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Sony a900 Manual
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Sony a900 Manual

Astrophotography
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USING SONY a900 for ASTROPHOTOGRAPHY

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Summary of Contents for Sony a900

  • Page 1 USING SONY a900 for ASTROPHOTOGRAPHY...
  • Page 2 • TELESCOPE ADAPTORS PRIME FOCUS EYEPIECE PROJECTION • REMOTE RELEASE SONY CABLE RELEASE RM-S1AM SONY REMOTE COMMANDER RMT-DSLR1 GADGET INFINITY RADIO S1 REMOTE JJC-JR-C IR MODULAR REMOTE HÄHNEL HW433S80 RF WiFi REMOTE JJC TM-F LCD DIGITAL TIMER / INTERVALOMETER •...
  • Page 3 USING SONY a900 for ASTROPHOTOGRAPHY The Sony a900 DSLR is capable of taking fine photographs of the Sun in H-alpha and white light, the Moon, and deep sky objects. It has a 35mm Fx format CMOS sensor specifically designed for low light level photography. The twin BIONZ processors are designed to produce high resolution, low noise, high dynamic range images.
  • Page 4 TELESCOPE ADAPTORS PRIME FOCUS The Sony 'Exmor' CMOS sensor size is 35.9mm x 24.0mm, giving a frame diagonal 43.2mm. The throat clearance I.D. of the prime focus adaptor needs to accommodate an image circle 43.3mm diameter (allowing 0.1mm clearance) otherwise the frame corners will be mechanically vignetted.
  • Page 5 For example: TEC140APO f/7 prime focus & WO Sony alpha T-mount & 2-inch sleeve The above diagram demonstrates that the WO adaptor's I.D. is just sufficient to fill the Fx frame at prime focus at f/7.
  • Page 6 This is an example of a T-Adaptor & 2-inch sleeve:...
  • Page 7 • TELESCOPE ADAPTORS EYEPIECE PROJECTION Eyepiece projection enables a far larger image scale at the expense of a slower effective focal ratio. The adaptor needs to have three parts: the focusing mount nosepiece that fits into the 2-inch eyepiece collet; the eyepiece section, preferably adjustable so the amplification may be varied;...
  • Page 8 Exposures have to be made without touching the camera. It is not possible to depress the shutter release button without imparting vibration. You could use the Sony a900 2s delay, but this would not completely address the issue of induced vibration. The electromagnetic mirror release also produces a recoil that imparts vibration. It is necessary to lock-up the mirror prior to releasing the shutter.

  • Page 9: Remote Release

    • REMOTE RELEASE GADGET INFINITY RADIO S1 REMOTE The S1 RF WiFi remote release enables shutter release from up to 15m, & also supports <BULB> mode, but does not enable mirror lock-up. It comprises a receiver that connects to the camera body via a short connector cable, & a transmitter.
  • Page 10 SONY CABLE RELEASE RM-S1AM The standard remote cable release for the Sony a900 is the RM-S1AM. It can control the shutter according to whichever <DRIVE> option is selected, <LOCK-UP> allows you to lock-up the mirror & then open the shutter. The...
  • Page 11 JJC-JR-C IR MODULAR REMOTE This IR remote is Sony RM-S1AM compatible. It comprises a bi-directional IR self powered receiver (which requires an ISO hot shoe adaptor 4-pin Hot Shoe Adapter for DSLR/SLR cameras as FS-100;) & a self powered transmitter, range 8m, with a direct 80cm cable option.
  • Page 12 • REMOTE RELEASE HÄHNEL HW433S80 RF WiFi REMOTE The Hähnel HW433S80 RF wireless remote enables mirror lock-up & shutter release & <BULB> mode from up to 80m, & the HF signal will penetrate concrete walls. It also can be used as a 2.8m cable release. Battery life is similar to the S1 remote.
  • Page 13 JJC TM-F LCD DIGITAL TIMER / INTERVALOMETER The JJC TM-F LCD Timer/Intervalometer cable release is Sony RM-S1AM compatible, enabling mirror lock-up, shutter release, self timer, interval shutter release, exposure timer, multiple exposure timer up to 399 exposures. It has a long...

  • Page 14: Drive Function

    • DRIVE FUNCTION MIRROR LOCK-UP With these latter three IR & WiFi & cable remotes, <DRIVE> menu option has to be set to <LOCK-UP>. Because either of these remotes use receivers connected to the camera remote shutter port, the option <DRIVE> <REMOTE> does not need to be selected.
  • Page 15 • FOCUS Having made all the necessary menu settings & exposure & drive options, the next aspect in securing a digital image is focusing. Focusing the image is the most awkward aspect of astrophotography with a DSLR. • FOCUS SCREEN L For focal ratios slower than f/4 gridded focusing screen L should be fitted.
  • Page 16 • FOCUS DIOPTRE CORRECTION Adjust the dioptric correction scroll wheel on the side of the optical viewfinder until the screen chevron markings appear crisp & clear. Do this against a bright daylight sky.
  • Page 17 • FOCUS RIGHT ANGLE MAGNIFIER Fit Sony right angle x2 viewfinder accessory to the viewfinder eyepiece, FDA-A1AM. Adjust the eye lens focuser until the screen grads are in focus. Use a bright star & adjust the rack & pinion focuser to bring it into sharp focus.
  • Page 18 • FINE FOCUS RACK & PINION FOCUSER Focusing a DSLR is far more critical than focusing an SLR because the DSLR sensor is flatter than the depth-of- focus, whereas 35mm film is bowed towards the pressure plate by several hundredths of an inch (by approximately twice the film thickness).
  • Page 19 • FINE FOCUS MOTORISED FOCUS Fitting a motor focus to the fine focus knob can help find & track focus. However unless the motor controller has a digital read out it can still be a hit & miss affair. • FINE FOCUS REMOTE DIGITAL FOCUSER The focuser I recommend for focusing a DSLR is...

  • Page 20: Depth Of Focus

    TEC's StarLight Instruments FeatherTouch 3545 rack & pinion focuser. It is possible to focus the Sony a900 using the Optec TCF-S to within ±4 steps (1 step = 80 micro-inches). This is the limit, it is impossible to obtain a finer focus. The Exmor CMOS sensor is flat to about 5 micro-inches, so the focus tolerance is approximately 64 times the sensor's flatness.

  • Page 21: Checking Focus

    (typically in the plane of the dec. axis). Un-damped vibration will prevent the critical focus being found. • CHECKING FOCUS The Sony a900 LCD view-screen can be used to check focus at x19 (raw file). It has sufficient resolution to make a precise check on focus at night.
  • Page 22 LAPTOP REMOTE CAPTURE & CONTROL vs LCD VIEW SCREEN The Sony a900 maybe controlled from a remote laptop using the bundled software package “Remote Camera Control”. The camera is supplied with a USB cable but it will not be long enough. You require a 5m repeater cable. All the functions of the camera can be controlled using a laptop and this software package.
  • Page 23 The disadvantage is the USB upload time which can be well over a minute. The twin BIONZ processors in the Sony a900 can transfer the raw 26Mb image file to the LCD view-screen in one or two seconds. By reducing the image size to <S>...
  • Page 24 ISO100. Sensor noise affects the sensor’s resolution and so does shooting jpegs. For the best resolution you should always shoot raw frames @ ISO100 to ISO800. Do not set ISO to <AUTO>. The Sony a900 ISO range is ISO100 to ISO6400. The ISO setting merely amplifies...
  • Page 25 The dynamic range of the Exmor CMOS sensor is 12EV @ ISO100 with DR-O off. Increasing the ISO rating decreases the dynamic range. The Sony a900 has a Dynamic Range Optimizer (DR-O). For Solar & Lunar photography this should be set either to <OFF> or <STANDARD>.