geocities.com/ultimaoptix/sampling_saturn.html
Sampling at less than Nyquist Critical will yield planetary images that are way below what your lens or telescope is capable of. If the magnification is way above Nyquist Critical you end up with dimmer videos and more noise than desirable, so Nyquist Critical Sampling is the best compromise, a little more magnification does little harm, but 2x or 3x that adds too much noise to your videos.
Logged

Bored? Peruse my website: Samir's Home
Romy Ocon
Newbie
*
Offline Offline

Posts: 9



« Reply #62 on: April 17, 2009, 07:37:01 AM »
ReplyReply

Quote from: samirkharusi
Hi, the pixel size does not matter all that much provided you know what it is effectively and you use sufficient magnification. Not having played with one of these HD-capable DSLRs as yet, I am still unclear as to what "effective pixel size" would mean in this context. Eg when one is shooting 1080 HD (2 megapixel screen size), is the Field of View (FoV) that of the full frame of the camera? be it APS-C or full 35mm format, or is it a 2 megapixel crop of the stills FoV? A full stills-frame FoV would imply that the pixels are binned in the firmware and that the effective pixel size is much larger than the native pixel pitch of the sensor. There is also another way of extracting video captures from DSLRs that have LiveView but no HD output, eg Canon 40D. The astro software ImagesPlus enables capturing the magnified LiveView as a video capture that can be processed very well for planetary imaging. In this context the effective pixel size, I suspect, is equal to the native pixel pitch. So, for successful planetary capture you need to know what is the effective pixel size, something trivially easy to do once you start playing with the actual camera body. Just compare the FoV using your chosen video capture (HD or from magnified LiveView) to the stills FoV.

Next you need some kind of tele-extender that will make your lens or telescope have a focal length that corresponds to a focal-ratio (f-number) that is at least 4x the effective pixel size in microns. Let us say that you have determined that the effective pixel size of your video captures is 4.7microns (this happens to be the native pixel pitch of a 50D but I could have picked any other number if the camera bins the pixels). 4*4.7 yields a desirable focal ratio of 19. If your lens wide open is f4 you will need a tele-extender that multiplies that 5x to get to f20. So, eg a TeleVue 5x Powermate will do the job, but a 1.4x + a 2x will be insufficient magnification (makes it an f4*1.4*2 = f11) for Nyquist Critical Sampling. If you are using an f10 SC Telescope, a 2x tele-extender already gets you to f20. I have a write-up that explains why you need that magical 4*(pixel pitch) as an f-ratio for Nyquist Critical Sampling here:
http://www.geocities.com/ultimaoptix/sampling_saturn.html
Sampling at less than Nyquist Critical will yield planetary images that are way below what your lens or telescope is capable of. If the magnification is way above Nyquist Critical you end up with dimmer videos and more noise than desirable, so Nyquist Critical Sampling is the best compromise, a little more magnification does little harm, but 2x or 3x that adds too much noise to your videos.


For the 5D2 (and for the 500D too, as far as I understand from early product literature), the effective video pixel size is much larger than the native pixel size, as the 21 MP capture is downressed/binned to 2 MP HD video. Hence, the 5D2 is actually a 2MP video imager on a 24x36 mm sensor, while the 500D has somewhat "more reach" - a 2 MP video imager on an APS-C size sensor. OTOH, the extracted video capture from Live View on other DSLRs has a resolution no greater than 1080p. I guess one needs to use massive focal lengths to use well the very large effective  video pixel size of these DSLRs.
Logged

Philippine Wild Birds in HD video - http://exposureroom.com/members/RomyOcon.aspx/videos/
samirkharusi
Full Member
***
Offline Offline

Posts: 196


WWW
« Reply #63 on: April 17, 2009, 10:46:00 AM »
ReplyReply

Quote from: Romy Ocon
For the 5D2 (and for the 500D too, as far as I understand from early product literature), the effective video pixel size is much larger than the native pixel size, as the 21 MP capture is downressed/binned to 2 MP HD video. Hence, the 5D2 is actually a 2MP video imager on a 24x36 mm sensor, while the 500D has somewhat "more reach" - a 2 MP video imager on an APS-C size sensor. OTOH, the extracted video capture from Live View on other DSLRs has a resolution no greater than 1080p. I guess one needs to use massive focal lengths to use well the very large effective  video pixel size of these DSLRs.
Looks like the binning is 3x3. If correct, then the effective pixel size is about 14 microns and you need tele-extending to get the focal ratio to f/55 to f/60. In my film days I used f/120, employing eyepiece projection, not difficult with a suitable adapter on an SCT, but could be unwieldy with a camera lens. Presumably one could still use magnified LiveView as the video capture mode. In that case f/20 should be enough. But LiveView capture requires ImagesPlus, version for 500D not yet released.
Logged

Bored? Peruse my website: Samir's Home
BJL
Sr. Member
****
Offline Offline

Posts: 5124


« Reply #64 on: April 19, 2009, 01:10:03 PM »
ReplyReply

Quote from: Romy Ocon
For the 5D2 (and for the 500D too, as far as I understand from early product literature), the effective video pixel size is much larger than the native pixel size, as the 21 MP capture is downressed/binned to 2 MP HD video.
Is it downressed/binned or simply sub-sampled, reading only every third row and column of pixels and discarding the rest? I suspect the latter, as I doubt that the 5DMkII is capable of reading all 22 million pixels at video frame rates: after all, its stills frame rate of only 4fps is slow compared to comparable film bodies, and so almost certainly due to a speed limit in read-out and processing, and active pixel CMOS sensors like Canon's have to do some amplification on-chip for each pixel read, even if then binned. Also, 3x3 is natural for sub-sampling from a Bayer CFA, since 2x2 sub-sampling would give all pixels of the same color!

Likewise, all video-output DSLR's probably use sub-sampling, not binning.
Logged
Romy Ocon
Newbie
*
Offline Offline

Posts: 9



« Reply #65 on: April 19, 2009, 08:15:26 PM »
ReplyReply

Quote from: BJL
Is it downressed/binned or simply sub-sampled, reading only every third row and column of pixels and discarding the rest? I suspect the latter, as I doubt that the 5DMkII is capable of reading all 22 million pixels at video frame rates: after all, its stills frame rate of only 4fps is slow compared to comparable film bodies, and so almost certainly due to a speed limit in read-out and processing, and active pixel CMOS sensors like Canon's have to do some amplification on-chip for each pixel read, even if then binned. Also, 3x3 is natural for sub-sampling from a Bayer CFA, since 2x2 sub-sampling would give all pixels of the same color!

Likewise, all video-output DSLR's probably use sub-sampling, not binning.


I used the terms downressing/binning loosely (and inaccurately) to mean that the 2 MP HD video output used the angle of view of the whole 24 mm x 36 mm sensor of the 5D2, rather than just cropping a 1920x1080 pixel portion of the sensor. This was in light of the resolving properties of the 5D2's video.

As regards the actual method of extracting a 2 MP video output from the sensor, I've not seen any technical literature yet from Canon that describes this. However, given the apparent limited processing and throughput capacity of the 5D2, I'd tend to agree with you that sub-sampling is the most logical method that's used, rather than downressing or binning in the strict sense.
« Last Edit: April 19, 2009, 08:18:23 PM by Romy Ocon » Logged

Philippine Wild Birds in HD video - http://exposureroom.com/members/RomyOcon.aspx/videos/
BJL
Sr. Member
****
Offline Offline

Posts: 5124


« Reply #66 on: April 20, 2009, 03:53:49 PM »
ReplyReply

One claim that I read recently, supposedly based on image analysis, is that the 5DMkII reads only every third row, but uses all pixels in each row read, with some kind of downsampling/binning.

Yes, there is no question that the full width of the sensor is being used by these DSLR video modes, not just a central crop.
« Last Edit: April 20, 2009, 03:54:58 PM by BJL » Logged
Derry
Jr. Member
**
Offline Offline

Posts: 61


WWW
« Reply #67 on: April 20, 2009, 06:04:21 PM »
ReplyReply

my long lens is a Tele Vue TV85 scope,, is f7 -  600mm,, I use an Oly E3 on it and love the resolution the system offers,, have included a photo of it,, some want to say it is 1200mm due to the Oly E3 2X crop factor but I just call it 600mm and any of my Oly lens as they are built to the 4/3 format so I don't consider any crop factor these days, just the X factor,,

not the most portable and certainly not to be considered hand holdable but certainly light enough to haul through the woods on the shoulder a brief distance,, I use the system mainly for my bird and wildlife photography,, I normally try to capture my species in the 100 feet or less range and will use a blind or hide when needed,,

I did a crop on the birds breast so you can see the fine feather detail the scope is capable of providing,, the bird was at a measured distance of 60 feet,,

as for those real long distance photos here is one about 250,000 miles out taken with an Old Nikon 990, 3.3 meg camera back in 2001 on the TV85,,

Derry
« Last Edit: April 20, 2009, 06:08:34 PM by Derry » Logged
cmox
Newbie
*
Offline Offline

Posts: 26


« Reply #68 on: May 11, 2009, 07:28:03 AM »
ReplyReply

By the way, here I have some examples you might be interested in. I used my Noflexar 5,6/400mm and my Telyt 560mm with the 1,5x and 2x converters, and with both converters. All images with EOS 5D2, 100 ASA, captured in RAW, converted to small JPGs, no sharpening. All images with converters are 2 f-stops down.

400mm Noflexar, this is the scene how it looks through a 400mm lens:

[attachment=13590:2_400stop2at72.JPG]

And here all cropped results. I did not check the corners, though, I was looking at the center only.

1.  at 5.6: [attachment=13592:3_400_open2.jpg] f11: [attachment=13591:2_400stop2crop.JPG]

1.5x: [attachment=13599:_5_Novo_..._Cropped.jpg] 2x: [attachment=13600:5_Novo_2..._Cropped.jpg] Both: [attachment=13601:5_Novo_2..._Cropped.jpg]

3. Telyt 6,8/560

At 6.8: [attachment=13594:4_Telyto..._Cropped.jpg]
2 stops: [attachment=13595:4_Telyts..._Cropped.jpg] 1.5x [attachment=13596:6_Telyt_..._Cropped.jpg] 2x [attachment=13597:6_Telyt_..._Cropped.jpg] Both: [attachment=13598:7_Telyt_..._Cropped.jpg]
« Last Edit: May 11, 2009, 07:34:13 AM by cmox » Logged
cmox
Newbie
*
Offline Offline

Posts: 26


« Reply #69 on: May 18, 2009, 07:11:35 AM »
ReplyReply

Can someone chip in some examples with a similar subject using a good mirror lens like a Mirorat, Reflex-Nikkor or similar?
Logged
studiocarter
Newbie
*
Offline Offline

Posts: 8


« Reply #70 on: May 30, 2009, 04:50:34 PM »
ReplyReply

Dinner is almost ready, but I just wanted to address this topic and get started with it.
I have a Pentax 600mm for a 6x7 camera, an adaptor for a Canon 5D digital, teleconvertors but not tried them yet.
I went wild with large format and got one 8x10 that extends over 48" long.
My subject matter is city pictures of buildings on hills or seen from hills and bridges.

Now to read all of the pages here...........
Logged
studiocarter
Newbie
*
Offline Offline

Posts: 8


« Reply #71 on: May 30, 2009, 06:39:14 PM »
ReplyReply

After dinner the Luminous Landscape LLVJ 04 was purchased, loaded, and finally uncompressed and viewed correctly. It has a video all about the Pentax 600mm lens and 6x7 camera on a special tripod mount set.  I GOTTA HAVE IT! I got the video, now I must get the holder and the other holder.

How does that air release work? Where does one get one? I never saw anything like that for the 6x7.
« Last Edit: May 30, 2009, 09:47:48 PM by studiocarter » Logged
Pages: « 1 2 3 [4]   Top of Page
Print
Jump to:  

Ad
Ad
Ad