Learning Curve - again!

[johnst]

Hi,

Had a mixed night last night as I was imaging M42 with my WO Megrez 72 on my Star Adventurer and my Canon 700D. A couple of issues, first, when I used my Bahtinov Mask, it is the correct one purchased from FLO btw, I can't see the star spikes very well on the screen, can I make the image bigger?

Also, I took 22 lights and 22 darks at 1600 iso but put everything away. I'm thinking now that my flats and bias frames need my scope and camera at the same focussing position so I need to image again, is that right, so, learning curve!

Any advice from this brilliant forum is welcome.

John

[smashing]

29 minutes ago, johnst said:

Hi,

Had a mixed night last night as I was imaging M42 with my WO Megrez 72 on my Star Adventurer and my Canon 700D. A couple of issues, first, when I used my Bahtinov Mask, it is the correct one purchased from FLO btw, I can't see the star spikes very well on the screen, can I make the image bigger?

Also, I took 22 lights and 22 darks at 1600 iso but put everything away. I'm thinking now that my flats and bias frames need my scope and camera at the same focussing position so I need to image again, is that right, so, learning curve!

Any advice from this brilliant forum is welcome.

John

It is always a learning curve.

What software are you using to capture your images with? APT for example has a zoom function for live view which I use to get a better image of the star I am focusing on...if you are just using your camera then it may have this function built in but I am not sure.

Flats certainly need the same configuration as the lights, do these at the end of the run. Bias frames do not and can be done pretty much anytime and the same bias frames can be used across multiple images i.e. you don't need to take them each time.

I found darks not that helpful and dither instead but not sure if that is available with the star adventurer

[johnst]

Thanks for the quick reply, I'm not using any software as yet, still getting equipment together so am relying on live view on the camera, will check out if I can zoom at all.

[rickwayne]

I'd  be  shocked if you can't zoom the live view. Two other dodges to maximize the signal you have to work with: Rack the ISO to something completely ridiculous, and use a long exposure now and then instead of live view to confirm where the spikes actually lie.

Also, it can help to use a dimmer star for final tweaking, paradoxically enough. The spikes and  diffraction "beads" get fatter with brighter stars and so give a less precise indication.

Bias frames are short-exposure darks, and so needn't be shot in the same session. Dark current for such a short exposure should  be  negligible, so the temperature really needn't  be close (although it's a good practice to use the same ISO). Since the sensor temperature varies during an imaging session, close enough is probably good enough for darks -- once you have a set at a given temp  (use the EXIF data to find  the actual sensor temp, instead of ambient), you can safely reuse them for awhile. Focus position doesn't matter for darks and bias, there's no light anyway.

Flats, however, should be shot every session, at the same focus point. A cheapo LED tracing pad has a sufficiently consistent brightness across its width, I find, and can be used in the dark after you've achieved good focus, unlike twilight flats. And IMO it's less bother than a T-shirt, just point the scope straight up  and lay the panel across it.

[Thorney]

I have a Canon 600D and you can zoom in on live view so I would say you can do the same. I normally just stick my ISO way up zoom in on the star and focus that way. Failing that just take a 1 second exposure with the mask on and zoom in that way to see the spikes and make minor adjustments until focused.  

[johnst]

Thanks a lot folks, a good few suggestions there for me👍

[Erling G-P]

I have a 700Da and yes, you can certainly zoom in live view.  In the upper right corner of the rear of the camera body are two small round buttons which zoom in & out.