Newbie DSLR questions.

[VincentMcKenzie]

I'm pondering getting a DSLR for DSO and Planetary Astrophotography. However, I don't want to fork out a load of money and be disappointed. I understand how to attach it (i.e. T-ring), the difference between prime focus, projection, and using a camera mount, etc. I've also taken planetary pictures using a decent point-and-shoot camera and an eyepiece mount, but I've not been successful with DSOs.

Question 1: With my point-and-shoot camera you can see absolutely nothing on the LCD display unless you're pointing it at the moon or a big bright planet. You have to align the scope using a normal EP, then VERY carefully attach the camera. This fails 95% of the time as the scope invariably moves enough to knock the target completely out of the FOV. Is it any easier with a DSLR? Can you see stars through the view finder or on the LCD screen?

Question 2: I currently own an auto-tracking Dob (not Goto). I understand how the field of view rotates because it's an alt-az mount, but how much does this actually affect things? Obviously the rotation is greater the closer the object is to Polaris, but surely you can get away with 30 second exposures further away from it? Is that long enough? Can stacking overcome any of this by taking lots of shorter exposure pictures (I noticed Deep Sky Stacker can auto-rotate images)?

[pederv]

Answer 1: Nice thing about Canon DSLR's is Live View for setting focus or locating bright objects. The PC interface is nice for taking very high ISO short exposures for centering your target. These can be done without a PC (laptop) but touching the camera can result in the same problems that you're having with the point and shoot.

Answer 2: I'm not sure about how long it takes for rotation to show up in your shots but 30 second exposures can result in some nice shots when stacked. If all of your images show some tracking errors then the stacked image will also show some tracking errors.

Good Luck

[Dublin sky watch]

Answer 2. Check here [Registered users can see links. ] or here [Registered users can see links. ]
Answer 1. Verne gave a good answer...
Clear skies.

[VincentMcKenzie]

Thanks both of you - very helpful

[jenniferchristine]

DSLR LCD viewers are not particularly sensitive, but you can see the major stars in say M42 (trapezium) and can get focus that way too using x10 - or using the PC (prog like APT and a bahtinov mask)
However you CAN see through the viewfinder which is one reason DSLRs have always been good.- I can even see things like M20 (lagoon neb) in there provided there's no external light.(Laptop screen going for instance)

20 - 30 seconds on the exposures can produce some excellent stuff - but for dim DSOs you need quite a few shots!

This is Tarantula and it took a lot of shots - but it's alt az and no guiding

[sxinias]

I do a lot of azimuth photography using lightweight azimuth mounts. See: Flickr: Sxinias' Photostream

1. In addition to what was previously said, one thing that will help you focus using the view finder is a 3X right angle finder. Not near as good as live view though but you can focus on fainter stars.

2. Field rotation. The link that was provided earlier has some excellent information. A simple rule of thumb is to stay at least 30 degrees from your zenith. This will allow you to have exposures of 30 seconds with only 0.1 degree or less of rotation which is not noticeable.

3. Even though you can take exposures of 30 seconds without field rotation, your mount may limit you to shorter exposures. My SkyWatcher SynScan AZ goto mount is statistically good for 20 second exposures before something causes vibration (wind, tracking motor, etc.). You will need to experiment with your scope to determine the limitations of your mount.

You may want to try a different approach; piggy back your camera on your scope. This way you can find a bright star and focus on it, then find the DSO you want to photograph. A 200 mm camera lens will give approximately a 8x image size. You will need to find some way to balance the added weight of the camera so your scope will track properly.

[VincentMcKenzie]

Thanks people

For balance I've got two wrist weights that people use to build up muscle tone on their arm by wearing them a bit like a big heavy watch. I found some long velcro straps that fit them perfectly and allow them to wrap around the bottom of the tube. You can adjust the balance by moving them along the tube or removing them altogether.

Originally Posted by jenniferchristine

However you CAN see through the viewfinder which is one reason DSLRs have always been good.

So... coming from someone who has never used a DSLR before, does this mean you can look through the viewfinder, and it'll see the image coming down the OTA? Or in other words the light from the sky is coming down your OTA, off the primary, off the secondary, into the camera, and out of the viewfinder on the camera (assuming you aren't currently taking a picture of course)?