SLT 102 Skywatcher - Limitations and Exposure Settings

[daverave83]

Hi All

I know own a SLT 102 Goto Scope and from reading various forums there are limitations due to the Alt/Az Mount.  i looking at getting a tube ring to piggy back my Camera.

I currently own a Panasonic Lumix LZ-20 Bridge Camera, and tried reading through the not so great instructions of how to set the exposure to the limits.

From reading the specifications the shutter speed is 15 - 1/2000 secs?

im guessing thats 15secs to 2000 thousands of a second?

There are various Focal Lengths which one would i need? the current iso setting is 1600 is this correct? 

I want to start with an easy object M42, but 15 secs of exposure won't capture that much detail i assume.

Any advice and guidance would be greatly appreciated.

Thanks

David

[dph1nm]

15 secs should be OK - I have got some reasonable results out of my Panasonic tz18, although that will do 60sec exposures. I stick to ISO400, as the in-camera processing tends to make a mess of high ISO star shots.

This is Perseus, 4x15s F4.1 ISO400, 8.7mm focal length, done from a fixed tripod. On a alt-az mount you should have no trouble doing 15s at a higher zoom (focal length) than this. Full zoom might be pushing the tracking accuracy of the mount though - I would stick to 10x.  I don't know about the LZ20, but my TZ18 automatically subtracts a dark frame from long exposures, so a 15s exposure actually takes 30secs.
 

NigelM

[jgs001]

David, The limitations in AltAz are defined by where in the sky you're shooting. You can shoot up to 2 minutes low in the east and west dropping to around 35 seconds at the Zenith and north/south.  So at 15s that's not an issue. Focal length has no direct bearing on the actual exposure times. However, longer focal length will 'magnify' any errors introduced by the drive train, and my little SLT mount had a fair few of them once I started longer exposure imaging. To the point that at 400mm, using 2 minute exposures, I was losing 50% of the exposures to drive errors.

At 15s, you're maximum exposure time, you won't have any problems directly. I would suggest though, you'd be better served by getting a dovetail bar, and mounting the camera, either directly to the bar, or via a ball head, as this will be easier to balance out. You want a slightly tail heavy balance, so that the drive motors always have something to push against, or the backlash/slop in the drive gears will get you. 

Give it a try on M42 at 15s exposures, and play with the settings.. the ISO may be too high for the camera, but then, with 15 second exposures, you can capture a heap load of them. If you can, turn off in camera noise reduction. Also, and whilst it's not normally recommended, set the aperture value to the smallest number you can. 

Good luck

[daverave83]

Thanks

When i set the camera to Manual there is a exposure value at the bottom of the LCD screen + to -

Example.

ISO1600     F3.6 1/60

I'm new to this so does the F rating and the setting mean adpature settings and shutter speeds?

How do i set this to 15 secs exposure?

The manual isn't very helpful as it only give's you a brief overview of what exposure is but does not tell you the settings, leaving you more confused than before of how you get it correct. 

Thanks

David

[jgs001]

David, hmmm... I see what you mean.. ok, here's my guess... set the mode dial to M(anual), use the cursor keys to select the shutter speed, select it and use the cursor keys to set it to 15s. Do the same with the aperture value to the smallest number (biggest hole), and I'd guess you can do the same with the ISO.

[daverave83]

David, hmmm... I see what you mean.. ok, here's my guess... set the mode dial to M(anual), use the cursor keys to select the shutter speed, select it and use the cursor keys to set it to 15s. Do the same with the aperture value to the smallest number (biggest hole), and I'd guess you can do the same with the ISO.

OK thanks

I have ordered a Tube rings from FLO, I'm guessing in regards to where you place the tube rings will be the center of gravity i.e. you put it too close to you this would strain the motor and guidance whereas you move the Tube Rings up the scope slightly the weight would be more central.

Ta

David

[jgs001]

You want to set it so that the rear (eyepiece end) is a little heavier than the objective end of the tube. You'll get smoother motion, you don't need to go a long way that way, just a little. Best bet is to try it and see... I used to dismount the scope and camera setup, and determine the exact balance point with the aid of a round pencil... then just sit the kit slightly backwards from there. I'd suggest also, mounting the tube ring so the camera is vertically above the scope, rather than out to the side.

[daverave83]

Thanks

Will give this ago once the tube ring arrives.

D