转一个资料，说明单反暗场差异的重要原因之一是传感器...
http://dslrmodifications.com/SL1Review/SL1Review.html比较有意义的一个测试
I took a series of test images using a new Canon SL1 (100D) for comparison to test images of other Canon DSLR (1.6 crop factor) APS-C models popular for astro imaging. Comparison tests below also include those for a Full Frame Canon 6D. The test images include long exposure dark frames in bulb mode. Some information on the SL1 model along with tests and comparison results follow.
Note: The test results below for the T4i (650D) model are identical to the T5i (700D) model, because they are identical camera models with different labels by Canon.
SL1 Specifications:
In the chart above are specifications for the SL1 model compared to a few of the Canon models that are available for sale at this time and are popular for astro imaging. The prices are based on refurbished body only kits available from Canon, and online camera shops such as B&H Photo and Adorama. A more complete listing of models dating back to 2003 can be seen HERE.
The SL1 model became available in March 2013 and was introduced at the same time by Canon along with the introduction of the T5i (700D) model to replace the T4i (700D). The SL1 was advertised as the "the world's smallest, lightest APS-C DSLR". The SL1 model was built by Canon to offer an alternative to mirrorless cameras while maintaining compatibility with Canon EF and EF-S lenses. The SL1 is significantly smaller and lighter than the T5i, while offering the same 18MP resolution and DIGIC 5 processor. Differences between the SL1 and T5i models are below:
Model SL1 (100D) T5i (700D)
Display Screen Fixed Articulating
Continuous Shooting 4 fps 5 fps
Cross Type AF Points 1 9
Battery Life (shots) 380 440
In-Camera Audio Record Mono Stereo
Size (Inches) 4.61 x 3.58 x 2.72 5.24 x 3.94 x 3.11
Weight (Ounces) 14.0 20.3
In the table above showing the differences between the two models, I think the most important for astro imaging is the articulating screen. If you've owned models with fixed and articulating LCD display screens, you understand the advantage of the articulating screen if you mount your camera on a telescope or a tripod. An articulating screen allows the display to be easily flipped out to the side and pivoted up or down 270 degrees and avoids having to bend into awkward positions to see the camera back display or cricking your neck.
The advantage of having a lighter camera for astro imaging is important to most, in order to avoid extra stress on the telescope's focuser. The smaller size of the SL1 may also be advantageous for those imaging with HyperStar SCT systems. From the chart above you can see that the sensor of the SL1 is the same as used in the T4i and T5i models. The T4i and T5i models test very well for long exposure noise and sensitivity as can seen in my tests posted HERE.
The photos below show the difference in size between the SL1 and T5i models:
Front View:
http://dslrmodifications.com/SL1Review/SL1T5frontview.jpg
Top View:
http://dslrmodifications.com/SL1Review/SL1T5itopview.jpg
Side View:
http://dslrmodifications.com/SL1Review/SL1T5sideview.jpg
Battery:
The battery used in the SL1 model is different from other recent Canon APS-C models. It is the same battery (LP-E12) that is used by the Canon EOS M mirrorless camera. The LP-E12 battery is an 875mAH battery as opposed to the more powerful 1120mAH LP-E8 battery used in other Canon APS-C models. Canon claims the SL1 can take 480 stills if using the viewfinder on a fully charged battery. The T5i can take 550 stills. A comparison of the T5i battery (LP-E8) to the smaller SL1 (LP-E12) is shown below:
http://dslrmodifications.com/SL1Review/SL1battery.jpg
This review is from an astro imaging perspective and focuses mainly on camera features that are most important for astro imaging. You may want to see other camera websites for normal daytime imaging reviews of the SL1 model if you plan to do regular photography or infrared photography with a modified camera. The Canon models tested and compared here for long exposure dark frame noise were all non-modified.
Dark Frame Noise Testing:
My first testing with this camera model was to take a series of 5-minute dark frame exposures at room temperature and ISO 1600 over a two hour period as was done in previous testing that I have done for the 450D, 500D, 550D, 600D, 650D, 700D, 1000D, 1100D and 6D models. A 15-second delay was used between each exposure. Camera settings were adjusted to be similar to those used for other models and found to be most conducive for astro imaging. All testing was done at room temperature. The settings information from Canon's DPP for the 100D, 600D and 650D camera dark frame test images is below. Please note that the setting of "High ISO speed noise reduction" was disabled for all models tested:
http://dslrmodifications.com/SL1Review/SL1T3iT4isettings.jpg
Below are the histogram displays using Canon's Digital Photo Professional software for the initial 5-minute ISO 1600 dark frame exposure of eight Canon models for comparison.
http://dslrmodifications.com/SL1Review/SL1eightrmodelsuncooledDPP.jpg
As seen in the above graphic, the 450D model that was king of the APS-C models for lowest initial dark frame noise is still best, but the SL1 (100D) is close behind. The 1000D continues to have the highest level based on DPP histogram displays. The initial 5-minute dark frame noise of the 550D and 600D are similar with the 650D being slightly better. For the purpose of these tests, please be aware that the dark frame noise levels for cameras of the same model type that I have tested over time can vary from unit to unit as discussed HERE.
The image below compares the initial 5-minute ISO 1600 dark frames of nine Canon models. RAW dark frame files were converted to 16-bit TIF files using Canon's DPP software and the TIFs were then cropped at center to 300 X 300 pixels using Photoshop CS5. The 6D image has the lowest noise.
http://dslrmodifications.com/SL1Review/ninecamerascentercrop.jpg
For the Full Frame TIF dark frame images, image pixel standard deviation values for luminosity of the initial dark frames were recorded using Images Plus for all nine Canon models and are displayed in the graph below:
http://dslrmodifications.com/SL1Review/ninemodelstandarddeviationinitial.jpg
Relying on the initial dark frame performance is not representative of how DSLR cameras are used in the field for multiple continuous exposures. The histograms for four camera models are shown below, for both the initial 5-minute dark frame and the last 5-minute dark frame of the two-hour imaging sessions. Between the four cameras, the 600D has the highest noise level at the end of the imaging session based on the histogram display with the 650D having the lowest.
http://dslrmodifications.com/SL1Review/SL1firstlastcompare.jpg
The image below compares the final 5-minute (after two hours) ISO 1600 dark frames of four Canon models. RAW dark frame files were converted to 16-bit TIF files using Canon's DPP software and the TIFs were then cropped at center to 300 X 300 pixels using Photoshop CS5. The SL1 appears to be the noisiest.
http://dslrmodifications.com/SL1Review/SL1fourcamsfinal.jpg
For the final Full Frame TIF 5-minute dark frame images (end of 2-hour period), image pixel standard deviation values for luminosity were recorded using Images Plus for six Canon models and are displayed in the graph below:
http://dslrmodifications.com/SL1Review/SL1sixfinal5minsstandarddeviation.jpg
For the 5-minute dark frames taken continuously over a two hour period, I recorded the EXIF temperature readings from the RAW dark frame files over the two hour period for all eight camera models and plotted them below. In the past, with each new in-camera video capture model, Canon has been able to lower the internal temperature recorded in the EXIF data, but that didn't happen with the smaller SL1 model.
http://dslrmodifications.com/SL1Review/SL1ninecameralmodelsEXIFover2hours.jpg
Summary:
Based on my review and testing of the SL1 camera and earlier Canon camera models, these are my observations most applicable for astro imaging:
What I liked:
[*]Small size andweight of the SL1 camera body
What I didn't like:
[*]High temperature increase over two hours of continuous exposures.
[*]High standard deviation value of luminosity of final darkframe after two hours of continuous exposures.
[*]Lack of an articulating (swivel) display screen.
[*]Different size battery than used by other recent APS-C models.
Because the SL1 camera had a higher level of dark frame noise than recent APS-C Canon models when taking continuous exposures, I decided to return my SL1 kit to Canon. The advantage of having a smaller and lighter camera comes with the disadvantage of increased temperature and dark frame noise for long exposure deep sky imaging. I did not do my usual long exposure sensitivity tests, because I returned my SL1.
接下来是6d的制冷改造资料，似乎难度有点高：
http://www.centralds.net/cam/wp-content/uploads/2014/12/astro6d_excooler.jpg
Astro 6D is a cooling modified camera of canon eos 6D camera.
Until now we are modifying canon’s DSLRs to cooled camera with two type.
The one is to insert cooling module into camera body, the others isthe re-configureing of camera system as in case of CDS-5D.
The inner space of 6D, A7s is so tight and it’s impossible to install the cooling module into body. And we introduced a new modification concept to modify 6D and A7s.
A. Take out of Image sensor
We tried to take out the image sensor in a camera body and moved it to lens direction and make cooling module. We think it’s proper solution to modify 6D camera having tight inner space.
http://www.centralds.net/cam/wp-content/uploads/2014/12/sensor_move2.jpg
We have a question about the reliability on extended CMOS connection cable and try to test it.
Before we perform this test, we strengthen the ground circuit and make heat sink and cold block to unite in to camera’s ground circuit and made shield covers.
With the extended cable the camera works well without any errors in still shot photography and movie mode. I guess that the CMOS cable delivers only digital signals and the lines are composed with pairs and additional ground and shield helped to increase the stability of circuit.
The Image sensor taken out from body is having merits and demerits.
Demerits:
First is ignored mechanical shutter because the CMOS is moved from the back of shutter to front of shutter.
Canon’s DSLRs control the amount of light into image sensor by the combination of mechanical shutter and electric shutter.
And modified 6D’sexposure time will be controlled only by electrical shutter and the exposure control of sub second shots is not reliable.
You can see more informations from below link:
http://www.centralds.net/cam/?p=7533
Second is the fact that we can’t use optical viewfinder any more. But you can focus using Live view mode.
Merits
http://www.centralds.net/cam/wp-content/uploads/2014/12/back_focus-650x268.jpg1.Drop-In Filter system : The back focus distance between image sensor and lens mount became the space for drop-in filter holder. This system make possible to install the filters without lens detaching.This is very useful for narrow band imaging.
Astro 6D’s back focus distance is aligned to 44mm as same to canon EF mount.
http://www.centralds.net/cam/wp-content/uploads/2014/12/heatsink.jpghttp://www.centralds.net/cam/wp-content/uploads/2014/12/vignetting.jpg
2. The cylindrical heatsink and cooling module in front of camera body is simillar to the shape of normal DSLR cameras and it’ll give more good user experience.
3.The mirror holder of full frame DSLR cameras cast a show to the image sensor when it is lifted to take shots.
The amount of the light is not so serious but this make t the irregular he background in brightness.
This is so troublesome when you try to make mosaic images but modified Astro 6D has no obstacles in front of CMOS sensor.
B. New cooling system
[*]Passive cooling
A7s is so good camera for movie recording. But when it’s in recording or shooting shots the temperature of image sensor rise to ambient air temperature + 7C over. This rising temerature gives the noise to output image. Particularly in case of low light photography this internal heat is major target to overcome.
http://www.centralds.net/cam/wp-content/uploads/2014/12/heat-transfer-0-650x460.jpg
We designed a cylindrical heat sink through 3D modeling and manufactured by MCT machine. This heat sink having sufficient radiation areas and it can cool down the temperature of image sensor ambient temperature – 6C~7C when 4V DC powered to TEC without cooling fan.
Because the sensor temperature of unmodified 6D is Ambient temperature +7C~8C, The passive cooling of Astro 6D is having 14C~15C cool down effect than unmodified 6D. This will help to produce good quality movie and low light images.
Passive cooling is fanless cooling system and the camera is silent. The current consumption is about only 0.8Amp and in case of you use 12V 12Ah read sealed battery you can operate the cooling system about 15hours continuously
2. Active cooling: If you attach EXcooler to the bottom side of heatsink and operate the cooling fan. In this case 8.5V DC is supplied to TEC and though this ‘active cooling’ the temperature of image sensor will drop to ambient air temperature -18C (+2C ~ -2C).
http://www.centralds.net/cam/wp-content/uploads/2014/12/active_cooling1s-650x268.jpg
3.Detachable EXcooler: the products of ‘Noctua’ Austria company is famous as silent and high performance cooling fans.
We installed two 40mm notch fans to EXcooler and power circuit board for 18.5V out for TEC. This EXcooler easily can be attached to bottom side of heat sink using one 1/4” screw bolt.
4.Digital Thermometer: For monitoring of the temperature of image sensor we offers digital thermometer as basic accessary with Astro 6D set.
C. Dark Fram Comparison of Cooled 6D
1. Indoor temperature, ASA1600, 450sec, RAW, 500x500pixels center Crop (Original)
http://www.centralds.net/cam/wp-content/uploads/2014/12/6d_compare_original-650x324.jpg
2. Indoor temperature, ASA1600, 450sec, RAW,500x500pixels center Crop (Photoshop Level255 -> 30)
http://www.centralds.net/cam/wp-content/uploads/2014/12/6d_compare_level30-650x324.jpg
D. Adapters for Astro A7s
http://www.centralds.net/cam/wp-content/uploads/2014/12/adapters-m1.jpg
Information of the product :
＊Cool down the temperature of CMOS sensor about 18 Celsius degree(±2℃) from that of ambient air.
＊Absolutely high-Quality image in B-shutter use compared with usual DSLR
＊Realtime Monitoring of the cooling temperature by digital thermometer
＊Drop-in filter system
http://www.centralds.net/cam/wp-includes/js/tinymce/plugins/wordpress/img/trans.gif＊Use of high efficiency Thermo electric cooler module.
＊Power: 12V, 3.0A DC
＊Low Pass Filter Removed.
＊Optimal design by 3D CAD modelling
＊Precision manufacturing by CNC machine
＊Perfect tuning of optical axis of CMOS sensor by 3 point alignment
＊Permanent Anti-dew system applied.
*Detachable Excooler (40mm cooling fan 2pcs & Power supply) included.
*Live-view Focus function alive.
*Mechanical Shutter and Sensor Cleaning function are disabled.
Various Adapters for Astro 6D
http://www.centralds.net/cam/wp-content/uploads/2013/10/cds-5d-accessary-650x305.jpg
然并卵{:2_186:} 仰望浩瀚寰宇 发表于 2015-6-18 16:39
然并卵
请文明讨论 人比黄瓜瘦2007 发表于 2015-6-18 16:54
请文明讨论
我错了呜呜呜
谁给翻译翻译？ 450D碉堡了 这个转贴真好！
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